RevMen, Fort Collins, CO, on the Studio Central Forum, writes:

Since I’m starting work in 2 weeks as an acoustical engineer, I figured this is something I should know. I did some googling and found a whole bunch of references to this number, but no explanations.

Then I found a paper written by Kevin Surace of Quiet Solutions here.

Quote:

At approximately 194dB, the sound pressure would have to change more than the ambient air pressure. At this point, the sound wave would have to create a negative air pressure to get any louder than this. Since that cannot happen air itself distorts sound by “clipping” the sound wave. This is also known as a sonic boom.


Interesting. Pretty much just like you said.

I figured I’d do a little numerical investigation to see what the max pressure corresponding to 194 dB is. I fired up MathCAD and started plugging away.

Pref = 20E-6 Pa
SPL = 194

P = Pref * 10^(SPL/20)

P = 1.002E5 or ~100kPa. ie atmospheric pressure

At 194 dB, sound pressure doubles atmospheric pressure in the compression stage, which requires a vacuum in the rarefaction stage.

That’s loud

So yes, if you were on Mars or the Moon or somewhere with very low pressure, the maximum SPL you could produce would be significantly lower, assuming you’re still using 20 micropascals as your reference pressure.

OK, I’m done geeking out for now.