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SPKR cable for 4x1200 amp @4r ?

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valve head777 View Drop Down
Old Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 29 January 2017 at 4:09pm
Thanks Ceharden
Freedom of choice, choice of freedom.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote U.Viktor Quote  Post ReplyReply Direct Link To This Post Posted: 29 January 2017 at 4:16pm
so the 10m long cable is effectively 20m conductor.

Source: https://commons.wikimedia.org/wiki/File:Copper_cable_resistance.jpg

From the 2.5mm^2 wire it is 0.28R
From the 4mm^2 wire it is 0.175R
while the 6mm^2 wire is 0.117R

Since the Damping Factor(Df)  = Z_load /  Z source  (source: https://en.wikipedia.org/wiki/Damping_factor )
and the cable itself added to the source impedance, even with the best amplifier with 0 output impedance (infinite Df) you could have the following possible best damping factors for the 10m long cable:

2.5mm^2 : < 14.28 ( it would be as low as just 7! with 2R load )
4mm^2 : < 22.85
6mm^2: < 34.2

Do not you think how this physics is such a shameful when you have Df > 5000 amplifier?!  ;-D

It is obvious too why low impedance system is bad idea on higher power levels.


Edited by U.Viktor - 29 January 2017 at 4:19pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dutchman Quote  Post ReplyReply Direct Link To This Post Posted: 29 January 2017 at 4:33pm
Hahaha, too funny this thread. Copper is copper!

2.5mm² will do just fine 90 procent of the time!! 
Almost every big PA company has 2.5mm² cables for mains (16A) or for speaker use.
Damping factor doesn't exist!! 
We need more SPL!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 29 January 2017 at 5:48pm

Even if you took the resistance of 0.28 from the 2.59 mm cable into factor, it would basically mean the 1207.56 watts (69.5 volts @ 4 ohms) would be reduced to 1118.11 watts which, offers a dB differential of -0.3 dB loss in terms of SPL.  

I would imagine Safetyman can determine if a dB gain of 0.3 dB in larger cable is worth it or not. 


Best Regards, 







Edited by Elliot Thompson - 29 January 2017 at 5:51pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 29 January 2017 at 6:15pm
Originally posted by Dutchman Dutchman wrote:

Hahaha, too funny this thread. Copper is copper!

2.5mm² will do just fine 90 procent of the time!! 
Almost every big PA company has 2.5mm² cables for mains (16A) or for speaker use.
Damping factor doesn't exist!! 


That's a big statement there. Damping factor does exist, but maybe not as important as some people state. I think that Rod Elliott has an article somewhere on his site and IIRC concludes that a (real) damping factor of 50 or so is ok for most applications.


"In general I'm also in the 2.5mmsq camp.  However I did used to notice when doing live gigs that having about 15m of cable to one stack and less than 5m to the other (amps on one side of the stage), the stereo image was slightly shifted towards the shorter cables."

+1

I've noticed that as well on one of my systems. I generally just boost the gain of the far side by a couple of dB on the LMS and it's fine. You do have to be dead center to really notice anything.






Edited by Earplug - 29 January 2017 at 6:17pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Safetyman Quote  Post ReplyReply Direct Link To This Post Posted: 29 January 2017 at 9:06pm
Thanks to all, much appreciated.

 My 'normal' cable is Van Damme Pro Touring 2x2.5 twinax, as well as some 5-6 metre lengths of their 2x4mm version. The amplifier is one of Andy's  XT6004EQ's, which on recorded music at least, has never been on more than half power ( it is just too loud above that ).
I have ordered some Klotz SY225 as, having used their 1.5 version for tops on my small EV system, it sounded rather better than the 2x2.5 Van Damme Pro Touring. Hoping that the 2x2.5 Klotz will sound ok, too.
Yes, I get it, that keeping the cables as short as possible, of equal length and with both stacks equidistant from the amp rack is preferable . Not always possible, though, as the last thing you want are muso's falling -over the cabling or the rack as they move about the stage area in low light.
Doubling up the cables sounds like an idea I might try in the future, if all else fails.
Protect your hearing, and feel the music.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jasonstry Quote  Post ReplyReply Direct Link To This Post Posted: 29 January 2017 at 11:48pm
I use 4mm for my main PA and I have two reasons for doing that nobody can argue with. The first one is that I was given a load of it (mostly VDC) for nothing and the second is that I am a small operator so the weight isn't an issue. If either of those things hadn't been true I would be using 2.5mm. I plan to add another two high/mids soon and will need more speaker leads. I will be using 4 core 2.5g HO7RNF.
Hope that helps!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote B_Bender Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2017 at 9:16am
You're telling us that one speaker cable 'sounds better' than another speaker cable over short runs?

I needed some comedy on a monday morning, thanks for the laugh! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Safetyman Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2017 at 9:34am
Glad it 'made your day' LOL



Edited by Safetyman - 30 January 2017 at 9:35am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2017 at 11:29am
Originally posted by B_Bender B_Bender wrote:

You're telling us that one speaker cable 'sounds better' than another speaker cable over short runs?

I needed some comedy on a monday morning, thanks for the laugh! 

A PKN amlifier is so good and so much better than anything else that you can hear the difference in cables lol LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote U.Viktor Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2017 at 12:19pm
Originally posted by concept-10 concept-10 wrote:

Originally posted by B_Bender B_Bender wrote:

You're telling us that one speaker cable 'sounds better' than another speaker cable over short runs?

I needed some comedy on a monday morning, thanks for the laugh! 

A PKN amlifier is so good and so much better than anything else that you can hear the difference in cables lol LOL


Well , if you have an "INUKE-category" power stage (with so variable source impedance..) likely will not hear the difference between 2.5 and 4mm^2 cables without very sensitive ears..

However if you want to bring out the best sound from your drivers, it would need a good power source and the influence of cabling is noticeable mainly NOT in SPL but in sound quality.
The amplifier is a living "coupled system" with the moving coils of drivers, and things like cable resistance has effect on the system behavior!


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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2017 at 12:40pm
maybe I am missing something here but I've never understood why damping factor matters for amplifiers other than valve amps.

if I were to connect a resistive test load to an amplifier then we would understand the resistance of the resistor as being the load impedance. but when that resistance is a speaker cable it is said to be part of the source impedance. WHAT?

doesn't the resistance of the voice coil make other smaller resistances in the circuit irrelevant?

damping factor is about behaviour at driver resonance. at resonance the impedance of a loudspeaker is very much higher than its nominal value. so aren't damping factors calculated using nominal values out by a factor of ten?

isn't a more significant value the ratio of acoustical impedance (at resonance) to electrical resistance (voice coil + cable + source impedance)?
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