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Author Topic: 18 wireless microphones at once question  (Read 3636 times)

Kent Thompson

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18 wireless microphones at once question
« on: April 09, 2010, 09:41:38 pm »

A local performing arts school a family member attends is putting on a show where they want to use 18 wireless microphones. They have contacted 2 rental companies more than 300 miles away to supply said wireless systems. I am a little worried which maybe I shouldn't be but, my experiences with many wireless channels has not been good. What are the chances of a rental company(in Austin Texas or Dallas, Texas) setting the frequencies on 18 units to not only work together but work in the civic auditorium in Harlingen, Texas without issues?
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Henry Cohen

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Re: 18 wireless microphones at once question
« Reply #1 on: April 10, 2010, 10:36:21 am »

If they have a truly competent RF shop, and know how to use the FCC database (not some manufacturer website) to look at the nearby TV transmitters, I'd give it about an 85% to 90% chance of being problem free without an RF site survey and without a somewhat knowledgeable RF tech to set up the system and confirm performance.

How much is it worth to the production to have near perfect RF performance of 18 mics?
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Henry Cohen
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Kent Thompson

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Re: 18 wireless microphones at once question
« Reply #2 on: April 10, 2010, 01:08:08 pm »

The rental companies seem to be reputable places. One I have talked to personally before. I am not sure whether they have an RF shop or not though. From what I was told they seem to be confident that they can do it. There will be no on site tech only phone support as the distance is too far to send someone. The local sound guy is competent but, not sure of his wireless experience. I suggested they might want to find a local radio tech that could help them.

This is for an annual recital and will be a bunch of kids in a musical skit. So not the end of the world if something goes wrong. I suppose 15% odds are not too bad as long as I am not the one taking the chance. For some reason I always find that 15% first  Confused
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Brian Ehlers

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Re: 18 wireless microphones at once question
« Reply #3 on: April 12, 2010, 01:00:38 pm »

Kent, from you post, I'm not sure if you're saying you will rent all 18 channels from one shop or split the rental between two shops.  If the latter, it is essential that the two shops coordinate the frequency selection with each other.

Henry, would you care to expound at all about "some manufacturer website"?  You don't have to name any names, but I'd like to hear what kind of problems you've experienced (or heard of) when using the manufacturer's recommendations.
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Brad Weber

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Re: 18 wireless microphones at once question
« Reply #4 on: April 12, 2010, 04:03:27 pm »

Henry Cohen wrote on Sat, 10 April 2010 10:36

If they have a truly competent RF shop, and know how to use the FCC database (not some manufacturer website) to look at the nearby TV transmitters, I'd give it about an 85% to 90% chance of being problem free without an RF site survey and without a somewhat knowledgeable RF tech to set up the system and confirm performance.

You probably won't find a better source than Henry for a response to your question.

The one thing I would add is that if they are not told about any existing wireless mic or IEM systems that might also be in use at the same time then the chances of problem free operation could go down significantly.
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Brad Weber
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Keith Shannon

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Re: 18 wireless microphones at once question
« Reply #5 on: April 13, 2010, 06:51:16 pm »

Kent Thompson wrote on Fri, 09 April 2010 21:41

A local performing arts school a family member attends is putting on a show where they want to use 18 wireless microphones. They have contacted 2 rental companies more than 300 miles away to supply said wireless systems. I am a little worried which maybe I shouldn't be but, my experiences with many wireless channels has not been good. What are the chances of a rental company(in Austin Texas or Dallas, Texas) setting the frequencies on 18 units to not only work together but work in the civic auditorium in Harlingen, Texas without issues?


A rental company from Dallas, Texas that can supply you with 18 wireless systems will know what they're doing in terms of frequency coordination. A job like that may just require every available whitespace UHF frequency in the Metroplex, and if they can make it work there they can make it work anywhere. Austin's almost as bad; not as many different markets in such proximity but they'll have their fair share of low-power repeaters and translators.

