constant gain for mic amplification

[Newo]

I need to measure the ambient sound level in dB. I am going to use a
small electret microphone. I was looking at the MAX4466 for
amplification but I noticed that there is not a constant gain across
the audible frequencies. I've notice this on all amps suited for
microphone amplification. Am I missing something or won't high
frequencies be amplified less than lower ones?

Should I instead try to find an opamp that has constant gain over
audible freqs?

Thanks, Stephen.

 

[N. Thornton]

I need to measure the ambient sound level in dB. I am going to use a
small electret microphone. I was looking at the MAX4466 for
amplification but I noticed that there is not a constant gain across
the audible frequencies. I've notice this on all amps suited for
microphone amplification. Am I missing something or won't high
frequencies be amplified less than lower ones?

Should I instead try to find an opamp that has constant gain over
audible freqs?

Thanks, Stephen.

Hi Stephen.

When it comes to opamps, the open loop gain may not be flat, but once
you put it into circuit it is the closed loop gain that counts, and
that will be flat. So with opamps you neednt worry.

Regards, NT

 

[John Crighton]

I need to measure the ambient sound level in dB. I am going to use a
small electret microphone. I was looking at the MAX4466 for
amplification but I noticed that there is not a constant gain across
the audible frequencies. I've notice this on all amps suited for
microphone amplification. Am I missing something or won't high
frequencies be amplified less than lower ones?

Should I instead try to find an opamp that has constant gain over
audible freqs?

Thanks, Stephen.

Hello Stephen,
have a look at this site.
http://sound.westhost.com/index.html
The man is in Sydney so if you decide to buy something
he might be close to you. There is some interesting
reading on the web site.

This might be what you are looking for. A measurement
mic. probe. about one third down this page.
http://sound.westhost.com/project93.htm
I think you can buy it as a kit or just the bits and pieces
that you want.

Regards,
John Crighton
Sydney

 

[Watson A.Name - 'Watt Sun']

Hi Stephen.

When it comes to opamps, the open loop gain may not be flat, but once
you put it into circuit it is the closed loop gain that counts, and
that will be flat. So with opamps you neednt worry.

If you use the very common 741 or its equivs such as the 1458, you
will _not_ get flat response at higher audio freqs if the gain is
higher than about 10. That's because the open loop gain at 20 kHz is
so low that even with feedback, there is a rolloff. Look at the
graphs on the data sheet.

So do not expect high fidelity out of a cheap opamp.

Regards, NT

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