Which ESS AMT Monitor do I have?

[Johnny_Law]

Very excited to have these, and trying to figure out which version they are. They seem to have low-ish serial numbers (1440 and 1596). One woofer is the half rolled damped fabric (?) and the other has a foam surround. Both PRs have foam surrounds. (All the foam looks to be in great shape, thankfully!) The Heils are silver, not black.

I'm referencing a helpful post from a while back, and it makes me suspect that these are early, original build Monitors with later-replaced PRs and one woofer? Problem is, I don't see that they ever came with PRs that had bextrene cones and open cell foam surrounds.

Reason I want to know is that I'd like to get a woofer to make a matched pair, so I'm trying to figure out which woofer is the correct woofer for the particular revision.

I guess it goes without saying that when the crossover says AMT MONITOR that one would surmise they are AMT MONITORS.

Not trying to be the fly in the ointment but hey...

Four unpublished revisions took place on those AMT MONITORS. None of these four were labeled anything other than, AMT MONITOR.

Early versions were with silver AMT units, metalized capacitor films, bextrene woofer cones w/ open cell foam surrounds, and .75in styrene disc radiators on the aluminum rings w/ the same suspension.

1st mid-build revisions came with flat black AMT units, bextrene woofer cones w/ rolled-edge treated surrounds, and .5in styrene discs w/ open cell foam suspension.

2nd mid-build revisions incorporate a huge change to the radiator, they were made to reflect the same outer rolled-edge suspension of the bextrene woofer and updated to a conical bextrene passive. When this radiator was introduced, it attached to an entire cast woofer frame (less the magnet and motor structure) obviously. The inner coil area behind the dual dustcaps was sealed up with an inverted pulp disc.

Final build revision on the AMT MONITOR came circa 1979 when they utilized the SBR (styrene butadiene rubber) half-roll suspension on both the bextrene woofer and conical bextrene radiator. This final build was in production during the outphasing of the 1B towers hence the SBR suspension changeover, which the 1C line of towers took on exclusively.

Thanks in advance for any help. Haven't listened to them beyond verifying that the tweeters work, very excited that they both work.

 

[SaturationPt]

Based on the silver Heil, I'd believe early. However, I believe that the ones I bought are in the 1500s S/N range, and they are late with the bextrene woofs and passives w/ doped fabric surrounds, black Heils.

The only woofers that are still available from ESS are pulp, so matching them with new will mean either sending the drivers off to ESS for re-cone or two new woofers to match.

I do not know of bextrene woofers with foam, perhaps others know the answer to this. If the doped fabric developed rigor mortis as mine did it is possible that someone has replaced with a foam kit?

According to ESS, there's no reason to stick with the bextrene cones, they consider pulp to be an improvement (?).

 

[Johnny_Law]

Thank you ... really strange. However, through happenstance I found pictures of another pair that appear to have the same configuration (silver Heils, all foam surrounds). So maybe this configuration did exist at some point?

http://theartofsound.net/forum/showthread.php?19008-ESS-Amt-Monitors-restoration

His picture (before he had them re-done with rubber surrounds):

 

[SaturationPt]

Could very well be.

The best source of information on these is ESS, might give them a quick call.

 

[automojo]

Well, I think you're making a big mistake replacing fabric surrounds with rubber. Fabric and foam are close, but in general you're better off sticking with the same type if possible.
Replacing foam, or fabric with rubber is going to change the characteristics of woofer, and performance, not a good thing.
Ricky at ESS is just going to try to sell your new parts.
I prefer paper, but you're original woofers Bextrine, paper, whatever IMHO, are better, or at least as good as the "new" China models ESS touts.
The AMT3, and early AMT 1, with a 10 inch paper cone woofers are the exception. So so.

 

[SaturationPt]

So what would your suggestion be with mine mojo? AMT Monitors, bextrene woofs and passives with hardened cloth surrounds, ... re-dope?

 

[automojo]

No, re-doping is just going to change the FS, Not in the range you want it
I'm assuming it's not a foam slab?
If it's a cone passive, take it to any speaker reconing place and get a new surround put on it

 

[automojo]

They have piles of fabric surrounds from pro drivers, I'm sure someplace like mid west speaker in this area or the like can fix them

 

[automojo]

You have to remember, that the tuning of a passive radiator is just as critical as a portage speaker because essentially they are the same.
And on top of that you have the added physics of the passive radiator it's self
You should get excellent bass out of those if repaired correctly!!

 

[automojo]

And you have to remember, redoping the surround, just adds mass to the cone, which throws the tuning way off
Same thing with the AR redoping.
You're never going to get the right sound out of it, because you're not doing the correct repair by replacing that surround.
It just the same thing as a bad foam surround

 

[automojo]

Ess, probably used a number of different surround materials.
Foam or fabric in my opinion is the best for sound
The woofers are way more sensitive, and also foam and fabric keep the whole tone assembly in voice coil better aligned in the frame and gap.
The drawback with foam is that it has a tendency to go away, the newer forms are much more resistant to UV and environmental issues.
I played with a number of different woofers in my AMT three upgrades and I have to say foam, and fabric usually sounds better.
Just because rubber lasts longer, does not make it a better surround material for sound reproduction.
Exception, car audio in outdoor usage, rubber is going to survive better in those conditions, but it doesn't mean it's going to sound better.
There is a reason the Tekton, Zu Audio, old Altecs have detailed, sensitive and super realistic bass....
Regardless replace the surround with the same type and you should be good, otherwise I wouldn't lose any sleep over it.
If you don't like the sound from the water, then try to find a suitable replacement that will work better.
Good luck, it's a lot of work and will cost you more than a few pennies.

