# Simple speaker wire question - can multiple grounds be common? - Ars Technica OpenForum

# Simple speaker wire question - can multiple grounds be common?

14 posts

Zeus "Purveyor of Rantage" Ars Legatus Legionis Tribus: In the land of Bourbon and gold Registered: Jul 28, 2000 Posts: 17265 | Posted: Mon Oct 08, 2007 10:18 am

Just like the title says: Can multiple speakers share a common ground? Is there some reason this would be a Bad Idea(TM)? With my very basic understanding of electrical theory, I see no problem with it.
I want to put a single custom-made 'plug' on my wall behind the entertainment center, which would connect to behind-the-walls wires leading to each of my 5 speakers (not worried about the subwoofer). If there are no contraindications to using a common ground, I need only use a 6-conducter plug at the wall. Otherwise (obviously) I need to move up to a 10-conducter connection.
I don't see a reason why a common ground would be an issue, but I'm not exactly an audiophile, and my electrical theory is pretty light.
What say the experts?

ZPrime "HA-HA! Not to scale." Ars Legatus Legionis et Subscriptor Tribus: Cleveland (Mayfield Heights), OH Registered: Jan 22, 2000 Posts: 17875 | Posted: Mon Oct 08, 2007 10:51 am

Why don't you just use a normal terminal block? They have nice wall-mount units that will give you 3 or 4 pairs (+ and -) of binding posts in a single-gang box size. Put in a double-gang and two of these plates and you've got your hookups.
Also, it's my understanding that the negative on an amplified speaker run is NOT ground / common across all lines. IOW, I believe it is a +/- system, rather than a positive with a ground reference. My physics/electronics knowledge isn't that great either but I think I'm getting my point across.
I mean, if you COULD share the negative across all the speakers, don't you think they would've done this already on the back of the amps?
[edit]
Howstuffworks tells all.
This animation should explain why you need a separate + and - line for each speaker. -- View image here: http://episteme.arstechnica.com/groupee_common/emoticons/icon_smile.gif --
The + or - voltage will make the voice coil move a different direction, which is how it produces sound at all. If you hooked the -'s together you'd have problems, and the - isn't a "ground" here, it's -.

Zeus "Purveyor of Rantage" Ars Legatus Legionis Tribus: In the land of Bourbon and gold Registered: Jul 28, 2000 Posts: 17265 | Posted: Mon Oct 08, 2007 11:11 am

> quote:
> The + or - voltage will make the voice coil move a different direction, which is how it produces sound at all. If you hooked the -'s together you'd have problems, and the - isn't a "ground" here, it's -.

That's what I was afraid of, oh well. -- View image here: http://episteme.arstechnica.com/groupee_common/emoticons/icon_frown.gif --
I was hoping to integrate a custom-built connection into my existing plate (keystone with coax and a pair of cat5 connections) and keep things to a single-gang hole.
Thanks for the input before I bought something that wouldn't work.

Jim Z Ars Legatus Legionis et Subscriptor Tribus: (x) added to foe list Registered: Nov 5, 1999 Posts: 43716 | Posted: Mon Oct 08, 2007 11:27 am

> quote:
> Also, it's my understanding that the negative on an amplified speaker run is NOT ground / common across all lines.

it can be, if the amplifier is single-ended. I think most home amplifiers are, assuming it's not bridgeable.

> quote:
> I mean, if you COULD share the negative across all the speakers, don't you think they would've done this already on the back of the amps?

it's quite possible that they do actually do this inside the box.

> quote:
> IOW, I believe it is a +/- system, rather than a positive with a ground reference. My physics/electronics knowledge isn't that great either but I think I'm getting my point across.

a single-ended output put the signal out on the + terminal and leaves the (-) terminal as the reference ("ground," if you like.) A differential/BTL amp like in most car radios outputs signal on both terminals; the signal on (+) and its inverse on (-).

> quote:
> The + or - voltage will make the voice coil move a different direction, which is how it produces sound at all.

right, but you can do that just fine with one signal lead and one return/ground. It works for AC mains power, after all -- View image here: http://episteme.arstechnica.com/groupee_common/emoticons/icon_smile.gif --

ZPrime "HA-HA! Not to scale." Ars Legatus Legionis et Subscriptor Tribus: Cleveland (Mayfield Heights), OH Registered: Jan 22, 2000 Posts: 17875 | Posted: Mon Oct 08, 2007 11:55 am
jz: I see... Zeus, I defer to others here because as I said, I don't know much more than basic/practical experience in this stuff.

