Monolith refresh - Panels, woofers and rail stain updates

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Jan 16, 2005
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ATL Area, GA
I’ve had Monolith III’s for eight years now, having bought them used in ‘98. They were made in January of ‘93.

They sat unused for more than a year as I finished up the custom home theater room designed around them and the rest of Martin Logan gear I have.

Once in full deployment in the new HT, they were marvelous, although running on their factory passive crossover for the first months. After playing with placement, tuning the room acoustics and all other non-invasive approaches, it was clear that a better sound should be possible with these great speakers. So I went with an active external crossover and bi-amped. Big improvement.

However, in measuring the new x-over setup, it was clear something was not right in the bass, especially the mid-bass. Keep in mind I’ve always used subs (back in those days it was two Velodyne ULD-18’s) so the Monolith woofers were not being taxed by ultra-low frequencies. The x-over then was at 60hz.

Looking at the stock 12” driver, it was clear the distortions and ‘flabbiness’ I was hearing were a product of one tired speaker. So I updated the driver with an ACI SV12 unit. Read the specific story and see pics of that one at my site.
The sound, especially the 100hz region was vastly improved. Been very happy with them as long as the x-over is below 160hz.

Having experienced dramatic improvements from the active x-over, I then went all-out with a Speaker processor, the DriveRack 260. This allowed true panel to woofer (and to sub) integration on a level that seemed a pipe-dream before. This unit is awesome, and results are likewise.

Now, here we are in the spring of 2006 and the panels have significant high-end frequency drop offs, the ETF measurements also show some panel resonances that I don’t think had been there before. Also, the original panels are now 13 years old. Time for a refresh of the panels.

The Monoliths I bought (since I got them used) came with Oak rails. They look nice, but don’t really go that well with my HT setup, where everything is either black, grey or uses purple for a highlight color. When using front projection, light control and reflections are critical. The light Oak rails pick up the light of the PJ and are somewhat noticeable when playing a movie. Since the replacement of the panels requires some disassembly of the Monolith, I’ll be removing the rails and refinishing them.

The plan is to use an Aniline dye to stain them a dark purple and then put a satin finish poly coat over that.
First, lot’s of sanding to get down to the bare wood.

In addition to the panels and rails, I’ll also be doing something with the woofer, but that’s detailed in another post.

Some of you have PM’d me or posted asking for details on ‘how-to’ perform some or all of the above, so this thread is for you guys. Pics, measurements, descriptions and crying on your shoulders if I screw-up, all to come in the next few days.

Lot’s of work in the next day or two :)
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Woofer Update selection

Since the woofer project a few years ago, I’ve been doing two things, one is testing higher crossover points to move out of the dipole rear-wave cancellation issue area, and the other is researching drivers that can play cleanly at up to 500hz. Turns out there are a couple of suitable drivers, one is a Peerless brand unit, the other is an AudioTechnology Flexunits model.

The Flexunits seems like a good choice if you do not use a sub, as it has better LF response and a better motor. However, it’s more expensive and does not quite go as high as the Peerless, but definitely goes high enough for the factory x-over points or even higher.

I settled on the Peerless 830669 12” driver. This unit will play clean past 1KHz, and bass was reasonable considering I’ll be crossing over at 24db/oct at 80Hz. It is not suitable for a full-range Monolith, as it’s low-end extension is limited. But for my purposes, seems like a good choice. Proof will be in the measurements.

As seen the pic below, the woofers and panels are here.
The other stuff is for my little center channel project ;)


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As-is measurements of ACI SV-12

Before we go moving and ripping anything up, I captured some ‘as-is’ measurements of the current ACI woofer.

This graph shows both the detailed Bode response (blue line) and the smoothed third octave response (green line) as measured at 1m distance

As you can see, the smoothed response is reasonable, being +/-3db from 35 to 435Hz. It falls off pretty rapidly after that. In the Bode response, the distortion elements at >250Hz start accumulating. The cone is pretty massive and does not do mid-bass that well.
The big peak at 64hz is a room mode. I don’t have anechoic chamber, so we live with spikes here and there ;)

I expect the peerless to go higher and smoother.

