Speaker Cable Runs

[djgorey 0]

I was just wondering if somebody could give some guidance as to the maximum length speaker cables should be from the amp.

 

I bought a 100m reel of 2x2.5mm Van Damme cable (and Neutrik NL4 speakons) and made up a load of speaker cables of varying lengths to cater for most venues. I have one set that are about 15m-20m long and I was wondering these will be ok to use on my side fills.

 

I understand that, for bass, it would be better to have shorter runs and/or 4mm wires and that's fine because, generally, the bins are close to me and I don't need to have long runs down the other end of the room, but I will shortly be doing a gig for 600 where I will be using at least one, if not two pairs of side-fills. The power handling of the cabs is 300w and will probably be supplied with about that. Should this be ok with my 15-20m cables? Does the impedance seen by the amp make any difference (if so, might have to borrow a 4th amp)?

 

Sub-question, what are the effects of using cable that is too thin and/or too long?

 

Thanks for your help tongue out icon

[YourBigEvent 0]

20m is not a long run for Speakon cables

[djgorey 0]

What is a "long" run? Of course, the speaker cables are only 2 core, not nice XLR.

 

I've done some more research and the impedence seen makes one huge difference! I can only find reference to AWG ratings but on a 50 foot (less than 20m) 10AWG cable run, the power loss for a 4 ohm nominal impedence is 0.15% but only 0.01% for 8 ohm. A factor of more than 10!

 

I got the info from here

 

So that's power loss - what other effects should I be aware of? Perhaps the damping control of the amp?

[superstardeejay 0]

speaker cables are only 2 core, not nice XLR

 

It doesnt matter what connectors are used, its the cable that counts! Maybe you're getting confused with balanced mic cables that use 2-core plus screen cable with 3-pole XLR..they do this due to the fragile nature of signals at this level.

 

 

[Bouncy Dancefloor 0]

you wont have any noticeable problems at 20 metres

 

when you start going to 50+ metres, then do the sums

[YourBigEvent 0]

All too technical, 20m is not very long, and any DJ will not have too long runs.

 

Only need the maths if you are installing numerous speakers around a hall.

[djgorey 0]

Superstar - Yes indeed, I know that balanced cables experience almost zero signal loss whereas unbalanced do.

 

Bouncy - Thank-you, that's the sort of answer I was after.

 

and any DJ will not have too long runs.

 

With respect, a generalisation such as that ignores completely the huge variety of different work and different djs out there. I wouldn't dream of saying "all djs do such and such" or "no dj would need ..."

 

Only need the maths if you are installing numerous speakers around a hall.

 

I am installing numerous speakers around a hall (well, ballroom), that's why I asked. I'll admit quite happily that it's not a stadium or a club with multi-zones but it is still worth considering the effect of the placement of the speakers. As for "too technical", I haven't even begun loking at the delays required yet.

 

[Kingy 0]

It would be un-usual to have this sort of requirement though in all fairness. As you rightly say, you will need to calculate the delays carefully so that it doesn't sound awful!!

 

By far the vast majority of DJ's will never have to do this. By the same token, the vast number of DJs will not know how to work out the delay times either!!

 

And when working with delayed FOH stacks I have to wear monitoring at all times personally.

[norty303 0]

There seem to be some other issues creeping into this discussionj about speaker cables.... smile icon

 

Not sure where the balanced signal cable in relation to speaker cable came from but the point of a a balanced cable is for noise rejection, typically over longer runs where a cable is likely to pick up more noise. Runs under 10m don't really require balanced, although most people use them as its easier to just carry one type of cable.

 

A good rule is to minimise the lengths of speaker cables. Better to do long runs of signal cable. I know some big installs that suffer badly because of length/guage of speaker cable used for the impedance being presented to the amp.

 

For mids and tops and most mobile applications you probably won't have any problems using 2.5mm cable unless you're running low impedances, and even then perhaps not too much of an issue. Running high power bass at low impedances is another matter and you should try and keep cable runs short and of high guage. Also try and use single pieces of cable per run, any join (speakon couplers for example) can have an impact on the sound (I have a link to an interesting investigation into this if anyones interested....)

 

When placing speakers in a big room, you really have a choice of 2 setups, either in the round, with all speakers facing inwards, or having a focal point from one side, with delays to pick up where the level drops off.

 

The first method requires no delays, but does result in a sweet spot in the centre, with ever increasing 'clatter' as you move away from this point. Delaying only serves to move the sweet spot around the room in this case, leaving the clatter elsewhere. Can work at low levels and with very careful speaker placement, but requires speakers with very good patten control.

 

The second involves all the speakers facing the same way, with 'delay' stacks to re-inforce where the main speakers drop off. Much easier to get sounding right, and most LMS on the market these days offer delay correction as both time and distance units. Simply pace the floor between FOH and delays and enter this distance. Usually its as simple as that.

[YourBigEvent 0]

1ms/ft was what I was told many years ago Kingy, or do you use the Haas effect ?

[Kingy 0]

That is about right, and no, the Haas effect is not necessary nor relevant.

 

Delay (milliseconds) = 1000 x ( D (distance in feet) ) divided by 1130 to be precise!! This only works for one tower ( or two at the same level)

 

 

[supersound dj 0]

this is getting quite in depth and complicated now.

 

interesting tho

[djgorey 0]

this is getting quite in depth and complicated now.

 

interesting tho

 

As mentioned above, in a lot of situations, one doesn't need to worry about delays and speaker cable length and stuff like that, but it is worth learning about it now so that when you have a gig that requires the knowledge, you at least have a basic understanding. I always liked the technical side just as much as the dj-ing itself.

 

As Norty said, most LMS units like the Behringer Ultradrive have delay function built in where you just tell it how far away the speakers are (and what temperature the room is!!!) and it works out the rest for you.

Edited January 7, 2009 by djgorey

[Kingy 0]

Temperature!! Well, yes, it is a factor but not until you get well below the average temperature of a function room, and then its a very small consideration!!

 

It's not worthy of consideration in this example.

[YourBigEvent 0]

Like I say too technical for most people, including Kingy and myself !!

 

If it were me I'd buy a delays unit to do the maths for me.

[Kingy 0]

I am surprised you manage to breath both in and out Mr Harris...... tongue out icon

Edited January 7, 2009 by Kingy

[Welsh Audio Man 21 0]

I have comfortably run 2.5mm speaker cable (happened to be van damme too), at a distance of 35m for an install... this run was for centre fills.

 

Give me a call if you want any help/ advise in regards to delay.

[djgorey 0]

I have comfortably run 2.5mm speaker cable (happened to be van damme too), at a distance of 35m for an install... this run was for centre fills.

 

Give me a call if you want any help/ advise in regards to delay.

 

Cheers mate! I know we discussed it, I was just after a figure like you and Bouncy have given me of "x metres is ok, don't do more than so and so".

[Welsh Audio Man 21 0]

Cheers mate! I know we discussed it, I was just after a figure like you and Bouncy have given me of "x metres is ok, don't do more than so and so".

 

no problem mate.. plus, your only using it as fill, its not as if your running your main FOH that distance ...

[norty303 0]

If it were me I'd buy a delays unit to do the maths for me.

 

What are these 'delays units that do maths' of which you speak?

 

I'm sure that DJGorey's suggestion of the Berringer Ultradrive (LMS) is one such clever box of tricks. You simply input the distance your delay speakers are away from the main speakers on the screen that controls the signal going to them, and it magically applies the neccessary delay!

 

Distance is the only thing you have to consider, signal travels at near the speed of light so can be safely ignored as far as delay is concerned, even if you're using cables still connected to that 500m drum you thought was a good idea from ebay.......

[YourBigEvent 0]

Thats the ones Norty

[djgorey 0]

What are these 'delays units that do maths' of which you speak?

 

They're called calculators!

 

Speed of Sound is 340m/s (speed of light is 3x10^8m/s) so if a you are stood 21 meters away from the front stack and 1m away from the in-fills the sound from the stack will reach you in 21/340ths of a second and from the in-fills in 1/340th of a second so you need to delay the in-fills by 20/340ths of a second or 1/17th or 0.05882352941176 seconds.

 

I'm told, if you squeeze the speaker cable, you can slow down the signal to apply the appropriate delay. Can't remember who told me though

 

[Andy Dunn 0]

They're called calculators!

 

Speed of Sound is 340m/s (speed of light is 3x10^8m/s) so if a you are stood 21 meters away from the front stack and 1m away from the in-fills the sound from the stack will reach you in 21/340ths of a second and from the in-fills in 1/340th of a second so you need to delay the in-fills by 20/340ths of a second or 1/17th or 0.05882352941176 seconds.

 

I'm told, if you squeeze the speaker cable, you can slow down the signal to apply the appropriate delay. Can't remember who told me though

 

 

 

Oohhh steady this is getting far too complicated!!!!!

[djgorey 0]

I've remembered who it was who told me about the cable delay thing - it was the same guy that sold me the sky-hooks for hanging my Martins in difficult venues.

 

I knew I'd remember!

 

[norty303 0]

They're called calculators!

 

 

 

Wow, those things process delays too?!

 

'System Control by Texas Instruments'TM

Edited January 8, 2009 by norty303