Radio mic receiver placement

[ukdeveloper]

Just wondered what the opinions of the pros on here was regarding the placement of radio mic receivers?

 

I'm going to be doing doing for a small theatre show over Xmas and they use 10 or so radio mics.

 

Should the receivers go in the wings or up near me at the back. It's a relatively small theatre (900 seats).

 

I'll also have a screen to monitor levels etc so don't physically "need" the boxes with me if its better to have them nearer the stage?

 

UKD

[JCC1996]

What make and model are the mics? And are they rack mounted with an antenna distribution unit or are they just individual receivers with their own antenna?

[ukdeveloper]

I knew you ask. And the simple answer is as of yet I have no idea.

 

I'm pretty sure they are sennheisers and would probably have the paddles rather than individual aerials.

 

But opinions on both would be appreciated.

[JCC1996]

I know that one sound tech I have shadowed used sennheisers with paddles and ADU in a much smaller theatre (about 300 seats) and they were sat at the stage and run up the multi to the desk. I certainly wouldn't have been confident using the individual antennas, even at that distance.

 

If the paddles would be on/near the stage (which I presume they would) and the signal from these would be cabled to the ADU with the Rx's then it doesn't really matter where the Rx's are. One thing to consider is how cramped the control position is? It may make more sense to keep them in the wings simply from a space point of view- 10 rack mounted receivers with ADU and aerial cable (which is pretty bulky) can take up a fair amount of space.

[Bobbsy]

At the risk of stating the obvious, it's the placement of the antennas which is more important than the receivers themselves. For good diversity performance, you want the antennas well-separated and placed in such a way that, if one of them is blocked, the other is likely to have a clear line of sight.

 

On top of that, be aware of the cable used to connect the antennas to the ADU/receivers. Things like the normal RG58 can be pretty lossy at the frequencies used by radio mics--there are lots of other options depending on your supplier.

[laolu]

I use 2 sets of an older version of the Mipro ACT747 (4-in-1) in the theatre where I work, the receivers sit on top of each other, right in front of me, they have individual antennas, distance to the stage is about 15 m. Never had a problem with them receiving clear signals. I even can hear the actors talking in the dress rooms, when they are out of sight. :P

 

Norbert

[mackerr]

At the risk of stating the obvious, it's the placement of the antennas which is more important than the receivers themselves. For good diversity performance, you want the antennas well-separated and placed in such a way that, if one of them is blocked, the other is likely to have a clear line of sight.

 

On top of that, be aware of the cable used to connect the antennas to the ADU/receivers. Things like the normal RG58 can be pretty lossy at the frequencies used by radio mics--there are lots of other options depending on your supplier.

 

To expand a bit on this, not only is RG58 pretty lossy, it is essentially a pad. Use low loss 50Z coax, at least RG8U, better yet RG213 or even better LMR400. I would notuse RG58 even for the 18" jumpers from an antenna distro to the receivers.

 

This has been discussed a few times here in the Blue Room. There is a lot of information already here with a little searching.

 

Have the antennas as close to the stage as possible, and the antenna cables as short as possible, even with good cable.

 

Mac

[ukdeveloper]

Thank you all for your replies.

 

Most informative!

 

UKD.

[paulears]

From a purely operator perspective - being able to see the displays is very helpful when you have issues, but getting the receivers to the mix position often has an impact on signal strength - so with well planned RF distribution and cecent aerials you can get the best performance and operational convenience. If RF is a problem, then stage side helps no end, and you lose the metering. In my venue, for instance, out front receivers is bad news, simply because of distance - line of sight around 30m, but cable route adds another 15m - and RF down the best cable at that length is a problem. Of course in most cases, the cable performance is critical for the null spaces, not the best ones - the benefit of all the low loss tricks detailed above really impacts on those moments when the talent is standing in a null that give little or no signal to both aerials. Even with RG58, a good path give full scale readings - misleading you into assuming signal isn't a issue. RF systems are essentially magic!

[Bobbsy]

I always preferred to have the receivers at the mix position so I could see the readouts of RF level and battery warnings. However, I was in the fortunate position of being able to borrow tens of thousands of pounds worth of HP or Tektronix spectrum analyser and some very expensive low loss cable normally used with our satellite dishes.....

 

However, the OP mentions he has a remote read out screen for the information I used to get from the receivers.

 

Anyway, the point of using the spectrum analyser was to try and avoid serious nulls and always have at least one antenna with a good signal. It usually worked!

[mackerr]

From a purely operator perspective - being able to see the displays is very helpful when you have issues, but getting the receivers to the mix position often has an impact on signal strength - so with well planned RF distribution and cecent aerials you can get the best performance and operational convenience. If RF is a problem, then stage side helps no end, and you lose the metering. In my venue, for instance, out front receivers is bad news, simply because of distance - line of sight around 30m, but cable route adds another 15m - and RF down the best cable at that length is a problem. Of course in most cases, the cable performance is critical for the null spaces, not the best ones - the benefit of all the low loss tricks detailed above really impacts on those moments when the talent is standing in a null that give little or no signal to both aerials. Even with RG58, a good path give full scale readings - misleading you into assuming signal isn't a issue. RF systems are essentially magic!

