Help Me Understand

[Bako-Dan]

I'm having difficulty understanding the following statement taken from Bluejeanscable.com:

Because speakers are driven at low impedance (typically 4 or 8 ohms) and high current, speaker cables are, for all practical purposes, immune from interference from EMI or RFI, so shielding isn't required.

I don't doubt the validity of this statement since almost all speaker cable is unshielded, but I don't understand it. Why wouldn't speaker cable to susceptible to 60 Hz EMI from close-by electrical wiring? It would seem to me that a voltage, and therefore current, could easily be induced in the speaker cable through electromagnetic induction.

 

[jaxvon]

Yes, you are right. If you put your cable next to an electrical line, you would have problems. The thing is, your IC's can pick up a bunch more RF and EMI interference without shielding. Then that garbage is amplified. Your speaker cables aren't going to have any garbage they pick up amplified.

At least, that's MY take on the situation.

 

[Dan Banquer]

Shielded speaker cable

In general their correct. I suspect the problem is not at audio band at all, but that HF EMI/RFI is " received on the speaker cable" due to the whatever the impedance might be in the speaker at these very high frequencies. In short: the speaker cable appears to act as an antenna with the loudspeaker as the receiver. Unfortunately I don't know anyone who is measuring loudspeaker impedance at Ham radio or CB radio frequencies. From what I have experienced, is that if the field is strong enough it does happen, which is why I use shielded speaker cable. Ah, the blessings of living 50 yards from a Ham Radio operator and his 100 watt transmitter. The good news is that shielded speaker cable is pretty cheap.
d.b.
Go Here for more info: http://www.audioholics.com/techtips/audioprinciples/interconnects/bulletproofingsysteminterf.php

 

[Bako-Dan]

Then that garbage is amplified. Your speaker cables aren't going to have any garbage they pick up amplified.

Yeah - that makes sense. I have never heard a 60 Hz hum coming out of my speakers do to an induced current. I suppose any current induced is simply too small to create an audible response from the speaker. Maybe I'll try to experiment with this someday.

Thanks for responding!

 

[Bako-Dan]

Go Here for more info: http://www.audioholics.com/techtips/audioprinciples/interconnects/bulletproofingsysteminterf.php

Thanks for responding Dan! I read your article earlier - great information! I guess I still struggle with the statement from Blue Jeans. A low impedance (4 or 8 ohms) would mean that a large current could result from a relatively small induced voltage. So... I just can't seem to follow the logic in their statement.

 

[tbewick]

Older speakers/amplifiers I've used suggest using lighting flex as speaker cable unless the cable needs to be verg long (>50ft). Newer speakers suggest a maximum cable impedance or a recommended thickness.

Speaker cables are supposed to affect the sound, but I've never noticed any difference. I've used thick QED cable and it sounds no different to lighting flex. Stuff which sounded bad on the cheap cable sounded just as bad on the thicker (more expensive) cable.

I've never heard any background noise through my speaker cable.