AMT3 Rock Monitors - The Automojification

[Porkloin]

A few months back, I was reading a thread by Squirrley about choosing between a pair of ESS AMT1s and a pair of ADS L-1230's. Eventually the thead evolved to the work that others had done with their ESS speakers.
I became fascinated with Automojo's work on his rock monitors. He was able to determine suitable replacement drivers for the existing stock drivers that worked with the stock enclosure and crossover. It all made perfect sense - a bit of new manufacturing performance while maintaining the "old school" flavor. As I don't have the equipment to measure and test the findings, I took his findings and incorporated them into my own living room.
The initial impression: The woofers (Dayton ST255-8) are still breaking in, so they're a bit leaner than I'd like them to be. Compared to the old woofers, they're very tight and controlled - string bass recordings are having some new detail revealed.
The Eminence Alpha 6a midranges are a big improvement over the old driver. My biggest complaint about my AMT3s was the image of any given groups front man standing in the back. The Alpha seems to correct that. NOTE: The Alphas, as far as my ear was concerned, needed the L-Pad that I put in. It's at about 50% right now.
I've started to assemble a photo album over at Shutterfly as the albums here at Audio Karma leave a bit to be desired. It's a work in progress, so it's by no means complete at the moment.
It's been a lengthy project. As much as I like to tinker, I'm happy to see it coming to an end.
So I can start the next project.

 

[Porkloin]

The Woofers

Initial quote about the Dayton ST255-8 from Automojo that got me going on the upgrade: "The VAS of the ST255.8 is 48.7, which makes it close to ideal in the AMT3 enclosure.
Not perfect, but it provides a nice even/flat response that tapers so slightly below 100hz on down to box tuning (42.1hz) and then fairly steeply after that of course. 2x3" ports 6"l.
What this woofer does is gives you increased output without compression at higher volumes with out a trace of boom. or midbass humps. The transient response is outstanding. With room gain you have usable output to 32 hz or so with no doubling etc-nice and clean, like the rest of the speaker.
But you have to port it."
He's had a few refinements since that posting: " I'm glad I finally, as promised, got some pro help getting the tuning optimized for the Dayton's.
There was a difference is sound between my original tuning 6" vs 3.8-it tightened up a bit, but did loose some extension.
However once Ben figured out the optimal tuning vs power handling for my dual setup, the transient response and tone of the woofers changed dramatically for the better.
He found out in short order these woofers like to be tuned higher, around 47hz not only to maintain power handling, but to flatten their response-probably accounting for the dramatic (IMHO) difference in sound. Something you won't see in the spec or simulations
Room gain seems to fill out the balance (both setup will be next to cabinets-which enforces the bass in the 40hz range." (Cutting and pasting is a beautiful thing - other people write my posts for me)
As my cabinets shrank a bit due to the cubic inches lost to the thicker baffle, my ports are an inch longer.

 

[onwardjames]

Impressive project, following with interest.

 

[Leben]

Subscribed! :thmbsp: I have read a lot of Automojo's information on his upgrades as well. I am looking forward to more reviews as they break in.

 

[Porkloin]

The Alphas

Everywhere I turned, the Alpha 6a's were the recommended replacements for the AMT3 "transition" drivers. Replacement may be an understatement. They exceed the original drivers.
Not knowing whether or not an L-Pad would be needed, I wired one in. It was indeed needed. My initial adjustment is at about 50%, but that will probably go up as the woofers break in.
Automojo gives a brief review over at Parts Express: "This speaker is a true bargain IMHO, and really out performs most drivers I have come across, even at more then twice the price. In my experience it clearly out perform the stock AMT3 mid driver, the Peerless and Heppner drivers. Much clearer ,detailed and very smooth. I would recommend adding the PE 50 watt mono l-pad to dial it in."

 

[Porkloin]

Alpha Enclosure

The original Sonotube midrange enclosure was adequate, but had a few issues. First, if you wanted to add T or hurricane nuts to the back of the baffle, there was clearance issues. Second, it was twice the volume of the sealed enclosure recommended by Eminence (see the PDF at the Alpha's page over at PE). Eminence recommends a high pass crossover at 200 or greater, which the stock AMT3 crossover covers, so why would I want anything but a nice, tight, well-stuffed sealed enclosure?

 

[essNeff]

Those Rocks look like the "Purtiest Girl at the Dance".
They look Outstanding!
I received the Alpha's I ordered yesterday and they are pretty impressive.
Nice build quality. Do you think 2db attenuation is a good place to start with a fixed L-pad?

