Best method of using a Radio Shack SPL meter? - diyAudio
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Old 19th January 2014, 03:54 AM   #1
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Default Best method of using a Radio Shack SPL meter?

Hi what is the best method of using a Radio Shack analogue SPL meter? I have had a recent rebuild of a 3way 12 inch sealed cabinet adding new speakers, under some excellent guidance from this site.

I assume I need a test CD. What is a suitable cd and who supplies them?

I assume: Playing this test cd, I take a reading of the bass speaker with the other two disconnected? Same for the mid and then the tweeter? Do I need a reading of the three speakers playing, which would indicate what?
As far as my subjective ears go my speakers sound fine. However I am 68 and worked in noisy ship interiors (like tin cans)so I would have lost certain levels and frequency lowering. So what am I actually looking for? In anticipation many thanks.
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Old 19th January 2014, 06:54 AM   #2
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Hi, John:
Your Radio Shack analogue SPL meter will serve as a decent measurement tool, within its limitations. It's important to use the "C" (un-weighted) setting, as the "A"-weighted setting will deviate from the maximally flat frequency response that you want for speaker testing. "Fast" or "Slow" setting isn't critical, as you'll only be able to measure steady tones in any case; I find that "Slow" makes it easier to get a reading. There are calibration curves kicking around for that SPL meter to improve its accuracy, but frankly, I wouldn't worry too much about it at this stage. Set up your meter on a stand at the desired location, and start testing!

You could use a test CD (I have Stryke's BassZone Test CD Vol.1 - 1999 by John E. Janowitz http://www.stryke.com), but there are better ways. Basically, you need a source of constant-level sine-wave tones over the audio range. Either an audio frequency signal generator (old-school - like your SPL meter!), or a software implementation via your computer's sound card would likely be more convenient. The CD is handy for checking out speakers where a signal generator/amplifier can't easily be set up, such as in a vehicle.

Sorry, I don't have time to write a tutorial on speaker testing (plus I'm sure I'm not the best qualified to do that!), but it shouldn't be too hard to get the knack of plotting frequency responses of your speakers. Testing each driver separately will reveal response range, resonant peaks, dips, etc., while testing the entire system connected should show how well the bass, mid, and tweeter are matched in levels and crossover points.

All this is pretty rudimentary compared to modern computer-based testing methods, but don't discredit the value of data obtained by this setup - it can go a long way in designing, testing, and tweaking speaker systems and their constituent elements.

Hopefully, this can get you started!
Regards,
Wilf

Last edited by w_oswald; 19th January 2014 at 07:01 AM.
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Old 19th January 2014, 10:38 AM   #3
tvrgeek is offline tvrgeek  United States
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It's mic output is probably good enough for rough crossover region use going into your sound card. ARTA, HOLM etc. I really only use mine to set a crude reference for my calibrated mic, as it is calibrated for freq, not absolute levels. I agree with W, enough to get started. What it can do is reign in ones uninformed ideas on how loud something is or should not be. Check the OSHA (https://www.osha.gov/pls/oshaweb/owa...ARDS&p_id=9735 (Shameless plug for our Government)

If you are new to all of this, you will very soon find out use of steady state pink noise tells you about the room, not the speaker, and even at that, not very informative. You need to jump right into gated pulse (MLS) measurements unless you can put your speaker on a 60 foot pole in the yard and live on a dead quiet farm.

I always recommend Joe D'Apolitto's book Measuring Loudspeakers as a place to start. Read the instructions for HOLM and ARTA (free)
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Old 28th January 2014, 11:30 PM   #4
dangus is offline dangus  Canada
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1/3 or 1/6 octave filtered noise or warble tones. Steady sine waves will be just about useless for acoustic measurements. I'm sure there are programs to generate those signals using some kind of portable newfangled data-processing machine.

There are also audio test CDs. The following in my collection have octave and/or 1/3 octave noise tracks:
Denon Audio Technical CD
Pierre Verany Compact Test
HFN/RR TEST DISC II

If those are OOP, you may be able to find a "backup" copy on the internet somewhere.

Last edited by dangus; 28th January 2014 at 11:49 PM.
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Old 1st February 2014, 04:25 PM   #5
tvrgeek is offline tvrgeek  United States
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Siegfried Linkwitz also sells a test CD.

Pure tones are handy for finding things that rattle in the room. Don't need the meter for it, just a sweep tone.
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