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Speaker power distribution

jpatt2

jpatt2

Jul 27, 2009
74
1
Rochester, NY
#1
This may be an easy and stupid question, but no one at Guitar Center nor the local stores ever know what I'm talking about, so I figured I'd ask here. How does the speaker cab (or is it the amp?) know how to supply the right amount of power to each speaker? I can run my 8x10 fine bridged from my svt4-pro. How would this work in cabs with different speaker specs, such as a 4x12 with two 30w and two 70w speakers (using a smaller head of course)? What splits the power up?

Thanks for any and all help :) !
 
#4
jpatt2 said:
This may be an easy and stupid question, but no one at Guitar Center nor the local stores ever know what I'm talking about, so I figured I'd ask here. How does the speaker cab (or is it the amp?) know how to supply the right amount of power to each speaker? I can run my 8x10 fine bridged from my svt4-pro. How would this work in cabs with different speaker specs, such as a 4x12 with two 30w and two 70w speakers (using a smaller head of course)? What splits the power up?

Thanks for any and all help :) !
Click to expand...

If the speakers have the same impedance, nothing tells the amp where the power goes...it flows evenly to all speakers.

So if you have a cab with 2 30w and two 70w speakers and the cab shows am 4ohm load to an amp than can produce 200w at a 4ohm load...each speaker gets 50w, whether or not their rated for it.
 
#6
Yup...

Nothing "splits up" the power. You can wire different speakers together different ways to get higher or lower impedance and thus "make" more or less power go to different ones but the amp just sees a load and puts out power, it doesn't split it up, that requires crossovers, more than one amp, etc.
 
#7
If all the speakers have the same impedance, the power just goes pretty much equally to all of them.

In the case of speakers with different impedance, just think about the word "impedance." Impede.

In the case of an 8 ohm speaker and a 4 ohm speaker, the 4 ohm speaker will get more power because its impedance is lower. The 8 ohm speaker 'impedes' the power more.

This is probably a gross oversimplification, but without a crossover or other stuff, this is basically how it works.
 
#13
It depends. Some speakers can work well together, some won't. You won't know if a specific cab will work with another specific model of cab until you try them. And even then, it'll depend on the situation.

In addition to volume considerations, there are phasing issues to worry about. If you don't mind them, well, cool. But if you do, then it can be annoying.

As well, you won't get the same sort of... I guess it's speaker coupling... with different cabs. One of the things I noticed switching to a 2x15, after using a 1x15/2x10 rig for years, was that everything sounded a lot more powerful at the same volume, but without sounding muddy at all. This, despite either of the smaller cabs having better specs on paper than half of the 2x15. They didn't work as well together as the two 15"s in exactly the same design of box did (the cab is divided somewhat into two halves).
 
#14
this is sorta off the top of my head , But , you would get the most out of 2 different speakers by placeing them appart by a significant enough distance to give the audiance the illusion of a stereo effect.
Otherwise ... stick with same drivers out of 1 location
 
#15
beyondthe48 said:
cant you use a stereo power amp though and control the volume that each cab gets - for instance if you had a 4x10 and a 2x15 - wouldn't that (if dialed in correctly) result in an even sounding volume dispersion?
Click to expand...
Sure, if you have a stereo amp. But there's nothing to be gained by using a 4x10 along with a 2x15 anyway. If one 4x10 isn't enough use two, if one 2x15 isn't enough use two.
Mktavish said:
this is sorta off the top of my head , But , you would get the most out of 2 different speakers by placeing them appart
Click to expand...
Low frequency sources should almost never be split.
 
#16
Mktavish said:
this is sorta off the top of my head , But , you would get the most out of 2 different speakers by placeing them appart by a significant enough distance to give the audiance the illusion of a stereo effect.
Otherwise ... stick with same drivers out of 1 location
Click to expand...

Multiple sources of low end are terrible. You're much more likely to have cancelling effects doing that.
 
#17
hence I said stick with same drivers out of same location.

But on the off chance your sound for a particular song might be what your looking for ... 2 cabs that sound different not alike ... spaced enough distance so the audience can hear it (left right) might sound good.

There is almost absolutely no reason to go stereo without different responses left and right.
 
#18
Mktavish said:
...But on the off chance your sound for a particular song might be what your looking for ... 2 cabs that sound different not alike ... spaced enough distance so the audience can hear it (left right) might sound good.
Click to expand...

No "might" about it.

Think about your home stereo for a moment. Any differences between the drivers are be between lows and highs, not left and right. Besides, running a stereo bass rig isn't as simple as it sounds, especially if the cabs are widely spaced.

This is all acoustics 101:

Issue #1: from about 200hz on down, there's no such thing as stereo. In a FOH PA with a single subwoofer, people can't pinpoint the location of the sub. The low end seems to be coming from "everywhere."

Issue #2: compared to the PA system, your bass amp straddles the range of the the top bins AND the subs.

Issue #3: controlling cancellations between subwoofers is something of a black art. In stadiums and big concert halls, sound companies sometimes "steer" the low end output by placing subs in special configurations.

#'s 2 and 3 are why sound guys get their knickers in such a twist when your stage amp is too loud- you cause cancellations that mess with the bass response at FOH. Adding a second bass cab on the other side of the stage (even if they were identical), would just add an extra source of unwanted cancellations.

A full-range "stereo" stage rig with the same signal fed to widely-spaced dissimilar cabs, violates issues 1, 2, AND 3. Take whatever objections engineering types have against mismatched stacks like a 4*10 and a 1*15, and quadruple them, if you're going to separate the two cabs side-to-side instead of stacking them.

A properly-engineered stereo bass rig would be bi-amped, with spacial effects only injected into the top bins, in order to preserve the integrity of the low end. Even then, FOH sound would be better served by reserving any stereo effects for the PA...
 
#19
Mktavish said:
2 cabs that sound different not alike ... spaced enough distance so the audience can hear it (left right) might sound good.
Click to expand...
That scenario only applies above 100Hz, never below 100Hz. That's why subwoofers...be it PA, auto sound, hi-fi or home theater... are not run above 100Hz, and crossovers for subs sum the L/R feed to mono.
 

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