Maximum length limit on Speaker Cables?

[dmusoke]

Hi:

I have a 5.1 system using Spires as my mains, Stage as my center and the FX2 for my surrounds. My speaker wire is 20ft or less for the mains but 50ft for the surrounds. All speaker wire is generic 10-gauge wire boutgh from e-bay .

I noticed hum in the surrounds when i mute my pre-pro but hardly any in my mains. All these are fed from my Sunfire 400W x 7 amplifier. This hum is very audible only when i place my ears next to the speakers.

What could be going on here? I don't think its the amp since the hum is almost non-existent in the front speakers run from the same amplifier.

The only change i did to my system was to move all my stuff into a vertical AV rack from Sanus (CFR2136, which took like forever!). I also changed power conditioners from an APC15 unit to a Torus power conditioner (AVR 15+) which has an isolated transformer on its secondaries.

Any help provided is very welcome!

 

[jmschnur]

The spires have their own amp so hum may be filtered out.

I would circumvent your torus and any other conditioners and check for the hum prior to looking for ground loops or rf pickup.


J

 

[roberto]

Hola. Perhaps your front signal is clean and your rear signal is dirty with hum. There is no filtering at the input of your Spires. To track the unwanted noise, first, turn of your amp and disconnect the amplifier rear inputs. Short a pair of RCAs connectors and plug them in at the input of the amp. Turn on the amp and check the noise. If there is no noise, then it is coming from the audio processor. If you do still have hum, then the amp is the culprit. If the speaker cables are near to any AC cable, you could have an interference inductance from the 60Hz of the AC mains. Separate the speaker cables from the AC cables. One inch will do. Each channel of your amp has over 70 dB or more of crosstalk. You could have bad rear channels and good at the front. The only thing in common is the power supply, and if you have at least one channel OK, then the voltage that you are feeding to the other amps is the same. But you might have a bad semiconductor or a bad capacitors at the rear channels. Also, if you are running the interconnects closed to any AC power cables, there is your problem. You must isolate AC cables from audio cables. They can not be near. I hope this might help you a little! Happy listening!

 

[dmusoke]

Thanks guys ... So far, i've eliminated the pre-pro as a culprit. It must be the amp or speaker wires nest to the power cables. Since its a mess at the back of my rack, i'd do this tomorrow. But still the question stands, is there a reasonable maximum speaker cable length? What electrical specs should one be looking at for long cable runs?

- David

 

[jmschnur]

Gauge vs distance. Keep the resistance as low as possible. The damping factor is affected by higher resistance .

As said before be sure the wires do not run parallel to current carrying cables.

Why not feed on of your fronts from one of the surround outputs of your amp to see if that gives you hum?

 

[JonFo]

as for length, no real max, 50' is long but not unheard of. I run 30'+ to my rear speakers.

Use good quality, low gauge cable. For longer runs, twisted pairs are recommended, as they reduce inducted noise, such as powerline hum or transformer ballast hum.

For longer runs through walls or crawl-spaces, I highly recommend this Belden 5000UTP from BueJeans cable: http://bluejeanscable.com/store/speaker/index.htm

My rack is also chock full of gear, and I also use sunfire amps to drive that cable over those 35' or so feet to my rears. Zero noise.

 

[roberto]

Hola. Good advise Jonfo. Please read this: http://en.wikipedia.org/wiki/Speaker_wire Happy listening!

 

[dmusoke]

Thank you so much guys ... your inputs have been very helpful. I have separated the power lines from the signal cables as best as possible and nothing(almost) runs parallel. The noise has now 'moved' primarily to the left surround speaker. Little is left in the right surround speaker. Here's where i stand so far:

1. The noise in the rear speakers is still there even after I swapped the rear channels on the amplifier with the front channels. It doesn't seem to follow the speakers.

2. I shutoff the pre-pro (to eliminate its influence) and the noise is still there. I disconnected its XLR outputs to the amplifier and the noise is still there.

3. I bypassed the Torus conditioner (amplifier only which was connected directly to the wall) and the noise is still there.

4. Now for the kicker ... I shorted the RCA inputs into my amplifier and the noise virtually disappears!!! I then disconnected the RCA input as well as its XLR input and the noise is still gone. I plug in the XLR input, which i use normally, and the noise appears!!!

So its seems the noise is on that one XLR input channel for the right surround speaker. Again, if i use the RCA input of this channel, the noise is gone. Remember the pre-pro that feeds this channel has no effect on the behaviour on the amplifier whether the pre-pro muted or turned off.

5. I disconnected my cable TV feed (as its been a source of ground loops in the past) but also had no effect on noise behaviour.

The other 4 channels which use simular XLR inputs seem to be quiet and almost noise free.

Any hints as to the cause of the problem? Why is the RCA input noise free but the XLR noisy? Doesn't that defeat the purpose of using these balanced inputs?


