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ESS Heil AMT tweeter measurements
This will be a thread for posting ESS Heil AMT tweeter measurements.
I'll be testing and posting data for the pair of original AMT's I got from @LifeOfBrian at the IowaDIY event. (EDIT: Please note that these are VERY old ESS AMT's, dating back to the early 1970's, that I am testing!) I know that others also have the newer versions of these tweeters, so please feel free to post your own measurements for comparison purposes.
I'm currently gluing up a tower enclosure, using Menard's value shelving, and I expect to start testing later next week. I still need to run out to the hardware store and pick up some 3/8" x 7" long bolts and T-nuts to complete the mounting. Hopefully they will have some in stainless steel.
I plan to do full 180 degree spinorama type SPL's, both vertically and horizontally, using Soundeasy and my dual channel mic setup. Will also do distortion measurements and run impedance curves with OmniMic and DATS V2.
Comments
As the one who initially advocated using that building material, it warms my heart to see it used so much.
Looking forward to how this develops.
I've got a pair that is 5 years old, and has the well known bumps in the FR. I got a new pair about a year ago and it is significantly flatter. But even the older ones sound awesome. So much radiating area.
In drilling the particle board to accept the T-nuts, I just noticed that the maximum size bolt that will fit my unit is actually 5/16", not 3/8" as I noted in my initial post. 1/4-20 would also work, but it would probably be a bit too sloppy. So I need to find 5/16" x 7" long bolts and T-nuts at the hardware store tomorrow.
One of my two original (classic 1970's) AMT's might have a damaged diaphragm. So I will be measuring both tweeters. If one of the tweeters measures a little wonky, I'll try popping in one of the new diaphragms I got from @LifeOfBrian . Then re-test. Found a youtube vid showing the process. Looks fairly straightforward. Any tips on what to avoid when swapping out diaphragms? How delicate are the diaphragms? Can they be tested without a series protection cap, of approx 50uF or so, between the amplifier and tweeter?
The ESS mounting kit uses 1/4-20 bolts.
Carriage bolts are super common in long lengths. The dome heads would look more sleek than hex. A quick search is showing they can even be found in black finish. A top strap is easily made with aluminum flat bar and made to accept the carriage bolt square by shaping drilled holes with a small triangle file.
Could not find carriage or regular bolts beyond 6 inches long in either 5/16" or 1/4" at the store that I usually buy most stuff. But I did find some 7 inch long 5/16" regular bolts at another store. They also had polished black plastic caps that fit over the heads, so I will give those a try and see what it looks like. Putting an aluminum flat bar across the top seems like a good idea, might try that later if this does not work out.
The copper bar Nick made for his was slick.
Those black caps look identical to the ones ESS has in their photo of the mounting kit.
Acorn Nuts . . . https://www.amazon.com/Acorn-Nuts/b?node=16409871
Spikes!
The test enclosure is done. I mounted the tweeter and am ready to start measuring. It has the same length and width dimensions as the tweeter base, which should help to reduce cabinet top reflections somewhat. It is 3 feet tall and uses an old piece of stair tread material as the base (approx 12x12"). Since the baffle width is the same as the tweeter, about 6.75" or so, the future completion plan will be to use two 5.25" woofers just below the tweeter, not 6.5 or 8 inchers. I eased all edges with a 1/2" roundover bit and then beveled the top edge to match the tweeter's black plastic facets. Then I wound masking tape around the joint between the tweeter and enclosure to make everything nice and smooth. I filled the tweeter's upper and lower triangular front cavities with 1/4" thick denim triangles. When placed on my DIY polar turntable, the tweeter will be approx 58" above the floor and 86" below the sloped ceiling.
Too late. Threads and T-nuts are on the bottom side. I'd have to redesign similar to Nick's speakers in order to use spikes or acorn nuts on the top.
A search today for a long 1/4 x 20 bolt in stainless steel (non magnetic) proved fruitless.
Suggest stainless steel 1/4" all thread and a nut brazed on the top and a plastic cover.
This is what I used - 1/4-20 threaded into the nuts and 8-32 threads on top.
Ran across the troubleshooting link on the ESS site and found this PDF with crossover schematics: https://www.dropbox.com/scl/fo/lbmwzuiaru85xhlpu9jmn/AIlYlRy30DADPs9fMjoZASc/ESS Crossover for almost all models.pdf?rlkey=vaj05dptd9jkhfdlywedwuwnn&dl=0
There much experience with these things in a non dipole configuration? or does that neuter them?
I have seen some ESS configurations that looked like possible enclosed back, but on the back of the enclosure I see an opening covered with cloth.
I ask because my current listening space is probably not a good candidate for dipole.
So if you measure and design and voice in a similar space to your listening area you will have good results, just don't plan on taking them anywhere else.
Unless you get extra deep in the measuring aspect there's no way to design for the back wave contribution. The best you can do is to adjust based on measured result compared to the design and start tweaking to get the on axis result you want.
I just completed a full set of spinorama measurements for the pair of classic 1970's ESS AMT's that I am working on. 68 measurements in all. Converted the files to frd's in VituixCAD so that I could look at all the curves. Looks like it will be a real challenge to pound the squigglies flat, both on and off axis. This is due to the fact that the open back config creates a few somewhat large cancellation dips in the power response. The on-axis response, for at least one of my two Heil's, is suprizingly flat. The other has large on-axis dips and peaks, but I think the diapgragm is damaged on this tweeter. Makes me wonder how they might work out using a closed back configuration.
You can easily make a removable back for them out of 1/4 inch BB plywood, some weatherstripping on the edges, and fill it with acoustic foam.
Are you thinking of a "press fit" type removable back, or would you bolt it on with screws? My enclosure is the same size as the tweeter, so I don't have room for screws.
I was thinking press fit. You could also incorporate some kind of springy "catch", using clothespins maybe. The attachment I don't think is critical, a quick test should show good damping of the rear wave. From there you can consider a "production" mounting.
Edit, essentially you are building an enclosure. Use quality materials for the final, as we all (try to) do.
From a previous post [of mine] relative to the Heil AMT: https://diy.midwestaudio.club/discussion/2007/original-great-heil-amt-test-sweeps#latest
If you're moving the speaker during measurements, you'll never really see how it's going to interact with the room in it's final listening position. OB speakers are not like building boxed ones.
I personally put the speakers where I want them, then take measurements to guage what's going on, then make position adjustments, and repeat.
As for squiggles, most AMTs I've encountered aren't very flat, but still sound great. Don't stress over hammering it's response totally flat.
My thought was to stuff it half way into a sealed (or possibly aperiodic) enclosure. I'm wondering if the response might get a boost below that 4khz dip with the cancelation arrested.
Ya, I forgot about this thread. Thanks for posting. Good info for comparison purposes. I didn't do distortion measurements on the pair that I am testing, but I plan to do that next.
These measurements are for a pair of classic 1970's ESS AMT tweeters. I'll start out with just my on-axis measurements of each tweeter, which I have marked "A" and "B". As you can see, the "A" tweeter diaphragm is clearly damaged, down in overall output by 2-3dB, with limited low frequency output. The impedance curve for this tweeter appears to have issues as well. I'll set up OmniMic next and do a distortion test comparison of "A" and "B". Clearly, I think I will need to replace the damaged diaphragm in tweeter "A". Tweeter "B", however, looks fairly good.
Maybe take it apart and reseat the diaphragm?
Visually, it looks somewhat wonky and distorted. I'll take a closeup photo and attach. And the putty to seat it is completely missing. Do you know why kind of putty was used on these? Just a small amount of putty is needed at the top and bottom to hold the diaphragm in position.