[Russtafarian]

I recall hearing that the reason speaker cables aren't shielded is because the shielding may drive the power amp into oscillation.  What's the technical explanation behind this? 

Is this issue tied to the type of amp (SS or tube) or type of output stage (transistor or transformer)?

If the cable has a woven or foil shield but the shield or drain wire is not connected to either the amp or speakers, can that still cause a problem? 

Thanks for your help.

Russ

[sts9fan]

Does it still sheid then?

[andyr]

I recall hearing that the reason speaker cables aren't shielded is because the shielding may drive the power amp into oscillation.  What's the technical explanation behind this? 

Thanks for your help.

Russ

Some speaker cables are shielded ... however, the shield will always be connected to the 'black' BPs on the amp - either because the speaker cable is coaxial (so the shield is actually part of the signal path) or if the speaker cable is twinax (ie. a pair of signal wires underneath a shield), the shield needs to be connected at the amp end to be effective as a shield.

The shield will increase the capacitative load of the speaker cables on the amp ... and some amps become unstable (and go into oscillation) with a high capacitative load.

If you think your speaker cables are picking up RFI (and so need to be shielded), I would suggest it is better to remove the RFI some other way - like by using a parallel cap of, say, 1nF, across the speaker BPs.

If the cable has a woven or foil shield but the shield or drain wire is not connected to either the amp or speakers, can that still cause a problem? 

In that case, I don't think the braided/foil shield will be very effective.

Regards,

Andy

[gerald porzio]

Spkr. cables w/ their lower impedence tend to resist RFI better than ICs, hence few shielded spkr. cables on the mkt.

[*Scotty*]

The shielding on the cable is to keep RFI out of the amplifiers feedback loop. As most amplifiers have a filter to reject RFI at the point where the feedback signal is picked up, the shielding on the speaker cable may not be necessary for correct operation. In over thirty years in the hobby no amplifier I have ever owned has required shielded speaker cables. YMMV however.
Scotty

[NagysAudio]

1.) Shielding speaker cables is completely unnecessary.
2.) If the shield is disconnected at both ends, then it's no longer a shielded cable.
3.) Any kind of design where the shield is connected to one end and not the other is complete nonsense.
4.) Audio signals are AC, connecting the shield to negative, or positive terminal will give exactly the same results. To indicate any sort of directionality in an AC cable is complete nonsense.

5.) In-spite all this, a coax cable could potentially make a terrific speaker cable. This would be a shielded design. However, a coax speaker cable could require a proper Zobel network, at the speaker end to work ideally.

[stereocilia]

I solved a problem with RFI causing me to hear my nearby a.m. radio station (clearly) by shortening my speaker cables.  The speaker cable length was the only variable I could find to make a difference.  It only happened with a tube amp, but if there were a cheap way to try shielded speaker cables I'd be on board.

[gerald porzio]

I would think a coax spkr. cable would be a Ga. # that increases resistance to the degree that the pwr. transfer & damping factor would be adversely affected.

[NagysAudio]

Well for one, you'd want to use an appropriate size coax cable so the damping factor is not diminished. There are many great mil spec'd coax cables available out there. Many have very low inductance and capacitance parameters which make great speaker cables.

Since coax cables are wider in bandwidth, they can be terminated with a Zobel network on the speaker side to minimize reflections and phase shift at high frequencies. For a 50 ohm mil spec cable, one can use a 50 ohm metal film resistor and a 0.1 uF ceramic disc capacitor. 

Zip cord type speaker wire usually does not require a Zobel network.