Does speaker impedance affect tone?

[Noval_novice]

I am in the process of recycling a combo amp. It has two 12" speakers, 8 ohms each wired in parallel. With my output transformer, I could use 4, 8 or 16 ohm loads. Is there any advantage to rewiring the speakers for series? Will it make any difference in tone? The reason I ask is that in one of his books, Gerald Weber points out that wiring speakers for the largest impedance will result in less coupling loss in the OT. Is this a legitimate issue? After hanging around her for only a few months, I am now uncertain when to take Mr. Weber seriously

[Gaz]

I think your inclination is right, that Mr. Webers pseudo-science is BS (although he's not completely full of it.)

My experience has been that matching impedances will give you the same tone, however mismatching will change power and frequency response, which you're probably already aware of.

Now, I have heard that wiring parallel vs. series does result in a different tone, although I can't remember the source off-hand. ...has something to do with high end response, IIRC. It seems like that kind of experimentation is more for the non-tech person, who may not be handy or confident enough to modify their own amplifier. It's always 'safer' to wire the speakers in parallel or series-parallel in case of a speaker failure, so I'd stick with the parallel wiring.

[azatplayer]

From Weber VST's Q&A:
From: Gerald C. Lopez

I have two 8 Ohm speakers that I can wire either parallel or series to my tube amp for an impedance of either 4 or 16 Ohm. My amp has both 4 and 16 Ohm output taps. Are there any sonic differences or benefits of series over parallel wiring or vice versa?

Gerald, connecting two speakers in parallel is an old trick to smooth out speaker response and enhance the damping of either speaker. HIFI designers took it one step further by connecting two speakers of different sizes in parallel. A speaker has a large impedance increase at its fundamental resonance, and depending on the installation, this can cause the speaker to sound boomy or out of control. By connecting two speakers in parallel, particularly two speakers of different sizes with different resonant frequencies, each speaker will tend to quench or dampen the boominess of the other. Since no two speakers are exactly alike, even two of the same size, that damping will occur, however slight, for any speakers connected in parallel. For speakers connected in series, there appears to be less control, and more of what is called 'back EMF' from the speakers fed back into the output circuit. While that seems rather chaotic, many players prefer the series connection, as it gives them a more textured tone, enhanced breakup, and overall a more desireable tone for guitar work. It's totally subjective, of course, and many factors affect the end result, such as voice coil size, gap energy, closed back/open back, output circuit damping, etc. The best thing to do, in my opinion, is try both arrangements since you have the luxury of impedance tap selection, and go with the configuration you like the best."


In a 2x12 i have at the moment, im running a blue and a gold alnico, both 8 ohm. I had them parallel for a 4ohm load, but decided to try them series the other day. With my 5E7 into that cab, it sounds very different to parallel.
I like it a lot. My feeling is with parallel, each speaker is getting the source directly, and reacting independently to the other, therefor you hear the 2 very different speakers doing their thing.
In series the signal has to pass thru both as a unit. I think theres more of a blending or softening of the edges this way. I certainly like what im hearing in this arrangement.
In my marshall cab, the factory series parallel wiring made the cab sound icepicky, really horrid bright, with my old superlead.
I did some research and discovered parallel/series wiring.
Tried that out and it transformed the cab into a thing of beauty.
Buddy of mine loves that cab and wants it, he cant have it... but there is a massive difference there.
All down to what you like with your ears huh?
Try it and let us know what you think!

[Jana]

There is a tiny bit of truth to the claim that the impedance does affect tone. Here is where that probably came from: The very early Marshalls had the NFB loop connected to the output jacks and not to one particular ohm tap on the OT. Hence, when the impedance selector was changed, say to the 16 ohm tap for a 16 ohm cabinet, the amount of NFB was quite a bit more that if the selector was at the 4 ohm tap for a 4 ohm cabinet. In short, the NFB moved with the impedance setting. I don't remember when it was changed but early on in the Marshall history it was changed so that the NFB went to a specific OT tap and not through the selector switch.

