I intend to use a pair of Heil AMT’s with a pair of Audio Concepts AC-8’s to make a mid/small stand-mount speaker. I need help with the crossover design for this unusual mid-tweeter. In the ESS AMT1, these were crossed over from 700-1200Hz, with a steep 3rd order 18dB/octave crossover, but that was paired with a large 12” woofer. Since I’m using a 8”, I plan to cross a bit higher to take some of the burden off the AMT.
Questions…
How do I handle the fact that the AMT is 4ohm, and the mid-woofer is 8-ohm? I can buy 4-ohm mid-woofers if that's the right way.
How do I determine resistor values to account for the different efficiencies of these drivers?
I don’t have T-S values for either driver, so does anyone have a DATS set-up, or another way to measure speaker values, to whom I could mail these drivers for measurement, so I can import that data into a crossover design software like WinPCD?
Any advice is appreciated.
Questions…
How do I handle the fact that the AMT is 4ohm, and the mid-woofer is 8-ohm? I can buy 4-ohm mid-woofers if that's the right way.
How do I determine resistor values to account for the different efficiencies of these drivers?
I don’t have T-S values for either driver, so does anyone have a DATS set-up, or another way to measure speaker values, to whom I could mail these drivers for measurement, so I can import that data into a crossover design software like WinPCD?
Any advice is appreciated.
Dave, thank you very much for responding! I have read many of your posts regarding the AMT during my Googling of the subject.
Since I don’t have any specs. on the AC8, I imagine that 1500-2000Hz is well within the range of any 8” mid-bass. ESS and other sources have always recommended a steep slope of 18dB/octave, but most are crossing at or below 1000Hz. Since you crossed at 2k, I suppose that affords the more gradual 1st-order slope, as well as the benefit of a simpler circuit. Would you mind sharing the schematic you ended up with after your testing? Honestly, I don’t trust that my hearing is sensitive or trained enough for tweaking, so I’m trying to do my best to get it right the first time. Is that even reasonable?
Additionally, I keep coming across folks saying to skip the passive crossover all-together, in favor of modern digital pre-amp crossover and bi-amping. While this would be more expensive, their argument seems to point out many advantages. Any thoughts?
Since I don’t have any specs. on the AC8, I imagine that 1500-2000Hz is well within the range of any 8” mid-bass. ESS and other sources have always recommended a steep slope of 18dB/octave, but most are crossing at or below 1000Hz. Since you crossed at 2k, I suppose that affords the more gradual 1st-order slope, as well as the benefit of a simpler circuit. Would you mind sharing the schematic you ended up with after your testing? Honestly, I don’t trust that my hearing is sensitive or trained enough for tweaking, so I’m trying to do my best to get it right the first time. Is that even reasonable?
Additionally, I keep coming across folks saying to skip the passive crossover all-together, in favor of modern digital pre-amp crossover and bi-amping. While this would be more expensive, their argument seems to point out many advantages. Any thoughts?
Dave,
Thank you very much for responding! I have read many of your posts regarding the AMT during my Googling of the subject.
Since I don’t have any specs. on the AC8, I imagine that 1500-2000Hz is well within the range of any 8” mid-bass. ESS and other sources have always recommended a steep slope of 18dB/octave, but most are crossing at or below 1000Hz. Since you crossed at 2k, I suppose that affords the more gradual 1st-order slope, as well as the benefit of a simpler circuit. Would you mind sharing the schematic you ended up with after your testing? Honestly, I don’t trust that my hearing is sensitive or trained enough for tweaking, so I’m trying to do my best to get it right the first time. Is that even reasonable?
Additionally, I keep coming across folks saying to skip the passive crossover all-together, in favor of modern digital pre-amp crossover and bi-amping. While this would be more expensive, their argument seems to point out many advantages. But for analog sources, this would require a A-D stage and then twin D-A stages which seems less than ideal. Unless one could somehow use digital sources and feed the crossover before converting to analog. Probably there’s a lot I don’t know about new-era digital options.
