Impedence Pros & Cons

[PUCKBOY99]

O.K. all you electronics whiz-kids....try to keep this on a 3rd grade level, will ya' !!!! :13:

What are the pros & cons of wiring speakers parallel vs. series?

Are there any reasons I would prefer to run 4 8ohm speakers in parallel for a 2ohm load as opposed to 4 8ohm speakers in series/parallel for a 8ohm load OR 4 8ohm speakers in series for a 16ohm load?????????????

Does the overall load affect your tone & more importantly, does it have an affect on your amp????


THE THINGS THAT KEEP ME UP NIGHTS!!!!!!

 

[Artie]

Re: Impedence Pros & Cons

Relative to a tube amp, you want to achieve whats called "maximum power transfer". Which simply means that the amplifier is transfering as much of the power as possible, that its producing, into the speakers. If you don't match the output impedance of the power transformer to the load of the speakers, some of the power will be absorbed, (as heat), in the output transformer. Thats a loss of power.

The next thing is, and this applies to both tube and SS amps, the higher the speaker ohms, the lower the current at a given power level, and subsequently, the higher the voltage. IMO, this is better because lower current generally equates to lower heat.

So, for me, I'ld want the highest ohmage on the cabinet as possible, and in the case of tubes, as high as possible, within the output rating of the transformer.

 

[PUCKBOY99]

Re: Impedence Pros & Cons

So, ideally, you would want 4 16ohm speakers wired series/parallel @ 16ohms???

 

[aleclee]

Re: Impedence Pros & Cons

There's a lot more to this question than you might think.

First, as ArtieToo points out, there's the question of impedance matching. All other things being equal (and they never are), an amp will sound subtly different at different impedances (assuming you can set the output impedance and are using a cab of appropriate impedance). This is because you're using different settings on the output transformer which affects the load placed on the power tubes. As for whether the 4/8/16 Ohm tap sounds better, that's a matter of taste and IMO it's fairly presumptious to say that one sounds better than the others (see my sig ).

Another factor that's rarely mentioned is damping factors. This can have an effect on how "tight" or "loose" an amp responds. There are two ways you can connect four 8 Ohm speakers into an 8 Ohm load of greater handling capacity: series/parallel or parallel/series. One wires each pair in series (16 Ohm load) and then connects the pairs in parallel. The other wires each pair in parallel (4 Ohm load) and then connects the pairs in series. Though each presents an 8 Ohm load to the amp, they'll sound different due to the differing damping factors.

One more word about impedance mismatches. Though a mismatch by a factor of 2 is generally safe, with a tube amp it's generally easier on the trannys to run with too low a load (e.g., 8 Ohm amp into a 4 Ohm cab) than too high a load. Never run a tube amp without a load as it can fry the output transformer.

Never run a SS amp into a load that's lower than its minimum rated impedance as that can fry the output transistors.

 

[aleclee]

Re: Impedence Pros & Cons

So, ideally, you would want 4 16ohm speakers wired series/parallel @ 16ohms???

That would be very much preferable to wiring them all in parallel @ 2 Ohms.

 

[muttonchopsrule]

Re: Impedence Pros & Cons

aleclee covered a lot of it, and i'm sure someone will come along soon to put it in better words than i can. but basically, it's best to have the impedence of your cabinet match the impedence of your amp. it's more important when dealing with tube amps, as they are more sensitive to this. and in most cases, it's safe to mismatch higher, but not lower. (for instance, an 8 ohm load into a 16 ohm cabinet would fly, but an 8 ohm load into a 4 ohm cabinet would be bad news). but if you did this, you would notice a significant drop in volume and probably a change in tone.

 

[PUCKBOY99]

Re: Impedence Pros & Cons

Thanks fellas...I appreciate your expertise & keeping it on my level!!! :beerchug:

 

[JumpMarine]

Re: Impedence Pros & Cons

This is a great thread and it answered some questions that I had about safely running a different cab with my Marshall combo.

 

[aleclee]

Re: Impedence Pros & Cons

and in most cases, it's safe to mismatch higher, but not lower. (for instance, an 8 ohm load into a 16 ohm cabinet would fly, but an 8 ohm load into a 4 ohm cabinet would be bad news). but if you did this, you would notice a significant drop in volume and probably a change in tone.

You have this reversed. With an 8 ohm tube amp, it's safer (for the output transformers) to run into a 4 ohm cab than into an 8 ohm cab. It's harder on the tubes but it's a lot easer (and cheaper) to replace tubes than transformers.

For SS amps, it's the reverse. It's perfectly safe to run an 8 ohm SS amp into a 16 ohm cab but you risk frying the output transistors if you run into a 4 ohm cab.

The easy way to remember this is that it's safer to run a tube amp across a short circuit than an open circuit. I suspect this is why very few tube amps have headphone jacks--it would need a dummy load to keep the OT from frying.

SS amps, on the other hand, often have headphone jacks and they're perfectly happy running with no load.

 

[Kent S.]

