ATC SCM40A speakers

admranger   I do not know your particular amp, but I do know ATC transducers.  They can be quite demanding and particular, wringing the life out of respectable power.  I’ve a pair of SCM 20s run by a Luxman 509X and they need all of it.  
125 wpc of solid stable Luxman current.

@lonemountain --

Good post and insights on ATC speakers and their high quality drivers.

However:

For example, many performance attributes depend on other attributes and you cannot have all of them- you must choose. For example, there is a clear link between efficiency and LF performance in a driver: want more efficiency? Expect less bass- and vice versa.

The takeaway with high efficiency in conjunction with LF performance (i.e.: extension) isn’t that the latter aspect can’t be had, but that it requires large size - given of course proper implementation with the right type of driver mated to its intended cab design and tuning. Hofmann’s Iron Law, as a premise, merely states that you can’t have high eff. as well as LF extension from a small size factor, but I’m guessing to many audiophiles the general deduction is being made that high eff. precludes deep bass simply because most don’t have, or won’t make room for very large size subs and the designs they reflect. In other words: large size isn’t even considered as a viable option.

Some believe ATC speakers to be on the "light" side in the bass area, whereas I find they provide for a more natural and musically integrated bass response, a trait they share with higher eff. bass systems - no doubt from a common outset of low distortion; ATC achieves this in particular by using underhung voice coils with massive motors, whereas high eff. bass systems have low distortion in the bass not least due to prodigious headroom within a given SPL range (also from designs with massive motor force, in addition to very high power handling), which is to say: less woofer excursion = lower distortion.

As Roy Gregory puts it in his review of the Göbel Audio Divin Noblesse speakers:

Those of you looking for the traditional, rib-rattling thud that many audiophiles associate with big speakers are going to be disappointed. In common with many other more efficient and dynamically responsive speaker systems, the Divin Noblesse delivers bass that’s pitch-agile, articulate and fast on its feet -- as opposed to leaden, thick and turgid. It’s not unlike live, acoustic bass. How often does an orchestra generate the sort of low frequencies that communicate on a skeletal rather than aural level? Very seldom.

I've had my ATC SCM40s(V2 Passive) for around 18 months. I first had them driven by Marantz Model 30, then by a Heaven 11 Billie Mkii. 

Recently I've added an Atoll AM200 power amp (120w) and use the Billie as pre-amp. I guess the bass produced is partly room dependent, but in a modestly sized room like mine which is partly treated, I've stopped using my sub as there's no need. Acoustic bass/double bass is wonderfully reproduced, to the point you can feel it in your gut but with no bloat.

Since I've added tubes by way of the Billie, especially now in pre-amp mode, and the gutsy Atoll power amp (dual-mono), which really takes control of the ATCs, for me this is a match made in heaven (excuse the pun 😊)

A few days ago I came to the realization the only complaint I have with my 803 D3s was a somewhat strident treble. 

So I did the stupidly simple task of reducing toe-in of about 30* to zero (speakers are aimed straight ahead).

Viola! Treble glare gone! Now sounds coherent from bottom to top.

To me, sounds wonderful. Happy camper. Think I'll keep em.

Thanks to all who have contributed to this thread.

Boom!