Thank you very much for responding! I have read many of your posts regarding the AMT during my Googling of the subject.
Since I don’t have any specs. on the AC8, I imagine that 1500-2000Hz is well within the range of any 8” mid-bass. ESS and other sources have always recommended a steep slope of 18dB/octave, but most are crossing at or below 1000Hz. Since you crossed at 2k, I suppose that affords the more gradual 1st-order slope, as well as the benefit of a simpler circuit. Would you mind sharing the schematic you ended up with after your testing? Honestly, I don’t trust that my hearing is sensitive or trained enough for tweaking, so I’m trying to do my best to get it right the first time. Is that even reasonable?
Additionally, I keep coming across folks saying to skip the passive crossover all-together, in favor of modern digital pre-amp crossover and bi-amping. While this would be more expensive, their argument seems to point out many advantages. But for analog sources, this would require a A-D stage and then twin D-A stages which seems less than ideal. Unless one could somehow use digital sources and feed the crossover before converting to analog. Probably there’s a lot I don’t know about new-era digital options.
Wax just to add some info, I called ESS and spoke to the CEO, random i know. He said crossing the AMTs at 800 is fine. I’m choosing 1000. Also important he says make sure the AMt driver is aligned with the backplate of the woofer. If you’re building a cabinet it has to be resessed in order to be properly time aligned. This is essential when using passive crossovers and no DSP.
Those were built by me, about 18yrs ago as a commission for one of those customers with frequent changes of mind. They were originally configured for use in bi-amped mode, with a pair of Decware Zen84C amps as seen in the mess on the floor. That was my first attempt at PLLXO onboard an amp, and it worked out rather well. The Zen was a cute little amp with a couple of interesting features, one of which - the toggle switch to adjust bias of input tube- was easily re-purposed to bypass the rear panel RCA line input where the filter caps were installed to allow full-range operation when using the top panel RCA.
They ended up coming back to me, and as I recall sounded best with the simpler version of the XO ( i.e. no zobel) . Woofers were clearout special Fostex FW series woofer - I can't remember the exact model number.
The AMT's placement was attempt to both time align to the front woofer and to mitigate diffraction from front of enclosure. The narrow perimeter ledge at top of lower section was for top-hat grille cover, much like that on the ESS AMT1 . Not shown in the photos is the rear panel woofer. Whether you chose the term dipole or bipole to describe this model of AMT's radiation pattern, the bipole configuration of the woofers was a big factor in the system's spacious and highly detailed soundstage.
For a real fun project, try squeezing a 6" high efficiency mid-range driver into an enclosure the same overall dimensions as the original AMT1 - to allow use of grills rebuilt to match factory stock and both woofers and PRs that had surrounds replaced. The construction quality of the factory boxes was a joke, and it was only noticed that they were literally falling apart went brought to the speaker tech for installation. The owner decided to throw " few more hundred$" at the rebuild, and was pretty happy with the end results. As you can see, the XO is a bit more complicated. Don't know if the schematic for this one survives on any of our hard-drives.
If doing something like this again, I'd be very tempted to try minidsp and play with steeper slopes.
They ended up coming back to me, and as I recall sounded best with the simpler version of the XO ( i.e. no zobel) . Woofers were clearout special Fostex FW series woofer - I can't remember the exact model number.
The AMT's placement was attempt to both time align to the front woofer and to mitigate diffraction from front of enclosure. The narrow perimeter ledge at top of lower section was for top-hat grille cover, much like that on the ESS AMT1 . Not shown in the photos is the rear panel woofer. Whether you chose the term dipole or bipole to describe this model of AMT's radiation pattern, the bipole configuration of the woofers was a big factor in the system's spacious and highly detailed soundstage.
