Bare Knuckle Pickups Forum
Forum Ringside => Guitars, Amps and Effects => Topic started by: hamfist on December 10, 2007, 07:33:27 PM
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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.
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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.
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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
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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......
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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.
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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.
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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
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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.
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My 2x12 is 16ohm - two 8ohm speakers in series.
My 4x12 is 16 ohm - four 16ohm speakers in series/parallel.
Sounds good to me ;)
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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.
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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
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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).
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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
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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.
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Oh, I should add that VOX compounded the bass damping issue by using an open backed cabinet.
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OK, this i have to read again tomorrow morning :lol:
I do have a (probably very stupid)question.
What if i had a 2x12 cab with 2x8ohm speakers in series and would use my amp at 8ohm anyway, would that counter the damping loss?
I also think my vintage 4x12 'Bass' cab have all 4 speakers in parallel, which do sound pretty tight in the low end allthough they are not the same kind of greenbacks then in my London City cab. Its been a long time since i had a good look whats inside my cabs though :oops:
Very nice food for though actually, thanks.
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Great posts jpfamps - some of the most informative stuff on series/parallel speaker circuits that I have read on the www. Thanks.
You're making me wish that I'd got two 16ohm speakers to run in parallel, instead of my two 8 ohms......but the Lord giveth and then taketh away ...... at least with a 16ohm load, I get to use all the windings in the OT. I'm hoping the tonal advantage of that will be worth the loss of a bit of speaker damping.
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I allways thought the ohmage selection taps were on the second stage and the bigger primary stage was the bulk of like 1,5k of windings.
Anyway, alot of vintage combos were wired 2x12 in parallel and ran at 4 ohm, like the fender twin for instance and so on.
If you have time just try it, i think it will be a treat if youre used to 16ohm/series.
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Indeed most of the windings are on the primary.
Generally you are advised to use the highest ohmage tap to employ as much of the secondary as possible. Conventional wisdom suggests that the amp sounds better when this is done, however I don't really have an opinion on this either way as it is very difficult to make a sensible comparison.
To make the correct comparison you would first have to ensure the load is correctly matched. I personally think that valve amps sound best when the load is correctly matched, as does everyone who I've had a chance to test this with. I was chatting recently to Andy Marshall of THD electronics (who REALLY knows what he is doing) and he also concurs with this view.
Thus if you have a 16 ohm series parallel 4 x 12 cab it will of course sound different (and almost certainly better) when connected to the 16 ohm tap than the 4 ohm tap. You could of course rewire the cab for 4 ohms and it will probably sound better on the 4 ohm tap, but you now have a cab wired with all 4 speakers in parallel. This will course sound different to a 16 ohm cab wired in series parallel regardless of any transformer utilization. So as you can see (hear!) to do a worthwhile comparison is hard, and when someone says they prefer the sound of a Marshall run at 16 ohms you really have to know what exactly they are doing before you can draw any conclusions.
To further complicate matters, you also need to consider how the transformer is wound. For example Hammond wind most of their transformers so you will use virtually all the secondary whatever load you match. You can also wind a transformer with secondary windings that can match 4 and 16 ohms whilst using all secondary windings. So secondary usage is less of an issue with this style of transformer, although winding topology may be.
Many vintage repro Marshall transformers are made with unused windings eg a 100 V line secondary, or 9K primary windings in the case of the old RS-style JTM45 output transformers. Many people think that this affects the sound of the transformer, although my guess this is due to the topology of the windings as a result of having the extra taps rather than any effects of the unused windings, although to tell the truth there probably isn't a definitive answer to this.
My advice to you would be to try the speakers in series and parallel attached to the appropriate taps and use whichever you prefer.
By the way vintage Fender Twins only have single secondary winding which matches the amp to 4 ohms, so as you are using all the secondary windings which tap you should connect to is not an issue.
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Very insightfull post, thnx again jpfamps.
Allthough the OT does contribute alot to the final amp sound i never felt it sounded less good on any ohm setting with the appropriate cab, it does however sound different, simple as that IMO.
When i think about what my amp sounds like on either cabinet options i think the 4 ohm parallel 2x12 sounds alot tighter and clearer then the series 2x12 option, however the 16ohm setting has a real nasty growl to it when pushing the amp a bit. I personally dont like the somewhat darker sound at a 16 ohm setting on my JCM800, dont know why that is but anyway i do. I feel i can compare this fairly reasonably because i have a total of 10 geenbacks in 3 cabs which have a similar signature.
Ill try a carefull mismatch later today or maybe tomorrow, see what that brings, if my memory is correct it just sounds like they are out of sync with the sound, kind of frizzy highs deal.