8 vs 16 ohms (Marshall content)

petejt

Active member
I tried searching the forums but nothing seemed to show up...


Anyway, I feel like I should know this already but I don't.

Is there any major discernable difference between running a particular guitar amplifier at 8 ohms or 16 ohms?

Is it a larger factor when using the amp into a 4x12 cab vs a 2x12 cab? Mono vs stereo, etc.?


I have a single channel early '80s Marshall JCM 800. I've always run it at 16 ohms, sometimes into a mismatched 4x12 cab.

I've since used it via an attenuator into a 2x12 cab loaded with an older Celestion Vintage 30 and a Mesa/Boogie Black Shadow MC90. Both speakers are 8 ohms. I run it in stereo, i.e. 8 ohms per side.

I really like how it sounds, even at low volumes. It seems to have a really good edge to it, whereas before (with the mismatched cab) it was way too midrangey and less crunchy.
I think what is happening is that more power is going to the speakers, so they are getting pushed harder.



Anyway, I "discovered" that some speakers I had ripped out from another cab, are actually 8 ohms rather than 16 ohms. So my mind starts ticking into putting this pair of speakers with the pair of speakers from the 2x12, into a 4x12 cab. Then I just run the JCM 800 at 8 ohms mono.

Would it be worth it? For some reason I think it would, but I can't work out how. Hence my opening question.
 
Gerald Kendrick (of Kendrick amps) talks about this in one of his books, I forget the theory he put forward, but in his opinion, Yes, the ohm load plays a part in the tone, and Lynch seems to agree as I believe his Lynchback speakers are only available 8 ohm. Something about 16 ohm uses the most windings in the output transformer so it changes the sound. In a 4x12 cab, there is more than one way to wire the speakers too, series-parallel or parallel-series, each is supposed to sound different.
 
paulyc":36ocgkby said:
Gerald Kendrick (of Kendrick amps) talks about this in one of his books, I forget the theory he put forward, but in his opinion, Yes, the ohm load plays a part in the tone, and Lynch seems to agree as I believe his Lynchback speakers are only available 8 ohm. Something about 16 ohm uses the most windings in the output transformer so it changes the sound. In a 4x12 cab, there is more than one way to wire the speakers too, series-parallel or parallel-series, each is supposed to sound different.

I'll have to chase down that book.


How does the amount of windings used in the output transfer affect the sound? Does it sound more saturated?


I've tried all sorts of speaker wirings, but my memory is vague about it because there was too much room reflection interference at the time, I guess.
Also I think I mucked things up by having mismatched impedance (e.g. had it it 12 ohms where the amp was running at 8 ohms).
 
There’s endless debate about this if you google it. Some say it makes a discernible difference, others say it doesn’t matter at all.
 
I think all transformers are also inductors to a certain degree, so using more of the core can change the sound...I'm no electronics guy so I don't know how/why, but inductors are used in Varitone circuits and such so maybe the theory makes sense. If you were designing an amp, you would go to the transformer maker's catalog and order what you need, and there would be WAY more than one "correct" choice too. Using a too small transformer would make it distort early or saturate, but there are impedence curves and all kinds of shit at play there, also the type of output tubes, etc... my local amp tech is a transformer engineer in his day job, he'd talk about this shit forever.

Gerald Weber's idea was "branch inductance", that's what he called it in the book.
 
For my money I always seem to prefer 16ohms and parallel/series wiring in the cabs.
 
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It's not something you can easily test for by trying different speakers or different wiring, without changing variables in the process. Getting apples-to-apples comparisons aren't easy. So as for 8 ohms versus 16 ohms and if it's the transformer, I'd say "throw that line of thinking out" and just decide what sounds best to you: 8 ohm speaker cabinet versus 16 ohm speaker cabinet with the specific speaker choice you make. That's a much more practical way of looking at it.
 
Several years back Dave Friedman and I did this experience with George Lynch in attendance.

8 ohm tap with M75 speakers, a hair more mids and aggressive tone.

16 ohm tap with M75 speakers, more bass and vintage feel.

The difference is subtle, but it's there, Lynch heard it as well.

Probably why GL spec'd 8 ohm speakers is my hunch.
 
So I've played around with this quite a bit, and yes impedance does make a difference.

Couple of things going on:
1) The voice coil of an 8ohm speaker has less winding using thicker wire. A 16ohm has more windings using thinner wire.

2) The 16ohm tap of the output transformer uses the full secondary windings.

Comparing 16, and 8ohm Greenback reissues:
8ohm sounds darker, more punchy.
16ohm sound brighter, more open.


You will hear different characteristics with different speakers, amps, and cabs. So there is no hard rule of how it will sound different, but it will sound different.
 
It seems to depend on the amp. When playing bass through my 1972 Fender Bassman 100, there is a clear difference in headroom when I run 8 ohm instead of 4 ohm. At 8 ohm, there is less headroom and I get more overdrive in my bass guitar tone than I do at 4 ohm. On my Bogner Shiva, I have tried different settings and haven't heard a difference.

One difference between the rigs is that I'm not running the Bogner master volume as high whereas I'm pushing the bass channel and master volume harder on the Bassman. 100 watts is far more than I need for guitar but is relatively underpowered for bass guitar. Maybe I just don't push the Shiva hard enough to get to the point where there is a difference?
 
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