AKG D58 Professional Microphone
Contents
1. Supercardioid pattern On Off dynamic switch metal windscreen and handle ideal for on stage vocal D3700 Handheld 50Hz 20kHz 2 5 mV Pa lt 600 Ohms _ Hypercardioid pattern very durable dynamic 20Hz 20kHz Ideal for on stage vocal or instrument at 1 2 D3700S_ Handheld 50Hz 20kHz 2 5 mV Pa lt 600 Ohms Hypercardioid pattern On Off switch dynamic very durable Ideal for on stage vocal or instrument D3800 Handheld 40Hz 21kHz 2 8 mV Pa lt 600 Ohms Hypercardioid pattern very durable dynamic ideal for on stage vocals D230 Handheld 40Hz 20kHz 2 5mV Pa lt 230 Ohms Omni pattern ideal for close in speech dynamic hum compensation low handling noise 15 AKG Acoustics U S 914 Airpark Center Drive Nashville TN 37217 Tel 615 620 3800 Fax 615 620 3875 Visit our Web Site at www akg com2. taught the rudiments of microphone usage The rule for avoiding wind noise and popping is to hold the microphone toward one side pointing it at the talker s mouth but not allowing the person to talk directly into the microphone This will prevent puffs of wind that are so annoying to the listener The real key here is in positioning the microphone on the podium in the first place so that the popping of air blasts against the microphone will not happen Figure 14 Locate microphone For handheld microphones performers simply have to learn to Wind goes in here hold it off to one side while pointing it directly at the mouth this direction Here a foam windscreen will be useful just as a safeguard Figure ea 14 shows how and how not to position the microphone Talker Basic rule point microphone at talker s mouth but do not point talker toward the microphone positions including pulpit lectern altar and free standing locations We will discuss these in order 3 1 1 Pulpit and Lectern Microphones Figure 15 shows a pulpit in top view A and in front view B There is normally a reading desk in the center and the ideal microphone position is to the right or left of it depending on the preference of the principal talker An excellent microphone choice here would be AKG s Discreet Acoustics modular series GN 30E gooseneck with a CK80 or CK47 condenser capsule These capsules narrow profile designs have integral rifle sectio
3. with a microphone If the distance between microphones is at least three times the distance from each microphone to its associated performer then the leakage signal from the distant performer into the nearer performer s microphone will be about 10 dB lower low enough not to be a problem If however source 1 is louder than source 2 as shown in Figure 11B then the softer source will have to move in on the microphone as needed Figure 11 P 3X O 9 3X 2 1 2 Multi microphones on the Podium l Omni microphones Siaumacaneens jx If there are two or more microphones on a source2 Podium each going in a separate direction never to be combined with each other then pale as ate the placement is of little concern except to Bari sourees areiedual Source 2 ensure that each microphone gets a clear shot A B at the voice and is not hidden behind other microphones This situation is common in news gathering activities However if two microphones are combined to keep a talker on mike then extra care must be taken Figure 12A shows how this is often done by inexperienced persons Here two microphones are placed far apart angled in so that they cover all of the performer s possible locations This is the wrong way of doing it the correct way is shown in Figure 12B Both microphones should be placed in very close proximity to each other and splayed so that their common coverage angle will be large enough to capture the talker in any posi
4. 0kHz 8 mV Pa lt 400 Ohms Extended frequency range omnidirectional clip on condenser universal powering CK77WR Clip on 20Hz 20kHz 8 mV Pa lt 3500 Ohms Extended frequency range omnidirectional condenser wireless applications 1 5 12 Volt powering Boundary C400BL Boundary 150Hz 15kHz 13 mV Pa lt 200 Ohms Small size hypercardioid effective layer layer at large distances universal powering condenser C547BL Boundary 30Hz 18kHz 8 5 mV Pa lt 200 Ohms Extended frequency range supercardioid layer switchable bass cut universal powering condenser C680BL Boundary 60Hz 20kHz 30 mV Pa lt 200 Ohms Extended frequency range layer supercardioid universal powering condenser 14 M ODEL DESCRIPTION FREQUENCY SENSITIVITY IMPEDANCE COMMENTS RESPONSE Vocal C5900 Handheld 20Hz 22kHz 6 mV Pa lt 200 Ohms Switchable bass roll off and cut low Microphones condenser handling noise universal powering C535EB Handheld 20Hz 20kHz 7 mV Pa lt 200 Ohms Switchable bass roll off and cut condenser excellent for on stage vocals universal powering D660S Handheld 70Hz 20kHz 2 mV Pa lt 500 Ohms Hypercardioid on off switch dynamic D770 Handheld 60Hz 20kHz 2 5mV Pa lt 600 Ohms Cardioid pattern metal windscreen dynamic and handle ideal for on stage vocal or instrument D880 Handheld 60Hz 20kHz 2 5mV Pa lt 600 Ohms Supercardioid pattern metal windscreen dynamic and handle ideal for on stage vocal D880S Handheld 60Hz 20kHz 2 5 mV Pa lt 600 Ohms
