DSP-PC for 5 - Bodzio Software
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1. room frequency response to 17 70Hz 115 140 10 Zo 30 40 AL a0 100 200 Hz Figure 10 Room equalization THX Certification Well this is not about getting the official THX certification but it s perhaps worth to consider if your design would qualify as a commercial THX system As you may imagine directors and movie producers have every intention to deliver a high quality sound and picture to your living room so that impact of both is exactly as they intended To accomplish this on the acoustical side you need to recreate the bandwidth and intended SPL levels for the surround and subwoofer loudspeakers The THX defines OdB reference level to be 85dB SPL basically at your listening position And then you must provide 20dB headroom Therefore your surround speakers should be able to provide a peak undistorted sound at 105dB SPL level Subwoofer requirements are even more demanding The reference level is 10dB SPL and the peak is elevated to 115dB SPL This is seriously loud However accommodating these requirements is easily accomplished by selecting appropriate power amplifiers and loudspeaker drivers to attain the required SPL levels Our multi channel MA1240a amplifier would possibly suffice for smaller to average size room but if you have larger size room then you may need to beef up on the audio power The same goes for subwoofers Playback Control Job s done You are now ready to sit down2. B Figure 9 Complete Front Left channel loudspeaker system Similar process would be applied to midrange and tweeter drivers and final outcome is depicted on Figure 7 and Figure 8 As you can see I employed Linkwitz 2 order filters with crossover frequencies of 500Hz and 5000Hz In this design I have included RoomEQ component as well and it is available for each of the loudspeaker boxes in the HT system giving you six built in room equalizers to work with Also one shelving element is included for in room voicing tweaks on the bass side Sensible Room Equalization Before I close the design part of this process it is worth to measure the in room SPL performance of each loudspeaker The Ultimate Equalizer is furnished with it s own MLS measurement system so this task 1s relatively simple The goal of this design phase is to check for any obnoxious room modes Typical audio visual room will exhibit modal resonances which essentially add unwanted coloration to the sound You can measure the SPL in several up to 6 locations and automatically obtain averaged SPL as well The effect of gentle room equalization can be observed on a subwoofer measured in room see Figure 10 Here the room modes result in excessive SPL from 25 55Hz For instance 32Hz tone will sound disproportionably louder than 20Hz Applying sensible room equalization blue curve will result in flattening the unwanted bumps and effectively extending flat in
3. DSP PC for 5 1 Home Theatre System By Bohdan Raczynski Bodzio Software Pty Ltd Is it becoming quite common these days to see a personal computer sitting somewhere in the audio video room and providing centralized audio video server capabilities Additional functionality described in this article brings the audio performance of an active 5 1 HT system to a new level Basic functional concept DSP based audio systems such as Ultimate Equalizer UE offer attractive new sound processing functions which are not available in traditional passive crossover loudspeaker systems The four most important DSP contributions would be 1 Acoustic amplitude SPL and acoustic phase equalization of individual drivers and complete system 2 Linearization of system phase to a flat line 3 Intelligent room equalization 4 Precise crossover filtering function It 1s perhaps worth mentioning at this point that active loudspeaker system discard all issues related to impedance of the driver making the design of such loudspeaker system significantly less complicated and more accurate As a general concept a device described above and implemented as a Windows software program can be running on a personal computer equipped with a suitable sound card s This device would be used to compliment Windows Media Player for audio only sessions or Windows Media Player for a video sessions running on your PC Connectivity Windows 7 Home Pr
