I was flicking through my copy of the sound reinforcement handbook (actually looking for something completely different, but it caught my eye) and came across the bit on snakes - and one of the things it warns against is using snakes bidirectionally.

I understand the theory behind it, it explains it well, but practically I've done this loads of times, know of others that do and I've never heard of any problems like that before! In fact I thought it was pretty standard practice - is it? Or is it instead common to run a seperate snake for return feeds like it suggests?

Out of curiousity, what page?

Certainly I've never had a problem doing this and snakes are pretty normally used that way. Other than the normal advice not to use a snake for an amp output to speakers (for obvious reasons) I can't see any problem and have certainly never experienced problems. Thinking about it, multicores in TV and radio installs frequently carry signals going both ways with no problem and this is pretty much the same as using a snake.

Bob

Page 289 - near the bottom on the left hand side.

yeah I see it, in the context they are talking of is that of Amplifier ---- snake----- Speakers...

Excert from S.R

"snakes can save a lot of time in setting up a system, and are certainly neater then a large bundle of cables. They do have drawbacks. For one thing, it is best to avoide using bidirectional snakes in which some line level feeds are sent from the console to the stage. This is sometimes to drive on-stage power amps with the output of the console, but can result in feedback."

so in fact, they are from that cherrypicked statement they are saying do not do this:

Mix L/R ---snake---- on stage amps and speakers.

That's what I initially first thought, but it doesn't sound like it to me, it says:

"This is sometimes done to drive on stage power amps with the output of the console"

Which, in my mind, means Desk --- snake --- amp --- speakers...

yes, hence the bottom of my previous post. (now in bold)

another excerpt

"To avoid this problem, run a seperate snake or mic cables back to the stage from the console..."

how bizzarre, so it begs the question, what do you RETURN down the RETURNs?? if not a line level signal?

I do actually use my returns as balanced line ins (jacks)

You edited after or while I wrote my last post



I understand that, and I understand what the section is saying. At least I think I do! My point is, I've never seen the NEED to run a seperate snake for returns feeds, I've always run it through the same as everything else and I've never experienced any problems with it. I'm not shouting the guys that wrote the book down for it, heck they know far more about this stuff than I ever will, and besides I like to get to grips with the theory even if it may never happen in practice. Instead I'm simply wondering what other people thought, because this is something I thought was pretty much a standard.



I beg to differ, they mention nothing specifically about L/R at all - they just mention the output. The way I interpret it, this sounds like any output going back along the snake to stage.

Keeping a sense of proportion, any decent snake will not be a problem with a mixture of balanced mic and line level signals in either direction. If you feed speakers then expect probems and possibly severe damage!
Brian

Only possibly? More like melted snake innards I would've thought!


It seems like it's just suggesting not using them...

So judging by what people have said so far, I take it this is really a problem just confined to the theory books?

I certainly wouldn't worry about it. It's quite normal to send signals both ways down the multi and to mix mic and line levels in the same multi. If there are unbalanced signals in there, then yes, a problem may arise, but then unbalanced signals have no place in a multi so when used sensibly, I wouldn't envision there ever being a problem.

I can only think that the book reference was considering an overall screen cable - or indeed a mix of balanced and unbalanced signals. The book - although very good - is a few years old now!

Simon

I can only remember one occasion when this was a problem and that was nearly 30 years ago using an unbalanced MM desk probably with a cheap multicore with just an overall screen. There was a high pitched whistle in the PA which changed as the volume on certain channels was changed.

I only remember it because it was one of my first live recordings and the whistle came out all over the recording.

Cheers

James.

In this day and age of sending goods back because you can, if this didn't work, nobody selling a premade multi would ever make any money. Most of these have 8+4, 12+4 up to 32 + 8 - if the returns couldn't be used, they'd not sell many?

You've just jogged my memory; back in those days we had a H|H 16 channel desk, with an H|H multicore, about 30 metres, and it had a very strange cable by modern standards. There were 16 balanced pairs of mic channels, unscreened, and three balanced pairs of returns (L/R/FB) which had their own common screen, then an overall common screen. Worked fine as H|H intended it, but when I tried to send six unbalanced post crossover returns down it went ultarasonic haywire, needing a seperate return multicore...

Never had a problem with balanced signals down a multi where each pair is screened, which is the norm and has been for yonks. I guess Yammie's concern is that the cable will not isolate sensitive mic signals from line level returns which have been amplified by the console, and it'll all go ultrasonic feedbacky like my old thing tried. Ancient history at best.

We've never had crosstalk problems doing this. We also run MIDI (using a Philip Rees line driver) down the snake from stage to FOH, and also a line to control the smoke machine from FOH.

It's a nice VDC snake, so well built with good cable.

w.r.t. speaker levels being returned - you'd be turning the snake into a nice central heating system more than anything else I guess, and losing so much power to the speakers.

Sommer cable do their nautilus stuff, never heard any reviews about it though. That includes 8 (or 12) balanced lines, a pair of speaker level lines back, and mains! Ideal for powered mixer setups, and the cable types inside the snake are appropriate for the level they carry.

Jason