Yes, the insulation matters. Use cotton, but keep the wire pair close together, then add a layer over that.
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what kind of voltage are speaker wires subject to?
You can calculate a reasonably good approximation of that based on the relation P = (E^2)/R. Power (in watts) = Voltage (in volts) squared divided by Resistance (in ohms).
So the maximum voltage would be the square root of the maximum power that would be fed to the speakers times their rated impedance.
That is an approximation because speaker impedance is not purely resistive, and is not constant with frequency, but it should be good enough for your purposes.
Also, however, power in this context is usually specified as rms rather than peak, so the calculated voltage would be rms also. If you want to know the worst case instantaneous voltage more precisely, to assess insulation requirements, multiply the worst case rms result by 1.414 (the square root of 2) to get the corresponding peak voltage.
Cotton is a terrible suggestion as a dielectric for a copper conductor. Untreated cotton will absorb moisture from the atmosphere and allow unabated access of the atmosphere to the conductor. In the form that you will be using it in it's dc is a min. 3.9 a bit higher then PVC (not good for this app.)BTW I believe anti-cables use a polyester varnish like magnet wire not PVC.
The only thing cotton has going for it is that it reduces vibrations that is why it is used as a filler not an insulation.
Try something with teflon...
Al: thanks for the explanation and running the numbers. My amp is 2x75 W so taking 57 V peak is more than safe. Still, 57V is rather low voltage in terms of insulation, so that's good news.
CPK: thanks for pointing out anti-cables are insulated with poliester. Maybe insulating mine with mylar (which is a poliester) is a good start. I didn't understand your comment: "In the form that you will be using it in it's dc is a min. 3.9 a bit higher then PVC (not good for this app.)" Could you elaborate?
You're welcome! 75W into an 8 ohm speaker would be only 24Vrms or 35Vpeak.
By "dc" CPK meant "dielectric constant," which is proportional to the capacitance the cable will have, and the amount of "dielectric absorption." Thicker insulation will also increase capacitance, everything else being equal, and thinner insulation will reduce it.
My own feeling is that as long as it is within reasonable limits capacitance in an 8 foot speaker cable is not especially critical. It would be more important in an interconnect cable, because of the much higher output impedance of the component driving the cable. The opinions of others may differ on this, and I readily acknowledge that other factors, known or unknown, might in some systems make capacitance more important than I am envisioning.
Enjoy your project!
From what you have written it seems that you are planning to use a un-insulated wire that you have and insulate it.
Not a good idea. First there is already a layer of oxidation on the copper if it is un-insulated, second whatever you put on most likely will not be air tight, third it is not the safest idea.
Get 14awg teflon insulated OCC wire, try 8-10 twist per foot, solder on some spades with some silver bearing solder...
BTW mylar DC is between 2.8-3.7 for cable passing a signal you shooting for low DC...
I'm with Al it should not matter enough to worry about. As some have mentioned wire geometry can have a small effect - especially placing wires far far apart (best place them close together). Twisting wires is most important for small signals into high impedances or for signals lines passing through very noisy RM/RF environments - I should not think it matters for speaker cables.
However, solid core versus stranded is probably not enough to worry about either (other than teh stiffness may cause connection integrity problems at each end). So I guess this makes a full circle - it must all be critical!! ;-)
I was thinking of getting wire from some guys who wire electric motors (electrolitic copper), and they offer to insulate it for me. I believe the wire is not completely bare but rather has a very thin enamel-type insulation. Would this be a good idea?
Am I looking for a lower or a higher DC? Mylar is 2.8 to 3.7...is that good??