4. He Fo 1000 0 Hz Fo 1000 0 Hz Fo 180 4 Hr areal Darrai Darrai Darsa is Darel Dasal feral Gare F Daszal Darsa LB OeByoot LP dimot LP 6d8ot LA SaB oot LP OdBfot LS tiiat LA OdBvoct LP Od Boot AN Le bayor LP Sd Bfoot Le dBat Po 1000 0 Hz Fo 1000 0 Hz Fo ldd Hz Fo iodd Hz Fo 1000 0 Hz Fo i0000 He Fo 10002 Hz Fo lit d Hz Fo 1080 0 Hz Fo IM66 0 Hr Po 00 0 He Fo iddd He Dessal Dare i Dessai Daira a Deteal LP 6d ot LB dBat LF daoo LP OdB oot I LP OdBfoot LB dijoa Fo 1000 0 Hz Fo 100 5 He Fo 000d Hz Fo 1008 0 Hz Fo 1000 0 Hz Foi 1800 5 Hz 1 e IN Phase Ozin 0 0 48 Gon 1 0 d Barsa Hertel p r Neccal Bestal Lr gwon LE yawo ti e es slfk LY o oavroct Lt yawo Te 1000 0 tie Fs 000 0 Ite rae Fe 1000 0 lie Fo 10000 he Hat tatra accel of a s Lr Odivoct LY Gobet LY Udo LY Oguoct tettel n Fe 1000 0 tle Fo 10000 1i Fo 10000 Ie fo 1000 0 lie heoa batrai tettel Lr tdtvoct LY favo LY vemost LP Gayot Fa 1000 0 lle Te 1000 0 tie Fa 1000 0 1e fa 10000 tir bercel Harcsa Lr yayan LP Yawo vah uu dy LY Odwioct k Yast To 1000 0 te Pa 1000 0 Iie To 00 0 tle fe 10000 te gt tk a HFI Thos a Ma T barrat Bartel HOut13 s Vain UY oe Lr Qdb oot Lt Robot LY pawos Lr Dawo ghee Loaded Fo M00 D0 ile Fe 10000 hie Fe 10000 lm fer 1000 0 ile A th Wane FI 10000 0 tle Figure 1 Example of a 15 channel surround sound system design This system would consume 15 sound card output chann
5. aay EE eT z i P y i Right Powered Subwoofer 3 way Front Right i AudioVideo Music Server Er si X Gri a _ E E uw 12 channel Mukiamplifier 2 way Rer Left 2 way Rear Right p m J a ea od d 1 peal y b p 3 J w 9 way Centre F iy Figure 2 14 amp channel surround sound DSP PC based loudspeaker system DSP PC hardware implementation The Ultimate Equalizer is an advanced complete software package allowing you to measure loudspeaker SPL process the results of measurements model diffraction effects design 6in l6out loudspeaker setup and finally play the sound through it as a fully equalized crossover with an addition of intelligent room equalization This is actually quite a lot of functions However this article will not involve loudspeaker SPL measurements performed by the Ultimate Equalizer 2 The intended focus of this article is on the design of the 5 1 HT system The program has been written using the new exclusive mode WASAPI audio engine and runs on Windows 7 64 bit and Windows 7 32 bit operating system The motherboard eg MSI X58 Pro E Series shown on Figure 3 requires two PCI slots as there are two DeltalO1OLT sound cards used This configuration will allow you to design and run loudspeaker system with 6 inputs and 16 outputs just right for a large 5 1 HT system For additional information about sync
6. al transfer functions of your loudspeaker or frequency and phase responses if you like are both flat lines Such loudspeaker will reproduce square waves at the listening location Butterworth ut2 LP 48dB oct a 4 Nb File Loaded Fo 1000 0 Hz EQ Range T 2 200 0 Hz Del 0 000 ms IN Phase Gain 0 0 dB Driver And Output Port Control Driver File Name F ASplitter_Window_RoomEQ_work Test_18_W7_l_new wit Driver s Frequency Response HBT Equalized Between Sound Card Output Assignment Graphical Output Control Fl 20 00 Hz F2 200 00 Hz Port 2 Node 1 IW Include This Port in Filter Plots Channel Delay Distance cm Channel Phase Channel Gain Cancel 0 000000 ms 0 0000 Reverse Phase 0 000000 dB Done Next the Filter element incorporates a large selection of filter configurations and types cut off frequency and also gain and Q factor of notch peak and shelving elements As mentioned above you can cascade a number of these elements to make filtering channels for each driver in the enclosure Filter And Voicing Element Data Filter Configuration LF 24dB oct Fo 1000 0 Hz HP 4dByoct HP 12dB oct a Parametric bel Element cut offfcenter frequency O Circuit and shelving 1000 0 Hz Gai 10 000000 dB By pass This Element 0 000000 Done Here is an example of frequency response of the filtering
