P.S. Of the 6 Heil AMT's I've received, 2 were wired out of phase. ESS needs to do a better job of checking the polarity BEFORE sticking on the ESS sticker on the "front" and taping the bottom wires to the "back."
One easy way to check this is to stack one Heil on top of another Heil (that is known to be correct). If there is significant magnetic repulsion felt, the top AMT is wired out of phase. One can try to send it back to ESS for replacement, but since there is no guarantee the replacement will be correct (I wrote a note with the order and also emailed them to check polarity before sending), one can rotate the wrongly-wired one 180 degrees, then move the ESS sticker to the new "front" and move the wires under the bottom sticker to the new "back."
One easy way to check this is to stack one Heil on top of another Heil (that is known to be correct). If there is significant magnetic repulsion felt, the top AMT is wired out of phase. One can try to send it back to ESS for replacement, but since there is no guarantee the replacement will be correct (I wrote a note with the order and also emailed them to check polarity before sending), one can rotate the wrongly-wired one 180 degrees, then move the ESS sticker to the new "front" and move the wires under the bottom sticker to the new "back."
I played around a little more with the foam inserts and they really do wonders.
I read many times the Heils are hard to integrate because they are so fast that they don't blend well with moving coil drivers.....nothing apparantly is fast enough to keep up. But now I think it may be the dispersion that is the problem. With the foam inserts it sounds so much more coherent playing with bass and midrange drivers. Probably because the reflected sound is more similar due to the vertical dispersion being so much wider.
I still have to try other materials but maybe the foam is perfect. The lower the frequency the more acoustically transparent the foam is.....so it works where it needs to and doesn't where it shouldn't.
I would be very interested to see what power tapering does to a stack of three. Something like this:
With C2 at 2.2 or 3.3 uF
And then I would try foam inserts on the middle one.
I would love to hear a pair of these - perhaps with a touch of EQ
Recommend an experiment using the three-stacked AMTs, but instead using Don Keele's CBT idea, but simplified down to three elements instead of 42 drivers, inserting tapered spacers between the three AMTs to spread out their vertical polars, or alternatively, inserting delays in the top two AMTs via multi-amping to approximate a phased array (i.e., configuration "f" in the bottom figure):
Figures above from Don Keele's CBT webpage and from Floyd Toole's book, respectively. This basically solves the vertical polar coverage issue of the AMT design.
I use two AMTs stacked on top of each other, with the top AMT leaning backwards about 15-20 degrees via a wedge custom neoprene spacer, and the whole assembly placed on top of Belle Klipsch bass bins and dialed-in using a miniDSP 2x4 HD as my surround loudspeakers in a 5.1 array (fully horn loaded)--configuration "d", above. Solves the narrow vertical coverage problem of the AMTs.
Chris
Last edited:
I use two AMTs stacked on top of each other, with the top AMT leaning backwards about 15-20 degrees
After the photo above was taken, I did already end up placing small neoprene spacers under the top AMT to angle up a tiny amount. Found the optimal angle by listening tests from the listening seat distance, which also needed listening height adjusted a little bit.
I need to stop messing around further because the whole system sounds scary good right now.
ESS sale price is a ludicrous bargain because one can buy 5 pairs of Heil AMT's for the price of 1 pair of Beyma TPL-150H, which is sadly sitting on my floor right now.
I need to eventually come up with all kinds of other speakers, e.g. perhaps open baffle using the Beyma with open back plate, something for my horns/CD's.. But I have to ask myself..why?
After the photo above was taken, I did already end up placing small neoprene spacers under the top AMT to angle up a tiny amount. Found the optimal angle by listening tests from the listening seat distance, which also needed listening height adjusted a little bit.
I need to stop messing around further because the whole system sounds scary good right now.
ESS sale price is a ludicrous bargain because one can buy 5 pairs of Heil AMT's for the price of 1 pair of Beyma TPL-150H, which is sadly sitting on my floor right now.
I need to eventually come up with all kinds of other speakers, e.g. perhaps open baffle using the Beyma with open back plate, something for my horns/CD's.. But I have to ask myself..why?
