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[Mark Croushorn]

I run sound for our church and I ran into a very strange problem yesterday that I have never seen before.  We had just connected an iPhone 4S to run some pre-service music and on the board we had the iPhone channel and our wireless mic channel open.  Then we suddenly got a huge, loud burst of static through the mains and as I looked at the board the peak indicator was lit on the wireless channel.  Muting that channel killed the sound but when we turned it back on we got another similar burst of static a few seconds later.  With the wireless channel muted I looked at our wireless receiver and it was indicating a low level of signal going in to the receiver continuously and every so often it would spike to max signal for a bit and then go back to just a low level signal.  The kicker is that the wireless mic was completely powered off during this entire time.

We run an XLR straight from our receiver to our board and so I checked the connections there and also checked the power connection into the receiver and into our power conditioner.  All of the connections seemed to be good.

At this point we had to get our service started so we just left the wireless channel muted on the board and turned the music off on the iPhone.  We still didn't really have a solution but after observing things for a few minutes it looked like the problem cleared itself up and we ended up being able to use the mic throughout the rest of the service with absolutely no problems.  The low level continuous signal no longer showed up on the receiver at this point.

I have done some research online and read that smartphones can cause interference with wireless microphones.  I listened to a couple of clips that people had posted of what they called interference from a phone and it was kind of a weedle-weedle-weedle noise and not really the all out burst of static that we experienced that caused the channel on the board to clip.  But the iPhone was the only thing that I could tell that had been introduced into our sound environment that was different than normal and it was sitting on the edge of our board.  Typically we play music from either an iPod or an iPad and so usually we don't have a phone in the mix.  Does anybody have any experience with anything like this?

We were not using Phantom power.  I checked and the antennae were not touching each other or anything else.  Admittedly power is kind of strange in our building but to the best of our ability we have isolated the lights and the audio from each other though that was done before I came to this church so I don't actually know for sure that they are.

We use a Yamaha MG 32/14fx board.  We are using a Sennheiser Wireless Mic.  I don't know for sure the exact model that we have but it looks like the Sennheiser EW145.  http://www.mrgadget.com.au/2007/11/wireless-microphone-sennheiser-ew145.html for a picture of the model.  We are running JBL passive mains and JBL powered subs.  We are using a Crown Amp to power our mains.  We are utilizing a snake that I don't know the name of off of the top of my head.  We are in a venue that can seat ~150 people.  We have fairly minimal processing equipment that we use other than your basic graphic eq processor (I guess that is what you would call it).  I can definitely get more details about our equipment but this is all the info that I know off the top of my head.

Thanks so much for any insight that you can offer!

Mark Croushorn

[Jacob Robinson]

Sounds to me like you are getting wireless interference, and the iPhone was just a coincidence.  We had a similar problem at my former church, randomly (usually during the quietest part of the service) we would get the most frightening loud sound and it ended up being that, for some reason the transmitting frequency we had been using for years was no longer clear.  Make sure you are well clear of the 700MHz range and you can also use your zip code to find good clear frequencies in your area.

If it is the same problem I had, a higher squelch setting might help keep weak rogue transmissions from causing the problem.  You may also find that as long as the microphone transmitter is powered on you will never have this happen because the receiver always has the strong signal of the microphone to drown out other noise in the spectrum.  But then when you turn off the transmitter and leave the receiver powered up (not uncommon) ALL BETS ARE OFF.


See my thread here: http://forums.prosoundweb.com/index.php/topic,135875.msg1270518.html#msg1270518

[Mac Kerr]

The kicker is that the wireless mic was completely powered off during this entire time.

Whether the interference was from the iPhone or some other source, here is an important piece of advice about RF mics: Do not leave the fader open with the transmitter turned off!

When the receiver is locked onto the transmitter you will have much less chance of spurious RF breaking through. When the transmitter is turned off the receiver is wide open to any RF signal. If you continue to get the interference with the transmitter on you may want to increase the squelch, and check the RF signal path from the mic to the receiver.

