Multichannel Speaker Cables

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
As long as the amplifier outputs are single-ended, and the minuses are grounded, what's wrong with using a pair of 4 wire cables? One wire connected to speaker ground, and each of the other three carrying the low/mid/high signals?

Mike


Well that will leak quite a lot of bass power directly into the tweeter, due to the shared ground. Typical wires runs are somewhere between 0.05 and perhaps 1 ohm in total in practice, so you can get volts of IR drops over them.


Some multichannel amps will show increased distortion if the speaker returns are not kept separate.


You might want to run thicker wires for the woofer anyway as that's the transducer that cares most about damping and carries the most current.
 
Typical wires runs are somewhere between 0.05 and perhaps 1 ohm in total in practice, so you can get volts of IR drops over them.

How does a voltage drop manifest itself? The total wire run to my left speaker is about 16 feet, but it's about 27 feet to my right speaker if I remember correctly. Does this disproportionately attenuate the signals and thus reduce the SPL to the right speaker more than the left?
 
How does a voltage drop manifest itself? The total wire run to my left speaker is about 16 feet, but it's about 27 feet to my right speaker if I remember correctly. Does this disproportionately attenuate the signals and thus reduce the SPL to the right speaker more than the left?

I'll give it a shot.

Let's assume you are going with 13 AWG wires. I'm assuming by total wire run you mean distance from amps to drivers, so double the wire length for the return wire. Also assuming copper.

The DCR of the 32 foot run is .064 ohms.
The DCR of the 54 foot run is .108 ohms.

Adding 30% (?) for AC losses gets you .083 and .140 ohms respectfully.
The loss for the woofer run will be less that the loss for the tweeter run.

Now assume an 8 ohm driver (totally resistive) in series with the wire.

2.83 volts into an 8.083 load = .35 amps.
.35 amps through an 8 ohm driver = 2.8 volts.

2.83 volts into an 8.140 load = .34766 amps.
.34766 amps through an 8 ohm driver = 2.78 volts.

2.78 volts vs 2.80 volts = .0623 dB difference.

If my calculations are right, you'll never notice it.

Mike
 
I'll give it a shot.

Let's assume you are going with 13 AWG wires. I'm assuming by total wire run you mean distance from amps to drivers, so double the wire length for the return wire. Also assuming copper.

The DCR of the 32 foot run is .064 ohms.
The DCR of the 54 foot run is .108 ohms.

Adding 30% (?) for AC losses gets you .083 and .140 ohms respectfully.
The loss for the woofer run will be less that the loss for the tweeter run.

Now assume an 8 ohm driver (totally resistive) in series with the wire.

2.83 volts into an 8.083 load = .35 amps.
.35 amps through an 8 ohm driver = 2.8 volts.

2.83 volts into an 8.140 load = .34766 amps.
.34766 amps through an 8 ohm driver = 2.78 volts.

2.78 volts vs 2.80 volts = .0623 dB difference.

If my calculations are right, you'll never notice it.

Mike

Mike, thanks very much for taking the time and trouble to give me this worked example - it's much appreciated...and I agree that I'm not going to hear a difference of 0.06 dB!

My left channel (the shorter run) seems to be slightly, but consistently, louder than the right channel. All drivers are working correctly and are in phase, so I'm going to have to look somewhere else.
 
Have you tried swapping the left and right cables at the amp to see if the imbalance moves?

Not yet, I'm still cleaning up the mess I've made developing these speakers and rearranging the room and wiring.

The first thing I'll do is just to switch the routing in the miniDSP so that the left channel is routed to the right speaker and vice versa. If the symptoms move to the other speaker, that eliminates the speakers and everything else downstream of the miniDSP. If there's no change, then I'll try swapping cables and then swapping the speakers themselves.

I'd like to make it look like I'm not spending too much time on these speakers now, but I should get to it in the next day or two.

FWIW, I did pull all the cables out of the wall plate and measure the round-trip resistance of each driver and cable in turn. The channel differences were typically about 0.2 Ohm on totals of 5 or 6 Ohm. It was the left channel that had the slightly higher resistance.
 
To clarify my earlier comment to the effect that my left speaker sounds slightly louder than the right speaker, it might be more helpful to say that the sound stage has a bias towards the left. A good example is Jacintha's "Willow Weep for Me", which opens with a sax on the left, other instruments towards the right, and with her voice taking centre stage. I am hearing the sax on the left, the other instruments between the right speaker and the centre, and her voice a little to the left of centre.

A useful feature of the miniDSP digital signal processor is the ability to turn off any or all channels at will. Thus it is easy to turn on just the left tweeter and to then confirm that that is indeed the driver that is producing sound. This makes it easy to confirm that all drivers are working and are connected to the correct left and right speakers.

I have also tested the woofers and mids for polarity using a 9V battery. I can't really do this with the tweeters, but I don't think they could account for the difference I'm hearing.

Here's what I did this morning...

First, I listened to Jacintha with everything connected as usual and heard this left bias on the sound stage. I then routed the left channels to the right speaker and the right channels to the left speaker in the miniDSP. I expected to hear a "mirror image" but, to my amazement, I heard a normal full soundstage! My reaction to this was to suspect a technical issue in part of the routing in the miniDSP.

I then repeated the experiment, but this time with the cables reversed at the wall plate. Same result, which seems to eliminate the miniDSP as the cause of the problem (this is a bit of a sweeping statement).

I returned the cables to their correct position and repeated the first experiment with another of my favourite test tracks: Arne Domnerus' "Lady be Good" from "Jazz in the Pawnshop". As with Jacintha, with the miniDSP routing correctly, the sound stage has a slight left bias, but when the routing is switched around, "WOW"...the performance is magnificent!

I am at a loss to explain how this can be. The finger appears to be pointed at the digital processor, but the experiment with the reversed cables should have confirmed this, and didn't. The best I can come up with is a problem elsewhere in the digital processor.

I'm going to have to repeat the cable-swapping part of the experiment to confirm or otherwise a routing issue.

It can be a little mind-boggling trying to follow the logic-flow through all this, but I would welcome anyone's insight into explaining what I'm hearing. At the moment, my immediate solution is simply to listen to the system with the left and right channels reversed, but that's not really the "solution".

I guess I should really move this to the miniDSP forum...
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.