Expert: Paul Soderman - 4/8/2009

Question
Dear Mr. Soderman,

For many years I have read about a 48 foot steel and concrete experimental noise maker that NASA made that produced a sound of 210 dB.  I have not been able to find any information about it.  I was wondering if you knew anyhing about it.  Any help would be greatly appreciated.

Thank You

Answer
I have not heard of this and would be surprised if it existed. An acoustic driver such as a loudspeaker or piston generates a sound wave that is comprised of sinusoidal pressures oscillating about the atmospheric pressure. A maximum sound level is reached when the negative peak goes to zero pressure. At sea level that occurs at a sound level of 191 dB. If the noise source is driven harder, the sound waves distort into non-linear waves similar to shock waves.  Those waves would have a greater intensity than 191 dB, but they would no longer be true linear sound waves.  This might be desired for vibrational testing of hardware, but there are easier ways to create such an environment than building a huge noise maker.  Echo sounders for oil exploration use high pressure discharge devices for example that are fairly small.  But who knows, maybe in some laboratory at some time a NASA research team built a large noise maker for a special purpose.

That said, it is common to build special enclosures such as reverberation chambers to test hardware exposed to high energy sound and vibration.  Perhaps that is what you heard about.
Paul