Background
I recently upgraded my monitoring speakers from Adam S2Vs to ATC SCM25as. I work in a dedicated, treated, but small studio space (10x10x8). I occasionally use a sub (Adam sub12) and use Trinnov's ST2 room correction system. I mainly produce and do mix down work. I do not master.

Sound Quality & Accuracy
These are fantastic revealing yet enjoyable speakers. Whereas the treble in the Adam S2Vs led to recurring fatigue on long sessions, I can have the ATC SCM25a going all day without listening fatigue. They are both unforgiving (revealing the flaws in your work ruthlessly) while being enjoyable and inspiring to work through. The sweetspot is large (side to side) while the sound image is deep and allows for excellent spatial positioning of content. I can personally attest to the accuracy of the mid range driver as I have been able to mid range discern content I have not heard on the S2Vs or much more expensive HiFI systems I have access to for reference. It is an absolute pleasure to work with these speakers, most of all so far my production and mix decisions have translated very well.

Limitations
First of all there is the price - a time limited recent sale made these speakers more attainable for me. That being said, the added pleasure of working with them, the time savings of making mix and production decisions that translate well, the fact that these are 3 ways with (to me) relatively unproblematic cross over frequencies and lastly the overall small dimensions (vs the overall sound I get) all in my book added up to a 5 star value rating. Here you really do get what you pay for!
Another couple limitations to note: the speakers linear frequency response rolls off around 74Hz. I am producing EDM with a lot of important content sub 70Hz. You may need an additional sub. The speakers are functioning entirely in the analogue domain, no DSP, no digital inputs, no DSP based EQ tweaking. This is not a problem for me as I am using a separate room correction system, but may be more problematic for others

All up, an amazing pleasurable extremely revealing monitor speaker with very high build quality that works in relatively small spaces.

ATC SCM 25a Mark 2 monitors

ATC — The Acoustic Transducer Company is a British manufacturer. The SCM25A was initially released in 2009. It was ATC's first compact three-way active studio monitor. The tweeter is mounded above the mid-range dome and the bass driver is positioned adjacent to the other speakers. Today there are many monitors out there now that have this common design.

History: The original ATC ACM 25 had a glued baffle. Then they switched to using bolts rather than glue. In addition, the port was moved. It did not change the sound but just relocated it. The latest version has a new tweeter in the Mark 2’s. It is the SH25-76S tweeter that is also in the SCM 45A and 20’s. They did not installed in the prior SCM25a as it did not fit in the cabinet. The mid-range driver is mounted just a little lower than the previous model as to make space for the new tweeter.
The bass driver is a 6.5-inch short-coil low-frequency driver; there isa also a 3-inch soft-dome midrange driver; 1-inch soft-dome tweeter. It reproduces from 47Hz–22kHz frequency range. 235W, tri-amped Class AB design delivers 109dB SPL. 4th-order critically damped, phase-compensated crossover and a passively cooled, FET-limited amplifier block. Continuously variable +6dB bass boost at 40Hz provides precise low-frequency control. Foam port bung reduces low-frequency output in smaller listening spaces.

ATC's proprietary dual-suspension drivers are handmade and wound to exact specifications. This tri-amplified monitor delivers 150 watts to the woofer, 60 watts to the midrange driver, and 25 watts to the tweeter. ATC's renowned low-distortion technology, apparent throughout the speaker, includes a fourth-order critically damped, phase-compensated crossover and a passively cooled, FET-limited amplifier block.

Lower distortion they say allows you to hear more small details that you would not hear otherwise. The voice coil sits in between the magnet without touching it. When the voice coil vibrates in and out. When you increase the volume of the music, the coil vibration goes further out of the magnet and that is when distortion can get much higher. ATC has found a way to address that issue and keep the coil cool. The woofer SL technology lowers distortion by 10-15 db.

The previous tweeter - 25mm (one-inch) neodymium had a ferrofluid-cooled tweeter that used a silk dome which was made by Vifa. The concern with this original tweeter was that in about 15 years the ferrofluid could dry out. In addition the news on the street is the original tweeters were no longer available from the manufacturer.

