ML-2C PROJECT COMPLETED: Custom mid-tweeter arrangement

Nick Offerman, fine woodworking #222

The sled allows you to keep the router under control perpendicular to the cut.

Got a email from parts express showing their 5 inch mid woofer with a concentric tweeter......the cone flare (wave guide) might help in projecting the highs beyond the complications of the heavy grills. On sale even......
 
c_dk said:
A good plunge router with a sled that spans the width of the speaker cabinet would be the place to start.

You would need to limit the horizontal travel of the router to keep it under control but once you cut a groove half the depth of the baffle the inner part could be cut through with a jigsaw.
Click to expand...

c_dk said:
The sled allows you to keep the router under control perpendicular to the cut.
Click to expand...
Is this the type of sled to which you are referring? I put it together a while back, to assist in cutting straight grooves in something I was working on. It works well, and is simple to make.
RouterSled.jpg
 
Yes, just need a movable stop or two to control the length of the groove. Do you use a Porter Cable?
 
No, I have a Bosch and a Hitachi. The Bosch is mounted to my router table.

I do have a Porter Cable Reciprocating Saw and Pocket Hole Jig, though.
 
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You did a lot of nice work, there. Audio classics uses Morell drivers when they rebuild ML series and XR series speakers. Even with the XR-7 they only use one tweeter and one mid tweeter. Roger Russellls up date for ML-1's he designed personnaly uses one Morel tweeter and one mid tweeter. That way you don't get destructive interference between drivers. The only real serious fault I see is that you place two of your drivers side by side. You should have stacked them vertically. If your HF drivers were at ear height you could have placed the super tweeter in the center and placed the two matching just above and below to keep bad reflections off the floor and insure broad horizontal coverage with out serious anomalies. I liked ML-2s, I just refoamed a set of drivers for a close friend. Ml-2's were very popular with musicians in our city. The Concert Master and a former director of our Symphony owned pairs. I do prefer line arrays of tweeters. My two favorite Mac speakers were the XR 290 and XRT 28. I have a copy of a schematic somewhere if you need it.
 
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Thanks @twiiii - but those first pics are my starting point. I'm undoing that and trying to design & build something better. The plan - now that I figured out the front baffle won't be coming out - is to cut a clean square into the baffle, and install a new section of wood with whichever upper mid/tweeter drivers I decide to use, in the optimum configuration.

As of right now I have Celestion HF1300s to use as the upper mids, and Philips domes to use as the tweeters. My idea was to installed them in a vertical M-T-M configuration, to avoid the issues you describe.

I will look into those Morel drivers that Roger recommends. However, the idea of a concentric upper mid / tweeter driver is growing on me. My homework to do is to figure out from an engineering standpoint whether there is anything along those lines that will work from performance, impedance, sensitivity, space, and cost perspectives.
 
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OK, here is my cabinet plan. PLEASE let me know if this is a bad idea - this makes sense in my head, but I've never done it before, so maybe I'm forgetting something.

I've marked a 9" x 9" square to cut out of the mid/tweeter quadrant of the baffle. This cut will cleanly remove all off the hack job nonsense and leave a clean square in its place.

I plan on drilling holes at the four corners of my tape marking. The tape marking is more precise than it looks, I spent the day measuring / drawing / marking this (and made me remember back when I was a mechanical engineer, haha).

Then I plan to join the four holes in straight lines along the tape with a jig saw by hand. I want the most precise & straight cut possible, but I don't have any other fancy tools to do this.

IMG_20180721_174633.jpg

Then, I will use a router to create a 1" wide by 1/2" deep step / recess along the perimeter (similar to how the woofer mounts are recessed). I will use one of those bits with a bearing on the tip, so it will ride along the (hopefully straight a clean) edge that I previously cut with the jigsaw.

So I will then have a recessed mounting shoulder for an 11" square baffle. I like this idea because (1) it will look clean, because I will use black painted MDF/plywood which will match the baffle, (2) I will be able to try new mid/tweeter drivers and/or arrangements simply by cutting and painting new 11" square baffles whenever I want to, and (3) I will run threaded inserts into the stepped shoulder and will be able to maintain an acoustically sealed chamber.

