[labnetwork] Paging system

[John Shott]

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
>