MC352 into varying-load speaker?

As with any speaker that uses a passive crossover, some of your power is lost in the crossover itself. On top of that, speakers that use contouring networks, notch filters, impedance compensation, etc... all end up sucking up more power. While the end result might be a speaker that measures very well in terms of amplitude linearity ( flatness of frequency response ), the sound produced is typically lifeless and lacking in "dynamic jump factor". That is, unless one feeds them with GOBS of power.

As far as impedances varying with frequency, all speakers do this to some extent. SS amps without output transformers deal with this by varying their available power in large fashion. That is, big impedance swings result in big differences in available power. Tube amps and / or SS amps with output transformers are also susceptable to impedance swings, but the transformer itself acts as part of the load. This tends to stabilize the available power to some extent, but not enough to provide equal power at any given impedance. The output variance that does occur with impedance changes are what making playing with the various output taps on the amp worthwhile. Not only can this change the available power output, but also the tonal balance and distortion characteristics.

With that in mind, Usher's are designed by Joe D'Appolito. Joe is a speaker guru and i'm sure that the crossover is relatively complex and parts heavy. This tells me that the impedance may not swing all that wildly compared to some speakers, but that it may take considerably more power than the speakers that are simpler in design. If it were my system, i would not hesitate to play with the output taps and see what worked best for your specific speakers and listening tastes. Sean
>

Sean, thank you for the excellent analysis and background info. I will try to talk with someone at Usher Monday. I do not have the Mac but am contemplating purchasing it used, but at its weight and cost it is something I would like some more knowledge on before committing to.
Did you imply that even with a rating of 4 ohm the Ushers just may sound better on the 8 ohm or 2 ohm taps and the only way to know is to try it?
Also, without getting too much into the search function again (I am really tired of doing that) do I recall correctly that at times you might have been a little critical of the Mac design philosophy? Forgive me if mistaken, but if not I would like to understand why, with a view to gaining knowledge prior to purchase.

I drove Infinity kappa 7's with my 352 for years. The Kappas are all over the impedance road. I have heard from 2-32 ohms. At least that is various dealers told me. But the 352 came through flawlessly. The autoformers seem to adapt with no problem.

Kck: I am not a fan of "autoformers" in the least. To me, they are blasphemous. If you really want to know my thoughts on them, fire away with questions. Just don't expect "politically correct" answers. Sean
>

Sean, confused. Your first post in this thread seemed to imply that autoformers could work. But the blasphemy comment is pretty strong in the opposite direction.

Not knowing where to begin picking your brain, perhaps you could summarize the idea, if it's not asking too much. Essentially, the question would be: "Do autoformers hurt, help or are neutral to sonic quality under most/average circumstances, and in what circumstances do they veer from this stated path"?