 

[Johnny_Law]

I just realized that my one woofer with the doped cloth surround may need attention anyway - the doped cloth is rock hard! So I suppose it'll be straightforward to replace it with new foam and make it match the other one in the process.

 

[SaturationPt]

ESS will replace the cone, or just sell new (pulp) driver and passive, I'd really like to stay with the original bextrene (I would hope that there's a reason that the last generation migrated to the cone/bextrene/cloth woofer and passive from the original and that the new pulp driver is a downgrade, but I have no data to tell me so.

Replacing surrounds is always going to change the tuning and alter the sound, no matter how careful you are and how close the new surround is to the original so that's not my preference either.

 

[automojo]

Well there are advantages and disadvantages of each cone material. Bextrine is definitely less sensitive, and has a strong resonance @ 1.5 hz. They do have a different sound. The advantage is they are more consistent batch to batch then paper. I'm sure the resonance was the reason they lowered the Heil crossover in those later models, given the 12/db slope. I don't mean to discourage you replacing the drivers with new, those new ESS woofers may sound fine. For a couple hundred bucks it may be worth the experiment. You may like the sound better then the Bextrine, and you may be able to adjust/tune the crossover better. You can always sell them. If you want to experiment further, get a copy of the loudspeaker cook book, and the book by Weems.

 

[BigMikehifi]

Picked up these 2 weeks ago, sound great, doing a bit of wood repair.Will finish with Howard's finish restore in dark walnut. I really don't like the orig fabric on the grills. I plan to replace with mellotone fabric from parts express..with the grills on..sound veiled..off is sooo much better..I blame that dang carpet on the grills!!

 

[SleeperSupra]

Well, I think you're making a big mistake replacing fabric surrounds with rubber. Fabric and foam are close, but in general you're better off sticking with the same type if possible.
Replacing foam, or fabric with rubber is going to change the characteristics of woofer, and performance, not a good thing.
Ricky at ESS is just going to try to sell your new parts.
I prefer paper, but you're original woofers Bextrine, paper, whatever IMHO, are better, or at least as good as the "new" China models ESS touts.
The AMT3, and early AMT 1, with a 10 inch paper cone woofers are the exception. So so.

The new ESS woofers are made in the USA.

 

[Porkloin]

Picked up these 2 weeks ago, sound great, doing a bit of wood repair.Will finish with Howard's finish restore in dark walnut. I really don't like the orig fabric on the grills. I plan to replace with mellotone fabric from parts express..with the grills on..sound veiled..off is sooo much better..I blame that dang carpet on the grills!!

Before you go replacing the grill cloth with something unbefitting a 70's walnut classic, see if you can get a couple of youngsters to help you with a blind test. While you sit in a chair with your eyes closed, with some music playing, have them move your grills in front of the speakers WITHOUT laying the top board on. Have them alternate between top board on and off and no grills at all.
I found that it wasn't the total lack of grills that made the difference, but the top board blocking the radiation of the Heil upwards. Some here will badmouth the effect of the timing of the wave from the back of the diaphragm, but I found that I preferred the effect - it added a bit more "openess". I liked it so much that I wound up cutting a "drain grate" into my top boards when I re-did the grills.

 

[GD70]

Very excited to have these, and trying to figure out which version they are. They seem to have low-ish serial numbers (1440 and 1596). One woofer is the half rolled damped fabric (?) and the other has a foam surround. Both PRs have foam surrounds. (All the foam looks to be in great shape, thankfully!) The Heils are silver, not black.

I'm referencing a helpful post from a while back, and it makes me suspect that these are early, original build Monitors with later-replaced PRs and one woofer? Problem is, I don't see that they ever came with PRs that had bextrene cones and open cell foam surrounds.

Reason I want to know is that I'd like to get a woofer to make a matched pair, so I'm trying to figure out which woofer is the correct woofer for the particular revision.



Thanks in advance for any help. Haven't listened to them beyond verifying that the tweeters work, very excited that they both work.

Damn nice speakers! Nice score!

 

[Porkloin]

Picked up these 2 weeks ago, sound great, doing a bit of wood repair.Will finish with Howard's finish restore in dark walnut. I really don't like the orig fabric on the grills. I plan to replace with mellotone fabric from parts express..with the grills on..sound veiled..off is sooo much better..I blame that dang carpet on the grills!!

If you haven't already done so, you may want to contact ESS about getting one of their Eclipse active crossovers. They still have some new/old stock down there for around $200 each.

 

[BigMikehifi]

Thanks for the idea Porkloin, reason for new fabric is age, dust, color and well, they are nasty dirty. What did you use, it looks good. I just want it to sound better than this original thick rug.