Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!sco!rosso
From: rosso (Ross Oliver, x537, ionesco)
Newsgroups: sci.electronics
Subject: Re: Speaker phone needed (circuit?)
Message-ID: <6584@viscous.sco.COM>
Date: 14 Oct 89 01:30:16 GMT
References: <3268@puff.cs.wisc.edu>
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Reply-To: rosso@sco.com (Ross Oliver)
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In article <3268@puff.cs.wisc.edu> aber@gumby.cs.wisc.edu (David Aber) writes:
>I am looking for a GOOD speaker phone.  Most of the ones I have seen are only
>half duplex.  The one full duplex one I found has very low volume.  I don't 
>know if this it to prevent the echos from being picked up or what.  

Since the speaker and microphone are usually right next to each other
on the phone, most speaker phones are half-duplex to prevent feedback,
and the ear-splitting whine that results.

>What I would really like is a speaker phone with:
>  
>         Lots of volume;  both ways (Its not fair to make the other person 
>                                     listen to you from the end of a cave)

You're fighting the inverse-square law here.  The sound energy of your
voice receieved by the microphone falls off in proportion to the square
(or is it the cube?) of your distance from it.  However, the background
noise and echoes remain at the same level.  A studio-quality directional
microphone might help.  Getting the microphone away from the speaker
would also reduce feedback and allow you to use full duplex.

>         Full key pad;  some phones use the # and * keys for other functions

Nothing technically difficult here.

>         Decent sound quality;

Impossible on any phone line  :-)

>Does anybody know of such a device?  Any ideas how to fabricate one?  Any help
>would be greatly appreciated.

There is a company called Exar in San Jose, CA that makes chips that are
virtually complete speakerphones.  Adding a high-quality microphone
preamp and speaker amplifier might give you the results you're looking
for.  I don't have Exar's address/phone handy right now, but feel
free to mail for more info.

I think a speakerphone with one or more microphone input jacks would
be a big step forward.  This would be great for conferences, where you
could give everyone a lapel mike or have serveral desk mikes sitting
around the table.  This would improve the caller's reception, and
eliminate the need to shout at the speakerphone.

Ross Oliver
rosso@sco.com