Author Topic: Series or parallel wiring in speaker cabs (Read 12735 times)

hamfist · « **on:** December 10, 2007, 07:33:27 PM »

I'm about to buy a couple of speakers for a 2x12 cab and it has been suggested to me that I run the speakers in parallel, as this is "better".
I currently run two 12" speakers in series in the cab. Does anyone have any good opinions or links about the pro's and con's of running speakers in series/parallel. I'm talking tone/electronics and logic please. No rumours/hearsay/bollocks, please !
There seems to be an awful lot of rumour and "old wives tales" about on this particular subject. I'd love to know a bit more from a highly credible source, if at all possible.

gwEm · « **Reply #1 on:** December 10, 2007, 07:41:54 PM »

well, i don't know if its 'better' or not but my experience is this:

two 8 ohm speakers in a 2x12, tried both serial and parallel combinations. they sounded both fine, but a little different. in the end i went with the parallel combination, think the treble seemed a little clearer.

hamfist · « **Reply #2 on:** December 10, 2007, 07:46:33 PM »

Quote from: gwEm

well, i don't know if its 'better' or not but my experience is this:

two 8 ohm speakers in a 2x12, tried both serial and parallel combinations. they sounded both fine, but a little different. in the end i went with the parallel combination, think the treble seemed a little clearer.

Thanks gwEm. That concurs with some other opinions I've heard, where people claim that a series arrangement gives a rather fuller midrange. If it's true, it would give the impression that a parallel arrangement is a bit more "sparkly", with a rather more restrained midrange.

Alan

Twinfan · « **Reply #3 on:** December 10, 2007, 08:37:16 PM »

The same speakers wired series/parallel will have different resistance e.g.

8ohm and 8ohm series = 16 ohms
8ohm and 8ohm parallel = 4 ohms

This is where the sound difference comes in as your using a different output from the transformer in the amp (if you match impedances between the cab and the amp like you should!).

Also, an 8ohm speaker will sound slightly different to a 16ohm speaker (you can buy both types of most Celestion speakers, for example).

The fact that it's wired series or parallel alone makes zero difference - it's the other things that go along with it......

Twinfan · « **Reply #4 on:** December 10, 2007, 08:40:37 PM »

Oh, and running a Marshall (or clone ;)) at 16ohms is what most people think sounds "better". The tone is fuller as you're using all the windings of the output transformer.

I certainly prefer the sound of the amps I've tried it with at 16ohms rather than 4ohms for tat very reason - the sound seems "bigger" to my ears.

Henk · « **Reply #5 on:** December 11, 2007, 07:22:59 AM »

Twinfan is right, there is no other reason. I dont fully agree with the bigger sound from a 16 ohm cab, it all depends on the speakers.

IMO Parallel mode works best at lower volumes and series at high volumes, running a cab at 16 ohm sounds muffled compared to 4 ohm, clarity is max at 4 ohm, tradeoff is that you get more volume at low ohmage but you also get a bit more noise.

If you have 16 ohm speakers i would not set them up in series mode, 32 ohm is just too much resistance and signal gets lost. Same with 4 ohm speakers in parallel, its just too much and too loud. Also note that if you use 2 cabs your actually run them in parallel so if both cabs are rated at 8 ohm you should set you amp at 4 ohm.

As you might understand, with lower resistance it is easier to damage your speakers if the amp/speaker powerhandling (wattage) is higher, your speakers should be able to handle twice as much watts then you amp is able to deliver at least IMO.

hamfist · « **Reply #6 on:** December 11, 2007, 07:58:56 AM »

Quote from: Twinfan

The fact that it's wired series or parallel alone makes zero difference - it's the other things that go along with it......

That has always been my suspicion Dave, despite all sorts of comments otherwise that I have read/heard elsewhere. Electronically, it seems to make sense (not that I'm an electonics genius at all, but I know a bit).

Alan

hamfist · « **Reply #7 on:** December 11, 2007, 08:00:38 AM »

Quote from: Twinfan

Oh, and running a Marshall (or clone ;)) at 16ohms is what most people think sounds "better". The tone is fuller as you're using all the windings of the output transformer.

That is EXACTLY why I have decided to get two 8 ohm speakers, to run in series for a 16 ohm cab, as this is for my Jtm45.

Twinfan · « **Reply #8 on:** December 11, 2007, 10:16:18 AM »

My 2x12 is 16ohm - two 8ohm speakers in series.

