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I'm curious why a wireless microphone system for school plays requires a multi-channel receiver while a home telephone system allows as many conversation participants as there are handsets with only one base receiver???

My daughter in law is a school drama teacher and needs good wireless microphones for her 6th through 8th graders play productions. How do home phone systems work that multiple people can be speaking on one base receiver, while each wireless microphone requires it's own frequency and receiver? I'd like to build a lavalier microphone w/pocket transmitters for the kids that can all be received by the same base model and amplified out to the speakers. I think it would be fun to base it on a home wireless phone set with 8 or more handsets. Is that possible?

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    \$\begingroup\$ The sound man will want to get each microphone as a separate signal, so he can adjust the sound level from each mic as required - this requires that each mic be on a separate radio channel into an individual receiver per channel. \$\endgroup\$
    – Peter Bennett
    Commented Apr 4, 2017 at 20:02
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    \$\begingroup\$ Also: Have you recently tried singing to someone over the phone? You may find your beautiful arias are no longer all too well received after they go through the narrow bands used by telephony. \$\endgroup\$
    – Asmyldof
    Commented Apr 4, 2017 at 20:05
  • \$\begingroup\$ @Asmyldof, I get that! But some phones have pretty good quality reception, substituting more expensive mic's and amplifiers I think it could get some pretty good sound out of them. Not for my singing of course! But for the kids. Plus most home cordless phones have longer ranges than wireless mics. Usually about 300 meters vs 60 meters. \$\endgroup\$
    – John Muggins
    Commented Apr 4, 2017 at 20:13

2 Answers 2

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The "dedicated channel per voice" is only true for analog systems. Digital ones can have quite a lot more voices in a smaller area of radio bandwidth; not just cordless phones but mobile phones. Cordless phones use a system called DECT to achieve this.

What may be a factor is compression. Phones generally do terrible things to the sound - limit it to a band of a few kHz, apply lossy compression (AMR @ 10kbit is nowhere near MP3 @ 128kbit), and so on. There is also an unavoidable latency in digital systems. Phones also tend to do silence culling and "comfort noise": if the other person isn't speaking, transmit nothing and rely on the other end to play a bit of hiss instead.

But there's no good reason why you couldn't have a multi-channel high-bandwidth digital microphone system. I'm a bit surprised such a thing doesn't exist, although I've not gone looking for it.

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  • \$\begingroup\$ Oh yes they are available. Expensive. We have a drive on attempting to raise money to purchase a good one. 8 microphones for example, comes with an 8 channel receiver. And as @Trevor pointed out there is a lot more control for each channel. I was just trying to think of an easier, cheaper alternative. It's middle school. I was also looking into Bluetooth and having the kids plug the lavalier lapel mic into their own cell phones and then amp up the receiver, but there is a tiny lag there with Bluetooth. \$\endgroup\$
    – John Muggins
    Commented Apr 4, 2017 at 20:36
  • \$\begingroup\$ @JohnMuggins what you describe is Microphones with one channel for each microphone. What pjc50 wonders about are digital microphone that can share the same channel. These do exist, pjc! They're not all that sexy, since even high quality digital mic channels are rather narrowband, so you don't need much spectrum even without a Multiple-Access layer.. \$\endgroup\$
    – Marcus Müller
    Commented Apr 4, 2017 at 21:06
  • \$\begingroup\$ You ought to be able to manage up to 7 bluetooth mics if you can accept the quality+latency. Marcus, do you have an example? I found Sennheiser do one but it looked rather gold-plated. \$\endgroup\$
    – pjc50
    Commented Apr 4, 2017 at 21:12
  • \$\begingroup\$ exactly those :) I know Sennheiser had a project a while back, when the TV whitespace (which was before exclusively used by stage equipment) became available for 3G/4G, tackling exactly the things you wonder about in your answer. \$\endgroup\$
    – Marcus Müller
    Commented Apr 4, 2017 at 21:14
  • \$\begingroup\$ @pjc50 , yes, that time lag for the blue tooth is a problem. I looked into single receivers and could only find systems using two mics. The 8 channel ones come in a variety of qualities, from $180 to about $500, which are the more economical ones. They all seem to be limited to 60 meter range. Sometimes the actors go into the audience out of range. Substituting dipole antennas away from the transmitters would help, but that's a lot of work. My current home phone system gets about 400 meter range. \$\endgroup\$
    – John Muggins
    Commented Apr 5, 2017 at 12:43
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Telephones switch channels to find one that is currently available. Some channels may currently be "occupied" by your neighbor.

Stage microphones use dedicated channels so the audio technician can balance the sound from each channel separately. For example, they know that channel 1 is the lead singer etc..

What you are describing is quite possible though. But your neighbor may not be impressed.

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    \$\begingroup\$ So when I am on one phone, and my wife is on a second handset of the same system, she and I can both talk at the same time and clearly hear each other ( and talk over each other - which unfortunately is not uncommon) because we are automatically being shifted to different frequencies and then automatically mixed back together? It actually sounds like a lot better system for stage mics.... And perhaps we can even run earbuds to the actors so they can get stage direction from the teachers at the same time...... Sounding better all the time! \$\endgroup\$
    – John Muggins
    Commented Apr 4, 2017 at 20:18
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    \$\begingroup\$ @JohnMuggins the issue with stage mics though is not in the RF part but in the mixer. The sound guy can't have the lead singer suddenly go from channel 1 to channel 7. \$\endgroup\$
    – Trevor_G
    Commented Apr 4, 2017 at 20:23
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    \$\begingroup\$ @JohnMuggins for phones, it's a bit more complicated than just the frequency channel thing in practice (because in fact, you and your wife's phone need less time to transmit a let's say 10ms piece of audio data than it needs to record that (10ms) – and then they alternatively use the channel to send those). But the problem really is that in larger audio installations, you can't have the latency that such systems introduce. Still, it can be done, and is done, especially for spatially larger systems. But I don't think these mics will be any cheaper than those you're looking at... \$\endgroup\$
    – Marcus Müller
    Commented Apr 4, 2017 at 21:09
  • \$\begingroup\$ For example, you can get really cheap with Bluetooth headsets - and maybe even the audio quality isn't that bad. But you'd typically get some 100ms – 0.5s delay – and tell a band they need to play half a second before their singer sings, and get that in shape. \$\endgroup\$
    – Marcus Müller
    Commented Apr 4, 2017 at 21:13
  • \$\begingroup\$ Thanks @Marcus Müller. I was thinking of using an old 8 handset Panasonic system I have laying around. It was costly in its day, about the same as a cheap 8 lavalier mic system today - $200 or so. But it's just gathering dust now. Everything is give and take. They just finished "Singining in the Rain" play and needed a remote control light for the battery lamp post that the main character danced around. I could have built one for $50 bucks, but Hoover puts out a 4 light package that worked for $20! \$\endgroup\$
    – John Muggins
    Commented Apr 5, 2017 at 12:36

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