With the current SCM25A Mark 2 version, ATC created their own tweeter. The box is about 7 mm taller which has a lower distortion tweeter than the prior generation. The tweeter is a 1-inch/25mm soft-dome design employs a dual-suspension system designed to better support and control the coil and dome motion. The company claims that this makes for a narrower magnetic gap, resulting in higher magnetic flux and allowing the unit to offer an extended high-frequency response whilst lowering third harmonic distortion. I found the tweeter to sound very detailed and pleasant to listen to. Cymbal crashes were never harsh sounding.

There is a large, flared port vent is located on the side panel adjacent to the woofer, which is a carbon-paper bass driver. One of the key strengths of all ATC monitors is their very wide horizontal dispersion — around ±80 degrees — which provides a broad sweet spot and stereo imaging that is well defined even when listening to the left or right of the monitors.

I setup these speakers on my stands in my studio, The first impression was they sounded clear and detailed without being clinical. The bass is full but not tight like some Adams speakers I have heard. With only going down to 47Hz, the bass sounds good, but it will not provide that extra low-end bass that you may want for dance, pop, or mastering situations. The mids on the instruments and vocals are forward. Compared to my Focal Twins, the improved clarity and cleanness of the music was apparent. With the mid driver separating the instruments on their own shelf, your able to focus for example on drum toms and hear how the dynamics are, and if they need to be a little more controlled or not. Reverb tails are heard with a clarify that is wonderful. The front to back is also excellent with the ATC’s. Being able to hear how to adjust the instruments from the vocals, guitars, and keys is easier with them. These monitors make you work harder however as with monitors like Focal Twins or Genelec 8050’s that provide a more cohesive sound of your mix (which is good in some ways,) does not allow you to hear the little details. With the ATC’s providing the extra details, with not having a cohesive sound that you hear on listening speakers, headphones or in ears, it takes a while to learn how to mix with them. In addition, I found having headphones or a 2nd pair of monitors like the Yamaha HS5’s that provide a cohesive sound very helpful as you want to hear how the music sounds on standard speakers.

These monitors are not fatiguing. The tweeter and mid-range do not use the cabinet volume but are sealed and self-contained. On opening up a song I mixed on my Twins, the ATC’s revealed the bass guitar needed to be a little louder. In addition, the kick drum needed a little more thump by 90Hz. I opened to a second song I previously mixed and the ATC’s revealed the piano track during the lead guitar section was competing with it. I took the piano a decibel or two lower which fixed this problem. The SCM 25a’s also revealed the e piano solo had too much reverb. When playing Owner of a lonely heart by Yes, I heard the reverb tail better and I heard panning on the song better. In addition, when they sing “much better than a”, the chorus/flanger effects on the vocals were heard much better. On Hotel California from Hell Freezes over, the guitars popped more without being clinical.

The one negative thing about the mid-range driver is that it is a little sticky. So if a piece of lint in the air hits it, it will cling to it which I found out first hand. In addition, the speakers are heavy and these will built speakers will need good stands to be on.

These speakers cost $9,490 which are expensive monitors. If they are in your budget, I would recommend checking them out. I enjoyed the time I had them in my studio and was sorry to see them go.

• 6.5-inch short-coil low-frequency driver; 3-inch soft-dome midrange driver; 1-inch soft-dome tweeter. Reproduces the 47Hz–22kHz frequency range. 235W, tri-amped Class AB design delivers 109dB SPL. 4th-order critically damped, phase-compensated crossover and a passively cooled, FET-limited amplifier block. Continuously variable +6dB bass boost at 40Hz provides precise low-frequency control. Foam port bung reduces low-frequency output in smaller listening spaces. LF Driver Power Amp:150W
• MF Driver Power Amp:60W
• HF Driver Power Amp:25W
• Total Power:235W
• Frequency Response:47Hz-22kHz
• Crossover Frequency:380Hz, 3.5kHz
• Maximum Peak SPL:109dB SPL
• Height:10.4"
• Width:16.9"
• Depth:14.5"
• Weight:53.79lbs (per cabinet)