Sheilded speaker wires...

[BentMike]

I do data acquisition and control - when ever I have a signal I care about I use shielded and preferably twisted pair cables.

Why are we told not to use shielded cable for speaker wire? Is it just a waste of money, or does it mess something up?

BM

[djk]

There may be an amplifier instabity issue with the capacitive load the amplifier sees.

I suggest looking at star-quad connected 4-conductor wire for longer runs, less HF loss.

[Don Richard]

There may be a benefit to using shielded speaker cable in certain instances. With some amplifiers electrical noise can get into the amplifier's input through it's fedback circuitry. The use of coax cable with the shield connected to the output terminal that is grounded to the amp's chassis can reduce this noise pickup. RG-8 coax has about 26 pf/ft with very low inductance and won't generally cause instability problems. If it does, a Zobel termination at the speaker input will null out the reactance.

[MikeFord]

I do data acquisition and control - when ever I have a signal I care about I use shielded and preferably twisted pair cables.

Why are we told not to use shielded cable for speaker wire? Is it just a waste of money, or does it mess something up?

BM

One wire that comes to mind is IIRC Mogami, which actually used a pair of shields as the conductors and had more capacitance than some early amps were stable with. Nothing AFAIK is inherently bad about shielding the speaker wires, but to what end?

The speaker signal has no power above 20k so its not going to "annoy" other circuits, and its fairly high level, volts not millvolts, so seems unlikely anything is going to annoy it.

I use cheap 12 gauge clear zip cord, but no harm from twisted pairs, again though to what end its a low impedance high level signal.

[BentMike]

I use zip cord , too. But I have a lot of coax around, and I have read a couple of times, "DO NOT use coax for speakers." I was just curious.

My Crown D-75A is nearly impervious to external influence. I can probably use whatever I want with it.

[djk]

"One wire that comes to mind is IIRC Mogami, which actually used a pair
of shields as the conductors and had more capacitance than some early
amps were stable with. Nothing AFAIK is inherently bad about shielding
the speaker wires, but to what end?"

Mogami?

Love it, no other speaker cable I know of blew up so many expensive amplifiers (and I got paid to fix them).

The Crown is probably OK, but something that does not have a choke in the output network (like many Adcom) will probably 'let the magic smoke out'.

[tigerwoodKhorns]

"One wire that comes to mind is IIRC Mogami, which actually used a pair of shields as the conductors and had more capacitance than some early amps were stable with. Nothing AFAIK is inherently bad about shielding the speaker wires, but to what end?"

Mogami?

Love it, no other speaker cable I know of blew up so many expensive amplifiers (and I got paid to fix them).

The Crown is probably OK, but something that does not have a choke in the output network (like many Adcom) will probably 'let the magic smoke out'.

Huh? How did that happen? Curious.

[djk]

With an un-buffered output an amplifier driving a 90° capacitive load will frequently blow up. Electrostatic speakers, piezos, and wire are the biggest culprits here.

[tigerwoodKhorns]

Uh oh. I vaguely remember this from school.

So capacitive loads are like opening a valve all the way and letting too much current flow?

I am using the W3102 (2 conductor) wire. Should I be worried? I piece if about 10 feet long, the other is about 35 feet long.

http://www.mogamicable.com/category/bulk/speaker_cable/conventional_configuration/

Ranges from 32.3 pF/ft at 100 hz to 22.6 pF/ft at 100 Khz.

Capacitance (20°C)	Frequency	100Hz	1kHz	10kHz	50kHz	100kHz
W2972	1-2	130pF/m (39.7pF/Ft)	100pF/m (30.5pF/Ft)	81pF/m (24.7pF/Ft)	74pF/m (22.6pF/Ft)	71pF/m (21.7pF/Ft)
	1-3	110pF/m (33.6pF/Ft)	79pF/m (24.1pF/Ft)	63pF/m (19.2pF/Ft)	57pF/m (17.4pF/Ft)	56pF/m (17.1pF/Ft)
W3103	1-2	106pF/m (32.3pF/Ft)	93pF/m (28.4pF/Ft)	83pF/m (25.3pF/Ft)	76pF/m (23.2pF/Ft)	74pF/m (22.6pF/Ft)

[djk]

Normally, maximum current in a resistive load is when the voltage into the load is at maximum and the voltage across the outputs is at a minimum.

A 90° capacitive load would cause the maximum current to flow with the maximum voltage across the output devices.

[BentMike]

So then any capacitance, the more the merrier, is going to approach that max I and max V point. Could get hot before 90 degrees?

You said the Crown amps would probably be OK and mentioned chokes on the output. Is that what my amp has, a big enough inductor?

Since Adcom and other amps lack an output buffer (is that always equivalent to an inductor?), presumably there is a reason for the absence?

BM

[djk]

The real issue is whether the amplifier can drive high capacitance without ringing or oscillation.

If it can't, then you have a problem. Some magazine reviews showed waveformes into a pure capacitive load to help you evaluate this.

If you are really inclined to use co-ax, you may need to add a damped inductor in series if your amplifier does not have one.

Inductor inside an early MIT interface box.

A later MIT interface box.

[MikeFord]

Conductors inside coax often suck for use with speakers, too small, solid wire not very flexible, and copper plated steel.

[Don Richard]

That's why I suggested RG-8 (or RG-11) coax if one hears problems that a shielded cable can fix. The center conductor is 14 ga. copper, but it's not as flexible as 14 ga. zip cord.

[BentMike]

So an Adcom amp, for example, With a capacitive load there would be some audio content that would resonate causing too high peaks that breakdown some components in the amp?

Any idea what the range of capacitance this might be? There is some capacitance between the conductors even of zip cord...

Again, I am not likely to be using coax after this discussion, but I still want to understand as fully as I can.

Then there is the question earlier that went unanswered - why would Adcom or any amp designer choose not to include this buffering? To economize? Are there auditory advantages or disadvantages?

BM

[MikeFord]

Cost is always a factor, so I suspect a main reason is that nobody expected the wave of wacky wire. Most amps aren't waterproof either, but its not an issue in a normal setup.

Nothing in audio is free. Protection circuits either add cost, or mess with the sound or both.

Many audiophile type systems depend on pleasant artifacts, so advantages, disadvantages, you could make a list as long as desired. I remember a time when pretty much everybody in the audio community used system formulaes, this cartridge with this arm and table, needs such and such preamp, etc etc. I don't think that is still a common thought outside of people who like coloration.

[djk]

The inductor lowers the DF spec too. I don't think it's audible, but a high number looks nice in add print.

[BentMike]

Hello Mike,

That is what I thought. I am all for zip cord then. Are there issues with solid Cu wire? Other than it is springy, and annoying to handle and look at? I can see romex under the floor as an interesting choice. Cost effective.

OT stuff:

I just had a fussy conversation in a different venue where those with audiophilia were really down on mp3s (the breadth of music available in the format is hard to ignore or discount). Some are insisting on perfect reproduction, as if there is a reference for that, or anyway to tell if our perception of it is perfect even with a "perfect" system. So coloration, pleasent artifacts (I like that one), how can a true audiophile ever seek such a thing?

djk,

What is DF?

thanks,

BM

[djk]

Damping Factor

[grimmreapersound]

Shielded cables are typically used for high impedance low power signals like a 4-20 signal for SCADA systems. Speaker wire is for low impedance high power signals. If you are getting interference thru the speaker wires you probably should run the wires away from that nuclear power generator.