Reactive Load volume trick (re: Pete Thorn)

mlj_gear

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2,907
Try plugging in a 16 ohm cabinet vs a 4 ohm cabinet with the same exact speakers in them, with your amp impedance selector set correctly for each. Are you saying the 16 ohm cabinet will not be lower volume than the 4 ohm cabinet?
That's what I would say, although I haven't done that exact comparison.

It's not really possible for versions of the same model speaker with different impedances to be exactly identical, but their sensitivity ratings are measured with the voltage applied adjusted for the impedance, so if the sensitivity ratings are the same, they should produce the same SPL when matched to the proper tap. Tube amps deliver maximum power when the load is matched to the tap, and they shouldn't provide any less power when using the 16-ohm speaker with the 16-ohm tap than they do when using a 4-ohm speaker with the 4-ohm tap.

I've not heard any difference like what you've described when I've compared 16- and 8- ohm speakers, but I've never tried with 16- and 4-ohm speakers. Of course the impedance ratings are nominal, and in a particular case it might be true that one of the cabs is actually better matched to the tap than another, but I suspect that would be a rather modest factor at most, and it likely wouldn't represent a general rule.

Now if we we're talking about solid state amps, using a 4-ohm speaker would definitely generate more volume than using a 16-ohm speaker. People with a lot of experience with solid-state amps -- guitar amps or otherwise -- could potentially suffer from confirmation bias when doing non-blind comparisons with tube amps.
 

ProfRhino

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6,638
This is what I figured. Like plugging two cabinets into the head.

My issue is the cabinet I want to use the head with is 16 ohms, which I wouldn’t worry about if the head was set to 8 ohms, but what I’m thinking needs to be done is:

Amp set at 4 ohms
Speaker Jack 1 to 8 ohm cabinet
Speaker Jack 2 with Suhr RLIR (8 ohm)

correct?
your amp will see 5.3 Ohms (on paper). :idea
1/(1/8 + 1/16) = 5.333
that's close enough to 4 Ohms in real life, these "measurements" are only a decent ballpark approximation anyway, Z vs Ohms and all that. :dunno
Rhino
 

ProfRhino

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6,638
Interesting...
Ohmmygod ... :D
in reality, this only applies to DC resistance, aka "R".
R is independent of frequency and other variables, which would be described by "Z", aka AC resistance or impedance.
the most common examples include speakers, PUs and all audio I/Os.
for our shady purposes as musicians, it's usually safe to treat Z as if it were good old R - great news, as measuring Z is beyond the capabilities of a DMM. :jo

sorry for the simplification,
Rhino
 

ProfRhino

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6,638
Like when you measure a 16ohm speaker.......

Your multimeter will never actually read exactly 16ohms.......

At least based on what I've seen.
right, most measure quite a bit lower.
I'm not sure if Z vs R is the only explanation for this, but it's very likely related.

pardon me, I only know my everyday stuff, maybe a proper, studied tech can explain better.
Rhino
 

Tone_Terrific

Supporting Member
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31,796
Yep, they always read a good bit lower in my experience
If you look at an impedance curve vs freq it is all over the place.
But who plays with a straight sine wave signal?
Between the freq and levels continuously changing I don't think anyone can even come with a truly accurate 'average' impedance as it depends even upon the cabinet's dynamic reaction.
Mind bogglingly complex. The nominal impedance is an estimate.
 

Shiny_Beast

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9,994
You could also buy a really small high wattage speaker, one that is very inefficient. The impedance curve might not be perfect, but it would be cheap.
 

ProfRhino

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6,638
If you look at an impedance curve vs freq it is all over the place.
But who plays with a straight sine wave signal?
Between the freq and levels continuously changing I don't think anyone can even come with a truly accurate 'average' impedance as it depends even upon the cabinet's dynamic reaction.
Mind bogglingly complex. The nominal impedance is an estimate.
yup.
but that's stuff the engineers may worry about.
just like with PUs - Z is only one among several factors defining tone.
I might use it as a rough guideline for pre-selection, well knowing there are many exceptions.
Ultimately, hearing is believing (or better, actually playing through a known rig).
with guitar speaker combinations, it's usually safe to treat them as straight resistors.
doesn't tell you how they will sound, but it definitely helps you keep your amp safe.
ymmv,
Rhino

FTR, I always keep a dedicated DMM around with a female Neutrik jack on the other end - super useful ! :cool:
cabs, guitars ...
 




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