Not sure where to post my question so I thought I’d say hello here & hope the mods will point me in the right direction. Excuse the long post but I wanted to give sufficient background for a sensible reply.
My village in UK has a small theatre group which uses a ex-hire Canford Techpro coms kit for communication between the tech team and stage manager. This wired system comprises a base station with 4 beltpacks & headsets which plug into outlets around the hall (belt packs have both input & output sockets so can be chained together). It’s apparently a “two-wire” system so all connected parties can both hear and speak simultaneously on a single channel. Microphones can be muted on the beltpack but when live are continuously open.
The problem for our stage manager is that he needs to move around backstage during the performance both listening & talking and that’s difficult when he’s tethered by the wires. We’d like to get a wireless headset for him but the Canford solution is a full professional job and way outside our budget.
I’ve seen some PTT bluetooth headsets which seem to do exactly what we’re looking for if it could be adapted to plug into the headset input on our Techpro beltpacks. It’s way outside my expertise, so can anyone tell me whether this would be technically possible, please?
NB. I’m not expecting detailed tech instructions at this stage, just feasibility & what problems would we need to solve.
Many thanks, Simon
I work in the theatre industry in the UK, and understand perfectly what you mean. Our American cousins have a similar wired system from Clearcom - it’s very similar but subtly different so they don’t mix well. At my theatre in Norfolk, I have a system that I use for the same thing. I have a VHF repeater - it lives in the flys, and anything on the Tecpro ring gets transmitted by the repeater on Frequency 1. We have a pile of kenwood VHF radios and anyone with one can hear the comms. If they press the transmit button, then the repeater hears them on frequency 2, and injects that back into the ring. What you need is a 4 wire converter - Canford sell them - they split out the ring into a receive and send circuit for just this kind of thing. Cost wise, the repeater is an old one I had laying around - they can be found for two or three hundred quid - the 4 wire converters occasionally pop up on ebay for £50 or so - add radios, and a licence from OFCOM and you are done.
If you are radio competent, you can bodge things - but a few things are important.
The expensive systems are duplex, you can speak and listen at the same time. My kenwood system relies on pressing a PTT and that is a real pain. Vox (as in voice operation) is useless - we have too much noise for it to work properly, and false triggering is so annoying to the others.
The Canford system is wide band - decent audio quality. Sending my kenwood users into the ring is immediately obvious - thin and narrow audio band and the other users really don’t like it when I speak on a radio - but it does the job. If any other readers are a bit lost on theatre practice - I made this video.
For what it’s worth, there is a bit in it where I mention the very expensive radio comms systems we use on this more er, ‘financed’ production. Everyone hates them - just mega expensive and awful! Seriously though - even my normal venue means money has to be spent for reliable comms - all the cheaper systems sort of work. My experience of bluetooth and other things has been seriously unreliable.
UK Stage manager Video
Hi Paul. Thanks for the reply. Lot of useful info I need to absorb but I can’t get your YT link to work on my mobile - it wants me to create a channel. The link id has a special char in it that means it’s not recognised.
S.
Hi Paul,
So is that your theatre? 'Fraid that’s way above our pay grade. I’m more in the “what can I do if I manage to wrest £50 from the committee” !
I only need one wireless set for the stg mgr.
The protec bp511 wiring spec has 4-pin XLR with 2 wires for mic & 2 wires for speaker.
I’m wondering now if I can pick up a plantronics (or generic) wireless headset with base station that plugs into a landline phone. That seems to have similar wiring scheme on the RJ9 plug.
The resistance doesn’t match but would it be near enough?
S.
the thing to remember is that tecpro has been doing it with cables since the 80s in the UK and is virtually 100% reliable. Radio systems are ALWAYS worse and cost is not a cure. Walkie talkies can be bodged. We have been doing it for years. The snag in making it work is that it means you must have one that permanently transmits, so everything said on the ring goes out to another radio. 100% transmit is not something walkie talkies are good at. They usually overheat. Repeaters are designed to do this. As I said, even a radio with voice operated transmit fails because they chop off the start of words, trigger when the drummer goes bang. Small amateur groups can make it work with a couple of cheap bubble pack low power radios, but operating separately from the proper ones. However, show wise, it is a pain. It has always been traditional for some things to have to be done comm-less. If the person has to say “off comms” go and do the cue and then come back and put them on again, that is quite normal. In my panto, my job is problems, so i have a sennheiser IEM transmitter plugged into the comms circuit. I can hear what is going on, and can magically appear when a problem happens. I cannot speak, but I do not need to.
4 wire is NOT the headphones connection. That has a mic on two conductors and the headset speakers on the other. Connecting to the mic is a nighmare, as the impedance is critical for the tecpro sidetone circuit to work and while experimenting is fine, they often screetch and become unstable. The others on the ring will hate you. You can usually tap into the speaker circuit for a radio transmit, with a 20 or 30 dB pad, but be aware some radios have 5v or so on their mic connection to power electret mics or switch to transmit. That is not a standard. 4 wire adaptors convert the line level common circuit to separate in and out. Any wrong impedance tap to the XLR common line causes all kinds of issues if done badly.
There is a UK forum called the blue room. One of their members designed a comms system enthusiasts could build themselves, with all the parts available when tecpro discontinued the old system.
A telephone standard system is wrong impedance, wrong level. The common system used by tecpro and clearcom has a fairly low impedance line that has a termination in the power supply. The individual packs are high impedance and bridge the line, sort of ‘sniffing’ what is happening on it. As soon as you have too many packs, the stability breaks down and crazy things happen. Your phone system could possibly be impedance adjusted to listen without impact on the line, but then the injection level would be the wrong way and they wouldnt hear you.