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dB SPL - A Weighted vs C Weighted, Fast vs Slow

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Douglas Cyr:
Hello, I just got a RadioShack SPL meter and am curious about the most accurate way to use it, as well as the general differences between the different weightings. I know they're meant to reflect our ear's changing frequency responses at different pressure levels, and I've read that if measuring above 90 dB SPL I should use C weighting, below 90, A weighting.

Any other information I should consider?

Thanks,
Doug

Caleb Dueck:

--- Quote from: Douglas Cyr on May 11, 2021, 05:39:14 PM ---Hello, I just got a RadioShack SPL meter and am curious about the most accurate way to use it, as well as the general differences between the different weightings. I know they're meant to reflect our ear's changing frequency responses at different pressure levels, and I've read that if measuring above 90 dB SPL I should use C weighting, below 90, A weighting.

Any other information I should consider?

Thanks,
Doug

--- End quote ---

Generally, A-weighted Slow mimics human ear perception the best. 

Slow doesn't 'catch' the transient spikes, so will give a lower number.  The human ear gathers info over time, so super short duration spikes don't seem as loud.

A weighted doesn't take the bass into account (Google A vs C vs Z weighting curves).

Scott Bolt:
For PA speaker measurements, I generally advocate for C weighting which (as Caleb pointed out) actually takes into account the lower frequencies.

Pretty much any cheap crap HF horn can put out TONS of HF noise (even if it is REALLY bad noise) to make an A weighting show impressive SPL numbers IMO.

The original purpose of the A weighting was to assess SPL levels that would damage the human ear.  As a result, little to no LF is considered.

Now, the real problem is that SPL is just a poor way to assess a speaker.  Let me explain....

SPL is a weighted average of a bunch of frequencies.  A speaker with a very unbalanced frequency response .... with lots of annoying HF, and lots of holes in its frequency response can show very impressive numbers.

Many people (especially the many highly knowledgeable people here) can use either speaker processors, or even a multi-band eq on a mixer to "tame" most speakers to make them decent sounding; however, what you find once you have done this is that while the speaker now sounds much better, it can't put out much SPL at that quality of mix.

There really needs to be another measurement that ISN'T so subjective.  140db SPL of crap noise is STILL CRAP ;).

If there was a way to force a speaker to put out a balanced sound and then to measure that with a flat scale, it might make a nice measurement.  Seems like this is a great dream to have, but for now, we are left doing real world ear testing and requesting opinions of others that have heard many different speakers ;).

In general, more expensive (especially powered) speakers are capable of putting out higher output levels while sounding good doing it.  In fact, many of the better powered speakers remain pleasant even into full clip.

Russell Ault:

--- Quote from: Douglas Cyr on May 11, 2021, 05:39:14 PM ---{...} Any other information I should consider?

--- End quote ---

Like any measurement tool, the first question you need to answer is "what am I trying to measure?"

dB SPL (weighted or otherwise) is used in many different contexts. Are you concerned about hearing loss? Regulatory compliance? Sound system potential? Night-to-night consistency?

Without knowing what you're trying to measure it's impossible to make suggestions about how to measure it.

-Russ

Luke Geis:
The only time I pull out my dB meter is when I have the volume police in my area. Where I live we have an 80db A-weighted limit at any adjacent property line. A very hard limit to heed to!

I prefer C weighting because it does show you a little more of a picture of what is coming out of your PA. As mentioned, it is really only useful for measuring above about 90db. I peek at the A-weighting to get a sense of how bad I could be hurting people. If you see 100+db of A-weighted media, it is pretty darn loud. I try and keep my shows at or around the 105db C-weighted mark. It is a pretty visceral experience when you have 110db+ of media spanking you, but you can't bludgeon people like that for long.

I have come to find that the more linear the PA, the more muted and tame the volume appears to be even though the meters say it is set for slay. If your PA seems quiet even though you know you are pushing hot levels, be sure to check your SPL meter for safety. Well tuned PA's seem to sound quieter and more tame, giving a flase impression of the actual SPL.

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