Unusual Balanced audio distribution Question


2010-05-02 10:00 pm
Ok folks it goes like this:

On a farm used for weddings we have the main dinner saloon, another cocktail / reception room and obviously the outside garden and on the far end of the garden we celebrate the wedding cake ceremony with Music, candles, fireworks, balloons and so on..

I was in need of some sort of audio distribution from the main saloon to the other room and to the outside garden for powered speaker placement.
Wireless was out of the question because it simply doesn't work well with entry-level equipment. I've tested some in-ear monitoring, wireless speaker adapters, including 2.4 and 5 GHz TV transmitters.
I've tried also the computer streaming approach but had to much latency.

For the last weddings I was using a 100m cable drum with 4 individually shielded wires for sending two balanced channels and it always worked well.

This year I did a permanent install approach that goes like this:

On the main room we connect the main PA mixer to a box on the wall.

From this box we feed 2 balanced mic cables to other 5 plastic water-sealed boxes 4 in the garden and 1 in the reception room, connected in parallel. In each box there are two males and females connected together.

box 2 (reception)
| (20m)
Main PA --------- box 1 -------- box3------------------box4 (garden far end)
(25m) (20m) | ( 40m)

(Box 1 1st tap, box 3 second tap)

There is no distribution amp, but I intend to put some sort of line amplifier in the main saloon between the mixer and the wall box.

Before you open the flame cannon ...

It's were we play most and I've offered the cables and connectors and my work, and it had to be a cheap solution. You know ...the ******* farm owner doesn't understand nothing about audio ...and doesn't want to invest... and I had to use the existing tubing infra-structure. You know what I mean... They all want to be the best but when it comes to money the only invest on decoration stuff...

Sometimes we do sunsets in the garden during the reception in summer, that's why I put males and females in the boxes. The idea is to feed one of the box and get the output on any of the others.

Yesterday we tested the system playing music from a DJ console in the garden and it worked well. I've put two speakers in the garden near the DJ and another in the reception room, and another at the far end. there was a slight hum or buzz but wasn't noticeable while playing. The main saloon box wasn't connected.... and it was cheap Numark and Behringer stuff.
Main ball PA is Pioneer DBX and Yamaha stuff.

Now the Million Dollar Questions:

Let's assume a standard 600 ohm output impedance.

Since when I feed one of the boxes and get output on one of the other, and leave the remaining unconnected / floating, should I solder in each box some sort of termination / loading resistors ?

When I daisy-chain 5 amplifiers, the cables are terminated with the input impedance of the amps, so perhaps this makes sense... Assuming 10k input impedance, the loading would be around 2K... perhaps 47k or 100k resistors from pin 2 & 3 to GND or just pin 2-3... time to make some plugs.

I didn't notice treble weakness, but

Since the total cable length for 1 ch (1,5 roll ... around 125m) assuming 40pf/m = 6000Pf, should I put on the main feeding cable series resistors like 100 or 120 ohm ?

Hope someone can give me some ideas.

Thank You for your attention.
6000pF = 6nF is high but can be driven by any 600ohms balanced impedance source/mixer/pre-amp to PA levels.

Although often described as 600ohms capable, balanced impedance sources generally have output impedances (padding resistors) between 10ohms and 100ohms.
The input impedance of balanced impedance Receivers are usually in the range of 10k to 1M. Transformer inputs will be even higher to ground.

Standard PA type equipment designed properly for balanced impedance in the aggresive PA environment should be interference free and of acceptable quality.

Monte McGuire

Paid Member
2013-07-28 2:58 am
There's no need for extra loading on the unconnected 'destinations' - it's OK to let them float. Additional loading will just tax the driving device for no good reason.

If you have no RF problems - basically hearing demodulated radio stations on some of the outputs - then you won the grand prize, and you don't even have to add extra RF filtering.

Simple parallel cabling works far more often than it's supposed to, even in some fancy professional situations. For example, I've used some parallel mike splitters for remote recording inside of a live venue a number of times, and never had a problem. Common wisdom says that one needs a snake with splitter transformers, but in practice, nothing went wrong, and I can guarantee that plain cable sounds better than any transformer. Sure, I wasn't running hundreds of feet to a remote truck, or spanning more than one breaker panel of AC power, to need the isolation. In short: simple is good.

Andrew addressed the capacitive load issue, and I agree - no problems there. No need to add extra impedance to the driving amplifiers - let them do their thing as designed. As Andrew said, competent gear already has output isolators built in, and adding extra resistors will just make the HF roll off sooner, probably for no reason.

It seems like you got it to work, and kept it delightfully simple, so enjoy the setup!


2010-05-02 10:00 pm
Well there was some ... I don't know strange background sound like wind blowing with low volume, but I presume since the mixer is probably impedance balanced that could be the cause or the console mixer combination background noise. I had also power issues, since the Dj console was resetting when playing cd's, phantom mikes for the legal ceremony didn't also work, but then we changed the power source and mikes and played from the computer and all was fine. On that wall plug I was measuring 203V the next day (should be 230V nominal). The weather was also ugly and rained and winded after 2 PM, but sound was fine. No hum no Brrr.. no distortion nada. First I was thinking in using network cable, but we are transmitting audio and not bytes...

Thank you for Your time.

Please take a look at the venue photos.

If anyone wants to merry here in Northern Portugal... Oh last Year we had a Welsh couple marrying, but French Spanish Italian and American are common, since we have there many emigrants... Sometimes under the gests we have some important people like Showbiz, Politicians and soccer players.

Solar do Burguês - Eventos - O Solar do Burguês (sorry no English page yet)