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thylantyr
12-11-2006, 02:12 PM
I've noticed alot of people on forums jumping on the CAT5 speaker wire
bandwagon. They are taking networking wire and making into speaker
wire as they think it's superior.

To make matters worse, these guys did a wire test;
http://www.audioholics.com/techtips/setup/interconnects/DIYSpeakerCablesp1.html

This test is misleading to the consumer as they rank cables implying that
certain brands aren't good as speaker wire.

I did some basic electronics math to see what the skinny is all about.

Wire has resistance, capacitance and inductance. They measured those
variables and formed a conclusion. But there is more to the story than
what was told. How does the particular wire perform in it's 'line driving'
application ?

How much resistance, capacitance and inductance is ok before your
speaker wire behaves like a low pass filter which will attenuate the higher
audio frequencies? We can look at wire gauge and know it's current
ratings per foot, so I don't need to talk about this as we already know.

Preamp Line Driving
This Rane article "Practical Line-Driving Current Requirements" is a good read.
http://www.rane.com/note126.html

It talks about small signal line driving {preamp level}, but the same is true
for large signal line driving, ie amplifier to speaker.

Look at figure 2.

Ro = Source output impedance
Cw = Total cable capacitance
RL = Input impedance of the load.

Look at figure 3. The formula.

You use this to analyze your signal path, either preamp or power amp.

For instance, lets say you bought some cable to make your own RCA
or XLR preamp cables. If you know the cable capacitance, source output
impedance, and destination input impedance, you can see if that cable
you chose will will in the audio range with no low pass filter effects in
the audio range.

Lets say your preamp is 100 ohms output impedance, and your amplifier is
10,000 ohms input impedance and the cable you chose has a rating of
50 pF {pico Farads} per foot. You decide you need a 100 foot cable.

Math.

Ro = 100 ohms
Cw = 50 pF x 100 foot = 5000 pF {or 0.005 uF, or 0.000000005 Farads}
RL = 10,000 ohms

Because the Ro is significantly less than RL, you can use the short formula.

Fc = 1 / (2 pi Ro Cw)

Fc = 318 khz

318khz is way higher than the audio range, 20khz so this cable would
work in this application.

Power Amp Line Driving

Amplifier output impedance is very low vs. the speaker load. Amplifier damping factor gives you a clue on how low output impedance is. Damping factor is
a ratio.

DF = load / amp output impedance.

or

amp output impedance = load / DF

If your amp has a damping factor of 100 {assume @ 20khz} driving an 8 ohm
load, then the amp output impedance is about 0.08 ohms.

Fc = -3dB point, cutoff frequency.
Ro = 0.08 ohms
Cw = 50 pF x 100 foot = 5000 pF {or 0.005 uF, or 0.000000005 Farads}
RL = 8 ohms

Lets use the same 50pF capacitance and lets say you are running a 100 foot
speaker wire.

Because the Ro is significantly less than RL, you can use the short formula.

Fc = 1 / (2 pi Ro Cw)

Fc = 379 Mhz

This is way outside the audio range.

Speaker Wire Inductance

Speaker wire is like an inductor and when you connect your amplifier
to speaker wire to the speaker, it's as if you are adding an inductor in
series just like a first order woofer crossover.

The math is simple.

Fc = RL / (2pi L)

Fc = -3dB point, cutoff frequency.
L = cable inductance
RL = speaker load

The worse speaker wire of the bunch tested has an inductance of 0.3 uH
per foot. Lets assume you are going run 100 foot between amp and speaker.

L = 0.3uH x 100 feet = 30 uH
RL = 8 ohm speaker

Fc = 42.4khz

This is way outside the audio range of 20khz

Conclusion
Unless I analyzed wrong, cable capacitance even using cheap cables doesn't play
a big role in affecting the audio signal. Even cheap speaker wire with high inductance
and a 100 foot run is still 2x beyond the audio range where you have low pass filtering effects.
To add, inductance in preamp cables connecting to high input impedance equipment doesn't
play a big role either.

Calikid
12-11-2006, 02:14 PM
:ohsnap:

long thread

thylantyr
12-11-2006, 02:16 PM
Cost

CAT5 vs. generic speaker wire

I see two simple ways to wire up the CAT5. CAT5 is 4 pairs of conductors,
24 awg each.

