New DIY MTM Towers designed by Dennis Murphy and Paul Kittinger

[Alex2507]

Roadrune, I'm interested in what you're using for a router bit on the mitered corners. I think I know what's going on but I don't think I've ever seen that method of joinery in action. Nice going.

 

[roadrune]

Hi, i use this bit http://www.precisionbits.com/lock-miter-router-bit-45-degree-large-yonico-15122.html

It was a PITA to set up, but offcourse youtube could help

 

[Alex2507]

It was a PITA to set up

I spend way too much time thinking about that joint. No pun/s. That has to be the ugliest cloud of MDF dust ever but locking a miter like that would be a dream come true for me.


I have the perfect project for that bit.

 

[roadrune]

Once its set, its a great joint. If you are going to use, check out the videos on youtube, helps a lot

 

[FingerlessHackWoodworker]

Try rubbing out the scratches with 0000 steel wool and clear untinted Watco Danish Oil. It may not remove all of the scratches, but it will improve things.

The danger with solid hardwood on a closed six-sided cabinet is cracking. The wood will expand and shrink as the humidity changes. MDF has no grain and doesn't expand or shrink, and veneer is more flexible. I don't know what will happen with ¼" hardwood glued over MDF.

Those polyurethane foam grills on mine crumbled and turned to dust a long time ago. That happened to everyone.

Thanks for the tip on the Danish Oil and extra fine steel wool.

You are correct about the nature of wood. I have had success and failure with gluing 3/4" (maybe it was 1/2") onto 3/4" plywood for a TV cabinet. The sides of the cabinet were wrapped with 3/4" Qtr Sawn White Oak and the top was wrapped with 3/4" Cathedral grained White Oak (maybe was Red Oak). The Cathedral grain split very badly. However, the Qtr Sw held up quite nicely as was expected due to the nature of the species and cut. I am also banking on the stresses of expansion to be over come by the glue's strength... hopefully linear force generated by end-grain-expansion will not exceed strength of glue. Also hoping 1/4" thickness is thin enough to act more like a veneer rather than a solid thick piece. I believe a very good sealer or some sort of oil finish should serve as a good vapor/moisture barrier. Banking on the finish being able to suppress enough of the moisture ingress, there by limiting the expansion to a point where it is not damaging.

Question about the braces. I have seen two styles in this thread: square and holy ones. Of these two, it would seem to me that the square brackets give adequate strength and plenty air-gap. Any opinions on the square ones vs. the round holy brackets?

 

[FingerlessHackWoodworker]

Not much happening theese days, but i got both the boxes glued With sides, back and braces, ready for insulation crossovers and terminals.View attachment 18169 View attachment 18170

I do not have enough clamps, so i use everything available to help...
View attachment 18171

All the driver holes are cut, hope they fit....
View attachment 18172

roadrune, thanks for the progress report! It's looking great!

 

[roadrune]

Question about the braces. I have seen two styles in this thread: square and holy ones. Of these two, it would seem to me that the square brackets give adequate strength and plenty air-gap. Any opinions on the square ones vs. the round holy brackets?

You should always go for holy braces, since divine intervention will make the speakers out of this world

But really; the original design says square, so they should be good enough, the round ones is more "because we can"

 

[Swerd]

You are correct about the nature of wood. I have had success and failure with gluing 3/4" (maybe it was 1/2") onto 3/4" plywood for a TV cabinet. The sides of the cabinet were wrapped with 3/4" Qtr Sawn White Oak and the top was wrapped with 3/4" Cathedral grained White Oak (maybe was Red Oak). The Cathedral grain split very badly. However, the Qtr Sw held up quite nicely as was expected due to the nature of the species and cut. I am also banking on the stresses of expansion to be over come by the glue's strength... hopefully linear force generated by end-grain-expansion will not exceed strength of glue. Also hoping 1/4" thickness is thin enough to act more like a veneer rather than a solid thick piece. I believe a very good sealer or some sort of oil finish should serve as a good vapor/moisture barrier. Banking on the finish being able to suppress enough of the moisture ingress, there by limiting the expansion to a point where it is not damaging.

It seems you've had some experience doing this already. Good. I do remember about quarter-sawn white oak being less prone to splitting and maybe is more stable to changes in humidity than straight grain oak. But I've always avoided doing anything like this.

Question about the braces. I have seen two styles in this thread: square and holy ones. Of these two, it would seem to me that the square brackets give adequate strength and plenty air-gap. Any opinions on the square ones vs. the round holy brackets?

I cannot argue with Roadrune's explanation, holy braces lead to divine sounding speakers . Roadrune – when you first listen to your speakers, please tell us whether you hear angels sing, and please also let us know just how many angels you heard. That will help us determine how necessary the round holy braces are .

The most important parts about internal cabinet braces are:

1. That they exist. Don't skip them.
   
2. That they are placed along the length of the cabinet asymmetrically, as shown in the diagram. Don't space them out evenly.
3. That they don't seriously impede the movement of air inside the cabinet.

It looks to me that round holy braces and the square ones both get the job done. Do what ever is easiest with the tools you have.

 

[Swerd]

Hi, i use this bit http://www.precisionbits.com/lock-miter-router-bit-45-degree-large-yonico-15122.html

It was a PITA to set up, but offcourse youtube could help

I always was told that bits like that work poorly with MDF. They apparently work well with plywood or hardwood. I've never tried them. Do they require a router table?

I love your work-in-progress photos! Keep posting more. I am envious of your shop and your skills.

We have one regular here at Audioholics who is from Norway, Haraldo. I believe he lives in Bergen, but I am not sure about that. Haraldo has (apparently) highly developed tastes in speakers, and of course highly developed opinions about them. I, and others, have tried to get him interested in speakers designed by Dennis Murphy, something difficult to do in Norway. I wonder if you are close enough to him, so that he could listen to them one day. Just a thought.

 

[roadrune]

I always was told that bits like that work poorly with MDF. They apparently work well with plywood or hardwood. I've never tried them. Do they require a router table?

I love your work-in-progress photos! Keep posting more. I am envious of your shop and your skills.

We have one regular here at Audioholics who is from Norway, Haraldo. I believe he lives in Bergen, but I am not sure about that. Haraldo has (apparently) highly developed tastes in speakers, and of course highly developed opinions about them. I, and others, have tried to get him interested in speakers designed by Dennis Murphy, something difficult to do in Norway. I wonder if you are close enough to him, so that he could listen to them one day. Just a thought.

I would say the lock miter bit need a table, you could do it with a side fence but it would be realle difficult.
I see what you mean with mdf, couse the edge following the thickness of the plate is really fragile, but if you are careful its ok. Once its glued its strong as hell.

Bergen is my closest "big" city (compared to US cities its small,with a population of about 300.000) and its about an hour and half drive plus 45minutes with a ferry.

Really busy this weekend, and tuesday its back to work offshore for a couple of weeks, so i wont finish them for a while

Thanks for your kind words, im trying my best

 

[Researcher]

They are built for a cinema, however i dont have anything else than the amp yet, so obviously i will test them in my livingroom once they are finished, and then on a Hegel H80. Do they sell Hegel in the US? Fantastic amps, made in Norway.

Never heard of Hegel, but I've been reading some reviews, and that particular amp seems to be a very decent piece of hardware.

Great pics, keep them coming!, are you planning to veneer, paint, bare MDF ???

 

[Alex2507]

I always was told that bits like that work poorly with MDF. They apparently work well with plywood or hardwood. I've never tried them. Do they require a router table?

To me it looked like he used them on MDF. I could maybe see particle board not doing well with that bit but MDF should take a profile without a hitch. I think I know that but you know, the 80's ...

We have one regular here at Audioholics who is from Norway, Haraldo.

Don't let him in your house.

 

[roadrune]

Never heard of Hegel, but I've been reading some reviews, and that particular amp seems to be a very decent piece of hardware.

Great pics, keep them coming!, are you planning to veneer, paint, bare MDF ???

I have no idea, but right now im leaning to high gloss black with grilles covering the entire baffle.

 

[FingerlessHackWoodworker]

You should always go for holy braces, since divine intervention will make the speakers out of this world

But really; the original design says square, so they should be good enough, the round ones is more "because we can"

Laughed Out Loud I suppose I have always been a pretty square guy and the square one seems to speak to me.

 

[Swerd]

… and tuesday its back to work offshore for a couple of weeks, so i wont finish them for a while

Heard about the helicopter crash that took place. If you are flying to an offshore location, we wish you safe flying.

 

[FingerlessHackWoodworker]

Got a good start today. Inner cabinet walls have been cut to widths. Hopefully tomorrow can cut to length and rabbit joint.

 

[FingerlessHackWoodworker]

The most important parts about internal cabinet braces are:

1. That they exist. Don't skip them.
   
2. That they are placed along the length of the cabinet asymmetrically, as shown in the diagram. Don't space them out evenly.
3. That they don't seriously impede the movement of air inside the cabinet.

It looks to me that round holy braces and the square ones both get the job done. Do what ever is easiest with the tools you have.

Swerd, thanks for the feedback!

 

[roadrune]

Heard about the helicopter crash that took place. If you are flying to an offshore location, we wish you safe flying.

Yes, i am flying, but in a different heli (Sikorsky s-92), never really liked flying that much, and this definativly didnt help.

That sayd its the first fatal offshoreheli accident in Norway for almost 20 years, so its about the safest way to travel.

Really sad for those involved anyway.

 

[highfigh]

Thanks.

Then i'll stand clear of oak and go for veneer.

I'm thinking bi-amp since my plan is to build a 7-channel amp, and a cheap and great diy amp is the 2x50w 3116, so i thought i could use 7 of those were i use the same input for 2 and 2 channels, making it 7-channels in but 14 outputs divided in 7 channels (hope this is possible to understand)

If Oak is easier to buy than MDF or other materials, you can use it without needing to worry about resonances by placing the grain of one layer perpendicular to the other. I don't know if you way a way to mill it to 1/2", but that would make a very stiff panel. Well glued, that would be stiffer than MDF.

 

[FingerlessHackWoodworker]

Tip on moving those bloody awkward 3/4" MDF sheets. For those who have never seen this handy little device: (CAUTION, make sure the joint between Stretcher and Load pieces is strongly bonded (long and thicker than standard dry wall screw and glue if you like)... this joint should not consist of any of these pieces being MDF, chip board, or like. I had one of these pieces made from chip board and secured with dry wall screws. Joint failed and luckily did not break my toe, but lost a toe nail. I hate MDF. However, it serves its purpose for speakers.) As The Samurai Carpenter says, "Get out there and build something."