I also happen to find another article.
The tweeters I build are a direct descendant of the classic EPI "airspring" tweeter designed in the late sixties by Winslow Burhoe. Over the years it has been improved, from the introduction of Ferrofluid™ magnetic cooling liquid, to better dome materials, through its use and further development at Genesis Physics, where the aluminum dome version that I have refined was first introduced.
I build the tweeter in a variety of formats, from several diameters of round faceplates to a few curved- or sharp-cornered rectangles and squares. It is also possible for me to make very small quantities of tweeters using a faceplate made to your specifications.
This tweeter is a remarkable machine. The carefully designed magnet structure is the launching pad for an overlength, highly linear voice coil.
The concave dome allows a smaller diameter voice coil which is then better coupled to any given point on the dome. This concave shape also produces an almost perfect waveform (its main strength), reproducing the original signal with an accuracy that a convex dome never can. This accurate sound is also dispersed widely (its second main strength), down only a few dB at the highest frequencies even at 180 degrees off-axis.
The electrical and physical resonances are both well below 1300 Hz, with a smooth frequency response starting around 1600 Hz and extending to 26 kHz. The distortion level is at or below 0.1% when driven with less than ten watts above 2.5 kHz. This gives a sweet, open, uncolored sound that you can really listen into.
The tweeters I build are a direct descendant of the classic EPI "airspring" tweeter designed in the late sixties by Winslow Burhoe. Over the years it has been improved, from the introduction of Ferrofluid™ magnetic cooling liquid, to better dome materials, through its use and further development at Genesis Physics, where the aluminum dome version that I have refined was first introduced.
I build the tweeter in a variety of formats, from several diameters of round faceplates to a few curved- or sharp-cornered rectangles and squares. It is also possible for me to make very small quantities of tweeters using a faceplate made to your specifications.
This tweeter is a remarkable machine. The carefully designed magnet structure is the launching pad for an overlength, highly linear voice coil.
The concave dome allows a smaller diameter voice coil which is then better coupled to any given point on the dome. This concave shape also produces an almost perfect waveform (its main strength), reproducing the original signal with an accuracy that a convex dome never can. This accurate sound is also dispersed widely (its second main strength), down only a few dB at the highest frequencies even at 180 degrees off-axis.
The electrical and physical resonances are both well below 1300 Hz, with a smooth frequency response starting around 1600 Hz and extending to 26 kHz. The distortion level is at or below 0.1% when driven with less than ten watts above 2.5 kHz. This gives a sweet, open, uncolored sound that you can really listen into.
Know the text. Have to stop at Huw's on the way back from aine this week, let him copy some literature for old EPis, hopefully pick up a couple 6+" woofers. Yes, the Human and Focals are descended from Burhoe's original tweeter(the Humans are about a third the price of the Focals, less output, about 89db, but much smaller and lighter. My big Focal 120s are not getting cozy with the woofer for mini builds). It's still marketing, though. I'm not clear on the test procedures that Burhoe used but the power response into the room from a relatively wide baffle is really nice. I'm not sure how Mark(I think it's Mark) at the old audioheuristics site tested them, but at what seemed to be .5 meter it was hardly universally superior to any dome, but at 1 meter they measure pretty well. When I'm able to measure reliably this spring, I'll post some comparisons.
https://www.audioblocks.com/stock-audio/oil-can-click-sound-effect.html
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In 1985 I've built a 3½-way speaker combo pair called Focal Onyx that I still own. It sounded great and convincing, including crisp and detailled treble by the T-120 inverse dome tweeters. And yes, their diaphragm and voice coil diameters are 1" and about 20mm, respectively. Their foam suspensions still are intact, no need to complain for me.
Sadly, due to severe presbyacusis following two acute hearing losses I'm not able to enjoy these remarkable highs any more.
Best regards!
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