Flow Impedance Measurement Module
Contents
1.2.
3. 0 15 Time seconds 3 Select NEXUS and thermocouple meter RS232 ports Select the RS232 COM port for the NEXUS micropho
4. RS232 COM port for B amp K NEXUS This listbox is where the COM port for the B amp K NEXUS microphone amplifier is specified The B amp K NEXUS must be connected to an RS232 COM port so that its microphone gain levels can be controlled Copyright 2012 2013 McIntosh Applied Engineering LLC 36 NOTE As already mentioned with the sound card devices if the PC s RS232 configuration changes the Setup controls can be updated by selecting another option in the tab controls such as Acquisition and then selecting Setup again IMPORTANT NOTE The NEXUS must be properly setup This includes the correct microphone sensitivity levels must be entered the serial interface for the NEXUS must be set to 2400 BAUD with echo turned on the power supply levels for the microphones must be
5. 0 15 Time seconds input sound card level LEFT
6. surfaces smooth and in oan good condition Copyright 2012 2013 McIntosh Applied Engineering LLC System Block Diagram A block diagram showing how the components are connected together is shown below stereo sound USB or card output Left CHJ stereo CH 1 output audio jack p either USB amplifier sound card such Right CH2 such as CH 2 output as MAE204 MAE202 USBSC A AAMP A or PC sound card PC es T1 or T2 RS232 thermocouple ipu a BEE Optional RS232 MAE203 THERMO A USB or audio jack CH 1 CH2 input input E RS232 high frequency low frequency Host B amp K NEXUS microphone amplifier speaker enclosure MAE100 HFSP A speaker enclosure MAE100 LFSP A MAE201 NEXUS A CH 1 CH 2 output output stereo sound card input either USB Left input sound card such as MAE204 USBSC A or PC sound card Right input Copyright 2012 2013 McIntosh Applied Engineering LLC 10 Controls All of the interaction with the Flow Impedance Measurement module is performed with the controls on the left side of the Ares window These controls are dynamic changing based on what feature have been selected At the top of these controls is a series of four tabs that are used to select one of the four main functionalities of the module These are Acquisition controls data acquisition Setup controls instrument setup Plotting controls plotting the collected data sets Fil
7. Type of measurement to perform al DIRRS 4000 microphone calibration v Frequency parameters start stop Magnitude dB points O log frequency spacing Target SPL for microphone calibration pressure 90 target 6 Initial normalized drive level for target level 0 1 0 01 Phase deg Quantity to graph magnitude phase O pressure O drive level CO SNR estimate Copyright 2012 2013 McIntosh Applied Engineering LLC 15 At the bottom of the controls there are graphing options These allow you to plot several different quantities which are listed below These provide additional information about levels and signal quality during the microphone calibration measurement magnitude the magnitude of the complex phasor transfer function between the two microphones phase the phase of the complex phasor transfer function of the two mics pressure the pressure at the microphone surface for the measurement drive level the normalized sound card drive level that was used to achieve the calibration pressure SNR estimate a signal to noise estimate of the measured microphone signal for the measurement MAE102 Microphone Calibration The MAE102 uses a different calibration setup than the other apparatus s The MAE100 MICCAL A is not used but rather the system is setup as for a measurement but no sample or sample holder is put in place The
8. However Ares will interpolate the calibration for any measurement frequencies that are between calibration frequencies so the number of points can be different for the microphone calibration and the impedance measurements When calibrating the microphones the MAE100 MICCAL A microphone calibration cap must be mounted on the MAE100 HFSP A high frequency speaker enclosure It s best to have the Copyright 2012 2013 McIntosh Applied Engineering LLC 14 MAEI100 150MM A 150mm spacer between the speaker and the calibration cap as shown in the picture below To ensure that the microphones are calibrated at a reasonable sound pressure level SPL there is a Target SPL for microphone calibration that is to be entered Ares will adjust the drive level to the speaker until the desired SPL is reached if possible The maximum normalized drive level is 1 0 If the pressure is still too low at the maximum drive level it will perform the measurement at as high an SPL as possible The calibration data for two microphones are shown in the Ares window below Normally the phase is close to O degrees for all frequencies but the USB sound card tested had a constant delay between the left and right channels that created this linear phase delay between the two microphones ware module 1 Flow Impedance Measurement BAR E File Edit View New Module Modules Window Help D a MEEN e FEOF Acquisition Setup Plotting Files Clipboard
9. Engineering LLC 41 Data sets The Save or Load buttons under the Data sets section export or import the material impedance data to ARES_ZF files This feature is useful to maintain individual impedance data files for each material These files are also useful for importing into the Acoustic material and Acoustic resistor elements in the modeler module so exact measured impedance data can be used in a model Copyright 2012 2013 McIntosh Applied Engineering LLC 42 Copyright 7 Using the 1 sample cutter The MAE100 comes with a 1 cutter that s been modified to create samples with a slightly reduced diameter so samples cut with it will easily fit into the MAE100 tubes The photos below show an example of using some paper to help hold some felt material in position while a sample is cut from it For some material using a drill press to spin the cutter to cut through the material works well For other material using the cutter to push through the material may work better When used this way the drill press is used more as a press than a drill Only experimentation will tell which method will work best for your material Either way mounting the cutter in a drill press 1s helpful for producing a sample When using the cutter as a press cutter don t turn the drill press on but simply press down firmly with the cutter until it pushes through the material Experimenting with more or less sacrificial paper can produce better re
10. Hz felt 250 Hz Copy data set to clipboard as text C use Matlab format else Excel Microphone calibration files The microphone calibration data from the Acquisition microphone calibration measurement can be exported or imported from a file using the Save or Load buttons It is not expected that multiple sets of microphones or sound cards will be used so exporting importing the microphone calibration data may not have great use However this can be useful if you d like to see if the behavior of the microphone calibration which is dependent on the recording sound card as well as the microphones is stable over time Note that the microphone calibration data is automatically saved to the ARES cfg file when Ares exists so any changes to the microphone calibration data should be present when Ares is re run Sample holder impedance files These Save or Load buttons export or import the sample holder impedance data This feature is useful if the samples that are being tested are being mounted by different types of holders In this case a single sample holder impedance data set isn t sufficient Use these buttons to save load the sample impedance to a file so you don t have to remeasure it every time you change the sample holder As with the microphone calibration data the current sample holder impedance data is saved to the ARES cfg file when Ares exits and is reloaded when Ares is run again Copyright 2012 2013 McIntosh Applied
11. McIntosh Applied Engineering LLC 34 The blue curve is the output signal and the green curve is the input signal from the microphone There are three very important aspects of the recorded signal that must be observed to verify that the sound cards are working properly First the input signal green curve must lag the output blue curve signal Note that the large central recorded signal green curve starts after i e to the right the output signal blue curve If the central green pulse happens before the blue pulse then there is a problem with the sound cards the central blue pulse must start before the central green pulse in this example it does Bees 8 8 fj 8000 9000 0 25 Second the recorded green pulse must begin within 100 ms of the output blue signal This can be easily seen by the requirement that the central green pulse must start within the central blue pulse If it occurs after there is too much delay in the recording sound card the central green pulse must start a before the end of the central blue n pulse i in this example it does Bf es amp amp 8000 MARS Finally the length of the recorded central green pulse must have the same 100ms length as the output central blue pulse This can be verified by observing the length of the large green pulse to be the same as the large blue pulse Copyright 2012 2013 McIntosh Applied Engineering LLC 35 the length in seconds of
