ESS amt1a-rebuild w/additional drivers to improve soundbut keep the box-anyone do it?

[robmeister]

I am a noobie, have a pair of ESS-1a 's that Ive had since 1976. It has a 12" woofer and passive radiator. I replaced the foam surrounds twice, and replaced all caps a few years ago.
I would like to improve the low end, but maintain the original look when covered by the mesh cover.

I would be willing to gut the cabinet and replace with different drivers .
I have checked the ESS threads on this forum, and I dont just want to replace the woofer/passive radiator. The bass is somewhat "thuddy".

One person built a new cabinet with 2-8" focals. If I replace the drivers, I would like to Keep the existing look (if possible).

Has anyone actually done the rebuild to significantly improve the bass on these speakers.

Regarding the crossover. I would need significant help here also.

Would an active x-over be an option?

Would I be able to cover the passive radiator, install 2-8" speakers in the front or side and get rid of the 12" and still keep the existing box???

Thanks for your help.
I realize the ESS speakers have been discussed significantly, but I dont want to build a new cabinet (it has a little nostalgia for me since Ive had these for 30 years and will probably keep them till I cant hear.)

Thanks for your help.

[planet10]

Some info & pics on the 2 we did here:

planet_10 hifi

dave

[chrisb]

I'm the culprit involved in most of the grunt work on the 2 speaker projects in Dave's link above, and have a couple of observations.


About 4 years ago I was asked to upgrade a pair of AMT1's after the owner had just had surrounds replaced on all 4 woofers/PR's, and new top covers fabricated.

The first thing noticed on close inspection of the cabinet was that the mitre folded glue joints were failing - the boxes were literally falling apart, and a simple reveneer and finishing was out of the question - it was much simpler to just build new cabinets.

The stock XO in this system was rather complicated to achieve that midrange "prescence" control and furthermore was populated with very low quality parts (I'm being extremely polite) .

At this juncture the owner had invested over $400 on the driver repairs and new grilles. Since new cabinets were now in order, he decided to take a leap of faith and spend some more and modify the system to 3-way, with the addition of a high efficiecy 6" midrange driver ( Emminence Beta in this case). A complete new passive 3-way XO circuit was optimized with the help of a friend with LEAP/LMS system. (more parts than some of my SET amps!)

While even then I was a big fan of as simple as possible crossovers, (and have since been indoctrinated into nonxo/FR cult), the result was quite sastisfactory, even with low powered tube amps (3-5wpc). Freeing the AMT from hazardous duty below 3K unleashed its potential as an absolutely stunning tweeter, and the factory woofer is surprisingly good. It's the crappy XO and very poorly braced box that are limiting the performance.

Subsequently the second pair was fabricated, using Fostex 2 FW227 (now discontinued) in a bipole arrangement, and with a simple 1st order XO (about 3.2K IIRC)

By all means you can elicit far more performance from these drivers than the stock box and XO will allow. Unless the woofers/PR's foam surrounds have been replaced since new, you're on borrowed time. You might want to consider having them professionally repaired - it's still likely to be much cheaper than any new driver of equivalent performance.

If budget allows, bi-amping with passive line level XO would definitely be the way to go, you can eliminate the need to waste power in attenuation of the tweeter to match the woofer (we measured over 10dB sensitivity difference in the circa '73 units), the required parts are much cheaper at the front end of the amp, and you'll notice a huge improvement in transparency, dynamics and soundstage. Just don't get hung up on "flat" FR curves.


p.s. if you do bi-amp, just ensure some protection to the AMT via reasonable quality input capacitor (needn't be Cardas or Mundorf Silver); i.e. first order filter about 1200HZ would be good

[JohnL]

You know I had to stick my 2 cents in here as well. Robmeister, I am currently using an AMT on top of a pair of RS225 8's like the AMT/Focal combo you described. It sounds great (much better that the original AMT1B), but I'm currently working on a 3 way dipole with the AMTs I hope will sound better. Neither share the original box idea. So let me give some suggestions for your situation.

First off, I have to agree with chrisb, the original boxes stink. Poorly made, poorly braced and amazing they sounded as good as they did. If you want to keep the original box (or build a new box similar to the original) here's my best idea. Look at a 10" driver from PHL and just fashion a 10"-12" adapter plate out of MDF. The PHL will probably be your best compromise between efficiency, price, midrange and bass, and will work well in a box that size with a port or a PR. You might want to get a little better PR, though. Parts Express has some 12" PRs for about $23 that would be a bunch better than the originals. Which 10" PHL? My first choice would probably be the 3430, but Zalytron has some 3000s (or 3001s) on sale for $99. You probably wouldn't hear a difference, and that's a great price for that driver.

Actually tuning that combination shouldn't be that hard. First calculate the box size (PHL rec's a .7 cu ft box tuned to 70 hz, that's about 95g on that PR or a 4" port 6.5" long). For the crossover I'd start with a 2nd order at about 1500-2000, zoebel on the woofer and lpad on the AMT. Without measurement equipment it might be a little tough, but they are both forgiving drivers, so even little off should sound OK.

Originally, when I brought home my AMT1B's the foam on the drivers and PRs was so bad, I just yanked them out and stuck a pair of Lambda TD12S's in the box in place of the original 12s, then I cut some MDF blanks to cover the PR holes, even with the original xover they sounded ok. Once I tuned a better xover they sounded great. I did refoam the originals and put everything back the way it was, but the Lambdas sounded much better. The Lambdas aren't currently available, but I think the PHL's will sound very good as well. That's my suggestion.

John