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Old 3rd February 2009, 10:07 PM   #1
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Default Hgh inductance, high impedamce speaker cable

I'm running bi amped Exposure Super 18 power amps into a pair of Acoutic Energy AE1 mk2 speakers. I'm about to move my racks and will need longer lengths of cable (10m).

I understand my power amps are happier used with a high inductance, high impedamce cable, (I think that they don't have a Zobel network on the output, but don't quote me on this).

I'm currwntly running 24 yr old Linn LK20 for bass and Gale ? silvered for top, but these cables will be to short for my new location in any case.

I'm happy to spend sensible money on cables but not looking at crazy uber wires costing over £5 per metre, esp given lengths required.

Any cable recommendations?
Do I need to worry so much about what I use for the tops?
What in speaker cable terms are considered to be high capacitance and impedance values so I can check Blue Jeans, RS etc?

Any suggestions or advice for suitable cables would be appreciated. Bear in mind I'm no techie.
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Old 3rd February 2009, 10:20 PM   #2
Pan is offline Pan  Sweden
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The resistance is of no concern from the amp's "point of view" but it will have a small effect on the FR of the speaker if it deviates much from the R that the speaker was designed for.

A low capacitance/high inductance cable is easily made by running any two conductors separeted by an inch or two from eachother.


/Peter
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Old 3rd February 2009, 10:31 PM   #3
pjpoes is offline pjpoes  United States
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inductance causes the highs to roll off, impedance adds resistance, throwing away energy as heat. There is nothing good about a cable with high inductance and high impedance. A cable should have low inductance, low impedance, and low capacitance.

My personal opinion after lots of experimenting is that you should be smart, but expensive cable isn't really needed. I found benefit of using shielded speaker cables, or minimally, 4 wire twisted designs to cancel radiation. Speaker cables carry a lot of voltage and current as compared with other wires, and thus will create greater radiation, like power cables. They won't likely pickup radio signals or other forms of emi, but they will produce it, and if you have things like low level signal cables running along them, it might be beneficial to shield one from the other.

My favorite cheap speaker cable is to buy a few rolls of teflon coated silver plated copper wire from surplus shops, and twist my own. Last time I bought some I was able to buy 500 foot spools of 16 gauge wire for 18 cents a foot, and 20 gauge for 10 cents a foot. I use connectors I bought on Ebay from a chinese supplier, they are identical to the many "high quality " connectors offered by other manufacturers, and work fine. I twist it all together, put a few pieces of heat shrink to hold it all in place, solder on some connectors, and I'm set. I've been dumb and purchased cotton coated copper wire, silver wire, audioquest, cardas, and Kimber Kable and never found a big difference in sound.

Another cheap ready to go option is to buy a 4 wire power cable from the hardware store and use that. Or you could use a 3 cable wire and cut off the plugs, then connect ground and neutral together as the "-" connector, and the hot for "+", as thats a cheap and commonly suggested DIY option. I don't like that it's not symmetrical, call it an OCD thing, so I think buying a 4 cable wire, which they often have for 20-30 amp multiphase cables, and use that instead. Belden also makes a nice speaker cable with similar construction, but they often charge too much. It's the same thing as Bluejean cables sells, but in 4 conductor version. Grey pvc exterior, and red, black, white, and I think green for the conductors. It's a nice cable though, and large 500 foot spools brings the price down, but then, what do you do with the rest.
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Old 3rd February 2009, 10:40 PM   #4
Pan is offline Pan  Sweden
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Quote:
Originally posted by pjpoes inductance causes the highs to roll off,
Yup but that can be compensated in the speaker and if you have an amp without output filtering you may not have a choice unless you want to see your amp go up in smoke and possibly take the speakers with it.

Quote:
impedance adds resistance,
Impedance doesn't add resistance, impedance is the sum (with some phase angle) of reactance and resistance.

Quote:
throwing away energy as heat.
No big difference since the speaker load will be the dominant load. If you conncect 0.1ohm or 0.01ohm in series with 8ohm doesn't make a significant difference except for some small change of system Q and frequency response.


Quote:
There is nothing good about a cable with high inductance and high impedance. A cable should have low inductance, low impedance, and low capacitance.
A cable should have parameters that makes it suitable for the specific job. In this case it's about keeping the amp alive!! :-)


/Peter
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Old 3rd February 2009, 11:06 PM   #5
pjpoes is offline pjpoes  United States
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ok but high impedance means high resistance at various frequency.

I don't see how a cable with a high impedance will keep an amp alive, the load of the speakers will be much higher. As for inductance, same thing, how does the inductance of the cable have any effect above and beyond that of the speaker? Is it parallel inductance people are concerned with?

