My Morel MTM Project

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Just another Moderator
Joined 2003
Paid Member
OK so I’ve been working on this for what seems like forever. I recently built a gainclone in what for me was record time. I attribute that mostly to the fact I put up a post showing what I was doing, and felt motivated to post progress reports ;) so I’m hoping if I start a thread on my speaker project maybe it will magically accelerate in its completion ;)

On the how long I have been doing this project well, I started thinking about it back before I joined up here at diyaudio (and I joined in Aug 2003). The first post I made here was a question on the focal 6W4311 which was what I was thinking of using for the mid in a WMT config. I’d already decided I wanted to use a morel tweeter at that stage, but was thinking an MDT33 at the time, and the woofer was already decided as I had two perfectly good Vifa M26WR09-08’s. I had some concerns about difficulty of crossing over the focal, as this was to be my first foray in to xover design, and I was heading straight into the newbie trap of going for a 3 way ;) (though in my defence did have a lot of practical, experience (without the theory behind it) at that stage ;) )

I hadn’t considered the Morel MW144 at that point because I thought its sensitivity was too low, that was before someone suggested an MTM to bring up the efficiency level. After reading up on MTM’s I decided the MW144 was a good choice.

Though not strictly shielded it has a very low magnetic field due to the dual magnet setup, and these speakers will be in close proximity to the TV (and I may decide to make a centre and surrounds at a later date), this limited my choice of drivers somewhat dramatically (or so I believed at the time).

So what did I decide on in the end?? After contacting the Australian Morel distributor, I decided on an MTM with MW144’s and DMS37s. The DMS37 is a horn loaded tweeter, which was designed by the Australian Distributor of Morel. He designed it so that if you flush mount the tweeter it is time aligned with MW144’s which are surface mounted. As I was initially thinking I’d try a 1st order crossover (which I now think is impractical with these drivers, though I haven’t yet completely ruled out the possibility, some notch filters may make it workable) this was a huge incentive to use the DMS37 over the MDT30 or MDT33 (and the DMS37 is shielded too). I also decided to make the MTM's stand alone, and make separate cabinets for the Vifa 10" drivers, crossing over somewhere between 200 and 300 Hz with a bi-amped setup.

I purchased the drivers around Nov 2004, I made a test baffle over Christmas, whilst I had access to my Fathers tools, (mostly to test the circle jig I made, and make sure I could accurately cut rebates)… shortly after this I made a test box to match the baffle (the baffle was made with no original intention of making a box so the box shape was somewhat different to my final design). I did lots of tests and didn’t achieve much at all ;) apart from learning that rebating the tweeter into the baffle with a flare (because at that stage I wanted to rebate the woofers and maintain the time alignment) was a bad idea!!!!

Skip forward to August 2005 and I went to my parents place with a couple of sheets of 25mm MDF and the drivers and made extensive use of my Fathers triton workbench and router. Lots of activity for a couple of weeks and then back to not much, which is where I am now. I’ll post some pics from along the way starting with the drawings I did in Aug this year of the cabinets.

Well this has ended up a mighty long post so I’ll give it a rest for now ;) well I might post the second dawing...

Tony.
 

Attachments

  • plan1.1.gif
    plan1.1.gif
    35.7 KB · Views: 2,800
Just another Moderator
Joined 2003
Paid Member
Ok here is the second cabinet drawing. I actually changed the positioning of the woofers slightly the dimention showing the distance between the center of the tweeter and the center of the woofer is 122mm which allowed for 4mm between the edge of the woofer and the edge of the tweeter, I cut it to 120mm giving a 2mm distance between the edges of the drivers.

I decided to not offset the drivers due to stuff I read on Duntechs web site on what this does to the dispersion of the sound. After simulating in BDS I decided I could live with the extra ripple that I'd get, and thought I could try the felt trick to reduce diffraction effects, I do plan on chamfering the edges of the baffles.

