Running Speaker Wire in Cavity Walls

[Christopher Key]

Hello,

I'm wanting to put in a few short runs of cabling to a pair of wall mounted speakers, and am wondering what sort of cable is best to use. It's going to be run within cavity walls, terminating at a face place at one end, and running into the back of the speaker at the the other.

The obvious solution is to run a sufficient gauge of zip wire, although something seems inherently wrong about using stranded wire for a permanent, fixed installation. The alternative seems to be to use something like T&E, and switch to zip wire via a concealed (but accessible) choc block connector at the speaker end. Again, however, this seems like it could be potentially confusing to any future occupant.

What would the group suggest?

[David Hansen]

On Sun, 18 May 2008 12:38:10 +0100 someone who may be Christopher Key wrote this:-

Why?

[Christopher Key]

Why in the cavity walls? Well, the amps all floor level, and the speakers just below ceiling level, so I've either got to have a visible drop of cable, or run it inside the walls.

[Christopher Key]

Sorry, I'm talking rubbish. I don't mean cavity walls, these are internal stud walls.

[stevelup]

I would recommend Van Damme 'Black Series'.

can get it from CPC - it is very robust and won't get damaged when you pull it through sharp holes and bend it round tight corners.

Steve

[Roger Mills]

How are you proposing to get the cable inside the stud wall? There are likely to be a couple of horizontal noggins between floor and ceiling height. You will need to drill through these, but won't be able to get at them without removing some of the plasterboard. Do you *really* want to wreck the wall?

Why not just run sone square white plastic trunking up a corner, and put the wires inside that? With regard to the cable itself, use good quality stranded speaker cable - as fat as you can accommodate - far better than solid core house-wiring cable.

[Christopher Key]

There are noggins in the wall, and I was expecting to have to remove an area of plasterboard around them to drill through. As I'm going to have to have to cut holes in the ceiling too though[1], the extra work of one additional hole to make good in the wall is minimal, and in my opinion worth it to avoid anything visible.

I'm not wanting to start a flame-war here on speaker cable. I've always been of the opinion that cable is cable, as that for speaker level voltages, it's only the cross sectional area that matters. At audio frequencies, the skin effect is negligible (a rough calculation suggests a skin depth of ~1mm for copper at 20kHz). Obviously stranded is much easier to run, and I certainly wouldn't use solid core cable anywhere where it'll be subject to movement, but are there any other reasons that I've missed? Is there any specific reason why house wiring is always done with solid core cable, or is it just cost?

[1] This is a flat, hence no access from above via floorboards. The ceiling is a suspended one, with a ~8" void above in which all the cabling etc is run.

[Dave Liquorice]

Proper heavy gauge speaker wire would be better than yer average "zip wire". Anything less than 2.5mm^2 is not heavy enough. I'm not bothered about oxygen free or aligned crystal bollocks, just lots of copper between amp and speaker. That is the only thing that I have found to make any genuinely audible difference before/after, particulary to the bass.

[Christopher Key]

I've taken a look, CPC only seem to do it in 100m lengths (or 50m for the version heavy gauges). The price doesn't seem too bad, similar to Maplin's standard zip wire of a similar gauge, although I don't need anything like 100m. At most, I'd need 50m if I also used the same for the outdoor speakers.

I'm still interested by the recommendation for stranded rather than solid core though. For trailing cables across a stage etc, it makes perfect sense, but for permanent installations with no movement?

[David Hansen]

On Sun, 18 May 2008 14:54:57 +0100 someone who may be Christopher Key wrote this:-

If the aim is a neat installation then I suggest splashing out for some suitable sockets as well. is one supplier of such things.

[Dave Plowman (News)]

No reason not to for things like speakers. Solid core is cheaper - that's all. Alarm cable, for example, is flexible.

[Chip]

On Sun, 18 May 2008 15:18:04 +0100,it is alleged that Christopher Key spake thusly in uk.d-i-y:

[snip]

I think it's originally down to cost, and also to the terminations used (solid core or a small number of strands is easier to terminate successfully on terminals of the type used in sockets etc.)

Certainly many conduit installations use stranded cable, and not always 7 strand, sometimes it's 32 strand, I recall using 32 strand

2.5mm flexibles in conduit, the cable was made by BICC and complied to the relevent standard.

So to sum up, I don't think there's any reason at all why stranded core cable shouldn't be used in this case, it certainly makes the routing easier than using a house wiring cable.

[Andy Wade]

Not necessarily so (IMHO of course). The size needed depends totally on the run length involved. The only thing that matters is the total resistance and a good rule of thumb is to keep that below ~5% of the nominal speaker impedance - so 0.4 ohm max for 8 ohm speakers. Hence

0.5 mm^2 is OK for runs of up to 5 m, 1mm^2 for 10 m, 1.5 mm^2 for 15 m, and so on.

There's no reason why the OP shouldn't use flex. I did mine in 1.5 mm^2 arctic flex (run under the floor, clipped to joists).

[Peter Scott]

I've used single mains cable of the kind used to pull through conduits, that is no outside sheath just the single pvc insulation. I had a 15m run of cable and powerful amps so I chose 6 square mm. Worked a treat. Though thick, the cables have many cores so are reasonably flexible. I have now terminated them in wall plates that I made myself with the despised 4mm sockets.

Peter Scott

[Dave Plowman (News)]

My dislike of them - apart from the look - is they don't normally have a decent cord grip and also pull out too easily. Not a problem at an amp connection but can be for a wall outlet. But mainly the look - they are the pants if used with sleeved cable.

[David Hansen]

On Mon, 19 May 2008 09:06:58 +0100 someone who may be "Dave Plowman (News)" wrote this:-

Wall outlets, for speakers, I would have thought are likely to have a short length of cable plugged into them, leading from the socket to a wall mounted speaker. Unlikely to be pulled out I would have thought.

Even floor mounted speakers tend to be placed with not enough space to walk behind them. If there is space behind them, which is better tripping up and possibly felling the speaker, or pulling the cable out of the socket?

[stevelup]

Hi

Stranded cable has a greater surface area as well - not sure if it makes any practical difference. It will also be easier to terminate at the speaker end.

I'm always against using any kind of 'mains' cable for speakers purely because I don't think it is particularly safe from an identification point of view'.

VDC trading will sell by the metre (my original link), and I'm pretty sure they will sell direct to the public with a credit card number.

It's good stuff and worth the small price premium over using flex.

Steve

[Gordon Hunt]

In message , Christopher Key writes

Not a "HiFi" installation then!

You should use proper speaker cable which is multistrand. I would advise

90 strands as a minimum unless you're using crap Japanese speakers of course.

[dennis]

Which will make zero difference to the sound compared to a solid conductor. We are not talking RF here.

[Bob Mannix]

Ah but we are talking "esoteric hifi" (it's better but you can't hear the difference).

Power lead anyone?....

where did rationality just run off to...?