Why do tube amps often subjectively sound more powerful than SS ?

@dynamiclinearity I'm going with 'a fair amount'.

The venerable Dyanco ST70 has a damping factor of about 15. This does not change with a 4 Ohm load since you'd be using the 4 Ohm taps. It would be cut in half if you ran a 4 Ohm load on the 8 Ohm tap.

ElectroVoice made a number of tube amps (such as the A30) that had a damping factor of 15 back in the 1950s. It was EV and MacIntosh who came up with the idea of the amplifier being a Voltage source and the speakers being Voltage driven; this to enhance plug and play.

Prior to that speakers had adjustments on the back (midrange and tweeter level controls) to allow the speaker to be adjusted to the unknown output impedance of the amp.

The Mac MC275 had about 15:1. The Marantz 8b amplifier had a damping factor of 16:1.  The famous Fisher SA100 was 20:1.

FWIW no speaker made needs a damping factor of over 20.

Then why do almost all the damping factors measured by Streophile fall below 10 and usually well below. And mor observationally why isn't the frequency response of amps shown by Stereophile into a simulated speaker load so far from flat?

High damping factor in my opinion gives artificially tight bass, or one note bass 

This has been my experience as well in terms of tube amps sounding more powerful, at least for their wattage.  Maybe not all but certainly some that I have used. 

 

Conrad Johnson premiere 12 tube mono blocks - 140w side.

 

I’ve had a very large variety of loud speakers in my room over the decades since I’ve owned those amplifiers , and they have been able to easily drive every single one of them, always sounding powerful.  That includes even tough to drive Thiels and MBLs.

 

But once in a while, I try another solid-state amplifier in my system  “ just to see.”

 

The last time I did it, I borrowed a Bryston 4B3 solid state amp (300 W into eight ohms, 500 into four ohms).

 

Just to take one example 1st :  before I borrowed the Bryston amplifier one of the tracks I’ve been playing quite a bit was Basil Poledouris’ incredibly dynamic score for Conan the barbarian.

Especially the opening track The Anvil Of Crom.

 

It’s performed by an augmented symphony, Orchestra , extra instruments, especially extra horns, and Timpany, and it’s just a massive, powerful charging sound.

It had been blowing me away on my system .

 

So when I got the Bryston amplifier, I thought, since it was more powerful, put on really powerful music that will take advantage of it like the Conan soundtrack.

 

I put in the Bryston, cranked it up and…huh?  Where was that power?

Why did it actually sound thinner? 

Less impactful?  

 

The Bryan did have better grip from the upper bass on down - it unravelled some of the in their power range down there, that were a little bit more muddy on my CJ amps.   And it was perhaps a tiny bit cleaner on the horns when playing their loudest.

 

But otherwise , it just sounded actually weaker and thinner, and it didn’t have the punch and drama I was used to.

 

I put this down to the type of distortions from the CJ amp - less damping factor probably allowed for a little bit rounder sound in the power region.  And that little bit of tube distortion over the whole thing, thickening out the sound.

Essentially, I think the tube was acting something like a mild bit of compression, at least in Sonic analogy terms.

 

The Bryston did better on some other stuff.  But most often the CJs sounded richard and fuller, and I often liked even the bass better. 

It was a little bit more round and had more feel, without being slowed down or losing any pace or snap.

 

So anyway, every time I do this comparison, I go running back to my CJs.  Which is why I’ve had them for like 25 years.

Then why do almost all the damping factors measured by Streophile fall below 10

@dynamiclinearity I don't read Stereophile so I've no idea if this is actually true and if so, what amps to which you are referring.

It might be a better question to ask who the designer was and what was their intention. Did the designer have a degree? FWIW, most of the tube amps designed in the old days were designed by actual engineers. That's a lot less common these days. Not saying you need a degree to know what you're doing but it helps!

Some speakers, for example some open baffle designs, really don't do well if the amp has a high damping factor. Nelson Pass demonstrated this about 15 years ago a RMAF using a set of open baffle speakers and a solid state amp he built that was constant current rather than constant Voltage, so its damping factor was fractional since the amp's output impedance was about 50-60 Ohms. It sounded just fine and made good bass despite the small size of the OB speakers. 

So intention is a big variable here and Stereophile does not recognize that certain speakers need a higher output impedance from the amp to sound right. They just have their standard simulated speaker load and that's that.

Basil Poledouris’ incredibly dynamic score for Conan the barbarian.

Especially the opening track The Anvil Of Crom.

@prof I really like that LP. I think Poledouris did a great job on that.