4 ohm taps on an 8 ohm speaker

Right on Al. Actually, what I had in mind was a speaker with low'ish impedance in the bass/lower midrange frequencies, with a peak at the mid/tweeter crossover point. As I'm sure most would agree, matching a high'ish output impedance tube amp to that kind of load would tend to attenuate bass and augment the mids and low treble.

I would add one more point. Current delivery capability, albeit a subset of my comment about an amp operating within its design parameters.

More specifically, many speakers not only have low'ish impedances in the bass frequency region, but also capacitive (negative) phase angles. In other words, tough loads. Hopefully, regardless of the tap used, the amp in question will have enough power supply reserve to muscle its way through the tough spots.

Best,

BIF

Thanks a lot for the explanation Al, you ARE the man!!!
I think you nailed it with the first line in your last paragraph: "The bottom line: It pays to experiment with the different taps, and no harm will result regardless of which tap is selected."

Cheers,
John

Thanks for the responses gentlemen. Interesting stuff. Glad to hear I'm not hurting the amp. It does sound much better on the 4 ohm taps.

I've read through most of the tap vs. tap threads and get the gist. But my results from trying 8 and 4 ohm taps would seem to contradict the predictable, at least as I hear it. Maybe just proves "The bottom line: It pays to experiment with the different taps, and no harm will result regardless of which tap is selected."

Just curious if any of you have insight on why I hear better base, maybe a little tighter, and less emphasis on highs using the 8 ohm taps. Here are my speakers' impedance and phase vs. frequency graphs: Minuetto, and my amp's measurements : RM 200. I've read that early SF speakers were developed using tube amps, but not sure if that's true or even applies, especially to the low-end ones.

The sound quality difference is not huge, but still there. True will all music types played at moderate volume in a medium-smallish room (so not pushed to clipping) Also, I haven't tried 1 or 2 ohm taps, but figured why bother if 8 is preferable. Any insight would be appreciated.

Tmcclintock, thanks for including the links in your post. My suspicion is that the main reason you have found the 8 ohm tap to provide the best results is simply that it is the tap that is the closest match to the speaker's impedance, at all frequencies. Therefore it is probably the tap which results in the lowest amount of amplifier distortion, and that also maximizes the amp's power capability.

I note that the speaker's impedance, while varying widely as a function of frequency, is always at least 6.5 ohms. And the amplifier's output impedance on the 8 ohm tap is not much over 1 ohm at any frequency, which is low for an amp having a tube output stage.

Therefore the effects on tonal balance of the interaction between amplifier output impedance and variations of speaker impedance as a function of frequency, which I referred to earlier in the thread, figure to be relatively insignificant in this case, because the speaker's impedance, while varying considerably, is always much higher than the amplifier's output impedance.

And the relation between the relatively low output impedance (for a tube amp) of the 8 ohm tap and the speaker's impedance at bass frequencies apparently (based on your findings) results in adequate bass damping for the particular speaker. Presumably helped by the fact that the speaker's impedance rises to very high values in the 60 to 120 Hz area.

So I don't find it surprising that you've found the 8 ohm tap to work best with your particular combo.

Regards,
-- Al