Powered Signal over Low-Imp snake

[EWCguy]

I'm thinking that it's bad practice to send an amplified signal down a low-impedance snake, but I don't have a reference for such thought. Can someone please point me in the right direction?

We have an 8-ch Whirlwind mic snake, and one of our techs connected an amplifier to one end and a speaker at the other (with various XLR to 1/4 connectors). I wanted to confront him about it but he's the type of guy who will need reference in order to accept that he is wrong. Or, maybe I'm wrong!!

Thanks!

 

[MNicolai]

It's a pretty simple concept at play. The connection between amplifiers and loudspeakers has much more voltage and electrical current than line or mic level signals you'd put onto a mic snake. The wiring isn't meant for those current levels, and if you connect a loudspeaker to a mic snake, it'll probably seem to work okay at low volume levels. That first kick drum hit or loud sound and you'll burn up the conductors in your mic snake.

This is why conductors for driving loudspeakers tend to be anywhere between 16AWG and 8AWG, while those for mic cables are a mere 22AWG. 22AWG is to 8AWG what dental floss is to aircraft cable.

There are other reasons not to try this at home, but the above reason is among the more important ones.

 

[theatricalmatt]

Many audio snakes are designed with both sends and returns, which might lead some into thinking they can handle both microphone and speaker runs at the same time. As MNicolai suggests, look at what gauge cable is being used, and then compare it to the type of cable you would normally use for an individual microphone or speaker signal.

It sounds like this was done for simple ease of use -- ie, rather than have to run another cable. Is there a built-in speaker run in your venue?

 

[WooferHound]

A speaker signal is 1000's of times stronger than a mic signal and will melt a mic cable, plus the chance for crosstalk back into the mic lines is highly possible.
Then there is the very real chance of plugging a microphone or amplifier input onto a speaker line in the snake which would destroy them.

 

[FMEng]

A high current signal in a snake cable is likely to cause cross talk into the mic channels. Balancing and shielding are wonderful things, but they are not 100% effective. The cross talk could cause supersonic oscillation of the system, meaning feedback at a frequency above what you can hear. The result would be blown high frequency drivers with no obvious explanation as to why they failed.

 

[EWCguy]

Is there a built-in speaker run in your venue?

We only have powered runs from the FOH to the stage; high gauge wire terminating at Speakon connectors, from which I run 12g cables to the speakers. Mixer feeds the amps in the booth to drive the speakers on stage. There's a pair dedicated for the house mains, and a pair dedicated to house subwoofers, then 6 more lines on the stage for monitors or proximal sound effects.

I'd love to turn around a couple of the mic lines to send line-level signal down to some powered speakers. That would be nice, but there's no spare lines to convert.

 

[StradivariusBone]

Why not put your amps on stage and use a balanced line in the snake to feed them from your console? I'm not sure I understand your problem if you've got enough copper for your powered runs. You probably would run into issues using your speaker runs as line-level since they're unbalanced.

 

[EWCguy]

Why not put your amps on stage and use a balanced line in the snake to feed them from your console?

Oh yes, that's a good idea, but the distance from booth to stage is longer than our snake can reach (and up a floor). The speaker lines I mention are hard-wired into the building booth to stage, as are 12 mic lines. The snake scenario I described also went through one of those built-in mic lines--which seems ok so far. The setup he used was a temporary turnaround of the connectors, and he could/should have put the amp on stage, but I'm sure he wanted control of the volume from the booth.

 

[FMEng]

If you have enough lines to run speaker level through, you have enough lines to run line level to amps through. The amplifier gains should only need to be adjusted during setup. After that, control volumes from the mixing console.

 

[EWCguy]

If you have enough lines to run speaker level through, you have enough lines to run line level to amps through. The amplifier gains should only need to be adjusted during setup. After that, control volumes from the mixing console.

So, you're suggesting run the line-level signal down the 10g, unshielded copper and putting amps on stage. Hmmmm. I'd have to build some special connectors or swap out the termination, but that sounds possible. Something tells me I should anticipate issues from the unshielded cable, though. Am I following you correctly?

 

[StradivariusBone]

I'm thinking that it's bad practice to send an amplified signal down a low-impedance snake, but I don't have a reference for such thought. Can someone please point me in the right direction?

We have an 8-ch Whirlwind mic snake, and one of our techs connected an amplifier to one end and a speaker at the other (with various XLR to 1/4 connectors). I wanted to confront him about it but he's the type of guy who will need reference in order to accept that he is wrong. Or, maybe I'm wrong!!

Thanks!

I'm still not sure I understand your problem. You're saying the tech put speaker level on a low-z channel which implies a balanced run. Speaker level is not balanced, but if your tech is using a low-z balanced run at speaker level, what's to stop you from putting line level into that same snake channel and putting your amp on stage? Or a powered speaker for that matter? It's already been established that it's not a good idea, why is it not possible to reposition the amp?

You're mentioning controlling the volume from the booth, but like @FMEng said, typically you don't alter the amp attenuation once set. That only affects the input side anyways, how much line level it takes to drive the amp essentially. If you've got a mixer and you're continually setting volume at the amp, that is a woefully incorrect way of operating. If your amp output and your speakers are matched then most of the time I see people running wide open and attenuating at the board. This is tricky though because it does allow the possibility of damaging your speaker and amp. There are other schools of thought with regard to setting attenuation at the amp, but that really depends mostly on what amp/speaker combo you have. I've never seen anyone outside of someone plugging a mic directly into an amp using the input gain to adjust volume on the fly.

Depending on the length of the run, you will garner noise running line level down unbalanced runs.

Can you list out all your input requirements, your output requirements, and the available channels of balanced and unbalanced runs between your desk and the stage? I'm just not picturing this. You said the snake doesn't reach the stage from the booth, but some channels are patched into your hardwired mic lines?

 

[EWCguy]

I'm still not sure I understand your problem.

Thanks for your comments and interest. Really, my problem is the tech running the amplified speaker signal through our balanced, low-impedance building wiring and through the snake he connected to it. I simplified my explanation of the connections because the electrical configuration was ultimately the same.

As to your suggestion of moving the amps and running line-level signal to the stage via that same building wiring and/or the snake, yes, I fully understand and agree with all you are saying. If I had the budget, I would run a few dedicated low-imp lines--wired with the appropriate gender XLR at each end--to serve this purpose. However, I don't. When possible, I could use gender-changing adapters and make use of the existing lines if I don't need them for input. At the moment, I don't have enough adapters to make it easy.

Our amps are mounted in a rack in the control booth about 2 feet from the audio desk. Indeed, we don't adjust the gains on those amps, and someone at some time set them to some "optimal" level that still provides some headroom. Part of the original situation above was that we needed one more amplified signal--this guy chose to set up an outboard amp there in the booth and send that amplified signal, as I said. He had disconnected my solution, whereby I had a separate mixer connected to some localized powered speakers that (I thought) would suffice for the need. He opted to use some different speakers that required the amp. I'm sure he chose to put the amp in the booth out of convenience to himself.

 

[venuetech]

There are snakes designed to do such a thing, such as the Medusa Power Series, made for the typical powered mixer, but they have larger 14ga returns that have additional shielding.
Your guy may have seen such a snake and not realized that it had special construction to accomplish the task at hand.

 

[EWCguy]

There are snakes designed to do such a thing, such as the Medusa Power Series, made for the typical powered mixer, but they have larger 14ga returns that have additional shielding.
Your guy may have seen such a snake and not realized that it had special construction to accomplish the task at hand.

Sounds very plausible. Thanks