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I was looking at a few different SPL meters, as I need to buy one, and I noticed that every one of them measured from 31.5hz to 8khz. Why? Why not 20 - 20? I'm guessing it has to do with the equal loudness curve, but I can't find a definitive answer anywhere.

Thoughts?

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Links to some of the ones I was looking at, plus an expensive one or two for comparison: hartcol.in/brNyHn hartcol.in/9gIrhI hartcol.in/8YwBev hartcol.in/9waJFa hartcol.in/bsd3xD –  Colin Hart May 27 '10 at 1:42

4 Answers 4

up vote 4 down vote accepted

Being an engineer and an audio consultant I have had the chance to spend time with a number of persons/companies that perform room design as well as room tuning. EVERY person I have worked with or contracted has used the SPL meter from RadioShack, this includes Dolby. The key is to go and have the meter calibrated for 85db, which is the SPL your going to be looking for most of the time, with the occasional 82/88 for surrounds and sub.

Nick

RadioShack Digital-Display Sound-Level Meter

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All the SPL meters I've worked with have both A and C weighting. A weighting is measured from 500 Hz to 10kHz. C weighting is measured from 32 Hz to 10KHz. Sounds like you have one that is C weighted, but it should go to 10k. The cheapo Radio Shack one follows the specifications above. Might be that the response starts to diminish after 8kHz, so they just stop there.

If you have one that goes to 8k, try running a pure 10k tone and see if it responds. I wonder if they're just listing the prime range, not the full range.

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+1 for Radio Shack's analog meter. –  Matt Cavanaugh May 27 '10 at 2:17

The 31.5 Hz to 8 KHz is the standardised 1/3 octave division range of frequency analysers. Noise regulation standards and rules are based on this range.

Proper analyzers are sensitive to the entire spectrum, the 31.5-8000 range is just a setting.

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Here at my work we regularly use Bruel & Kjaer meters and analyzers, and they are linear across the human hearing range, even beyond that. For example, the Bruel & Kjaer 2260, which can measure from 6.3 Hz to 20 KHz.

The disadvantage of these devices is the price, which is in the five figure range. I'm afraid a decent, calibrated SPL meter (no spectral analysis or other fancy stuff) will set you back several hundred dollars.

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Interesting article I found on the Radio Shack SPL meter (pdf). This guy has tested its accuracy using proper methodology and equipment.

Short summary:

  • The device is surprisingly accurate for overall SPL measurements.
  • The digital meter deviates by several dB from the expected C-weighted low-frequency rolloff. The analog one is better at this.
  • The digital meter is less suitable for measuring low-frequency response, unless you compensate for the deviation.
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