149. When Is It Too Loud?

So the nerdy stuff is this, is that our ears don't perceive frequencies the same way that they are as intense that we can measure scientifically, right? So sound waves, we can measure with their absolute pressure and we can reference that to something specific.

That's kind of the reference point that we get when we talk about dB or decibels, SPL or sound pressure level, right? We can actually measure how much pressure these wiggling air molecules are creating.

But our ears don't perceive those frequencies the same way.

So we're more sensitive in certain areas and less sensitive in other areas.

If every puff of wind passing by or branch waving in the wind made a low frequency sound that we perceived at the same frequency, intensity that we do for, uh, say the consonants in a person's speech, we would be constantly overwhelmed with how much information is there.

There's just a lot of low frequency rumble happening.

And so we're less sensitive to it.

And we can ignore more of it.

So the most sensitive part of our range of hearing is in the range between around, say, 1,000 hertz or 1 kilohertz up to about 5,000 hertz or 5 kilohertz.

That's the range where our ears are most attuned to lower level sounds.

So these guys named Fletcher and Munson came up with the equal loudness curve.

And they measured how sensitive we are to different frequencies relative to other ones.

So they put kind of 1k in the middle, right? And so they're like, when 1k is this loud, as we give different tones, how much louder or quieter does this tone have to be for most people to perceive this? Now, not everybody's hearing frequency response is exactly the same, so we're working from averages.

But it's not a huge variation from one person to another, except in low frequencies.

For instance, my wife hears low frequencies like 10 dB higher than I do.

And so we'll be sitting somewhere quiet, and she's like, do you hear that rumble? Somebody's playing some bass music.

And I'm like, I don't hear that.

What's going on? So...

That's a close to home story to say that some people's perception is different.

So in our physiology, both our outer ear, our inner ear, our middle ear, all of that combines to say, I hear these frequencies a little bit more than what they measure as far as absolute intensity.

So for our DBSPL or sound pressure level, we have on our meters two different weighting networks.

What that means is some of the frequencies we ignore and some of them we are going to emphasize.

So for A weighting, which is the one that we recommend when you're measuring how loud something is and how much it might be damaging to someone's hearing, That's what the NIOSH and the National Institutes of Safety and Health and OSHA, the Occupational Safety Hazard Administration, something like that.

I might be missing some...

I think