Question: Does ATC have the best midrange driver?

Tweekerman, you are right in that there is a shortage of excellent quality dedicated midranges. Most high-end speakers these days use a woofer, a midwoofer, and a dome tweeter. One problem that these systems tend to have is a narrowing of the radiation pattern in the upper range of the midwoofer. But with the 3" diameter ATC dome crossing over to a dome or possibly ribbon tweeter, it is possible to maintain a more uniform radiation pattern through the crossover region.

Why in the world would this matter? Because a characteristic which generally distinguishes live music from reproduced music is how natural the reflected, or reverberant, energy sounds. What we call "off-axis" response determines the tonal balance of the reverberant field. And the tonal balance of the reverberant field is a significant factor in both timbre and listening fatigue. Basically, you want a fairly well energized, diffuse reverberant field that has the same tonal balance as the first-arrival (on-axis) sound.

And the ATC dome midrange has more uniform reverberant field response than a larger-diameter cone would, without having the dynamic non-linearities that plague other dome midranges which don't have that double suspension system.

The emphasis on flat on-axis response stems from research done back in the 60's and 70's. It was determined that the on-axis response played a greater role than the "power response" (summed omnidirectional response) in establishing the perceived timbre of a speaker system, and flat on-axis response has been the holy grail ever since. But another way to interpret the data is temporally: the first-arrival sound plays the dominant role in determining timbre, but the reverberant sound still plays a significant role. I believe that minimizing the discrepancy between the first-arrival and reverberant sound is a worthwhile pursuit, as this mimics the characteristics of live music.

Anyway, I'm not saying the ATC is necessarily the best midrange by all possible yardsticks, but I think it's probably among the better units of its type. I've heard the smaller ATC speakers and think well of them, though I did not choose to become a dealer (I could still hear a bit of boxiness, and for that much money I prefer speakers that don't let you know the music is emanating from boxes). I've actually never heard the ATC dome midrange, so my comments here are educated guesses at best and SWAG speculation at worst. As I write this I have a pair of ATC dome midranges on order to dink around with - perhaps when I've had a chance to get to know them well, I'll have something more useful to post.

Best of luck to you in your brave and bold projects, intrepid Tweekerman!

Thanks Duke for the clarification on this "muddy and murky" area of midrange, THE critical fq's. You should know the midrange area, your Sound Labs shine like no box can in the mids. You answered some doubts i had,about which mid to use. I was going to reconsider using the Seas W12CY or W15CY cone midrange. But your post points to a dome mid as better choice choice for "narrowing radiation pattern". Especially with a ribbon. And maybe i need to go with the C-44, as being "faster" and better match with the ribbon than the C-79. I've received a big vote for ATC and the other for ACCUTON C-79. Both have over 20 yrs experience. I think i would prefer the ATC but am having trouble ordering the driver and the one building prefers the Accutons. Your explanation of the "reverberant field" brings me to a better understanding of what i'm after in a speaker. Please keep us posted on your findings of the ATC.

Audiokinesis makes the point well. With a midrange driver, or any driver, when the wavelength becomes less than the radius of the cone/dome is when the beaming begins. I don't now the math off hand, but this is why 4-4.5inches is about as big as you can get away with if you're going to try an get up to 6,000hz and still be able to cross as low as 100hz. If I was going to do I diy three way, which I hope to one day, the ATC and Skaaning would be on the top of my list. Personnaly, I wouldn't do the Accuton, for lack of internal damping. With the Manger's I've heard less than favorable experience from others with them-like "they were ok, but nothing spectactualar and I've heard betters stuff." I did hear there are some distortion peaks somewhere in the driver which may account for why they don't sound that great despite having some otherwise impressive specs. And they are $$$, but in defense easy to design for/with.

Ezmeral i've heard simular things about the Manger, even the word, "junk" was said. I just checked the Accuton specs. , is ferrofluid internal damping? One speaker designer says ATC, the other Accuton. I'm going Accuton, will let you know in about 3 months.

Internal damping, crudely, is the ability of the driver's material to absorb the standing wave/refelcted wave that forms on the front "inside" the cone. Someone else please say it better if you can cause I know I know what I'm talking about halfway here :) Aluminum and ceramic have virtually no interanl damping. This is all on the front of the cone; the ferrofluid damping has to do with the backwave of the cone-its different. Birotechnology.com and vmpsaudio.com both have good designer notes sections on the various cone materials you might want to look at short of the books for better explanations than mine. I know dunlavy slams most of those ritzy cone materials. If you get accuton to work great let me know. They are attractive looking and I'd like to design with'em, but the rational side of me still says the Skaanings would have a nicer sound in the end. But I'm no authority.