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#1
Posted to rec.audio.tech
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Sound proofing
I am working on a device which uses a sensor that is very sensitive to
vibration (an unintended consequence of it's construction). In fact it is so sensitive, it makes an excellent microphone! The sensor is flat and thin as a CD or DVD, and about 1.5X2.5 inches oval. Anyway, I need to find a material to sound proof it so it is insensitive to sounds. I tried putting 1/4 inch of dense foam rubber on each side of it (the kind that is used for insulation which is sticky on one side), but it did nothing as far as I could tell. I put it into an aluminum box, and that increased the sensitivity by 10 or so db, even wrapped in foam rubbber! Does anyone have any suggestions. Potting in epoxy or polyester resin might work, but the device cost $50 and I really don't want to do that unless I am sure it will work. Thanks, Marshall |
#2
Posted to rec.audio.tech
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Sound proofing
In article , Marshall Dudley wrote:
I am working on a device which uses a sensor that is very sensitive to vibration (an unintended consequence of it's construction). In fact it is so sensitive, it makes an excellent microphone! The sensor is flat and thin as a CD or DVD, and about 1.5X2.5 inches oval. Anyway, I need to find a material to sound proof it so it is insensitive to sounds. I tried putting 1/4 inch of dense foam rubber on each side of it (the kind that is used for insulation which is sticky on one side), but it did nothing as far as I could tell. I put it into an aluminum box, and that increased the sensitivity by 10 or so db, even wrapped in foam rubbber! Does anyone have any suggestions. Potting in epoxy or polyester resin might work, but the device cost $50 and I really don't want to do that unless I am sure it will work. Thanks, Marshall Was the rubber touching the device ? what is the mounting scheme ? Any vibration sitting on a table, for example, will transfer into it. It needs mass, and suspension for the overall box, and that box needs insulation on the outside and inside. A lead box would be better, or steel. greg |
#3
Posted to rec.audio.tech
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Sound proofing
"Marshall Dudley" wrote in message
I am working on a device which uses a sensor that is very sensitive to vibration (an unintended consequence of it's construction). In fact it is so sensitive, it makes an excellent microphone! The sensor is flat and thin as a CD or DVD, and about 1.5X2.5 inches oval. Anyway, I need to find a material to sound proof it so it is insensitive to sounds. I tried putting 1/4 inch of dense foam rubber on each side of it (the kind that is used for insulation which is sticky on one side), but it did nothing as far as I could tell. I put it into an aluminum box, and that increased the sensitivity by 10 or so db, even wrapped in foam rubbber! Does anyone have any suggestions. Put the sensor into an evacuated chamber, suspended by springs that give it a very low resonant frequency, but keep it from touching the sides of the chamber. |
#4
Posted to rec.audio.tech
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Sound proofing
"Marshall Dudley" wrote ...
I am working on a device which uses a sensor that is very sensitive to vibration (an unintended consequence of it's construction). In fact it is so sensitive, it makes an excellent microphone! The sensor is flat and thin as a CD or DVD, and about 1.5X2.5 inches oval. Anyway, I need to find a material to sound proof it so it is insensitive to sounds. I tried putting 1/4 inch of dense foam rubber on each side of it (the kind that is used for insulation which is sticky on one side), but it did nothing as far as I could tell. I put it into an aluminum box, and that increased the sensitivity by 10 or so db, even wrapped in foam rubbber! Does anyone have any suggestions. Potting in epoxy or polyester resin might work, but the device cost $50 and I really don't want to do that unless I am sure it will work. How is it attached? By the edge? Is it the flexing of the center part of the oval that is microphonic? Can you touch it (top or bottom) to keep it from vibrating without impeding the main function (undisclosed) of the device? If you can pot it, why can't you clamp the flat surface (top and bottom) in a foam/steel sandwich? If you really want to suspend it then you have to deal with the "sprung mass" and the strength of the "springs". Suspending something rather lightweight with stiff foam would predictably do almost nothing to isolate it. This is really more a "mechanical" question than an "audio" question. |
#5
Posted to rec.audio.tech
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Sound proofing
Marshall Dudley wrote: I am working on a device which uses a sensor that is very sensitive to vibration (an unintended consequence of it's construction). In fact it is so sensitive, it makes an excellent microphone! The sensor is flat and thin as a CD or DVD, and about 1.5X2.5 inches oval. Anyway, I need to find a material to sound proof it so it is insensitive to sounds. I tried putting 1/4 inch of dense foam rubber on each side of it (the kind that is used for insulation which is sticky on one side), but it did nothing as far as I could tell. I put it into an aluminum box, and that increased the sensitivity by 10 or so db, even wrapped in foam rubbber! Does anyone have any suggestions. Potting in epoxy or polyester resin might work, but the device cost $50 and I really don't want to do that unless I am sure it will work. Without knowing what the device is and the mechanism by which it is affected by sound, any reply would be pure guesswork and therefore likely worthless. Graham |
#6
Posted to rec.audio.tech
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Sound proofing
Marshall Dudley wrote:
I tried putting 1/4 inch of dense foam rubber on each side of it (the kind that is used for insulation which is sticky on one side), but it did nothing as far as I could tell. I put it into an aluminum box, and that increased the sensitivity by 10 or so db, even wrapped in foam rubbber! When you want to prevent sound from reaching your sensor, you need to create an impedance mismatch between the sound source and the sensor. This means you have to put something very heavy (or something very stiff) in between. Neither foam rubber nor aluminum satisfy these criteria. You can also build a sandwich of mechanical mass/spring lowpasses. This could e.g. be a heavy box inside another heavy box with something elastic (e.g. air) in between. But you'll need to adjust the weights and elasticity properly, which can be next to impossible. Then you need to prevent any direct sound paths, i.e. the box must be air tight so sound cannot travel through air and the device must not touch the box so sound cannot travel though solid matter. If its a small device and you cannot e.g. place it inside a concrete block, all this will be very difficult. |
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