5. AKG Microphone Basics and Fundamentals of UsSage eescccccrcccccccccnncccnccninrrn 14 INTRODUCTION The outline of this manual is simple first we will present an overview of the basic technical characteristics of microphones including how they work what their acoustical pickup patterns are and what their electrical characteristics are We then move on to a discussion of basics of usage such as how multiple microphones interact with one another what their target working distances are and how they behave in a variety of operating environments Our aim is to keep our coverage as simple and as user friendly as possible Finally we will pick a number of basic applications and teach you what to look for in choosing an AKG microphone for those applications For the most part these applications will be areas of speech and vocal pickup since they easily account for 80 to 90 of all microphone applications Our primary vehicle for this study will be applications in worship spaces since those applications are varied enough and by analogy extend to all other speech requirements The specific requirements of modern musical recording and sound reinforcement will not be covered here these will be discussed in another manual If you have ever wondered why there are so many models in the AKG microphone line to choose from you will have no doubt by the time you have finished studying this manual There is a purpose for each one of them 1 0 0 A H
6. S BY USAGE CATEGORY The accompanying chart details the principal specifications of microphone types discussed in The ABC s of AKG Microphone Basics and Fundamentals of Usage Pertinent models are listed by usage category model number and description of transduction type The frequency response limits will give the user an indication of microphone choice for the fidelity requirements for a project at hand At the same time the sensitivity and impedance data will dictate the electrical input conditions that will be required Final comments underscore the specific uses of a model within a given category MODEL DESCRIPTION FREQUENCY SENSITIVITY IMPEDANCE COMMENTS RESPONSE Pulpit CK80 M odular 60Hz2 15kHz 30 mV Pa lt 600 Ohms High directivity hyper cardioid Lectern condenser universal powering Hanging CK31 M odular 50Hz 20kHz 20 mV Pa lt 600 Ohms Extended frequency response Condenser cardioid universal powering CK47 M odular 20Hz 20kHz 16 5 mV Pa lt 600 Ohms High directivity hypercardioid extended condenser frequency response universal powering GN30 Modular 30 cm 12 in gooseneck used with Gooseneck the CK Discreet Series modular capsules HM1000 Hanging 10 m 33 ft or 20 m 66 ft Module non twisting hanging module used with the CK Discreet Series modular capsules C477WR_ Headworn 20Hz 20kHz 8 mV Pa lt 3500 Ohms Extended frequency range condenser wireless applications 1 5 12 Volt powering Lapel C577WR Clip on 20Hz 2
7. The ABC s of AKG M ii i Basics Fundamentals of Usage es Eajeatale Biel clo le pene memeree terre tree aaa rrr tame terete ERE a oe arte a 1 EO ARPS TOWW NY Work uggnt sg t su M s t at alah a a a eae 1 1 1 0 Microphone Pickup Pathernsiic nus cites inilo nnn iene 3 LLI AVS GTN GI a teen utsetecine Dade au death ppt a iad um beds a A 3 MU 2 Ee Ol Gsm a ll i tg ie r ee ste nD ees Gaeta tc 3 1 1 3 _ Hypercardioid and Supercardioid c c e cs uhh a rcaeedeanatn ak ih hence mien 4 1 2 0 Some Important Characteristics of Omni and Cardioid Family of Microphones 4 DDR MOM AE eek stan cage ea a E aie ap aaa acas os Shack slestaths aes ela ban 4 1 2 2 Cardioid Family satin nen ratio wtiniid Gola a rar a Saa aah a l knassar 4 1 3 0 Electrical Aspects of AKG M 1CFOPNON GS shisecce eecccunnesisbediba dacloe dui udldsis saususaugeongedatenedebeesil widsaulbanadrnns 6 EIA MD OCU AINCE aena Sect a tae tea a i 6 1 3 2 SENIN tsu Bias Baa wie ie ra d 6 13 3 cSeIf N 01s amp eV elta eila a eie aa fe j a Oa Db Bv alas 6 EBAY mOVGrlo dsPoNn b ar ra s O Skt K A R a a aa l ara 7 13 5 Handling NOISE nunana Bata l a Orla latan tla VB la talt taS Bale alat l as g 7 1 3 0 ROWING ts tre tele te la a arabs ato its H t E Hl a iga da blaa E e 7 2 0 0 B Basic Principles of Microphone Usage sua A See ea Oa 8 2 1 0 Multiple Microphone Interference vistas scnsuaiesetotwancw ee ntncteksneseiaubnsind dan wainaviaisai
