I've never done a direct comparison. I've heard various ATCs enough times to be fairly sure in my opinion. I've only heard the M40.1 three times at shows, under less than ideal circumstances, so I'm not sure how valid my impression is.
That said, my impression is that the Harbeth sounds more relaxed and a bit warmer than the ATC 100A, which would be the equivalent model. There's a lot of guff making the rounds on forums that the ATCs have midrange distortion. That may or may not have been true 20 years ago, but the current version is superbly low in distortion over the entire frequency range. A German magazine, stereoplay, has done measurements on a version of the 100AT which are pretty convincing. Haven't seen measurements of the Harbeth.
The ATC is really, really good in bass and midrange but not perhaps as well resolved in the treble region as the Harbeth. The Harbeth is really, really good in midrange and treble but perhaps not quite as well as resolved in the bass. Neither would dictate the type of music you listen to.
All not very helpful. At this price level, a home demo is a must. The speaker/room interaction will be more important than differences between these two speakers, I suspect. Why not contact your nearest Harbeth dealer, or even our own hifi_dave, about a home audition for the Harbeth, and contact ATC about which dealer could arrange a home demo of the 100A for you (IIRC Musicraft Derby have mentioned in the trade announcement section here that they have the 100A on demo, for example). I'd love to hear how a direct comparison would turn out for you.
That said, my impression is that the Harbeth sounds more relaxed and a bit warmer than the ATC 100A, which would be the equivalent model. There's a lot of guff making the rounds on forums that the ATCs have midrange distortion. That may or may not have been true 20 years ago, but the current version is superbly low in distortion over the entire frequency range. A German magazine, stereoplay, has done measurements on a version of the 100AT which are pretty convincing. Haven't seen measurements of the Harbeth.
The ATC is really, really good in bass and midrange but not perhaps as well resolved in the treble region as the Harbeth. The Harbeth is really, really good in midrange and treble but perhaps not quite as well as resolved in the bass. Neither would dictate the type of music you listen to.
All not very helpful. At this price level, a home demo is a must. The speaker/room interaction will be more important than differences between these two speakers, I suspect. Why not contact your nearest Harbeth dealer, or even our own hifi_dave, about a home audition for the Harbeth, and contact ATC about which dealer could arrange a home demo of the 100A for you (IIRC Musicraft Derby have mentioned in the trade announcement section here that they have the 100A on demo, for example). I'd love to hear how a direct comparison would turn out for you.