The first baffle I make will have my Celestion mid-tweeters and Philips tweeters arranged in an MTM configuration as I mocked up on a piece of foam.

IMG_20180721_182115.jpg

The beauty of it is, if those drivers and/or driver arrangement don't work out, it will be a cinch to try alternatives. Once I settle on a final driver compliment I'll be able to make a fancy baffle out of walnut if I desire, and perhaps adorn it with a metal cage and McIntosh logo in the same style as the original.

Would love any input. Thanks!
 
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Typically a jig saw cut is not sufficiently "square" to use a bearing type router bit ...but if you can make your cut to insure you have enough material between your cut and the cabinet wall you really do not need a rabbit.....just glue and screw a series of backers to form the recessed stop to the inside perimeter of your cutout. Just use material that will accept screws well like Baltic birch ply or a hardwood.
 
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c_dk said:
Typically a jig saw cut is not sufficiently "square" to use a bearing type router bit ...but if you can make your cut to insure you have enough material between your cut and the cabinet wall you really do not need a rabbit.....just glue and screw a series of backers to form the recessed stop to the inside perimeter of your cutout. Just use material that will accept screws well like Baltic birch ply or a hardwood.
Click to expand...

On the jigsaw - I believe what I'll do is clamp straight plywood in a position to act as a guide for the jigsaw. That way I can keep the jigsaw in contact with the straight edge of the plywood while cutting, which will hopefully result in a straight cut.

On the backer idea - what do you mean by "a series of backers"? Apologies for not being familiar with the terminology here. I think I see what you are saying though, you mean like little blocks of wood attached along the inner face of the cutout, to mount the baffle to? My first thought about that is, I'm not sure I can achieve an acoustic seal if I do that? What I want is to have the MTM baffle flush with the rest of the baffle - and if I offset backers to accomplish this, I fear I'll lose any kind of seal.
 
Basically make a frame with inside dimensions 1.5 to 2 inches smaller than your baffle cutout. Screwed to the back inside of your baffle you have created your step. If you use lap joints to secure the 4 boards together you will create a seal beyond the seal that chauk would make.

I have made the mistake of trusting a jigsaw blade to not wander with its unsecured end.
 
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Ok I'm trying to visualize a lap-jointed frame on the inside of a baffle - is that what you mean @c_dk ? How would I get it flush with the main baffle? Actually I'll call the main baffle that, the baffle, and let's call the new small baffle the "MTM insert". So do you mean attach a lap-jointed frame to the inside surface of the MTM insert, or to the inside of the cut I make in the main baffle?

And @turnitdown thanks, I had no idea those tools even existed! I watched this video and now I think that it could be perfect for making that initial cut.

Either that or, how about if I used a compact circular saw instead of the jigsaw? It seems like it'd be easier to get a hand held circular saw, cutting while guided by a straight edge, to make a perfectly straight cut.

I did realize something problematic about using the router - I don't think I have enough room along the top and right edges! The edge of shoulder will only be a couple inches away from the top and side of the baffle so I don't think the router will physically fit in that space.
 
It appears your sub baffle cutout will be 11x11. Make sure you have At least 1 inch of the old baffle left between your hole and the side wall.

Using 3/4 inch hardwood that is 2 3/4 wide make a square 12.5 X12.5 inchs outside. You will need 4 pieces 12.5 long. A half lap joint means that the two joined prieces will have 1/2 of the material of each piece removed (3/8s by 2 3/4s) Since those pieces overlap it is strong and air tight once glued.

Glue and screw this square inside the speaker cabinet giving you a nice "ledge" to attach your sub baffle. I think assembled it will fit through the 11x11 opening corner to diagonal corner but measure twice, 11X1.414=15+
 
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Ah, understood! Thanks!