12. frequency speaker enclosure which is optimized for high intensity low frequency measurements The high frequency speaker enclosure is likely to be used more often microphone rigid termination spacer tube sample holder Copyright 2012 2013 The system works by driving the speaker which sends an acoustical wave up through the tubes The wave must pass through the sample mounted in the sample holder and then into the spacer tube up to the termination microphone The Ares software then uses the microphone signals to determine the pressure drop and velocity through the sample from which the flow impedance is calculated While the measurement sounds simple and straightforward it s complicated by the necessity of having to deal with a wide range of frequencies and their associated wavelengths This necessitates that two different spacer tube lengths be used requiring the operator to change the tube stack up midway through the measurement Two different sized excitation speakers are also used one for low frequencies and one for high frequencies The temperature of the air must be known so a thermocouple meter has been incorporated into the system Sound cards are used to generate the speaker signal and measure the microphone response so a means to calibrate the sound cards 1s required A picture of all of the hardware components to accomplish this is shown below B amp K NEXUS mic amplifier eee Dowie micro
13. t work well If USB sound cards are being used then it is likely that two different USB sound cards must be used Ares does not have control over the sound card volume and so it will likely be necessary to go into the Windows Control Panel and adjust the output level of the Playback device It is recommended to set it to maximum The discussion for the sound card calibration has some detail for setting the sound card input volume Release sound card resource This option selects how the sound card resource is handled between calling the sound card device It has been observed that some sound card drivers require that the device s resource must be released between uses and other drives cannot be released If the sound cards don t work with one condition try the other Select output channel behavior This option selects the behavior of the output to the playback device during an impedance measurement It does not select the behavior for the microphone calibration The left right or both left and right options should be straightforward The left low freq right high freq option is a bit more complicated It selects the output channel based on whether a low or high frequency measurement is being done For a low frequency measurement where the MAE100 apparatus stackup is for a low frequency measurement using the 150mm spacer between the sample holder and the rigid termination the output on the playback device will only be on the left cha
14. the carrier thickness Note that we ve magically attached the sample to the carrier at its edge For this sample carrier configuration extra dist 1 would be t as the carrier would increase the distance from the side o sample holder microphone and the lower sample surface t t Cc 12mm Yt 25 4mm With this configuration the sample would actually extend up into the 12mm diamter of the upper volumes and so the distance from the rigid termination microphone and the sample surface has decreased by the sample thickness so extra dist 2 would be t If the 2 5mm space is used extra dist 2 would be t 2 5mm Copyright 2012 2013 McIntosh Applied Engineering LLC 21 Unfortunately there are two different items being called the sample holder One is the MAE100 SH A item shown below in which the samples are mounted And the other is any of the rings that are used to support a sample held in place in the MAE100 SH A such as those shown below The image on the right shows a felt type sample held between two MAE100 10OMMSHD A 10mm sample holder disks The sample holder rings are mounted into the sample holder fixture as shown below The sample holder impedance is understood to be the impedance through the sample holder disks and not the MAE100 SH A Copyright 2012 2013 McIntosh Applied Engineering LLC 22 As with the microphone calibration the frequency range over which the sample holder impedance is measure
15. the centra green pulse must be the same as the length of the central blue pulse in this example they are the same length 0 15 Time seconds Presently these requirements are not automatically verified but can only be verified by observing the Play Record pulse from soundcards graphs Examples of the sound cards not behaving properly are shown below In the first two graphs the recorded green pulse is happening before the output blue pulse And in all three examples the length of the green pulse is shorter than 100ms Note that this problem was cleared up by rebooting the computer but in some instances you may need a different sound card with better driver behavior 10000 10000 output output input input sound card level LEFT sound card level LEFT 8
16. the part s impedance Zpart you must first measure just the impedance of the sample holder Zholider and then subtract that from the total impedance measured The controls for the sample holder impedance measurement are shown below They add a number of parameters not seen in the microphone calibration Copyright 2012 2013 McIntosh Applied Engineering LLC 17 The new parameters are sample holder thickness sample holder diameter extra dist I extra dist 2 velocity target initial drive level Acquisition Setup Plotting Files Clipboard Type of measurement to perform sample holder impedance sample holder thickness 1 mm specify area else calc from diameter diameter 3 mm F extra disti 0 mm y extra dist2 0 mm F Frequency parameters start Pa Hz stop 5000 Hz points 200 log frequency spacing Target particle velocity for linear measurements velocity 0 1 mis target 0 02 mis lt Initial normalized drive level for target level 0 1 0 01 Perform measurement Quantity to graph v Z real imag particle velocity drive level Pend Pside xfer driving pressure SNR estimate velocityfdrive how thick the sample holder is the diameter of the sample holder s open area that the sound passes through alternatively the specify area checkbox can be selected and the area can be directly entered additional spacing between the lower sample holder microphone and th
17. thickness of the lower sample holder disk needs to be used and the effective volumetric effects of the top disk is to be used so d 2 extra dist 2 t t 25 4mm So for a values of 1mm fot and 10mm of d extra dist 2 will be 14 1 10 25 4 2 1 155 mm Copyright 2012 2013 McIntosh Applied Engineering LLC 20 MAE102 is different from the MAE100 in that the sample is expected to actually lift the stackup when placed in the sample holder The sketches below show an expanded stackup left and the stackup with all of the pieced put together right With this arr Note that the inner diameter of the MAE102 is 12mm but the sample is expected to have a 25 4mm diameter the same size as for the MAE100 In this case the lager sample actually lifts the entire stackup and so L1 and L2 will ideally remain unchanged However this assumes that the 5mm spacer is being used the MAE102 SMM A The MAE102 also comes with a 2 5mm spacer the MAE102 2 5MM A This can be used when the sample is more than a few mm s thick and causes the stackup to be lifted out of the 25 4mm diameter recess When the 2 5mm space is used L2 should be 2 5 mm Additional corrections will need to be made depending on the structure of the sample Suppose that the sample is actually composed of a 25 4mm diameter carrier with a 12mm diameter sample adhered to its top as in the cross section shown below where t is the sample thickness and te 1s
