[b0dhi]

Anyone know where to get calibrated (flat to within 1dB or better) electret mics? My regular microphone seems to be distorting since I used it as a speaker

I will be running some tests on headphones and need a fairly flat and very low distortion mic. Thanks.

Edit: this is now a Panasonic WM-61A thread

 

[pabbi1]

Of course it must be a Telefunken U47.

 

[LFF]

Here is what I would do:

I would generate a white noise audio file and play it back over a single loudspeaker. Place the loudspeaker directly in front of your mic at about 4-6 feet away. Play the white noise and record. Try to get a good strong gain from the mic by turning up the noise volume. Also, do your best to control reflections in the room by hanging blankets or sound baffles on the walls.

Normalize the recordings to 0 db. The end goal is to flatten the peaks and valleys of the frequency response for your mic.

So what do you do?

Analyze the EQ of the white noise and apply the INVERSE EQ to what you recorded. This should give you a FLAT response.

For example - let's say your mic has a boost in the mid with the peak being at 2,000 Hz by about 7db. So, using a graphic equalizer (or a parametric with a Q of 1), apply the inverse EQ, -7db at 2,000 Hz. Most importantly, record something you know well and use your ears.

Now, everytime you make a recording with that same mic, all you need to do is apply the same presets for your mic EQ and you should be good to go.

 

[b0dhi]

Thanks for the responses. I should have mentioned low cost as well

Did a bit more digging and the Panasonic WM-61A seems to be a good choice. There's a Linkwitz mod for it which apparently reduces the distortion, but to what degree? Would they have less than 0.5% distortion? I need low distortion because I will be measuring intermodulation distortion on various headphones and comparing them. It doesn't have to be extremely low, however, because the measurement procedure I'm using exposes the distortion and brings it up to (or close to) audible levels, so around 0.5%. I haven't been able to find any info on how much distortion this mic actually has. A kick in the right direction would be much appreciated.

 

[LFF]

Quote:

Originally Posted by b0dhi /img/forum/go_quote.gif Thanks for the responses. I should have mentioned low cost as well

That is probably the cheapest way of doing it. There are tons of free apps which can help you do what I recommended above. All you need is some free time.

Good luck!

 

[b0dhi]

Quote:

Originally Posted by LFF /img/forum/go_quote.gif That is probably the cheapest way of doing it. There are tons of free apps which can help you do what I recommended above. All you need is some free time. Good luck!

Thanks

I appreciate your help. I would go down that path except I had just assumed that microphones had lower distortion than headphones, and that doesn't seem to be the case. Although I do need fairly flat response (to preserve phase), it looks like getting low enough distortion is now the biggest problem.

 

[error401]

Have you seen this page?

John Conover: Using the Panasonic WM61A as a Measurement Microphone

 

[b0dhi]

Thanks!

That's exactly what I was after.

Quote:

However, all that can be claimed is that all seven of the WM61A measurement microphones exhibited less than 0.1% second harmonic distortion amplitudes at 997 Hz., 100 dB SPL sound intensity levels.

Awesome.