air con causes buzzing in speakers

[the_pasty]

hello everyone,

I've got to go and check out a problem at a recording studio that has a problem with 'buzzing' thru the speakers when the air con is switched on. This problem never occurred before the air con was installed. My first guess is that when it was installed they've layed the power cable too close to the speaker wire causing interference. Does anybody know of anything else that could be the problem that i should be aware of before i go?
Many thanks

 

[ban-all-sheds]

If you can't quickly find an obvious cause like the power cables running alongside signal ones, then make your excuses and leave - getting sucked into an EMI investigation will bankrupt you, unless you're on an open-ended T&M contract...

 

[Adam_151]

Another thing to check for is L/N not summing to zero in cables groups of cables, things like a broken conductor in a ring can cause this, and 'weird rings' in singles (if the phase is taken from one point in the ring , and the neutral from another, this might happen if the ring doubles back on itself and someone doesn't take care to pick 3 corresponding cables... Also the good old borrowed neutral.

 

[stem]

Friend of mine works for a company that designs induction loop systems for use with hearing aids in public buildings and auditoria. The biggest problem they come across is hum that is induced where cables are run singly ie single red (oops brown now) instead of live and neutral together where one cancels the other out.

 

[plugwash]

i've also heared of some aircon equipment having electronic motor control systems with inadequate supression that spew out emi.

 

[martin43]

I would venture to suggest that the problem is more than likely to do with the recording equipment and it's grounding, which may or may not be at earth potential. The usual practice is to provide a technical ground star point which is then connected via a single cable to earth. This should be a suitable rod or plate buried,not the elec supply earth. There are a whole host of earth related problems which can affect induced noise, the more "professional" the studio installation and its equipment is, the easier it is to resolve, but it usually involves a lot of tech earth disconnections. Induced noise due to cable proximity is surprisingly rare except where there is a lot of domestic Hi Fi type equipment.

Regards
Martin

 

[RF Lighting]

You might be better asking this question in the blueroom (which sadly is offline at the moment)

 

[Job_n_knock]

Might I suggest a few anti-surge sockets fitted in the studio. The clean earth suggested above is a good idea. A/C splits arent usually fitted with suppression caps but you can fit them. Im far too old to remember the calcs Im afraid.

 

[Bright_Spark]

there's a piece of audio equipment called a feedback destroyer. its purpose is to help artificially filter any unwanted noise/feedback in the auido set up.

behringer make one. ive used one before and i found them very useful. you could perhaps suggest that. being a set of studio boffs they might even have one...but never thought to try...

the need for a feedback destroyer, grounding of audio equipment and mains/audio wires next to eachother are the main causes of feedback.

if the problem still persists tell them to take their speakers down and check the cross-overs for faults - if theyve skimped and bought a 2 way cross over and attempted to utilise it as a 3 way - that can cause certain amounts of feedback after much use.

 

[ninjacat]

I think Martin43 is onto it.

Please don't use feedback destroyers all they do is harshly cut frequencies - not good for recording. They only workfor lazy monitor engineers in a live situation.

The Blue room is up and running again - post there in the sound forum and there are many good techs who will be happy to advise.

 

[the_pasty]

Thanks for all the replies. I'll let you know the problem (should i find it!)

 

[ACOperson]

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[Moss5]

New Air Con units use 'Inverter' technology'. They vary compressor speed to control refrigerant flow rate.
I bought an inverter to vary the speed of a 3-phase motor and the 'CE' noise control device cost as much as the inverter.
I believe there are known earth-leakage problems with inverters and much expensive effort to overcome the effect.