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Natural Science Forum / Physics / Acoustics / July 2008Comparison of ten room testing microphones
Folks, People often ask which affordable microphones I recommend for measuring their room. To answer this question I tested ten popular microphones ranging from an inexpensive DIY model to a Josephson with Microtech Gefell capsule costing $1,800, and wrote up the results for this article: http://www.realtraps.com/art_microphones.htm Enjoy! --Ethan > http://www.realtraps.com/art_microphones.htm Too bad you didn't include one of the miniature omnidirectional back electrets such as the Panasonic WM-063 or WM-60A, which have ruler-flat frequency response from 30Hz to 20KHz. At one time DigiKey was selling them for under $2. >> http://www.realtraps.com/art_microphones.htm > >Too bad you didn't include one of the miniature omnidirectional back >electrets such as the Panasonic WM-063 or WM-60A, which have ruler-flat >frequency response from 30Hz to 20KHz. At one time DigiKey was selling them >for under $2. The Mitey-Mike does use the Panasonic. The orginal Panasonic capsule has been replaced. Well, the response is not ruler flat. Some of the charts from Panasonic would look ruler flat. The Mitey-Mike seems to be the only commercial system using it. The mike DIY forum was busy a few years back getting the most out of DIY systems. The Mitey-Mike uses selected capsules. ANybody looking for more info here.. http://www.pitt.edu/~szekeres/mic/mic.htm greg Greg, > more info here.. > http://www.pitt.edu/~szekeres/mic/mic.htm Excellent, thanks, I just added that link next to the Mitey-Mike. --Ethan >Greg, > [quoted text clipped - 4 lines] > >--Ethan I take it the Mitey Mike is not around any more ?? At least i didn't find it. greg > I take it the Mitey Mike is not around any more ?? Yes, apparently not. But it was still fun to include in my round-up. > In article <FuSdnZQ3p-mrixTVnZ2dnUVZ_sednZ2d@giganews.com>, "Too_Bad" > <me@home.com> wrote: [quoted text clipped - 16 lines] > > greg I just measured a WM-60A against a Bruel&Kjaer 4138 1/8" reference mic side by side, exposed simultaneously to the same sound field. The distance between the center of the WM-60A and the center of the 4138 was less than 1/4". The sound field was generated by a Panasonic leaf tweeter EAS-10TH1000 which has a power bandwidth in excess of 100KHz. I have recently run an electrostatic actuator response on the the B&K 4138 and know that its pressure response is flat +/- 0.2dB from 100Hz to 50KHz. The response of the WM-60A was measured relative to that of the B&K 4138 using a Bruel & Kjaer 2035 dual-channel FFT analyzer equipped with 100KHz input modules. The two channels of the 2035 analyzer are matched to better than +/- 0.2dB over the full 100KHz frequency range of the analyzer. Relative to the the 4138, the WM-60A is down 0.5dB at 10KHz and 2.0dB at 20KHz. The WM-60A remains at about -2dB between 20KHz and 30KHz, and at 32KHz begins a very steep rolloff. The response between 10KHz and 30KHz shows a slow, gradual rolloff that is devoid of any bumps or dips. These are the numbers, and whether one chooses to refer to the response of the WM-60A as "ruler flat" depends on one's reference and perspective. >> In article <FuSdnZQ3p-mrixTVnZ2dnUVZ_sednZ2d@giganews.com>, "Too_Bad" >> <me@home.com> wrote: [quoted text clipped - 35 lines] >response of the WM-60A as "ruler flat" depends on one's reference and >perspective. Without looking up the specs of current models, there was talk on the MIC DIY forum explaning there seem to have been manufacturing problems within the last years, with response varying between capsules. greg > In article <UuCdnbvrjIttbRTVnZ2dnUVZ_h7inZ2d@giganews.com>, "Too_Bad" > <toobad@home.com> wrote: [quoted text clipped - 44 lines] > > greg Perhaps it's time for you and others on the MIC DIY forum and elsewhere to say goodbye to twenty year old technology and get up to date on current, cutting-edge technology that is available today. http://media.digikey.com/pdf/Data%20Sheets/Knowles%20Acoustics% 20PDFs/SPM0204UD5.pdf While the data sheet does not show the response below 10KHz, it is flat + 0/-1dB to 300Hz and has a lower limiting frequency (-3dB) at about 30Hz. Additionally, the unit can be easily modified to eliminate the broad bump that is centered at 47KHz and provide a nearly flat (+0/-2dB) response out to 100KHz. >> In article <UuCdnbvrjIttbRTVnZ2dnUVZ_h7inZ2d@giganews.com>, "Too_Bad" >> <toobad@home.com> wrote: [quoted text clipped - 57 lines] >that is centered at 47KHz and provide a nearly flat (+0/-2dB) response out >to 100KHz. Thanks for sharing. I would have never found it, like I did i the old days. I don't