OT: SPL check for live sound

[Audio_by_Goodwill]

There was a discussion this morning at church about how loud to run the sound system. One person mentioned a standard number that we were under. He'd prefer to run it louder....... more inline with the number he was throwing out.

My question is this....... any measured number of decibels will very with distance, correct? Assuming yes, then what is the standard positioning of a meter for making that measurement? Any comparison to a standard or recommended range seems irrelevant, to me, until that's established.

I guess the sound guys have the meter in the booth and use it as a guide. None, are professional sound men, but they do strive to do a good job.

[Old Guy]

(Open large can of worms)

SPL is only relevant if measured at a specified distance on a calibrated device with a specified weighting.

99.9% of people discussing SPL know very little about the subject.

SPL DOES vary with distance. In free space, it drops at 6 dB every time distance is doubled. In a confined space, it depends on the acoustics.

A voice will carry farther and clearer in a well designed opera house than outdoors. The house is designed to reinforce the parts of the voice range affecting clarity. So it will NOT drop at 6 dB with each doubling. How much it drops has to be measured pretty much.

Anyway, I tend to assume if nobody is complaining, there isn't a problem...I tended to mix sanely as I didn't want to risk my livelihood (ears).
Now we get to measuring. If your sound meter is set to "voice range" (not a setting, just weighted to measure the voice range) it isn't going to hear loud frequencies outside the voice band as loudly. So you won't get a REAL SPL just the level inside the meter's bandwidth.

Columbus has a specified noise level. At one street concert in the 80's I convinced a cop we were legal by showing him a reading on a RAT Shack meter well below the city ordinance. Of course I measured it well away from the stage....

[Audio_by_Goodwill]

(Open large can of worms)

SPL is only relevant if measured at a specified distance on a calibrated device with a specified weighting.

99.9% of people discussing SPL know very little about the subject.

SPL DOES vary with distance. In free space, it drops at 6 dB every time distance is doubled. In a confined space, it depends on the acoustics.

A voice will carry farther and clearer in a well designed opera house than outdoors. The house is designed to reinforce the parts of the voice range affecting clarity. So it will NOT drop at 6 dB with each doubling. How much it drops has to be measured pretty much.

Anyway, I tend to assume if nobody is complaining, there isn't a problem...I tended to mix sanely as I didn't want to risk my livelihood (ears).
Now we get to measuring. If your sound meter is set to "voice range" (not a setting, just weighted to measure the voice range) it isn't going to hear loud frequencies outside the voice band as loudly. So you won't get a REAL SPL just the level inside the meter's bandwidth.

Columbus has a specified noise level. At one street concert in the 80's I convinced a cop we were legal by showing him a reading on a RAT Shack meter well below the city ordinance. Of course I measured it well away from the stage....

The church is actually using a Rat Shack meter. I read most of a paper I found online dealing with house of worship sound, and it spoke of using these cheap meters, but didn't mention anything on any kind of standards for meter placement, except mentioning that it shouldn't be near surfaces. If on a surface some of the inaccuracy could be mitigated by tilting the meter up.

The paper did speak of A and C weighting, and recommended C, since it wasn't a question of OSHA compliance. I don't know what the church is using, or what the particular meter is capable of.

-6db...... if I recall correctly -3db is a drop by half, so -6db must drop by a factor of 4, correct?

The acoustics in the church are poor. I was told that by a friend that's a professional soundman, and I can see it. There is a spot near where the pulpit would typically be where the ceiling and floor must be parallel, as the sound bounces between the two. The over hang from the balcony is also a big bass trap. The sound booth is right in the area of that bass trap, I beleive.........maybe that's out of the meter range, Though.

It sounds like the best thing I could mention, if the opportunity arises, is that the meter measurements are only really good when compared to other like measurements, and can't be reliable compared to printed recommended levels since we don't have a standard for taking those measurements. Although, maybe distance doesn't matter as much in this instance since the mains aren't on the stage. They're up on the ceiling with placement designed for even coverage..... or so I would assume designed for even coverage.