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cheap-o decibel meters

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cheap-o decibel meters

Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 6:48 pm

Has anyone got any experience with decibel meters in this range?

It would be good to have some form of empirical measurement of sound levels as opposed to "pretty loud" or "fairly quiet", without spending too much.
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Unread postAuthor: Dr meat201 » Tue Dec 14, 2010 6:56 pm

Unfortunately, i can't say that I have any experience with db meters. If you get one, be sure to bear in mind the distance from the sound when you test. You should establish a set range to test sound from, so that you can accurately compare the performance to other things. You might know this already, you seem like you are well versed in your physics knowledge. Of course, there is probably some standard distance that i'm unaware of. Good luck with finding one!
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Unread postAuthor: Technician1002 » Tue Dec 14, 2010 6:59 pm

Study them before purchase. Some are averaging. Some record peaks. Most have weighting. Some frequencies are more damaging to hearing.

What exactly are you trying to measure? Is it the crack of sound of gunfire? If so you will want to upscale from one used to measure OSHA sound compliance at the local band.

Some are more sensitive than others. Some won't register the sound level in a quiet office. Others won't register a nearby jet.

Find one that meets your requirements. Do you need to measure below 60 db or above 120? Do you need to measure peak pressures?

Image

note the display from the first choice in the list. it has A and C weighting. it has peak and average reading.

It's range is 40 to 130 DB.

It will record a peak pressure.

I do have recording studio, high end audio, and broadcast studio experience.
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Last edited by Technician1002 on Tue Dec 14, 2010 7:09 pm, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 7:08 pm

I was thinking peak dBs to be able to compare launchers.

According to howstuffworks, these are some typical dB readings:

* Near total silence - 0 dB
* A whisper - 15 dB
* Normal conversation - 60 dB
* A lawnmower - 90 dB
* A car horn - 110 dB
* A rock concert or a jet engine - 120 dB
* A gunshot or firecracker - 140 dB

Sounds like something like this would therefore be in the right measurement range, but would it give me a peak reading as opposed to a constant one...

edit: seems you edited and preempted me in the meantime :D cheers
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Unread postAuthor: Technician1002 » Tue Dec 14, 2010 7:15 pm

I would not buy that one for use with a band sound system. It's frequency range is way too limited.

From the specs..
# measurement frequency range: 300Hz ~ 8K Hz

It would be useless for balancing the drum set and bass guitar.

The stuff I use is flat from 20Hz to 16KHz. I can measure the rumble of the building ventilation system. That one won't measure a quiet studio's ambient noises.

Other than the limitation of prosumer goods, it is good for general ballpark measurements.

A good omni reference mic for use on upscale equipment costs more than that SPL meter.
http://www.interstatemusic.com/webapp/wcs/stores/servlet/product_201409
Image

Edit Here is a mid priced one that meets calibration standards.
Conforms to the IEC61672-1 Class 2 and ANSI S1.4 Type 2 standard for sound level measurement
http://www.metershack.com/metershack-industrial-high-accuracy-digital-sound-noise-level-meter-data-logger-with-usb-interface.html
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Last edited by Technician1002 on Tue Dec 14, 2010 7:49 pm, edited 6 times in total.
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Unread postAuthor: D_Hall » Tue Dec 14, 2010 7:19 pm

Not sure how it would apply to "normal" sized guns, but a Bikini Gauge might work well. Or at least, something similar in concept to one.

(been considering throwing some up for Vera)



edit: For those not familiar with Bikini Gages... See page 11 of this file http://proceedings.ndia.org/5550/tues_a ... napote.pdf

edit2: Ah... Found a picture that isn't mid-document. http://media.photobucket.com/image/biki ... G_4110.jpg
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Unread postAuthor: Hotwired » Tue Dec 14, 2010 7:35 pm

That's a nifty idea. Sound is pressure after all.
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Unread postAuthor: Ragnarok » Wed Dec 15, 2010 5:09 am

My experience with fairly cheap dB meters (same sort of price range) is that they'll average too much to really be useful. The Fast and Slow settings mean they'll either average over about 1/10th of a second or a whole second. This, of course, is far too long to get a good peak reading of a firing crack.

