aber@gumby.cs.wisc.edu (David Aber) (10/11/89)
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.
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)
Full key pad; some phones use the # and * keys for other functions
Decent sound quality;
Does anybody know of such a device? Any ideas how to fabricate one? Any help
would be greatly appreciated.
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aber@gumby.cs.wisc.edurosso (Ross Oliver, x537, ionesco) (10/14/89)
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
morris@jade.jpl.nasa.gov (Mike Morris) (10/15/89)
In article <6584@viscous.sco.COM> rosso@sco.com (Ross Oliver) writes: % %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. Years ago a ham radio acquaintance built a wireless mike in a small box that would fit in a shirt pocket. The device ran a few mw on a FM frequency (i.e. license free) and worked very well as a "microphone" for a speakerphone since the "mike" was kept away from the speaker. He later added a jack for a "plantronics" style headset - he had picked one up with a dead earpiece for free. Another cute trick that can be done with a "PC-4" style speakerphone from Ma Bell (the kind with a rocker-style on-off switch) is to disassemble the mike unit, and install a 1/8" closed-circuit jack in the mike element leads. Plug in a good quality electret desk mike. This trick will improve the speakerphone audio quality 100% (and it's pretty good to start with... Well, pretty good as far as speakerphones go...). ZZ Mike Morris UUCP: Morris@Jade.JPL.NASA.gov ICBM: 34.12 N, 118.02 W #Include quote.cute.standard PSTN: 818-447-7052 #Include disclaimer.standard cat flames.all > /dev/null