Most UHF systems of professional caliber have "auto-tuning" features; turn them on, tell them to look for an open channel and they'll perform their own UHF sweep. Then you just leave that one on, fire up the next one and tell it to find an open channel. Rinse and repeat for the rest of em. This is pretty close to fail-safe, but for 18 transmitters it'll take a while, so most outfitters will perform a single UHF scan, or use available FCC data, to pre-pick transmitter frequencies with a few spares in case a couple are too noisy. I very strongly doubt that you will fail to find 18 open UHF frequencies in Far South Texas.
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Lee Buckalew

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Re: 18 wireless microphones at once question
« Reply #6 on: April 14, 2010, 12:51:34 am »

Quote:

Most UHF systems of professional caliber have "auto-tuning" features; turn them on, tell them to look for an open channel and they'll perform their own UHF sweep. Then you just leave that one on, fire up the next one and tell it to find an open channel. Rinse and repeat for the rest of em.


Not quite,
If the units are all in the same frequency range and are not networked so they can communicate with a computer then you need to scan with one unit, choose a frequency group that that unit has found to have enough available frequencies and then tune the others manually or allow scanning but be certain to use the same channel group when you set your frequencies.
Also, it is important that you set your squelch levels the same from unit to unit or one unit may see available frequencies that another unit does not.

His,
Lee Buckalew
Pro Sound Advice, Inc.
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Kent Thompson

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Re: 18 wireless microphones at once question
« Reply #7 on: April 14, 2010, 02:18:20 am »

Just to clear things up the rentals will be from a single shop. One shop is a couple units short so they are supposedly trying to contact another shop in Austin. The Dallas shop I know has a radio shop. The owner was bragging about it so if they go with them I figure the odds are pretty decent. The Austin shop I don't have a clue. There should not be any other wireless happenings going on their clear com system is wired so no issues there and no in ears systems either. The only other issue might be some walky talkies of some sort. There have been several large Broadway plays come in there with lots of wireless so I know it can be done. I just got nervous when I heard how many channels and that things were going to have to be done over the phone if there were issues.

I will make sure to mention that they should inform the shop about any existing wireless that might be present.

Thanks for all the advice as usual this place is a plethora of great information.


P.S Keith you would be surprised how many TV station we have down here Since we are right on the border We have Stations in Mexico to contend with which DO NOT follow US guidelines. There transmitters are poorly maintained and do not always function correctly. Our companies ex 2 way radio shop owner use to complain all the time about it. I bet we have more channels than Austin does when you include all the low power ones and the mexico stations. Then there are the freaking cell phone towers every few blocks :/
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Mac Kerr

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Re: 18 wireless microphones at once question
« Reply #8 on: April 14, 2010, 06:45:37 pm »

Lee Buckalew wrote on Wed, 14 April 2010 00:51

Quote:

Most UHF systems of professional caliber have "auto-tuning" features; turn them on, tell them to look for an open channel and they'll perform their own UHF sweep. Then you just leave that one on, fire up the next one and tell it to find an open channel. Rinse and repeat for the rest of em.


Not quite,
If the units are all in the same frequency range and are not networked so they can communicate with a computer then you need to scan with one unit, choose a frequency group that that unit has found to have enough available frequencies and then tune the others manually or allow scanning but be certain to use the same channel group when you set your frequencies.
Also, it is important that you set your squelch levels the same from unit to unit or one unit may see available frequencies that another unit does not.

His,
Lee Buckalew
Pro Sound Advice, Inc.


While the available frequencies in a particular group are "supposed to be" free of intermodulation artifacts, using intermod software often disagrees with this. It will also be hard to find 18 frequencies in a single group. It will be important that whoever provides the mics, they do a comprehensive RF coordination that includes checking for intermod on all the frequencies, as well as any others that may be in use, like RF comm or IEMs.

Using the "clear channel" method for that many mics is an invitation to disaster.

Mac
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Lee Buckalew

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Re: 18 wireless microphones at once question
« Reply #9 on: April 14, 2010, 08:00:13 pm »

Mac,
I wasn't trying to say that using the built in finder was as good as having proper coordination done.  That said, a decent finder on the 2000 series Sennheiser typically finds me 40 or more useable frequencies in a single band.  IM between transmitters and other factors then can limit this.

I was trying to point out that you don't just want to pick any useable frequency on each receiver separately when you use a scanning feature as you may then pick different groups that will interact with each other.

Hope I explained that better this time.

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Lee Buckalew
Pro Sound Advice, Inc.
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Re: 18 wireless microphones at once question
« Reply #9 on: April 14, 2010, 08:00:13 pm »


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