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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
nrchy's avatar
nrchy
2,124 posts
 
Do those amps really drive a two or three ohm load? Some amps which are great on paper fall short in the listening room. Wait till the 'measurement only' people see that!!!
joeabrams
132 posts
 
The problem may not be what you think it is. For example, if your preamp had high output impedance, like 500 ohms, and you were running long interconnect from that to the amp or to the AA's crossover box, that might be the cause. Why?
Because the Rowland and the Halcro both have _low_ input impedance, but the Classe' and the Krell both have input impedance over 47 K ohm.
In other words, the impedence mismatch -- if that were the case -- would be enough to make the difference in apparent (lack of) bass drive in the Rowland and Halcro.
Just a theory ...
philefreak
423 posts
 
Why have such a hard speaker to drive in the first place?
ulf's avatar
ulf OP
103 posts
 
Both Rowland and Halcro was used with Rowland Synergy pre and in the case of 8 TiHC that would be hard to call it a mismatch.IC was standard 1 meter long both btween pre and xover and 1,5 m to amp. I have asked Rowland about the problem but they never answered. Halcro deny that there should be a problem. In Stereophile august 2005 Wilson MAXX test they say "the combination of 3.8 ohms and 33.4 capacitive phase angle at 162Hz, a frequency where music has considerable energy, will also demand an amp that can sorce a good amount of current".Perhaps Beethoven has the same "problem" and perhaps Rowland and Halcro has problems with handling "capacitive phase angle" (whatever this is).

Philefreak:
When properly driven the AA Beethoven outclass evey other speakers I have listen to. Have you have a chance to listen to them?

My point is that some of the best high end full range speakers like Wilson, Avalon etc can t be driven by some high end amps in spite of the normal sensitivity (Wilson has a high 90 db) of the speakers and i spite of these amps high watt and current figures.
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