18. Ares Acoustical System Flow Impedance Measurement Module User Manual Acoustical and Audio Measurement and Design Tools McIntosh Applied Engineering LLC MAE MAELLC COM info MAELLC COM support MAELLC COM Copyright 2012 2015 by McIntosh Applied Engineering LLC Eden Prairie MN USA Copyright 2012 2013 McIntosh Applied Engineering LLC Notice Ares is copyrighted and licensed by McIntosh Applied Engineering LLC MAE Ares and all of its hardware and software components are provided as is MAE makes no representations or watranties concerning the compatibility of Ares to the user s computer system or any potential damage caused to any computer peripherals digital storage systems or personal physical safety Further the accuracies of the measurement modeling and design components are not warrantied and should not be used as the sole source of evaluating an engineered system or component for commercial suitability or physical safety The user agrees not to distribute the Ares software to any non licensed third party attempt to disable the licensing system or reverse engineer the operation of the program or its hardware components Table of Contents NOU Oaea at Mare econ oasis Gada a Mata E eet ean A aeeeee 2 TOR OM OIG MS e E E E eect ewe gt naa se ease ee eecee teens 2 Pocument Revision Histo acsi ne a r E 3 Flow Impedance Measurement Module wisaitccsccsscssicetixcetonnsdascveradxeratiscavonetiaxeiinastauscandeenenit
19. Set up feature Copyright 2012 2013 McIntosh Applied Engineering LLC 37 RS232 COM port for EXTECH 421509 or temperature The air temperature is needed for computing the flow impedance It is provided in one of two ways Either an EXTECH 421509 meter is used to read the temperature from a thermocouple mounted in the MAE100 RTMIC A rigid termination or by manually specifying the temperature The selection is made by using the RS232 COM port for EXTECH 421509 listbox If a valid COM port is selected then the temperature is read from the meter s thermocouple T1 or T2 must be selected If Not present is selected then the temperature is to be manually entered If a valid COM port is selected then the Test thermocouple meter button can be used to test the COM port connection to the meter If the test 1s not successful then you must verify that the meter is connected to the correct COM port the meter is turned on and that the thermocouple is connected into the specified T1 or T2 channel R3232 COM port for EXTECH 421509 R5232 COM port for EXTECH 421509 a eee E 4 thermocouple g i manually enter air temperature Test thermocouple meter j temperature 25 z lt 4 A photo of the thermocouple mounted in the rigid termination is shown below The metal thermocouple tip must not make physical contact with the brass material Also care must be taken to ensure that the thermocouple tip doesn t become damaged when the rigid terminat
20. When this occurs look for a setting for using the sound card in shared mode Again go to the control panel sound recording right click on the sound card and select properties select advanced and then select 2 channel 16 bit 44100 Hz CD Quality from the drop down box The dialog boxes for doing this in Windows 7 are shown below Copyright 2012 2013 McIntosh Applied Engineering LLC 13 Sound x Microphone Properties 7 F Playback Recording Sounds Communications General Listen Levels Advanced Select a recording device below to modify its settings Default Format f s y Select the sample rate and bit depth to be used when running Microphone in shared mode 2 USB Audio CODEC ay Default Device annel 16 bit 44100 Hz walit P Microphon 1 channel 16 bit 11025 Hz Dictation Quality Realtek High Definition Audio 1 channel 16 bit 16000 Hz Tape Recorder Quality lt q Ready E1 channel 16 bit 22050 Hz AM Radio Quality 1 channel 16 bit 32000 Hz FM Radio Quality 1 channel 16 bit 44100 Hz CD Quality 1 channel 16 bit 48000 Hz DVD Quality 2 channel 16 bit 11025 Hz Dictation Quality 2 channel 16 bit 16000 Hz Tape Recorder Quality 2 channel 16 bit 22050 Hz AM Radio Quality 2 channel 16 bit 32000 Hz FM Radio Quali 2 channel 16 bit 44100 Hz CD Qual 2 channel 16 bit 48000 Hz DVD Quality Restore Defaults Configure Set Default Propert
21. ard calibration microphone calibration measurement types _ sample holder impedance sample impedance nonlinear sample impedance Perform measurement Copyright 2012 2013 McIntosh Applied Engineering LLC 11 The measurement types are soundcard calibration calibrates the sound card input levels microphone calibration calibrates the complex transfer function between the microphones sample holder impedance _ measures the flow impedance of the sample holder sample impedance measures the flow impedance of a sample nonlinear sample impedance measures the flow impedance as a function of velocity Soundcard Calibration The sound card calibration controls are shown below Acquisition Setup Plotting Files Clipboard Type of measurement to perform soundcard calibration ha Maximum peak to base input voltage Right channel 1 Left channel 1 Perform measurement Sound card calibration determines the maximum input level into the right and left sound card channels by placing a known voltage signal onto the sound card inputs The MAE200 ACVC A voltage calibration source is used to generate the signal Place the voltage calibration source onto both the left and right channels of the sound card as shown in the picture below and press the Perform measurement button If the correct recording sound card was selected in the Setup section a plot of the recorded signal w
22. aveccdimars 4 Plow Ti pe Gan Ce aise saeneesinteecisaateateaindsin aa a a a 4 INA EQOA a U a a E EE T O Sal traahe 5 Care OF the VIA ma MAET reenn A nanale esa destathalbeos 9 SS tee BIOCk Didera iiec a E E A 10 COn rega E E E O 11 ACHUI CONTO Sre aa EA 11 Sounded C Orano a a a a a E E 12 Microphone Calibrations a aos Gorta deck teieien hats aides late A 14 Sampik Holder IM PCG an C Cate dencssisasdtencivnn T 17 Sampe MMP eG ANC Seca sisi a a sacueoaeneuapeectansseoee 24 Nonlinear sample IMpPCdanC Sciam nme racunchan eaen trie A 29 SUD een Once Se ere a eran DIRS ther ene ewe eee en me E en em eae eee ee 31 POUDO ratte Wes WOveent rae erin ce ne etre We TOvteed eee ee Sept E Tr ree Re ed Beem ere rte eee 39 Files WORE reon E e EEA E S 4 Usina the Sani le cutiei a E A O 43 Step by Step Flow Impedance Measurement Example cccccccssseesseececeeeeeesseeeeeeeeeeenaas 44 Copyright 2012 2013 McIntosh Applied Engineering LLC Document Revision History Version Date Comments 1 00 October 2012 Initial documentation release 1 01 April 2015 Separated manual into individual documents Copyright 2012 2013 McIntosh Applied Engineering LLC Flow Impedance Measurement Module The Flow Impedance Measurement module uses the MAE100 apparatus from McIntosh Applied Engineering LLC to measure the flow impedance through acoustical parts such as porous materials membranes or ports The applications are only limited to items that can fit int
23. bove 500 Hz it drops off dramatically However the behavior from 500 to 1000 Hz is misleading as the data over that range is actually a weighted average of the data taken from the low frequency and high frequency stackups and does not fully represent the capability of a single stackup and speaker Also the data shown above used the high frequency speaker enclosure for the high frequency stackup This speaker has a much lower output capability than the much larger low frequency speaker enclosure which further contributes to the sudden velocity drop off above 500 Hz While the particle velocity sensitivity graph provides an indication of the velocity that s possible at each frequency it cannot be used accurately over the 500 to 1000 low frequency to high frequency transition range Drive level for nonlinear measurements The start stop and points parameters detail the range for the nonlinear drive levels The stop level cannot exceed 1 0 and will likely always be set to 1 0 unless you want to limit the upper drive level The start level is to be set as low as possible while still being able generate a Copyright 2012 2013 McIntosh Applied Engineering LLC 30 sufficient microphone signal that can be accurately analyzed A value of 0 001 has been determined to work well which will provide three orders of magnitude in the velocity range Finally the points is usually set to a fairly small value such as 20 Since the nonlinear behavior
24. correctly setup the high and low pass filters should be set to as wide a range as the start and stop frequencies The microphone sensitivities are provided on their calibration sheets An example of a calibration sheet for a microphone with a sensitivity of 1 486 mV Pa is shown below Pressure field NSK 1 4 Microphone Type 4938 Bruel amp Kjzer Calibration Chart Serial No 2538105 Open circuit Sensitivity So Equivalent to Uncertainty 95 confidence level Capacitance Valid At Temperature 23 C Ambient Static Pressure 101 3 kPa Relative Humidity 50 Frequency 251 2 Hz Polarization Voltage extemal 200 v Sensitivity Traceable To DPLA Danish Primary Laboratory of Acoustics NIST National Institute of Standards and Technology USA IEC 61094 4 Type WS 3 P Environmental Calibration Conditions 102 1 kPa 23 47 RH Procedure 704744 Date 3 May 2006 Signature S J Ko 26 Sp Example Ko 26 26 2 0 2 dB The NEXUS setup screen for entering the microphone sensitivities 1s shown below Note that the microphones entered had sensitivities of 1 576 and 1 376 mV Pa Neither one was the microphone from the example calibration sheet above The NEXUS setup screens for the serial port transducer supplies high pass and low pass filter settings and finally the rear electrical connections are shown below for reference Note that these settings can be saved using the Store Recall