What do you think I should use to make that 11x11 cutout as straight and true as possible, if not the jig saw? The problem is I don't think the router I have will fit close enough to the upper and side edges of the baffle.
 
I will build a plywood sled that will bridge across the speaker cabinet edges. Clamping in place will make for a controlled cut E and W and then with clamps restricting the sleds E W movement but would allow it to move N and S with the router locked in place.

see GMCs picture of the sled.

If you uses a backer frame the perpendicularity of the jigsaw is not nearly as important because you will not be trying to follow it with a bearing.
 
Alright I tried it with the jigsaw using a 2x4 section clamped as a guide - gee, that blade looked great from the top but bent towards the bottom. So I picked up a little 1/4" router that I'll use to straighten it out! Then I'll make that ledge for the baffle to mount to.

IMG_20180905_200044.jpg

In other news, I picked up 4 original midranges that I'll use instead of the Celestion HF1300. I'll probably mount them MTM at first but the beauty of this is that I'll be able to swap it out for a baffle with the original TMM configuration if I want to.
 
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Well, I was bad and forgot to update this thread as I went, but I did remember to snap a picture here and there. Unfortunately I now have a surprise move coming up, and they're up for sale because they're so big. I'm listening now and they sound great (even w/o the MQ-102).

So ... I'll get this thread up to speed. I'm really pleased with how they came out and happy I could save them.

In parallel to getting the baffle sorted out, I decided to refoam the woofers. After I took the old crappy aftermarket foam off, I noticed one woofer had a sagging spider. I did some research and found one subwoofer spider repair method that seemed promising: spraying water on the spider, propping the cone up, and then drying it with a heat gun. I tried it ... and presto! Spider was 100% back in action. New foam from Rick Cobb went on. Woofers were sorted.

Saggy spider:

IMG_20180902_180627.jpg

All better!

IMG_20180903_122211.jpg

With the cabinets, I had left off where I was trying to make the cuts with my jigsaw. Bad idea. I got a 1/4" router from Harbor Freight and evened out the cuts on one cabinet, and made nice clean cuts in the other.

I also decided to drop the Celestion upper mids in favor of the original orange dome mids that I got from someone parting out a pair of ML-4Cs.

With the squares cut out of the baffles, the inner framing went in. I had realized that I was limited by the space between the sides of the baffle, so I couldn't make that 1/2" shoulder I had originally envisioned. The step frame was a great idea and paid off. I sealed all the gaps with wood glue.

Next, I cut the new MTM baffles out of 1/2" thick 5-layer plywood.

IMG_20181006_152051.jpg

After measuring twice, I cut the driver holes and mocked it up. This was challenging with the space alotted but I had JUST enough room.

IMG_20181006_171651.jpg

Drilled out all the screw holes and put in 10-24 t-nuts, the machine screws will impart much better clamping force and make a better acoustic seal.

IMG_20181009_182740.jpg
 
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After this, I didn't take pictures for a while. I completed the following tasks:

-Filled the missing wood on the driver mounting baffles with wood filler, and sanded flat
-Filled and sanded the leftover holes in the baffles from that original mounting cluser4uck
-Painted the all baffles with satin black paint
-Extended the driver wiring where someone had cut it too short
-Installed diffraction foam trim on woofers (I know, for looks)
-Stripped the original varnish off the cabinets, two coats of Howard's restor-a-finish in Walnut with 0000 steel wool, followed by heated feed-n-wax
-Restuffed with the exact original filling that came out
-Rope caulk under the MTM baffles, tested to make sure they're sealed
-Assembled with the lower mid under the tweeter and the upper mid over the tweeter
-Disassembled and cleaned each of the 4 grilles

Then, together they went, took pictures on the way from the garage to the music room.

IMG_1426.JPG

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Got them set up where my Cornwalls had been for the last month or so ... crossed my fingers ... and started up some music.

WOW! I'm VERY pleased with them. They sound GREAT. Planning on celebrating with some Scotch the moment it turns 5:00. Thanks for following along!

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