For a real fun project, try squeezing a 6" high efficiency mid-range driver into an enclosure the same overall dimensions as the original AMT1 - to allow use of grills rebuilt to match factory stock and both woofers and PRs that had surrounds replaced. The construction quality of the factory boxes was a joke, and it was only noticed that they were literally falling apart went brought to the speaker tech for installation. The owner decided to throw " few more hundred$" at the rebuild, and was pretty happy with the end results. As you can see, the XO is a bit more complicated. Don't know if the schematic for this one survives on any of our hard-drives.
If doing something like this again, I'd be very tempted to try minidsp and play with steeper slopes.
Last edited:
I've been out of the loop for a couple decades, so I need a "Active Crossover for Dummies". I see the active crossovers that are analog devices, like the RANE AC22. It divides an analog signal into two signals the feed to two amplifiers, and gives adjustable crossover points, adjustable output level for each channel and some adjustable time delay for each channel. This I can understand. How does a DIGITAL crossover work? What would I use for a source, all of my sources are analog (ipod, phone, streaming device like Alexa, CD player, turntable, etc..) I'm guessing you capture a raw digital signal from a PC somehow, and separate the signal digitally, before the first D-A stage? Can someone point me to a "DSP in the Hi-Fi realm" intro site? I'm tempted to buy a 2nd amplifier and the RANE active analog crossover and forget about the passive crossover.
If your signal sources are all currently analog only, I think you’d want to avoid the extra A/D conversion that would be required with any of the digital XO products.
As for how do DSP work? Very well indeed, including some functions not possible in the analog domain - but there’s certainly a learning curve, and in most cases the temporary need for connection to a computer for set-up and calibration.
As for how do DSP work? Very well indeed, including some functions not possible in the analog domain - but there’s certainly a learning curve, and in most cases the temporary need for connection to a computer for set-up and calibration.
Well, "fine" doesn't mean "good".
I have a pair of AMTs I experimented with years ago. I'm not a speaker expert by any means, but I did a blind test with an infinitely variable 24dB x-over and found I didn't like the way they sounded with anything under 1200Hz. I would close my eyes and adjust the x-over until I liked the sound and it was always somewhere between 1200-1500Hz. I believe I had them paired with 8" Hawthorne Audio Silver Iris drivers on OB at the time.
WaxhawFive, I just came across this thread and I'm immensely interested in this project No posts in thread for almost a year and am hoping for pictures and more information on the project....also hoping for more input on some of the other projects discussed in this thread. Surely there is someone out there who has built and tweaked some 2 and three way designs using the Heil.
A reverse engineered AMT 3 with updated drivers, cabinets, and crossovers would be bucketlist nirvana for me.
A reverse engineered AMT 3 with updated drivers, cabinets, and crossovers would be bucketlist nirvana for me.
Heil AMT
I am working out a crossover for my AMT's. I have a vintage pr. of FOSTEX MR1000s with one bad tweeter. After months of searching for a replacement ribbon, I purchased a pr. AMT's. I also have the 10" ESS woofers purchased earlier. I wanted to try something where most of the heavy lifting has been done previously, so to remain safe, I opted for the original mixed 2nd/3rd order Xover and feel the sound of the AMT/Fostex a good match in spite of the Fostex woofer being 12". I figured that since the engineers at Fostex and Heil have done their homework, I'd start with just a replacement Tweeter using the AMT's The original MR1000s has a Isodynamic tweeter mounted in front of woofer like vintage public address Altec or JBL's
So far I have bypassed the presence and treble controls and replaced 2 caps and one resister, but haven't realized a notable difference, but I have to add... that the airy spaciousness the AMT brings to the match is by far the notable factor. One feature about the AMT that I really like is (by design) the ability to time-align the speaker just by how far fore and aft the tweeter is in relationship to the woofer V-Coil!
I do pose one question: Seeing how many tweeters benefit from a waveguide, what if the AMT had a waveguide fixed such a way as to direct the dispersion top to bottom? extend the plane (at the same angle as the sides) where the logo ESS is located and its identical top plane.