25. d is important as all subsequent impedance measurements must be over a frequency range that s covered by the sample holder impedance data Also as with the microphone calibration frequencies Ares will interpolate the sample holder impedance at any measurement frequencies that are not at the exact frequencies at which the sample holder impedance were measured This means that the number of points can be different for the sample impedance measurements and the sample holder impedance measurement The velocity parameter controls the particle velocity that passes through the part during measurement As discussed in the nonlinear sample impedance section the impedance of acoustical parts can be a function of the velocity through the sample In general a part impedance usually changes at high intensities and so nonlinear effects are seen under high SPL or velocity levels Linear behavior is seen at low SPL s and velocities When performing a sample holder or sample impedance measurement it is generally desired to measure the impedance under linear or low intensity condition This is controlled through the velocity parameter The impedance of this sample holder is shown in the screen capture below Note that the impedance is mostly imaginary which is common for a hole or port such as the 10mm sample holder rings Also note that the real part is positive The real part of the impedance must always be positive If it is negative this is a sign of an i
26. data set with the frequency appended to the name Quantity to graph Z real imag C driving pressure drive level SNR estimate C air temperature Pend Pside xfer velocity drive Copyright 2012 2013 McIntosh Applied Engineering LLC 29 The main differences between the nonlinear and linear measurement controls are the additions of the Discrete measurement frequencies and the Drive level for nonlinear measurements Discrete measurement frequencies In this control you are to specify the discrete measurement frequencies at which the nonlinear measurement will be performed The frequencies are separated by spaces In general these are just a handful of frequencies chosen to achieve a large velocity through the sample Due to the resonance behavior of the MAE100 s tube arrangement and the drive capability of the speaker enclosures the maximum velocity varies from frequency to frequency One of the plotting options for the linear impedance data is to plot the velocity drive level or the particle velocity sensitivity This graph provides a good indication of the maximum velocity that can be achieved at each frequency An example of the graph is shown below felt Particle velocity drive level sensitivity m s drive level N 0 1000 2000 3000 4000 5000 300 Frequency Hz As can be seen in the graph the maximum velocity is achieved from about 100 to 500 Hz A
27. data set is created with the flow impedance data in it and added to a list of data sets in the module these data sets are identified by the name given to them in this field note that once a measurement is made the name can be changed in the Files Clipboard section data set comment a string giving a full description of the sample or measurement condition can be entered into this field Copyright 2012 2013 McIntosh Applied Engineering LLC 24 An example of a sample mounted in the MAEI00 SH A sample holder is shown below The sample holder disks are held in place with putty which not only ensures that the sample holder rings stay in place but also prevents sound from going around the ring s perimeter Suggestions on how to apply the putty are made in the measurement example presented at the end of this module s documentation The typical frequency range for a measurement is from 20 to 5000 Hz To ensure accuracy the MAE100 s configuration must change for the low frequencies and for the high frequencies For low frequencies a long tube is needed between the sample holder and the rigid termination For high frequencies this tube needs to be much shorter This necessitates that the MAE100 stackup be changed for low and high frequencies The transition between low and high frequencies is around 800 Hz Also a larger speaker is better at producing low frequencies and a smaller speaker is better for high frequencies For this
28. e sample additional spacing between the sample and the rigid termination microphone the target particle velocity through the sample at which the measurement is to be taken the particle velocity range for the measurement taken about the target velocity the initial drive level out of the playback sound card to the audio amplifier that Ares uses for the initial measurement Ares then adjusts the drive level about this value until the target particle velocity is achieved the closer this drive level is to the final value the less time the measurement will take Copyright 2012 2013 McIntosh Applied Engineering LLC 18 The extra dist I and extra dist 2 parameters require further discussion The MAE100 and MAE102 use slightly different assumptions about the distance from the microphones to the sample surfaces Depending on how the sample is actually mounted these distances may need to be adjusted The extra dist 1 and extra dist 2 parameters allow for these adjustments rigid termination microphone L2 L2 L1 Ll side microphone MAE100 MAE102 For the MAE100 L1 will be the distance from the center of the side or sample holder microphone to the top of the retaining lip that the sample rests upon L2 will be the distance from the top of the sample to the rigid termination microphone L2 will be computed from the physical size o the MAE100 which is programmed into Ares minus the sample thickness The sample holder disks inc
29. ed Engineering LLC 45 The parameters for the sample holder are 2mm thickness each disk is 1mm thick and there are 2 disks being used and the diameter is 10mm the diameter of the open hole in the disk sample holder thickness 2mm F Ol specify area else calc from diameter diameter Press the Perform measurement button Once the measurement is complete you should be able to graph the results by selecting Z real imag and see a plot something like that shown below 3e 006 real imag 2 564006 oa i bi a note that the real part is 2e 006 ri e e e e e e a positive indicating valid ae data if the real part is ever Ea F negative that indicates an P error 5 2 1e 006 E 500000 a Let at very low frequencies the On impedance has gone negative indicating that Ares ai 1000 2000 3000 4000 5000 6000 1S having a hard time Frequency Hz accurately measuring such small impedances Copyright 2012 2013 McIntosh Applied Engineering LLC 7 Sample impedance measurement After the sample holder impedance has been measured you now remove the sample holder disks and mount the sample between them as shown in the image sequence below the sample cutter is shown to remind you how to make a sample from a bulk sheet of material this final picture shows the high frequency stackup of the MAE100 compon
30. ement without having to move the electrical power connector between the speakers When the Perform measurement button is pressed Ares will look at the measurement frequencies and instruct you as to what the stackup should be For low frequencies the following dialog box will appear and the appropriate stackup is shown on the right Place the 150 mm spacer between the sample holder and the ridig terminaton The stackup should be rigid terminaion MAE100 RTMIC 4 150 mm spacer MAE100 150MM 4 sample holder MAE 100 5H 4 speaker box MAE1O0 LFSP 4 or MAE100 HFSP 4 Cancel After the low frequencies are acquired it will prompt you for the high frequency stackup Place the 15 mm spacer between the sample holder and the ridig terminaton The stackup should be rigid terminaion MA amp 4E100 RTMIC 4 15 mm spacer MAE100 150MM A sample holder MAE100 5H 4 150 mm spacer MAE100 150MM A lt optional but recommended speaker box MAE100 LFSF A or MAE100 HFSF A Cancel Copyright 2012 2013 McIntosh Applied Engineering LLC 26 During the measurement the Perform measurement button changes to Stop measurement which allows the user to abort the measurement If a measurement is aborted a new data set will not be created When the measurement is completed the data is copied into a new dataset and the results from the measurement will be displayed on the right side of the Ares window as shown below The new dataset wi
