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RE: Sound associated hearing damage.

Posted by tomservo (M) on March 3, 2025 at 10:40:36

In Reply to: Sound associated hearing damage. posted by Nicoro on March 2, 2025 at 22:29:31:

This, like many things in hifi and loudspeakers is not easily distilled into one simple number.

For example there is frequency aspect, examine an equal loudness chart. The threshold of audibility at 20Hz is around 80dB spl. In other other words, at 20Hz, it takes about one hundred million times more acoustic power to be detectable than at 3-4KHz.

The extremely low sensitivity and damage to low frequency sound is why weather events don't deafen us and a shuttle launch only makes you grin and your pant legs flap (a safe distance). Thanks to our ears little tubes that equalize the pressure on the back side of the ear drum.

We can't even hear loud events in the single digit range.
In the 90's I designed a sonic boom simulator to emulate the NASA space plane they were planning, this "speaker" could produce 132dB down to 3 Hz, outdoors of an old house used for testing.

We could play anything we wanted through the system music, sine waves and the "boom" signal.
My conclusion was that around 3Hz, the threshold of "tone" vs air movent sound was around 130dB. What that was very similar to was the buffeting one feels riding in a car going 55 with the windows down, and like going under a bridge one after another.

So it turns out if you invert the equal loudness curve, that new shape is roughly also where it's easiest to cause hearing damage.
Your ears are most susceptible is exactly where they are most sensitive.

As other have pointed out in the industrial / safety area, they use A weighting as it counts the LF area less heavily for the reasons above.
Note too, there is a level vs time spec trend in the research.

It may come as a surprise that very short high intensity sounds are part of our lives and nature, but consider why Sound level meters and VU indicate what they do, they show "how loud it sounds" (not an instantaneous value but integrated over some time).

Consider what an RMS or analogue AC voltmeter shows looking at you amplifier with music or pink noise, it shows the same thing, a time average not a single peak value, an oscilloscope shows that

Use an audio tool and examine the dynamic properties some of your favorite recordings and then consider, ok, i want to make some speakers, I see what's there but how much of what's there dynamically is it necessary to reproduce accurately?

And at what distance?
Tom

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