Passive bi-amping works ?

I have a pair of Legacy Classics I am driving with a Sunfire Cinema. I have tried driving them with single channels then biwiring and then passive bi-amping and there was a steady improvement in the sound. More highs and lows with each change and better clarity and definition. A rather interesting thing, which I can't explain is that the speakers response got much flatter when I went to vertical biamping (as confirmed by my SPL meter). I had a +3 to +5 dB boost over much of the bass range and after the vertical biamp, it's now +-1.5 dB down to 40 Hz. Now I'm just waiting for the funds to go with Active crossovers...

Gpalmer-
(Someone with an EE can say this better than I, but bear with me.) When you passively biamp you are removing the crossover elements of the high and low pass sections of the speaker from each other. Because there is no series or parallel interaction between these elements, the impedance variations with frequency the amp sees are gentler (and the lower amp is not forced to put high current into the high frequencies.) The frequency response improvement is probably due to the smaller impedance slope,phase angle, and possible higher overall impedance from the bass to the mid range and from mid range to highs when you biamp compared to it run as a single speaker. This slope/phase angle causes frequency response/tonal interaction with the amps. As the slope approaches zero (ala a classic 8 ohm resistor)there is less frequency reponse interaction, all other things being equal, (eg see the Stereophile tests of many tube amps to see such a plot.) Bravo on your disciplined investigation and sharing of information that truly benefits this discussion.

Ivanj
Thank you for that explanation. I have done quite a bit of reading up on the web on passive biamping and most of the discussions of improvements seemed to focus on the benefits to the higher frequencies due to lessened intermodulation distortion with the lower frequencies, so I really wasn't expecting the result to be apparent in the bottom end. (Although I'm very, very happy with the response I got).

Greg

I'm still looking for a real test of bi-amping. Like two 100 watt amps vs a single 200 watt amp. Obviousl adding a second 100 watt amp is superior to a single 100 watt amp, but are two 100s superior to a single 200? Most experts say no. It's better to get the higher power amp.