7. and enjoy the new sound of your 5 1 HT system Playback controls are very simple Just press the Play button and adjust Volume level to your taste The Inputs and Outputs LED will show audio programme level Player Control Inputs Ode Outputs wo W 12 _ 12 34 k 5 F FS QAO 36 Bi 13 14 15 16 3l vamplng Hz W Use HET Data 4000 SPL Only EQ Volume 10 _Flay ae 2 _Stop Processing Time ms XAA Figure 10 Playback controls Conclusions Well I hope that for you as well the design process has been very simple I picked the functional elements on as needed basis and created the complete functional block diagram of a crossover intended for front left loudspeaker system accounting for room equalization as well Then I proceeded to complete all other loudspeakers in the system This approach offers you simplicity accuracy of the DSP algorithms significant versatility large number of design choices and ability to make tweaks and changes at the press of a button Cumbersome issues associated with passive crossover design and particularly optimization issues associated with impedance measurement and equalization and much of the soldering is gone from the process Finally I will repeat the four advantages that only a DSP engine can deliver 1 Acoustic amplitude SPL and acoustic phase equalization of individual drivers and complete system 2 Linearization of system pha
8. element described above 3 Ultimate Equalizer Frequency Domain Fiter 1 Filter 1 SAL Front Left 20 30 40 60 80 100 200 300 400 600 1k 3k 4k 6k 8k 10k 20k 30k 40k Hz And finally the Room EQ element This element is more complex and allows you to incorporate minimum phase room equalization for each enclosure This element combines up to 6 measured room SPL responses to calculate spatial average and then calculates room correction function to be applied to this particular loudspeaker Typically you would focus on the low end frequency range say below 150Hz and apply the room correction carefully with caution to avoid over equalization Minimum Phase Room Equalizer MLS Measurement Control o Window Width o o oO Add dB To SPL E 00 gO Add Delay ms V Use Saved IR Volume 10 Room EQ Plotting Controls EQ Threshold 0 dB Sau a El V Show Measured Phase Ne a V Show Room EQ Phase V Show Room EQ SPL V Equalized Room SPL i peaini Room EQ Frequency Range From i50 Hz To 2000 Hz Projected Slope Below 10Hz dB 10 00 M Scalar Average V EQ Amplitude Only Re Calculate EQ Global Function Conrols Bypass Room EQ Clear All Data The Input element is not involved in calculation of transfer functions it s only purpose is to allow you to select sound card port for the selected loudspeaker Enter Sound Card INPUT Port Ed Fort Node 0 The equalization proce
9. els Please note that there are two subwoofers in the system This configuration may come very handy 1f decide to augment the bottom end of your stereo configuration Our DSP processor should have the ability to link the LS subwoofer to FL channel and link the RS subwoofer to FR channel Obviously providing appropriate frequency and phase characteristics Additional aspect of connectivity can be exploited by creating special effects For instance when using your system for stereo listening on the top of subwoofer augmentation you can utilize RR and RL channels as well One option would be to band limit the RR and RL channels and add some time delay to these channels so when played in normal stere mode such configuration would create the overall effect of much larger venue You could also connect the RR and RL speakers 180deg out of phase for further experimentation There are quite a few possibilities to explore and create your own version of acoustic signature for the venue It should be clear by now that the DSP PC may require at least as many individual amplifier modules as there are drivers in the whole system Some designs will employ less amplifiers if there are dual loudspeakers in one enclosure that can be powered from the same amplifier module All choices are up to the designer An example of another but smaller 14 amp channel 5 1 HT system is conceptually shown on Figure 2 3 way Front Left Left Powered SumanarET
