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Multiple wireless mics during theatre production - issues to look out for with mixed kits?

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Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Ben » Sat Mar 20, 2021 12:05 pm

Hi all. I film and edit video and have limited experience of wireless mics. I normally use a maximum of two during filming and use the free 606-648MHz UK range. Wireless audio unnerves me and I like cables...

I'm due to film a stage production (no audience) with six actors and would like them all on wireless mics, if workable.

With a limited budget, the director is hoping to pool various borrowed mic systems and I'm warning that we can't expect them all to play nicely together. A sound/lighting tech will be appointed soon and I'll be able to explore this in a production meeting, but in case there are some holes in their experience, I want to be aware of pitfalls.

I understand the 'proper' solution is to be in a venue with a purpose built system, license and workflow for this. Or to rent in the same arrangement.

What sorts of challenges might we face with, say, mixed Sennheiser UHF G4/G3 kits? Are the challenges about finding a broad enough range of separate frequencies, kits being on different channels, etc? Would it become even more complicated to introduce kits from different manufacturers or kits in the newer 2.4 GHz band?

Apologies for the 'I don't know enough to ask the right question' question. I've searched around but can't quite hit the understanding I'm after. Thanks.
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Sam Spoons » Sat Mar 20, 2021 12:29 pm

You will definitely have an easier time of it if you hire in mics from a proper supplier, they should be able to sort the channels out so they play well together (it's not as simple as spacing them so many MHz apart) and advise on licensing. The 2.4GHz band is probably easier if they are all the same make (and are license free in the UK).

BTW CH38 (606-648 MHz) is not free but requires a licence in the UK, the free band in CH70 and spans 863-865 MHz
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Mike Stranks » Sat Mar 20, 2021 12:38 pm

Hi Ben!

Just endorsing and amplifying Sam's comments...

The frequencies you reference are not 'free'.

You can use Channel 38 : 606.500 - 613.500 MHz if you have a licence.

The licence free frequencies in the UK are:

173.8 MHz - 175 MHz and 863.1 MHz to 864.9 Mhz (Channel 70) (and 2.4Ghz, but that's where Wi-Fi lives too... might be problematic with lower-spec kit)

which may be used straight out of the box.

Check the ofcom site if you want to know more about licence-free, licensable and illegal UK frequencies. In theory you can be heavily fined and have gear confiscated if you're using illegal frequencies; it's not just pirate radio stations! And, of course, you may get interference from legitimate users of that frequency.

The most systems you can safely use simultaneously in Channel 70 is 4. (In theory you can use more, but I wouldn't risk it... I tried to use 5 once in a high-profile gig... :blush: :oops: )

Channel 38 would allow you to use more rigs simultaneously... six should be fine.

In your situation I wouldn't be doing anything but hiring in...
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Ben » Sat Mar 20, 2021 1:07 pm

Thanks both. I checked and misunderstood the channels - my own G4 system is 863 - 865 MHz. We have an offer of an additional 4-channel Sennheiser system (purchased as a kit) with license, but I'm not sure which channel.

It sounds like it'll be a couple of boom mics in front of the stage for this project. Hooray!
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby DGL. » Sat Mar 20, 2021 1:12 pm

Of course if more channels are needed that what fits in CH38 + the small section of CH70 then with a shared licence you also get 823-832 MHz and 1785-1805 MHz.

Noting that,
1785 - 1805 MHz: Not available in Northern Ireland
1800 - 1805 MHz: Not available within 10 km of Oakhanger,(SU776357), Colerne (ST808717) and Menwith Hill (SE210560).

https://www.ofcom.org.uk/manage-your-li ... ors/shared

https://www.ofcom.org.uk/manage-your-li ... nce-exempt

And if that is not enough then co-ordinated licences are available for a specific site and dates.

https://www.ofcom.org.uk/manage-your-li ... -ordinated
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Ben » Sat Mar 20, 2021 2:05 pm

DGL. wrote:Of course if more channels are needed that what fits in CH38 + the small section of CH70 then with a shared licence you also get 823-832 MHz and 1785-1805 MHz.

Thanks DGL. The license I've just looked at for Channel 38 covers 606.500 - 613.500 MHz. Some possibly rental mics I can see list the range 606-648MHz and I can't see how the upper part of that range is licensed...? Sorry to use you as OFCOM...
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Sam Spoons » Sat Mar 20, 2021 2:19 pm

DGL. wrote:Of course if more channels are needed that what fits in CH38 + the small section of CH70 then with a shared licence you also get 823-832 MHz and 1785-1805 MHz.

