Gain before Feedback with radio mics

[Keith_]

Here is one that I find surprizingly puzzling and may draw out some good advice.

I can plug a Sennheiser MD46 (nice mic) direct into the back of mixer amp (or into a mixer / amp setup) and get pretty good gain before feedback (GBF). Using the same mic in the same position etc. feeding a SKP100 radio mic transmitter with EW100 receiver plugged into the back of the amp (etc.) the GBF is awful. I have tried this with different bits of kit all the way through the system - the effect is always the same: cable from the mic is fine, radio link dreadful. Any ideas ?

Note - no eq or dynamic processing, nothing other than switching between radio and mic cable and I mean GBF, so gain itself is not the issue. I can, of course, fiddle with eq and the compressor gate and feedback destroyer and all that stuff, but the point is I don't need to with the cable connection and actually I can not get the wireless to be anything like as good GBF.

Stumped.

Thanks,

K.

[J Pearce]

Analogue wireless will use companding (it compresses going into the wireless link, then expands coming out) to get a better through dynamic range than the radio link could otherwise realise.

The ew100 is the cheapest of the Sennheiser EW range, and this may mean the companding isn't as good as EW500, and definitely won't be as good as 2000 series or a more modern digital link which won't use companding.

To get the best out of the companding you do need to set a good gain structure through the wireless setup, so check that you've got a sensible gain on the transmitter. If you have a different SKP100 it wouldn't be silly to try swapping it out, your current one may be faulty.

[Keith_]

Good point, JP. I have tried a different rx and tx, but it was just another SKIP and EW100 pair (that's all I have). I will look at lowering the AF output on both tx and rx - there is plenty of room for that. By the way, the RF carrier is super strong.

Thanks,

Keith.

[richardash1981]

As said, you are putting a compressor then an expander in the path, and they are supposed to cancel each other out. The various older beltpacks I measured (with a sequence of stepped amplitude tones) didn't - they all had quite a lot of residual compression end to end, so the gain came up when signal was low and dropped when the signal was high (I didn't have any Sennheiser kit to test). This will of course make (effective) gain before feedback worse, which could be countered using further expansion at the console to drive down the gain at low signal levels.

I don't know why things would be set up that way, except that it does make it pretty hard to actually clip the RF link, because somewhat too-hot inputs just end up riding on the compressor curve (I presume at the beltpack end) rather than clipping the RF. It does mean (at least on the Trantec receiver I was using) that by the time the audio peak lamp comes on, you are substantially compressing the signal!

[Keith_]

Sure, I will try a bit of expansion and different combinations of sensitivity and gain at tx and rx end. I will let all here know how it works out. Right now kit has just come back from a morning in the rain, so it's getting some warm dry kindness.

One day I might be able to afford better stuff 😉.

Thanks.