TELECOM Digest OnLine - Sorted: Re: X-Bar Switch Noise Levels

Re: X-Bar Switch Noise Levels

Scott Dorsey (
20 Jun 2006 15:59:31 -0400

Audrey Nardachioni <> wrote:

> I am trying to find out what typical Central Office switch room noise
> levels were for #5X-Bar, 4A-XBar and XBar Tandem switchers
> manufactured by Western Electric and Nortel (formerly Northern
> Electric Company of Canada). If you know of any source for this info,
> I would appreciate it. I've scoured the NET but haven't been able to
> find anything but then again, I'm not an Internet search wizard.

> There seems to be a large number of us old X-bar Techs who now suffer
> from hearing loss and we may be able to get workman's compensation to
> help us with hearing aid costs if we can produce some data for the
> Workman's Compensation Board.

My personal suspicion is that the levels varied considerably depending on
time and place and the number of calls active at any given time.

You may want to contact the Telephone Museum in Seattle, which has an
operating #5 crossbar. If they have any sort of traffic simulator
hooked up to it, it should be possible to measure SPL under various
simulated loads. It might be an interesting exercise.

Note that during much of the era when crossbar switches were in use,
exposure-related deafness was not very well understood. Not
surprisingly, a lot of the early research on environmental hearing
loss was done by Bell Labs. --scott

"C'est un Nagra. C'est suisse, et tres, tres precis."

[TELECOM Digest Editor's Note: I know that in the early/middle 1960's
the Chicago-Wabash central office -- in fact all of Chicago -- was
either crossbar or stepping switch and you could hear it a block away
on a hot summer night walking down the street, mainly because they
did not have air conditioning in those days and all the windows would
be open wide. When it started to rain, someone would go around and
close all the windows. Quite deafening. PAT]

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