31. ents 47 Copyright 2012 2013 McIntosh Applied Engineering LLC For a highly resistive material such as the felt tested the impedance should look something like that shown below Again note that the real part is positive Any negative values in the real part indicate that something 1s wrong with the measurement 4e 006 real aS img a ee aie 3e 006 A t gear A J D Eoy P 7 i G T ff A 2 2e 006 r 3 3 ae J 3 E o ae QO S 3 a 1e 006 to ke Pits RE S ee A ws ae S d m prr 0 ae y 0 1000 2000 3000 4000 5000 6000 Frequency Hz Copyright 2012 2013 McIntosh Applied Engineering LLC For more information about Ares and acoustical measurement and modeling tools and services contact MAE at info MAELLC COM support MAELLC COM 678 234 5079 Or see us at MAELLC COM Copyright 2012 2013 McIntosh Applied Engineering LLC 49
32. ere the sound cards and RS232 ports are specified The sound cards are used for playing the excitation signal out to the speakers and for recording the signals from the microphones for analysis The serial RS232 COM ports are used for accessing the B amp K NEXUS amplifier and the EXTECH thermocouple meter Copyright 2012 2013 McIntosh Applied Engineering LLC 31 There are also a few other setup options that will be discussed NOTE these settings are saved to the Ares cfg file when Ares exits so they don t have to be reset every time Ares is used The setup controls are shown below Acquisition Setup Plotting Files Clipboard sound cards for measurement Recording device connect to mics Left channel NEXUS Ch 1 termination mic Right channel NEXUS Ch 2 side mic Playback device connect to speaker USB Audio CODEC 2 release sound card resource select output channel behavior left low freq right high freq Play fullscale chirp out L amp R chans Play Record pulse from soundcards R5232 COM port for B amp K NEXUS COM100 w Note the NEXUS must be properly programmed with the microphone calibration values Also set baud to 2400 and echo on R 232 COM port for EXTECH 421509 COMS TZ thermocouple v Test thermocouple meter Apparatus to use MAE100 k Recording device connect to mics The recording device is the PC sound card that measures the signal from the B amp K NEXUS micro
33. es Clipboard allows for data to be exported or imported to individual files or clipboard JS Ae module 1 Flow Impedance Measurement my File Edit View New Module Modules Window Help Oa ENE TO i Acquisition Setup Plotting Files Clipboard Type of measurement to perform soundcard calibration v Maximum peak to base input voltage Right channel 1 y Left channel 1 Perform measurement _ to lo f La on co oO Acquisition Controls The Acquisition controls are used for all data measurements and so will likely be used the most of the four tab items For this reason they are the first set of controls on the tab However before the Acquisition controls can be used the hardware must be configured in the Setup controls We will discuss the Acquisition controls first but understand that the Setup controls need to be configured first Once the Setup controls have been configured they will be saved to a default configuration file when Ares terminates and so will not have to be configured again There are five different types of data acquisition operations or measurement types each with its own set of controls The type of measurement to be performed is selected with the list box at the top of the controls as shown below Acquisition Setup Plotting Files Clipboard Type of measurement to perform drop down listbox pee soundcard calibration soundc
34. evels should be in the range from 1 to 10 V Ares does not have control over the microphone gains applied by the sound card so the user must go into the Windows Control panel and make any necessary adjustments to the input microphone levels to get the calibration values within this 1 to 10V range Since every sound card driver interface is different due to drivers and Windows versions the user is left to himself to figure out how to do this for his particular sound card However in general you want to go to the Control Panel select Sound select Recording right click on the sound card being used for recording and then go through the controls to adjust the microphone gain The dialog boxes for doing this in Windows 7 are shown below p Sound 2 Z Microphone Properties ex Playback Recording Sounds Communications General Listen Levels Advanced Microphone Select a recording device below to modify its settings Microphone 2 USB Audio CODEC ay Default Device Microphone Fr Realtek High Definition Audio Ready Configure Set Default Y Properties OK Cancel Apply IMPORTANT Ifthe maximum input levels for the left and right channels are computed to be identical then it s very likely that the sound card is set to mono and not stereo The sound card MUST be set to stereo to function properly
35. generally has a fairly simple behavior greater detail provided by more points generally isn t required Also if too many points are requested at high drive levels this may cause the speaker to get too hot and burn out so some care should be taken when deciding to drive the speaker hard for long periods of time An example of nonlinear measurements of a highly resistive felt material at three frequencies 100 250 and 500 Hz is shown below It s readily seen that the curve for each frequency very nearly lie on top of each other This is largely due to the real part of the impedance dominating the imaginary part and the real part having very little frequency dependences at lower frequencies 5e 006 teal 100 Hz imag 100 Hz teal 250 Hz 4e 006 imag250 Hz real 500 Hz ae all imag 500 Hz 3e 006 Acoustic Ohms Impedance 2e 006 1e 006 0 0 5 1 1 5 2 25 Particle velocity m s The behavior of the real part is very typical of the nonlinear behavior of resistive materials At low velocities the impedance is constant and at higher frequencies the resistance rises linearly with the velocity forming a linear nonlinearity if you don t mind a term with a bit of contradiction Then there is a parabolic transition between the two extreme regions Setup The setup controls are wh
36. ies a ma O Ca Ee Microphone Calibration Microphone calibration measures the relative amplitude and phase difference between the recorded signals from the two microphones This is a function of not only the microphones but the microphone amplifier and the sound card hardware The microphone calibration controls are shown below Acquisition Setup Plotting Files Clipboard Type of measurement to perform microphone calibration v Frequency parameters start 20 Hz Wh stop 5000 Hz v points 200 j C log frequency spacing Target SPL for microphone calibration pressure 90 SPL vi target 6 SPL vi Initial normalized drive level for target level 0 1 0 01 Perform measurement Quantity to graph magnitude phase C pressure C drive level C SNR estimate These are quite a bit more complicated than the sound card calibration All measurements with the Flow Impedance Measurement module are performed at discrete frequencies so you must enter the starting and stopping frequencies and the number of frequency points to be taken There is also the option to space the frequencies linearly or logarithmically The frequency range is important as all subsequent impedance measurements must be over a frequency range that s covered by the microphone calibration frequency range If you start the microphone calibration at 20 Hz you cannot perform an impedance measurement at 10 Hz
37. ill appear in the Ares window This is a high frequency signal recorded over many periods so it just appears as a solid color on the graph However if you right click on the graph and select Zoom from the popup menu you can draw a box around the data to zoom in on it The original data and the data zoomed in on are shown below Copyright 2012 2013 McIntosh Applied Engineering LLC 12 085 ieee module 1 Flow Impedance Measurement SS module 1 Flow Impedance Measurement E File Edit Yiew New Module Modules Window Help E File Edit View New Module Modules Window Help BEA EESE 2 Dae bel DRO Sound Card Calibration Data i Acquisition Setup Plotting Files Clipboard Type of measurement to perform la Acquisition Setup Plotting Files Clipboard Type of measurement to perform soundcard calibration v soundcard calibration Maximum peak to base input voltage Right channel 1 71065 ly v Left channel 1 70007 v Maximum peak to base input voltage Right channel 1 71065 iv a Vv i Perform measurement Perform measurement E amp o recorded data 2000 0 10000 20000 30000 40000 50000 o000 70000 80000 90000 15800 15900 16000 16100 16200 sample NUM When completed Ares calculates the maximum input levels into the sound card channels and displays them in the Right channel and Left channel fields These l
