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

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

I've had a few speakers with powered bass and a few without, and weirdly it was easy to tell amp changes on the powered guys. Even though they don't have a load on the low end of the spectrum, the amp still typically contributes down to 80hz, maybe lower, depending on the crossover. 

Anyways, the powered bass gives you a lot of flexibility to try different amps so I really like them. Trust me, you'll hear amp differences just as fast as you would with a passive full ranger. 

MIKEPAUL that tells you all you need to know about all audio magazine reviewer not about audio but money

ALL speakers (with/without bass amplification) holistically respond to amp changes, and they are typically immediately discernible. See for yourself. Powered bass readily responds to speaker cable changes and power cord changes. Ditto for subwoofers. 

The Legacy Audio Valor Speaker System I reviewed for Dagogo.com, with its internal bass and subwoofer amplification, responded just as any passive speaker would to amp changes on the mid/treble. 
Even if  the change is to the midrange on up, the entire speaker will sound distinctly different due to the change in interaction between the drivers. The relative strength of the bass, it's tonality, dynamic power, etc. relative to the mid and treble has changed. 

This thread is fine evidence of the hubris of readers who default to distrust of reviewers, thinking they know better. Well, in the majority of cases, you don't.  :)