Purely out of curiosity and to gain further knowledge my question simply
is how does the 14 watt (Tubed) Luxman accomplish this feat? If its output impedance is low enough, it will make its full power into the lowest impedance of the speaker (BTW its actually rated at 20 watts). At higher impedances its negative feedback will throttle back the power so as to keep the frequency response even. Since most of the power is in the bass, this really isn't a problem since the the higher frequencies need so much less power. But what is afoot here is really (as I'm sure you already know) that a watt, if nice and clean, is really a bit more power than you might expect. I'm sure that the amp doesn't like the load all that much, and so its probably making more distortion as a result. But most tube amps are pretty well-behaved when it comes to distortion in that they tend to not make as much of the higher ordered harmonics as solid state amps. So I would expect it to sound smoother, even though it might be working hard, than a solid state amp. But if the load impedance were doubled, I bet it would sound even better if all other things were kept equal! About the closest was I know of to do that would be to use a set of ZEROs and see :) www.zeroimpedance.com |
In a follow up post I specifically mentioned amplifiers capable of
doubling their power as the speaker impedance is halved. This would
demonstrate high current output/delivery from the amplifier. This is
what some have said the Sony speaker requires to drive it properly.
There's no evidence to suggest that the Luxman has this high current
ability as defined by this criteria.. @charles1dad What you are talking about is the amplifier behaving as a voltage source. Usually that means 'doubling power as impedance is halved' but it does not have to work that way; an amplifier can be a voltage source if it cuts power in half as impedance is doubled. The former is often how solid state amps behave if they have enough power supply current and the output section has the current handling capacity; the latter is how tube amps and smaller solid state amps do it (or somewhere in between, where there might be slightly more power into a lower impedance but definately half the power if the impedance is doubled). So the Luxman wouldn't need all that 'high current' to be perfectly able to do the job. The 'high current' thing tends to be overblown in audio to the point of being mythological- current can't exist without voltage and the two together make power, defined by the relationship of 1 watt = 1 volt/1 amp. |
My point is if you look at the Sony SS AR1 speaker measurements they are
as George and others have rightly noted, a ’challenging ’ speaker load
given its impedance curve and phase angle characteristics. Armed with
this knowledge the last thing you’d recommend is a 14 watt tube
amplifier. @charles1dad In looking at this statement I think you might be conflating high power with the ability to drive difficult loads. But I suspect this load isn't as difficult as it appears, but regardless a small amplifier can easily deal with difficult loads if designed for it. Anyone making a tube amp these days has to deal with the simple fact that 4 ohm speakers and difficult loads are a lot more common than they were even 20 years ago! And I suspect that Luxman didn't go into that product design blind to this fact! |
One has to ponder that there are things listeners can clearly hear that
(At least for now) aren’t being measured or maybe can’t be measured. In this case I don't think so. The Luxman is able to behave as a proper voltage source within certain limits, and the 8 ohm power they are getting out of it suggests that it might be set up so that it can put out a bit more power into lower impedances. This is done by simply 'light loading' the tubes in the output section by setting the primary winding of the output transformer to a bit higher impedance. On top of that I'm pretty sure that Luxman did their homework on the output transformer and has something that is spec'ed decently in there. This all does not seem that mysterious to me- I've seen it before. |
I am really surprised/stumped as to the results, as I had high
expectations for the Accuphase and the SS AR1s. This Accuphase amp is
highly regarded and in all the literature I read I would never have
expected this outcome, but that's what my ears told me in the end.
Obviously this is all down to individual taste and opinion, but the
clarity of the Luxman was not bested by this entrant. In a nutshell, high damping factors are overrated! Duke LeJeurne of Audiokinesis gave an excellent reason why (as a speaker designer): " A high damping factor will provide very good control of the bass drivers."
Hmmmm.
For
a quick summation of my thoughts, skip to the last two paragraphs.
Apologies for getting fairly nerdy in between here and there.
In
practice, any series resistance in between the amplifier and the
woofer’s voice coil effectively ADDS TO the amplifier’s output
impedance, and correspondingly reduces the damping factor.
Let’s
run some numbers. Supposes our speaker has a nice 2.5 kHz second-order
crossover, which calls for a 1 mH inductor in series with the woofer.
Power handling requirements are easily met by an 18 gauge air-core
inductor, which can handle 300 watts before saturation. The series
resistance of this inductor is .51 ohms.
And let’s suppose we
have an uber-amplifier with a damping factor of one zillion. Or one
zillion zillion. Or one zillion to the zillionth power. It won’t matter.
After the signal passes through that inductor, our
uber-amplfier’s amplifier’s effective damping factor is now about 17.
And this is assuming only the one series inductor, and ignoring any
other wiring.
So in most cases it really doesn’t matter how high
the amplifier’s damping factor is. The series resistance in the
crossover (and/or speaker wires) dominates.
Okay, but what about this "very good control of the bass drivers" that we’re apparently missing out on?
Well,
turns out that it’s not nearly as dramatic as the wording implies. It
all shows up as a change to the electrical damping of the woofer’s motor
- the electrical system Q, or Qes.
Assuming a typical
high-quality 8-ohm woofer in the example above, the series inductor
effectively raises the woofer’s electrical Q by about 7%. So if the
woofer’s electrical Q was .28, the series inductor effectively raises it
to about .30. This could EASILY be an improvement! We'll get more bass
with a higher Qes, but the designer should take it into account by
sizing and tuning the box based on our modified Qes of .30. And if he
hasn’t, this difference can still be largely compensated for with a few
handfuls of stuffing material.
I think amplifier marketing departments may have oversold the benefits of having a high damping factor.
Or to put it another way, in my opinion, super-high damping factors
are, in most cases, of academic interest only. I certainly would not
trade off anything that really matters in order to get a high damping
factor.
Duke
This post is from https://forum.audiogon.com/discussions/how-to-accurately-gauge-speaker-sensitivity-to-match-with-tub...Our most popular amps have a fairly low damping factor- if DF were that important, we'd have been out of business decades ago. |
