ESS AMT-3 Rock Monitors from Down Under - Oz

[L@MB]

Hello to everyone,

My names Craig (Australia) and this is my first post on AK, please let me know if I get anything wrong on this forum and I hope I'm posting in the right location.

Only because of the much reading (past posts from the wonderful AK team) I have done on this forum did I recently decided to hunt down a pair of one owner AMT-3's.

I'm slowly going to conduct some repair and maintenance on these speakers to bring them back to as new condition so on and so forth as many others have done here.

I am confused and ask for the following guidance for the AK team.

1. My drivers are not sealed behind the speaker to the baffle face as many have spoken about, so my baffles are in very good shape and the speakers remove easy - has anyone seen or heard of this before? I'm unsure if I should seal behind the speakers when replacing - it is a ported model?

2. My low frequency drivers have butyl / rubber surrounds / suspension and not foam, I find this strange from the reading I have done on here - has anyone seen or heard of this before?

Maybe the foam deteriorated and was replaced with Butyl.. The previous owner said they did go into an audio store approximately 5 years ago but can not confirm the work carried out.

3. I have been told the butyl slows the drivers down unlike foam that allows the driver a better chance in keeping up with the speed of the Heil so with this being said is it possible to remove and replace with foam or the damage is done?

NB: I read this just now while searching the forum to self learn - is there any truth to this following statement?:

"Butyl is equally as compliant / flexible as Foam and lives decades longer. Foam was /is fitted cuz it's cheaper... not superior"

I do not have any other information than this to help you assist my queries sorry.

Please see the attached images for your information.

Many thanks in advance for your time and support.


Craig

 

[westend]

Hi Craig,
Welcome to AK!
I'd suggest to listen to your new Rock Monitors before doing anything. The rubber surrounds may be quite adequate for what they have to do with the sound. Sealing the woofer frames to the enclosure is easy and I would suggest to do that before anything else. I've used Mortite (a cheap plumbing supply) and also self adhesive gasket tape. The Mortite can get sticky after 20 years or so but is a good material.

 

[L@MB]

Many thanks for your reply Westend,

I appreciate what you are saying and it makes sense as I might be happy with they sound so why change the surrounds.

I guess it eats away at my OCD that by all reports these speakers never came out with Butyl surrounds and I... just... cant... let go until they are factory standard haha.

Silly I know as if it sounds good like you said then why change it.

Thanks for the tips and the welcome.

Craig

 

[Leben]

Congratulations on finding a pair of Rock Monitors and welcome to AK. I think you are quite lucky that your speakers didn't have the RTV sealant. When I rebuilt mine, I used foam gasket tape with good success.

If your drivers are original, I suspect that the surrounds may have been replaced with butyl after the foam deteriorated. I would listen to them as-is and if they sound fine, I would leave them. If the crossover capacitors haven't been replaced yet I would change them while you have the woofers out. Love those Rock Monitors!

 

[essNeff]

Welcome aboard..............Great speakers.
You might want to look into stiffening up the shredded Particle board Baffle where the woofers mount. It looks like there is a little deterioration occurring.
Perhaps a little epoxy?
Good luck with the resto!

 

[L@MB]

Many thanks again for the input,

Pen and note book are out keeping track of suggestions lol.

I will move forward with the crossover recommendations, replacing components to factory specifications with new items.

The baffles are in great condition but as suggested I will strengthen with apoxy as unscrewing the speakers, well the board felt very soft and the speaker started falling out with two screws left in.

NB: Mix up some two part apoxy, fill the screw holes and then smear epoxy over the surface of the speaker recess where the matting faces come together, is this the correct idea to strengthen?

I heard a mans man, real men use 'floating nut plates' hahaha. So I will do this when remounting the drivers then foam gasket tape as suggested.

Do the images I up load show for you gentleman??

I 'believe' with my limited experience that the drivers are original due to having a purple date stamp on them saying '1979' however the images I have seen of the low frequency drivers magnets here on AK look different to the magnets on my drivers, I could be mistaken.

