Infrasound detector
Last response: in Home Audio
Archived from groups: rec.audio.tech (More info?)
Hi,
Just wondering if anyone has constructed a detector for infrasound (i.e.
below 20Hz). I'm guessing that such a detector would need to be more
like an aneroid barometer than a microphone. Possibly make something out
of a tin can with a membrane stretched on top, with the gubbins of a mic
(or speaker) somehow attached to the membrane. Perhaps put a pinhole in
the can to allow slower changes in atmospheric pressure to even-out. Run
the output into an oscilloscope or via an A/D converter to a PC.
Sound practical? Any better ideas? Any plans online?
Cheers folks.
Hi,
Just wondering if anyone has constructed a detector for infrasound (i.e.
below 20Hz). I'm guessing that such a detector would need to be more
like an aneroid barometer than a microphone. Possibly make something out
of a tin can with a membrane stretched on top, with the gubbins of a mic
(or speaker) somehow attached to the membrane. Perhaps put a pinhole in
the can to allow slower changes in atmospheric pressure to even-out. Run
the output into an oscilloscope or via an A/D converter to a PC.
Sound practical? Any better ideas? Any plans online?
Cheers folks.
More about : infrasound detector
Archived from groups: rec.audio.tech (More info?)
David Skinner wrote:
> Hi,
>
> Just wondering if anyone has constructed a detector for infrasound (i.e.
> below 20Hz). I'm guessing that such a detector would need to be more
> like an aneroid barometer than a microphone. Possibly make something out
> of a tin can with a membrane stretched on top, with the gubbins of a mic
> (or speaker) somehow attached to the membrane. Perhaps put a pinhole in
> the can to allow slower changes in atmospheric pressure to even-out. Run
> the output into an oscilloscope or via an A/D converter to a PC.
>
> Sound practical? Any better ideas? Any plans online?
>
> Cheers folks.
Since the energy involved will be very small, I'd suggest creating a
motion detector. Use a very large membrane, a laser beam bouncing off it
to an interferometer, and a filter to pass the frequencies you want.
I'm pretty sure similar devices are currently used to measure
loudspeaker distortion. It should not be much of a stretch to measure
subsonic vibration of a membrane with such a device.
David Skinner wrote:
> Hi,
>
> Just wondering if anyone has constructed a detector for infrasound (i.e.
> below 20Hz). I'm guessing that such a detector would need to be more
> like an aneroid barometer than a microphone. Possibly make something out
> of a tin can with a membrane stretched on top, with the gubbins of a mic
> (or speaker) somehow attached to the membrane. Perhaps put a pinhole in
> the can to allow slower changes in atmospheric pressure to even-out. Run
> the output into an oscilloscope or via an A/D converter to a PC.
>
> Sound practical? Any better ideas? Any plans online?
>
> Cheers folks.
Since the energy involved will be very small, I'd suggest creating a
motion detector. Use a very large membrane, a laser beam bouncing off it
to an interferometer, and a filter to pass the frequencies you want.
I'm pretty sure similar devices are currently used to measure
loudspeaker distortion. It should not be much of a stretch to measure
subsonic vibration of a membrane with such a device.
Archived from groups: rec.audio.tech (More info?)
In article <MPG.1b40ce5c29b9eb01989687@news.individual.net>, David Skinner <branestawm2002@yahoo.co.uk> wrote:
>Hi,
>
>Just wondering if anyone has constructed a detector for infrasound (i.e.
>below 20Hz). I'm guessing that such a detector would need to be more
>like an aneroid barometer than a microphone. Possibly make something out
>of a tin can with a membrane stretched on top, with the gubbins of a mic
>(or speaker) somehow attached to the membrane. Perhaps put a pinhole in
>the can to allow slower changes in atmospheric pressure to even-out. Run
>the output into an oscilloscope or via an A/D converter to a PC.
>
>Sound practical? Any better ideas? Any plans online?
I've seen slow motions of the meter just using a Panasonic electret. Its
a matter of coupling the electronics at a low frequency. You can sometimes see,
vibrations of a few Hertz, caused by ventilation systems.
greg
In article <MPG.1b40ce5c29b9eb01989687@news.individual.net>, David Skinner <branestawm2002@yahoo.co.uk> wrote:
>Hi,
>
>Just wondering if anyone has constructed a detector for infrasound (i.e.
>below 20Hz). I'm guessing that such a detector would need to be more
>like an aneroid barometer than a microphone. Possibly make something out
>of a tin can with a membrane stretched on top, with the gubbins of a mic
>(or speaker) somehow attached to the membrane. Perhaps put a pinhole in
>the can to allow slower changes in atmospheric pressure to even-out. Run
>the output into an oscilloscope or via an A/D converter to a PC.
>
>Sound practical? Any better ideas? Any plans online?
I've seen slow motions of the meter just using a Panasonic electret. Its
a matter of coupling the electronics at a low frequency. You can sometimes see,
vibrations of a few Hertz, caused by ventilation systems.
greg
Archived from groups: rec.audio.tech (More info?)
