Auto's Super AMT3's:Design Finalized-Construction Begins!!

Ok, here is finally the start of this thread. I will try to be as through as possible, with plenty of information, descriptions, picutres and info.
I have been doing my testing with a "mule" crossover, a spare, and will be using a hardwired crossover.
First up is a hand drawn picture of this layout, and a stock schematic that I would appreciate a review of, to see if I have correctly connected the various crossover parts. If there are any mistakes, I would like to correct them before I commence with the construction. Reason being more eyes are better then one, and I did find a few errors before the final draft.
Any input would be much appreciated.
A quick rundown of the project.Aside from the custom crossover, the cabinet will incorporate 2x3 inch ports installed on the rear (only real option without major cabinet modification) and removal of most if not all the stock stuffing in favor of acoustic foam lining the interior. The new/non stock woofers seem to perform much better without all the stuffing, preferring a tradition ported enclosure. The stock front port will be blocked.
The cabinet will also incorporate a front baffle brace, a brace board stiffiner/crossover board on the rear.
The stock midwoofer is being replaced with a Audax HM130CO, mounted with a adapter plate to fit the stock opening.
The main goals here are cleaner bass and midbass output, and improvent in clarity in the transition region between the Heil and midwoofer. And a increase in efficiency, lower crossover ESR, and the ability to play louder and cleaner with even less distortion.
Hopefully this thread will be rewarding to all the Heil freaks out there.
It's been a slow progress so far, and will continue to be, do to family and business obligations, so please bear with me.
Thanks!

Preliminary Rundown/Summary

After more thorough listen, experimenting, I have finally settled on a final "Super AMT" combination.
Woofers: Dayton ST255-8.
Mid woofer: Eminence Alpha 6A.
Cabinets:
Front stock port blocked. Two 3" x 6" long ports added to the rear, between the terminal hole and mid woofer tube.
P.E. surplus 3" ABS tube.
Front baffle braced between woofer openings. All seams sealed with epoxy and silicone. Mid-tube sealed. Inner bass cavity lined with P.E. 1 1/2 Inch convoluted foam, rear lined with Auralex 2" foam. 1/8" felt applied to rear walls.
The rest filled loosely with the stock stuffing.
Exterior black surfaces repainted.
All woofer mounting surfaces strengthened with epoxy, and 8, #8 Hurricane nuts installed for each woofer.
Mid woofer mounting surface strengthened with epoxy.
AMT Heil blocked with foam on each front side.
1/8 felt added around the mid woofer.
Stock grills.
Crossover:
After some experimentation, will incorporate stock values, as this seems to be the best compromise, even with the Dayton's, and Alpha 6a's.
Hard wired crossover using a 1/4" thick ABS sheet w/felt damping.
New Digikey rotary brightness switch.
New fuse holder, and output terminals.
Erse PulseX Caps.
Meniscus Audio 14 gauge bass inductor.
Erse 15 ga mid/Heil inductors.
Mills resistors.
14 gauge internal wiring.
In early experimentation, this revision audible out preforms the stock AMT3 configuration. The bass response is flatter, and lower in overall distortion/coloration and rolls off just as smoothly. No boominess whatsoever.
Mid bass clarity is improved, along with the lower midrange in the crossover region. All this clarity and lower distortion is not at the expense of smoothness and musicality. This speaker sounds like one that rolled off the assembly line, not a mismatched home brew unit.
It eliminates the complaints of some of the O.E AMT3 overly warm, or boomy bass. The overall efficiency has also increased.
Overall I am extremely happy with the results. I did a lot of work finding the right combinations, but in the end, much was luck IMHO-I just happened to strike on the right combination fairly early in the process, with only a few mistakes.
I have posted allot of various information on more then a few threads, so I wanted to start out here with the basic information, and add a few different pics visually explain the above information, along with some frequency response charts etc.
For now if you need more detailed information, you will have to sift through past threads.
My first set will also incorporate the Dayton woofers/stock mids and rear porting.
Crossover is stock, with the exception of Dayton poly's and Dayton resistors, and all new wiring.
I also modified the stock PC mounting to threaded stand offs.
The difference is so dramatic (IMHO) in the bass mid-bass department, that I had to retire (for now) the stock woofers, and was more then willing to cut the rear ports.

Excellent! Can't wait to see the pictures and the finalized results.
It would help if you can list the "mistakes", and why you chose Dayton/Eminence/AUDAX over the huge number of drivers out there...(ex. Peerless, Dynaudio etc.).
Did you compare the old ESS woofers to the ones that are drop in replacements from Parts Express?
Reason I asked is I picked up a set of AMT3 yesterday and need to decide whether to restore them to the original specs or to "Improve" them. The AMT3 I got have all drivers replaced. The PE ESS drivers are too expensive for my blood.

