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Why dosome high pwr amps fail to drive some spkrs?

I have Audio Artistry Beethoven speakers. They are dipoles with main panel, active xover and separate unpowered subs. In the main panel ther are 2 10´ woofers covers the range 100-200 Hz. This speaker A A Beethoven was Speaker of the year by Stereophile 1998. According to S. test the speaker has a sharp drope in impedance in than region 100-200 hz to about 3 ohm. The problem is that some amps fail to move this 2 10´woofers. A Rowland 8TiHC (high current) of 400 w and lots of current fails to drive the woofers resulting in a lack of midbass (otherwise the Rowland was very good). Also "the worlds best amp (Stereophile cover)" Halcro DM 68 at mega bucks also fails to drive the woofers. Halcro says that this amps has no problems down to 2 ohms. BUT a 10 year old Classe 300 (300W) at budget price drove the woofers with no problem.I finaly settle with big Krell monos and they have absolute no problems in this area.
I was told by a well know audiophile on Audio Asylum that he had the same problem with the even bigger Rowland model 9 that fails to deliver midbass to Big Avalon speakers.
Can someone explain this to me or has anyone similare experince?
I can also say that the speakers are truly world class now with the Krells!! I use a Krell KSA 300 to power the dipole subs with exellent result and 20Hz wall shattering bass.
128x128ulf
justin_time
100 posts
 
An important variable to consider is the frequency response of the amps at various loads. Speakers' impedance varies with the frequency, often with large peaks and valleys. Since the frequency response of most amps changes with the speaker impedance (load), it is not at all surprising that a successful amp/speakers combination is usually the result of careful matching.

It is not unsual for an amp to sound too bright on some speakers and muted on others, bass shy on some and bass heavy on others. You cannot necessarily fault the amp or the speakers or make blanket statements on their capabilities. Not all great amps perform well on all great speakers and vice versa. For example, I have had great results with my Watts/puppies by using the Rowland Model 7, and BAT Vk-60. The Krells sounded unbearably bright and, overall, less refine with these speakers. Yet they perform well with your speakers.

So, in addition to other considerations, take a careful look at the impedance of your speakers from 20Hz to 20kHz and try to find amplifers that, among other things, compensate well for your speakers' characteristics.
ulf's avatar
ulf OP
103 posts
 
With drive I mean the ability to drive my 2 10`in each main panel of my speakers. I know that Audio Artistry used Rowland on shows 1998-99 so my logic choiche was the 8 TiHC where HC stand for High current" "more then double the current output" to the model 8TI. On paper there would be all the juice for a powerfull midbass but the cones hardly move. So I assume there is another problem (perhaps phase angle derivation). I make this tread to report my findings and hopefully it will help somebody the chose the rigth amp- speaker combination.
gregm
3,405 posts
 
Ulf -- you've got OUTSTANDING speakers, you lucky .....:)!
As to the drive issue: it's strange as these aren't insensitive speakers...
Could be related to the phase angle @ ~90-100Hz where (I think) the woofs kick in. In conjunction, the sound (or lack of it) could be related to the amps output impedance. Krell has tried (or its marketing has) to minimise effects of impedance/ energy transfer in the spkr-amp interface.

However, I would think an active biamp approach would serve best. Finally, why not try contacting Linkwitz himself -- he designed these spkrs and I'm sure he'd be interested! Cheers
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