Integrate speakerphone communication with my console

I've had some sessions where the producer is in another state while the artist is recording in the studio. I've used a cordless speakerphone for it, but was wanting to improve communication. I simply had the phone in the control room with a talkback mic by it feeding the artist cue phones.

I took a cable from a phone headset, it was double shielded wire (so both unbalanced). I ran one into the console pre and could hear the cordless phone great. However, no luck so far with the mic side of things. I'm trying to feed what would be the headset mic signal so console playback/monitoring will be fed to the cordless speakerphone so the producer can hear the client (the client can already hear the producer as that part works).

Does anyone know about interfacing a console line signal so it will drive the "mic input" of a cordless speakerphone?

most modern phone sets use an electret mic for the transmitter. This means you need to capacitively couple the console send to the electret "talk pair" of the phone. You'll also likely need to pad it down to a useable level. Better yet is to also transformer couple the line so it's balanced and isolated.

Keep in mind that telephones have a little bit of sidetone sent from the handset mic back to the earpiece so the person can judge how loud they are speaking into the handset.

Thanks Bill for the info. The "mic" wire is a center conductor with a shield. So are you saying I should solder a capacitor between the shield and the central conductor? How does one determine capacitor value?

The cue to feed the "mic" of the phone is variable, so I was hoping I could just have it way down to make up for the pad. I do have a couple 40db pads I made for going line out into a mic pre too. I also have an edcor 1220 transformer that should handle unbalanced to balanced, but I wasn't hoping to go into it that deep, just enough to get something a bit better than a speakerphone and control room mic.

Right now, the phone to console works fine (nothing special needed). To get the cue send into the phone, if I give it a tiny bit of cue signal with a cable with a capacitor connecting the shield and conductor, do you think that would work?

You want to connect the shields together, and connect the capacitor in series with the inner signal wire

Wow...this sure sounds familiar from my Ad Agency Studio days, except that we used a landline and  Gentner (later a Telos) "hybrid", such as used by the radio stations for "call in" talk shows.

I have yet to dig down into how to do this with Iphones, etc, but the same problems exist.  One issue is what is called "sidetone" whereby your Voice is intentionally fed back into your earpiece so that you won't SHOUT.  But, that complicates things when feeding a cue to the remote AND listening to their comments at the same time.

Hence the "broadcast hybrids"....but again, the ones I know of are designed for landlines.

http://www.telosalliance.com/Telos

I Do see they also sell VOIP devices now.....


Bri

Well, technically the hybrid is already in place within the telephone set, if the signal is tapped in at the handset connections. If the levels are more or less balanced, the sidetone shouldn't be too much of a problem.

Hmmmm...sidetone is already "mixed into" the earphone which is fed by the telephone set on ANY telephone....tapping off the "earpiece" lines guarantees that you will "hear yourself"....IOW, the cue feed back to the Far End.

Perhaps not a problem for a one-way feed "down the line" (Example:  feeding a mix of an Ad to a client for approval) , but a big problem for a "return path" when trying to listen to the far-end as that person attempts to communicate back to the VO announcer, singer, etc.

This all became apparent to me while setting up "Radio talk show call-ins" many years ago.

I call the newest/best hybrids a "Rush Limbaugh" cuz of the need to highly isolate send to/receive from the remote locations.  Telos is the best I've found.

Bri

This is not a critical situation for broadcast, just me trying to experiment with making the situation a bit better for the few times a year this comes up. I will experiment with the capacitor in series with the mic conductor/shield and see if that at least gets a signal from my console back into the "mic" of the phone.

I may have to simply put the phone into speakerphone mode if I can't get something working this weekend. Real high tech   But for a few times a year, I'm not going to invest in a pricey commercial solution.

If I understand, I connect the two shields (from the headset cord), then put a capacitor between the shield and the "mic" conductor. I'll try a small non-polarized ceramic capacitor that I have lying around and see what happens.

DRAT!!! So close yet so far... hearing the remote producer speak into his phone comes through the console great. I simply can not get the cordless phone "mic" to send signal from the console back to him. I connected the two shields together, then I put a Wima film cap (what I had lying around) connecting the shield and "hot" on the "mic" phone side. (doing this with allegator clips). Still get no signal from the phone "mic" which should be "playback" from the console (or live monitoring).  So we can hear the producer, but the producer can't hear the console monitor session feed.

I'm feeding the phone "mic" input line signal... I get silence. If it were too much, at least I'd think its a matter of reducing the signal. But its silent.  Am I understanding the use of the capacitor right? I know Radio Shack sells a phone control  device to record to a cassette (and turn it on and off) for around $10. Do I need to use something like this? Or is there a way to somehow feed the headset "mic" side that I'm just not understanding or I'm doing wrong?

Thanks for any help anyone might offer on things to try. I don't need to worry about "side feed", I just want to get the session to play back so the producer can hear it with a line feed right now.

More than once you mention connecting the capacitor to the shield. There is no such connection. Doing so effectively shorts the audio signal to ground. The capacitor is inserted between the handset mic line, and the signal send from your console,  only.  It's purpose is to block the DC bias voltage for the electret from  being applied to the output of your mixing console, while still passing the audio signal. I would try perhaps a 1 mfd non-polarized capacitor. More than likely, your console already has coupling caps built into the output drive circuit, so it's more of a backup , redundant situation.

The shield from the  console send,  connects to the handset mic ground lead. Nothing else.

If it passes audio but you run into hum issues, you may have to isolate the mic line with the transformer.

Thanks, that did the trick! I had misunderstood the use of the capacitor. Works great, and everyone sounds like they're calling from the the moon thanks to the great bandwidth of cell phones But it works as I'd hoped so now I can box it up.