8. also be useful on stage where two or more performers may be fairly close to each other The data shown in Figure 8C shows the nominal acceptance angle 3 dB that the microphones in the cardioid family provide 1 3 0 Electrical Aspects of AKG Microphones In this section we will discuss five items that have to do with electrical aspects of the microphone impedance sensitivity self noise level overload point and powering 1 3 1 Impedance In keeping with modern engineering practice AKG s condenser microphones have internal impedances in the range of 200 ohms while the dynamics have impedances that vary from 200 to 800 ohms Generally speaking these values fall collectively under the designation low impedance All AKG microphones are designed to be loaded by modern consoles and speech input equipment with nominal impedances in the 3000 ohm and higher range The advantage of low impedance microphones is that they can be used over fairly long distances from the console with negligible losses Distance up to 600 feet while rarely encountered in normal applications can be handled with no problem Since all low impedance lines are balanced they are virtually insensitive to normal external electrical disturbances High impedance microphones were once used in paging applications where there was a short run between the microphone and the associated amplifier Today there are no advantages for high impedance microphones inasmuch as the costs of h
9. crophones such as the AKG C1000S are capable of either 9 volt battery or phantom powering C1000S 1 1 0 Microphone Pickup Patterns The most fundamental characteristic of a microphone is its three dimensional pickup pattern Perhaps 90 of all microphones fall into two pickup categories omnidirectional also called omni and the cardioid family The cardioids are basically unidirectional and there are three variations the primary cardioid pattern the hypercardioid and the supercardioid AKG offers a variety of polar patterns in their hand held condenser and dynamic microphones A few designs often referred to as rifle line or shotgun microphones have a long interference tube which makes them highly directional at mid and high frequencies Such exotic designs as these are not used in normal applications but are very useful when sound pickup must take place at some distance from the source 1 1 1 Omnidirectional Figure 4 o D880 C535EB C568EB Dynamic Condenser Condenser Supercardioid Cardioid Hypercardioid 270 90 Figure 4 shows the basic omnidirectional pattern in a two dimensional representation known as a polar plot A while a 180 three dimensional representation is shown at B The omni A B pattern is attained by restricting sound entry into the microphone to a single point at the front of the diaphragm Because of this there is very little distinction based on the direction of the impinging sound and the mic
10. d average output Likewise the four condenser models listed may be used in classical recording and be placed perhaps 15 feet away from sound sources in the studio so actual operating voltages for all types of microphones will tend to average out to about the same value In fact this is an important consideration in the engineering of a particular microphone model 1 3 3 Self Noise Level The self noise of a condenser microphone is the audible noise level the microphone produces when it is placed in isolation from outside sound sources As an example a microphone that has a self noise level of 15 dBA produces roughly the same output as a perfect microphone placed in a room with a measured noise floor of 15 dBA AKG s new condenser microphone preamp combinations using the model C480 preamp pow ering module have noise floors in the range of 10 dBA This is as low as any studio condenser microphone in the industry and such microphones are targeted for digital recording in the studio CK61 C480B Dynamic microphones do not carry a self noise rating inasmuch as their effective noise floor depends on their sensitivity and the electronics they are loaded with For many applications we can safely ignore the self noise level of microphones since the acoustical noise in the operating environment is normally far greater than that of the microphone itself 1 3 4 Overload Point The useful effective upper limit in sound pressure level that a mic
