Condensor microphone with an audio analyzer - Page 1
Forum section: electronics / projects

author: Physikfan
author_rank: Regular Contributor
timestamp: August 27, 2017, 12:32:44 pm
content: With the help of this audio analyzer, I would like to record the frequency response of a condenser microphone.However, I still have the problem that I cannot connect the condensor microphone directly to the audio analyzer.For the operation of this microphone I need a DC voltage of about 40V DC.The board inside the microphone in detail:My question:Please, could somebody help me how to do with this condensor microphone,Is there a commercial module that provides this necessary voltage, or do I need a preamplifier?VGPhysikfan

author: Ian.M
author_rank: Super Contributor
timestamp: August 27, 2017, 12:47:12 pm
content: https://en.wikipedia.org/wiki/Phantom_powerAssuming your mike wants 48V phantom power, use the circuit in the article and 5x fresh PP3 9V batteries, stacked, to power it at 45V.

author: ciccio
author_rank: Frequent Contributor
timestamp: August 27, 2017, 12:55:40 pm
content: You need at least a power supply.The microphone uses "phantom power" (search Wikipedia for details : Jan.M has already posted the link).A simple phantom power supply is inexpensive (they start at less than 20 US$ on amazon or Ebay).Phantom power requires a balanced connection, so you'll need also a preamplifier to connect the balanced microphone to the unbalanced input of the analyzer.A microphone preamplifier with phantom power can be bought for about 100 US$, but sometrime for the same price you can buy a 2-3 channels audio mixerr with phantom power and 2 mic preamps.How do you intende to measure the mic's frequency response? Do you have an anechoic room and a calibrated acoustic source, or you want to measure only the electronics?Best regards

author: Fungus
author_rank: Super Contributor
timestamp: August 27, 2017, 03:25:26 pm
content: Shouldn't this be in the 'projects' section or something like that?

author: b_force
author_rank: Super Contributor
timestamp: August 27, 2017, 04:09:15 pm
content: Also a very old fashioned way to get the frequency response.There are much cheaper, easier and quicker methods.Also, what technique/source are you using to determine the frequency response?

author: Brumby
author_rank: Unknown
timestamp: August 27, 2017, 05:04:49 pm
content: Quote from: Fungus on August 27, 2017, 03:25:26 pmYep.

author: cdev
author_rank: Super Contributor
timestamp: August 27, 2017, 11:42:33 pm
content: Many cheap generic PC condenser microphones take a lot less than 48 volts. Do your research.For example, most of the microphone inputs on PC-centric audio equipment supply a low voltage (just a few volts, could measure it for you) to drive a condenser mike. Likely you could use that for many condenser mikes. You may even already have a suitable input on your computer.

author: cdev
author_rank: Super Contributor
timestamp: August 27, 2017, 11:52:00 pm
content: I have an adapter somewhere to use an XLR connected condenser mike with an unbalanced tape recorder or amplifier, it plugs into an XLR cable which is what plugs into the bottom of your microphone. On its back it has a full sized unbalanced microphone plug.It contains a transformer and a battery. Its response likely is NOT up to the standards of what you are looking for for measurement, however.

author: ciccio
author_rank: Frequent Contributor
timestamp: August 28, 2017, 02:34:15 pm
content: Quote from: cdev on August 27, 2017, 11:42:33 pmNo, it will not work.PC mic inputs are for unbalanced electret microphone capsules powered with a DC voltage in the ordere of less than 5 volts.The OP microphone requires a balanced input, with phantom power.Maybe that microphone will work with less than 48 volts (some operate from 12 to 48 V) but surely not with 5 volts or less.In any case, you cannot supply phantom power on an unbalanced input.Best regards

author: tszaboo
author_rank: Super Contributor
timestamp: August 28, 2017, 02:48:13 pm
content: That is a BM-800 isn't it?I have a "china special" phantom power supply with mine, is was about 20 EUR. The output level has to be boosted 20dB for normal volume levels. That is about the volume that you will get out of these. So yeah, probably you need a preamp for it.They are not bad at all. I mean for the price. I actually considering to order a second one, and mod it to use USB directly. Sure there are condenser mics with USB, but this one is mine.