 

LMR400 has a loss of about 3dB/30m at typical UHF mic frequencies, RF through the air follows inverse square law. If you can halve the distance between the mics and the antennas with 30m of LMR400 you break even, if you can quarter the distance with 30m of cable you have 3dB more signal through the cable than the air. If you can use shorter cable lengths to achieve the same improvement in location you are even better off. If you are using RG58 for the antennas out front you are losing even more in the "through the air" path.

 

With diversity receivers and 2 antennas spaced by at least 2m that both cover the acting area, there should be very little chance of dropout due to multipath interference. Cable type will have no impact at all on any mulitpath interference that does happen. That does not mean that there won't be dropouts due to the transmitter antenna shorting against a sweaty body, or metallic costume, or other masking of the transmitter.

 

Mac

 

ps. I prefer not to see the meters. There is little I can do about it in the middle of the show, so why make myself nervous by watching them dip down, which does not necessarily impact performance, or go away when the talent is away from the stage, If there is an A2 who could make changes backstage, he can watch the meters as well.

[Bobbsy]

 

 

ps. I prefer not to see the meters. There is little I can do about it in the middle of the show, so why make myself nervous by watching them dip down, which does not necessarily impact performance, or go away when the talent is away from the stage, If there is an A2 who could make changes backstage, he can watch the meters as well.

 

I partially agree--I certainly don't both spending my time stressing over every tiny drop in the RF level.

 

However, seeing the meters in general has saved me on a few occasions when the signal was lost entirely--usually when an actor has messed with the power switch despite the tape we put over it and once when the pack actually failed.

 

More often though, the useful bit is the battery life warning. I'm sure we've all been there when the brand new battery fails after an hour (thanks Procell). The red warning light (on my old Sony receivers) has saved more than one cue.

 

As for the A2 watching the meters, I usually keep them too busy to count on them watching!

[Nicktaylor]

For what it is worth. I have sets of four Sennheiser G3s mounted in flight cases with short extensions to the aerials. I have them rigged at the back of a hall maybe 30 metres from the stage. No problems at all. I can see whats going on and trying to find a point next to the stage not blocked by scenery or whatever would be a lot harder.

 

Am I the only one who finds the statement "only 900 seats" a bit on the high side to be small venue. Most receiving houses wont be much more than half that I would have thought! :)

 

Off to check capicities of venues I know of!

[S&L]

I will just preface this by saying that people here know far more than me but thought it worth passing on what I saw a colleague had done in a 450 seat venue a couple of weeks ago.

20 radio mics, some with costume impairment some not.

all receivers in the orchestra pit below the stage to save room in the wings for scenery.

all receivers wired to a pair of remote array antennas. antennas were mounted on vertical lighting poles (also being used by lights) about 2m above stage level.

from the pit the receivers were cabled to the multicore and thence to the rear of house mixing positions some 30m away.

what I found elegant about this is that the receivers were out of the way of child actors who my inadvertently knock them in the wings and next to all the rest of the sound sources making cabling back to the main multicore fast and easy.

the antennas were not as out of place as you may think, being black and either side of the stage, unless you know what they were you wouldn't have given them a second look. apart from a single costume foul up it was the clearest I have ever heard mics in that theatre - absolutely crystal.

[paulears]

The only really critical element is the journey from actor to aerial input on the receiver. Everything else is just a logistics issue. Mounting aerials onto vertical metalwork will either work for or against you by altering the directional pattern of the aerial. If by luck the pole begins to act as a reflector, then the omnidirectional pattern of a dipole (where 180 degrees is wasted) can be focussed in a sensible direction. Get it wrong and you can end up with a null towards the stage. Knowing your kit and how it works is the key. You can design some very odd RF systems - perhaps even combining aerials before they get split to the receiver inputs if you have specific problems to solve. Very few people give much thought to exactly what aerials they are going to use. Many swear by paddles simply because they see others using them - but very rarely do people ever consider if they really are the most appropriate - the feeling seeing to be, they are more expensive, pros always use them, so they must be the best. I always tend to think about what's best for each situation. I've often wondered about trying some aerials on fly bars up and down stage instead of left right, which is more usual. If you look at distance - and obstructions (as in people and set), then up/down could actually have less path loss when things get bad. We recommend paddles on stands to get them up, so why not up into the clear with the lights. My thinking is that if you lit the stage from where we put paddles and other radio aerials, there would be many shadows and dark spots - so we stick the lights up high where they can light everyone, yet we don't do this with RF? Thoughts?