microphone sensitivity

[numberwrong]

Hi

 

What level do I need to set the beltback sensitivity on a Sennheiser EW300 G3 kit with a tie mic?

 

Is it a calculation based on what mic is being used or does it vary depending on environment, the loudness of the speakers voice etc.?

 

I am thinking about use live applications but I have heard mics distort in the past which I think would be down to the sensitivity settings? If so why not lower the sensitivity to minimum so this can't happen and turn it up on the desk assuming you're not running in to the red.

 

any pointers?

 

Thanks

[Shez]

There really isn't any calculation involved. You set the gain in much the same way that you set the pre-amp gain on a desk channel - send in the appropriate level and set the gain according to the level showing on the meter, allowing for an appropriate amount of headroom.

With headset mics, I always end up with the gain on its lowest setting; with tieclips, it depends a little on the context. Someone who's used to projecting will need less than someone who's going to mumble their way through. If in doubt, err on the low side - a bit of background noise is far preferable to distortion.

[Bazz339]

Hi

 

Is it a calculation based on what mic is being used or does it vary depending on environment, the loudness of the speakers voice etc.?

 

any pointers?

 

Thanks

 

There is no set way, and it varies with person using the mic, the mic type and application.

 

If the mic kit is used predominantly for speech it is usually possible to set the TX mic sensitive to a level that works for all speakers. You might need to decrease the sensitivity on a specific pack if you have an exceptionally loud speaker. We had Brian Blessed once and I should have definitely turned the sensitivity down.

 

If the use is singing with a tie clip mic then you may find you have to reduce the sensitivy slightly and if using the actual performer be aware that you often don't get the level of them in a sound check that you will when an audience is in. You will almost certainly have to reduce the sensitivity if using head mic.

 

I set the level such that the meter is moving positively but not likel to peak even on the loudest notes/speech. Signal to noise on modern kit is not usually a problem so in my opinion there is no need to push the level into the transmitter too much, it is also easier to give a bit more gain further down the line if it is too quiet, but impossible to alter the TX input gain until a break if it is set too high.

[numberwrong]

Thanks for your advise -

 

Dose an increase in sensitivity make the system more susceptible to feedback at all? assuming the level was reduced further down the line to compensate

[Shez]

Feedback is a function of the system loop gain. If you add 10dB of gain at one point and then 10dB of attenuation at another, the loop gain (and hence potential gain before feedback) stays the same. Optimising the gain structure is about avoiding excess noise / distortion.

[Rob_Beech]

However, to continue on from what shez says. If we look at the sensitivity from another angle. When you have this too high, you overload the input. The input volume can get no higher, it is like a compressor or limiter. Sennheiser stuff IMO does a MUCH better job at this than it's competitors. However, do bare in mind that as you cross that bridge between getting louder and not (limiting) if the level NEEDS to be louder still and you turn up the fader, when the voice quietens down again you run into 2 problems.

 

Firstly, the quieter parts are now louder as you've turned it up, so you'll need to turn it down again, and secondly, you have created a potential feedback nightmare. As with a compressor, when the input level is high, it's compressing and reducing the gain. When the input signal is low, the gain is back to normal. If you turn the OUTPUT up as you've overloaded the input (from too high sensitivity) then when the limiter releases you run closer towards feedback. Which if you're already limited on gain before feedback might just send things over the edge.

 

I've found with headsets then the lower the better. -30dB would be a maximum. The G3 packs are great for their ability to go below -30dB. The older packs, and handhelds that only go down to -30dB are only just enough. It is only the well behaved compression with the kit that stops it being a problem like its competitors.

 

They're not particularly noisy, so you're not going to get much trouble with a lower setting.

 

A simple answer to this would be as follows. "Having a sensitivity set above -30dB is about as much use as tits on a fish. "

 

 

Rob

[Bobbsy]

...and another reason for using a low sensitivity setting (at least on multiple RF systems) is that the input level determines the FM deviation up to a certain preset amount. Now, in a decent radio mic system even maximum deviation shouldn't interfere with adjacent channels but, in the real world, RF filters aren't perfect and transmitting everything at high deviation is a recipe for interference between transmitters.