11. d microphone is much more complex than an omni microphone Great care must be taken in designing the back path so that its cancellation action for 180 sources is uniform over the widest possible frequency range An example of an excellent cardioid microphone measured at 0 90 and 180 is shown in Figure 7 As you can see the back rejection at 180 is of the order of 20 to 25 dB in the mid frequency range but the cardioid action diminishes at both very high and very low frequencies 1 1 3 Hypercardioid and Supercardioid These are variations on the basic cardioid pattern which may be very useful for certain applications If the back path length is varied slightly the off axis angle at which the output is minimum can be varied There are two additional patterns resulting from these changes and they are known as hypercardioid and supercardioid These patterns have the effect of changing the reach of the microphone and they may be very useful in certain sound reinforcement applications by providing more gain before feedback than the standard cardioid pattern These variations will be discussed in the following section 1 2 0 Some Important Characteristics of Omni and Cardioid Family Microphones 1 2 1 Omni 1 Most omni microphones especially the condensers have very smooth frequency response and as such are widely used in speech reinforcement and recording 2 Omni microphones have relatively little handling noise and do not exhibit the
12. e CK47 capsule is best since it has a tighter pattern and more extended low frequency response Figure 17 shows details on choir pickup In general four to seven microphones would be sufficient For a divided choir a symmetrical array of microphones would be desirable For a larger group than shown here the microphones may be flown somewhat higher generally keeping the same scale as shown here Figure 17 lt 0 HM 1000 0 Conductor lt O TOP VIEW SIDEVIEW 2 CK 47 The organ itself would rarely if ever be reinforced but of course would be picked up by dedicated microphones for the recording the service There may be some cases when a very slight amount of choral amplification might be necessary Ordinarily a vocal soloist singing with the choir would not be picked up separately but from his or her position in the choir by means of the overhead microphones CONCLUSIONS This manual has given you the fundamentals of microphone selection and basic application in speech and vocal work By now you should have a pretty good idea of why there are all those microphones in the AKG catalog They exist to make your job of specifying the right microphone a little easier Special thanks to John Eargle for the use of his graphics and his contribution to this project John Eargle is a consultant to AKG Harman International and is Director of Recording for Delos Records 12 NOTES 13 AKG MICROPHONES BASIC SPECIFICATION
13. entirely in terms of boundary layer BL microphones for this purpose In most cases two or possibly three of the directional models C547BL or C680BL would work best on the modern style table altar shown in Figure 16A Here the pastor faces the congregation and a directional BL microphone can be used to advantage in getting more gain before feedback Use as many of these as there are principal positions behind the altar Because the altar is invariably covered with a cloth permanent mounting of the microphones is not possible however double sided tape will keep them from slipping or moving during a service C547 BL In the case of the traditional altar shown in Figure 16B it is best to use an omnidirectional BL microphone located as close as possible to the intersection of horizontal and vertical surfaces of the altar Use as many as needed Asarule no more than one speech pickup location should be switched on at a time in a worship space This is especially true at the altar where a multiplicity of microphones if all were open at the same time would create a very unnatural sound We strongly recommend that some kind of automatic microphone mixing or gating be used in these applications 10 Fi gure 16 Pastor or other officiant stands here facing altar Pastor or other officiant stands here facing congregation Reading x BL microphone omnidirectional BL microphone desk Reading placed at junction of horizontal and direct
14. igh quality low impedance preamplifiers has come down drastically 1 3 2 Sensitivity In measuring microphone sensitivity the microphone is placed in a reference sound field in which a sound pressure level of 94 dB at 1000 Hz is maintained at the microphone 94 dB is the sound pressure level equivalent to one pascal Pa the metric unit of pressure The unloaded output voltage is measured and stated as the nominal sensitivity Sensitivity is also stated in decibels relative to one volt a designation known as dBV The following table gives the sensitivity range of typical AKG microphones Model Type Sensitivity dBV C414B ULS Condenser multi pattern 12 5 mV Pa 38 C480 CK61 Condenser multi capsule 20 mV Pa 34 C535EB Condenser vocal instrument 7 mV Pa 43 C3000B Electret Condenser two pattern 25 mV Pa 32 D3800 Dynamic vocal 2 8 mV Pa 51 D770 Dynamic vocal instrument 2 5 mV Pa 52 D58 Dynamic noise cancelling 0 72 mV Pa 63 Note The equation for converting from mV Pa to dBV is dBV 20 log mV Pa 60 Note that all sensitivities are in the low millivolt mV or one thousandth of a volt range The total range shown here is about 25 dB However taking into account the recommended usage for each of the models the average output voltage probably will not vary all that much For example the three dynamic models listed here are intended to be used fairly close in to sound sources and that will result in increase
