Lav mics?

[Chuck Simon]

I will start out by saying I have very little experience with lavalier mics. I recently got a Line 6 LM4T lav mic to use with my G55 belt pac for a specific gig I have coming up and I am very dissappointed with it. It seems you have to talk almost directly into it to get any usable signal. Is this the nature of the beast or are there better choices I should consider for use with my existing system(TA4F connector). My choices are limited to dynamic mics(?) unless someone makes a lav mic with a battery that uses the TA4F connector. Is there such a creature?

 

[Art Welter]

Re: Lav mics?

I will start out by saying I have very little experience with lavalier mics. I recently got a Line 6 LM4T lav mic to use with my G55 belt pac for a specific gig I have coming up and I am very dissappointed with it. It seems you have to talk almost directly into it to get any usable signal. Is this the nature of the beast or are there better choices I should consider for use with my existing system(TA4F connector). My choices are limited to dynamic mics(?) unless someone makes a lav mic with a battery that uses the TA4F connector. Is there such a creature?

Chuck,

Your Line 6 LM4T lav mic is a condenser mic, using phantom power from the beltpack. It is also cardioid, often not an improvement over an omni if the mic is chest worn.
Lav mics have small diaphragms, so are inversely proportionally less sensitive (less output) than larger diaphragms.

Dynamic mics are generally less sensitive than condenser mics, but all mics adhere to the inverse distance law: double the distance, loose 6 dB.
Talking "directly into it", say .5 inch,= "0" dBM, at 1 inch -6dBM, 2 inch -12 dBM, 4 inch -18 dBM, 8 inch -24 dBM, 16 inch -32 dBM.

If there are gain (or attenuation) controls in the belt pack, they have to be set to a much higher (or less attenuation) gain setting to work for a chest mounted lav than a headset lav or hand held mic, or the signal to noise ratio will be very poor.

Also, be aware the inverse distance law directly relates to gain before feedback and signal to noise ratio, at 16 inches the mic has 32 dB less gain before feedback, and will pick up room (and electrical interference) noise 32 dB more than if held at 1/2 inch. 24-32 dB less output is a huge difference, it only takes a 10 dB drop to sound half as loud.

The first time I had to use lav mics outside with adjacent stages, I quickly found the only way to get the (weak voiced) presenters audible was to make a "headset" out of a piece of wire and tape the mic on..

I did not find the sensitivity specifications of the Line 6 LM4T, but if you find microphones with better sensitivity specs (and smoother response curves) you might eek a bit more gain, but best insert a 1/3 octave EQ or parametric on the channel if your board does not have extensive channel EQ for whatever lav you use.
Chest resonances and feedback are not pretty..


Art

 

[Chuck Simon]

Re: Lav mics?

Thanks, Art. Since my original post I have talked to Line 6 and they confirmed that, as you have said, the LM4T is a condenser and the G55 will supply phantom power. I guess I just need a more sensitive mic. Any suggestions? Would a omni mic work better as a lav mic?

 

[Eric Snodgrass]

Re: Lav mics?

Thanks, Art. Since my original post I have talked to Line 6 and they confirmed that, as you have said, the LM4T is a condenser and the G55 will supply phantom power. I guess I just need a more sensitive mic. Any suggestions? Would a omni mic work better as a lav mic?

It depends on how you use them and where you are using them.
In my experience omni capsules generally sound better than cardioid capsules on lav mics, but GBF is a consideration for me when I can choose between the two patterns. In certain situations I definitely sacrifice the slightly better sound of an omni capsule for the boost in GBF that can come with a cardioid capsule, and this goes for chest-worn or head-worn lavs or even headset mics. You must choose the type of lav based on your mixing environment and intended usage.

With your Line 6 packs, have you adjusted the gain on the pack for more output?

 

[Robert Lofgren]

Re: Lav mics?

With your Line 6 packs, have you adjusted the gain on the pack for more output?

The line6 packs doesn't have any gain adjust.

The packs are designed so that it "emulates" a cable. I.e. 100mV input on the pack produces 100mV on the reciever.

According to line6 the dynamic range of the system allows for instrument levels up to line levels (6 Vpp?) so no gain adjustment needs to be done on the pack side and the mixer operates it's headamp as normal.

 

[Eric Snodgrass]

Re: Lav mics?

The line6 packs doesn't have any gain adjust.

The packs are designed so that it "emulates" a cable. I.e. 100mV input on the pack produces 100mV on the reciever.

According to line6 the dynamic range of the system allows for instrument levels up to line levels (6 Vpp?) so no gain adjustment needs to be done on the pack side and the mixer operates it's headamp as normal.

That's interesting. I have no working experience with these Line 6 wireless systems. Have there been any pitfalls to this design?

 

[Art Welter]

Re: Lav mics?

Thanks, Art. Since my original post I have talked to Line 6 and they confirmed that, as you have said, the LM4T is a condenser and the G55 will supply phantom power. I guess I just need a more sensitive mic. Any suggestions? Would a omni mic work better as a lav mic?

If you don't hear the mic self noise (mostly "hiss") over room noise, sensitivity is not a problem.
If actual mic self noise is not a problem you don't need a more sensitive mic, you simply need to turn up the gain on the console.

An omni mic has the advantage of being largely unaffected by mounting position, and generally smoother frequency response.
A cardioid can give better gain before feedback if mounted correctly, but can be very bad if the capsule gets turned sideways or pointed down, or if folds of clothing "cup" the mic.

"According to line6 the dynamic range of the system allows for instrument levels up to line levels (6 Vpp?) so no gain adjustment needs to be done on the pack side and the mixer operates it's headamp as normal."

Problem with this approach is poor signal to noise for low level inputs, such as a chest worn lav, where the gain should be at the source, not after the RF section.
It simplifies the design of the transmitter, and is a good idea for guitars with active pre amps and such, but not for lavs.

 

[Robert Lofgren]

Re: Lav mics?

"According to line6 the dynamic range of the system allows for instrument levels up to line levels (6 Vpp?) so no gain adjustment needs to be done on the pack side and the mixer operates it's headamp as normal."

Problem with this approach is poor signal to noise for low level inputs, such as a chest worn lav, where the gain should be at the source, not after the RF section.
It simplifies the design of the transmitter, and is a good idea for guitars with active pre amps and such, but not for lavs.

While true for analog systems this isn't really an issue with digital systems since the digital path shouldn't introduce any noticable noise.

Line6 are saying, if your mic can be used connected directly to your mixer then it will work with the line6 system as well and there should be no noticable difference.

If they have used the same approach as in their pods, the the stereo a/d converter (the input source is mono) is wired in a way to accomodate for two input level ranges seemlessly...