4, 8, 16 ohm taps - tone difference?

[Dave]

If an amp can accept 4, 8 or 16 ohm speakers/cabs is there a best choice, tonewise?

I've searched and found a lot of discussion on impedance mismatch, but nothing on this specific topic. Maybe I didn't search the proper terms, seems like a pretty basic question. Sorry if this has been covered.

[Dave]

Any thoughts on this?

[jlummaa]

No best choice that is for everyone, just different choices. I prefer 4 ohms with my Marshalls and with the divided by 13 RSA23 (the cab is 4 or 16 ohms).

[Fuchsaudio]

The general consensus is that higher impedances offer the potential to sound better. Reasoning is that it takes less windings to match the high impedance (4 to 6-K) of the power tubes to a 16 ohm speaker. A 4 or 8 ohm match takes more wire. No transformer is perfect. More wire means more resistance. It's a coil, which means more inductance. It has layers, which means inter-winding capacitance, and so forth. You can improve on all these factors, but never eliminate the effects, only minimize them. Less windings means less phase shift and wire between you and your tone. Depending on the transformer type and quality, it can be subtle or sometimes clearly heard.

I sometimes wonder when people say "the 16-ohm 1265 sounds better than the 8 ohm versions" if it's because of the transformer issue more than the speakers themselves.....

[Dave]

Thank you, Andy.

[jlummaa]

Originally Posted by Fuchsaudio

The general consensus is that higher impedances offer the potential to sound better.

Cool, definitely not in my case. I would say listen to your ears and deside yourself what ever sounds best to you.

[Plague Dog]

If that is the case than why not make 40, 80 or 160 ohm speakers and transformer taps?

[shallbe]

I'm cetainly no amp tech or builder. Just a long time player that has done many years of gigs with amps running all three impedances.

Here are my findings. They are not based upon "tone" as much as volume and feel.

The lower the impedance, the higher the volume of the amp for the wattage. A 30 watt amp at 4 ohms is going to be louder than the same amp with the same speakers wired for 16 ohms.

The higher the impedance, the more compression, resulting in a little sweeter feel.

Personally, I prefer 16 ohms. It attenuates the amp slightly and softens the attack a bit. Since I play cathode-biased amps primarily, I like the effect.

[Dave]

Originally Posted by shallbe

The lower the impedance, the higher the volume of the amp for the wattage. A 30 watt amp at 4 ohms is going to be louder than the same amp with the same speakers wired for 16 ohms.

Is headroom affected?

[JubileeMan 2555]

not to argue with Andy F. or anything, but if the general consensus is that higher is better, than why are super reverbs, with their 2ohm out, sound so good. Would you then say that putting an 8ohm tran out on that amp and rewiring the speakers would make a super sound better?

...personally, I think its all hearsay and voodoo talk. There may be an electronic scientific explaination, but I doubt any normal human being could tell the difference with all factors being equal.

[Plague Dog]

I know that when I run my PA power amps at 2 ohms they sound warmer and punchier. I know solid state amps are different than tube amps but if what AF said were true wouldn't it apply either way?

[michael.e]

Originally Posted by JubileeMan 2555

not to argue with Andy F. or anything, but if the general consensus is that higher is better, than why are super reverbs, with their 2ohm out, sound so good. Would you then say that putting an 8ohm tran out on that amp and rewiring the speakers would make a super sound better?

...personally, I think its all hearsay and voodoo talk. There may be an electronic scientific explaination, but I doubt any normal human being could tell the difference with all factors being equal.

If I am reading your reply correctly, I think you are concurring with Andy's statement.

Super Reverbs were meant to be clean, high wattage amps, thus the 2 ohm output, which is as clean and high headroom as you can get. If it was a 16 ohm output, it would compress and begin to sweeten earlier. It takes some serious pushing to get a SR to begin that process-and man, oh what a sound!

I can definately hear/feel the difference in impedences, both in the studio and live.
M.E.

[Old Tele man]

...speakers are AIR MOTORS and motors are AMPERE-TURN devices, so a lower Z means (SR at 2-ohms, for instance) means the WATTS are due more to AMPS than VOLTS, which means more power to the MOTOR action, which pumps out the different/characteristic SR sound we love.

...think about it!

[randall d]

Sorry, but volts x amperes = power (look it up). Another expression of power is watts (though there are several different ways of measuring watts in an audio device due to the frequency dependancy and distortion issues). Not to confuse the issue farther, but volts is electrical pressure, and amperes is electrical flow. It works very similar to liquid (water for example), pressure without flow = (almost) no work. Flow without pressure = (almost) no work. Pressure and flow = work (aka power).

[Old Tele man]

Originally Posted by randall d

Sorry, but volts x amperes = power (look it up).

...if you're referring to my post, that's exactly my point!

...for the same 50W output across a 2-ohm load and 16-ohm load, the AMPERAGE thru the speaker load would be 5A, but it'd only be 1.8A thru a 16-ohm load and the VOLTAGES would be different too: 10Vrms @ 2-ohm, but 28.3Vrms @ 16-ohm.

...and, since speakers are MOTORS, it's the AMPERE-TURNS that's important, not VOLTAGE, so the lower 2-ohm Z of the SR/Bassman/Bandmaster OT is functioning is a CURRENT-output mode more so than as a VOTAGE-output...which is what MOTORS prefer.