HES, High Efficiency Speakers

The number of (triode) valve amplifier producers today compared to two decades ago is phenomenal and there's a steadily increasing interest in high-efficiency speakers, thus this page on my experiences of high-efficiency speakers and some comments to what I've picked up from the web. 

  

Why bother about 95-100 dB/1 watt speakers when we have almost unlimited power available from solid state or digital amps? Why do people build two watt single ended triode valve amps with subsequent need for extremely efficient speakers? Is it pure nostalgia or do these systems have something to offer conventional hifi does not?

I guess it has to be heard to be believed, and not only that, you have to kind of "discover" the triode sound. Some will, some won't and taste cannot be argued, but not all will think flea-powered triode amps and high-efficiency speakers are the best since sliced bread.

The need for extremely low moving mass calls for serious compromises in terms of possible cone break-up and possible linear and un-linear distortion as I'll elaborate on later. 

There are not a whole lot of places to go and hear low-wattage SET amplification combined with good high-efficiency speakers. And even if we do find such a place, there's a fair chance we may leave, saying: "Is that it?" I've heard 50,000 USD triode systems that really didn't impress me. Silver trafos and everything to make the best of sounds and yet it didn't convince me at all. 

And I heard a system consisting of a cheap Chinese triode amp connected to pair of mock-up HES speakers that forever changed my ways of thinking hifi. 

Art Dudley/Stereophile has these comments:
"Bear in mind that even the hard-core single-ended-triode movement wasn't conceived as just a new branch of high-end audio: It was intended as a whole new tree, by hobbyists who considered the old tree to be very, very sick. To the SET pioneers, audio had gone from being an interesting way of enjoying recorded music to a turgid and fetishistic exercise in irrelevance in which wealthy men with too much time on their hands try to outdo each other in identifying arcane sound effects in a handful of guru-approved recordings. 

Also remember that the high-end audio establishment didn't take long to dismiss the SET guys as a bunch of self-conscious hipsters less concerned with fidelity than with the coolness factor: gracelessly aging punk wannabes whose willingness to live with grossly colored , narrow range sound reproduction is rivalled only by their disdain for any model of amplifier or speaker that might be owned by more than two other people.

The fact is, there's an archetypal high-end audio sound and an archetypal SET sound. At its best, high-end audio sound is impressive open and clear, with deep bass, shimmering highs, and a flair for thrilling spatial effects: At its worst, it's lifeless , boring, constricted, undramatic, uninvolving, and incapable of any suggestion of flow in the music.

At its best, SET sound has the kind of punch and drama that can startle you out of your pants - plus real musical drive, momentum, presence, and tone; at its worst, it has no bass, no treble, and a level of coloration and sheer fuzz that could drive you out of your house after a few songs". 

"The punch and the drama" - is what we're always looking for and sometimes SET + HES can deliver this kind of aural nirvana. I've been sitting next to people experiencing SET + HES for the first time and saying: "Holy crap, this sounds like music!" I've had people in listening to the OB7 and saying: " - whauu...this sounds like a live performance!" So, what do these people do after returning home? They start yet another project based on an 85 dB heavy alu cone driver. Either the prospect of bringing two 100-200 litre cabs into their living room is too scary or the last 30 years of hifi-tradition is so engraved into our way of thinking hifi that we resign and turn to well-known technology.

In some cases I'm sure the prospect of huge cabs and glowing valve amps is simply not the way they want their system to look. We may have fixed ideas of what our system is going to look like and that's what it's going to be. Period! 

From what I pick up meeting hifi people, most gear is bought on looks rather on sound. It has to at least look expensive and project potency. The drivers even have to look sexy! Very much like buying a fancy sports car, except that huge and expensive hifi systems do not attract (young) girls! On the contrary! Most likely it will only produce sympathy for the poor spouse that has to live with these weird looking monsters.

Expensive hifi gear is show-off to your (young) male friends and whoever is going to follow presentations on countless discussion forums, where people display pictures of their systems and are being congratulated every time they've made a new purchase.

Old farts - like myself - no longer care too much about visual appearance, although I do like to make nice products from time to time. The satisfaction and pride of good craftmanship is - hopefully - a never ending issue.

A lot of things can be found on the web on high-efficiency speakers and what these speakers can do - and not so much about what they cannot do. 

So, can high-efficiency speakers do things low-efficiency speakers simply cannot? Well, try a 12-15", 96-100 dB/1W bass driver on an open baffle - or in a huge vented cabinet - and hear what it does to a kick-drum and make your own judgement. 

Take an 8" Supravox, place it on an open baffle or in a TQWT, mate it with a proper 95 dB tweeter, do a proper crossover (the tough part) - and hear what it can do. Hearing treble from a good fullrange driver can be very special despite serious beaming and it may change our way of thinking treble as we're so intoxicated from 1" domes and how treble usually sounds. 

Somewhere I said we cannot accelerate heavy cones as fast as a light-weight e.g. paper cone and I immediately had a mail from an engineer who told me I was seriously wrong - and he was right. Acceleration has nothing to do with mass, only force. Problem is we don't have magnet systems that will accelerate a 200 grams subwoofer cone and kick butt like an old 15" ALTEC driver in a 200 litre vented cabinet. It's two worlds. Subwoofer drivers are supposed to say ooomph... in small cabs and being often used to reproduce electronic music we really can't tell what it should sound like. Electronic music can sound like anything, but it's not the kind of bass performance I like to hear from an up-right bass. Acoustic bass shouldn't say oomph and I don't even think a Fender bass sounds the way it should from a conventional heavy-cone subwoofer.

Aiming at really, really high-efficiency, there are prices to be paid like in any extreme direction. 2-3 watts from a 2A3 SET triode is not a whole lot of power. Some manufacturers claim their 2 watt SET amps to perform well with 90 dB (minimum) speakers. Yes, yes, if you never ever play at anything more than - to my volume setting - well below average listening levels. I know what it's like to sit 5th or 10th row in a club and listen to a jazz quartet. It's damned loud and I want my ultimate speaker to be able to recreate some of that drama. This doesn't mean I drive my speakers to 95 dB average level - far from - but I may play my speakers a bit louder compared to the average listener judged from the visitors I have. Playing the 15" Tannoys at realistic levels I remember one visitor who almost fell off the chair from hearing a snare drum being hit hard. I mean, this is what it's like at a concert...

When I visit our local Symphonic Hall and all 70 musicians are on the stage it sometimes goes pretty loud too. No wonder even classical musicians are complaining about damage to their hearing. And by the way, there's not a whole lot of deep bass, even from a full orchestra with 4-6 bass players. 

Now, recreating a live musical event from 2 watts take serious measures and I won't recommend anything less than 97-98 dB sensitivity, preferably 100 dB/2.8V. Some day I'll try to make a ~100 dB system from my Supravox drivers with the 215RTF in front and 2 x 215GMF in a double-tapered-quarterwave-tube. Simulation suggest a system sensitivity around 100 dB in the lower midrange.

If we fall in love with a 2 watt SET amp we do not set up a 100 dB system from a 15-18 inch bass and suitable mid and tweeter drivers. We need very light-weight cone drivers, around 5-10 grams and an easy impedance load too. Flea-powered amps can't handle 4-5 inch voice coils and heavy cones. Some say they can but I don't think it's an ideal situation.