Frequency Measurement - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 7 Old 08-16-2016, 04:43 PM - Thread Starter
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Frequency Measurement

Odd question. I own the original Omni Mic. I also own a company that has a large dust collector. It is very loud. The company that makes "silencers" wants a reading of the frequencies it is putting out. It has been a while since I have used REW and Omni mic. Can either of these give me a simple frequency/db reading?

Or is there someone who can do this for me quickly in SE Michigan. If you are a DIY speaker maker I am a very good friend to have from the cabinet side.

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post #2 of 7 Old 08-16-2016, 05:34 PM
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.02

this sounds like a quick question for Austin Jerry /and /or/ his REW guide
which many members here have as a link

and a search for REW and omni mike compatibility may prove a quick answer,

it may be good enough for dB and FR recording

it sounds like a reverse CS situation, i.e. backwards
you'd think they would walk in with a SPL meter for loud / FR and a laptop already to go,
how long could that take?
if you've ever made an REW sweep, you know . . . a quickie
and have an answer for your specific circumstance within their range of products

good luck

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post #3 of 7 Old 08-16-2016, 06:28 PM
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Put the omnimic in FFT/RTA mode (tab named "SPL/Spectrum"). Shoot the gun near the mic, look at the plot.

The difficulties will be:
1) Catching the shot on-screen and pausing the system at that point to freeze the graph, since there isn't any triggering in this mode. If you are using the most recent (v5.x) omnimic software, the space bar will pause/unpause it (don't forget there is about a second's delay). You may have to do a number of shots to be sure you've caught the highest amplitude graph.
2) Not overloading the mic. You'll see a readout at the top of the screen telling you to back off the sensitivity slider or move the mic further from the silencer if it overloads.

Your choice of FFT, RTA, smoothing or damping levels is up to you. Slower damping would make it easier to catch the shot, impulse mode would mean you'd have to catch it right-on..... I'd use "slow" or "slowest" if I were you.

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post #4 of 7 Old 08-16-2016, 08:58 PM
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There is a very good chance that the gun will be louder than what the mic can handle, you may have to put the mic at 3M or even 6M away, and then approximate the 1M value.

A TermLab or SPL Lab meter is capable of 180-190db which is more-than-enough to capture a gun shot, the problem is that I believe their sampling is only 1/4 of a second which might be too long for a gun shockwave.
I suppose if you put off 3 or so rounds in succession you'd get a "proper" reading of the SPL.

Most guns are in the 140-160db range unsilenced, and 110-130 with. I would imagine long-guns are still in the >130db range with a silencer, especially a 300.
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post #5 of 7 Old 08-16-2016, 10:41 PM
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He has a dust collector that is loud in his shop. Sounds to me like there is a company that makes silencers for the dust collector, and he needs to take readings of the dust collector so that they can make a custom silencer for the frequency it is putting out.

That what I take from the post.....
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post #6 of 7 Old 08-16-2016, 11:59 PM
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Seems like something SpecLab could do, but might be too much bother for a single measurement.
http://www.qsl.net/dl4yhf/spectra1.html

Dunno if your version supports RTA/Spectrum, but here's a link to the current tutorial:
http://www.daytonaudio.com/OmniMicV4/hs90.htm
Maybe your current mic is supported in the latest software.
http://www.daytonaudio.com/downloads/OmniMicInstall.zip

TrueRTA, in its free version, has a coarse rez (full octave), but it's probably good enough for this.
https://www.trueaudio.com/rta_down.htm
https://www.trueaudio.com/downloads/TrueRTA_Help_v3.pdf

Then there's REW.
http://www.roomeqwizard.com/
http://www.roomeqwizard.com/help/hel.../spectrum.html

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Last edited by Oliver Deplace; 08-17-2016 at 05:15 PM.
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post #7 of 7 Old 08-17-2016, 05:41 AM
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Quote:
Originally Posted by SeekingNirvana View Post
He has a dust collector that is loud in his shop. Sounds to me like there is a company that makes silencers for the dust collector, and he needs to take readings of the dust collector so that they can make a custom silencer for the frequency it is putting out.

That what I take from the post.....

Yes, me too. I am not sure how we got onto guns from the original post. He has a dust collector in a cabinet shop that he is getting a silencer (some sort of baffle) for.
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