Balanced 1/4" Necessary for Line Level Signal?

[DJNOBS]

The owner of the club where I do sound purchased a subwoofer. The club often has DJ's who in the past blew out the woofers of the monitors trying to get their beloved bass out of the system. The owner and I decide to take the Aux 2 send of the board into the sub instead of the actual "Sub Out 75 Hz" so that anyone mixing could choose which instruments go to the sub and adjust how much of the sub they actually want used.

This arrangement is good for me as I can then just send kick and bass to the sub instead of the entire mix, which can get quite loud and crowded as it is (it's a small club). So because we're goint out of the auxiliary send (1/4" balanced out) and the input to the sub is 1/4" (balanced in), I tell the owner to just purchase a 50' 1/4" to 1/4" cable. While at the store they tell him it HAS to be a balanced cable or else the signal will drop, you'll lose frequency information, and it might pick up interference. They didn't have a balanced 1/4" to 1/4" cable at that length, so they sell him a 50' XLR cable with an XLR to 1/4" adapters for each end, which added to the bill.

I understand that running cables, especially unbalanced cables, for a decent length does run the risk of picking up interference and reducing level and tone. But my understanding was that line level signals were sufficiently hot enough to be mostly unaffected by interference. Also, even if the signal did lose some high end, my opinion is that the subwoofer input has a LPF cutting off everything above 100 Hz anyway, so there would be no audible difference. The other thing that bothers me is that with these adapters now there is more risk for something to become unplugged in the middle of a show without easy access to hunt down the problem.

Did the store just try to sell this club owner (who doesn't pretend to say he understands much about audio) more crap, or is there a real benefit to keeping everything balanced in this case? Thanks for your thoughts.

[JohnRoberts]

You don't need a true balanced signal interface, as much as a differential audio input at the receiving end and 3 circuit wiring (+,-, and ground) between source and destination, to keep signal ground reference separated from power grounds.

Single ended audio is generally tolerated for very short runs like to and from console insert jacks to nearby effects units, but for longer runs, between gear that may be plugged into different outlets, differential wiring is good practice.

This could be accomplished by adding an isolation transformer at the far end. A full balanced interface is perhaps more than you need but not completely wasted.

JR

[paully]

Short of doing what John suggests(all good), the important thing is to make sure the sub amp's AC power is coming from the same breaker(and preferably the same outlet) as the house power amps.. even if it means running a 3 wire AC extention cord back to the booth. These ARE available in 50' lengths .

The store made valid points, just not necessarily applicable to your situation. I'd certainly try what you suggested first. All your points are valid. You're probably going to end up making your own cable. Use quality wire and plugs with metal shields. Any elecronics or TV repair shop can also do the job. JMHO.

Best, Paul

[nosebleedaudio]

If you use a transformer to balance the output I would have it at the console end, that way your long run is balanced.

[JohnRoberts]

For the record I am not suggesting the OP add a transformer, only that it is one way to differential the signal at the receiving end, and a possible after the fact band-aid.

True balanced sends are useful over long distances to insure noise pickup is symmetrical so it can be mathematically subtracted out later. A balanced isolation transformer output sending to a single ended input will A) not benefit from cancellation at the receiver, and B) will be unbalanced anyhow by the single ended termination so noise pickup will not be equal in both lines.

We are making this more complicated than needed. For line level sends, noise "pickup" is not the largest issue, signal ground integrity is. The OP will likely benefit from the more expensive option offered by the music store. The music store will also benefit but it is not IMO a salesman piling on. Now the extended warranty, and other BS may fit that description.

JR

[nosebleedaudio]

Originally Posted by JohnRoberts

For the record I am not suggesting the OP add a transformer, only that it is one way to differential the signal at the receiving end, and a possible after the fact band-aid.

True balanced sends are useful over long distances to insure noise pickup is symmetrical so it can be mathematically subtracted out later. A balanced isolation transformer output sending to a single ended input will A) not benefit from cancellation at the receiver, and B) will be unbalanced anyhow by the single ended termination so noise pickup will not be equal in both lines.



JR

But he mentioned the sub has a balanced input...
And yes we may be in the overkill mode, it is in a LIVE situation, so dead quiet may not be a issue...

[paully]

Originally Posted by nosebleedaudio

But he mentioned the sub has a balanced input...
And yes we may be in the overkill mode, it is in a LIVE situation, so dead quiet may not be a issue...

>>>>>>>>>>>>>>>>
Hmm.. I missed that balanced input reference. Don't know what The OP bought, but for a grab and go solution I'd buy one of these Shure - Accessories - A85F Line Matching Transformer , connect it with a long XLR mic-type cable, and terminate with one of these Audiogear.com . Probably similar to what the music store provided.

Best, Paul

[JohnRoberts]

Connecting a 1/4" balanced output (3 circuit) to a 1/4" balanced input (3 circuit) with 2 circuit wiring is defeating the functionality designed into the electronics at both ends. While it may pass signal with 2 circuit wiring, how well depends on how the send end tolerates being shorted, and ground potentials between the two locations. The modest saving is wire cost is IMO a false economy.

I have not seen too many 1/4 balanced inputs that were true balanced, but even if it is only TRS differential, the store advice to use 3 circuit wiring is spot on. I missed that balanced input detail also, while it doesn't change my advice to use 3 circuit wiring which seems to be the OP's primary question.

JR

[trevvahhh]

Originally Posted by JohnRoberts

A balanced isolation transformer output sending to a single ended input will A) not benefit from cancellation at the receiver, and B) will be unbalanced anyhow by the single ended termination so noise pickup will not be equal in both lines.
JR

just to clarify, the OP did say that the receiving end (sub) was balanced...

[JohnRoberts]

Originally Posted by trevvahhh

just to clarify, the OP did say that the receiving end (sub) was balanced...

Yup, and the sending end also..

JR

[paully]

Originally Posted by JohnRoberts

Yup, and the sending end also..

>>>>>>>>>>>>>>>>>
Crap! It must be age, but I missed that also. In that case all the OP needs is one of these Audiogear.com , one of these Audiogear.com , and an XLR mic cable in between.

..and as for me, it's off to the eye doctor..

Best, Paul