flip pages looking at new products in the DigiKey catalog because its too big. I Hate even putting it on the shelf. If DigiKey would carry half the products in the catalog, I would also have a better attitute toward them. Most of my speaker testing involved below 100 Hz, so this mic is very limited in usage. greg > In article <lYydne96dLLFpRfVnZ2dnUVZ_uudnZ2d@giganews.com>, "Too_Bad" > <me@home.com> wrote: [quoted text clipped - 67 lines] > days. I don't flip pages looking at new products in the DigiKey > catalog because its too big. I Hate even putting it on the shelf. I didn't find it by flipping through the pages of the DigiKey catalog looking for new products. > If DigiKey would carry half the products in the catalog, I would also > have a better attitute toward them. I gave the DigiKey reference only because, to the best of my knowledge, DigiKey is the only outfit that stocks Knowles mic capsules. While I rarely buy components from DigiKey I have never had your experience. Digikey has had in stock every item that I have ever ordered. > Most of my speaker testing involved below 100 Hz, so this mic is very > limited in usage. > greg Then I fail to understand your interest in this thread. It seems to me that ir would be difficult, if not impossible, to find a mic that does not have an acceptable response in the frequency range between 20Hz and 100Hz that would suit your purposes, whatever they might be. Were you able to measure the responses in Audio range, and if so, would you please post the results? Thanks. Tom ttonon <ttonon@peoplepc.com> wrote in news:4397ec3f-7042-4b4e-801f- dc47795b36e1@79g2000hsk.googlegroups.com: > Were you able to measure the responses in Audio range, and if so, > would you please post the results? Thanks. > > Tom Relative to 1KHz, the response at 10KHz is down 0.5dB. The response is flat +/-0.2dB from 2.5KHz to 100Hz. In order to accurately determine the response of the WM-60A below 100Hz, the response would need to be measured in a sealed coupler using a reference pressure sensor and a sound source that have response that extends to DC. While I have that capability, some of the fixturing that is required is currently being used for a current project and can not be disassembled. Hallo Ethan, your results are quite in line with my own experience. To me this is no great surprise: The basic design of a condensder microphone is so simple that you just cannot do much wrong, so any microphone manufacterd with some care should yield good results. The same applies to the circuitry needed for processing the signal of the capsule. In many cases the low-frequency roll-off of inexpensive microphones is intentional to block spurious noise, for instance footfall noise. In microphones with an early drop-off at high frequencies, diaphragm tension is obviously low, resulting in a relatively low upper resonant frequency. The deviations of your graphs from a straight line are caused not only by room resonances - there will be some, without question. But even the best loudspeakers available have some fluctuations in their frequemcy response, so the sound pressure at the location of the microphone will be slightly different at different frequencies, unless it is controlled in some way. But in your case it does not matter, your results are really enlightening. Just a suggestion: Why not use the measured response of the "best" microphone as a reference and plot the difference between each microphone and the reference one, possible corrected for the difference at 1000 Hz? In this way the differences between the individual types will stand out more clearly, because the effects of room resonances and loudspeaker frequency response cancel out. Regards, Heinz ----- Original Message ----- From: "Ethan Winer" <ethanw at ethanwiner dot com> Newsgroups: alt.sci.physics.acoustics Sent: Thursday, July 24, 2008 3:36 PM Subject: Comparison of ten room testing microphones > Folks, > [quoted text clipped - 8 lines] > > --Ethan > Folks, > [quoted text clipped - 8 lines] > > --Ethan Heinz, > Why not use the measured response of the "best" microphone as a reference > and plot the difference between each microphone and the reference one I sort of did that by repeating the Earthworks in the last two graphs. With an informal test like this I'm not confident to proclaim which of the "high-end" microphones is closest to flat. So I arbitrarily picked the Earthworks as a reference. Again, the main points are 1) the Radio Shack SPL meter is not very good even though it's popular, and 2) the Nady and Behringer microphones seem to be a good choice for about the same price as the Radio Shack meter. --Ethan |
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