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

@clhs04

Not to totally derail this thread but did @hilde45 ever mention what preamp he is using.? That’s a whole nother rabbit hole to go down in.

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heheh, ah just having some fun here with ya, it’s all good. He’s running a Quicksilver Linestage, non-remote control version preamp. They sound pretty nice with good vintage tubes and drive QS Mono 60 amps just fine.

To your point, and others, you cannot simply throw just any amplifier at these types of loudspeakers, agree 100%. I grew up here in the land of PASS, Coda, ESS where it all started with AMTs too and it truly does take a better amplifier to help these types of speakers sound their best. Even AMTs sound "right" with a ballsy amp. You are correct sir. I would not throw a dinky integrated tube amp at any of these Legacy speakers, but perhaps some small monos with really good transformers, maybe.

Thanks, deCooney. The capability of the mono 60s was what convinced me to get them over the mid monos (40s) and some other good tube stuff — and so it startled me to think that even by spending that much more, they would still not be capable.

I loved the part of one video where Duddleston says, "We're always having people walking in going well can your speakers be driven with a single ended amp, 16 watts or something, and so it's nice to be able to prove that, so there's a lot of flexibility."

The QS 60s weigh 30 pounds each; big honking amps. Not as big as they get, but certainly not backing me into a corner.

hilde45, 
Its seems folks are just wanting you to be aware some speakers may be better suited to your amps than others, and to try and avoid ones that are not.  This past year during a test I listened to some 82db sensitivity electrostatic speakers powered by a quality 10wpc tube amp. It was quite educational and surprising to say the least. 

Were they super dynamic and powerful, not really. Were they super punchy and detailed, no. They were extremely musical though, amazingly so. Something you could listen to for days and never get fatigued. So the other consideration is  is how you listen, at what levels, and what you enjoy - it varies from one person to the next, and YMMV.

This whole discussion around impedance only highlights what a can of worms you get with passive crossovers.  Here's WHY active crossovers are so very much better than passive. A single loudspeaker driver is an inductor, and provides a frequency dependent, reactive load to an amplifier. Looking at the image here, the blue line on the bottom is the frequency dependent impedance curve for an SB Acoustics SB29RDAC Ring Dome Tweeter, and it typical of any dynamic tweeter. As you can see, it is anything but flat, yet it is listed as having a 4 ohm impedance. It's 4 ohms at about 1200 hz, but at 600 hz, has an impedance of nearly 10 ohms.

Now if you put a passive crossover circuit in front of it, you add capacitors, resistors and inductors, which then give you a frequency dependent impedance curve which looks like a Coney Island roller coaster. And that's just for a tweeter high-pass circuit.

Now when you add in mid and bass drivers, with high and low pass filters there... It's a real mess. But we're not done there yet. Nope. Many of your extreme hi-end loudspeakers add in equalization to their crossover designs, which makes that impedance curve even worse. This is very hard for an amp to properly manage. That's why people drop many, many thousands of dollars on things like Krell, Threshhold, Bryston, or Rowland Research solid state power amps.

Now when you use an active crossover, an amp channel only has to manage a single driver. There's no passive, reactive component in between the amp and the loudspeaker driver. Then you don't need a megabuck amp to deal with it.

All of the Linkwitz loudspeaker designs use active crossovers. Earlier designs used analog crossovers, but his last designs were all digital crossovers. There are some digital crossovers that offer DSP EQ, which allows you to tailor the total system response for the room you are in. Then you're not just limited to whatever sound your speakers give you in the room you're stuck with.

The lowest cost active crossovers are typically pro grade, from manufacturers like Behringer, dbx, Rane or even Nady. There are many manufacturers. Some of the best known home audio digital crossovers are from miniDSP.

Another major benefit is that you can use much, much lower powered amps when you use active crossovers. A lot of power is wasted having to push through a passive crossover. You really don't need to push many watts into a tweeter or mid-range driver to get a lot of level out. You could even run a single ended tube amp on your tweeter, and a mid-level tube power amp on your mid-range driver, and a solid state amp for the bass driver. You have a lot of options.

Of course you've invested in a relatively high powered tube amp, and I'm sure you wouldn't want to use it only as a mid-range or tweeter amp.  But in insisting on running a high powered tube amp, you get to deal with the issues a passive crossover brings to you.

Hi Everyone, great discussion. I'm not sure if what I say applies. I too was worrying about measurements, Speaker and Amp match, but quickly tossed all the measurements aside.

I have Thiel 2.2's that I love but they run at 4ohms with an 86 sensitivity rating. They are fed by a VTL 2.5 Tube Pre-Amp and Mystere PA-21 Tube Amp @ 55 watts per channel connected with all Transparent Cabling and the 55 tube watts driver them effortlessly.

To me my system sounds amazing and to anyone who hears it. The true measurement for me was when i first placed a record on the turntable, my wife came from two rooms over, said that sounds really nice, then proceeded to sit with me to listen to the entire album.

I guess my point is, don't get too hung up on measurements. Trust your ears, and never ever forget to just sit back and enjoy the music.

Enjoy...