Woofers/Mids/Crossovers/Cabinets

The new ESS woofers are 4 ohm. Most AMT3's use a 8 ohm woofer, with the exception of the early 4 coil designs.
I agree they are expensive.
One problem is finding a woofer that will work with the enclosure volume of the AMT3, around 2.7l.
Most 10" woofers require a larger enclosure, and this can introduce a mid bass peak that need Zobel correction. I wanted to avoid this.
The Dayton is perfect for smaller enclosures, and has a very flat response, and a very smooth roll off, with no peaks or dips. It's seems to be quite popular with the Decca Wicked One setup. And for good reason. Efficient,quick, clean and clear, deep and smooth. All this without sounding dry, flat or unmusical. It uses a heavy steel frame, large magnet, 2 1/2 inch voice coil, an unusually large flat spider and treated paper cone with rubber surround. It's average output with the 2 woofer setup is around 94db/watt
Made in the US by Eminence. They routinely go on sale for around $65 ea. A real bargain IMHO.
One drawback with the AMT3 design, is the Dayton reaches Xmax quite quickly around the port tuning (around 38hz). This however doesn't seem to be a problem as this would only crop up averaging 175 watts continuios into the woofers with (extremely loud)and heavy low bass program material, or the bass control cranked to the right.
These can play very loudly and cleanly-better then the stock configuration-which does pretty good IMHO.
To realize all that this driver has to offer, you really need to add more port then stock. 2 3"x6" long specifically. With the PE ABS tube, the closest hole saw is slightly too small, so you will have to finish with a sanding drum. Tacks and silicone for attaching.
Another plus of the rear ports, is it moves any audible "port garbage' to the rear where you can't hear it. All ported speakers have some of this-just put your ear up to the port when they are playing.
You also need to add a baffle brace, and use all 8 Hurricane nuts for mounting. Each woofer weighs around 13 lbs, so it's more then twice the weight of the stock woofer.
The brace also reduces bass coloration as a added bonus.
I originally used the Eminence 1040SF, and really liked it, but it's mid bass rise was hard to tame without a Zobel. Adding a Zobel is no big deal, I just wanted to avoid the loss.
The Alpha 6A IMHO integrates better with the Dayton and Heil then the Audax. It also fit's most AMT3 mid-tubes without mods. The Audax requires a adapter plate.
The Alpha has a smooth response in the intended AMT3 range, and it's efficiency matches the Dayton and Heil perfectly. A real bargain @ around $40 ea.
It does have a rising impedance curve, but in the AMT3 set up, I can't hear any audible issues with this, as it's handed off to the Heil by the it might be a issue.
I would also recommend a complete recap,replace the resistors and redo ALL the connections. I would also recommend replacing all the internal wiring. With the stock PC board, 18 guage NTC hookup wire is fine. You have have to use a small drill bit with a pin vise to slightly enlarge the holes.
I would also use a threaded stand off for the PC board, as the stock one have a tendency to break their tops off when you remove the retainer.
Use a Dremel, with a small cutoff wheel to remove the post. Drill a small #4 hole for the attaching screw. The screw is small enough with the felt gasket to let the crossover lay flat on the cabinet.
Dayton's will fit on the stock board-barely, but they will fit.
Use the P.E. cable ties with the screw boss. Add some epoxy to the screw, and use black silicone on the cap body. Use a Dremel to cut off the protruding screw tips.
I would also recommend replacing the stock terminals and fuse holder. Cheap, for all new metal contacts.
I would also contemplate adding larger lower ESR ilarge guage nductor coils.
I experimented with slightly changing a few of the crossover points, but IMHO with these drivers the stock points are the best.
My goals in the crossover, and overall speaker design where to increase efficiency, lower network ESR, and lower bass (and mid bass/lower midrange)distortion and coloration.
I am extremely happy with the results.
IMHO with this setup these speakers can easily compete favorably with any speaker I have heard over the years, in terms of efficiency, dynamics imaging and tonality-and sheer musicality.
Sure there are better speakers, but what those speakers do better is fairly incrementally small. Yes- they really are that good.
Most of this has to do with the AMT Heil being mated up to a transition/mid woofer driver, no doubt about that.
But now it has a woofer that can keep up to the rest of the drivers not only efficiency, but low distortion and superior transient response as well.
The other stuff is just added tweaks, incremental improvements, nothing to drastic.
When you consider this, the upgrades/cost and labor involved are very reasonable IMHO.

Super AMT3?

automojo:

Have you run and simulations using the Daytons and compare them against the 1040SFs? On paper at least, the 1040SF appears to be a much better choice in terms of having a lower Fs, Fb and so forth...and costs less.