Can you more experienced members look at the photos, confirm if the drivers dust cap, cone, basket and magnet look how a factory AMT-3 should please??

The butyl the we suspect has replaced the foam, well it is very thick, they may as well have used a Heavy Ridgid Truck tyre - sarcasm.

Lastly, it is suggested that it's a good idear to seal the rear of the drivers with gasket tape even if it's a ported box? I guess it helps force all the air in and out where it should be for better sound??

Thanks again.

 

[L@MB]

Thank you ToolGuy,

With your info, the date stamps of 1979 on the basket, what Leben said plus the owner saying the speakers went in for a service 5 years ago, it does seem that the foams have been replaced with butyl.

Butyl surrounds are surely slowing the driver down compared to foam?

Heils are very fast I have been told and strongly suggested to me that a butyl surround on an original paper cone woofer is not a good thing for speed of the speaker???

 

[Leben]

If you like, refoam them. The downside to foam surrounds is that they will deteriorate faster than butyl usually does. There is no harm in enjoying them the way they are for a while and replacing the surrounds with foam if you think they need it.

Out of curiosity, what are you going to power them with?

 

[L@MB]

Thanks,

I want these speakers to be time period correct and if they didn't come with butyl then that offends my OCD nature baha.

Plus the butyl vs foam debate it appears to sway heavily to foam for better response speed and I need that to match the Heils.

If any modification to these speakers even bring the slightest question of reduced sound quality then I'm not interested - does that make me a Bigot or a purist in America haha?

Power Amplifier:

I will be using 2 X Carver M-500T power amps - Each speaker will be powered by one M-500T running mono 700w at 8 ohms for a total of 1400w with a Carver C-1 pre amplifier connecting the source to the power amps.

Will this work out OK to get the drivers moving to keep up with the Heil?

Any feedback at all is highly appreciated, I'm not one to be offended and thanks again to all for your help.

 

[Porkloin]

Don't condemn butyl surrounds without a listen. Plus, it's not a sure thing that they were foam to begin with. I would think the surround material of any speaker would have to be chosen in conjunction with it's spider and possibly it's magnet/voice coil combo, kind of like a car's spring and it's shocks.
What IS the noted effect of a woofer that is not "fast" enough for a tweeter? What makes a comparatively large, heavy chunk of treated paper "fast enough" for a mylar diaphragm? Since when did the use of foam translate into anything but cost savings, as demonstrated by the general rule that as you climb up the quality/cost ladder of woofers in loudspeakers, the better ones tend to be butyl?
Keep searching for the answer as to whether later model AMT3's came with butyl or not if originality is that important, but until then, let your ears be the guide on the woofers.

 

[L@MB]

Many thanks,

Appreciate you breaking that down as I am a noob to all this, the language used (lingo), terms and definitions.

Are my magnets Alnico? I assumed they were but you mentioned 1977 and my drivers are stamped 1979 sooooo Im not smart enough to look at the magnets and know what I have sorry, but your dates suggest I have ceramic?

So my magnets don't need re gaussing (if that's the correct term?) and hold their magnetism for effectively that Alnico?

Sorry for the long replies and many questions. I do use the search function on AK to find answers yet much is conflicting information and or not suited to my situation.

Thanks again.

 

[Porkloin]

Was 680-XXXX an ESS number convention or a driver manufacturer designation? I think I remember it on my old drivers. Odds are good that someone found a sweet deal on some butyl woofers of the right spec for the Rock Monitors late in the run or they were approved refurb replacements.

 

[Leben]

Power Amplifier:

I will be using 2 X Carver M-500T power amps - Each speaker will be powered by one M-500T running mono 700w at 8 ohms for a total of 1400w with a Carver C-1 pre amplifier connecting the source to the power amps.

Will this work out OK to get the drivers moving to keep up with the Heil?

Any feedback at all is highly appreciated, I'm not one to be offended and thanks again to all for your help.

