New DIY MTM Towers designed by Dennis Murphy and Paul Kittinger

[KenM10759]

If you look back some pages you will find pictures of my build.

If i recall correctly you will need one and a half sheet for this build, but one venered should be enough as the rest is hidden.

As long as you have access to CNC i would go for the veneered and mitre all joints. It is possible to do by hand, but it take some skill as every minor defect will show.

I'll pick up 2 sheets of the cherry veneered 3/4" MDF and we're going to practice lock miter joints and "miter folding" to get better at it before attempting the speaker cabinets. We want those to be as close to defect-free as is practically possible. We'll also be doing sample finishes and stains to find what looks best, and how good of a true shine we can get on them. I don't expect to be a Jim Salk in a couple on months, just don't want the job looking hacked.

The CNC machine I have is a metal-working one, a "Bridgeport clone" with a Prototrak control. It's not a CNC router, but we may use it to cut the round holes & counterbores for the drivers. I'd done that when my son built a subwoofer enclosure for his pickup truck.

 

[KenM10759]

My build can be seen from page 23: https://forums.audioholics.com/forums/threads/new-diy-mtm-towers-designed-by-dennis-murphy-and-paul-kittinger.68531/page-23

All photos still intact

Thank you!

 

[Swerd]

I'm going to pick up 2 of the 4x8 sheets of 3/4" MDF with the cherry veneer.

I wonder now how much more it costs to use the Seas W18 woofers, and would they be useable without modifying the crossover.

The Seas ER18RNX woofers cost $90.50 each, and the Seas W18EX woofers cost $273.60 each. You'll need 4 of them – you do the math.

When I said the ER18 MTM cabinets are the same dimensions as for the Salk HT2-TL, I did not mean to say you could substitute the drivers. These crossovers were custom made by Dennis Murphy for the ER18 drivers. To substitute W18 drivers, you would definitely have to design new crossovers – on your own. The HT2-TLs are a Salk-owned proprietary design and I'm sure Dennis would not provide that info.

I'll pick up 2 sheets of the cherry veneered 3/4" MDF and we're going to practice lock miter joints and "miter folding" to get better at it before attempting the speaker cabinets. We want those to be as close to defect-free as is practically possible. We'll also be doing sample finishes and stains to find what looks best, and how good of a true shine we can get on them. I don't expect to be a Jim Salk in a couple on months, just don't want the job looking hacked.

Do you mean to use a 45° lock miter router bit with results like this?

I've never done that. It's said to work with solid wood or plywood, but I don't know if it works well with MDF. Maybe something like a lapped miter joint could work alright in MDF.

I know Jim Salk uses plain miter joints. He lays out the panels, taping the joints edge-to-edge, and folds them up like a book as he glues them. I would have to practice that lots to get it right.

 

[KenM10759]

I wouldn't use the W18 if the crossover needed a change. I'm far from qualified to do that!

The kit seems to use the W18EX, so what's the reason for mentioning E18RNX? I would want to take my time getting the correct components and do it right.

I was consider the lock miter joints only because I know Totem stated they use it with their speakers. That's the whole reason I want to buy extra veneered MDF and try it. If it doesn't work because MDF has little torsional strength (but good compressive strength), I'd go to the lapped miter joints. Plain might shift around too much (for me) upon assembly and clamping for glue set.

 

[Swerd]

The kit seems to use the W18EX, so what's the reason for mentioning E18RNX? I would want to take my time getting the correct components and do it right.

I'm confused. The DIY plans (the downloadable pdf) for the ER18 MTM speaker use the ER18RNX woofers. Same for the kits sold by Meniscus Audio. What kit uses the W18EX drivers?

I was consider the lock miter joints only because I know Totem stated they use it with their speakers. That's the whole reason I want to buy extra veneered MDF and try it. If it doesn't work because MDF has little torsional strength (but good compressive strength), I'd go to the lapped miter joints. Plain might shift around too much (for me) upon assembly and clamping for glue set.

I once thought lock miter joints might be a good idea, but I talked myself out of it because it is said not to work with MDF. I've never tried it. I can't say what would work in your hands. Good luck and let us know how that works out.

 

[roadrune]

I used lock mitre on mdf, and its not a good solution as the mdf will not hold much in one direction.

When i build now i mostly use a plain mitre with biscuits to lock it, much easier.