Mac

[Tommy Peel]

I ran into this at a church where I regularly run sound in their youth room. They have 5 Sennheiser wireless systems(4 handheld and 1 belt pack for acoustic guitar). When I first started doing sound there they were having the same kind of noise when the transmitters were switched off; I found open channels, reprogramed all of them, and they all work fine now. If the AF meter is getting much signal while the transmitter is off or the signal is fluctuating more than other receivers you probably have a TV station or something eles causing interference. Anyway that's my 2¢, but I'm far from an expert.

Tommy Peel

[brian maddox]

Sounds to me like you are getting wireless interference, and the iPhone was just a coincidence.  We had a similar problem at my former church, randomly (usually during the quietest part of the service) we would get the most frightening loud sound and it ended up being that, for some reason the transmitting frequency we had been using for years was no longer clear.  Make sure you are well clear of the 700MHz range and you can also use your zip code to find good clear frequencies in your area.

just wanted to emphasize this point.  If your microphone operates in the range between 698 Mhz and 802 Mhz, it is operating in a range that is no longer legal to operate wireless microphones.  Aside from the legalities, what this means is that that frequency spectrum could be used by powerful transmitters in your area for Cellular phones or the like, which can come and go at random and cause exactly the issues you are experiencing.

For sure the iPhone is unrelated to the problem.  But you've clearly got something stepping on that frequency, and you need to find a clearer frequency to operate on.

[Mark Croushorn]

Thanks for all the responses folks.  I didn't know about leaving the transmitter off but the channel open causing problems but will definitely make sure not to do that anymore.

I'll definitely look into changing frequencies as well.  I will have to check but I believe that we are currently running around the 630 to 650 range.

[AllenDeneau]

Whether the interference was from the iPhone or some other source, here is an important piece of advice about RF mics: Do not leave the fader open with the transmitter turned off!

When the receiver is locked onto the transmitter you will have much less chance of spurious RF breaking through. When the transmitter is turned off the receiver is wide open to any RF signal. If you continue to get the interference with the transmitter on you may want to increase the squelch, and check the RF signal path from the mic to the receiver.

Mac

I agree 100% with Mac.. Mic transmitter in the off position = channel muted...

You ahve to remember, wireless receivers are looking for ANY signal it can find so if your transmitter was off and the receiver was open it was/is very succeptable to interference from any number of things...

Use this tool to help make sure you are operating on a good frequency as well as to see what's broadcasting in your area that may be an issue: http://en-us.sennheiser.com/service-support/frequency-finder It'll show you the best frequencies to use and what's broadcasting in your area, well anything FCC licensed at least. Even if somone is in the adjacent buidling, and there's any distance between you, if they're using a frequency within your group, you'll most likely not have any issues even though they're not listed on the sennheiser page. Remember, wireless mics are operating on white space which is "borrowed space" and aren't subject to licensure.

When I have the "choice" or "control", I prefer anytime we are in pre-service or during service, I like to have anyone on stage with a wireless to have them powered on at ALL times. When they're not in use, I'll mute them at the board.

This ensures a few things;
I can monitor the battery level in the transmiter (given you have the option on your wireless) No "forgetting" to turn it on before they speak then look at me like it's my fault
Reduces the possibility of interference but most importantly (when in a metro area) it ensures that the frequencies I am using "stay" mine unless a TV or radio station just happens to fire up and drowns me out..

If your transmitters are on and paired to their receivers, unless you get someone right next door with a HUGE FCC permitted transmiter, most devices won't interfere with your frequencies.. If your transmitters are off other wireless decives can encroach on your bandwidth and when you do turn on the transmitter, you may have issues..

I'd bet the iPhone had nothing do do with the static bursts, it was just a coincidence. More than likely, you caught some random RF interference breaking through since your receiver was actively looking for a signal and your transmitter was "resting"..

Good luck.

[Mark McFarlane]

I'm fairly new to using wireless mics, I've happily avoided them.

I had this same problem 2 weeks ago when I powered down a mic on stage during setup.  Luckily only the catering crew was around.  The immediate fix was to turn the squelch up a little.  The real fix was to find a clear range of frequencies.  I was in a 'secure facility' at the edge of an airbase. Lots of new RF sources. 