Krono Ars Tribunus Militum et Subscriptor Registered: Nov 18, 1999 Posts: 2302 | Posted: Mon Oct 08, 2007 12:53 pm
If it absolutely, positively has to fit in a single-gang box, have you considered a bulk wall plate? Here's a page that sells what I'm talking about: http://www.youdoitelectronics.com/id870.htm

stud Ars Tribunus Angusticlavius Registered: Mar 26, 2000 Posts: 7811 | Posted: Tue Oct 09, 2007 9:05 am

> quote:
> Can multiple speakers share a common ground?

Use your multimeter to check.

ZPrime "HA-HA! Not to scale." Ars Legatus Legionis et Subscriptor Tribus: Cleveland (Mayfield Heights), OH Registered: Jan 22, 2000 Posts: 17875 | Posted: Tue Oct 09, 2007 11:14 am

One thing I just thought of: even if they can share a common negative lead, you need to size that lead appropriately for the wattage your amps are pushing to the speakers. I've been using 12GA all around for my speakers and each one gets its own pair of copper. This is probably overkill with the cruddy JVC receiver I have, but it is something to keep in mind. If you're trying to run every channel with a shared negative and the wire gauge is too high you could limit your sound output.

stud Ars Tribunus Angusticlavius Registered: Mar 26, 2000 Posts: 7811 | Posted: Tue Oct 09, 2007 11:26 am

> quote:
> you need to size that lead appropriately for the wattage your amps are pushing to the speakers

Amps don't 'push' power to the speakers, speakers draw current from the amp.

jonah Ars Praefectus Registered: Dec 15, 1999 Posts: 4156 | Posted: Tue Oct 09, 2007 2:37 pm
As someone mentioned above, speakers do not use a ground at all. All they are is a positive and negative voltage. The positive voltage makes the magnet go one way, and the negative the other. It may look similar to other home wiring, but it's direct current. You can't just wire all the negative wires together - the speakers won't work properly.

Jim Z Ars Legatus Legionis et Subscriptor Tribus: (x) added to foe list Registered: Nov 5, 1999 Posts: 43716 | Posted: Tue Oct 09, 2007 8:48 pm

I'm going to be nicer than stud would.

> quote:
> As someone mentioned above, speakers do not use a ground at all.

They very well can, it depends on the amplifier design.

> quote:
> All they are is a positive and negative voltage. The positive voltage makes the magnet go one way, and the negative the other

right. but the amp can tie (-) to "ground" and the audio signal on (+) is then referenced to it.

> quote:
> It may look similar to other home wiring, but it's direct current.

No way. direct current will make the speaker move one way and stay there. The output of the amplifier is AC, with the "live" (+) and "neutral" (-). Just like mains power.

pipe13 Ars Tribunus Militum Tribus: Massachusetts Registered: Sep 27, 2004 Posts: 2794 | Posted: Tue Oct 09, 2007 9:08 pm

Well, as you see, whether or not (-) is common or "live" depends entirely on the amplifier. Some are single-ended, some are bridged. I'll posit for the sake of argument that *most* 5.1 HT amplifiers are single ended. But that doesn't mean all are, or will be. I have seen high-power high-end stereo amps that are bridged. And you don't know what you (or the next guy) is going to hook up to this thing in the future.
But if someone connects a bridged amplifier to a common-wired speaker system, severe damage will be done to the amplifier and/or its fuses. (An amplifier will not necessarily always fail to protect its fuse. Occasionally the fuse will blow first.)
Take ZPrime's suggestion and use standard terminal blocks. Minituratization is way overrated anyway.

DriverGuru Senator et Subscriptor Tribus: somewhere in nonpaged pool Registered: Mar 21, 2001 Posts: 20211 | Posted: Wed Oct 10, 2007 12:10 am

> quote:
> No way. direct current will make the speaker move one way and stay there. The output of the amplifier is AC, with the "live" (+) and "neutral" (-). Just like mains power.

Ah, but sometimes you have a positive live and a negative live. (And half the time, the "positive live" is actually negative with respect to the "negative live.") Just like certain types of mains power.

Jim Z Ars Legatus Legionis et Subscriptor Tribus: (x) added to foe list Registered: Nov 5, 1999 Posts: 43716 | Posted: Wed Oct 10, 2007 6:04 am

> quote:
> Originally posted by DriverGuru:
> Ah, but sometimes you have a positive live and a negative live. (And half the time, the "positive live" is actually negative with respect to the "negative live.") Just like certain types of mains power.

-

> quote:
> Originally posted by jz78817:
> a single-ended output put the signal out on the + terminal and leaves the (-) terminal as the reference ("ground," if you like.) A differential/BTL amp like in most car radios outputs signal on both terminals; the signal on (+) and its inverse on (-).

14 posts