author: b_force
author_rank: Super Contributor
timestamp: August 28, 2017, 10:40:11 pm
content: There are hundreds of very good USB soundscards out there with phantom powered XLR.Even with multiple inputs and very good THD+N and noise specs.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 28, 2017, 11:11:22 pm
content: Usually Phantom is applied thru two matched 6.8 K resistors from a source of up to 48 volts. Pins two and three of the XLR are biased positive via the limiting resistors and pin 1 is the DC return.I use a 40$ two channel mixer with my reference microphone, to obtain Phantom Power. The low cost box is a bit more noisy then our high end mixing console, but most people would not hear the difference.That Corporation and Analog Devices have good application notes on how to make high CMRR differential amplifiers with networks to block the DC and pass the audio.That Corp:http://www.thatcorp.com/datashts/AES129_Designing_Mic_Preamps.pdfI'm in a rush, but tomorrow I can find you an excellent AD app-note with something that is not too hard to build. I have it at work.Steve

author: Physikfan
author_rank: Regular Contributor
timestamp: August 30, 2017, 08:36:55 pm
content: Hi Ian.M, ciccio, Fungus, b_force, Brumby, cdev, NANDBlog and LaserSteveThank you very much for your links and comments, which have helped me a lot.Meanwhile, I think I know now how to connect the condenser microphones and what a phantom power supply means.Today I bought a mixer Q502USB by Behringer, whereby a microphone input with XLR jack allows the phantom power supply of 48V.I hope I can present very soon first results with the microphones.Also I would like to respond to your hints in detail.Best regardsPhysikfan

author: bitseeker
author_rank: Super Contributor
timestamp: August 31, 2017, 12:10:38 am
content: Looking forward to seeing your results and the HP 3561A in action.

author: Physikfan
author_rank: Regular Contributor
timestamp: August 31, 2017, 10:42:10 am
content: Hi Ciccio and b_force"How do you intend to measure the mic's frequency response? Do you have an anechoic room and a calibrated acoustic source, or you want to measure only the electronics?"Unfortunately I have no anechoic room and a calibrated acoustic source and other high sophisticated equipment (Brüel & Kjaer) and I can use rather only simple devices.For me the first step would be to connect a function generator (sine output) with an amplifier and loudspeaker as a "standard" source of sound at different frequencies.I am aware that I do not know the transfer function between electrical signal and the sound wave.The next step will be to measure the electrical signals of four different microphones (2 condensor and 2 dynamical microphones)by an oscilloscope and the HP3561A.The third step would be to analyze the data and possibly improve the design of this simple arrangement.Ad b_force:"Also a very old fashioned way to get the frequency response.There are much cheaper, easier and quicker methods."Please which cheaper, easier and quicker methods do you have in mind?RegardsPhysikfan

author: b_force
author_rank: Super Contributor
timestamp: August 31, 2017, 10:59:47 am
content: Ok, first of all there are roughly two methods of finding a mic's frequency response.1- use a calibrated well known mic as a reference and compare the two2 - (sometimes in combination with one). Use the pressure method. Were you use a mic inside a very small loudspeaker cabinet.In this method you'll need to measure the T/S parameters to get an accurate response.For higher frequencies there are little pressure rods/cabinets on the market.Just using a loudspeaker as a reference is very far from precise.By far the easiest way, is using a USB soundcard and using some software to directly measure the frequency response. Or even better, the impulse response (with a sweep)I personnaly really like ARTA:http://www.artalabs.hr/But there are many more on the market, like REW (which I think has a very confusing GUI) and some smaller ones.I personally don't understand why people nowadays still use the oscilloscope amplitude method.Which take forever and isn't that precise and more expensive.

author: ciccio
author_rank: Frequent Contributor
timestamp: August 31, 2017, 07:31:58 pm
content: Good mixer choice.An inexpensive meaurement microphone is this:http://www.music-group.com/Categories/Behringer/Microphones/Condenser-Microphones/ECM8000/p/P0118price is about 60 euros.An anechoic environment is not necessary: you may go outdoors and measure your speaker with two microhones, the one under test and the reference, placed one near the other.To reduce reflection effects, you can place the speaker pointing upwards.Many large loudspeaker systems, expecially the big "line array" used for PA, are tested this way, becaude a sufficiently large anechoic room is not available.Best regards

author: b_force
author_rank: Super Contributor
timestamp: August 31, 2017, 08:24:16 pm
content: Quote from: ciccio on August 31, 2017, 07:31:58 pmWell, even that is not needed!!(and pretty old fashioned)This is why people use 'time windows'.That way you can easily measure a clean response without any reflections.Depending on the height of your ceiling you can measure fine from 150-200Hz.Just combine that with a near-field measurement and your are good as gold.If I may give a suggestion for a microphone;https://www.parts-express.com/dayton-audio-emm-6-electret-measurement-microphone--390-801This one is even calibrated (and internally exactly the same as an ECM8000)

author: Physikfan
author_rank: Regular Contributor
timestamp: September 03, 2017, 01:57:53 pm
content: Hi b_force"I personnaly really like ARTA:http://www.artalabs.hr/"I am surprised by the quantity and quality of the material already existing.