Help with SPL meter.

[MattCXII]

Hello all,

I am looking for help on how to PROPERLY use an SPL meter. I have used one in the past but don't think I am doing it right. If anyone has a tutorial on how to use one properly it would be much appreciated.

Thanks,

Matt

[ThomasW]

The answer to the question of how to use it, is related to the question of what you want to measure?

[Burke Strickland]

That's right, the procedure does vary according to what function is being performed (what is being measured). For example, safety checks for noise levels in the work place may differ from environmental checks for compliance with noise ordinances, which probably also differ from procedures for home theater calibration and level setting (although I'm taking a WILD guess here that the original post was aimed at home system calibration.) :>)

Even narrowing it down to home theater use, multichannel calibration (where you are adjusting each channel in turn to a predetermined db level / calibration point) is different from setting an overall safe listening level (where you are reading what level is being produced and then deciding whether to turn down the volume or blow out your ear drums). :>)

But let's give it a go for calibration. The five-step short version is:

1) First, turn on the meter,

2) Second, check battery level (a weak battery can yield, pardon the scientific term that follows, "wacko" readings),

3) Then set the weighting for "C" and the response to "Slow" and then set the range for a reasonable level like 70 db and hold the meter straight up toward the ceiling about where your head would normally be during listening while playing the test tone for a particular channel at a reasonable volume (loud enough to activate the meter; not loud enough to send you screaming out of the room). Do NOT point the meter at each speaker unless you turn your head toward each speaker while listening. :>)

4) Adjust the volume for that channel until the meter indicator (needle or digital read out) shows that it is hitting your predetermined calibration point (say, 70 db or 75 db -- which level you choose as reference isn't as important as being sure to use and set the same level all the way around).
Then change the signal to the next channel and repeat step 4). It doesn't hurt to cycle through all the channels several times to make sure the readings are fairly consistent.

5) When all the channels are hitting your predetermined calibration point (db level), quit. (Turn off the meter. Change the program to something interesting.)

For setting an overall safe listening level, do steps 1) 2) 3) and then adjust the range until the indicator stays steady on a reading within the range (not "pegging" the needle at the extreme end of the range, for instance).

If the db level is too high, turn down the volume. Sustained volumes over 80 db for prolonged periods can cause hearing damage. Above 90 db for 8 hours is illegal in the workplace -- check out the OSHA charts for legal listening levels and, as an example, this article for the effects of noise on health. (Just because our ears are less sensitive to low frequencies does not mean it is safe to crank up the bass to 120 db for the length of a movie.)

Did that help?

Enjoy listening!

Burke

[MattCXII]

Thank you Burke,

You answered my question perfectly. Before, I was pointing it directly at each speak and standing about two feet away from it. Pointing it towards the ceiling and doing the test from the listening position makes a lot of sense now that it was explained to me. It was hard to be specific in what I wanted when I really didn't know.

Thanks for your help.

Matt

[ekkoville]

Should the measurements be taken from the listening position or the middle of the room?

[MattCXII]

I have been reading more and more on this and everything I can find says it should be from the listening position. Anyone with more understanding please chime in.

[David Meek]

The listening position. Targeting an area you won't be sitting in will do little to maximize your SQ at the listening position.

[aarsoe]

If I may add one small thing most people forget. If you have different speakers (and most of us dont have 5 or 7 identical speakers) you should check at different levels, if you processor allows you to do that. Why? Well if you have very in-efficiant speakers you may find that all match at one level (say 70 db) but not at a higher level or vice versa for very efficient speakers. Of course it only applies if you have in-efficiant and effeciant speakers combined in your setup.
Finally, I have also found that increasing your center 1 or 2 db above the rest of the speakers improves the dialogue - but that could very well be a personal preference..