I need to design a device with a microphone in a very small (2"x2"x2") enclosure. My problem is, whatever I do, I seem to be over modulating the microphone. I checked SPL with a CheckMate SPL meter, and both A and C weighted give me SPLs in the low 120s.
I've tried many variations on placing the microphone (put it inside tubes, shielded it with baffles and membranes, put it in a separate chamber), and I've tried about 6 different microphones (all condenser), and several headroom circuits, including a 4 wire mic and headroom circuit that is suppose to be good to 136db, but it still sounds like I'm over modulating - slamming the mic membrane to the wall. If I open the enclosure, the microphones all sound fine.
Any suggestions?😕
I've tried many variations on placing the microphone (put it inside tubes, shielded it with baffles and membranes, put it in a separate chamber), and I've tried about 6 different microphones (all condenser), and several headroom circuits, including a 4 wire mic and headroom circuit that is suppose to be good to 136db, but it still sounds like I'm over modulating - slamming the mic membrane to the wall. If I open the enclosure, the microphones all sound fine.
Any suggestions?😕
I did try stuffing the whole space with some foam, but it wasn't acoustical foam - it didn't make any noticeable change.
So then just what is doing the driving? In a sealed box, what was sound waves can become pressurization.
I have the enclosure vented with an open 1/2 diameter hole, so it isn't pressurizing. I would try to put some kind of acoustical dampening material in there, if I knew what to use. I was looking around for some cork, but being I filled the whole thing with open cell foam (the regular packing foam/sponge - polyethylene or polyurethane?) I'm not sure that is the problem. I am reading about room acoustics - anyone know what happens when you shrink a room to 2" x2" x 2"?
When I first read the original post, I thought of "echo chamber." Maybe a pic or a little more info will stimulate some solutions.
I have trouble drawing this - but - Take a paper cup (coffee cup), poke or cut a hole in it big enough to stick your finger through, hold it up to cover your mouth and chin, and talk into it. I want to stick a microphone in the cup, and record it.
When I try this - I get what sounds like totally over modulated recording. If I pull the cup away from my face 1/2 inch or so, the recording sounds fine. I need the recording to sound good with the cup sealed against the users face.
I think I've seen this type of a setup in a courtroom - I think there was a "court reporter" that was speaking into a cup - I couldn't hear her, but I think that what she was doing.
When I try this - I get what sounds like totally over modulated recording. If I pull the cup away from my face 1/2 inch or so, the recording sounds fine. I need the recording to sound good with the cup sealed against the users face.
I think I've seen this type of a setup in a courtroom - I think there was a "court reporter" that was speaking into a cup - I couldn't hear her, but I think that what she was doing.
Small electrets are going to have issues with SPL's more than ~110dB. 1/2" or 1" electrets might work better. Radio shack sells a cheap omni dynamic microphone that might also work fine for this. Even a headphone element might work well as a microphone in this situation.
Thanks Ron. I don't suppose the microphone manufacturers rate their mics on what SPL they handle, especially the cheap ones. Is there anything to look for that may reveal a higher SPL capability?
I just ordered a Sure SM58 microphone and I'll test this. It is a dynamic cardioid microphone. I also got a pop filter - a double screen that stops the direct air strikes on the microphone. I'll post how this works in my enclosure.
It will take up the whole cup.
mics are acoustical devices and like speaker drivers, there enclosures can have a huge impact on there operation
What are you trying to do.
mics are acoustical devices and like speaker drivers, there enclosures can have a huge impact on there operation
What are you trying to do.
Yep, I found that out. The small enclosure sure changed the microphone. If I can take the guts out of the Sure mic, I'll try using that. This is an experiment, I'm trying to do something similar to a court reporter thing - gotta seal a cup against the users face, so no one else can hear, and need to record the voice. Hi fidelity isn't necessary, but the lower the distortion the easier it will be to understand it later, so I'd like to get the lowest distortion possible without getting too expensive or big.
You mentioned you had put the mic in a separate chamber. You might try putting it in a separate smaller enclosure, with a pinhole (experiment with the actual diameter) in an attempt to control the amount of signal reaching the mic.
I don't know what you are doing, but any chance of moving the reporter? To make up an example, if I had a reporter sitting in a recording studio and didn;t want the mics picking him up, I could build your Dixie Cup thing, or I could move the guy to the control room. He'd still see and hear, but would be sonically isolated from the studio room. Like the translators at the United Nations.
I did try putting a pinhole in the wall and putting the mic behind the pinhole. What happens is that the mic has to be directly in front of the pinhole or else it doesn't pickup. When directly in front of the pinhole, the thing still overmodulates.
Maybe you could try using a small driver as mic, you then would have to make a separation on the end of the "cup" and mount the driver in it...
For a first test you maybe can try it with in ear headphones, put one in the "cup" and see what it does?
For a first test you maybe can try it with in ear headphones, put one in the "cup" and see what it does?
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