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Another telephone/speakerphone question

Posted: Tue Apr 24, 2007 10:15 pm
by ModRob
I work by myself in a railroad tower that has two two-way radio
channels and a large printer that tend to make a fair amount of
racket. Up until fairly recently we had been having good luck with
a phoneset that had a speakerphone that worked flawlessly thru
all that noise. After it gave up the ghost, I've not been able to find another that works correctly; I believe it's a half-duplex,
full-duplex issue. The room noise is not that bad really; I can turn
radios down, but printer does its own thing, and is at the opposite
end of the desk from the phone.
We use our phone constantly, and you know what a pain it can
be holding it to your ear with your shoulder and doing other
duties too. And the most recent two phones I've had don't have
to detect much noise at all to act up.
I know there are "conference" type gizmos out there, but that
is totally out of the budget.
Any ideas?
Thanks again,

Posted: Wed Apr 25, 2007 11:16 am
by haklesup
Dot matrix or daisy wheel? Try an acoustic box for the brinter. Heavy particle board lined with egg crate foam.

As for the phone, it wouldn't be hard to modify most phones with a push to talk button, just put a switch in series with the mic on the speakerphone.

Many phones now have hands free headsetds available. Same wiring as is used on cell phones, just a more substantial headset. Most cordless phones have a place to plug it in but many desktop corded ones do not. I'd go that way.

how about a free always on speakerphone?

Posted: Fri Apr 27, 2007 4:58 pm
Two speakers connected together
with DEAD phone wire may work.
The speakers must be good for high pitch sounds,
and the speaker resistances should be a lot more than 8 ohms
for any distance... 600 ohms will go over miles of extension cord.
The speakers used in speakerphones are usually high resistance,
such as 25, 50, or 100 ohms.

Two funnels or
brass horns connected together with hose or tube works too.
You can even make it a sonic wireless system with a pair of dishes.

Two tin cans and a "string" actually can work as well too, if you TRY.
(It's a lot easier than rubbing two sticks together in an igloo.)
The string needs to be tense.

All three ideas are entirely sound-powered and work well if you
put your face near the "horn". You may even be able to shout loud
enough to scare the guy at the other end. All ancient tech except
for the speakers, which are actually Bell's Telephone.

All three ideas are full duplex, and may sound like you're in
the same room, if well done, which isn't hard to do.

Posted: Fri Apr 27, 2007 5:11 pm
by Chris Smith
The principal is simple, its called noise canceling.

The microphone is open on both sides of the diaphragm so that omni directional sounds hit both sides and cancel out the sound.

Your voice is directional and near it,... so it come through just fine.

They have advertised the company on the TV lately [NASA and all] but I cant remember their name, but my neighbor worked for them in the 70s long after their first patents.

They used them on helicopters to cancel out blade noise and still leaving the pilot free to communicate. Most small planes also incorporate this technology.

Just research “noise cancelingâ€