4mm cable VS serious power

  I have to ask, why do you need cables that long? For mobile gigs I can usually get away with a 10m to one stack and a 5m to the other, It's rare that I need to use more than a 20m cable even on a permanent install. 

Edited by njw - 12 June 2021 at 11:35pm

Before covid the system was out 2,3 times a week in different configurations depending on what the client hired, festivals to clubs.. 2core was the best option because can use it in any situation any configurations so works out perfectly and never let me down in 10 years. Im not interested in moving amp racks closer with 2m cables or swapping amps because my system does what it needs to and promoters and customers go wild for it so no need to change. 

4D wrote: Aman Gebru wrote: Your problem is damping factor and power handling of the cable. The total system damping factor of a VZ5000 driven 2 ohms per channel on a single 4mm2 cable will be 19, which is ridiculously low. I wouldn't even go near an amp/speaker combo with a damping factor of less than 50, and ideally 100. Even if you doubled up the 4mm2 cable DF would only get to around 34. Power reaching the speaker on a single run of 4mm2 would be 4504 watts, so you've lost 500 watts. Max power handling for the single cable would be 1600 watts. All rise and hail..  Be interested the formula to calculate the damping factor for amps/swg/length

500 watts sounds like a lot, which is why I converted it to actual decibel loss 😅

Funnily enough the manual for the VZ5000 has a section on this, and a little tool to figure out the cable thickness needed for a given cable length and desired DF. It’s on pg. 18.

The load that msoundsystem is using currently is 4 ohms when connecting two boxes on one run of cable with a link, which gives a source resistance of .1 Ohms for a desired DF of 50. That means a minimum of AWG 10 for a 25 metre cable, or >5 mm squared.

For a more general way of calculating it, refer to John Eargle’s book Electroacoustical Reference Data:


Don’t forget that total cable length is 2x the distance from amp to cabinet.

But a little bit of maths on the cable and the driver’s DC resistance shows that DF is often misunderstood and very, very often over-rated in terms of it’s importance. A nice and easy to follow example is here:
https://linea-research.co.uk/wp-content/uploads/LR%20Download%20Assets/Tech%20Docs/Damping%20factor%20debunked%20-01a.pdf

Edited by toastyghost - 13 June 2021 at 1:02pm

So what sort of cable do you need to use to cover a long distance, using all the cores of an 8 core cable to drive a pair of scoops, 8 x 4mm in a single cable, everything else (kick, lo-mid, hi-mid, tops) on another 8 x 4mm core cable. Is there a better solution than this for 30m + runs (60m there and back).

I had a show lined up the other day (Cancelled because of Covid, proper shit) that we were going to have to run 75m+ of speaker cable and the plan was all on 2.5mm Socapex via NL8 tails because we wanted amps at FOH. How do they do the cable runs to delay stacks on main stage festival stages? Thats a huge distance to cover.

Or even fly the racks behind the arrays. It makes sense from every angle to put the amps as close as possible to the speakers.

Under those circumstances the gig shouldn’t happen.