38. ill refer to both as acoustic impedance or flow impedance and differentiate the two by providing the appropriate units One of the critical assumptions behind the concept of flow impedance 1s that the velocity through the acoustical part is uniform That is the velocity into the left side is exactly equal to the velocity out of the right side This necessitates that the part be much thinner than the wavelength of sound Since the wavelength A is a function frequency f according to c f where c is the speed of sound the wavelength will be the smallest at high frequencies For air at room temperature c is approximately 343 m s The MAE100 device measures impedance up to a maximum of 6000 Hz so the smallest wavelength will be approximately Amin 343 6000 6 cm Thus the thickness of the acoustical part should be much less than 6cm So part thickness lt lt 6 cm or part thickness lt 6 mm So for the flow impedance measurement to be meaningful the thickness of the part should be less than 6 mm MAE100 Apparatus The MAE100 is the hardware system provided by McIntosh Applied Engineering LLC for measuring flow impedance It consists of an excitation speaker a sample holder a spacer tube and a rigid termination It uses two microphones one on the speaker side of the sample and one in the rigid termination A sketch of it is shown to the left below and a photo of an actual unit is to the right The photo is showing the low
39. ineering LLC 23 Sample Impedance The majority of the measurements will be done with the Type of measurement to perform set to sample impedance The controls are shown below Acquisition Setup Plotting Files Clipboard Type of measurement to perform sample impedance Sample holder thickness 1 mm Sample parameters thickness 1 mm specify area else calc from diameter diameter 3 mm x extra dist 0 mm z extra dist2 0 mm lt Frequency parameters start 20 Hz v stop 5000 Hz s points 200 log frequency spacing Target particle velocity for linear measurements velocity 0 1 mis target 0 02 mis Initial normalized drive level for target level 0 1 0 01 v subtract sample holder impedance data set name data set 1 data set comment Perform measurement The sample impedance controls are similar to the sample holder measurement section but with a few important additions sample thickness along with the sample holder thickness the sample thickness is provided the total thickness mounted in the sample holder will be the sample holder thickness plus the sample thickness subtract sample holder impedance _ this feature allows you to specify if the sample holder impedance is to be subtracted from the total measured impedance or not sometimes you want the total impedance in this case leave this option unchecked data set name every time a sample measurement is made a new
40. ion is placed on the MAE100 stackup pieces Copyright 2012 2013 McIntosh Applied Engineering LLC 38 Photos of the thermocouple meter is shown below with a thermocouple plugged into the T2 channel Apparatus to use This option selects which apparatus is being used for the flow impedance measurements Presently only the MAE100 is being supplied by MAE The other option is a DP which is an older device which is not commercially available Plotting The plotting section allows for the measured data sets to be plotted The controls for this section are shown below Acquisition Setup Plotting Files Clipboard Quantity to graph flow impedance real imag C flow impedance mag phase C plot impedance as MKS Rayls C particle velocity through sample C particle velocity sensitivity C normalized drive level CI SNR estimate C Pend Pside transfer function C temperature nonlinear data only C transmission loss TL from Zf C plot sample holder data Data sets sample holder 500 Hz felt felt 100 Hz felt 250 Hz felt 500 Hz C plot data for selected data set Copyright 2012 2013 McIntosh Applied Engineering LLC An asterisk to the left of a data set name indicates that data set will be plotted Data sets are selected or de selected for plotting by click on the data set name in the list check or uncheck the plot data for selected data set checkbox Linear data and nonlinear data a
41. laced ontop Copyright 2012 2013 McIntosh Applied Engineering LLC 27 Note that as the stackups are changed through the measurement process the 5mm spacer will remain on top of the sample Pressing Perform Measurement button instructs the user to place the 145and 5 mm spacer on the stackup as shown in the left image below Next the 22 and 5 mm spacers shown below in the center and then finally just the 5 mm spacer as shown in the far right below The impedance measured from the disk with a 2mm hole is shown below Note the behavior up until 1OkHz is essentially a damped mass reactance Then above 10 kHz the behavior becomes complex probably due to plate modes Flow Impedance Acoustical Ohms Copyright 2012 2013 McIntosh Applied Engineering LLC 28 Nonlinear Sample Impedance For a linear system the impedance of an acoustical part is well defined by the flow impedance Zt P U where P is the pressure drop across the part and U is the volume velocity through it However as the acoustic intensity of the excitation is increased this linear relationship typically breaks down and a change in Zr can be observed at higher levels While it s natural for a person to want to characterize behavior according to sound pressure level because that is what ears respond to the nonlinearities are better characterized by the velocity This is largely due to the fact that the velocity through the part is constant that is the velocity in
42. ll appear in the dataset lists in the Plotting and Files Clipboard sections ae manual measurements Oct 5 2012 00 module 1 Flow Impedance Measurement Mm File Edit View NewModule Modules Window Help DAE bhai Op Acquisition Setup Plotting Files Clipboard Type of measurement to perform sample impedance v Sample holder thickness 2 mm Sample parameters thickness 1 mm O specify area else calc from diameter diameter 10 i Frequency parameters start stop points Cl log frequency spacing Target particle velocity for linear measurements velocity 0 1 mis target 0 02 mis E oO oO a 3 8 s 113 i a amp Initial normalized drive level for target level 0 1 0 01 subtract sample holder impedance data set name Gore GAYW103 data set comment Perform measurement Quantity to graph Zreal imag C particle velocity O driving pressure drive level C SNR estimate Pend Pside xfer C velocity drive 3000 Frequency Hz Ready MAE102 measurements Measuements with the MAE102 are similar to the MAE100 but the components are different The left image below shows a white plastic sample with a 2mm hole through the center setting in the MAE102 SH A sample holder The 5mm MAE102 5MM A spacer is waiting to be placed onto the sample The right image below shows the 5mm spacer placed on top of the sample and the MAE102 RTMIC A rigid termination waiting to be p
43. luded with the MAE100 have varying diameters that a bulk sample disk 1s expected to be placed between these will be shown shortly When using these the sample stackup will look something like the cross section sketch below L2 fh ts gt nd L1 d sample holder disks L1 is the distance to the top of the sample holder lip but the sample holder disk increases this distance slightly For low frequencies this extra distance can largely be ignored but 1f its to be taken into account you cannot simply set extra dist 1 equal to the sample holder thickness tp Rather the extra dist should represent the extra volume of air at the MAE100 s internal diameter of 25 4mm So if the d is the sample diameter the value for extra dist 1 should be Copyright 2012 2013 McIntosh Applied Engineering LLC 19 d 2 extra dist 1 t s 25 4mm which will compute a value for extra dist 1 that will have the same air volume held in the sample holder So if the sample holder disk is 1mm in diameter and has an open area of 10mm extra dist I will be 1 10 25 4 42 0 155mm For most situations this can be ignored as the MAE100 generally measures lower frequencies than the MAE102 By default L2 will only be shortened by the thickness of the sample but due to the sample holder disks this means that Ares will expect L2 to extend under the sample as drawn To correct for this extra dist 2 will actually need to be negative In this case the entire