1. Four conductors in parallel to make an equivalent 19 awg speaker wire
run. This gives you two conductors per cable run, 19 awg each. 19 awg
is a little anemic as most people prefer to over-engineer their wiring needs
and run 14 awg - 16 awg wires from amp to speaker and heavier awg for
subwoofer runs. Depends on length of run, etc. I personally wouldn't wire up
my house with 19 awg speaker wire. I would use 18 awg for wiring up
the drivers inside a speaker box as the runs are short in length.

2. ALL eight conductors in parallel to make an equivalent 15 awg speaker wire
run. This only gives you one conductor so you need to run two seperate
CAT5 cables for each speaker. What a PITA if you are wiring up your home.

Cost:

500 foot CAT5 cost $60
1000 foot CAT5 cost $120

500 foot 18 awg generic speaker wire cost $60
500 foot 16 awg generic speaker wire cost $80

If you chose option 1 above for your application, then there is no cost
advantage to buying CAT5. Two conductor CAT5 wired for stereo would
yield 19 awg speaker wire. You can buy generic speaker wire 18 awg
for the same price.

If you choose option 2 above for your application where you use CAT5
to make a single 15 awg cable, then you need 2x more cable as you
need two cables per speaker vs. generic 16 awg speaker wire. Cost
$40 for CAT5 plus you have 2x more cables to run, more messy.

If I'm wiring a long run from amplifier to speaker, lets say a few hundred
feet, then I would now look at speaker wire inductance and do the line
driving math to see if the low pass filter is outside the audio range, etc.

Mitch86
12-11-2006, 02:25 PM
Wal-Mart speaker wire works for me.

RaiN
12-11-2006, 06:09 PM
^Shizzle

azbass
12-11-2006, 06:12 PM
ok

baseballer1100
12-11-2006, 06:13 PM
cool.

thylantyr
12-11-2006, 07:51 PM
The reason I like to hang out in car audio forums is because the older
crowd as found on dedicated home audio forums starts to lose their mind.
Lucky me, I'm still immune to this effect as I age - LOL......

All of a sudden, things that have been working for ages no longer works anymore and you need esoteric audio items like DIY CAT5 speaker wire
with a million braids, rocks in a jar, $500 AC power cord, etc., to make it sound
good again... ROFL ...

In car audio, people tend to keep an open mind and use more common sense. :)

azbass
12-11-2006, 07:53 PM
ok.

thylantyr
12-11-2006, 08:45 PM
Check out the article I linked, generic Sound King wire was tested,
4 versions from standard to esoteric braiding. All the braided versions
tested for higher inductance {worse} than the standard un-modified wire. lol

ivrex
12-11-2006, 08:50 PM
pear cables
http://www.pearcable.com/
speaker wire for $7.50 per foot

PV Audio
12-11-2006, 10:07 PM
I have trouble understanding how cables can be "accurate". Bullshit.

ballstothewall
12-11-2006, 10:58 PM
I have trouble understanding how cables can be "accurate". Bullshit.

But if you've got the money, who cares?

thylantyr
12-12-2006, 02:06 AM
Dielectric Absorption is another audiophile's weapon to justify the voodoo wire.

Don't take my word that this is also a bag full of donkey doo, these guys say
the same thing.

Debunking the Myth of Dielectric Absorption
http://www.audioholics.com/techtips/audioprinciples/interconnects/CableDielectricAbsorption.html

It's pretty bad to engage in amplifier ABX testing, but it's really ridiculous
when people *really* believe they can hear a typical run {lets say < 100 foot}
cable.

But on the other hand, as you can see from the math, one *can* make a bad cable
that will act like a filter in the audio band, but no manufacturer in their right mind
would even make such a product. lol

ngsm13
12-12-2006, 02:19 AM
Well durr.

nG

joetama
12-18-2006, 01:10 PM
To each his own. Because I want to spend the extra money doesn't mean I am crazy. It means I have it and I want to spend it. CAT5 I personally don't think would make a very good speaker cable unless you are running 70/140 volt line. And even in that case it's not made to carry that sort of voltage so there would be safety issues there.