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How to judge an amplifier's performance with a "powered-woofer" speaker?

Hello, I can't seem to find a definitive answer.  Nowadays,many speakers are made with a built-in woofer amplifier. Vandersteens, Martin-Logans , Von Schweikert,etc.
How will your amplifier affect the tonality or dynamics of this type of speaker?
What type of influence will your amp have on the bottom end? Will your million-watt amp be zeroed out by the speaker amp? 

Interestingly, I was reading a review of the Parasound JC1+ Mono's paired with Von Schweikert Audio VR-55 Aktives, and the reviewer raved about the powerful ,deep bass of the JC's. But wait! The speakers have a 525 watt amp driving the woofer!!! Does the 450 watt JC trump the 525 watt speaker amp??
If you are going to review an amplifier wouldn't you get a "truer" report by using traditional speakers?

====How does your amplifier and a powered speaker interact? Who does the heavy lifting?====

Thanks for your time.

michaelpaul


128x128mikepaul

Showing 2 responses by erik_squires

erik_squires
15,871 posts
 
Coming back to the OP's question:  Amplifiers are not independent commodities. You don't gauge their worth and put them in your closet, waiting for the to appreciate for years before you take them out and sell them still in the box.

Who cares if an amp performs well on speakers you don't own?

Amps are part of systems, tightly coupled to the speakers.  When evaluating the performance it is the system behavior that matters, not a test bench and not in a system you don't own.

In general, yes, most amps whether solid state or tube are more impedance dependent than we'd like to believe.  Using a powered bass section in a speaker will stress this particular issue less than a traditional multi-way speaker would.  It does not by itself change the value of an amp, unless you are a reviewer, of course. :)
erik_squires
15,871 posts
 
Hi mike,

Great questions.

While designs may vary, usually the bass section will offer the amp a high resistance value, say 800 Ohms instead of 8. This limits the current the amplifier has to provide in this range to 1/100th of the original. This lets the amp perform like it has a much bigger power supply and with a much higher effective damping factor, but the tonal qualities, including distortion and noise, of the amp are still in play.

However, without a line level (before the amp) high pass filter, the main amp still has to cover the entire voltage swing of the original signal.  In other words, it's a small win for the amp, but it could be even bigger.

Vandersteen seems to have this part covered pretty nicely, with a line level high pass filter and the speaker’s amp designed to compensate with it. Quite clever.  This effectively removes the bass V signal (most of it!) from the amplifier output, making the amp's voltage swing much smaller.  It's a feature professional systems take advantage a great deal, but usually we don't worry about it for home.  To give you an idea though, maybe you can now use a 30W Class A amp if you have a high pass filter, to reach the same levels than before you had a 200 W. 


Best,

E
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