[3dem] question about acoustics

[Steven Ludtke]

(The music thing was a joke BTW) The fact that it was there when the room was empty is clearly an important gotcha. So, the expensive survey you commissioned couldn't locate the source ?  I'm assuming you had them turn off the ventilation system temporarily to see if it went away ?  For fans, this is useful:

http://www.engineeringtoolbox.com/fan-blade-pass-frequency-d_1137.html

Certainly most building ventilation systems would come out in this general range, but if that's it, they should be able to install some dampers to reduce the problem...

http://www.engineeringtoolbox.com/noise-reduction-silencers-d_81.html

Always better to eliminate the source if you can find it...

On Dec 10, 2013, at 9:41 AM, Qiu-Xing Jiang <Qiu-Xing.Jiang at UTSouthwestern.edu> wrote:

> Thanks Steve. 
> Humming  would be more accurate. It is a one-fl building, and the humming  noise was there when the building was completly empty.  We had a sophisticated survey done in the empty room, could not locate the source easiy. I will try the app you were talking about. 
> Best, Qiu-Xing
> T-Mobile. America’s First Nationwide 4G Network
> 
> ----- Reply message -----
> From: "Steven Ludtke" <sludtke at bcm.edu>
> To: "3dem at ncmir.ucsd.edu" <3dem at ncmir.ucsd.edu>
> Subject: [3dem] question about acoustics
> Date: Tue, Dec 10, 2013 9:34 am
> 
> 
> 
> It should be pretty obvious, but a "hissing" sound corresponds to frequencies up in the khz range. 160 hz is a low humming sound, roughly an E3 on the musical scale, and will have a wavelength of ~2m. Unfortunately this can make it a little harder to locate, for the same reason that it doesn't matter where you put a subwoofer in a room. If you have an iPhone or other i-device, there is a handy app called bs-spectrum, which will display a real-time audio spectrum from the phone's microphone (on the bottom). You could use this and walk around the room to try and better-localize the source of the sound. Physically resting the phone on any suspect devices should magnify the effect a lot, and help narrow it down. In this range, though, the two most likely suspects in my mind would be a fan in a piece of equipment or someone playing music in the room above you :^)
> 
> On Dec 10, 2013, at 9:07 AM, Qiu-Xing Jiang <Qiu-Xing.Jiang at UTSouthwestern.edu> wrote:
> 
>> Dear colleagues, 
>> The new EM space built for our JEOL2200 has excess acoustic noise at 160 hZ, above spec (43dB at the same frequency) by 10 dB. There is clear hissing sound from the ceiling (three vents there). We have applied egg shell crates to all four walls and the air supply comes from the perforated tiles below the raised floor. We are looking into different solutions. Before we land on any, I am writing to seek some advice from those who have successfully dampened acoustic noise in different ways. Please offer your thoughts. Thanks. 
>> Qiu-Xing 
>> 
>> 
>> UT Southwestern Medical Center
>> The future of medicine, today.
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> ----------------------------------------------------------------------------
> Steven Ludtke, Ph.D.
> Professor, Dept of Biochemistry and Mol. Biol.         (www.bcm.edu/biochem)
> Co-Director National Center For Macromolecular Imaging        (ncmi.bcm.edu)
> Co-Director CIBR Center                          (www.bcm.edu/research/cibr)
> Baylor College of Medicine                             
> sludtke at bcm.edu
> 
> 
> 
> 
> 

----------------------------------------------------------------------------
Steven Ludtke, Ph.D.
Professor, Dept of Biochemistry and Mol. Biol.         (www.bcm.edu/biochem)
Co-Director National Center For Macromolecular Imaging        (ncmi.bcm.edu)
Co-Director CIBR Center                          (www.bcm.edu/research/cibr)
Baylor College of Medicine                             
sludtke at bcm.edu





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