4 ohm taps on an 8 ohm speaker

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

Wow Tmcclintock .... and I thought my speakers had wild impedance and phase angle curves. :)

Thanks for responding, Al. That's pretty much what I thought but wanted to be sure I understood the science. Also, does it make sense that because the amp's output impedance starts relatively low on the 8 ohm tap and doesn't have a lot of room to go lower on the other taps, the sound quality would vary less from tap to tap relative to higher output impedance amps, for a given speaker? May try the 2 and 1 ohm taps just for grins.

Bifwynne, can you say "off the chart" - literally. Just one of the trade-offs, I'd guess.

Does it make sense that because the amp's output impedance starts relatively low on the 8 ohm tap and doesn't have a lot of room to go lower on the other taps, the sound quality would vary less from tap to tap relative to higher output impedance amps, for a given speaker?

Yes, with respect to the sonic effects that may result from the interaction of amplifier output impedance with variations of speaker impedance as a function of frequency. And yes, with respect to damping factor. Especially in the case of speakers such as yours where the impedance does not reach low values at any frequency.

However, if a mismatch between the speaker's impedance and the load impedance a particular tap is designed to work into is severe enough there are still likely to be adverse effects on the distortion characteristics and the power capability of the amp. In general, what constitutes "severe enough" is probably hard to predict with any precision.

Best regards,
-- Al

Hey TMcClintock .... wild curves??? Who cares? If your rig sounds good, that all that counts. Enjoy!!