Autoformer vs Speaker impedance Curve

The bass is markedly more pronounced from my tube amp (60 Watt push pull, KT88, “some” local negative feedback) than my SS CA-2300. It’s also seems “looser” or less defined.

Nonetheless, it seems reasonable to my novice brain that if an increase in speaker impedance increases the sound level “heard”,  that the bass should sound louder where the impedance spikes. No?

If the tube amp is able to act as a voltage source, then it should not make any more bass than the solid state amp. In your speaker, there are two bass impedance peaks, which represent the box resonance with the port. If the amp is behaving as a voltage source, it will make less power, not more, into these peaks. Otherwise the speaker is a fairly benign load for a tube amp- our amps would do fairly well on that speaker (seems to me we have customers with them too).

Solid state amps often have what is called 'tight' bass, but I've yet to encounter tight bass at any show I've attended. IMO/IME tight bass is a symptom of an over-damped speaker. Here is an older article, written by the head engineer at Electro-Voice back when the industry was trying to sort out the voltage rules (EV and Mac lead the charge on that one):

http://www.dissident-audio.com/Loudspeakers/CriticalLSDamping.pdf

As you can see from the article, not all speakers need high damping factors and there are some that need really low damping factors. That is still true today and is why equipment matching is still an on-going conversation!

73max OP 
Guess that explains the bloated bass when I run 802D3s on my tube amp.

From Stereophile:

" 802 D3's 8, because the bass was entirely devoid of bloat or emphasis or resonance. Despite this, there was no lack of authority when that was called for, and the speaker's reproduction of deep bass was formidable."

This was achieved with Parasound Halo solid state, and Theta Dreadnought, also solid state. 
The big MacIntosh 303 with output transformer was kindly referred as being leaning towards the power, which to me "kindly" says "bloat" (remember MacIntosh are huge advertisers in Stereophile.)   

 
Also this is said about the design of the 802's bass alignment.

"the 802 D3's low-frequency alignment is free from underdamped boom."

  And this is the load the 802's present to the amp. especially in the bass

The magnitude drops to 3 ohms between 100 and 130Hz, and again between 670 and 770Hz.
There is also a combination of 4 ohms and –64° at 69Hz, implying that this speaker does require an amplifier that is not upset by a low effective impedance.

This last paragraph will represent a EPDR load close to 2ohms to the amp.

As I said before with what you have without resorting to buying anything else, go with the bi-amping, your Classe on the bottom for control of the the bass and whatever the the tube amp you have on the mids/highs.

Cheers George
 
  

This is an interesting article.   http://www.dissident-audio.com/Loudspeakers/CriticalLSDamping.pdf

I like what he is doing in figures 2 and 5. However this is just about the woofer. There is no consideration to speakers that have a wide impedance variation over their range. In 1954 speakers had simpler crossovers without the frequency response modifying parts we see today. With at woofer and a tweeter all you need is a capacitor for the tweeter and wind enough inductance in the voice coil so its impedance rises markedly with frequency. 

Once again I encourage people to take off their damping blinders and look at what is going on in the interaction between impedance of the speaker vs the amplifier.

atmasphere. 

  It could also be the power cord, as a cord that limited the amplifier's ability to replenish its power supplies might come off with more distortion as well. This effect is quite measurable- I've seen power cords
rob a tube amp of nearly 30% of its total power!

I would like to know how to measure that. 30% is hard to imagine. I test amplifiers all the time with ordinary power cords and have never seen this. This reminds me too much of Bruce Brission's white paper which was a total embarassment to his distributor who promptly dropped his line.

I would like to know how to measure that. 30% is hard to imagine.

+1