More to come…


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Back on track

Well, after a few weeks of hard work, first on the SL3-XC center channel project , and then some catch-up at work, I finally had time to get back to the Monoliths.

The plan to deal with the trim rail is a bust. Here’s why:

The monolith is constructed of essentially three parts:
  1. The Bass cabinet, which houses the 12" driver and the ESL Electronics (but no Crossover, Monolith x-over have always been external, with a choice of passive or active)
  2. The ESL frame. This is what holds the panel and the trim elements.
  3. The Rails that tie the two together.
The rails are a part of the support structure and require some major bolts and screws to be removed. And I didn’t feel like a total disassembly project. So the rails will remain Oak, and their light color nature will be dealt with differently. I’ll post about that when I get around to solving that issue.

In the meantime, I had the new panels and the Peerlesss drivers to install.

So, doing one each weekend, I’ve updated the panels and woofers.

The speakers were repositioned and measurements taken.
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Woofer Update

As noted above, the ACI woofer as big improvement over the tired-out factory Eminence unit.
However, the ACI SV12 is really more of low bass /sub driver, which means it can’t go cleanly up into the mid-bass. Not too big a problem if you stick to the 125hz factory crossover point.
But as many threads have discussed, dipole speakers, no matter how big the panels, have issues with rear wave cancellation at low frequencies. Physics gets in the way it seems.
Therefore I like to cross-over around 312Hz to the Monolith panels.

To better match the higher crossover point (and use of 18db/octave slopes), I needed a speaker that would be clean up in the 800Hz range.
The Peerless also does not go down very far, its FS3 is 40hz. So it needs to be crossed over to the sub above 65Hz. In my application, I’m using 80hz.

As can be seen in this graph of frequency response, the old ACI and the Peerless are roughly equivalent in the 100 to 450 range. The ACI clearly is more of low-end driver, easily posting 3 or more DB better numbers down low.
But the Peerless goes substantially higher (and as we’ll see in the impulse graphs, cleaner) and is essentially flat at 800Hz. The graph does not show it because of the floor bounce (notice how both curves track it). I really need an anechoic chamber ;)

Measured from different distances (with different room modes affecting), it’s clear the Peerless is better at the mid-bass.


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Impulse response

The real difference is in the distortion products of these two drivers. The larger mass of the ACI will get in the way of clean mid-bass transients. This Impulse response shows us that the ACI can start and stop its initial impulse fairly well, but then the cone oscillates substantially more than the Peerless unit. The Peerless has a lighter mass cone, and less compliant surround, which is why it does better up in the mid-bass.

The Blue trace is the ACI, the Green trace is the Peerless.


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Pulling the old speaker

Here is a shot of the ACI pulled out. You can see the ESL electronics in the cavity.

Note the bolts screwed into the driver. That’s a little trick to pry out drivers without marring the surrounding box. They allow for leverage to be applied (crowbar or claw hammer) in an upwards fashion to loosen the driver from its seal.
Otherwise, you ain’t getting those out of there by hand, I can tell you that ;)


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Putting in the new

Here is a shot of the new Peerless going in.

Since I didn’t think that fully reflective set of electronics and back panel was quite right acoustically for a driver playing up into the mid-bass, I put a Deflex panel to hang over the electronics and absorb / deflect the mid-bass and hopefully reduce resonances.

Also, the Peerless basket holes do not align perfectly, so a bit of reaming of the metal was required.

Otherwise, it’s a drop-in replacement.


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Panel Updates - removal

Updating the panels is a bit daunting. First, the Monolith is a big puppy, weighing in at over 120 pounds per unit, you don’t just grab these, you need two people to safely move them about.

Also, since they are not square sided, they do not lie on their sides, they will rock onto their backs if not held.

So step one is to enlist a ‘volunteer’ to help here. My six foot tall gorgeous French wife, who can easily lift 100 pound bags was kind enough to ‘volunteer’ to help ;)

The instructions for the panels are easy to follow, and I really have no additions or corrections to them other than the color commentary here.

