What is the standard process of Microphone testing?

[abnerko1973]

Hello. Microphone is a simple device and its mechanism is also simple. The device converting sound waves into electrical energy is mic. But I am little curious about how microphone manufacturer company check their mics before selling? Means Can I test my mic at home using standard process? I just know some online tools to carry a mic test but they are very simple. These tools just shows if mic is picking sound. Share your information if you know the standard process of mic check.

 

[Baluncore]

Welcome to PF.
To test a microphone you will need an anechoic chamber with instrumentation.
https://en.wikipedia.org/wiki/Anechoic_chamber#Acoustic_anechoic_chambers

A “mic check” involves typically saying the words “testing testing 1 2 3” to verify that the mic was plugged in and ready for use.

 

[abnerko1973]

Thanks @Baluncore for your answer. But which instruments Do I need. Is it high quality Amplifier, equalizer transmitter. Is this process can carried out at home.

 

[Baluncore]

Is this process can carried out at home.

It is not a process you can carry out at home, unless you build an anechoic chamber.

But which instruments Do I need.

You will need;
1. Anechoic chamber.
2. Signal source, and a speaker to generate the sound.
3. Reference microphone, with a known frequency response, (transfer function).
4. The microphone you want to test.
5. A microphone amplifier and some way of digitising or measuring the electrical signals.

These days I would use a noise source. Record the two microphones on the Left and Right channels of a PC. Then use an FFT program to compute the spectrum of each signal independently. For each frequency in the spectrum, divide the “test mic amplitude” by the “reference mic amplitude”. That gives the relative transfer function of the microphones. Then correct for the transfer function of the known reference.

Swap the L and R channels and repeat, which should identify and cancel any differences between the two channels.

 

[abnerko1973]

So until I don't had an anechoic chamber I can't carry a standard mic test process at home. But I think there are some studios (may be another term) which I can hire to check my mic. I heard that getting bunch of microphones to them for testing purpose would be cheaper. I don't have clear idea about this but I heard this for other sources.

Such studios provides mic testing services. They own complete setup to carry a test. Obviously they should have an anechoic chamber, high quality sound sources, reference microphone, electrical signal measuring devices. But I am not clear if their services made for normal testing purposes.

Also, Isn't this standard process you mentioned time consuming? I think mic manufacturer companies checking their each mic by this method would cost them a lot. Can you explain how much it cost for them. Even if it is worth it why they don't simply use online tools available in internet for https://mictest.me. Online tools are simple to use and would eliminate their cost. Is it because tools doesn't deliver accurate results or is there another reason. I think testing mics in aenohoic chamber with instrumentation is professional way and it help company innovation team for improvement which online tools don't. Am I right? And thanks for you response in this discussion and providing valuable info.

 

[Baluncore]

So until I don't had an anechoic chamber I can't carry a standard mic test process at home.

1. What is the microphone used for?
2. Why do you need to test the microphone?
3. How accurate does the test need to be?

Online tools are simple to use and would eliminate their cost.

Without an anechoic chamber you would do the online tests in a space with unknown frequency response, unknown resonance, and computer room noise.

 

[f95toli]

I seriously doubt studios involved in music production ever "test" their microphones. Most microphones used for recording are not even close to being "neutral", i.e. they certainly don't have a flat frequency response. This is why music studios use many different types microphones for different purposes (and many singers only use their own favourite models).
Microphones made for acoustic measurements are very rarely used for recording.
Hence, microphone manufacturers do not need to measure each microphone they sell, they just need to make sure each microphone is identical (to some tolerance) and for that you only need a relative measurement where you compare it to some reference microphone; i..e you don't need an anechoic chamber.

There are companies out there who will calibrate microphones for you. Calibrated microphones are needed if you are e.g. evaluating the acoustics of a space, measuring the noise from some equipment or even developing new hifi equipment. This is a not a big market

Years ago I was into hifi as a hobby and I also built some speakers. I then bought a cheap(ish) condenser microphone which was known to be "flat enough" for this purpose.
There are lots of models to choose from
See e.g.
https://www.thomann.de/gb/microphones_for_measurements.html

 

[Klystron]

In general all of the equipment mentioned in this thread can be tested and, where appropriate calibrated to a standard. Testing laboratories such as Underwriters Laboratories (UL) often test electronic devices such as microphones from manufacturers to provide users with initial performance benchmarks. Calibration remains a vital repeatable step in the process as equipment ages and conditions change.

Look closely at your purchased equipment including cables and connectors. A good signal generator or oscilloscope should be tagged with date of laboratory tests and periodic calibration labels to ensure proper function as described in their operator manuals. Customers can arrange periodic calibration with the manufacturer or with independent laboratories.

Mics are ubiquitous and simple enough to test and calibrate in a DIY lab with an improvised anechoic chamber as @Baluncore and others describe . Weigh the cost of DIY against hiring an outside lab. Or do both: test your basic mics and send in the most expensive/sensitive equipment to a credited lab. 'Sound proofing' an area need not be fiendishly expensive but note that your lab equipment also requires calibration.

For reference, large organizations I worked with either contained precision equipment laboratories (USAF, NASA, university) or maintained contracts (SRI) with reputable test labs including UL; or both. The Speech Technology and Research labs at SRI routinely calibrated microphones and related audio equipment on a schedule depending on use.

 

[anorlunda]

Can I test my mic at home using standard process? I just know some online tools to carry a mic test but they are very simple. These tools just shows if mic is picking sound.

I disagree.

For example, zoom.us/test will let you say something, it will record it, then play it back to you. You can then judge the quality of the playback. That's more than just sound detected. If the playback sounds good, then the entire chain microphone/record/playback has been tested.

 

[Baluncore]

1. What is the microphone used for?
2. Why do you need to test the microphone?
3. How accurate does the test need to be?

Until you answer those questions you will get only general answers.

Apart from being sensitive to the required audio spectrum, the critical thing about a microphone is that it should NOT generate harmonics of the input fundamental. Clipping will generate even odd harmonics, asymmetry will generate odd even harmonics, non-linearity will generate sidebands.

Your ear performs a frequency separation along it's tapered cochlea, so it is very good at detecting harmonics. As the wave moves from the narrow end to the wide end, the higher harmonic frequencies are separated and detected first, before the remaining fundamental.

Your ear cannot detect the phase of a sound wave, it takes the brain to sense the phase of the low frequency AM envelope. For that reason the phase shift in an audio microphone is NOT important.

That is why your ears are sufficient for “testing, testing, one, two, three” an audio microphone. It is only specialist instrumentation microphones that need to be calibrated.

 

[alan123hk]

But I am little curious about how microphone manufacturer company check their mics before selling?

For the cheapest microphone, the manufacturer can only perform the most basic tests, such as sensitivity and distortion, while the finished product only needs to meet the most basic requirements.

However, for professional studio microphones, of course, professional hardware and software must be used for very strict quality testing before the product leaves the factory.

https://www.listeninc.com/applications/microphones/#tab-id-1