Ctsooner, I'm not really looking to start another lengthy discussion about tube vs SS amps. I'll leave it this way. It is plausible that a speaker designer, a dealer sales rep and/or a customer could be indifferent to plugging a tube amp or a SS amp into a speaker if either (x) the speaker has extremely benign impedance and phase angle characteristics, or (y) the tube amp has very low output impedance.
As Al and Ralph Karsten (Atmasphere) have said on numerous occasions, a speaker's ultimate acoustic presentation will be affected to the extent an amp has a high'ish output impedance and the speaker was voiced (intentionally or not) to be driven by an amp that has a low output impedance. This is not my opinion -- it Ohm's Law.
It is my experience that when I drive my speakers off the 8 ohm taps of my amp, the speakers sound bright and detailed, maybe too much so at times. In contrast, when driving the speakers off the 4 ohm taps, bass is more extended and tighter, imaging less forward. Admittedly, I am conflicted about which acoustic presentation sounds better to my ears. It just depends.
This is no coincidence. The output impedance of my amp off the 4 ohm taps is about .55 ohms in the lower frequency bands; and about 1.1 ohms off the 8 ohms taps. It is similarly notable that the impedance curve of my speakers is roughly 4 ohms between 70 Hz and 700 Hz, rising sharply and peaking at 21-22 ohms at the 2.2K Hz crossover point, dropping again to about 5 or 6 ohms as frequency increases.
Let's put a sonic face (sic, an oxymoron) on what I just said. John Atkinson's bench test report of my amp states that output voltage regulation is +/- .4 db off the 4 ohm tap and about +/- .8 db off the 8 ohm tap. What this means in plain English is that my speakers should be about 1.6 db louder at the midrange highpoint of about 2.2K Hz as compared to the bass saddle of 70 to 700 Hz -- IF I use the 8 ohm taps. In contrast, the SPL delta off the 4 ohm taps should be about .8 ohms. Those stats cogently explain what I hear.
Oh ... the damping factor of my amp is also affected. Theoretically, about 7 ohms off the 8 ohm taps and about 14 ohms off the 4 ohm taps. Although with my speakers, those stats should be halved because my speaker's impedance is about 4 ohms in the critical parts of the bass frequencies. But those stats explain why I perceive bass to be more extended and tighter off the 4 ohm taps.
This is Ohm's Law, not my opinion. So, unless a dealer's sales rep explains in plain English what I just said above, he's either ignorant or scamming the customer. Of course, he could be honest and say even though a tube amp may be causing certain acoustic colorations, they sound good, in his/her opinion. Then it's on the customer to decide.
Al or Ralph, if you can simplify or clarify what I just said, I'm sure I and the other readers would appreciate your edits.
Regards,
Bruce