First, we pull off all the trim and that allows the access to the frames where the panels are seated. Below is a shot of the speaker on its side, with the panel already removed.
You can see the frame slots the panels fit into.

The process of pushing the panel centers out from the middle (from behind) is pretty straight-forward. The panel flexes pretty easily (with the right amount of pressure) and one of the edges will pop out of its frame, making the rest of the removal a simple process of pulling the panel up and out of the other frame element.


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Panel Updates – Install

The installation process is a bit more involved, as sliding in the panel has to be done just so. The first detail is the ESL drive pigtail cable. It goes into a slot at the bottom of the left rail(as seen from behind) and is a tight fit. Then the rest of that side of the panel is fitted to its frame rail from the front. We then have to bend the new panel to slot it into the other frame slot.
Again, this is a bit difficult to get over the fact that you have literally bend the new ESL panel a good bit to get it in. But in it goes, no worse for wear. Just make sure you treat the foam edging on the panels very carefully and don’t rip it or get the tape off of it.

Once it pops in, remember to hook up the pigtail to a socket in the top of the woofer section (see pic below) and you’re done and can start reassembling the trim.


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All done

Once the trim is back on, we repositioned the speaker and are good to go!

Here’s a shot of the Monolith with the new panel and woofer. The ESL is much more reflective than the old panel was, with a nice ‘chrome’ metallic sheen. A combination of both the new vapor depositing process ML has, which leaves a consistent and thicker coating (for increased efficiency) of metal on the surface, and the fact that the old panels had accumulated dust and other particles that had bonded to the Mylar.


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Here is a shot of the ACI pulled out. You can see the ESL electronics in the cavity.

Note the bolts screwed into the driver. That’s a little trick to pry out drivers without marring the surrounding box. They allow for leverage to be applied (crowbar or claw hammer) in un upwards fashion to loosen the driver from it’s seal.
Otherwise, you ain’t getting those out of there by hand, I can tell you that.

Hi I don't fully understand the implications of this post Since I have had difficulty getting my loctited screws out of the panels I'm sure this post has some relevance for me.
What do you mean by bolts screwed into the driver? Did you pry loose the driver with a crowbar without trying to loosen the screws thereby ripping out the female metal sleeve receiver within the wood? Or does it mean something else?
Listening impressions

A quick tweak of the DriveRack settings and some initial listening test show that the new panel and woofer are indeed sounding better than the old set.
However, much measuring and tweaking to go.

Initially, the panel is very bright, not only is the efficiency a couple of DB better than the old, but as we’ll see in the measurements a bit later, the midrange has a serious rise in it.

But once the levels between panel, woofer and sub were tweaked, it was much better, still a noticeable ‘presence’ in the midrange. Not unpleasant, but a bit too ‘forward’ for my tastes. We’ll tame that with a combo of room treatments and EQ.

As I’ll update later on the SL3XC build thread, the tuning of the center along with time and phase alignment across all three front speakers results in an astounding soundstage.

The biggest difference is in the mid-bass of course. Not only do the new Monolith panels play louder and lower than the older ones, the higher crossover points and the new woofer conspire to really fill in the mid-bass. And since that it where drum hits, bass guitar and so many other instruments have either fundamentals or critical harmonics, it really brings the sound to a new level.
The big mid-bass line array in the SL3 based center now really keeps up (actually, it’s better than) the Monoliths. This is something that now gives the front soundstage its width and depth that I’ve never heard before. And that’s in a room designed for these ML’s ;)

Listening to ‘dance’ music, like Madonna’s latest (well produced and recorded dance stuff) ‘Confessions from the dance floor’ is actually an impressive experience on the MartinLogan set.
I always used to pick Jazz, vocals and other acoustic music to show off the ML’s because it highlights their strengths while hiding the fact that they are lacking in ‘punch’. Well, no more. They truly rock now.

Of course, they do subtle vocals and solo piano like no other. Frankly, with better authority than ever with the improved mid-bass foundation.

All in all, worth the effort and expense.

