These sit in different price classes - ATC SCM40 costs roughly 5.3x what KLH Kendall does. Expect it to lead on paper; the question is whether the gap is audible enough in your room to be worth it.
| Area | Better | Why |
|---|
| Bass |
B |
KLH Kendall digs deeper - 25Hz against 48Hz. |
| Amplifier needs |
B |
KLH Kendall is more sensitive (96dB vs 85dB), so it goes louder on the same amplifier. |
| Size |
depends |
KLH Kendall is easier to place; ATC SCM40 is bigger, which usually goes with fuller bass. Your room decides. |
| Cabinet |
depends |
Sealed vs Ported. Sealed is tighter and happier near a wall; ported digs lower but wants space behind it. |
| Expandability |
B |
KLH Kendall: bi-amping. |
| Price |
B |
KLH Kendall is cheaper - $1,500 against $7,999, about 81% less; arguably a different class. |
A ATC SCM40
B KLH Kendall
depends neither is better in the abstract - it turns on your room, placement or how you will use them.
Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
KLH Kendall is the easier recommendation: it leads on most of the measured areas and costs less. Take ATC SCM40 if its size, looks or fit in your room suit you better. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 48Hz anyway, so judge these on the other rows instead. If your amplifier is modest, vintage or valve-based, KLH Kendall is the safer partner - the other will want more current or more watts to sound its best.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.