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How to accurately gauge speaker sensitivity to match with tube amp?

I'm in the process of matching speakers to my amplifier and need a bit of advice. Most recently, I'm trying Focal 936 towers with my Quicksilver Mono 60w amp. They were sounding pretty decent until I experimented by hooking up my old Adcom 535L amp. All of a sudden, there was a giant jump in control, tautness in the bass, quickness in transients. The QS stuff was doing quite decently, but the Adcom really snapped these towers to attention. The mids and high ends, not to mention the soundstage, were worse with the Adcom — no question. But there was quite a difference with the other qualities just mentioned.

My question becomes one of sensitivity. The Focals self-rated as 92 db. Stereophile rated them as 89.5db. I realize that these are average measurements and a much bigger picture is told by the impedance graph (and other factors).

As I continue to search for the right match of speaker (I have a couple contenders), I'm sure one piece of advice is to look for speakers with higher sensitivity averages. But what else should I look for to help make a guesstimate about whether the amp will drive the speakers with the kind of control they are capable of? [Specs for this amp are here: http://quicksilveraudio.com/products/sixty-watt-mono-amp/ ]

I realize I need to hear speakers, in my house, with my gear, etc. to get a sense of them. I’m working in exactly this way. Your advice can help me eliminate candidate speakers that would pose similar challenges to my amp as these Focals have.

And I just bought the amp, so I don't want to change it.

Thank you for any thoughts. 

P.S. Anyone who has has had great success with this amp or similar, please shout it out.


128x128hilde45
twoleftears's avatar
twoleftears
5,320 posts
 

For a change of pace, try ProAc DT8.

Full tested specs here. https://planethifi.com/proac-response-dt8/#Impedance_and_electric_phase

Not as accommodating as the Fritz, but still recommended for use with tubes from 25W up.

For years I drove the ProAc Response 2.5s with a 12W 300B SET amp.  The modern "D" series needs more juice, though, but not the DTs.

ieales's avatar
ieales
1,201 posts
 
driver tubes ... have more influence on the sound than power tubes 
Nonsense. Tubes are like fine wine. They vary bottle to bottle and with temperature, age and side dishes [system and programme].

@hilde45 - IMO, there are better options than a sh.tload of tweeters, unless you happen to love phasy sound fields. Tekton's patent is one of the funniest I ever read, right up there with Michael Jackson's moonwalk shoes.
mammothguy54's avatar
mammothguy54
952 posts
 
Well, it seems that audiokinesis put me in my place.  Hey guys, it's just been my experience that woofers are quicker and tighter with a higher damping factor amp.  I saw the specs on the QS amps and made the comments that I did.  However, I have little experience with tube amps and my reference is primarily with SS amps that have at least 150 watts per side, a lot of output current, and high damping factor.  And NO, I am not referring to Class D amplifiers.  This is especially true when operating with speakers that have 10" or 12" woofers.

I hope that you land on a wonderful sounding set of speakers that work exceptionally well with your QS amps.  Enjoy the journey and, most certainly, the music.
hilde45's avatar
hilde45 OP
5,090 posts
 
@ieales The more I think about it the more I agree. I think this would be an experiment if I cannot figure out anything else to try that is different.
hilde45's avatar
hilde45 OP
5,090 posts
 
@mammothguy I’m not so sure you’re not on to something, as well as the others. This was an interesting article (1967!) which helps tamp down on whatever big debates were happening about DF back then. (Are the same debates happening today?)

It seems to affirm what both "sides" here are saying, namely that while astronomically high damping factors are irrelevant, that higher damping factors can make a difference.
From the article (link at bottom):

"CONCLUSIONS
It should be obvious at this point that the quoted damping factor of an amplifier is important only if the figure lies somewhere below 20 or so. Changing the damping factor from 2 to 20 does change the performance of the loudspeaker system (for better or for worse, depending upon the speaker). But trying to prove that a damping factor of 200 or even more is somehow better than one of 20 is pretty unconvincing because the effective difference in the practical case cited is only that between 1.25 and 1.32.

But someone is bound to insist that exhaustive tests have been made with such and such amplifier and that a very high damping factor is better than one down around 10 or 15. "The bass is just a little cleaner, just a little more natural and open" is the way the argument usually runs.

In a given situation, this may very well be true. Rs is a byproduct of negative feedback. The more such feedback that is thrown into a power amplifier circuit, the lower the generator impedance and the higher the damping factor. The point is simply that if a lot of feedback has to be used to lick the distortion in a particular circuit, fine - use it. But don’t believe that the reason it sounds good because of some astronomically high damping factor."
https://butleraudio.com/damping1.php

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