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.
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!!!
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 ...
Why have such a hard speaker to drive in the first place?
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).

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.
"May 17, 2004

As I'm in Europe, I will be pleased if you can help me. I own one system made with EMM Labs, Halcro dm10 and dm68, and Avalon Eidolons, and sometimes I think that the sound is a little thin, that it needs more weight. As I know that you have written about the new Lamm M1.2 Reference and you also know well the Halcro electronics, I will be very happy if you can tell me how these amps compare. Another amp I'm thinking about is the Tenor Audio 300Hp. If you have heard it, also please let me know your opinion. Sorry again, but here right now it is impossible to compare both amps.


Sorry to be so persistant but I just found this asking letter on www.ultraaudio.com It seems that this guy has the same problem with Halcro that I have. I am thinking that if you pay 40K or 50K for amp it should drive even the most difficult speakers on the market
Hi Ulf,- it remains a fact that not all amps will drive all speakers, in fact, you have to be very careful to make sure that the amp and speaker interface is doing what it should.

Speaker cables, the length of the cables, the use of negative feedback, input impedance (already covered), load reactivity, output section stability and literally a host of other issues define the arena of your question.

There are speakers that transistor amps cannot drive and there are speakers that tube amps cannot drive. As you have seen, the speakers that you might think would be OK for a given technology are not always what you might predict. Generally there are more speaker products on the market then any other type of high end audio product, and you simply cannot blame an amp manufacturer for not knowing how well their amp will interface with a speaker, especially if it is a little bit more obscure! There are just too many speakers out there for that. Of course the manufacturer is the one to ask first, but your experience is important too.
Ironic but the Rowland Model 6 is the first amp I have had that gives me the bass and midbass control. Major slam and can also sound delicate. I have not heard the 8ti so I am not sure while it would fail. I also use the Manley steehead preamp which is an excellent match.
Interesting discussion. Ulf, what exactly do you mean when you say drive? To some extent it sounds as if you don't like the tonal balance of certain amps with your speakers and you're attributing it to a fault in the amp. It makes sense that you might prefer one sound over another, but it doesn't appear that you've established any reference to which sound is more accurate to the source material.
At the 1997 CES Audio Artistry displayed the Beethovens with JRDG's Concentra integrated amp. If the speaker manufacturer is happy with their speaker's performance with the 100 wpc entry level Rowland amp, it would be quite odd that the more powerful, more refined Rowland products wouldn't work at least as well. Here's the show report from Soundstage.
Ulf : the Halcro ARE a bit thin... never heard the Avalon.
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.
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.
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