David Skinner <branestawm2002@yahoo.co.uk> wrote in message news:<MPG.1b40ce5c29b9eb01989687@news.individual.net>...
> Hi,
>
> Just wondering if anyone has constructed a detector for infrasound (i.e.
> below 20Hz). I'm guessing that such a detector would need to be more
> like an aneroid barometer than a microphone. Possibly make something out
> of a tin can with a membrane stretched on top, with the gubbins of a mic
> (or speaker) somehow attached to the membrane.
There are plenty of laboratory condenser microphones that routinely
respond far below 20 Hz. The Bruel & Kjaer capsule have lower limiting
frequencies specifed down to 1-3 Hz (-3 dB) and there specialized
microphon systems that have responses FAR below that. One example
being the B&K 4147, which is specified as being -3 dB at 0.001 Hz
(that's 1 cycle every 15 minutes).
Even some of the cheap electret condenser mics (cheap as in a couple
of dollars) have reasonable responses below 20 Hz.
Electrodynamic microphones won't work: they output a voltage that's
proportional to velocity and thus run out of steam fairly quickly.
> Perhaps put a pinhole in
> the can to allow slower changes in atmospheric pressure to even-out.
In fact, ALL microphones have such a contrivance specifically to
prevent biasing due to slow changes in atmospheric pressure. A great
deal of care is applied in the more expensive laboratory capsules to
ensure the time constant of the pinhole leak is within a small range,
since that leak determins the low-frequency cutoff of the microphone.
David Skinner <branestawm2002@yahoo.co.uk> wrote in message news:<MPG.1b40ce5c29b9eb01989687@news.individual.net>...
> Hi,
>
> Just wondering if anyone has constructed a detector for infrasound (i.e.
> below 20Hz). I'm guessing that such a detector would need to be more
> like an aneroid barometer than a microphone. Possibly make something out
> of a tin can with a membrane stretched on top, with the gubbins of a mic
> (or speaker) somehow attached to the membrane.
There are plenty of laboratory condenser microphones that routinely
respond far below 20 Hz. The Bruel & Kjaer capsule have lower limiting
frequencies specifed down to 1-3 Hz (-3 dB) and there specialized
microphon systems that have responses FAR below that. One example
being the B&K 4147, which is specified as being -3 dB at 0.001 Hz
(that's 1 cycle every 15 minutes).
Even some of the cheap electret condenser mics (cheap as in a couple
of dollars) have reasonable responses below 20 Hz.
Electrodynamic microphones won't work: they output a voltage that's
proportional to velocity and thus run out of steam fairly quickly.
> Perhaps put a pinhole in
> the can to allow slower changes in atmospheric pressure to even-out.
In fact, ALL microphones have such a contrivance specifically to
prevent biasing due to slow changes in atmospheric pressure. A great
deal of care is applied in the more expensive laboratory capsules to
ensure the time constant of the pinhole leak is within a small range,
since that leak determins the low-frequency cutoff of the microphone.
Related ressources
- Infrasonic detector - Forum
- Infrasonic detector - Forum
- Center Channel distortion when watching recorded TV - Forum
Archived from groups: rec.audio.tech (More info?)
In article <MPG.1b40ce5c29b9eb01989687@news.individual.net>,
branestawm2002@yahoo.co.uk says...
Thanks for the responses so far folks - gives me a few ideas. I'd
respond to ideas individually but my newsserver is playing up - I saw
three responses when I checked at work today, but I can only see one now
from home.
In article <MPG.1b40ce5c29b9eb01989687@news.individual.net>,
branestawm2002@yahoo.co.uk says...
Thanks for the responses so far folks - gives me a few ideas. I'd
respond to ideas individually but my newsserver is playing up - I saw
three responses when I checked at work today, but I can only see one now
from home.
Archived from groups: rec.audio.tech (More info?)
David Skinner wrote:
> Hi,
> Just wondering if anyone has constructed a detector for infrasound
> Sound practical? Any better ideas? Any plans online?
Although I've seen plans for building several configurations on-line, I
don't have a URL handy.
Here's a good starting point.
http://www.etl.noaa.gov/et1/infrasound/
Be sure to get the pdf doc:
http://www.etl.noaa.gov/et1/infrasound/atmospheric_infr...
-Greg
David Skinner wrote:
> Hi,
> Just wondering if anyone has constructed a detector for infrasound
> Sound practical? Any better ideas? Any plans online?
Although I've seen plans for building several configurations on-line, I
don't have a URL handy.
Here's a good starting point.
http://www.etl.noaa.gov/et1/infrasound/
Be sure to get the pdf doc:
http://www.etl.noaa.gov/et1/infrasound/atmospheric_infr...
-Greg
http://online.physics.uiuc.edu/courses/phys403/303Proje...
This is a very detailed article going over a few ways to make your own infrasound detector. The basis of the article was to find cheaper ways to construct infrasound detectors and he has a few different ideas of what might work ^_^
This is a very detailed article going over a few ways to make your own infrasound detector. The basis of the article was to find cheaper ways to construct infrasound detectors and he has a few different ideas of what might work ^_^
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