I have found a way to use it meaningfully, using it to get a reference dB level for a steady sound, then using a separate sound recording to compare the reference sound and the peak level (in Audacity, or something similar), then working out what the peak dB should be from that.

But it's no good for recording the dB level of a report directly.

It might give you a vague comparative measure, but mine usually reads well under 100 dB when I've tried it for measuring reports, and that's clearly false. Done in such a way I get a proper reading, I've recorded SPLs of nearly 160 dB @ 1m. (And you wonder why I use hearing protection.)

That's a discrepancy of in excess of six orders of magnitude. In short, don't expect it to read "gunshots" properly.
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Unread postAuthor: Technician1002 » Wed Dec 15, 2010 6:58 am

If you don't need absolute measurements, relative levels can be recorded on a laptop with proper manual gain control. A is louder than B and the Amplituede is douple so you know A is 6 DB louder. Distortion and clipping are easy to spot. Attenuation pads can be added for measuring loud sounds.

Image

This gunshot waveform shows the recorded level is too high.
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 15, 2010 7:01 am

D_Hall wrote:Not sure how it would apply to "normal" sized guns, but a Bikini Gauge might work well. Or at least, something similar in concept to one.


I was hoping to tell the difference between "tolerable" and "irritating" as opposed to "what, say again?" and "OMFG MY EARS ARE BLEEDING!!!!"

:D

Still, interesting concept... perhaps one could use differently sized soap bubbles to cater for lower sound levels.

Thanks for the input guys.
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Unread postAuthor: POLAND_SPUD » Wed Dec 15, 2010 7:12 am

Would a pressure transducer work?

I was going to suggest audacity an a cheap mic... it seems it would be good enough for this purpose
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Unread postAuthor: D_Hall » Wed Dec 15, 2010 9:44 am

jackssmirkingrevenge wrote:Still, interesting concept... perhaps one could use differently sized soap bubbles to cater for lower sound levels.


Actually, I was thinking more like replacing the aluminum foil with tissue paper.
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Unread postAuthor: Technician1002 » Wed Dec 15, 2010 12:56 pm

POLAND_SPUD wrote:Would a pressure transducer work?

I was going to suggest audacity an a cheap mic... it seems it would be good enough for this purpose


Most pressure transducers are for higher pressure and lower frequency. A mic with a flat frequency response will pick up a lot of sound the pressure transducer misses. A pressure transducer is good for picking up the primary pressure wave from a large volume event such as Vera or 40MM cannon fire, but will miss the bulk of higher order sound.

Audacity and a Mic is fine if you have a way to set calibrated levels so a recording made on Tuesday is exactly the same gain as a recording made on Friday. Most PC volume controls with a slider do not allow setting an absolute value for gain. A same day test where the volume is never touched would work fine. Audacity has some nice tools for adding filters and other advanced features.

Most all condenser microphones sold for PC's have a FET amplifier in them which is powered by the sound card. They tend to be unsuitable for loud sounds and will clip the signal before it gets to your instrumentation (PC sound card). Using an external sound board or mixer and then feeding into the line level inputs is recommended. A quality dynamic mic or pro condenser mic suitable for high SPL levels is recommended.

Be aware, many computer mic inputs are filtered for speech and are far from flat. They design them to help phone applications filter out background noise below and above talking frequencies.

Here is an example of a poor mic clipping the signal long before the sound card reaches peaks.
Image

Here is a waveform where the sound card was fed too much signal and the signal reached the hard limits of the sound card. Simply adding an attenuator to this mic would fix the waveform so it would be within limits.

Image
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 15, 2010 2:10 pm

D_Hall wrote:Actually, I was thinking more like replacing the aluminum foil with tissue paper.


I think it would have to be a hell of a bang to tear tissue paper though, especially as it's porous...
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Unread postAuthor: Ragnarok » Wed Dec 15, 2010 3:21 pm

Yeah, I think Bikini gauges are possibly a little too high in the SPL range.

You'd need to be able to make discs that could burst at around 1 - 1000 pa (corresponding to 94-154 dB, the kind of range you'd need to cover).
The 1 Pa disc would tear if a mouse coughed on it, a 10 Pa disk would tear in a mild breeze, and even the 100 Pa disc would be pretty frail.

Good luck making something that flimsy and actually getting far enough to use it.
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