15. ional To desk vertical sections of altar 2 congregation To grog congregation Modern style altar Traditional style altar A B 3 1 3 The Roving Talker In some worship spaces the entire front platform is used for speaking and a hand held wireless is normally the microphone of choice For this purpose a number of AKG wireless models should be auditioned and one chosen that best complements the talker s voice It should be supplied with a foam windscreen to limit the breath effects of too close use It is also advisable for the operating engineer to use a program limiter so that the output capabilities of the entire system will not be stressed by overmodulation The AKG wireless dynamic microphones WM S40 880 WM S81 880 and WMS81 3800 all provide a rise in the presence range that presenters will appreciate The wireless condenser microphone C535WL 1 has a smoother high end which will complement most voices SR81 HT 81 amp SR40 HT40 880 D880WL 1 3 1 4 Baptismal Fonts and Weddings For services at a baptismal font or for weddings which are generally held in a free standing area at the head of the congregation a tie clip on or lapel wireless microphone such as the C417 CK97 C477WR or C577WR is probably the most unobtrusive Weddings being the momentous events that they are it is customary today to document them via recording video taping and photography Do not be surprised at requests from both bride and groo
16. lpcwdiniess dens feds Fash wibunebatMenemasaeit 8 2 1 1 The Three to One Rule nn2222222222120 1dascs 1 r0 01 m ts a acca neta Sets cea eerie gias dura ys 8 2 1 2 Multiemicrophiones on the Podium w cssiacisiilnlnnisieiadanviniaisl dlubdbnnneie iis 8 2 1 3 Reflections from Nearby Surfaces and Boundry Effects cccceceeeeseeeeeeeeeeceeteetietietees 9 2 2 0 Wind and Microphones Don t Mss hess tates cies otehct ested caste teas sonata shaaioudlsdcdnonacnarnnsed saat teacs Gaeta means 9 3 0 0 UC Case Studi SS esisesiivacuaearesanr eee de tenon i stthur ilntteaesuabeeiueuise denies ine ley ail vl tkr altan kaa al teens ll 10 3 1 0 Miking Talkers Vocalist and Instruments in Houses Of Worship isivisavvnna rsss rssrss rs rssrs rsrransarnrannanna 10 3 1 1 Pulpit and Lectern Microphones wancisisiaiiiiiaa nani aondaditnlabhbiknnnrdnie 10 3 1 2 Altar NEOPA OT Se cet Nice m oes a d a Deild aia 10 Deed LS PROVING Jaka a i l a aa E a Gatos 11 3 1 4 Baptismal Fonts and WeddingsS snvavv gt vniav vnvnn gt ass rsrsrs rsrararsrrannarararnansananannannananannanan taran annara 11 3 1 5 How to Position the Clip on Microphone 2sisvnnn nv nvvavvrsr rs rsss r rsrsansrarannansananannnannananannanna 12 31 6 THEM USIG SeNI COS sms asasi sltkat i Va a a a a Mess gal aS Va a a pala a 12 ETUC S Ko i SVAR R ea a a a aa en inlet abel idl da a E tab av Mannie datues 12 Table of Contents The ABC s of
17. m for personal microphones so that their vows can be recorded loud and clear C577WR 11 3 1 5 How to Position the Clip on Microphone It is often appalling how ineptly tie tack microphones are applied Usually they are positioned on the tie or lapel at too great a distance from the talker s mouth to work well The tie position is best inasmuch as it centers the microphone However do not place it so high that the talker s chin gets in the way when he or she refers to written notes A microphone such as the CK 97 has the right degree of rolled off bass response to compensate for boom from the talker s chest cavity and the right degree of high frequency boost to compensate for the off axis location of the microphone It is also important to make sure that normal movements of the talker will not result in any stress or rubbing on the microphone s cable which could cause extraneous noises 3 1 6 The Music Service In many traditional religious denominations the music consisting primarily of organ and choir may need no amplification as such but there is certainly a move these days to record the music as part of the overall service The comments we will make here are general and apply to both recording and feeds for sound reinforcement The choir is best picked up by way of anumber of microphones of the integral hanging type such as AKG s Discreet Acoustics modular series HM 1000 with a CK31 or CK47 condenser capsules Of these th