10. emium Ultimate and Enterprise come with DVD playback capability built in If you re running Windows 7 Home Basic or Starter you can upgrade your edition of Windows 7 to add full DVD capability From the connectivity point of view it means that your Windows7 based PC can play a DVD and decode 5 1 Dolby Digital sound and output the analogue audio via the 6 channel built in motherboard Realtek sound system thus making it available to for external processing Obviously using an external Blu ray 3D DVD player is another alternative This is where the new DSP PC device comes in As the 5 1 surround sound DSP processor it comes with 6 analogue inputs ready to accept the decoded movie sound tracks After all processing is done the DSP processor puts out up to 16 channels for individual drivers built into the 5 1 surround system loudspeakers For instance your surround sound system could have the following components front left FL loudspeaker designed as 3 way system front right FR loudspeaker designed as 3 way system rear left RL loudspeaker designed as 2 way system rear right RR loudspeaker designed as 2 way system centre CT loudspeaker designed as 3 way system left subwoofer LS loudspeaker designed as 1 way system right subwoofer RS loudspeaker designed as 1 way system ee ae E ome Theatre Systom Configuration Desa Darzel 2 4 LE Oaboot La LP dBoot LA fdvoot Fo 1000 0 Hz Fo 1000 5 Hz Re Fo 0004
11. hronizing DeltalOlOLT sound cards please consult reference 1 Figure 3 Motherboard MSI X58 Pro E Series with 2 x PCI slots http au msi com product mb X58 Pro E html digital analog connector connector dotal cable connector S POF word WMO line outs connector line ims mics line fo PCI card fo clock i o to PCl card ins Figure 4 PCI sound card DeltalO1OLT You will need two of these http www m audio com products en_us DeltalO1OLT html Figure 5 An example of multi channel amplifier MA1240 from Parts Express http www parts express com pe showdetl cfm Partnumber 300 815 The MA1240 may be able to surprise you when employed in an active system This is because required peak power is greater if the signal has simultaneous peaks in two different frequency bands as in the case of passive loudspeaker systems A single amplifier has to handle the peak power when both signal voltages are at their crest as power is proportional to the square of voltage the peak power when both signals are at the same peak voltage is proportional to the square of the sum of the voltages If separate amplifiers for each band are used as in the case of MA1240 each must only handle the square of the peak voltage in its own band 20V Clipping level for Woofer 500 Hz 10V Clipping level for Midrange 30V Clipping level for Woofer Midrange combined 0 10 20 Time milliseconds Figure 6 Crest voltages for separate and c
12. n the next step you may want to audition each loudspeaker individually in their designated location While doing this you may want to adjust voicing of each loudspeaker to your individual taste by inserting voicing elements like high pass low pass shelving elements or broadband parametric Q elements to obtain BBC dip effect and so on This is an important step in tweaking the complete system because flat frequency response is one thing but whole system also has to sound right for your own ears as well Personally I always enjoy this part of the system implementation knowing that I start from perfectly optimized system already and this is just putting the final touches on the overall performance of he system E Home Theatre System Configuration inkwitz e ut LP 12dBroct l Test 3 Win wfr Fo 500 0 Hz EQ Range Fi 20 0 Hz F2 200 0 Hz l Del 0 000 ms InO IN Phase Gain 0 0 dE RoomEQ Shelving bd6 Ink waitz Oo LI t2 Fi 15 0 Hz Gain 0 0 LP 12d Boct Test 3 Wing vfr F2 200 0 Hz Feo 70 0 Hz Fo 500 0 Hz EQ Range Fi 20 0 Hz F2 200 0 Hz Del 0 000 ms IM Phase Gain 0 0 dB inkwitz Linkte HOut3 LP izdBioct HP 12dBfoct oJ Mo File Loaded Fo 5000 0 Hz Fo 00 0 Hz EQ Range F1 20 0 Hz Fz 700 0 Hz Del 0 000 ms IN Phase Gain 0 0 dB _ al Linkwitz p O ut4 HP 12dBoct Oct 13 Far twe Fo 5000 0 Hz EU Range Fi 20 0 Hz F2 200 0 Hz Del 0 000 ms IN Phase Front Left Gain 0 0 d