Another piece to consider is the impedance/resistance of the wire connecting the amp to the cabinet. All wire has a resistance--small, but it is there. If you have a 50 foot "zip cord" speaker wire going from an amp to a speaker cabinet the resistance in that lamp cord wire will have an effect--more so with a 4 ohm cabinet than a 16 ohm. Somebody will have to take some measurements to give accurate numbers--I am going to invent some specs just for illustration purposes.

Let's say that 50 foot wire has 1/2 ohm of resistance. The cabinet is 4 ohms. That means that the wire is 1/8 of the load and is burning up 1/8 of your power. With the 16 ohm setting that wire is only 1/32 of the load--4 times smaller in comparison.

This usually isn't a problem though because few people use long runs of flimsy zip cord quality cables.

Use good quality speaker cables and it shouldn't matter which route you go. I too prefer the parallel setup because if one speaker goes I still have one working and providing a load to the amp.

Edited a typo

[Noval_novice]

You guys are awesome! I may experiment with series wiring, but if I don't see a very desirable change, will leave it in parallel for safety. Thanks again.

[azatplayer]

Most of my gear is 1x12, so if a speaker was to fail...?
If that was a true concern you can always put the 10 watt 250R from the speaker out to ground, OT saver.

[Jana]

With a 1X12 if the speaker fails--it gets very quiet!

[Furtz]

Most of my gear is 1x12, so if a speaker was to fail...?
If that was a true concern you can always put the 10 watt 250R from the speaker out to ground, OT saver.

I agree with the 250R idea. Avoid arching in the O/T.

[Doctordog]

Just an addition.

If you go from 4 ohm parallel load to series with the same speakers, that means you are then making the load 16 ohms.
If the transformer is wired for a 4 ohm load that's quite a mismatch, and will change the tone considerably.

Also if the speakers are rewired to be series from parallel, then there is also a CHANCE (not danger) of wiring one speaker out of phase with the other. (actually this can be done in parallel too, but assuming it was done correctly in the first place.) This would also greatly affect tone.

With some amplifiers there may be a danger in large mismatches between the load and the transformer wiring. The danger could be a blown transformer. Many tube amplifiers though are pretty forgiving. Usually, it's just a different flavor of sound to try and see if you like. Closely matching the actual load to the proper wiring of the output transformer will get the highest bandwidth at the highest power, generally speaking. Everything else is just different flavors.

JB

[Cliff Schecht]

We just had a discussion about this over at TDPRI and somebody pointed out something I never considered before. When you do a 4:1 mismatch (output set for 4 Ohms, speaker at 16 Ohms) the flyback voltages from the speaker can become considerably larger than what they were at a matched load. While this isn't a problem in amps with a relatively low B+ the kickback voltages shouldn't be an issue but in bigger amps with high B+'s, the kickbacks can become higher than the insulation can take and the transformer will arc and be ruined (amongst other things frying).



I can't find any "danger" in wiring speakers out of phase. Mismatching too much either way can result in a few problems but usually isn't an issue if the user understands the downfalls and avoids them.

[azatplayer]

With a 1X12 if the speaker fails--it gets very quiet!

Hahaha!

[Reeltarded]

The "Rule of Dumb" I have always followed is 100% mismatch on a tube amp. I never do it on a Major though! Eeek!



Umm.. so a 10 watt 250R from the speaker out to ground... that is for any amp?

[azatplayer]

The 250R is parallel with the speaker, so across the hot and ground.
It was an Ampeg thing, protector for the moment you lose your cab/speaker/cable, gives you long enough to shut it down.
I built a B15N some time ago, was a little confused by that part of the schem till i learned what it was for.
Clearly hitting a big chord with a superlead at 3/4, would probably put a little heat in that lil' 10 watter..

[Crashtm1]

This may be over simplified ...but here is what I've found..
4ohms... Much more clean headroom..
16ohm ..much earlier break up ...
My 2 cents...

[Doctordog]

This may be over simplified ...but here is what I've found..
4ohms... Much more clean headroom..
16ohm ..much earlier break up ...
My 2 cents...

More than likely the transformer is wired for 4 ohms then.

JB