44. naccurate measurement WEP R57 module 1 Flow Impedance Measurement PN Fie Edit View New Module Modules Window Help D E EEE E n Acquisition Setup Plotting Files Clipboard Type of measurement to perform sample holder impedance v Sample holder thickness 2 mm O specify area else calc from diameter diameter 10 mm Frequency parameters start stop points C log frequency spacing Target particle velocity for linear measurements velocity 5 mso B target mis Impedance Acoustic Ohms Initial normalized drive level for target level 0 1 0 01 Perform measurement Quantity to graph Zreal imag C particle velocity C driving pressure drive level CI SNR estimate Pend Pside xfer Sol C velocity drive Pisum Ho Ready The sample holder plotting options include some new graphs particle velocity the particle velocity through the sample that was achieved driving pressure the pressure on the speaker side of the sample holder drive level the normalized drive level out to the speaker Pend Pside xfer the transfer function of the acoustic pressure at the rigid termination end over the pressure at the speaker side of the sample holder velocity drive the ratio of the particle velocity over the normalized drive level indicating the sensitivity of the particle velocity to the drive level output Copyright 2012 2013 McIntosh Applied Eng
45. ne amplifier If the EXTECH thermocouple meter is being used the COM port and thermocouple channel for that will also have to be selected The Test thermocouple meter button can be used to verify the thermocouple is properly connected to the PC 4 Select the MAE100 as the Apparatus to use in the Setup section Make sure the MAE100 device is selected in the Setup section Copyright 2012 2013 McIntosh Applied Engineering LLC 44 5 Microphone calibration If the microphones haven t been calibrated with the selected sound cards they will need to be calibrated See the microphone calibration section for details Magnitude dB Phase ep ve a ra Magnitude dB 8 yj A 02 0 15 T SET 0 1000 2000 3000 4000 5000 6000 0 1000 2000 3000 4000 5000 6000 Frequency Hz Frequency Hz 6 Sample holder impedance measurement If the sample holder impedance is not to be included in the sample impedance the sample holder impedance must be measured Below are a Series of pictures showing two sample holder disks being mounted in the sample holder for this measurement Note that the blue putty is necessary to not only hold the disks in place so they don t vibrate but it also prevents sound from passing around the perimeter of the disks and not through the sample area Copyright 2012 2013 McIntosh Appli
46. nnel For a high frequency measurement where the MAE100 apparatus stackup is for a high frequency measurement using the 15mm spacer between the sample holder and the rigid termination the output on the playback device will only be on the right channel The left low freq right high freq option is useful if both of the low and high frequency speaker enclosures are being used However if only one speaker enclosure is used for both the low and high frequencies this option won t be useful Play fullscale chirp out L amp R chans This button is helpful when setting the volume levels of the MAE200 AAMP A stereo audio amplifier It produces a fullscale i e maximum sound card volume chirp signal to be played out of the playback sound card The starting and ending chirp frequencies come from the Acquisition controls Copyright 2012 2013 McIntosh Applied Engineering LLC 33 The recommended use of this feature 1s 1 connect the speaker enclosure s that is are to be used to the MAE200 AAMP A sound card leave the tops of the speaker enclosures open so the sound can easily radiate from the speaker 2 turn the volume for ch1 and ch2 of the amplifier down to zero 3 press the Play fullscale chiro out L amp R chans button to begin the chirp signal 4 slowly turn up the audio amplifier s ch1 and ch2 volumes until the speaker on that channel is as loud as they can safely be without damaging them Step 4 is very subjective It has been the au
47. o the MAE100 one inch diameter tube Flow Impedance Flow impedance Z is the ratio of pressure drop P across an acoustical part divided by the volume velocity U through it TT TI U mM P Zt P U Pa s m or Acoustical Ohms where all the quantities P U and Zs are complex phasors NOTE Ares uses the el phasor representation common in electrical engineering and not the e phasor representation common in physics For MKS values P is measured in Pa and U 1s measured in m s Ares refers to the units of Pa m s or Pa s m as Acoustical Ohms When the acoustical part to be measured is a uniform material such as a cloth or mesh the flow impedance can be normalized by its surface area When this is done the volume velocity U is replaced by the particle velocity V which has units of m s or Zt P V Pa s m or MKS Rayls The resulting impedance will have units of Pa s m or MKS Rayls The unit of Rayl is named after Lord Rayleigh who was one of the founders of the field of acoustics Since U and V are related by the surface area S U S V The units of Acoustical Ohms and MKS Rayls can be related to one another by the surface area Zr Acoustical ohms Ze MKS Rayls S m Copyright 2012 2013 McIntosh Applied Engineering LLC NOTE The units of MKS Rayls 1s frequently referred to as specific acoustic impedance and Acoustical Ohms as just acoustic impedance However the author finds these terms confusing and w
48. phone erence amplifier calibrator Sanne thermocouple USB sound MAF202 AAMP A MAE100 MICCAL A cutter meter MAE203 THERMO A sound card calibrator MAE200 ACVC A rigid termination MAE100 RTMIC A Copyright 2012 2013 McIntosh Applied Engineering LLC 150 mm spacer MAE100 150MM A cards MAE204 USBSC A sample holder rings MAE100 1SMMSHD A MAE100 10MMSHD A MAE100 3MMSHD A 15 mm spacek MAE100 15MM A MAE100 1LINCUT A low frequency excitation speaker MAE100 LFSP A high frequency excitation speaker MAE100 HFSP A sample holder MAE100 SH A The smaller parts for the MAE100 come in a padded case A photo of it is shown below rigid termination MAE100 RTMIC A 15mm spacer MAE100 15MM A 150mm spacer MAE100 1S50MM A 1 sample cutter MAE100 1INCUT A spare fuses 1A and 3A 1 25x0 25 sample holder MAE100 SH A high frequency speaker enclosure MAE100 HFSP A Copyright 2012 2013 McIntosh Applied Engineering LLC sound card calibrator MAE200 ACVC A sample holder rings MAE100 3MMSHD A MAE100 1OMMSHD A MAE100 15MMSHD A sample with factory measured impedance data MAE100 SAMPLExx A spare speaker for the high frequency speaker enclosure MAE100 SPK A microphone preamp cables B amp K Type 4938 A 011 microphones B amp K Type 4938 MAE102 High Frequency Acoustic Flow Impedance Measurement Apparatus The MAE102 is an alternative measurement apparatus that can be used ins
49. phone amplifier The microphone signal must be connected to the sound card inputs sometimes labeled as microphone inputs The left channel is to be connected to the NEXUS Ch 1 output whose signal is to come from the microphone located in the MAE100 RTMIC A rigid termination The right channel is to be connected to the Ch2 output whose signal is to come from the side microphone located in the MAE100 MICHLD A sample holder As mentioned under the microphone calibration section in the acquisition controls it may be necessary to adjust the output type of the sound card to 2 channel 16 bit 44100 Hz CD Quality and adjust the input level sensitivity NOTE If the sound cards change due to plugging or unplugging a USB sound card the sound cards listed in the Setup controls will be inaccurate They can be updated by selecting another option in the tab controls such as Acquisition and then selecting Setup again This works for the other controls as well such as the RS232 COM ports Copyright 2012 2013 McIntosh Applied Engineering LLC 32 Playback device connect to speaker The playback device is the PC sound card that generates the audio signal for the MAE204 USBSC A stereo amplifier input that drives either the MAE100 LFSP A low frequency speaker enclosure or the MAE100 HFSP A high frequency speaker enclosure NOTE It has been observed that using the same USB sound card for both the recording device and the playback device doesn
