ATC buying advice

I came to ATC by way of producing music. The SCM25A's changed everything for me. I'd never heard a more accurate speaker which is essential for mixing/mastering. Everything you hear about the midrange and high end detail is true. The SCM25A has the same woofer, but different tweeter than the SCM40A in a smaller ported enclosure. I would expect the 40 to have more pleasing bass performance, but this is not an SL driver and while good, it is not going to fill a room with bass. When mixing, it is essential to know what is going on in the bottom octave. Subs are needed for this with these speakers. 

The 25's gave me confidence to purchase SCM19's for a fun room. These are beautiful sounding speakers. Thanks Brad at Lone Mountain, I agree they tend toward warm. While beautiful, the magic with ATC's is with the 3 ways. 

I then added passive SCM50's that are 2 generations old due to attractive price. As was pointed out earlier, these are entirely different beasts from the 25's in all the right ways.

I will back up and say you can't beat active ATC's. That is the way to go. Nobody mentions the zero phase crossovers along with discrete amps for each driver. ATC amps are excellent and zero phase crossovers make a world of difference with clarity. It's the same as using a linear phase EQ like the Manley Massive Passive; zero phase crossovers cannot be beat for clarity. That's why these are used almost exclusively in the Pro/Studio environment.

That said, the passive crossovers are insanely massive in the 50's and sound amazing nonetheless. The 50's use SL (Super Linear) drivers with underhung voice coils. This is big boy land. Brad at Lone Mountain can clarify, but my understanding is the mid and tweeter are SL versions as well with stronger magnets. This and the coffee can sized passives must be why they can handle 1500 watts if you decide to go that far. For me, the 50's fill the entire audio spectrum as they should. I still use subs, but they only fill in the lowest registers and don't work much other than to add dimension. I use a pair of 15's and always will. 

Beyond 50's, there's also the consideration of how loud do you want them. Aside from playing deeper as you go up the range, each model becomes 3 dB more efficient. 50's are quite inefficient at 85 dB SPL. You gotta hit 'em hard! They are a sweet spot size-wise tho.

I like it loud so I think I'd prefer 100's or 150's, but I do have a limited budget. It's interesting that the 150's 15" driver switches from rubber to foam as I understand it to better control IM distortion in larger drivers. Now we're talking tank like size compared to the relatively svelt 50's. SCM150's are used in mastering studios the world over. Check out Black Bird studio's various ATC rooms too if you want to see how room treatment is done. 

I say 50's or up and active if possible. Enjoy!
 

Jeff explains it well!.  FOr clarification, the "SL" (super linear)  LF driver is in the 50 on up, and the mid and tweeter of the 50 on up are much larger motors for higher SPL, wider dynamic range.  The amps inside the active 50s on up are also much larger for that increased dynamics. 

The SCM 19 passive and active is the one exception, it also has this super linear Mid/LF driver built just for that speaker,   This is a carry ovwer from ueyars ago when Billy developed a smaller SL  and the line was just the 20/50/100/150..   

Since I already had an integrated amp I really liked, with a lot of juice, I got a pair of passive SCM40s and a couple of SVB-3000 subs. I’m happy with this set-up. It feels like there are diminishing returns for me by going up the product line.

For a number of reasons, I have to use stand mount speakers.

Replaced my old (2004) Quad 11L with ATC SCM19v2. Will probably be my last set of speakers. Love them.

I've found Auditorium 23 speaker cables a good match, and love my Audience Au24SX RCA cables from Dac to amp.

Recently bought an I2S cable, Tubulus Argentus for DDC to Dac. As well as a Puritan PSM156.

All good matches with the ATC speakers.

I hear a lot of support for "active" speakers. For speakers to be active the signal has to be digitized. This can lead to a lot of back and forth conversions. I am a firm believer in digital signal processing, it is a necessity if you want to get to a SOTA system now and in the future. Like a symphony orchestra it is best to have one conductor and traditionally this role has been taken by the preamplifier. There are now several preamplifiers with full DSP capability including room control, bass management, crossovers and EQ. The DEQX is the best of them all. The DEQX Pre 4 and Pre 8 utilize a 64 bit floating point system with the most current processor and are constructed in SOTA fashion. The Pre 8 even has a 4 way crossover! You can make any current loudspeaker "active"!  It even has a phono preamp. You have almost total control over the way a system sounds withing the context of the speaker design chosen. You can not turn a point source speaker into a line source one.