[GreenKeys] Telephone equipment factory question

[Roy Morgan]

On Oct 26, 2008, at 6:43 AM, Alf Fisher wrote:

> Hi Greenkeyers,
>
> Has anyone ever heard of sound levels being measured in mm?
> Could this be millimetres or some other quantity?
>
> In America in the 1920's, a noisy factory was making telephone  
> relays for Western Union.
> They had 470 coil winding machines running and the sound level was  
> recorded as 0.85mm.
>
> Does anyone know how this would equate to the dB sound levels we use  
> today?

Alf,

I asked by buddy who still works at NIST in the Sound Building (PhD in  
Electrical engineering, ultrasonics, and co-worker with the US's  
expert in sound measurement and custodian of NIST's ultra-quiet room  
for such measurements.).  I knew he was the right person to ask.

He says:

"Sound (radiation) pressure measured with a manometer would generate  
data in mm. If the medium in the manometer were water, 0.85 mm would  
correspond to 113 dB, the sound level for a quiet jet plane at 100  
yards. Let's hope that the instrument didn't use mercury instead, as  
the same 0.85 mm indication would correspond to 135 dB, above the  
threshold of pain, and instant hearing damage.

I 'm pretty sure I have more than one textbook at work old enough to  
describe instruments of this sort. I hope to be able to take a look in  
the next few days; will let you know what I find."

Roy

Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073