 

[Porkloin]

Those Rocks look like the "Purtiest Girl at the Dance".
They look Outstanding!
I received the Alpha's I ordered yesterday and they are pretty impressive.
Nice build quality. Do you think 2db attenuation is a good place to start with a fixed L-pad?

Thanks essNeff. Don't think about trying anything funny on the dance floor with them.
I have no way of measuring the db. I can tell you that I've varied the L-pad between 1/2 and 2/3 all the way up. Uncorked, they're a little much. Automojo is running his wide open, but he's got a bit more breathing room behind his as he's using the stock sonotube.
I've also noticed an increase in what I believe is referred to as the soundstage - the Heils had an immersive, wall filling quality about them that has been enhanced by upgrading to the Alpha.

 

[automojo]

The Dayton's have treated cones, and stiff suspensions/spiders, so they take some time to break in. At least 10 hours, maybe more. Looking at my 4 unused woofers, to my used 4, that have been abused for sure, there is a big difference on the push test-so you have to be patient.
Some are hooked on fixed l-pads-IMHO why not take advantage of the good variable ones now available.
They are much better quality then the average 70's style one, and give you "infinite" adjustment.
Important as all listening environments, and listening distances are different.
You are never going to be able to tell the difference between the fixed and variable.
If they go bad in 10-20 years, solder in a new one-no biggie IMHO.
Alphas are a great driver IMHO.
I fiddled around with a few drivers, expensive, exotic cones, neo magnets, but always came back to the Alpha-at $40 it's a bargain.
The neo Alpha would be interesting, similar specs, and less weight, but I don't see a reason to spend twice the money in this application.
EssNeff-if your using the smaller tubes the have the 2 "external" (Peerless driver usually)screws for attachment, I would recommend using 4 #8 E-Z Lock Threaded inserts (Part#800832-10), and a large head screw, or screw and washer.
You could just silicone them in and use the 2 screws, but these drivers are much heaver then the Peerless driver, or Heppners for that matter-so the 2 stock screws are a bad idea.
If you have the larger tube, #6 screws are fine-I would probably rotate tem and drill new holes, or again use the E-Z Lock's
This part number by the way is designed for MDF, and is not the hardwood type units.

 

[Porkloin]

The Inner Baffle

AFter removing the stock baffle, I screwed and glued 1 X 2 firring strips at the correct depth in the original enclosure.
The next layer is the inner baffle of 1/2" birch plywood. It serves as the mounting flanges for the new woofers as well as four sides of the midrange enclosure. All holes are cut and drilled pretty close tolerance to help maintain a structural integrity. This means measure 14 times, cut once. Test cuts. Screwing everything down to the bench and cutting multiple layers simultaneously. It paid off - with two sets of three baffles with 20 driver hold down holes each, everything lined up.

 

[essNeff]

Porkloin,

I ventured over to your photo album to check up on your build.
I must say, you thought out everything in advance........and then some.
Every detail was painstakingly accounted for and attended to.
Your attention to detail is admirable. You massively overbuilt everything!

I see that you used Acoust-x. Nicely stippled and generously applied.
I like your use of Batten's for the front baffle for additional rigidity.
:tresbon:
Again, Outstanding work!!!!!!!!!![

 

[Rome]

Impressive project undertaking for sure!

They will be a fine set of speakers to enjoy!
Rome

 

[Porkloin]

Battens

Thank you essNeff.
The battens actually simplified the construction. The other option would be to recreate the existing baffle, which counted on a 3/8" rabbited joint for it's strength. It would be a more difficult cut to get accurate and I would lose the outer baffle which lays over the top of the installed (into the middle baffle) drivers. Once the adhesive is applied, I've got a lot of contact surface stuck together that should act as the additional internal bracing that I didn't bother with.
Thank you as well, Rome.

 

[automojo]

I have been watching Will's project come together, and he did a excellent job of dealing with the stock enclosures shortcoming's. Very well thought out, and is a perfect extension to past mod's done to these speaker-not just by me of course-RonC , MrB, bill144 to name a few.
Moving the AMT3's into the 21st Century.......awesome!
It's great to find those willing to put this kind of effort in, as it's a great benefit to us Heil Addicts. Easy to see he went more then a extra mile or two...outstanding!
I'm also extremely happy he has documented his mods in a very easy to follow fashion with great photo's.
I glad I was, along with the aforementioned, able to aid him some in his endeavor, and look forward to seeing the project mature.
Thanks Will!:thmbsp:

 

[Porkloin]

Moving the AMT3's into the 21st Century.......awesome!
:

....which begs the question: are we entitled to tell people that we own "vintage" speakers any more?
It seems that my most recent foray (back) into 2-channel audio has migrated from all vintage to all modern.

