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-   -   Which DIY Speaker Cable design for EMI polluted room? (http://www.diyaudio.com/forums/parts/167823-diy-speaker-cable-design-emi-polluted-room.html)

Galgo 1st June 2010 11:43 AM

Which DIY Speaker Cable design for EMI polluted room?
 
Greetings,
I'm looking for a DIY speaker cable design that will be suitable for my setup in a pretty noisy EMI environment...
There are many designs on the forum - from CAT5 based, COAX, braided silver plated wires etc... but I wonder which one will perform best sonically and still gives decent EMI/RF protection.

I'm afraid i might overdo the shielding and use cables that will eventually degrade the sound quality (too much capacitance? too little!?)...
.
I've used shielded cables for the rest of the system - CANARE starquad microphone cable for the interconnects (from the HTPC) and a Belden shielded power cable.

The only thing left is to replace my pretty decent 4X1.5mm Bi-wire speaker cable that still get noise from FL lights and the CRT TV near it...

I'll need around 1m-1.5m for L/R and preferably Bi-wire.
I don't need it to be too "heavy" since I'm using an efficient set of book shelfs at MAX RMS of 100W/8ohm.

I'll be happy to experiment with some Pure Silver/Silver plated wires that are pretty easy to source through eBay etc...
Also maybe play with the interconnects (braided silver/PTFE wires?)

So - what would you recommend?
A link to relevant references will be appreciated as well...
Gal

marce 1st June 2010 05:14 PM

If you have to use special cable to shield from EMI for speaker cable youve got some BIG EMI issues.
The level of signal going down the speaker wire and the circuitry connected at one end and the driver at the other mean that EMI is not usually a problem, as the level of EMI is of a much much lower level than the signal, usually! Also EMI that is radiated that can cause problems again is a much higher frequency than audio (hence the prolifitation of ferrite beads on most hookup wires these days)..
I'd be interested where you are listening to music if EMI interference is that bad.
Some good links can be found here:
http://www.diyaudio.com/forums/diyau...#content_start

and
EMC Information Centre - The EMC Journal (Free in the UK)

Galgo 1st June 2010 05:29 PM

Thank you for the reply...
It's not THAT bad - I just want to create new speaker cables and as an avid DIYer use the opportunity to experiment with an optimized cable design (just too many to choose from) and high grade materials (silver coated/PTFE lines!?).

I think most of the EMI pollution come from strong FL lights (Hi Tech aquarium) that goes On/Off in the vicinity of the cables and the second source is the big CRT TV adjacent to the speakers (the Center channel is actually standing on top of the TV and the front L/R are on stands very close to it...).

So - what will be the preferable design?
It may not have to be "heavily shielded" if you say it's usually not necessary - how about braiding an extra line to use as a "shield" that will be connected only at the source "ground" or something similar (saw it done in interconnects - but not too popular in speaker wires...)?

Any other suggestions for a good speaker cable design? (too many design debated with too many opinions out there - I just can't decide who makes sense anymore...)

zigzagflux 1st June 2010 06:32 PM

It's all about the geometry. Simple twisted pair (not zip cord, that's parallel) has excellent behavior in the midst of RF noise. Tried the fancy silver plated solid copper telfon thing: no difference between that and average copper pvc.

Galgo 1st June 2010 06:39 PM

Quote:

Originally Posted by zigzagflux (Post 2204424)
It's all about the geometry. Simple twisted pair (not zip cord, that's parallel) has excellent behavior in the midst of RF noise. Tried the fancy silver plated solid copper telfon thing: no difference between that and average copper pvc.

Is it good as speaker cables as well? what about all this extra "capacitance" when braiding the cables? or is it negligible?
What AWG would you recommend for MAX 100w RMS and Bi-wire (shall I braid 4 inductors together or in two separated pairs and then twist them or something else?)

Gal

richie00boy 1st June 2010 07:28 PM

Don't braid, twist. You must twist as pairs, e.g. the positive and negative wire for one speaker. Then simply lay the two runs required for bi-wiring, you could braid these for looks.

Actually, if you are really worried about interference you would be better off using a single wire pair instead, just of thicker gauge. 18AWG would be fine for the length you need.

Galgo 1st June 2010 07:38 PM

Quote:

Originally Posted by richie00boy (Post 2204464)
Don't braid, twist. You must twist as pairs,

Hmmm.... OK (whats the big difference!?) - how can I keep the "twist" from "untwisting" - with a heatshrink or something?
How much "twisting" - as dense as possible or just few per ft?

Would it be better to use a ready made twisted pair cables - there are quite a few with 2 twisted conductors and some kind of shield - would these be suitable for audio or too high capacity (like in the CAT5 designs...)

Gal

richie00boy 1st June 2010 07:57 PM

Just take a pair of wires and keep the end in one hand. Have your writing hand about 5cm further along holding the wires free. Now twist both hands in opposite direction like you would be wrapping a sweet (candy). You should find the wire has a tendency to twist at a 'natural' rate. The twist should stay in place by itself, but you could heatshrink segments or all if you wish.

It helps if you can work on the floor or other big clear space where the wires are free to flap around and will remain supported and level.

CAT5 cable is too thin and messy, having lots of terminations to do. A screened cable would be OK but for the screen to be any good it must be earthed (grounded) at both ends, something which you probably can't do. Earthing one end only is worse than no shield as it creates an antenna.

Galgo 1st June 2010 08:06 PM

O.K. - thank you for the TWISTING guide ;) sound simple enough..
Regarding the shielded cable - why not connecting it to the ground (black) wire at each side?
And if so - why not using a coax cable (or a pair of them) and run the signal through the center with the shield connected as ground (Like many interconnect cables are made AFAIK) - any reason it's inferior to twisted pairs for speaker cables?

Gal

richie00boy 1st June 2010 08:47 PM

Connecting it to the black wire each side would have little screening effect. You could use coax but I don't feel it's thick enough, and you have a bit of an issue doing the terminations.


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