spl perception

So lets talk a little about sound pressure levels. I am going to be a little vague due to legal entanglements. Any information given is for entertainment purposes only. And please stow any gear in the overhead compartments.

One of the most common complaints about sound is volume or SPL. So most churches will give the soundman an SPL meter (usually one from a place that rhymes with radiosnack) with instructions to keep it under a certain level.

Here's the deal. Go out to the OSHA website and read the documentation concerning sound pressure levels. You will find out a couple things about these magic numbers that everyone is screaming about.

First, every level must have a corresponding time associated with it. OSHA doesn't state anywhere that 100 dBspl nor any other dB amount will cause damage to hearing without a time period attached.

Secondly, you will notice that a unit called a dosimeter is used. This is different than using an SPL meter. It will take random spl measurements every so many seconds.

Finally, you will also notice that the dosimeter software will compute an AVERAGE SPL for the entire time period.

Very important.

I am not saying to not use an SPL meter, but use your brain as well. Most people that complain about volume are not really complaining about volume but HARSHNESS of the sound. 95 dBspl of 2 kHz hurts!

If you haven't read about the Fletcher/Munson curves or now known as the equal loudness contours, please do so immediately. This will tell you alot about people and their hearing. These curves were based on a subjective study (which is good in this case) of what people perceive.

My general rule of thumb is - if we can hear it well then why amplify it as much as what we can't hear as well.
Just think about that. Matter of fact.
Shut your computer off now and just ponder this until it clicks.
Then come back and read more.

Also, I have never heard of a study that states that frequencies below 85 Hz at what would be considered concert volume would damage your hearing. I have heard that the very low frequencies are perceived through bone conduction and not the ear canal. Again, think about it.

From my experience, a mix with a good solid low end foundation can be tolerated louder than one without. Prove it to yourself. Go to your PA or boombox or whatever. Turn the volume up fairly loud. Now take the tone control or EQ and roll the low end off. You will now perceive this volume as being louder. Why? I believe that this comes from the fact that our brains learned early on that when a person is whispering they are closer and there is more low end on their voice to due proximity, but when being yelled at, the person is usually farther away and the proximity of the low end is not perceived. Just an observation.

Now for SPL weighting. In my opinion, since the low frequencies are not as harmful as the upper ones to the hearer, a weighting that doesn't take these into effect can be used. According to the norms I would use an A weighting. But I have took 2 different SPL meters side by side and had them have the A and C weightings opposite of each other. Don't know why they are so. So I generally, with music playing, will turn on the meter and switch between the two weightings, the one reading the lower spl will be the one not including the low end of the spectrum.

Here's the point, I am not condoning loudness for the sake of loudness. I am condoning comfortable, emotional, musical sound quality over harshness. The actual SPL will vary from event and audience. Do what is correct for the situation but don't let stupid people ruin it.

My style of eq'ing and mixing will allow me to run at an measured spl that is louder than some others because of my attention to people's perceptions.

Remember an spl number without a time attached is not legal (OSHA approved).