Understanding radio mics

As this is the tech talk column I thought it may be a good idea to cover some of the common problem areas and start with this common problem. Now you will see mics with 16, 32, 300, 700 or 1440 channels, this does not mean that you can use anything like that number of mics together. Radio transmitters are like musical instruments [in that they produce harmonics which are multiples of the base frequency], and these harmonics interact with each other to restrict the number of usable channels. As an example, the Redback 16 channel mics have 6 channels which can work together, the main mics I hire are the 700 channel series but only 16-17 channels will work together.To get more channels I am now getting in the Sennheiser 1440 channel units and while they are coy about exactly how many channels I will get, it should be 24+. Now other areas to consider are interference from other radio sources like in ear monitors, which tend to use the same bands and radio talkback systems which I am now also importing as prices are lowering. If you are using half a dozen radio mics there is not likely to be a problem but once you start adding talkback and in ear monitors you will need some specialized assistance. And as I said in an earlier piece, the radio part is only the beginning, the complexity of multi mic mixing a live show added to the potential harmonic interference means that rehearsing with the full system is crucial and failure to do this and find potential problems can lead to disaster. In short, radio mics are not a panacea so please bear this in mind.

One item wasn't mentioned ... having the correct type of microphone with your radio mike transmitter. I saw a relatively good show earlier this year go off the rails due to equipment failures largely associated with the wrong selection of microphones (lapel vs headband vs tape on) Mark -- Tech & Server Wrangler

When using wireless mics in an amateur background, it is important to get the actors to rehearse with them for a lot of reasons: There may be local sources of interference that only pop up at irregular intervals so if you can use them on the same nights you will be performing on, there is less chance of getting caught out by interference during performances. If using large numbers of wireless mics, your crew needs to work out a discipline of testing each wireless mic with each performer and instructing them not to turn the beltpack off once tested to avaoid an actor going on stage with their mic turned off. Two actors wearing wireless mics can have proximity cancellation occurr, where the sound from an actor is picked up by their mic and a little time later is picked up by the other mic. These two different signals can cancel out in the mixer, so the director needs to be aware when this occurs and reblocks or gets the actor to change the side of their face that their wireless mic is on, or gets the sound tech to take one mic out of the mix for that moment. You need to set up a discipline of recharging you beltpack batteries or budget for battery replacement so actors always have fresh batteries for every performance. Try to get unobtrusive, flesh coloured mics and practice with them so they are an integral part of the actors costume and makeup. Wireless mics are great for actors who have colds or in large halls as it saves their voices for long seasons, however make sure they don't rely on the mic as a wireless mic cannot work well with actors whispering due the to signal to noise (hiss) limitations of the system. The person mixing a show with radio mics needs to have a script marked with who is using what mic when, so the mic is only added to the mix when required. This gives the actors confidence to leave their mics on at all times. When using large numbers of wireless mics, you need a tech backstage to check mics before and during a show and ideally have a spare set to swap out any faulty ones as wireless mics can be succeptable to sweat interfering with the mic capsule. And so the list goes on.

Here's a quick tip - if you are performing in close proximity to another theatre, check in advance what channels they've tuned THEIR radio mics to. Nothing like having an actor onstage, mid-song, and hearing snippets of next door's production coming loud and clear through your own mics. --- Louisa Fitzhardinge University Dramatic Society http://uds.asn.au

G'donya you! finally we have some real 'tech talk' for a change! Instead of the usual 'warm props' &/or 'Luvvies speakfest that this section has fallen into. I'm a sparkie by trade & when it comes to radio, I liken it to refrigeration & motor cars, have always been a black hole to me. Not from the basic principals, but all the the excuse given by pseudo audio engineers of why 'IT' don't work as it was designed to do! I shouldn't knock 'frigies' or 'mechanics', as some of my better friends are even audio techs 'n luvvies. as you mentioned 'talk back' systems as well, I'm in the process of applying for the new "ignite grant via DCA & ITA. Thus deciding whether to go for radio headset talk backs or to actually install a wired 'TB' system. I have had a few problems in the past with doing shows, using these mickey mouse toy radio head sets, with them drooping out on the cue or interference so bad they hurt the old ear drums. Especially at our old venue, which has just been refurbished [which we have christened the 'cockpit Theatre'] Phoenix Theatre in Cockburn. The venue is underneath a power network of High tension cables & luckily is not also a major Bus depot, which the Council got moved for the new 'CPAC" complex. But the power cable pylons was outside their budget & will still be there. This even happens with Jands gear, that we have hired on occasions, so it is not the fault of the toy Tandy sets & the like. I know I have mentioned this situation before with you recently, but I'm ancient & visually impaired when it comes to seeing sound & radio waves. Sorry to go off on a tangent, but the 'ignite' Grant is too good an opportunity to pass up & I don't want to go thru the drama of going back to using the good old 'traffic light' cuing systems. So I'm thinking of a basic 4 radio belt packs with Master station &headsets to suit? {as you mentioned you stock a TB range.] Also I agree whole heartedly with putting in place a regime of 'idiot checking' radio Mic's & the audio techie instigating a working list of Mic placement/logistics. 'Net Form' {[WWWW sheet]What When Where (& Who)} Prior to performance.[Keeping in mind the 5 P's, which should be 7 P's?] I realise that battery technology has change over the years, but I always used to have dramas with the rechargeable ones. Luckily that was sorted by being able to get a complimentary carton every now & then of fresh batteries, as part of a promotion for a particular brand. {I won't mention the brand name - But it is surprising what you can get for a few comp tickets!}

TOI TOI TOI CHOOKAS

[May you always play to a full house] Hear the lights & see the sound. 