50. re plotted on separate graphs This is necessary because linear data is plotted with a frequency abscissa axis and nonlinear data 1s plotted with a particle velocity abscissa axis The quantities that are plotted are those acquired during the measurements The one exception to this is the transmission loss TL This is a quantity that is computed from the flow impedance and sample area When the right mouse button is used to click on a graph several plotting options appear in a popup menu This menu is shown below oa hy Copy trace data to clipboard as tab delimited text For real Felt Copy graph imag Felt SOOM l l utoscale e g These options can be used to copy the data in text format for individual curves copy the entire graph as an image zoom into the graphs or autoscale the graph Copyright 2012 2013 McIntosh Applied Engineering LLC 40 Files Clipboard The Files Clipboard section allows for individual data files to be saved from or loaded into the module instance Note that all of the data in the module will be saved to a ARES file and none of them explicitly need to be exported However there are occasions when it s useful to do so especially for the sample holder impedance data The controls for this section are shown below Acquisition Setup Plotting Files Clipboard Microphone calibration files Sample holder impedance files Data sets sample holder 500 Hz felt felt 100
51. reason the MAE100 LFSP A low frequency speaker enclosure is better for the low frequency stackup and the MAE100 HFSP A high frequency speaker enclosure is better for the high frequency stackup Further it is recommended but not essential that the long 150mm spacer tube be placed between the speaker enclosure and the sample holder when performing high frequency measurements These two stackups are shown below The low frequency stackup is on the left and the high frequency stackup is on the right 25 Copyright 2012 2013 McIntosh Applied Engineering LLC The high frequency speaker enclosure can be used for all frequencies but it won t be able to generate very loud sound for frequencies below 300 Hz and so the quality of the low frequency data may suffer It s best if the low frequencies are measured with the low frequency speaker enclosure and the high frequencies are measured with the high frequency speaker enclosure However moving the banana power connector between the two speakers can be annoying so an option exists in the Setup section left low freqs right high freq that allows the excitation tones to only be played out the left channel for low frequencies and the right channel for the high frequencies In this way the low frequency speaker can be connected to the left channel and the high frequency speaker to the right channel You only need to transfer the brass stackup between the speakers when performing the measur
52. stackup is shown below with photographs of an actual measurement below that 3 g amp MAF102 RTMUC A Rigid mic termination NIAF 102 S INEA Sinm spacer BEK mic holder MAF 102 SH A Sample holder F xcitation speaker either the MAE100 HFSP_A or MAE100 LFSP A Copyright 2012 2013 McIntosh Applied Engineering LLC 16 The microphone calibration curves for the MAE102 are substantially different from the MAE100 An example is shown in the screen capture below Bac Acoustic System Ares1 module 1 Flow Impedance Measurement a i File New Module Modules Window Help O E mi R CALC Stop Acquisition Setup Plotting Files Clipboard Type of measurement to perform microphone calibration v Frequency parameters start 20 stop 5000 points 200 E log frequency spacing Magnitude dB Target SPL for microphone calibration pressure 90 SPL target 6 SPL Initial normalized drive level for target level 0 1 0 01 Perform measurement Quantity to graph Phase deg v magnitude phase pressure drive level SNR estimate 8000 10000 Frequency Hz NUM Sample Holder Impedance When measuring the flow impedance of a part you typically mount it in a sample holder so the total impedance will be the part s impedance plus the impedance of the sample holder Lrotal Z part holder To get just
53. sults NOTE Using the cutter as a punch where a hammer or mallet is used to punch the cutter through a material will likely result in bending the cutter shaft and it NOT recommended 43 Step by Step Flow Impedance Measurement Example Setup 1 Select sound cards for recording and playback 2 Use Play fullscale chirp out L amp R chans to verify that the correct playback sound card was selected and set the volumes of the stereo amplifier 3 Use the Play Record pulse from soundcards button to verify that the correct recording sound card was selected and that the sound cards are behaving properly You ll probably want to mount the microphones in the MAE100 MICCAL A microphone calibrator as shown below on the left You ll also need to verify that the sound cards are working properly as described in the Setup section where the Play Record pulse from soundcards button operation is described The recorded pulse should look like the image below on the right
54. tead of the MAE100 The MAE102 has an internal diameter of 12 mm as opposed to the 25 4mm diameter o the MAE100 The 12mm diameter allows the MAE102 to go to higher frequencies than the MAE100 The case that the MAE102 components come in is shown below with the associated part number for all of the components The MAE102 may not come with B amp K 1 4 microphone holders If not these holders will need to be shared with the MAE100 The MAE102 s operation is very similar to the MAE100 but there are some differences When appropriate the MAE102 s configuration will be shown after the MAE100 Rigid Termination 2 5mm Spacer MAELO2 RTMIC A MAE102 2 5MIM A 5mm Spacer MAELO2 5MM A 145mm spacer MAELO2 145MM A 225mm Spacer MAEL0O2 2 2 MM A Sample Holcder MAE1O2 SH A Copyright 2012 2013 McIntosh Applied Engineering LLC Care of the MAE100 and MAE102 The brass and aluminum parts of the MAE100 need to be kept in good condition The flat parts that mate together are smoothly machined so as to create a near airtight seal simply from their weight bearing down on where they are joined This means that complicated sealing mechanics aren t needed However to maintain a good seal condition these surfaces must be kept flat and smooth Since brass is a relatively soft material it s easy to damage these surfaces by accidentally hitting the brass parts together Treat these surfaces with great care and repair them if they become damaged
55. thor s experience that if one listens carefully to the speaker one can hear at what point the speaker starts generating nonlinear distortion This is usually just beyond the maximum drive level that the speaker can handle without damaging itself When that point is reached back the volume down a little to the point where the distortion isn t too severe and use that point as the maximum drive level for the speaker Hopefully the speaker s fuse will blow before the speaker is irreversibly damaged from being overdriven If a speaker is damaged spare replacements should have been provided with the MAE100 or can be ordered from MAE Play Record pulse from soundcards This button causes a very short tone burst to be played out the sound card both the left and right channels while simultaneously recording the microphone signals The signal is actually a 100ms 1kHz pulse at 1 40 of the maximum output level followed by a 100ms 1kHz pulse at 1 4 of the maximum output level followed by another 100ms 1kHz pulse at 1 40 of the maximum output level Place the microphones over the speaker so they can record the sound from the speaker The MAE100 MICCAL A microphone calibrator holder can be used for this If the sound cards are working properly the result should be something like that seen below There will be two graphs one for the left channel and one for the right channel sound card level LEFT Time seconds Copyright 2012 2013
56. to one side of the part is the same velocity exiting the other side The sample impedance measurements try to control these nonlinearities by performing the measurement at a fixed particle velocity through the sample at every frequency To perform a nonlinear measurement the frequency is held fixed and the impedance is measured as the intensity is increased The intensity is controlled by the output drive level from the playback sound card So instead of varying the frequency the nonlinear measurements vary the drive level Since when making nonlinear measurements the goal is usually to maximize the velocity through the sample the measurement will always want to go to the maximum drive level This being the case it makes more sense to specify a drive level range rather than a velocity range The maximum drive level range will automatically achieve the maximum velocity range The controls for the nonlinear sample impedance measurement are shown below Acquisition Setup Plotting Files Clipboard Type of measurement to perform nonlinear sample impedance v Sample holder thickness 2 mm wl Sample parameters thickness 1 mm v C specify area else calc from diameter diameter 10 mm vl Discrete measurement frequencies frequency 100 250 500 Hz Al Drive level for nonlinear measurements start 001 stop 1 points 20 subtract sample holder impedance data set name felt data set comment Note Each frequency generates its own
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