Jacques Mahul of JMlab: Inverted domes & otherwise... Page 5
Mahul: The dispersion characteristic of the tweeter is hemispherical and needs to "see" the baffle around it. You can't compare it at all to the baffle requirements of a positive-dome tweeter.
Scull: And where does it cross over?
Mahul: The inverted dome's bandpass performance allows coupling to the midrange from 3kHz. So transient signals are reproduced without any distortion, and minimum directivity.
Scull: You know, Jacques, Freud said everything in life had to do with sex. But I suspect it's all to do with food!
Mahul: [laughing] I see this is a good time to speak about our special sandwich construction technology, Jon-a-ten.
Scull: You are known for your specialization in this field?
Mahul: Yes, thank you. To achieve high efficiency without coloration, you have to work especially hard on the diaphragm, the cone. It must be light and rigid but also very well damped. Our sandwich "W" cones are fabricated of two layers of Kevlar on one side with two layers of fiberglass—randomly compacted spun-glass fibers—on the other, with foam in between. We adjust the mass of the driver by the thickness of the foam. It's very light, very rigid, and fast.
Scull: The sandwich construction must yield dividends in the bass. That's a 12" unit?
Mahul: Yes, and our sandwich construction means we have a rare success in combining lower-midrange transparency and extremely swift attack characteristics. It was considered for some time that high-efficiency designs couldn't develop any real bass. That's why our drivers have very long throws—to bring the bass fully to the listener. And we needed a cone that was not too large in diameter.
Scull: Ah yes, rigidity...
Mahul: Yes, it's everything. Remember that the force to move the cone is coming only from the center. If it's not extremely rigid, you can have rather bad oscillations of the diaphragm.
Scull: The 6" midrange units are wired in parallel?
Mahul: Yes, each is loaded individually by a closed-box volume. They use an ultrapowerful 560gm magnet with strong acceleration and a flat aluminum-ribbon voice-coil.
Scull: The Utopia is a bass-reflex design...
Mahul: Yes, we use either bass-reflex or transmission line to compensate for the bass in our high-efficiency systems. And you know, with a sealed-box design you don't easily find more than 90dB or more of efficiency, as we do. All of these qualities are of help in achieving better neutrality in our high-efficiency drivers.
Scull: Merci, Jacques.
Mahul: Je vous en prie, Jon-a-ten...