Impedance and impact on tone.

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jbrew1977
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Impedance and impact on tone.

Postby jbrew1977 » Sat Dec 20, 2014 10:24 pm

Something that I have seen tossed around from time to time is the issue of impedance having an impact on the tone of your rig. Now I'm not looking for an ohm's law lesson or anything regarding the need for properly matching the impedance of your speakers to the impedance of your transformer. What I am looking for is a testimony of a same amp, same speaker, same cab, same guitar, same player scenario where the ONLY variable is the impedance. For instance, I have a V3M with a 2x12 cab that is loaded with two GT12 16 ohm speakers wired in parallel, with my amp set to 8 ohms. Would switching to two 8 ohm GT12s wired in series with the amp set to 16 ohms alter the tone? Likewise would taking two 8 ohm speakers and running the amp at 4 ohms change anything? If so, what would change? Not looking to accomplish anything other than to satisfy my curiosity, as things like this fascinate me. Kinda like sitting down for a tube roll... from time to time people like to say the difference is negligible and that money is better spent on a speaker or pickup swap if you're looking to change the tone. While this can certainly be true, for those of us who are truly infected with the sickness that is playing guitar these subtle changes can be a paradigm shift. The way a note comes on, sustains and trails off might have a slight overtone that wasn't there before, and for us it's like someone just handed us the keys to the kingdom. It may also have such an impact that everybody that heard it before and after steps back slack jawed at what they just heard. Everyone's mileage of course varies to a certain degree and I have found that to be oh so very true with my ownership of the V3M. One guys says it's fizzy, or too gainy, or not enough this or that, unless you do this, that, or the other, and I'm sitting over here thinking "do we own the same amp?" but then I stop and realize it's all subjective, as is I'm sure the answer to my impedance question!

cristo
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re: Impedance and impact on tone.

Postby cristo » Sun Dec 21, 2014 9:58 am

This is from Hunter's Tone Manual:

"Wired in parallel, speakers in a pair or quartet will dampen and restrain each other
somewhat, yielding a slightly tighter response and a smoother breakup. Multiple
speakers wired in series (usually no more than two) run a little looser, giving a
slightly rawer, open, edgy sounds."

Tracks 8 and 9 on the CD supplied with the book demonstrate the difference with a
Matchless Spitfire amp through a 2x12 extension cab with Celestion G12H30 speakers
in parallel then in series.

I find the difference subtle but nevertheless audible.

Barnacle Bob
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re: Impedance and impact on tone.

Postby Barnacle Bob » Mon Dec 22, 2014 6:58 pm

Yes, speakers in parallel sound a bit different than speakers in series. When you put them in series, the voltage on the connection between them is nominally half the amp's output, but any mismatch between the speakers will cause additional voltage fluctuations there. In parallel, each speaker is connected directly to the amp, so there's less interaction.

But we're talking about impedance. If you set the switch correctly, there shouldn't be much difference on the amp side. The amp's power tubes see the same impedance.

If your transformers are beefy enough, and your bias is set reasonably conservative, you can do a 2:1 or 1:2 mismatch and nothing will blow up. You will here some changes in tone, etc., since the power tubes are driving a different load.

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re: Impedance and impact on tone.

Postby jbrew1977 » Tue Dec 23, 2014 11:19 am

That's along the lines of what I thought to be the case... I have however heard people claim that by using more or less of the transformer via the different taps to select the impedance that it made a difference. One clear and ever present issue in the subjectivity of tone is the power of suggestion. One guy says it does this or that and with that expectation the mind manifests said changes even if they don't exist. It's something none of us are totally immune to even though we'd likely never admit it!


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