Nice gear, I think those will work well with the monitors. I use a modified Carver C-1 pre and a M1.5T with my AMT-3s and like how the combination sounds.

 

[L@MB]

Haha nice, fancy another AMT-3 owner using Carver gear as well, mint.

I was concerned that 700w would kill the speaker, Will has already sorted me out on that topic, basically a controlled finger turning the volume knob is in order of the day.

Reason I want to run two amps is to give the amplifier more usable voltage from the power supply and yield a notable amount of headroom without endangering the core of the transformer with the added bonus of the soundstage improving as well as there would be 0 crosstalk between the amplifiers.

Cheers

 

[L@MB]

**Smashed Heil AMT
** Surrounds

After a long discussion just now with the previous owner I have found out that he personally doesn't know if the speakers were Butyl or Foam however the speakers went in for a service 6 years ago, the Audio shop called him and said:

- 'The woofer surrounds have rotted / deteriorated and need replacing' Trusting the Audio shop he said 'Yes'.

This information about the deteriorated surrounds being replaced coupled with no known AMT-3's having Butyl surrounds to date suggests the original surrounds were foam - fair hypothesis?

What type of plastic is the Heil AMT plastic case:

- Polypropylene or Polyethylene?

The freight company smashed mine Heil case.
After doing research I found out that 'plastic aren't plastics' and that I only get one chance to do this and I need to make sure I am using the right glue to the plastic.

Thoughts on Polypropylene or Polyethylene?

 

[L@MB]

Tool Guy,

Sorry for being a NooB...

There is meant to be an alloy plate going across the top of the plastic Heil case I take it from what you said? I never knew this, so much learning to be had.
I assume the alloy bar absorbs and redirects the vertical pressure of the bolts over a larger area avoiding excessive pressure in an isolated spot and then.... cracking?

****Shout Out!
Anyone have two spare alloy bars - I will pay PayPal I searched EBay and no joy haha.

 

[Porkloin]

I would be half (or 3/4) tempted to cut a piece of black ABS to the contour of the top of that tweeter and glue it on for aesthetics and reinforcement. See if you can use a hair dryer (not a heat gun - too hot) to salvage that sticker on the top. Maybe cut it oversize a bit and use a router with a laminate trimmer once the glue has dried. Mask off the wave guide, of course.

 

[VanArn]

Was 680-XXXX an ESS number convention or a driver manufacturer designation? I think I remember it on my old drivers. Odds are good that someone found a sweet deal on some butyl woofers of the right spec for the Rock Monitors late in the run or they were approved refurb replacements.

View attachment 742293

Of the few magnets from ESS speakers that I have seen, it seems that the '680' indicates the magnet type and the following four number sequence is a serial no. These all have 2'' diameter pole pieces,bumped rear plates and ceramic magnets with approx. 1 Tesla of flux density.

 

[L@MB]

Many thanks again Gents,

So I have ceramic magnets, not that I should get wrapped around the axels about the small details however how does my ceramic driver fair against the Alnico driver and are they of the same '1 tesla of flux density?

I assume flux is a unit of measure for magnetism of the magnet and or its strength of its field and ability to drive a speaker?

I have read but am unsure of the truth that ceramic are more punchy?

 

[VanArn]

I have never come across the alnico slug magnet version shown in a previous post and with the 0007 serial No ; (for the benefit of that Tool guy) it is obviously from a very early production period.There are differences in the way that magnetic materials behave and many manufacturers have designs that overcome the non-conductive nature of the ceramic material by using a shorting ring within the structure. Given that the AMT3 uses a midrange driver any inductive coupling non-linearity will be reduced simply by the fact that voice coil movement is kept low within the high frequency crossover range. Higher flux density magnets (1.4 Tesla plus) will certainly deliver more punch, but the cost goes up and there will also be a change in the parameters even with identical cone assemblies. Perhaps in hindsight ,tighter, more controlled and finer detailed would be a better description than punchy when a stronger magnet is used.