I guess it's the engineer in me that sees the same thing: value and real performance of the AMT-1s.
With AMT-1s, once you work around the narrow vertical coverage issue by stacking and "splaying" vertically, they are very difficult to beat. When I look at the corrected amplitude response (DSP on-axis), I get almost flat phase response out of them down to 700 Hz, and non-chattering on-axis amplitude response (SPL) up through 20 kHz with ~90 degrees of horizontal coverage. Subjectively listening, they are really quite amazing, with plenty of headroom due to their high efficiency and ±90 horizontal horn loading by the magnet structure down to ~1.4 kHz without having to add wings.
Only very rarely have I considered replacing the bi-amped AMT-1s/Belle bass bins with K-402-MEHs in my setup. I don't really think that I will gain much in sound quality and apparent source width (ASW) going that direction for the surround positions, however. Perhaps it's not worth the effort. I've allowed procrastination to make the decision for me thus far.
Chris
Last edited:
For the CBT to work properly, you have to eliminate the reflection of the back dispersed sound.
Typically, I use my ears to inform me in these sort of questions. And I find that's actually more toward the realm of how the loudspeakers are being used (5.1 surrounds fairly close to the side walls, in my case) and personal preference.
YMMV.
Chris
YMMV.
Chris
Just ignore C1. That is only there if you run a first order passive crossover. C2 is just in addition to your passive or active crossover crossover.
That's not a personal preference. A CBT works on the precise dispersion and reflection. If you add the back dispersion of a dipole driver, it will not deliver a CBT result, it's as simple as that. Maybe you'll like it, maybe you won't but that will not result in anything like the CBT was built for. I don't want to discredit the principle more than it already lacks in (bandwidth, horizontal dispersion, non-compability to other room shapes than rectangular, etc) but that dispersion does not come down to a 'matter of taste'
US postal service is not coming through for me.
I found and ordered NOS Pyramid TR46 tweeters, from two separate sellers, and one was apparently misdelivered to wrong address and nowhere to be found, and the other is missing in action for for about 8 days, without any update on tracking information since last week.
Maybe somebody is trying to tell me something.
I found and ordered NOS Pyramid TR46 tweeters, from two separate sellers, and one was apparently misdelivered to wrong address and nowhere to be found, and the other is missing in action for for about 8 days, without any update on tracking information since last week.
Maybe somebody is trying to tell me something.
Re. ABOVE >
I would call all that 'bad luck' and I guess a poor postage system.
In Australia we have 'Priority/Guaranteed' postage for a slight price.
Don't give up, I think such a Bullet Super Tweeter is very good 🙂
I would call all that 'bad luck' and I guess a poor postage system.
In Australia we have 'Priority/Guaranteed' postage for a slight price.
Don't give up, I think such a Bullet Super Tweeter is very good 🙂
Post office found one of my bullet tweeters, so I plopped it on top of my home theater speaker to break in. Without any adjustments, using the included cheapo electrolytic capacitor as crossover, I am liking what I'm hearing so far. This bullet tweeter is making it sound like the front and side walls have become Magnepan-like speakers with ambiance and air!
pyramid1 by drjlo2, on Flickr
pyramid1 by drjlo2, on FlickrOne bullet tweeter is still "arriving late" per post office tracking with doubts as to if it will ever show up.
So I bought a pair of another Pyramid model. It's really difficult to find NOS pairs of these available, but when they arrived, I could not believe how large and heavy they are! They are solid blocks of aluminum, weighing more than 10 Lb each. It sounds different than the smaller one..
What is the model number detail of those ???
They look a lot like Pro JBL Bullets that have 'sooper-dooper' high efficiency but surprisingly little output above 18Khz.
I'm guessing they also have quite a high power rating 🙂
They look a lot like Pro JBL Bullets that have 'sooper-dooper' high efficiency but surprisingly little output above 18Khz.
I'm guessing they also have quite a high power rating 🙂
The 075/2402 just kinda dies above 15K and turns into a flashlight beam. If you want extension above that you want 077/2405. All you have to do is look at the large format monitors none of them used the bullet.
And even a 2405 doesn't go higher just wider horizontal dispersion.
Rob 🙂