They only need six mics which will fit in CH38 with ease (but will need a license).
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Wonks » Sat Mar 20, 2021 3:30 pm

I believe you'll need to contact Ofcom direct about using channel 39, 40, 41, 42 and3 frequencies, as a Short Term PMSE License is required (per channel). This is date & venue specific, and isn't a blanket license like channel 38. So if someone in the local area is already using those channels on the days you want to use them, it's unlikely you'll get a license to also use them. But there area few channels in that range 606-648MHz, and each main channel should cope with between 4-6 transmitters, so you can but try.
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby DGL. » Sat Mar 20, 2021 3:56 pm

Ben wrote:
DGL. wrote:Of course if more channels are needed that what fits in CH38 + the small section of CH70 then with a shared licence you also get 823-832 MHz and 1785-1805 MHz.

Thanks DGL. The license I've just looked at for Channel 38 covers 606.500 - 613.500 MHz. Some possibly rental mics I can see list the range 606-648MHz and I can't see how the upper part of that range is licensed...? Sorry to use you as OFCOM...

It's all included as part of the shared user licence, it was added as part of an EU directive I believe, probably part of the fact that a lot of wireless space was lost with the growth of mobile phones and it was added to compensate.
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Ben » Sat Mar 20, 2021 4:02 pm

Thanks Wonks and all. I'm starting to understand what to explore. It seems the Ch38 range will comfortably allow 12 systems and that Sennheiser have a bank of 12 presets to help with this. Maybe I'll invest in some kit.

As an aside, I was browsing this otherwise sensible site, coded in the early 1930s and the audio expert claims that 'nervousness and anxiety' can impact radio mic performance, including complete loss of signal! It seems OFCOM have some quite powerful alien technology at their disposal...
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Hugh Robjohns » Sat Mar 20, 2021 5:44 pm

Ben wrote:As an aside, I was browsing this otherwise sensible site, coded in the early 1930s and the audio expert claims that 'nervousness and anxiety' can impact radio mic performance, including complete loss of signal! It seems OFCOM have some quite powerful alien technology at their disposal...

Nervousness can result in perspiration, and salt water can affect the propagation of radio waves. It is a recognised effect... But usually sweat and makeup build-up in the mic is a bigger problem!

As others have said, the only sensible solution to your drama is to hire in the requisite number of radio mics from one supplier. The good companies will sort out a compatible channel allocation and even take care of the licensing, if you ask them. and I should think you'd be able to negotiate a good deal at the moment too! There are lots of hire companies out there, but Terry Tew is a good one I can recommend.

https://www.terrytew.co.uk/hire/
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby DGL. » Sat Mar 20, 2021 6:43 pm

Ben wrote:As an aside, I was browsing this otherwise sensible site, coded in the early 1930s and the audio expert claims that 'nervousness and anxiety' can impact radio mic performance, including complete loss of signal! It seems OFCOM have some quite powerful alien technology at their disposal...

Well wireless is a black art, as any transmission engineer.
OT but I am always in awe of some of the methods used to get TV/Radio signals to transmission sites, the channel islands being one of the most impressive, ITV ending up being from Rowridge via France and BBC FM using NICAM via using a link from Stockland hill to Alderney, CH 30 at a poultry 250W ERP
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby MOF » Sat Mar 20, 2021 7:08 pm

As an aside, I was browsing this otherwise sensible site, coded in the early 1930s and the audio expert claims that 'nervousness and anxiety' can impact radio mic performance, including complete loss of signal! It seems OFCOM have some quite powerful alien technology at their disposal...

I don’t think the 1930s is correct, my internet research shows that the first radio microphone was invented in 1947.
However anxiety in an actor can cause sweat, this can lead to problems at the capsule and mic’ and aerial connections.
Also large bodies of water (a lake in my experience when I had non-diversity vhf systems) reduce signal power at the receiver.
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Ben » Sat Mar 20, 2021 8:10 pm

MOF wrote:
As an aside, I was browsing this otherwise sensible site, coded in the early 1930s and the audio expert claims that 'nervousness and anxiety' can impact radio mic performance, including complete loss of signal! It seems OFCOM have some quite powerful alien technology at their disposal...

I don’t think the 1930s is correct, my internet research shows that the first radio microphone was invented in 1947.
However anxiety in an actor can cause sweat, this can lead to problems at the capsule and mic’ and aerial connections.
Also large bodies of water (a lake in my experience when I had non-diversity vhf systems) reduce signal power at the receiver.

Sorry all - 'coded in the 1930s' was an attempt at a joke, in reference to how the site looks. The specific phrase he uses is 'The reaction of electrical circuits to personal electromagnetic energy fields is a difficult phenomenon to understand.' So I don't think he's talking about sweat, more tin-foil hat territory. Yikes.

Thanks for everyone's advice. I do appreciate the 'sensible' approach always wins. I also feel there is room for improvised solutions and they've often worked well for me. But perhaps wireless audio isn't one of those contexts.
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Re: Multiple wireless mics during theatre production - issues to look out for with mixed kits?

Postby Sam Spoons » Sun Mar 21, 2021 2:01 pm

Even the best configured wireless systems will turn around and bite you on the bum every so often (ask me how I know this :blush: ), definitely not an area for improvisation...
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