Also not shown in the plans is corner bracing, I put quarter round in some of the corners, this was a last minute decision and could have been done much better (mitering etc) but it adds some strength :) I also glued a 25mm square MDM block along the front baffle below (or above) the drivers, I've since decided this was not such a good idea, and have cut it back somewhat with the dremel ;)

Tony.
 

Attachments

  • plan2.1.gif
    plan2.1.gif
    36.6 KB · Views: 2,645
Just another Moderator
Joined 2003
Paid Member
OK and one post to show I actually have built something ;)

The partitions between the midbass' and tweeter are made from two sheets of 12mm MDF laminated together. The reason I did this was so I could get the MW144's close to the tweeters without being too close to the edge of the partition. By using two pieces of 12mm MDF I could make the tweeter side peice a bit shorter and hae room for the tweeters basket, the partitions also serve the purpose of bracing, and allowed me to use golden ratio (one of not the) dimentions for the midbass enclosures dimentions.... funny thing that, I actually decided to make it using all prime numbers, when I did a search to find out whether this was a standard practice, I discovered that my particular primes were one of the acoustic golden ratios :)

I actually did all of the gluing in one go for what you see in this pic... was quite frantic, and I was sweating quite a lot by the time I finished, probably took an hour from start to finish...

This was the box that I remembered to drill the holes for the speakers, and insert my hex nuts into before I glued it together ;)

Tony.
 

Attachments

  • img_0222.jpg
    img_0222.jpg
    98.5 KB · Views: 2,679
Just another Moderator
Joined 2003
Paid Member
and the current status

just to be complete I thought I better post a pic of what it looks like at the moment......

the straps you see are holding the rear baffle on.... I haven't glued it on yet as I'm not yet 100% happy with my driver fixing bolts and nuts... I've been doing tests with not 100% sealed boxes, but the tests I've done have been promising. Will hopefully get the bolts sorted soon, and then glue the backs on, and start applying the veneer, and finally champher the front baffle.

Then the serious tests for the crossover design can begin!!

Tony.
 

Attachments

  • mtm1.jpg
    mtm1.jpg
    89.9 KB · Views: 2,695
Just another Moderator
Joined 2003
Paid Member
Oh and another thing that deviates from the plan, I rebated the sides where the partitions fit in. Not really visible in the pic that I posted of it being glued together.

the rebate itself is only about 3mm deep, but it made it much easier to slide the internal baffles in and make sure they were straight!! My prototype box I just but jointed them and getting them square was a real pain. Had some problems with the fence on the Triton workbench not being 100% square which resulted in about .5mm difference front to back (between the two sides) but it wasn't enough to cause any problem.

Tony.
 

Attachments

  • rebated_sides.jpg
    rebated_sides.jpg
    67.6 KB · Views: 2,442
Just another Moderator
Joined 2003
Paid Member
Yesterday for whatever reason (procrastination??) I decided to revisit my BDS sims as I had never been that happy that my measured response seemed to agree with the simulated baffle diffraction response.

What I found by accident was that when I used the lowest complexity source (ie point source) but still used quadruple sampling, I did infact get what appears to correlate with my measured response. The magnitude is different, but I think this is driver related, but there is a definite (I belive) correlation between the sim and the measured result. Note that the scales aren't the same, but by skewing them like this it is easier to see a correlation. The thing I'm happy about is that when I sim with a 22mm chamfer (the size I'm probably going to use) the response flattens out significantly, how much this will help in the real world I guess I'll have to wait an see :)

attached sim and actual measured (gated) repsonse of the woofers.

so at least with this project it appears that the best model to use for the drivers is the point source one!! Interestingly the tweeters seem to match more closely when using the combined source model, I would have thought the tweeters would be closer to a point source than the woofers :rolleyes:

Tony.
 

Attachments

  • sim_vs_measured.gif
    sim_vs_measured.gif
    30.8 KB · Views: 723
Just another Moderator
Joined 2003
Paid Member
I'm using BDS (Baffle diffraction simulator) for the sim graphs I posted, for the actual modeling of the enclosure I used unibox. Both are excel spreadsheet based, which unfortunately rules some people out.

BDS here ---> http://www.pvconsultants.com/audio/diffraction/downloadbds.htm

Unibox here ---> http://home20.inet.tele.dk/kou/ubmodel.html

there is a lot of good stuff on the FRD consortium page ---> http://www.pvconsultants.com/audio/frdgroup.htm where I found both of these modelers :)

The magnitude of the difference between the simmed and the actual is quite a bit different (unfortunately worse in the real measurements) but the shape of the curve is quite similar, too similar me thinks to be a coincidence :)

I've just been cutting up bits of MDF to use as load spreaders for doing the veneering, I wish my speaker terminals would hurry up and arrive!! I now really appreciate my Dad's Triton workbench, using a jigsaw is not quite as accurate ;) at least it's not critical for this application.

Tony.
 
Just another Moderator
Joined 2003
Paid Member
No excuses now!!

Well my order from from Brass and Granite audio just turned up :) very happy!!

appart from the need to go out and buy a router and some bits (as my Dad's is 7 hours drive away) I don't think I have any excuses left!! (oh and I need to go get my M4 Button heads which should have come in today too :)

as you can see from the pic I bought a few extra terminals (though I will be using 6 pairs on these MTM's I'll have enough for the Woofers too, a center and two rear effects speakers if I ever get around to doing a full HT setup... thought I might as well get the most of my shipping $

Glad I didn't glue the backs on before getting the terminals, they have 30mm shafts so I will need to countersink the inside of the shaft hole to take the first nut.... I'll have to be very carefull on the depth too... hmmmm I'll need to think about that one, as I don't have a drill press... might be time to get the cheapy one from bunnings that you can mount a handheld drill in.

I'm off to do some work!!

Tony.
 

Attachments

  • no_excuses.jpg
    no_excuses.jpg
    77.6 KB · Views: 755
Just another Moderator
Joined 2003
Paid Member
Well It has been nearly four years, but I decided it was time for an update ;) I pretty much did nothing at all on my speaker project from The last post, Nov 2005 until probably about 6 months ago.

I thought that I needed to veneer the back bafle before I glued it on due to the tightness of the tweeter compartment and the feeling I could not connect the speaker terminals after the box was glued together, My veneer after being rolled up for nearly 4 years was rather curly when I cut it. I tried to flatten it but failed, finally tried a different approach (spraying with 90% water 10% glycerine and clamping for a few days) and it flattened out nicely. However I decided to try mounting the terminals with the backs clamped in place and found I could do it with no problem. The thing that prompted me to do this was the worry the baffles would warp after veneering if they weren't already attached to the box.

Anyway aside from all that I had never been happy with the dirver cutouts, or the fit for the rear baffle. I decided to attack the chamfers on the driver cutouts with a tungsten carbide tip on the dremel, and now have much nicer flares on the inside of my front baffles. After a lot of sanding (only one box so far) I got the rear of the box so that when the baffle was sitting on it there was virtually no differences (few thou at most), I was happy enough with it and this afternoon glued the rear baffle onto the one box that has been completed.

Tonight I also soldered on the connectors for the internal wiring for one box (just the two cables for the woofers, I'd already done the tweeter cables for both boxes.

I've attached a few photos of recent activity, showing the old flares and the new ones, and also my makeshift sanding block ;)

Also the shot showing the original flare, if you look on the left you will see another mod I made that wasn't on the original plan. I put some extra blocks in, in the tweeter compartment which are on the sides and glued to the font baffle.

Tony.
 

Attachments

  • DSC_4334.jpg
    DSC_4334.jpg
    74.7 KB · Views: 904
  • DSC_4353.jpg
    DSC_4353.jpg
    79.3 KB · Views: 845
  • DSC_4346.jpg
    DSC_4346.jpg
    98.4 KB · Views: 854
  • DSC_4358.jpg
    DSC_4358.jpg
    73.7 KB · Views: 808
  • DSC_4363.jpg
    DSC_4363.jpg
    111.9 KB · Views: 752
Just another Moderator
Joined 2003
Paid Member
OK Well I have made some progress since the last post. I have done a LOT of sanding since then. Glued the rear baffles on. More sanding, Filling, more sanding, and today I have decided to take the plunge and try putting the first peice of veneer on.

I'm doing it on the bottom of one of the cabinets. I originally wasn't even going to bother veneering the bottoms, but decided that A) it would mean that it was properly sealed on the bottom, and B) it was a good place for my first attempt, as if I completely screw it up then at least it isn't visible ;)

The first problem was that the front baffles were around 1mm to short (as mentioned earlier in the thread, I tried building up with filler but it hasn't worked particularly well, and I'm going to be chamfering the front baffles any way so decided to just go ahead anyway and forget about the front bit ;) Chances are this is more likely to be an unmittigated disater than a complete success ;)

I noticed last weekend when sanding, that the sides of my cabinets have small dips in the middles of the pannels.. I'd really like to have them dead flat, but I just don't know if I can do that much sanding :( , and after my dodgy filling I don't think filler is an option, but I'll probably regret it if I don't so I suspect there is more sanding to go before I takle the veneering of the main parts of the cabinet.

Anyway here are some more photos of the progress.

The 1st shows that a speaker box is an attractive drawing surface for a 21 month old ;) the second is the back of the box after a LOT of sanding almost perfectly flat and ready for gluing the baffle on. Said 21 month old can be seen in the background playing with the dirt in the potplant... Third shows dodgy attempt at filling the area where the baffle is uneven. fourth more filling (I screwed the second baffle after a nightmare of a time getting the first one lined up. Thanks To AndrewT for reminding me of the value of screwing and gluing. and finally the fifth one shows my efforts today. No glue seepage which is good in one respect as their won't be contamination of the other veneer if there is no seepage when I get to it, but bad in another as I'm not sure if I have used enough glue! I guess time will tell!

Tony.
 

Attachments

  • DSC_4372.jpg
    DSC_4372.jpg
    68.1 KB · Views: 235
  • DSC_4373.jpg
    DSC_4373.jpg
    33.1 KB · Views: 204
  • DSC_4407.jpg
    DSC_4407.jpg
    66.6 KB · Views: 193
  • DSC_4443.jpg
    DSC_4443.jpg
    42.6 KB · Views: 175
  • DSC_4408.jpg
    DSC_4408.jpg
    37.6 KB · Views: 159
Just another Moderator
Joined 2003
Paid Member
Well that went better than it could have ;)

Veneer seems to have stuck solid. No bubbles it even seems to have stuck down at the ends where it rolls over a little (I find it it is very hard getting a completely flat sanded surface, always seems to round off at the edges somewhat).

I went to do the second box and discovered to my horror that the top of it had a really deep (I assume sanding) gouge in it :( so I once again got out the filler and filled it up. Though I took a different approach this time. Rather than using the spatular and over filling and sanding down hoping it would be flat, I ran the straight edge over it and it pretty much took away all the filler it didn't need and left what it did.. heres hoping anyway. So the second box is now going to have to wait till next weekend, as this filler takes 48hours to properly cure.

Pic attached of the result.. Will trim once the glue has had 24 hours to cure.

I used Bostic MDF glue slightly thinned with a little filtered water and applied with a small foam paint roller. I then placed the piece of veneer on the surface, smoothed it out with my hands, and then rolled with a wooden rolling pin. finally put the caul on and clamped for about two hours. I'll try trimming it with my veneer trimming bit and router... hope that goes ok!!

fist pic is the other piece of MDF for the bottom of the second cabinet, not 100% flat, but very malleable after treating with 90% water and 10% glycerine, and flattening for a couple of weeks. The second is the first box with veneer attached, showing clearly the rounding on the ends :( Oh well at leat it won't be a problem at the front once I chamfer the baffle :) also note the first is probably a better indication of colour. Was taken in full sun, the second was in the shade after a lot of smoke from a bush fire came along.

Tony.
 

Attachments

  • DSC_4445.jpg
    DSC_4445.jpg
    107.5 KB · Views: 214
  • DSC_4448.jpg
    DSC_4448.jpg
    458.9 KB · Views: 229
Just another Moderator
Joined 2003
Paid Member
slowly making progress :)

Well I decided to get out the router and use the veneer trimming bit today (note I have never done any of this before so it is a learning experience) :) It worked very nicely along the grain, but I was a bit concerned with the result at first when trimming accross the grain... ended up looking very splintery and rough, but a quick go with some 220grit glass paper and a sanding block cleaned it up very nicely and all was well.

One very important thing I discovered was not to have the speed on the router set too fast! I have a variable speed router and it seems that speed setting two is about right. One was too slow and above three starts to burn the edge of the veneer (as can be seen in the attached photo).

Since I had the router out I decided to do a test with my chamfering bit (it is a huge one, 1/2" drive gives a 22mm chamfer (that is in 22mm and down 22mm not the distance along the chamfer). I got it for Christmas 4 years ago and till now has never been used. Again some important aspects. It worked best on about speed setting three. Additionally the direction of travel of the router is critical, it must be moving so that the leading edge of the bit is not biting in (this is quite possibly why I had the problem accross the grain with the veneer so will try this on the next bottom piece), if so it gets a very jerky and uneven cut. effectively cutting with the trailing edge is required.. Using a piece of scrap to work out which way works is mandatory! :) again attached is a pic of the piece of scrap which I sanded lightly with 220 grit glass paper after finishing the cut. I think the result when applied to the baffle will be quite acceptable :)

The veneer split somewhat on the font when I trimmed it, but this did not suprise me in the slightest (as previously mentioned this edge had been built up with filler and still wasn't flat). As the chamfer will be 22mm back, almost all of the problem area will be cut away anyway so I'm not concerned.

Tony.
 

Attachments

  • DSC_4450.jpg
    DSC_4450.jpg
    79.8 KB · Views: 247
  • DSC_4455.jpg
    DSC_4455.jpg
    277.9 KB · Views: 206
  • DSC_4452.jpg
    DSC_4452.jpg
    105.8 KB · Views: 223
  • DSC_4453.jpg
    DSC_4453.jpg
    55.1 KB · Views: 288
Just another Moderator
Joined 2003
Paid Member
Hi Badman, It may not be as bad as it looks in that shot, I had a hard time getting a decent shot of the woofer, and the camera tends to flatten the perspective quite a bit making things look worse... This one didn't make the cut quality wise, but probably is the best for showing how much (or little) breathing space there actually is.

It wouldn't be too late to take out more material, but it would be quite a lot harder now that the backs have been glued on, and it wouldn't actually be possible to inspect the results with the woofer inserted ;) Getting the dermel (or whatever) in through the front speaker cutout would probably be a bit awkward too.

I'm pretty pleased how it is coming along now, though I just had a bit of a nerve racking moment gluing on the rear baffle veneer. I smoothed it all down with my hands, went very nicely, realised I'd forgotten the rolling pin, raced in to get it, and when I got back the veneer had curled up on both long sides rather severly, probably should have wiped it down with the damp cloth I used for cleaning the surface but, somewhat panicked when it wouldn't stay down and just quickly shoved the caul on and clamped it... hopefully that wasn't a mistake! Oh well live and learn! I'll find out when I take the clamps off I guess... Might be able to iron it if there are any problems.

Tony.
 

Attachments

  • DSC_4341.jpg
    DSC_4341.jpg
    73.2 KB · Views: 358
Just another Moderator
Joined 2003
Paid Member
Hi Terry, ummm yeah it probably is... This was something I was concerned about originally even with my prototype but these drivers have strange flanges that I hadn't encountered before and I really wasn't sure how to deal with them. The only way I could see that I could get a seal on them was to use the flange on the inner edge right next to the basket.

I've attached a bunch of photos here which show the woofer (note it really is an MW144 it is mis-labled!) The drivers did not come with gaskets (from memory Terry Paget (Aus distributer told me he uses silicon, I'd have to go back through the emails it was a long time ago!).

SO probably I should have a thick narrow gasket just in the channel where the screws are, and my cutout should only be that wide (it did worry me that only the very thin rim of the basket would be in contact with the baffle if I did this)... That was what I thought originally, but I'm pretty sure TP told me to use the inner surface for the seal, could be wrong though, I'll have to find the emails...

If that is the case All is not lost, I can draw another circle as an absolute limit where to cut to and probably just dremel out to that. Some 6mm thick neoprene carefully cut would probably suffice for a gasget.

Thanks,

Tony.
 

Attachments

  • DSC_4463.jpg
    DSC_4463.jpg
    90.6 KB · Views: 206
  • DSC_4462.jpg
    DSC_4462.jpg
    98.2 KB · Views: 196
  • DSC_4461.jpg
    DSC_4461.jpg
    76.8 KB · Views: 264
  • DSC_4465.jpg
    DSC_4465.jpg
    54.3 KB · Views: 157
  • DSC_4466.jpg
    DSC_4466.jpg
    69.3 KB · Views: 123
Just another Moderator
Joined 2003
Paid Member
OK well it seems that the veneering of the back of the box this afternoon was successful. I guess once I trim the veneer I will have a better idea.

I've attached some photos of this afternoons effort, sans the one where the veneer curled right up which I didn't take because I was too busy panicking that the glue would dry as it was a warm afternoon.

The first problem I had to deal with was that I had some splits in the ends of the veneer, these were dealt with by placing some 3M magic tape on the non glue side, being carefull to make sure the split was as tightly together as possible before applying the tape.

I cleaned down the MDF with a damp sponge cloth, and also both sides of the veneer, being careful to fully ring out the sponge cloth so as to not get any surface too damp.

Then I mixed the glue with a little filtered water and applied with the paint roller. Smoothed down the veneer with my hands and it flattened out nicely. forgot the rolling pin as mentioned in a previous post, and discovered to my horror that the veneer had curled up by the time I got back, and wouldn't stay down by itself... in hindsight, I think at that point I should have sponged down the non glue side and it probably would have flattened back out again, but I instead ran the rolling pin over it (to no effect) and then wacked the caul on and clamped it for approx 1.5 hours.

I would have left it a bit longer but for the thunder storm that was coming up, and decided it was time to bring it inside! The result appears to be a completely flat, no bubbles surface which seems properly stuck down..

another barage of photos below :)

1st shows taping of splits. 2nd the setup before proceeding (sans rolling pin). 3rd surface of box after applying the glue. 4th clamping. 5th the end result. Note that for the back surface I didn't worry about matching the grain (note it is running the opposite direction to the bottom pannel) the veneer for the sides and top were cut from one continuous piece so will wrap around so to speak. I figured it was less important for the back..,

Tony.
 

Attachments

  • DSC_4457.jpg
    DSC_4457.jpg
    59.6 KB · Views: 135
  • DSC_4458.jpg
    DSC_4458.jpg
    88.3 KB · Views: 236
  • DSC_4459.jpg
    DSC_4459.jpg
    72.2 KB · Views: 141
  • DSC_4460.jpg
    DSC_4460.jpg
    85.2 KB · Views: 122
  • DSC_4470.jpg
    DSC_4470.jpg
    60.4 KB · Views: 231
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.