Anyway, i plan to get new speaker cable wire from BlueJeans Cable (Thanks JonFo) and maybe(?) from Zebra cables as well to rewire my whole system with clean looking cables. Red/blue cable doesn't look good on a white wall . How do you run white cable on a white stucco ceiling without looking tacky? This is the only way i can think of avoiding the long cable runs w/o moving my whole rack to the ther other side of the room which is quite a task to do ...

- David

 

[jmschnur]

Why not use RCA for the surround if that has no noise?


J

 

[dmusoke]

I may eventually but would rather find the root-cause of failure first, since the noise problem didn't exists before.

 

[tompa]

Regarding your question about running wire on a stucco ceiling, check one of the manufacturers of flat wire for audio.

Here is the flatwireready site. http://www.flatwireready.com/products/audio.html Up to 12ga is available

Run the wire along the ceiling/wall crease, then either run wire down the wall, or drop it between the studs. You can either pain or spray stucco to cover it

 

[tsv_1]

Thank you so much guys ... your inputs have been very helpful. I have separated the power lines from the signal cables as best as possible and nothing(almost) runs parallel. The noise has now 'moved' primarily to the left surround speaker. Little is left in the right surround speaker. Here's where i stand so far:

1. The noise in the rear speakers is still there even after I swapped the rear channels on the amplifier with the front channels. It doesn't seem to follow the speakers.

2. I shutoff the pre-pro (to eliminate its influence) and the noise is still there. I disconnected its XLR outputs to the amplifier and the noise is still there.

3. I bypassed the Torus conditioner (amplifier only which was connected directly to the wall) and the noise is still there.

4. Now for the kicker ... I shorted the RCA inputs into my amplifier and the noise virtually disappears!!! I then disconnected the RCA input as well as its XLR input and the noise is still gone. I plug in the XLR input, which i use normally, and the noise appears!!!

So its seems the noise is on that one XLR input channel for the right surround speaker. Again, if i use the RCA input of this channel, the noise is gone. Remember the pre-pro that feeds this channel has no effect on the behaviour on the amplifier whether the pre-pro muted or turned off.

5. I disconnected my cable TV feed (as its been a source of ground loops in the past) but also had no effect on noise behaviour.

The other 4 channels which use simular XLR inputs seem to be quiet and almost noise free.

Any hints as to the cause of the problem? Why is the RCA input noise free but the XLR noisy? Doesn't that defeat the purpose of using these balanced inputs?


Anyway, i plan to get new speaker cable wire from BlueJeans Cable (Thanks JonFo) and maybe(?) from Zebra cables as well to rewire my whole system with clean looking cables. Red/blue cable doesn't look good on a white wall . How do you run white cable on a white stucco ceiling without looking tacky? This is the only way i can think of avoiding the long cable runs w/o moving my whole rack to the ther other side of the room which is quite a task to do ...

- David

Have you swapped out the "bad" XLR for another just to rule out a bad cable?

 

[dmusoke]

Regarding your question about running wire on a stucco ceiling, check one of the manufacturers of flat wire for audio.

Here is the flatwireready site. http://www.flatwireready.com/products/audio.html Up to 12ga is available

Run the wire along the ceiling/wall crease, then either run wire down the wall, or drop it between the studs. You can either pain or spray stucco to cover it

Interesting concept indeed! Never heard or seen it before. Seems to fit the bill nicely... Thanks Tompa!

Have you swapped out the "bad" XLR for another just to rule out a bad cable?

I did and no change.

From what i've observed so far, i seem to be picking up hum somewhere in my signal chain. I now plan to tear down my system and re-wire everything cleanly in the rack and with current speaker wire and see what happens. I will eventually replace the speaker wire eventually ...

Thank you all for all the time, contributions and consideration you took in helping me attempt to solve my noise problem. I shall report back after the problem is fixed. Thank you all again !

- David

 

[SteveInNC]

As to the balanced XLRs, if the cable isn't bad, they shouldn't pick up induced noise because their whole purpose is to reject common-mode noise. Are you sure it's truly a balanced signal and not just a normal ground-referenced input wired with XLR connectors? You might also try swapping the right and left cables. Perhaps the input connections on the amp are bad (cold solder joint, etc.).

 

[dmusoke]

It wasn't the quality of cables or ground connection that was the problem. I've managed to conclusively prove its due to nearby AC power cables that were lying on top of the speaker wires that caused the hum. I'm in the middle of a re-org of my system with newer speaker wire, moving into a vertical AV rack and judiciously re-routing the power cables as well. I did a test where i placed a well shielded power cable(http://essentialsound.com/power-cable-technology.htm#MusicCord-PRO-shielding-lowers-noise-floor) on top of the speaker wire and there was no hum. Placing regular cable on top of that same wire generated the hum in my speakers.

 

[roberto]

Roberto..."If the speaker cables are near to any AC cable, you could have an interference inductance from the 60Hz of the AC mains. Separate the speaker cables from the AC cables. One inch will do"...
Hola... good to know that you found your problem. Yes, you should have all AC lines together and separated from the audio and video cables...happy listening!

 

[Speedskater]

For speakers or power, twisted pair cables are always good.