Inductance causes rising resistance in reaction to frequency, it won't cause amp instability, but I dont see it as a good thing.

I thought most of the oscillation issues in amps was caused by high capacitance? no?First watt Nelson Pass article
That article indicates, as I said, that low inductance and low impedance is important, that the opposite is not desirable.
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Old 3rd February 2009, 11:22 PM   #6
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Thanks for those quick respopnses.

Pipoes

You say 'There is nothing good about a cable with high inductance and high impedance. A cable should have low inductance, low impedance, and low capacitance'.

In a review of my power amps I read 'Apparently the design of all Exposure amps require cables that have both a high capacitance and high inductance'.
Quote talen from http://www.soundstage.com/mike02.htm

All adds to the confusion. Any comments on this discrepancy welcomed. I must say that my current cables seem to sound fine and would re-use them if they'd stretch.

I need to go away and read some DIY twisting recipes when I've understood this inductance/impedance thing.

Shielded cables are an attractive idea, but dont they tend to use a solid core and stranded wires too. Any non symettrical worries there?

I should manage to avoid running speaker cable alongside mains cables completely, though they will run parallel to a scart TV feed, 1 unbalanced line cable and 2 subwoofer cables for 4 or 5m (all shielded). I think this is about as good as I can get it.

All termination will be by banana plugs, but they take fairly thick cables and can be stacked if needed.

-----------

New posts came in while editing this. A little techie from Pan but I'll read carefully a few times.
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Old 3rd February 2009, 11:30 PM   #7
pjpoes is offline pjpoes  United States
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the issue isn't that a speaker cable will pickup emi, that is unlikely at the signal level that travels through speaker cable, it's that it produces emi of it's own which can interfere with lower level signals. It's really a minor issue, but if you have rca cables, digital coaxial interconnects, even scart cables in the vicinity of a speaker cable, there is a chance that it could introduce some interference. The digital and scart will work at different frequencies, and should be well shielded, so it probably is less of an issue with those.

Well if you read the report I linked from First Watt, it talks about actual tests they did. There are other tests like those on the web. I think the review has it reversed, high capacitance appears to be what causes the oscillation, unless I misread the article.
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Old 3rd February 2009, 11:50 PM   #8
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Well, after searching the threads here for help before my OP and coming up blank, guess what. Googled a query and got this very useful link.

here http://www.avforums.com/forums/hi-fi...le-dilema.html

Now, one interesting quote in particular

'I have emailed the product designer at Exposure and he couldn't see any problem. He did mention that I should try and use high inductance and low capacitance cable but as I don't have a clue what thet means I'll continue to use the QED XT-400. He said the best way to see if the cable was the wrong type is the amp will get hot'.

Note the designer says 'high inductance and low capacitance cable'. Does this make more sense?


For anybody who bothers to read the above thread, the Linn K20 cable I use at present is exactly the same as the Naim? cable with different printing. My amps stay stupidly cool even when driven hard. I must be doing something right.

The fog is lifting, I'm getting it. I think.
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Old 4th February 2009, 12:01 AM   #9
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High inductance = lowpass filter. As long as the inductance doesn't effect frequency response, it can act as a safeguard against HF oscillations in an amplifiers output stage. Of course, the amplifier should have been designed with this in mind from the start.

I seem to remember Spectral's wide bandwidth amps having problems with certain cables, but I can't remember what the properties were that made them unhappy.
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Old 4th February 2009, 12:14 AM   #10
Pan is offline Pan  Sweden
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Quote:
Originally posted by pjpoes
ok but high impedance means high resistance at various frequency.
Nope! Possibly you are thinking right but your statement is not correct. High resistance is not a necessity for high impedance.

Quote:
I don't see how a cable with a high impedance will keep an amp alive, the load of the speakers will be much higher.
Nope. Not at high frequencies.


Quote:
As for inductance, same thing, how does the inductance of the cable have any effect above and beyond that of the speaker? Is it parallel inductance people are concerned with?

Nope, parallel capacitance.

With low capacitance comes high inductance.

Quote:
Inductance causes rising resistance in reaction to frequency,
Nope, series inductance casue rising impedance towards higher frequencies.


Quote:
I thought most of the oscillation issues in amps was caused by high capacitance? no?
Capcitance can be said to be the problem but inductance as well since these two reactive phenomena forms resonant circuits.

Quote:
That article indicates, as I said, that low inductance and low impedance is important, that the opposite is not desirable.
For an amp that is stable (typically with an output filter which not all amps have) and a typical speaker load yes, low resistance and low inductance is usually good.


/Peter
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