Re: Impedence Pros & Cons

I'll be lazy and skip any explanation other than to say that it will cause a slight difference in tone ... It's not a TONE control ...Just wire it for what the amp wants to see. You can go higher than the load required, but not lower, and even higher isn't a great idea with tubes,S.S. doesn't seem to mind if you go higher than what the output wants to see.

 

[aleclee]

Re: Impedence Pros & Cons

You can go higher than the load required, but not lower, and even higher isn't a great idea with tubes,S.S. doesn't seem to mind if you go higher than what the output wants to see.

I hate to beat this topic to a pulp but I'd hate to see someone's amp get damaged 'cause there was confusion about what kind of impedance mismatch is less hazardous.

With a tube amp, having a cab whose impedance is too high is more likely to cause catastrophic failure than one that's too low. If you don't believe me, please believe Ted Weber [some stuff deleted to meet the 4K limit, click on the link for the text in its entirety]:

Technically, you should always provide a load that is recommended by the manufacturer of the amp. The designer of the amp chose a particular output device (tube) and specified all of the operating voltages for the output stage so the tube would work at its optimum efficiency while delivering maximum power to the load with minimum distortion. Ok, so let's discuss the problems associated with mismatches. When you use a load that is lower than the intended load, the output has to drive the load (speaker) with more current because it is a lower impedance than is expected. [...]
As the current draw in the secondary increases, the primary has a more difficult time transferring the signal to the secondary, so the secondary signal to the load gets squashed, or 'soft-clipped'. This soft clipping is called regulation. While regulation is desireable in a power supply, it is undesireable in a transformer. In other words, in a power supply, if the input voltage or the output load current changes, we don't want the output voltage to change. In a transformer, we want the output voltage to follow the input voltage and not regulate at all. [...]
OK, on to mismatching the other way. A speaker is a current operated device in that it responds to the current through it to generate a magnetic field that works against the magnetic field of the speaker magnet to make the cone move in and out. Thinking in very short amounts of time, when the output charges up the voice coil with current, then the signal goes away or gets reduced, the cone system moves the voice coil back to its home or resting position. As it is moving back, it generates a voltage that is fed back up the line into the transformer and appears in the output circuit of the amp. This generated voltage is often referred to as flyback voltage, because we are charging up an inductor, then when we disconnect or stop charging the inductor, the magnetic field in the inductor collapses and induces this big voltage into itself. This big voltage then 'flies back' to the source of the charging current. [...] The bottom line is that the voltage fed back to the output circuit is oftentimes much higher than the voltage that was used to drive or charge up the voice coil initially. This voltage gets transformed up by the turns ratio of the output transformer, and in many cases can be over 1,000 volts. What happens then is that arcing can occur between the pins on the output tube socket. Once this has occured, a carbon path forms on the tube socket between the pins. The carbon path allows a steady current to flow between the pins and eventually burns up the socket due to the heat that is generated.

 

[Kent S.]

Re: Impedence Pros & Cons

I hate to beat this topic to a pulp but I'd hate to see someone's amp get damaged 'cause there was confusion about what kind of impedance mismatch is less hazardous.

With a tube amp, having a cab whose impedance is too high is more likely to cause catastrophic failure than one that's too low. If you don't believe me, please believe Ted Weber[/URL] [some stuff deleted to meet the 4K limit, click on the link for the text in its entirety]:

The point is on driving a higher impedance (less of a load) say 16 when something wants to see 4, yeah you may have a lot of tranny saturation, it may drive the reflected impedance even higher (not sure about that), the inductance of the voice coil isn't all that great, so the flyback voltage won't be much, although I agree with the reversed transformer action he speaks of.
I've seen a few burned tube sockets, replace the sockets, okay that was easy ... if a tube amp is driven wide open into a higher load I can see it doing damage, but not say at a third to half volume. Also a mismatch of 4 into 8 ohms isn't as bad as say 4 into 16 ohms.
Driving to low a load say 8 into 4 ( or 2 SF super reverb cab configuration), presents a problem with the amps try to supply more current ... this leads to blown output trannies and and in some cases power supply failures as well.
Yes the older amps will try to brown out a bit, some of the newer tube designs will try to supply the increased current demands ... again blown output trannies are probably to be expected, they are the biggest, heaviest and most expensive part of the repair. Bear in mind also that in the first example the current/voltage is constantly pulsing back and forth to and from the speaker, and across it's terminals and the output trannies terminals before any flyback issues are even entered into the equation ... again at moderate to low levels problems will rarely occur ... Boogie even states to play with the impedance on some of there combos (those amps are very well built however ... overkill ). A burnt tube socket isn't that big of a deal, a toasted output tranny is (plus it can take a lot of other stuff with it).
Now, I'm not saying the guy is wrong, but in practicality it's is better to drive into a higher (8 into 16), than it is to drive into a lower (8 into 4), ideally a tube wants to see what it wants to see ... period! But at moderate levels you are still within the limits of the supply and tranny's output capabilities. A S.S. amp isn't as picky to the higher load, but they are to the lower load. The minimum load should never be exceeded on either design.
That's all I'm saying ... many, many people have born the out to experience.