18. microphones need some kind of power since they all contain a preamplifier section Some tietack and many electret microphones are powered by a self contained 9 volt battery When the microphone is not in use it should be turned off in order to conserve battery Bis 6800 ohms power Virtually all of the non electret condensers are powered via universal phantom powering as shown in Figure 10 The phantom powering standard covers nominal values of 12 24 and 48 volts dc The tolerance on the values is broad enough so that many AKG ESRR condenser microphones can be powered anywhere from 9 volts to 52 volts making 2 H them adaptable to a wide range of operating conditions Some of the studio models such as the older C414EB P48 will work only on 48 volt powering Figure 10 To preamps To preamps Signal is transmitted between pins 2 and 3 dc is provided between pins 2 3 and 1 To preamps C414EB P48 2 0 0 B Basic PRINCIPLES OF MICROPHONE USAGE 2 1 0 Multiple Microphone Interference M ost people tend to use too many microphones The simple rule is that less is very often more in terms of performance M ultiple open microphones not only cause coloration due to peaks and dips in response they also make the system more feedback prone Let s illustrate a few of the more common problems 2 1 1 The Three to One Rule Figure 11A shows the proper way to cover two closely spaced performers each
19. ns for increased directivity hypercardioid along their primary axis The bass is slightly rolled off CK80 to compensate for proximity effect and the dark matte finish makes them invisible at normal viewing distances An integral gooseneck section simplifies adjustment of the microphone s position 3 0 0 C Case STUDIES 3 1 0 Miking Talkers Vocalists and Instruments in Houses of Worship With the groundwork that has gone before we are now ready to examine in detail specific miking problems Since the vast majority of microphone applications have to do with the spoken voice let s start there The typical worship space of today requires speech amplification from all possible speaking GN30 CK80 CK47 We are assuming here that the talker will occupy basically a single position facing forward and that the microphone can be positioned so that normal movements of the talker s arms or vestments do not interfere with the microphone Another choice might be AKG s Discreet O Acoustics modular series GN30E gooseneck with a CK31 condenser capsule The CK31 capsule is a cardioid microphone that is less obtrusive than the CK80 or CK47 FI M ost of what has been said about the FE v pulpit applies to the lectern However gy the lectern is often smaller than the pulpit thus offering fewer options for microphone location Reading a desk Top view of pulpit Front view of pulpit GN30 CK31 A B 3 1 2 Altar Microphones Today we think
20. ow THEY Work There are two operating principles used in AKG microphones the dynamic principle and the capacitor principle The dynamic microphone consists of a light diaphragm coupled to a small aluminum coil immersed in a strong magnetic field When sound impinges on it the diaphragm moves in and out The motion of the coil in the fixed magnetic field develops a voltage across the coil that is analogous to the pressure acting on the diaphragm as shown in Figure 1 Figurel Magnet return Pole piece path Output voltage from coil Permanent magnet Pressure acts on diaphragm Time Output voltage o Acoustical damping ial Diaphragm Coil maena moves in and out generates voltage m Positive pressure mmm Negative pressure A B Here simple alternating sound waves are shown impinging on the diaphragm A producing the output voltage shown at B Microphones using the variable capacitor principle are universally referred to in the industry as condenser microphones the term condenser being a holdover from past engineering terminology A condenser microphone consists of a fixed backplate in close proximity to a diaphragm as shown in Figure 2 Figure 2 Diaphragm moves in and out Pressure acts on diaphragm Output voltage to preamp Time Change in capacitance I generates voltage Polarizing voltage Output voltage from preamp 1 o mamaa Positive pressure momma Nega