 

[KenM10759]

I was thinking the same. We have a Porter Cable biscuit cutter that can work on the miter, 3 different cutters and 3 different size biscuits for it.

 

[roadrune]

On 19mm (3/4") i use size 20

 

[highfigh]

I'll pick up 2 sheets of the cherry veneered 3/4" MDF and we're going to practice lock miter joints and "miter folding" to get better at it before attempting the speaker cabinets. We want those to be as close to defect-free as is practically possible. We'll also be doing sample finishes and stains to find what looks best, and how good of a true shine we can get on them. I don't expect to be a Jim Salk in a couple on months, just don't want the job looking hacked.

The CNC machine I have is a metal-working one, a "Bridgeport clone" with a Prototrak control. It's not a CNC router, but we may use it to cut the round holes & counterbores for the drivers. I'd done that when my son built a subwoofer enclosure for his pickup truck.

You're going to practice on cherry plywood? Kinda pricey for practice, eh? Why not call around and find someone who has cutoffs and damaged sheets? Cabinetmakers, big box stores, lumber yards etc will usually have some. Building boxes in this way requires extremely accurate setup.

You may find that it's easier (and less expensive & frustrating) to build the cabinets and add the veneer. You can also be more creative with the covering- I saw some Vandersteen speakers with inlaid pieces that were really interesting.

 

[KenM10759]

I'm debating one way or the other. The cherry-veneered material is CHEAP, relatively. It's 3/4" MDF, not plywood, and only $76 for a 4'x8' sheet. Regular 3/4" MDF is about $30.

 

[highfigh]

I was consider the lock miter joints only because I know Totem stated they use it with their speakers. That's the whole reason I want to buy extra veneered MDF and try it. If it doesn't work because MDF has little torsional strength (but good compressive strength), I'd go to the lapped miter joints. Plain might shift around too much (for me) upon assembly and clamping for glue set.

You really shouldn't have to worry about torsional strength, once the front and back have been attached.

There are many ways to deal with corners when working with MDF and not all of them require fastening MDF to MDF. One way uses a piece of solid wood (Poplar is great for this and it's not very expensive)- use a tongue & groove bit (or dado set) to create additional gluing surface on the ends of the sides, top & bottom and make the strips to fit. Glue them and if they're cut accurately, they'll be ready for veneer or finishing after any excess glue has been removed. You can also do this with matching or complementary wood if you use veneered plywood or MDF. Cabinetmakers do this to avoid having exposed end grain or raw edges on plywood.

 

[highfigh]

I'm debating one way or the other. The cherry-veneered material is CHEAP, relatively. It's 3/4" MDF, not plywood, and only $76 for a 4'x8' sheet. Regular 3/4" MDF is about $30.

"Only" $76?

I knew someone who made speakers and at some point, they bought a V-groove machine from a cabinetmaker. They had to do a lot of setup on it and if the sheets had any areas that weren't flat, the cutter would slice through the veneer. When it worked, it was great, but it's tricky. That particular machine's cutter was similar to the old moulding cutters that were/are available for table saws, but it cut from above. Also, if the material's thickness varies, it can be a problem.

When I built my cabinets, I used dado and rabbet cuts- set up properly, there's very little cleanup WRT uneven edges.

 

[Swerd]

I just remembered the easy way to see photos of ER18MTM speaker cabinets, Google Image. Here is what I got when I searched "ER18 MTM speaker":

https://www.google.com/search?hl=en&tbm=isch&source=hp&biw=1078&bih=632&ei=dBxJWqDLOuGN_Qa5lYPwBA&q=ER18+MTM+speaker&oq=ER18+MTM+speaker&gs_l=img.3...2314.16794.0.18905.16.5.0.11.11.0.59.279.5.5.0....0...1ac.1.64.img..0.9.293...0j0i5i30k1j0i24k1j0i30k1.0.eigu812y40o#imgrc=_

 

[KenM10759]

"Only" $76?

I knew someone who made speakers and at some point, they bought a V-groove machine from a cabinetmaker. They had to do a lot of setup on it and if the sheets had any areas that weren't flat, the cutter would slice through the veneer. When it worked, it was great, but it's tricky. That particular machine's cutter was similar to the old moulding cutters that were/are available for table saws, but it cut from above. Also, if the material's thickness varies, it can be a problem.