Kwing

Here are some pictures of the 2 3"x6 tubes I cut and installed. After the first speaker, the other 3 went fairly fast.
So now all of my AMT3 are officially rear ported.
The front O.E. port will be sealed over.
I had to adjust the size of the hole with a 1.5" sanding drum that works slick.

The holes were centered (from the inside) 2" up of the floor, and 1 1/4" from the walls.
Plenty of space for the crossover board.
The board seen in the first pic is a additional woofer baffle brace.
The baffle now sounds like a safe when you rap it.

kwingylee said:

automojo:

Have you run and simulations using the Daytons and compare them against the 1040SFs? On paper at least, the 1040SF appears to be a much better choice in terms of having a lower Fs, Fb and so forth...and costs less.

Kwing

Click to expand...

Yes-as well as listening tests.
Both woofers really need more port.
I only did listening test's with the stock port and the 1040SF.
Prices are the same-$79.99 ea-P.E. has free shipping.
The Dayton works well the the AMT3 cabinet volume, and 1040SF really needs some more cabinet volume.
The Dayton has a much flatter response with the AMT3 cabinet-almost ruler flat, and falls off smoothly, were the 1040sf has a mid bass bump @ around 100hz that needs a Zobel, this is what I wanted to avoid overall.
Then Dayton has usable output down to around 32-34 hz (which really is plenty for most music) in this set up with out any port noise or compression.
The 1040's really need more port and more cabinet volume to realize clean output to 29 hz as advertised.
The Dayton will go down lower, @ lower volumes/power, with no doubling etc, but you have to be careful at higher volumes as you will reach x-max-the 1040SF doesn't have this problem.
In my simulations, @ 150 watts into the Dayton, X-Max is reached around 31hz, but this is very loud, even for my tired ears-so the compromise works well for me.

As a addition, if one isn't willing to do some mods to the cabinet, I would try to find a set of stock woofers first-if these aren't available (fairly hard to find/sporadic), go with the 1040sf, and figure out the correct Zobel to smooth the mid bass peak.
I wanted to use the stock crossover setup, with a few tweaks, but no additional Zobel to rob any efficiency I gained. But if you do it right-the results should be fine.
The Dayton's are twice as heavy as the 1040SF's, and much more then the stock Alnico's so you need to strengthen the baffle, and the mounting surfaces, and use Hurricane nuts to mount them. The baffle brace IMHO should be considered mandatory with the Dayton's.
They also really need the twin ports to sound there best. You can stick with the stock single port, but you will get into compression @ higher volumes.
IMHO, if your going to all that trouble in the first place-step up and go the extra distance and be done with it.

Aura Mid Adapter Rings

These turned out very well-nice tight tolerances that fit well even without the attaching screws installed.
The mounting will be #6 screws plus gasket tape for the driver to adapter attachment, and (4) #8 machine screws, plus threaded inserts/gasket tape for the adapter to baffle attachment.
http://meniscusaudio.com/8x1-ss-ms-p-382.html

Damping

After quite a bit of fiddling and testing, I have finally settled on (more or less) the preferred damping for the Dayton ST255-8 in the dual ported enclosure.
The rear panel will have a loose (big enough to be wedged in place) 2" Auralex foam piece. The sides and bottom will use P.E. 1 1/2" convoluted foam. The Auralex is a bit too thick for the sides-and too much of the Auralex seemed to reduce the mid bass.
For now I'm skipping any of the loose stock stuffing-as again it's too much damping with the new ports, and the Dayton's don't seem to benefit from the stock resistive loading, and only seems to reduce the bass output a bit.
These woofers need to breath IMHO.
The tuning for the cabinet is classic bass reflex, tuned 42 hz (FS 41.1).
I experimented with a 46hz tuning point (recommend by another member) and IMHO the Dayton's didn't like the higher tuning point.
Part of this could be the dual woofer set up.
While the Dayton's advertised x-max is 5.5mm-it really appears to be quite conservative.
I was playing some bass rich Pink Floyd @ very loud levels and couldn't detect any distress-they can take some power for sure.
I'm really impressed with these woofers, along with the Aura Sound mid woofer.
Very clean and responsive tunefully bass, and no hint of muddiness or compression at very loud levels.
The mid bass is truly outstanding, and they go plenty deep with out stress.
These woofers (and the Aura Sound) seem to be a near perfect match for the Great Heil.
They aren't over powering by any means-but blend perfectly with the mids and highs.
Like the stock you're listening to the music, instead of the individual drivers, but the bass is much more cleaner, yet still has that rich paper cone tone.
I'm looking forward to getting the custom crossover pair done with the larger gauge inductors to see if I can here any difference in efficiency, etc.
Now I just need to get my mule crossovers out and both set of new ones in, and finish the rest of the bracing.
Still a lot of work left-but I'm excited with the results so far!