Speaker choice: impedance, sensitivity, and tubes


Looking at most speakers' specifications I cannot help but notice that very few are rated 8 ohms, and most dip well below their nominal specifications at certain frequencies. This makes makes me wonder how audiophiles with tube amplifiers select their speakers. Most tube amps have 8 and 4 ohm taps only, and from what I understand tube amps don't take kindly to dips in impedance. Is there a rule to abide by when selecting a speaker to match well with a tube amp when it comes to impedance?

Same with sensitivity. Perhaps not as important as impedance, but a lot of popular brands out there have disappointingly low sensitivity (85-86 dB). Why is that? I never understood it since the higher sensitivity, the easier it is to drive a speaker without having to have a beast of an amp. Seems all manufacturers should be striving to design their speakers to have higher sensitivity. Is is more expensive to make speakers with higher sensitivity?

Case in point, I own two pairs of speakers, one rated 88 dB and the other 91 dB. The 91 dB pair has an impedance of 8 ohms flat (according to the manufacturer) while the 88 dB pair has a nominal impedance of 6 ohms (not sure about dips). The difference is quite dramatic in terms of volume on my 180 watt tube amps. I often have to crank the volume way up to get sufficient loudness level in my rather small listening room (11x12) with the less efficient pair. That to me is crazy. The speakers are my fall-back pair from my digital past, and knowing how they behave, I'd never purchase them for my all-analog system today.

So as I'm thinking of upgrading my speakers, I'm quite perplexed about finding a speaker that would match well with my tube monoblocks - provide an easy load and good loudness level without strain. I've been considering giving Harbeths a shot, but I'm really turned off by their low sensitivity of 85 dB (30.1) and impedance of 6 ohms. How big an amp would I need if speakers with a sensitivity of 88 dB barely generate sufficient volume with 180 watts per channel?!

Can anyone explain in technical terms how tube amps handle speaker impedance and, secondarily, sensitivity? And perhaps more important from the practical standpoint - how does one select a speaker to match a tube amp?
actusreus

Showing 2 responses by xti16

Not many - but only the good ones. I think all dealers try their best but sometimes profit margin or price point (lower) means more sales. Well established dealers have been though it. Took my local dealer a couple of years to get it. Now that is his strong point. Total system synergy. But it does come with a price.
Out of curiousity, I called Paradigm to ask whether the S8s (my speakers) were designed to work best with SS or tube amps. The tech service rep said the S8s soak up current, as much as the amp can push out. In fact, he said SS was the way to go.

Now, . . . my amp is tube. Would my rig sound even better with a high quality SS amp, I rhetorically ask?? Maybe, just maybe. In the meantime, the rig sounds pretty good as is. I have a great subwoofer, which back-stops the fronts, so if I have low quality bass output, it's pretty well masked.
I have an Octave V70se (70w @ 4ohm) driving Dyn C1 Signatures (85db) and I can turn it up a lot louder than I can stand. Not because it's fatiguing but because for me it's jut too loud. That being said the Octave was designed for 4 ohm speaker and more important the Dyn is very stable at 4ohm. Now my son had Klipsch KLF30's (103db) and holy cr@p could they get loud. With either his Bryston 3Bsst or my Octave. But all I can say good about the KLF's is they could get super loud. Couldn't stand the sound except at super super low volumes. But in general when comparing anything side by side louder will win 95% of the time (short term comparisons).

So would a SS amp sound better. Yes with the right amp. I'd take a Burmester 956 over the Octave V70SE any day. But my Bryston B100sst and my sons 3Bsst were not as good sounding as the Octave V70se with the Dyn's.

But with tubes you can swap them out any change up the sound a bit (warmer - more musical or more linear and detailed).

Last I believe specs are a very general guideline. Any 2 pieces of equipment with the same specs will sound quite different. It's all about system synergy.