When I built my cabinets, I used dado and rabbet cuts- set up properly, there's very little cleanup WRT uneven edges.

$76 isn't a lot of money because I'd only be using a 1/3rd of a sheet for practice. If it doesn't work out, we'll try the plain MDF with veneer over it. We also have a good selection of dado, rabbet and dovetail cutters, plus my cousin is a very experienced cabinetmaker who will be available for guidance. He's said he'll also be willing to do some pieces for us with his Powermatic machinery if we're having any trouble.

I might just go with the plain MDF if we can round the corners to 1/2" radius and wrap veneer around it. I think it would be very cool to have rounded edges and it's useful in reducing diffraction.

Please don't get too critical, this is a long term (6 months or more) project that is still in proposal stages.

 

[highfigh]

$76 isn't a lot of money because I'd only be using a 1/3rd of a sheet for practice. If it doesn't work out, we'll try the plain MDF with veneer over it. We also have a good selection of dado, rabbet and dovetail cutters, plus my cousin is a very experienced cabinetmaker who will be available for guidance. He's said he'll also be willing to do some pieces for us with his Powermatic machinery if we're having any trouble.

I might just go with the plain MDF if we can round the corners to 1/2" radius and wrap veneer around it. I think it would be very cool to have rounded edges and it's useful in reducing diffraction.

Please don't get too critical, this is a long term (6 months or more) project that is still in proposal stages.

I was only offering options.

If you decide that a contrasting/complimentary wood corner might be a good thing, even after the cabinets are technically 'done', you can route the edges and glue a strip of different wood in- if you want, this can be rounded-over before it goes on.

 

[KEW]

If you decide that a contrasting/complimentary wood corner might be a good thing

I vote cherry (since you have it in mind) with Walnut or Mahogany edging!

 

[Swerd]

If you want rounded edges on the front baffle of the speaker cabinets, I wouldn't try bending veneer around the rounded MDF edge. It can crack the veneer, especially if a ½" round over is used. I've seen it done with ¾" round overs, but I've never tried it. And besides, you'll probably want that MDF that already comes veneered in cherry.

Instead, glue hard wood strips, roughly 1"×¾", to the sides and top edges of your cherry veneered MDF. There is no need to do this for the bottom edge (see the illustration below). Next, trim the hard wood flush to the veneered surface of the MDF, and round the outer edges with a ¾" round over router bit. Rounding over hard wood will work better than on MDF. You want the final size of the front baffle to be 9×44½", including the hard wood edges, so start with a smaller MDF panel.

Here are some Salk cabinets with hard wood edges on the front baffle. The veneer is light maple veneer and darker (dyed maple?) hardwood strips on the top & sides of the front baffle. For cherry veneer, you can use solid cherry strips, or any other contrasting wood you want.

I linked a video that shows a useful general method for this. It doesn't show exactly the details I described for speaker cabinet panels, but I think it helps.

 

[KenM10759]

I love that look of the Salk's you posted! I'm thinking it would be cool to do that using the 3/4" cherry veneered MDF. We could beef up the corners where the 1/4 round goes with a 1x1 triangular strip on the inside corner and secured with biscuits.

One other thing I was thinking might be cool would be to drill flat-bottomed holes in the front baffle to just shy of the veneer and sink small high carbon steel slugs down to the bottom of the holes. Plug 'em up with dowels. Now I could build grill frames from softwood and add soft magnets to the back on the corners and midway on the long side, like the grills on my KEF R500's have.

 

[Swerd]

One other thing I was thinking might be cool would be to drill flat-bottomed holes in the front baffle to just shy of the veneer and sink small high carbon steel slugs down to the bottom of the holes. Plug 'em up with dowels. Now I could build grill frames from softwood and add soft magnets to the back on the corners and midway on the long side, like the grills on my KEF R500's have.

Parts Express sells a set of magnets to attach a speaker grill. https://www.parts-express.com/parts-express-magnetic-grill-guides-0395-dia-x-02-h-8-pcs--329-045

 

[highfigh]

Parts Express sells a set of magnets to attach a speaker grill. https://www.parts-express.com/parts-express-magnetic-grill-guides-0395-dia-x-02-h-8-pcs--329-045

Rockler has them too, in several diameters. FYI for anyone who might want to tap them into a hole with a hammer- they're extremely brittle.