The event made me very happy that I spent a few extra bucks to buy a G3 300 series Sennheiser system that has a built-in scanner with display on an attached laptop. 2 minutes for a frequency scan and voila, I found a few open slots and was back in business with a smile on my face

[AllenDeneau]

I'm fairly new to using wireless mics, I've happily avoided them.

I had this same problem 2 weeks ago when I powered down a mic on stage during setup.  Luckily only the catering crew was around.  The immediate fix was to turn the squelch up a little.  The real fix was to find a clear range of frequencies.  I was in a 'secure facility' at the edge of an airbase. Lots of new RF sources. 

The event made me very happy that I spent a few extra bucks to buy a G3 300 series Sennheiser system that has a built-in scanner with display on an attached laptop. 2 minutes for a frequency scan and voila, I found a few open slots and was back in business with a smile on my face

Mark, that's exactly what I was talking about... Once I have my frequencies, I keep things powered on, if I'm in an area or event that may have transient wireless usage, so I don't lose my frequencies. I haven't yet, but need to invest in one of the frequency scanner devices or software to keep an eye on things. It can get really tricky downtown Chicago, when I'm back there..

[Scott Wagner]

I haven't yet, but need to invest in one of the frequency scanner devices or software to keep an eye on things. It can get really tricky downtown Chicago, when I'm back there..

Things can get tricky in Nashville, too.

[Bob Nafzinger]

Brian is right...(just wanted to emphasize this point.  If your microphone operates in the range between 698 Mhz and 802 Mhz, it is operating in a range that is no longer legal to operate wireless microphones)

We have the same issue and it's from iphones.  Once these frequencies were taken from our wireless systems it was given to Mobile Phone providers.  We put the receivers by the stage and then had less of a problem.  We also  put up a slide to ask people to "Turn off Phones"

[AllenDeneau]

Brian is right...(just wanted to emphasize this point.  If your microphone operates in the range between 698 Mhz and 802 Mhz, it is operating in a range that is no longer legal to operate wireless microphones)

We have the same issue and it's from iphones.  Once these frequencies were taken from our wireless systems it was given to Mobile Phone providers.  We put the receivers by the stage and then had less of a problem.  We also  put up a slide to ask people to "Turn off Phones"

It can't be stressed enough that not only is it difficult to use these frequencies, it is absolutely illegal and very costly WHEN they find you. Not saying that's the OP's problem but it deserves to be repeated.

As far as mobile phones being the issue, I really couldn't tell you. Part of that big block of frequencies that was sold by the FCC will/is going to mobile device usage BUT, it shouldn't be an issue, for now, because they're within their frequency range and we're not. NOW, RF interference and overall signal saturation and bombardment, that's a whole different story.

Anytime you can put the receivers within the area where the transmitters are located it's going to give you an optimal signal, as long as there's a good line of sight. When it comes to wireless, strongest signal wins and if your device and another device both put out 30mW but your transmitter is closer, you win..

Things can get tricky in Nashville, too.

Absolutely, fortunately it's not as bad as Chicago but it's still fun especially when channel 5 has petitioned, and won, the right to up their power. When I moved here in 2011, my H5 frequency band was 100% clear, all of the sudden, I lost 2 presets as channel 5 got "more power, argh argh argh".

It is always fun to be in the Sears (Willis) Tower and try to use wireless, you can usually get one part of the room to work or another but rarely both since you're only 20' below 2 of the largest radio transmitters in North America... If you have powered speakers you can plug a 25', quality sheilded, XLR cable into the speaker and leave the other end unplugged, when you power it on you can literally lissten to B96 Radio

Drury Lane Theater was fun too. Serious wireless coordination necessary there too. 5 banquet rooms PLUS a theater just down the hallway, quite easy to lost a frequency once you power down.

Then there's Soldier Field during game day. Over 300 wireless units in play at any time. Once we're assigned a frequency, it's ours and our alone but sometimes finding a slot big enough for us can be a trip. NFL wireless frequency coordinator is a job I'd never want..

I haven't yet had that experience in Nashville yet, but I'm sure it's a possibility.

[ProSoundWeb Community]