Tube-friendly speakers

Silverline used to be tube friendly some years ago, but the current stuff is not. There are two design paradigms used in speakers, and the Silverline stuff now subscribes to the idea that an amplifier must be capable of constant voltage, regardless of load.

There is no tube amp that can do that.

BTW it is not important that the impedance curve be flat. It **is** important that the impedance curve be high enough, once it gets above a certain level, it can vary quite a bit without ill effect. FWIW, even if you have a transistor amp, the speakers with higher impedances are going to sound better because while many transistor amps can drive 4 ohms or less, that is not the same as saying that they are sounding their best. That comes with higher impedances. IOW there is no good argument for 4 ohms in high end audio, although there is for sound reinforcement.

4 of the speakers in Tvad's list seem to have been designed using OTLs- Audiokinesis, Coincident, Merlin and Classic Audio.

To add to the list of tube friendly speakers:
Quad 57 and 63, but not the later models
any 'full range' driver like a Lowther or PHY
all horns, with the exception of the AvantGarde Trio
High Emotion Audio
Vandersteen
Wilson Audio

Roblanger, all the Vandersteen 2 varients are tube-friendly. I know the Dali Mega-line is but I am not familiar with their smaller models.

Tvad, in the case of the Merlin, the impedance swing is well within the capabilities of almost any tube amplifier, even our S-30, which can be quite sensitive to lower impedances. I don't consider 6-8 ohms to be challenging for our amplifiers at all- that sounds easy to me.

As far as 'high enough'... this has to do with the maximum power transfer of the tube amp in question, which is usually a function of the output transformer and the load of the speaker. For example if you load the 8 ohm taps of a tube amp with a 4 ohm load, the load presented to the power tubes by the transformer will be significantly less than the intended design- the amp will make less power. In some cases it could cut it in half. A speaker designer can take advantage of this phenomena in crossover design. I think a classic example is the old Wilson Watt.

The Watt had a reputation for being detailed but bright in the old days. This was because of a tweeter resonance. Wilson had a substantial trap that measured about 2 ohms at the resonant frequency of the tweeter. When you put a transistor amp on that, the amp simply made more power to deal with the 2 ohm load. So this did exactly the opposite of the intention of the design. But when you put a tube amp on that same load, the tube amp made no power, thus preventing the resonance from being a problem. IOW, the reputation of the speaker came from transistor amplifier users, not tube amp users.

Once the inpedance of the load is high enough, the amplifier will exhibit a sort of 'constant power' phenomena- it will be a slowly decreasing amount of power as the load is increased; the power curve looks a lot like an airfoil curve in profile. With OTLs the effect is increased; once above the maximum power transfer point the load can be tripled without significant power loss. All that is required of the speaker designer is to understand that this phenomena occurs, thus my paradigm conversation:

http://www.atma-sphere.com/papers/paradigm_paper2.html