Microphone Transfer Function

B

Brent Venter

Freshman
Mar 31, 2011
22
0
1
Hi Guys,

Any ideas on how to do a transfer function of a microphone, cannot seem to think how / where to start. Is this even possible?

The query is related to podium microphone installs. Center cluster with gooseneck podium cardioid mic is severely more unstable than handheld wireless cardioid. Is the distance from source to microphone the only thing at play here?

Thanks
 
Re: Microphone Transfer Function

Brent Venter said:
Hi Guys,

Any ideas on how to do a transfer function of a microphone, cannot seem to think how / where to start. Is this even possible?

The query is related to podium microphone installs. Center cluster with gooseneck podium cardioid mic is severely more unstable than handheld wireless cardioid. Is the distance from source to microphone the only thing at play here?

Thanks
Click to expand...
Knowing the transfer function of the mic is of little value here.

You also have in the "equation" the freq response of the loudspeaker system at the mic position-reflection paths etc.

The simplest thing to do is to put a "dummy head" or piece of cardboard where a typical face would be behind the mic and simply use an RTA and turn up the system till it feedsback and notch it at that freq. Don't do to many or you will end up at the point of dimensioning return.

Now whether you do this tuning on the system eq or the channel eq-really depends on the particular situation. Is this the only mic? If so-then a system eq may be the way to go. If there are other mics-you have to do it on the channel-so you don't destroy the other mics
 
Re: Microphone Transfer Function

Mark DeArman said:
Take a known reference measurement microphone and measure a speaker.
Use the measurement of the speaker to create an inverse filter.
Measure unknown microphone and apply filter.
Click to expand...

Or you can do a transfer measurement using the reference mic and the unknown mic as the inputs. Assuming the reference is flat-the difference is the response of the unknown. mic. Just make sure the elements are very close to each other so they are getting the same signal.

It really doesn't matter what the freq response of the loudspeaker is-as long as it is wide enough for the area of interest for the mic. It is difference in the response of the mics that you are interested in-NOT the response of the loudspeaker.
 
Re: Microphone Transfer Function

Ivan Beaver said:
The simplest thing to do is to put a "dummy head" or piece of cardboard where a typical face would be behind the mic and simply use an RTA and turn up the system till it feedsback and notch it at that freq. Don't do to many or you will end up at the point of dimensioning return.
Click to expand...

Thanks for the tip. This can work great when I am alone. I try and use a real person with speech when I want to eq the system for gain before feedback to simulate real world use. I am just trying to get to the bottom why the two "types" of microphones behave so differently even when they have similar pickup patterns. Is it just the distance between source and mic that creates this difference or are there elements to a gooseneck mic that changes the game.
 
Re: Microphone Transfer Function

Brent Venter said:
Is it just the distance between source and mic that creates this difference or are there elements to a gooseneck mic that changes the game.
Click to expand...
The podium which the goose neck is mounted to is a reflective surface, there are path length differences between the voice direct path and the reflected path.
This causes a comb filter response (peaks and dips) as well as the difference in tonal response dependent on the cardioid pattern, as the reflected sound hits the mic from a different angle than the direct sound. The funky response really can't be cured with EQ, and reduces gain before feedback.

If you can use a boom or longer goose neck to get the mic close to the speaker's mouth the podium reflections will be so far down in level they won't be a problem.

Remember to put glasses and hats on the dummy head if the speakers wear them.
 
Re: Microphone Transfer Function

Ivan Beaver said:
Or you can do a transfer measurement using the reference mic and the unknown mic as the inputs. Assuming the reference is flat-the difference is the response of the unknown. mic. Just make sure the elements are very close to each other so they are getting the same signal.

It really doesn't matter what the freq response of the loudspeaker is-as long as it is wide enough for the area of interest for the mic. It is difference in the response of the mics that you are interested in-NOT the response of the loudspeaker.
Click to expand...

You're right, that probably is easiest. It's not like you care about 20kHz in this instance :-)
 
Re: Microphone Transfer Function

Brent Venter said:
Thanks for the tip. This can work great when I am alone. I try and use a real person with speech when I want to eq the system for gain before feedback to simulate real world use. I am just trying to get to the bottom why the two "types" of microphones behave so differently even when they have similar pickup patterns. Is it just the distance between source and mic that creates this difference or are there elements to a gooseneck mic that changes the game.
Click to expand...
There is more to the overall "character" than a name of a pattern. Just because the name is the same does not mean the pattern is the same.

You also have to consider the freq response-which can be wildly different.

If you run through the PAG NAG equations and play with the numbers-it should be quickly apparent that the thing that makes the biggest difference is the operating distance.
 
Re: Microphone Transfer Function

For the mic measuring part, EarthWorks has an instruction sheet:
[h=6]"How Earthworks Measures Microphones"
How to measure microphones and the implications relating to measuring loudspeakers.[/h]http://www.earthworksaudio.com/support/technical-articles/

But that doesn't take into account each mic's pattern which varies with frequency.
 
Re: Microphone Transfer Function

Tim Padrick said:
According to Neumann's tests, many mics' patterns change as the source (such as a human head) gets closer to the mic. They found that some even get more sensitive behind than in front.
Click to expand...

Tim...

Would you happen to have a link to the test results? That would be some good reading and might explain a thing or two that need clarification.
 
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