I am working out a crossover for my AMT's. I have a vintage pr. of FOSTEX MR1000s with one bad tweeter. After months of searching for a replacement ribbon, I purchased a pr. AMT's. I also have the 10" ESS woofers purchased earlier. I wanted to try something where most of the heavy lifting has been done previously, so to remain safe, I opted for the original mixed 2nd/3rd order Xover and feel the sound of the AMT/Fostex a good match in spite of the Fostex woofer being 12". I figured that since the engineers at Fostex and Heil have done their homework, I'd start with just a replacement Tweeter using the AMT's The original MR1000s has a Isodynamic tweeter mounted in front of woofer like vintage public address Altec or JBL's
So far I have bypassed the presence and treble controls and replaced 2 caps and one resister, but haven't realized a notable difference, but I have to add... that the airy spaciousness the AMT brings to the match is by far the notable factor. One feature about the AMT that I really like is (by design) the ability to time-align the speaker just by how far fore and aft the tweeter is in relationship to the woofer V-Coil!
I do pose one question: Seeing how many tweeters benefit from a waveguide, what if the AMT had a waveguide fixed such a way as to direct the dispersion top to bottom? extend the plane (at the same angle as the sides) where the logo ESS is located and its identical top plane.
The big Heil tweeters is already arranged so that the magnet structure forms a waveguide on the sides. The nature of the construction (height of the diaphragm) means that it is very directional in the vertical plane, so a waveguide will be pointless, especially for the Greai Heil (8" model).
Johan-Kr
Kingfisher, Here's a link to an old thread on "Audioholics". See post #6 for a schematic used in the "Heil Heavens", a two way using the Great Heil and a 8 inch Visaton crossed over around 1600. If you Google "Heil Heavens" you'll find a couple of different threads on the same project. Heil Air Motion Tweeter in a 2-way speaker | Audioholics Home Theater Forums
I'm also curious about the vertical dispersion of the Heil, which can be a very beneficial characteristic. I'd like to know some actual measured degrees of vertical dispersion. I had some ESS AMT's back in the day and am of the opinion that the limited vertical dispersion was a good characteristic and not negative at all....I was living in several different military housing units at the time with 9 foot ceilings and hard wood floors and the lack of floor and ceiling reflections gave it a quality the domes at the time couldn't touch.
I'm also curious about the vertical dispersion of the Heil, which can be a very beneficial characteristic. I'd like to know some actual measured degrees of vertical dispersion. I had some ESS AMT's back in the day and am of the opinion that the limited vertical dispersion was a good characteristic and not negative at all....I was living in several different military housing units at the time with 9 foot ceilings and hard wood floors and the lack of floor and ceiling reflections gave it a quality the domes at the time couldn't touch.
Sorry Chief, I've been pulled away on other projects lately. I plan to get back to the AMT project soon. I have decided that I'm going to go with an active crossover. The deeper I went with the passive design, the more intimidated I became with the details.
I will be using a miniDSP 2x4 HD for the crossover.
I bought this very fine 2-channel amp, based on Tom Christiansen's Neurochrome Modulus-86, and built by billshurv in this thread...
Modulus-86 build thread
I will use it to power the AMT, and am considering modding it to four channels with two additional amplifier boards from Tom, and a larger power supply, since the chassis is plenty large enough. It would be nice to do active two-way with just one amp chassis.
I'll follow up with the results once it's done.
I tend to agree that the high vertical directivity is a positive characteristic.
I will be using a miniDSP 2x4 HD for the crossover.
I bought this very fine 2-channel amp, based on Tom Christiansen's Neurochrome Modulus-86, and built by billshurv in this thread...
Modulus-86 build thread
I will use it to power the AMT, and am considering modding it to four channels with two additional amplifier boards from Tom, and a larger power supply, since the chassis is plenty large enough. It would be nice to do active two-way with just one amp chassis.
I'll follow up with the results once it's done.
I tend to agree that the high vertical directivity is a positive characteristic.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.