[labnetwork] Paging system

Wed Oct 29 10:39:08 EDT 2014

A consideration for paging systems in a noisy environment with vaulted, 
cavernous space is the use of sound reinforcement rather than 
loudspeakers. A loudspeaker is typically a horn capable of high sound 
pressures. This results in echo and feedback in paging systems. Around 
the late 1960's Rudy Bozak came up with vertical arrays of speakers 
placed at close intervals to reinforce sound in concert halls. Each 
sound source was run at low power and covered a limited area. This 
reduced echos and feedback and gave better coverage. Similar solutions 
are now used for auditoriums, i.e. many individual speakers, placed at 
relatively close intervals and run at low volumes. We had good  results 
with this approach in adding paging to the UC Berkeley Microlab.

Bob Hamilton

-- 
Robert Hamilton
University of California at Berkeley
Marvell NanoLab
Equipment Eng. Mgr.
Room 520 Sutardja Dai Hall
Berkeley, CA 94720-1754
bob at eecs.berkeley.edu
Phone: 510-809-8600
Mobile: 510-325-7557 (Emergencies only poor cell phone service in lab)e-mail preferred

On 10/28/2014 1:30 PM, Iulian Codreanu wrote:
> Thank you very much John!  As usual, very useful information coming 
> from you!
>
> iulian Codreanu, Ph.D.
> Director of Operations, UD NanoFab
> University of Delaware
> Office: 163 ISE Lab
> Mail to: 250N ISE Lab
> Ship to: 165 ISE Lab
> 221 Academy Street
> Newark, DE 19716
> 302-831-2784
>
> On 10/28/2014 10:47 AM, John Shott wrote:
>> Iulian:
>>
>> I've dug up our Sound Level Meter (the best that Radio Shack has to 
>> offer ...) and have made a few measurements to provide you with some 
>> example numbers.  Note: my measurements were made using the dB(C) 
>> frequency compensation ... although I will give you a couple of 
>> references using dB(A) frequency compensation.
>>
>> In general, clean rooms are pretty noisy.  Just the noise of the air 
>> handling equipment can be significant.  In fact, about 3 years ago we 
>> dropped our mean vertical air velocity from about 90 to about 70 feet 
>> per minute.  At the time, everyone commented on the fact that it was 
>> quieter in the clean room.  That said, even with lower air 
>> velocities, I could only find one area of our lab that had a reading 
>> of less that 60 dB(C).  That was the room in which our Raith 150 
>> ebeam tool is located and it registered 53-55 db(C).
>> The next two quietest rooms were an in-process measurement room (AFM 
>> and friends) coming in at about 60 db(C) and our gowning room at 
>> 61-62 db(C) and there is essentially no noisy equipment in either of 
>> those rooms.
>>
>> Most areas of the lab with "real" process equipment in them 
>> registered in the range of 69-72 dB(C).  Note: most, but not all, of 
>> our pumps actually live in the sub-fab.  However, there are enough 
>> in-tool and near-tool pumps, fans, and other noise generators to 
>> increase sound levels significantly.
>>
>> The two loudest areas of our lab are near a bank of LPCVD tubes that 
>> have their pumps in the cabinet, rather than in the sub-fab. There we 
>> measured sound levels of 79-80 db(C).  Even though the pumps for our 
>> AMAT Centura epi reactor are in the sub-fab, sound level readings 
>> near that tool are about 74-76 dB(C).
>>
>> Note:  our sub-fab is quite noisy with peak readings of about 86 
>> dB(C) near the big scrubbers with average readings down there of 
>> about 82-83 dB(C).
>>
>> In areas dominated by equipment noise (which is most places in the 
>> clean room) and certainly in the sub-fab, I found that dB(A) readings 
>> were only about 2 dB lower than db(C) readings due to the fact, I 
>> suspect, that the noise of pumps and motors is dominated by 
>> higher-frequency components.  In an area with less equipment noise, 
>> however, I found that dB(A) readings were about 5 dB lower that the 
>> dB(C) reading at that location.
>>
>> While I expect that there is significant variation from lab to lab in 
>> these numbers with, I suspect, newer labs being somewhat quieter, I 
>> think that it is reasonable to design for an average background sound 
>> level of about 70  dB(C) with some areas closer to equipment probably 
>> reaching as high as 80 dB(C).
>>
>> As a bit of corroborating evidence, I believe that the folks who had 
>> tried to do various forms of video training and collaboration have 
>> found that using headphones and a microphone produce more 
>> understandable communication than relying on "field microphones".
>>
>> Finally, we clearly did not spend much on our "sound level 
>> instrumentation package" ... in fact, while I haven't compared 
>> performance, I think that there are a collection of free apps for 
>> smart phones that are probably just as suitable for spot checks.
>>
>> Let me know if you have any further questions,
>>
>> John
>>
>> On 10/24/2014 10:41 AM, Iulian Codreanu wrote:
>>> Dear Colleagues,
>>>
>>> I would like to not allow cell phone use in the Delaware cleanroom; 
>>> I recall a long thread on this forum with various opinions on this 
>>> topic.  Since I would very much like for my customers to be in touch 
>>> with the outside world while in the cleanroom, I have been trying to 
>>> develop a paging system that would work with the VOIP phone system.
>>>
>>> The many pieces of the puzzle are coming together but I am 
>>> struggling answering a basic question posed by the "speaker guy": 
>>> how noisy will your cleanroom be?  That's a tough one because I will 
>>> not know for a number of years until the cleanroom is filled with 
>>> equipment.
>>>
>>> I would like to get an idea of how noisy fully operational 
>>> cleanrooms are (both the bay and chase areas).  Would you please 
>>> share your knowledge?
>>>
>>> Thank you very much!
>>>
>>> Iulian
>>>
>>
>>
>>
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