21. proximity effect of bass rise that cardioids have See Proximity Effect in section 1 2 2 3 Because of their well damped diaphragms omni microphones are generally more rugged than cardioids 1 2 2 Cardioid Family 1 A cardioid microphone has greater reach than an omni Because of its forward oriented pickup pattern it has a high ratio of on axis response to random directional response Figure 8A shows a comparison of omni and the cardioid microphones in terms of equivalent working distances W hat this figure demonstrates is that cardioid microphone may be used at 1 7 times the working distance of an omni while still giving the same overall suppression of random noise in the room The hypercardioid pattern can be used at 2 times the distance of an omni for the same overall effect while the supercardioid pattern can be used 1 9 times the distance for the same effect In terms of dB when used at the same working distance the cardioid will reject randomly arriving sounds 4 8 dB more effectively than the omni as is shown in Figure 8B By comparison the supercardioid would provide 5 8 dB more rejection and the hypercardioid would provide 6 dB more rejection Figure 8 ie ene Ad K SON S ey Ge om M sahil 1 0 lt Cardioid eo Cardiod Supercardioid Hypercardioid CARDIOID SUPERCARDIOID HYPERCARDIOID 131 115 105 C 2 Proximity effect is a blessing and a bane M any singers love the low f
22. rectly on the surface as shown in Figure 13B effectively making the direct sound and its reflected image one and the same Also remember that the effect is worst with omnidirectional microphones inasmuch as that pattern has no off axis discrimination Cardioid microphones can minimize the effect through off axis discrimination but it is best to avoid the condition altogether The long standing problem with wall and floor reflections has over the last two decades given rise to what is generally called boundary layer microphones These are microphones whose profile is that of a flange They are made to be mounted flush on a plane boundary surface and in that position the microphone will pick up both direct sound and its reflected image virtually in phase As a result of this the output of the boundary layer microphone will be twice 6 dB that of a single microphone located away from the wall Early versions of boundary layer microphones were usually omnidirectional today there are a number of cardioid family pickup patterns available AKG makes both types 2 2 0 Wind and Microphones Don t Mix Whether outdoors or indoors it is imperative to keep wind away from microphones especially directional ones Never blow on a microphone to find out if it is working Thisis an imposition on the audience and it also runs a risk of getting moisture on the microphone screen It is surprising how many people who regularly do public speaking have never been
23. requency boost it gives their voices and would never think of using an omni microphone On the other hand proximity effect makes the cardioid microphone very sensitive to handling noises and to the effects of wind Figure 9 shows typical proximity effect with a cardioid microphone Low frequency response is shown for operating distances of 3 inches and one foot This microphone has been designed with rolled Figure 9 off low frequency response at a distance relying on proximity effect to restore the low frequencies when used close in M any so called vocal mikes are designed in such a manner so that they may be used close in with little trace of boominess rr 3 In normal sound reinforcement applications the cardioid pattern will offer extra immunity to system feedback although perhaps not quite as much as the 4 8 dB mentioned in point 1 Relative level dB ie i i 4 As we have seen the hypercardioid and Baa Ti e EF ik a ix Supercardioid patterns offer slight improvement Frequency Hz over the cardioid in terms of immunity to random sounds While the studio engineer may prefer the standard cardioid for its 180 null in output the sound reinforcement engineer will often prefer the super and hypercardioid for their added reach By opening up the rear 180 lobe in the directional response see views of these patterns in Figure 8B the frontal pattern is actually tighter than that of the standard cardioid This can
24. rophone can handle is that value at which the microphone s output exhibits a stated amount of harmonic distortion General industry standards set a value of 0 5 or 1 for this and the distortion value is always stated in any listing of specifications For most AKG studio condenser microphones we are looking at levels in the range of 130 to 140 dB SPL for distortion values of 0 5 or 1 Dynamic microphones are often rated by stating the acoustical level which will produce harmonic distortion values of 1 and 3 M any of the models can be used in sound fields up to 156 dB producing output with no more than 3 distortion For most purposes involving speech communication and reinforcement we can ignore these limitations but in the recording studio and in music reinforcement with microphones placed very close to loud instruments we can easily reach levels in the range of 130 dB 1 3 5 Handling Noise Many older microphones intended for hand held operation were very susceptible to handling noise Today most manufacturers have solved this problem through careful shock mounting of the capsule within the microphone case and through electrical roll off of low frequencies of those microphones intended for close in operation There are no standards for measuring handling noise and its relative absence is simply a mark of the manufacturer s attention to design details AKG microphones are noted for their low handling noise 1 3 6 Powering All condenser