13. ombined 100Hz and 500Hz waveforms adopted from http clas mg edu au acoustics waveforms adding waveforms html and modified For instance please assume 80hm load impedance and consult Figure 6 above 1 Single amplifier is required to deliver audio power to a passive loudspeaker system with crossover with crossover at 300Hz Woofer branch requires 20V and midrange branch requires 10V maximum voltage level Amplifier satisfying these requirements would have to be able to deliver 56Watts of undistorted power at clipping level of 30Volts 2 Bi amped system is required to deliver audio power to an active loudspeaker system with crossover at 300Hz Woofer branch requires 20V and midrange branch requires 10V maximum voltage level same as above Here the woofer amplifier only needs to deliver 24 5Watts at clipping level of 20Volts Midrange amplifier is required to deliver 6 2 Watts at clipping level of 10Volts This is very important aspect of active systems in general they require much smaller amplifier to play as loud as comparable passive systems In the example above woofer requires only 44 of the passive amplifier power It would be fair to say following the example above that 40Watt active system woofer amplifier would be equivalent to 90Watt amplifier in passive system 5 1 HT system design process in details Imagine you can have a large selection of filter configurations and types and the ability to cascade them any way y
14. ou like On the top of this you are able to cascade other filtering elements like notches shelving and peaking elements with adjustable Q factor Each one of these long chains can be applied as a filtering channel for individual driver in the enclosure In order to visualize the whole crossover you would simply pick and place filtering elements from the available tray of component and then place and link them on the screen to effectively built the whole crossover as a block diagram with interconnected filtering elements The tray is shown below To keep things simple there are only three active elements using which you can built the entire crossover Diagram Editing Ww Draw Move Wipe Wire Wipe Come Ww Show Nodes i Show Raster Copy speaker Curve selection Clear Plots Frequency Response Plots Front Left Centre Front Right Rear Left wb Rear Right First the Loudspeaker element incorporates measured driver file name equalization frequency range channel delay channel phasing channel gain and sound card output port assignment data Equalization of the loudspeaker is implemented as inverted Hilbert Bode Transfrom HBT function It is very effective in equalizing the measured SPL to a flat line and equalizing the measured phase to straight line as well Final phase equalization to a flat line is performed by running the DSP PC in Linear Phase Mode This way the acoustic
15. se to a flat line Intelligent room equalization 4 Precise crossover filtering function oS References 1 Synchronizing Deltal010LT sound cards Bohdan Raczynski Bodzio Software Pty Ltd 2011 2 Ultimate Equalizer User s Manual John Kreskovsky Music and Design 2011
16. ss incorporated in Ultimate Equalizer was described in details in Audio Xpress June 2010 therefore it will not be presented in details here However as a remainder please consider Figure 7 below Depicted here are the following curves Green curve SPL of the measured driver Dark Blue curve SPL correction curve calculated by inverted HBT Red curve filter transfer function 2nd order 1000Hz Butterworth Pink curve final equalized SPL Equalization frequency range 60Hz 6000Hz Grey curve final equalized phase Equalization frequency range as above ee a a The final flat phase response is accomplished by employing time inverted filtering method This example shows the crossover and equalization design for the woofer drivers in the Front Left speaker system 2 Ultimate Equalizer Frequency Domain 8 Outputs 300 400 30k 40k Hz Figure 7 Woofer filtering and equalization design Ultimate Equalizer Frequency Domain 30 40 60 80 100 A m isis a J T A ra a 10k 30k 40k Hz Figure 8 Front Left loudspeaker system fully equalized SPL pink curve and phase grey curve transfer functions The process I have just described needs to be applied to all other loudspeakers in your 5 1 HT system Having finished you will be left with a superbly performing loudspeakers having frequency and phase responses flat and possibly extended by an octave into low and high ends of the old operating frequency range I
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