If you have Monoliths with >12 year old panels (or panels that have sat in the light or harsh environments). Call ML pronto and order your new panels. You will not regret it.
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ted betley said:

Hi I don't fully understand the implications of this post Since I have had difficulty getting my loctited screws out of the panels I'm sure this post has some relevance for me.
What do you mean by bolts screwed into the driver? Did you pry loose the driver with a crowbar without trying to loosen the screws thereby ripping out the female metal sleeve receiver within the wood? Or does it mean something else?

Ted, the drivers are held in by hex drive screws. Those come out pretty easiliy.

Prying the driver out of the hole may or may not be an issue. My ACI's were bonded into the leather by some sealant strips they had on the backs.

Since sticking a screwdriver or anything like that around the edge of the driver would A) risk damaging the leather or B) risk damaging the driver, I decided to try a different approach.

By screwing in some bolts that thread into the woofers holes (which normally are designed to let smaller screws through) I now have some big metal items that are two inches long, have a 'head' that I can pull on and are secured to the driver.

By placing a hammer on a piece of metal, which itself is on top of a cloth, I can now use the hammer nail removal claw to pull 'up' on the bolt head with a good bit of leverage. I'm just trying to break loose the bonding between the driver an the enclosure.

I recalled the factory drivers required a bit of effort to get out as well. This trick would have speeded up the process.

I hope this clears it up.
Hehe...good trick. We were once trying to replace the woofer in a B&W ASW850 sub and it was really sucked in there good. We ended up holding upside down an inch or so off the floor, and playing 5HZ through it with a generator. It broke free. :)
great rite up so far ! Don't expect any thing great till the Mylar and the panel break in for a few months . Then watch out it is like night and day with them . They suddenly sound fantastic. great stuff! :D
Woofer fritzed

Well, after almost a year, one of the Peerless drivers gave up the ghost. I just noticed it yesterday while running some test tones (sine sweeps from 16hz to 160Hz), all of the sudden at around 80hz and up, there is this nasty buzzing sound from the left Monolith. Approaching it, it's the dang 12" woofer.
The right speaker is fine.

Guess I played a movie or some music with a little too much gusto sometime in the recent month or two :eek:

With 200w into each driver (which while not rated, I’d guess nominally 150w), I think the amp outguns the driver by a good bit. Guess the fritzed (voice coil rub) driver is proof. ;)

So, what to do? I guess I was upset at the peerless for dying so soon, so I looked around and will try something a bit different just for grins. If it doesn’t work out, I’ll just order another peerless.

During research, I found there are few 12” designed for mid-bass that aren’t pro-music oriented (which means more care is placed on efficiency and thermal management than on ultimate sound quality), although some of those drivers did look good. But no SQ measurements on them anywhere I can find.
I did find a nice mid-bass woofer that’s been used in several commercial home speaker designs, and is fairly popular with the DIY crowd.

The HiVi M12 is nice unit with very nice looking mid-range extension and decent performance down to 60 or 80hz. In a sealed 85 liter cabinet, it should be F3 at 60hz, just right for my application. So I ordered 2 (on sale at $105/ea at


Compared to the peerless it has slightly higher mass, but still has good extension. The aluminum cone should help with cone resonances. It’s SPL abilities will still need to be determined. If I’m nervous about anything it’s that.

Will pop them in next Saturday and tune them quickly (SleepySurf shows up the next day for a demo, yikes, got to get going fast).

Frankly, I’m getting closer and closer to just building a line Array of mid-bases for the Monoliths. These 12” drivers are just too wimpy, even when constrained to a limited frequency range. Ideally, 4 X 10” or 12” mid-bass drivers per column would do the trick.
I actually looked into that driver for a direct replacement for the Quest 's I have. I didn't end up doing it as I moved them into another room that was much better suited for the bass. I would like to know your findings on these !
Hi Jon,

The Rives reference system on Audiogon used to feature Monoliths powered with Krell and Levinson via a Bryston 10b. He had replaced the woofer with Focal Audiom drivers. I know Focal went through a phase of not supplying when they transitioned to JM Labs but I think this is no longer the case. It may be that he could point you to a path that has already been travelled.

Jon, don't knock yourself out trying to do the repair on short notice just for me. I'd be happy just to SEE your setup, even if I can't actually HEAR it!