It's good to see some feedback, I originally tried to keep things simple to explain the problems to the non technical fraternity, however I would like to address a couple of points raised.There are 3 styles of mics generally used, the tie clip type is pretty useless as it will pick up clothes noises, the headset type of mic is fine for rock'n'roll situations where it does matter about the look but by far the most useful are the "bud" mics, taped to the face below the ear, there is no clothes rustle and the mic picks up the resonances of the voice and sounds more natural, this is why it is universally used in opera and musical reinforcement, placing the mic too close to the mouth will give a "breathy" sound and will overdrive the mic causing distortion. The interference from other sources is an ongoing problem and was the main reason for me buying mics with more available channels. Once again I would like to encourage other techs to use this forum to bring forward aspects of the tech side of the business so that actors and directors can get the most out of their sound, lighting, scenery and props.

A working set of wired cans is a joy to use. The problem is that they are so darn expensive (for no good reason) and when the headsets break through use and abuse you'll need to budget for replacing them. Mark -- Tech & Server Wrangler

Louisa mentioned a great tip, which has always worried me, using radio Mic's. That being on the same frequency as an adjacent venue, which could be a wee bit embarrassing. I doubt we would have to worry about here too much in Perth, but you never know? I know sweet fanny adams about them beyond setting up & turning on. So what is the average range of the units & is there any precautions to take to avoid this happening? Beyond scoping out & keeping your ear to the ground in the local area. I think it would be more of a problem in the eastern states than around here.

TOI TOI TOI CHOOKAS

[May you always play to a full house] Hear the lights & see the sounds. 

It did happen here in Perth, at the Octagon and the Dolphin, both using my mics but not co-ordinating, very embarrassing.This was the catalyst for me searching out the Sennheisers to get more channels.By way of defense it was a dry hire and there was just enough channels to co-exist but something went wrong.

At the UWA? I wouldn't have thought that area at Crawley, would have been a problem. Although there a few odd pubs & couple of entertainment areas around it. Did you happen to find out what venue it was on the same frequency David?

TOI TOI TOI CHOOKAS

[May you always play to a full house] Hear the lights & see the sounds. 

So with that sort of range it is not beyond the realms of possibly, for this to happen, even in the remotest areas. Good point Taureen! Personally with Comeatre i have only used Radio Mic's once. When i directed Man Of La Mancha at the Old Mill, in South Perth. The female lead Aldonza [Karen Smith] had a bout of laryngitis. She could speak just, Burt no way was I going to allow her to sing. So i hired in a radio Mic, getting her to wear the lapel Mic. Then the young girl playing Cervantes [Hywell Williams] Niece [Rebeca] volunteered to sing Aldonzas songs of stage, via the hand held radio Mic. With Aldonza delivering dialogue reinforced over the speakers, & gold fishing her songs. It went off seamlessly without any hookups. The SM [Karen Hall] informed the punters of the change & speaking to a few afterwards, they had forgot that the songs were being sung off stage. Some reviewer however had a go, because the Niece was not given a special walk down curtain call. Which was totally my fault, by not asking the SM to organise it. also this reviewer nit picked the style of Sancho's sandals? However did not mention the engineering theatrical skills, of having a 20 odd foot staircase descend & be flown out, from the Fly's, between the boarders. [The Old Mill has no fly system] The Cast used them to enter & exit above the stage. Which was quite amusing to see the number of punters, after the show. Walking around the building looking up at the gable roof , wondering how it was done? Ah! illusion is always great to play around with!

TOI TOI TOI CHOOKAS

[May you always play to a full house] Hear the lights & see the sounds. 

I work for a corporate A.V. company and regularly use Sure ULX, UC and Mipro Radio Mic's in the UWA Club IU doubt that the mics would interfere with the theaters mentioned, I guess I'm just pointing out that we being one of the companys who operate on the 'dark side' (corporate functions) instal radio mics all over the place all the time. One such venue is Subiaco Oval, they have Mipro wireless mics in every function room as a result if we use Mipro at Subiaco there is almost always a reciever in another room that picks up the signal. As a rule now we only usr Sure radio mics. I came across this forum as I have been researching information to help me set the best posible frequencies for my mic's at my functions as I find that I get drop outs regularly. It is common for me to have up to eight Radio mics as well as sending wireless audio to the camera crew.