My 4x12 is 16 ohm - four 16ohm speakers in series/parallel.

Sounds good to me ;)

jpfamps · « **Reply #9 on:** December 11, 2007, 11:09:32 AM »

Actually there IS an electrical difference between running speakers series or parallel. In a parallel configuration the speakers are damped better, which is a significant issue with valve amps as they generally have a high output impedance and hence poor speaker damping. A consequence of better damping is a tighter bass response. It is for this reason most bass amps use speakers in parallel eg the SVT.

One advantage of running speakers in parallel is that if a speaker voice coil burns out then the amps still has a load on it. In a series configuration the amp will see no load and this could potentially damage the output transformer.

I would recommend two 16 Ohm speakers in parallel to give an 8 ohm load.

hamfist · « **Reply #10 on:** December 11, 2007, 11:37:08 AM »

Quote from: jpfamps

One advantage of running speakers in parallel is that if a speaker voice coil burns out then the amps still has a load on it. In a series configuration the amp will see no load and this could potentially damage the output transformer.

I've never really accepted this as a real benefit. In parallel, if one speaker blows then, yes, you will still keep a load on the amp. BUT, you may not even notice what has happened, and may continue to crank your amp into an increased impedance load, thus doing further damage.
At least in a series speaker arrangement, if one speaker dies, then you get silence and immediately you know to switch the amp off and investigate further.

It's interesting what you said about better speaker-damping in parallel circuits. I've not read that before. Interesting !

Alan

Henk · « **Reply #11 on:** December 11, 2007, 01:10:38 PM »

I have had the same recommendation to put 16 ohm speakers in a 2x12 cab, parallel wired and 8 ohm series/parallel wired for 4x12 cabs.

Great info jpfamps, i allways thought the first speaker in series would get the 'motherload' from the amp and this would couse the little less dampening i had with an old London City cab(8 ohm greenbacks) i have(which i made stereo serial 2x12(2x16 ohm) or 4x12 so it runs the amp either way at 8 ohm).

hamfist · « **Reply #12 on:** December 11, 2007, 02:49:08 PM »

Quote from: Henk

i allways thought the first speaker in series would get the 'motherload' from the amp

I have heard this before, and I am sure this is an "old wives tale". A speaker is just a transducer which ultimately transfers electrical energy to sound energy (and some heat and kinetic energy, of course). Much the same as a light bulb is a transducer which converts electrical energy into light and heat energy.
If you connect up a load of light bulbs in series, the first one in the circuit is no brighter nor dimmer than the last. The energy (power) is spread evenly.

Alan

jpfamps · « **Reply #13 on:** December 11, 2007, 03:16:20 PM »

Yes, for speakers wired in series all the speakers must pass the same current, so assuming that they are all the same impedance then they will all dissipate the same amount of power.

The reason parallel wired speakers have better damping requires a slightly more complicated explanation. Essentially for a speaker to be optimally damped it would like to see a dead short between its terminals (as this would allow the back EMF generated by the speaker and which opposes its direction of motion to have the greatest effect); so the lower the impedance a speaker "sees" the better the damping.

For a single speaker the impedance seen between its terminals is the output impedance of the amplifier, which for valve amps, even with negative feedback applied, is relatively high.

For two speakers wired in series, each speaker "sees" the other speaker impedance in series with the output impedance of the amplifier which is greater than the output impedance of the amplifier alone, and thus speaker damping is reduced.

For two speakers in parallel, each speaker "sees" the output impedance of the amplifier in parallel with the other speaker. Thus each speaker will see a lower impedance than if wired in series and thus damping will be better. Obviously this effect will be enhanced further by wiring more speakers in parallel, and this arrangement is often employed in bass guitar cabs. An SVT 8X10 cab has 8 speakers in parallel!

As mentioned above valve amps have quite high output impedances cf a solid state amp which might have an output impedance of less than 0.1 ohms before application of any negative feedback. Negative feedback is employed in most guitar amps and this has the effect of reducing output impedance. Negative feedback definitely helps to tighten up the bass response.

It is interesting to note that AC30s which employ no negative feedback around the power stage also have there speakers wired in series and this can account for the sometimes flappy bass of these amps, especially when coupled with humbucker loaded guitars.

Hope that this is helpful.

jpfamps · « **Reply #14 on:** December 11, 2007, 05:58:29 PM »

Oh, I should add that VOX compounded the bass damping issue by using an open backed cabinet.