Audio Compatability

[Beastly]

Apologies if this amounts to a really stupid question but I have recently been given responsibility for the audio system in a new school theatre and wanted to know if I'm barking up the wrong tree trying to get different systems to speak to each other...

 

I have inherited some Kam KBP UHFA wireless packs with transmitters and various mic attachments. The new theatre has been fitted with a Smart Wireless TurboX system ( a brand I know nothing of), and I have myself some Sennheiser EW500 and 550's which I have to add to the mix. I assumed that the smartwireless receivers which are plumbed into the main system and desk, and which have many selectable frequencies and channels should be able to receive transmissions from the other brands as long as they transmit to the same chosen frequency, and as long as the frequencies are far enough apart not to interfere and there's only one item transmitting on that channel and frequency. But for some reason the Smart wireless LED's seems to peak when you connect either of the other two transmission sets but won't actually pick up the transmission.

 

Am I being really stupid or do I have to plumb in each set of receivers and play musical XLR's on the back of the desk when we want to use different kit?

 

Thanks if you can help

 

Steve

[paulears]

mixing and matching can work really well, or be a disaster - and you can't predict what will happen.

 

In simple terms, setting a frequency that is the same on both usually makes something happen. Some receivers need a pilot tone, but like with Sennheiser, you can turn the feature on or off. However - there is another parameter you can't tweak - bandwidth. A signal that reaches the peak of the transmitters maximum will have a deviation component, away from the centre frequency - and this is not the same for every piece of kit. On top of this, radio systems have a poorer signal to noise ratio than a piece of cable, by a long way - so the manufacturers tend to use companding to squeeze the best performance from their kit. So the audio is compressed for transmission, then expanded back in the receiver. This has the useful effect of lowering the noise on the signal. Again, this ratio of compression and expansion is different for each make - some cheap units cutting it out altogether! So - you can mix and match, but the results could be very unpleasant when the characteristics clash. I use Trantec and Sennheiser G2 systems and a few years ago had a rack of Trantec 4000 receivers already wired in, and for an experiment I tried the Sennheiser transmitters. There seems to be a little bit of extra compression, and the sound is a little 'warmer' - I actually liked the sound, so have been deliberately running like this. However, the trantecs on the sennheiser receivers have a rather 'brittle' sound and the wrong compression works the other way making feedback more likely - and the sound needs pretty harsh eq to sound nice.

 

John Willetts at Sennheiser always tells people NOT to do the mixing of kit, and I think in general he's correct to say this - my experience was just a lucky accident, not something that could be guaranteed.

[Bobbsy]

My experience mirrors that of Paulears...but without the lucky accident side of things. Early attempts to mix and match receivers were disastrous enough that I stopped bothering to try.

 

Besides the frequencies used (and different channel spacings can mean that it can be difficult to tune to exactly the right frequency) different manufacturers can use a different FM deviation standard and differing companding schemes. Also, the extra data being transmitted (TX pack battery info for example) is different from manufacturer to manufacurer.

 

All this adds up to it being a major lottery whether or not you get acceptable results when you mix RX and TX gear from different companies--or even different ranges from the same company. Like any lottery, the odds are stacked against you.

 

Bob