Problem with Sennheiser G3

M

Matt-btlm

New member
Ran into a big issue on set last week with audio. I'll start by saying that audio is not my specialty by any means, and this particular client calls for me to be a one-man band so I have to look after it myself. That being said I normally have no issues using a Sennheiser G3 wireless system plugged directly into the XLR input of my Canon C100.

Using the same frequency I usually do, and at the same location, I ran into frequent and huge changes in audio levels throughout the recording. Without touching any settings or levels, I watched the levels drop to an inaudible range and also spike way too high on other occasions during the recording. Once I got home I tried to see if I could replicate the issue but everything worked normally in my office. Is this a signal strength or interference issue? There were quite a few people around so not sure if cell phones, etc. may have been causing interference with the signal.

A couple notes of things that may matter:

-We just got a C100 Mark II so the audio was running into that camera instead of the C100 previously, but all settings were identical and no audio issues when testing with other mics

-I use rechargeable batteries with the Sennheiser G3, I've heard this may cause problems in some cases but again I've never had issues previously

-There wasn't ever a total loss of signal, only significant changes in recording levels without anything being touched


Would really appreciate any help with this!
 
Also just because a frequency worked before doesn't mean it is going to work in the future. Even if the big broadcasters are not there you could be getting hit by another wireless mic in the area or??? So you really should check each time.
 
If the RF stays within a limited range and the audio goes up and down, then it is a fault. Interference causes noises. Signal strength reduction increases noise. There's nothing that can lower the audio level, without introducing unwanted artefacts. You need to do some testing to try to localise the problem.
 
As has been said many times in many threads, wireless is a last resort. Not first -- last. If you can use an XLR cable, then use it. Solves these kinds of problems and sounds better in the bargain.

Next, be careful with rechargeable batteries in wireless systems. Most wireless systems are hard on batteries, and want the voltage and discharge rates you get from fresh new alkalines. Rechargeables and less-than-fresh alkalines can cause problems like you've seen.

Finally, always do a frequency scan before using a wireless system. Each and every use. If your favorite frequency is being used already, pick a new, uncontested frequency to use this time.
 
I have never, ever, seen low voltage cause volume to go up and down. It frequently causes RF issues, or early shut down.

Frequency scanning, in my humble opinion is a feature that should never have been introduced, because it doesn't do much more than find you a channel that is at that moment, empty. Proper selection of intermod free channels that most manufactures put in their banks are much better choices when you look for channels. I've had far more problems over the years by people operating on random channels than those working on the common ones.

Sennheisers, are pretty good when it comes to operating properly on slightly lower voltages, caused by failing alkaline, or rechargeables. Random audio ups and downs are a different issue altogether. I have in excess of 30 channels of radio mic systems in my stock, and none exhibit this problem. The only ones that did it in the past both had microphone problems. Both were caused by condensation/water ingress.
 
paulears said:
I have never, ever, seen low voltage cause volume to go up and down. It frequently causes RF issues, or early shut down.

Frequency scanning, in my humble opinion is a feature that should never have been introduced, because it doesn't do much more than find you a channel that is at that moment, empty. Proper selection of intermod free channels that most manufactures put in their banks are much better choices when you look for channels. I've had far more problems over the years by people operating on random channels than those working on the common ones.

Sennheisers, are pretty good when it comes to operating properly on slightly lower voltages, caused by failing alkaline, or rechargeables. Random audio ups and downs are a different issue altogether. I have in excess of 30 channels of radio mic systems in my stock, and none exhibit this problem. The only ones that did it in the past both had microphone problems. Both were caused by condensation/water ingress.
Click to expand...

So the lav mic itself may be damaged and/or malfunctioning?
 
Matt-btlm said:
So the lav mic itself may be damaged and/or malfunctioning?
Click to expand...

I would be suspicious of that, as well as the cable from the lav to the transmitter. I've had to replace hundreds of those wires over the years. The very thin cables used on lavaliers are much more fragile and not as well shielded as traditional mic cables. A hard yank, or coiling it too tightly, or closing it in the lid of a case or something, can easily break enough of the internal strands to cause intermittent problems. These may manifest as crackly noises, total dropouts, level changes, or increased RF interference.

- Greg
 
Audio level shifts has virtually nothing to do with RF problems.
A bad microphone or mic cable on the transmitter would be my #1 suspect with a bullet.
Intermittent problems, especially where that thin cable enters the mic head (or the transmitter connector) are notorious for failure.


Parable: A small, rural town prided itself in getting together a respectable number of singers and instruments to do Handel: Messiah every Christmas.
The singers and players were a rag-tag bunch of local farmers, shop-keepers, etc. Some were rather predictably cantankerous like old Bob who played double-bass.
Just as the director was stepping onto the apple-crate to give the down-beat for the first rehearsal, old Bob comes rushing in with his big bass.
The director waits while Bob hurriedly gets the instrument out, and grabs his bow, nodding that he is ready to play.
The director, incredulous, says: "Bob! Aren't you going to tune that thing?"
Bob replies: "Why? Isn't it in the same key as last year?"

In many places, usable wireless channels vary from hour-to-hour. You can NEVER assume that a channel is OK just because it was clear "last time".

Note also that rechargable batteries, even when FULLY CHARGED, have only as much output voltage as a well-used primary cell.
So most wireless equipment sees even a new, fully-charged battery as nearly-depleted.
 
The g3 are designed to be able to run a reasonable amount of time on decent condition and charge nimh cells, we get more than 8 hours run time in our studio per set of nimh batteries. That said, I may still buy the Sennheiser lithium battery pack and chargers.

And I agree with the others, you have a failure somewhere that could be a simple as the mic capsule being dropped one to manys times onto a hard object. If it was the cheap stock mic that comes with the transmitters, then I would look at the connector at the end of the cable, we've had a number of these break with intermittent results like you are seeing.
 
Did I understand correctly you to say that this was the first shoot with a new camera? Could it be the audio level control was left in 'auto' instead of being switched to manual? Audio level pumping can occur when automatic gain is used.
 
I concur, level changes are typically not symptoms of RF interference.
I would suspect the 'new' camera and/or connection is the problem. Lav microphone cable/connector issues usually produce static, pops, or no signal at all.
I've never had issues with rechargeable batteries.. except when they crap out, but the same can happen with any batt.

OT: " (G2/3) Frequency scanning, in my humble opinion is a feature that should never have been introduced"
+11
 
Guys, thanks for everyone's suggestions and help. Sounds like a lav mic problem of some kind is most likely, the camera was definitely on manual mode during the shoot. I have a second G3 system that doesn't get used as much so I will try that and see if I can isolate the problem.
 
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