 

[PUCKBOY99]

Re: Impedence Pros & Cons

I don't understand when you guys say what impedence the amp "wants to see" ??!!

Here's the deal: I have a tube amp that has a switch for running either 4/8/16 ohms....I currently have a 2x12 speaker cab w/2 8ohm speakers wired in series (16ohms)....Is it better to run it in series @ 16ohms OR in parallel @ 4ohms OR Is it more efficient to throw in another 8ohm speaker running 4x12 wired in series/parallel @ 8ohms??? :smack:

 

[Kent S.]

Re: Impedence Pros & Cons

I don't understand when you guys say what impedence the amp "wants to see" ??!!

Here's the deal: I have a tube amp that has a switch for running either 4/8/16 ohms....I currently have a 2x12 speaker cab w/2 8ohm speakers wired in series (16ohms)....Is it better to run it in series @ 16ohms OR in parallel @ 4ohms OR Is it more efficient to throw in another 8ohm speaker running 4x12 wired in series/parallel @ 8ohms??? :smack:

In that case set the amp for 16ohms for 16 ohms on the cabinet; if you wire the cabinet for 4ohms (parallel) then set the amp for 4ohms ... It doesn't matter, neither one is more effecient then the other ...4 into 4 is the same as 16 into 16, as your tranny is set up for that.
Adding 16 ohms (2x12 wired in series) in parallel with a 8ohm 4x12 gives you 5.33; and adding 4ohms (2x12 wired in parallel) in parallel with an 8ohm 4x12 gives you 2.66ohms to low for your amps lowest setting. The 5.33 would be better for your amp set at 4ohms ... BUT, the amp will be most effecient and happiest at either 4 into 4, 16 into 16 (or if you had it 8 into 8) ... Whatever it wants to see (whether it's set for 4,8,or 16 on the amp).
More speakers move more air, but it's not much louder at all, just more coverage.You still need to match it to the amp.

 

[PUCKBOY99]

Re: Impedence Pros & Cons

So it really has nothing to do with one setting being more efficient than another. It's more matching the draw vs the load....right? The setting options on the amp is just for matching to different cabs.

Isn't it amazing how simple things tend to confuse the sh!t out of ya' sometimes????

I think I just started to confuse myself in looking at the different wiring options I was reading about on a cabinet building site. It's more a matter of matching the cab to the amp as opposed to one being more efficient than the other.

Again, thanks fellas! :beerchug:

 

[PUCKBOY99]

Re: Impedence Pros & Cons

I forgot....one more question: If you run 2 2x12 cabs wired @ 16ohms each, do you still set the amp at 16ohms???

 

[Kent S.]

Re: Impedence Pros & Cons

So it really has nothing to do with one setting being more efficient than another. It's more matching the draw vs the load....right? The setting options on the amp is just for matching to different cabs.

Isn't it amazing how simple things tend to confuse the sh!t out of ya' sometimes????

I think I just started to confuse myself in looking at the different wiring options I was reading about on a cabinet building site. It's more a matter of matching the cab to the amp as opposed to one being more efficient than the other.

Again, thanks fellas! :beerchug:

Well, that being said Boogie overates their stuff so much (by that i mean they built the stuff bullet proof, everything is overated) that one some of their amps the encourage you to mismatch the loads, as a mismatch does alter the tone a bit ... but it's not recommended unless the amp manufacturer builds the amp to put up with it.

 

[Kent S.]

Re: Impedence Pros & Cons

I forgot....one more question: If you run 2 2x12 cabs wired @ 16ohms each, do you still set the amp at 16ohms???

You need to check your amps manual to see how the cabs are hooked inside the amp via the external speaker jack or what have you. 95% of all amps (I have to pick some number ... ) combine the cabs in parallel meaning two 16 ohms cabs will hook in parallel equalling 8ohms so set the amp for 8 ohms ... again matching the load.

 

[PUCKBOY99]

Re: Impedence Pros & Cons

You need to check your amps manual to see how the cabs are hooked inside the amp via the external speaker jack or what have you. 95% of all amps (I have to pick some number ... ) combine the cabs in parallel meaning two 16 ohms cabs will hook in parallel equalling 8ohms so set the amp for 8 ohms ... again matching the load.

MANUAL....WE DON'T NEED NO STINKIN' MANUAL!!!

IT'S A 1982 HIWATT FOR CHRIST'S SAKE!!!

It's got 2 outs, so I was guessing you would just 1/2 it.

 

[Kent S.]

Re: Impedence Pros & Cons

MANUAL....WE DON'T NEED NO STINKIN' MANUAL!!!

IT'S A 1982 HIWATT FOR CHRIST'S SAKE!!!

It's got 2 outs, so I was guessing you would just 1/2 it.

Like I said 95% ... nah ... 97 ... 98 ...98.9 ...99% of all amp outputs are wired in parallel ... so two 16 ohm loads become 8 ... so set the amp for 8.
Other than that, you'd have to check with the manufacturer ... but I really don't think that's going to be necessary. :laugh2: