Fun with Damping Factor

J

Jason Lavoie

Junior
Jan 13, 2011
459
0
16
Ottawa
I've got my brain running around in circles..

let's say I have a cluster of 4 speakers that can all be run off the same signal.
at the other end of the wire (say, 200' away) I have a 2 channel amplifier that is bridgeable.

if I have 2 #14 pairs of wire, am I better off with a pair of speakers on each pair of wire, to each amp channel (4ohms per channel)
OR if I run them in series-parallel then parallel the 2 #14 pairs of wire, and then bridge the amp (8 ohms, 1 channel, double the wire thickness)

Am I right in that the load doubling plus the wire doubling would give me a better overall damping factor? and the same (or better) wattage to the speakers?
it looks like we would have to double the amp's output impedance in the calculations, but other than that we should be looking at almost 4x the original DF? with the same pile of hardware?

Is it that simple? or am I overlooking something?

Jason
 
Re: Fun with Damping Factor

This may not be one of your proposed options but putting all 4 speakers in series (32 ohms so to speak) and then running the 2 sets of conductors in parallel back to the amp would give you the best damping factor. You would get a theoretical improvement in damping by not bridging the amp (run it parallel if it's a Crown that can do it) but, the difference in damping is likely minuscule and you probably need as much voltage swing as possible to drive the speakers to their fullest potential. Whether or not this is the best way to configure the system.... we need more information. What kind of speaker are they?
 
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Re: Fun with Damping Factor

Jeff Williams said:
Why not put the amp by the speakers?
Click to expand...

Sometimes it's just not possible.
I installed a large sports complex once and even with the amp rack on the catwalk we were still pushing close to 200' to some clusters -which were only accessible by a very large boom lift so we really didn't want electronics up there too.
(Although nowadays with networked monitoring it probably would have been more seriously considered)
 
Re: Fun with Damping Factor

Craig Hauber said:
Sometimes it's just not possible.
I installed a large sports complex once and even with the amp rack on the catwalk we were still pushing close to 200' to some clusters -which were only accessible by a very large boom lift so we really didn't want electronics up there too.
(Although nowadays with networked monitoring it probably would have been more seriously considered)
Click to expand...

I was questioning the OP's application, your example shows sometimes it's not possible. In a perfect world all amps could be in a single rack and close to the speakers. But if the choice is one amp out of the rack to avoid 200' of speaker cable, I would try to find a way to get the amp closer.
 
Re: Fun with Damping Factor

200 ft of 14 gauge wire represents a series resistance of over half an ohm. Running any sort of series-parallel configuration puts at least one voice coil between any given speaker and the amp output. If you are trying to deliver large amounts of power to low frequency speakers that really depend on that low impedance / high damping factor control that an amp can exert on a big, heavy voice coil you're in a can't get there from here situation. If this is a band limited signal driving some cone mid range or high frequency drivers then moving up a couple wire gauges will probably work fine in series parallel pairs.
 
Re: Fun with Damping Factor

200 ft is roughly 61m. According to my calculations, running a 4 ohm load requires a wire with a cross section area (square) of 7,6mm for that kind of cable length.
That is roughly 8 awg.

14 awg is roughly 2mm square. I wouldn't use that kind of cable thickness for more than a 16 m run on a 4 ohm load :)
 
Re: Fun with Damping Factor

Jeff Williams said:
I was questioning the OP's application, your example shows sometimes it's not possible. In a perfect world all amps could be in a single rack and close to the speakers. But if the choice is one amp out of the rack to avoid 200' of speaker cable, I would try to find a way to get the amp closer.
Click to expand...

And I'd run heavier wire. Not only does it make maintaining the system easier, the cost of the extra copper is usually much less than the cost of running the extra power circuits and the extra mounting enclosure. And in those sort of environments, the difference is unlikely to be audible.
 
Re: Fun with Damping Factor

Jeff Williams said:
Why not put the amp by the speakers?
Click to expand...

Because the speakers are in an unforgiving, damp, cold environment (hockey arena) and unless I literally mounted an amp rack to the ceiling the absolute shortest possible wire run would still be over 100'. and in some cases with 2-4 ice pads under one roof in order to get those runs down to 100' would require a separate amp rack at each rink (just for one amp) and that's IF there is even a warm enclosed space nearby that I can use.

Jason
 
Re: Fun with Damping Factor

OK, maybe I should have qualified this a bit better..

assuming that we ALL know the following:
shorter speaker run = better
thicker speaker wire = better
lighter load at the end of a long speaker run = better

the question is: if you're stuck with no other option but to use a really long run, and let's say the customer doesn't want to pay for 200' of 2" conduit so that I can run a few #8 pairs, which configuration in the OP would net the better performance?

Jason
 
Re: Fun with Damping Factor

Riley Casey said:
200 ft of 14 gauge wire represents a series resistance of over half an ohm. Running any sort of series-parallel configuration puts at least one voice coil between any given speaker and the amp output. If you are trying to deliver large amounts of power to low frequency speakers that really depend on that low impedance / high damping factor control that an amp can exert on a big, heavy voice coil you're in a can't get there from here situation. If this is a band limited signal driving some cone mid range or high frequency drivers then moving up a couple wire gauges will probably work fine in series parallel pairs.
Click to expand...

Interesting.. are you saying that the speaker in series contributes to the damping factor? I hadn't really thought of that but it makes sense..
that would mean that any configuration involving a series connection might do more harm than good..

Jason
 
Re: Fun with Damping Factor

I am too lazy to do the math.

For speakers bolted to a hockey arena ceiling, damping factor is probably pretty low on the list of (audible) concerns.

Ignoring damping, the next concern is wire losses vs, cost of copper for heavier gauge. Common practice is to push up voltage to reduce current. Series wiring of multiple speakers could be a service nightmare as one open would impact others in a loop.

Perhaps a quick calculation of using 70v/100v distribution. (Cheaper wire, vs added transformers).

I like powered speakers, and have heard about them being bolted to ceilings, while this means distribution of both power and signal that could be more expensive, unless power is already there.

JR
 
Re: Fun with Damping Factor

Jason Lavoie said:
OK, maybe I should have qualified this a bit better..

assuming that we ALL know the following:
shorter speaker run = better
thicker speaker wire = better
lighter load at the end of a long speaker run = better

the question is: if you're stuck with no other option but to use a really long run, and let's say the customer doesn't want to pay for 200' of 2" conduit so that I can run a few #8 pairs, which configuration in the OP would net the better performance?

Jason
Click to expand...

Jason,

Ignore the idea of damping factor here, its a relatively foolish notion in the world of audio that should go away.

If the boxes are vented (a good assumption for pro boxes) then the one thing that actually does matter is how will the series resistance change the electrical damping (Qes) of the driver. The increase in Re raise the Qes and change the shape of the LF response near the box tuning frequency (Fb). This effect can be on the order of several dB.

This series Re will also make minor changes to the behavior of the passive mid high crossover, but that's a topic for another day, and that effect is comparatively minor compared to the LF behavior.

Generally the purely parallel method is preferred, but perhaps when I'm not in the office we could do another post with a comparison of both. wiring types. It can get rather involved as the drivers have an impedance, and not merely a resistance.
 
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