 

[Porkloin]

Grills

Although my existing grills hang fine (one broken frame) and they're not officially a part of this project, I've been chit-chatting with a guy over at a local plastics shop about a suitable material that's a better combination of flexible/rigid than the masonite that they're made of at the moment.
I've embedded grill magnets into the back of my outer baffles (can't see when assembled) and will embed corresponding magnets into the new frames.
I'll also get a higher contrast grill cloth, oddly from a place called "Mojotone", when they get it back in stock. It may be seen as some as "pimping" my AMT's, but I'd more like to have a British sport coat look than the existing brown.

ADDENDUM: I finally got around to replacing the grill cloth and frames in this thread.

 

[automojo]

Sure, I know what your saying.
Well the badges help.
I have little problem with saying they are upgraded to modern standards.
Personally I never understood the why people think it sacrilege to take a great vintage design and upgrade it.
IMHO that says more about the design then just settling for something you know can be better. Why not?
Everything can be improved on, might not be easy, or currently feasible but the possibility is there.......
Obviously all components color the sound, but for me, many vintage components overly color the sound in a way I don't like.
AMT3 woofers are a classic case.
I appreciated the strengths, but the draw backs, overly warm bass got in the way after awhile. The AMT's correct tonality and speed make these deficiencies tiresome after awhile. I found my H/K Sig 1.5 minimized this attribute the best, but the compression at higher levels was the last straw. My old PS1220's could play much louder and cleaner in the bass region (although the bass was slightly fat with the slab-but enough tone quality to not sound dry-good enough! and the small Heil was great, but not a AMT)
so I set out trying to improve this. A lot of trial and error, but that's part of the fun, the hobby, DIY, the good stuff....
I liked the idea of the twin 10" woofers-my old Klipsch KG 5.5's had outstanding bass (albeit lacking some tone) for the most part, but the mids/ highs were fatiguing-I figured a good set of twin 10" should be enough to keep up with the AMT's and move it into the modern age of audio.

 

[automojo]

Although my existing grills hang fine (one broken frame) and they're not officially a part of this project, I've been chit-chatting with a guy over at a local plastics shop about a suitable material that's a better combination of flexible/rigid than the masonite that they're made of at the moment.
I've embedded grill magnets into the back of my outer baffles (can't see when assembled) and will embed corresponding magnets into the new frames.
I'll also get a higher contrast grill cloth, oddly from a place called "Mojotone", when they get it back in stock. It may be seen as some as "pimping" my AMT's, but I'd more like to have a British sport coat look than the existing brown.

Nice- I was looking at those over the years-at some point, I kinda dug the blue/black/ silver scheme.
You may want to get a sample patch first, some of it was a bit too transparent looking for my taste...
I found a ground down razor blade and epoxy work great on the typical break points.
One could probably make more of a typical grill with horizontal and vertical bars, but it might not work as well with the non stretchy fabric.
The vintage look (good or bad-depending on your perspective) to the overall AMT3 looks, it's purposeful design, usually sparks a conversation up with guest
who haven't seen them before.
Interesting as well, when you look at some of the old vintage design boxes, with all their know shortcomings are coming back into fashion, thin boxes/baffles etc.

 

[Porkloin]

One could probably make more of a typical grill with horizontal and vertical bars, but it might not work as well with the non stretchy fabric.

There's already some repairs on the broken one. It looks like some thin steel hobby strips with epoxy, similar to your fix. I'll probably do the razor thing to get me by until the cloth I want gets stocked or until I decide on the black and gold instead.
I think all of that coarse weave stuff says "vintage" - a brighter color is just a matter of saying it a little louder.

 

[automojo]

There's already some repairs on the broken one. It looks like some thin steel hobby strips with epoxy, similar to your fix. I'll probably do the razor thing to get me by until the cloth I want gets stocked or until I decide on the black and gold instead.
I think all of that coarse weave stuff says "vintage" - a brighter color is just a matter of saying it a little louder.

Sure I agree on the coarse weave, some of it is more "holey" then I remember with actual vintage stuff.
I tried the "Mellow Tone" from P.E. and returned it-figured I would splurge at a later point. With kids I don't want to clean new cloth.
On the other hand, with you great looking baffles either would be fine.
I like black and gold as well.
One set of mine has mint cloth-that one I will leave, the other is average with some staining up top-that would be the candidate for new cloth.