25. rophone will respond equally to sound from all directions At very high frequencies there will be some departure from this and the microphone will show a preference for sounds arriving from the front For many applications this will be negligible 1 1 2 Cardioid Figure 5 lt x 0 180 gt FJ Q Acoustic resistance CY A Figure 5 shows details of a cardioid microphone Note here that there are two paths to the diaphragm one in front and the other openings on the sides For sound sources which are located on axis or 0 incidence shown at A sound arriving at the microphone at the front opening will always lead or be ahead of sound entering by way of the back opening This is because it travels over a shorter path and as a result there will be output from the microphone For a sound source located at the back 180 incidence the two sounds arriving at the diaphragm will be opposite and equal and thus will cancel as shown at B Acoustical resistance is used in the construction of the microphone to ensure that the front and back paths will be equal for signals arriving from 180 incidence Figure 6 Figure 7 Relative level dB A For intermediate positions the response will vary as shown in the polar plot of Figure 6A A three dimensional representation 1299 22280 o Tie 2 RHR S Ae CORRES AG KHz of the cardioid pattern is shown in Figure 6B Frequency Hz The internal structure of a cardioi
26. tion Figure 12 W hat are the differences In the case shown in Figure 12A there is only one correct position for the talker and that is in the center equidistant from both microphones As the talker moves away from this position the relative signal delays from talker to microphone will shift values and their combination will show interference effects of cancellations and reinforcements In fact if you have never heard this effect it is instructive to set it up and hear for yourself just how bad the combinations can be Then Speaker Speaker move to the setup in figure 12b and hear how much more WRONG CORRECT consistent the audio quality is for all positions of the talker Cardioid microphones Crossed cardioids 2 1 3 Reflections from Nearby Surfaces and Boundary Effects Figure 13 Relative level dB Relative levet dB o l l 1 L L 1 00 500 1K 2K 5K Frequency Hz 200 500 1K 2K 5K Frequency Hz Figure 13A shows common problems encountered in sound reinforcement and recording The reflecting surface can be a tabletop a pulpit a wall or a floor In the case shown here there are effectively two sound sources the direct one and the reflected one These combine at the microphone with a delay between them producing response that will look something like that shown in Figure 13A The rule is to keep the microphone as far away from a reflecting boundary as possible or flush mount it di
27. tive pressure A fixed electrical polarizing charge is maintained between the backplate and diaphragm and when the diaphragm moves under the influence of sound waves the voltage between the diaphragm and backplate varies accordingly Today the polarizing charge used in most condenser microphones is built in to the microphone by means of what is called a prepolarized electret a permanently charged layer on the backplate or on the rear of the diaphragm itself External polarization is normally used in the highest quality studio microphones Figure 3 shows a section view of an prepolarized condenser microphone with the electret polarizing material located on the backplate Figure 3 Backplate Metallized diaphragm m Preamplifier 9 volts Electret material Electret capsule Output to preamplifier A B All condenser microphones are provided with a preamplifier located adjacent to the diaphragm The reason for this is to convert the very high electrical impedance of the variable condenser element to a suitably low value so that the signal can be easily transmitted down a standard low level microphone cable with negligible losses Some prepolarized microphones are directly powered with an internal 9 volt battery as shown in the diagram By far most condenser microphones are remotely powered by a 48 volt dc source so called phantom powering provided by the console or other speech input equipment Some mi
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