My Modula MT build..with a few Q's

[rob17]

I started my modula mt's this weekend. I went with the pe box design but I think I messed up on the depth. The depth of mine are 11-1/4" so with the front baffle they will be 12". I think what I should have done was to make the box depth 12" for a total of 12-3/4".

Is the way I did it fine or should I start over?

Here are a few pics. This is my third speaker build and I am 18 so be easy on me.














Another question should I make the front baffle 3/4" or 1". I have mdf in both sizes so it does not matter to me. Also what is better for the woofer cutout, a round over or a chamfer? I have round overs in 1/8", 1/4", 3/8", 1/2" and 3/4" and I have two sizes of 45deg chamfer bits all are Freud and are in good shape.

[ThomasW]

Hi,

I split your post from the main thread so it gets more attention.

The options are

1) leave the box as is and live with the slightly different port tuning

2) change the port length slightly to accommodate the bigger box.

3)if you haven't permanently attached the fronts or backs carefully run the box through a table saw to cut down the depth.

[Dennis H]

Nice looking job so far, Rob. PE uses a 1" baffle rabbeted 1/2" into the cabinet. If you just glue it onto the front, that will recover 1/2" of the missing 3/4" and I don't think 1/4" net missing depth is enough to worry about.

A chamfer bit is good for the back of the woofer hole.

Bigger is better for the front roundover or chamfer. 3/4" is good although PE uses 1/2". It's all about helping to eliminate diffraction when the sound from the tweeter hits a sharp edge.

[Rolex]

Maybe I missed something, but the original poster is stating that he built the boxes too small. He has an inside depth of 11 1/4" while it should have been 12". Both reponses above talk about how to make the cabinet smaller while they should be disucssing ways to make it bigger.


Rob, you could try adding a 3/4" filler strip all the way around the face of the box, and then put the baffle on. Not pretty, but depending on your choice of finishing, it could be hidden fairly easily.

[rob17]

So then if I glue the baffle on to the front then I will gain a 1/2" of what PE lost when they dado the back of it. So I will be short just 1/4" which equates .019ft^3. So I don't think that will be too much different.

What do you guys think?

[ThomasW]

It's not enough difference to be of concern.

[JonP]

A note on the baffle thickness... having both, go for the 1". You want a good, solid platform for those drivers. Thicker is more stable, will vibrate less, which makes for clearer, undistorted sound.

[Xander]

A note on the baffle thickness... having both, go for the 1". You want a good, solid platform for those drivers. Thicker is more stable, will vibrate less, which makes for clearer, undistorted sound.

Only if you can chamfer out enough MDF to give the woofer some room to breath in the back. If the baffle is too thick it will choke it, causing more issues than it solves.

[1Michael]

Always make your baffles at least double thickness :T

[rob17]

Always make your baffles at least double thickness :T

Are you suggesting 2" or 1.5"?

Anyhow I got them veneered this weekend. I used blistered Brazilian mahogany. They turned out gorgeous I think. I put one coat of polyurethane on them to seal them up and then I will do the cutouts for the ports.

I got the woofers friday and the binding posts cups from PE. I cut the front baffles and made them a 1/4" bigger in length and width. So I will glue it on to the boxes and then use a flush trim bit on the edge and then use the 3/4" round over on it. First I will cut the driver cutouts and things. I should have the rest of the stuff from madisound tomorrow or something. So this weekend should be fun.

a few pics-

[Hdale85]

Looks pretty nice

[JonP]

Cool... they look great!

I did mine in African Mahogany... a striped or ribbon figure, it was nice stuff. Actually glued the baffles on, roundovered just the long sides, and did a solid veneer wrap around. Lost the benefit of the roundover on the top and bottom of the baffle, but it is a nice look.

I'd say 1" to 1.5" would be good, but 2" would be starting to be overkill (though depends on who you ask!). Mine were done with 5/8" Baltic Birch, with a two layer laminated front baffle at 1.2". The Birch is somewhat stiffer. Still, you notice a bit of sound energy if you put a mechanics stethoscope near the drivers while playing. But, they are pretty close to quiet.

[rob17]

I will continue on with them this weekend. I am going to stick with the 1" baffles I cut last weekend and I will hopefully get the driver cutouts done. I finally have all the parts for the speakers and crossovers so I may assemble the crossovers this weekend or at least get them laid out. I bought some WBT 4% silver solder on ebay the other day. Is it worth while to use that on the crossovers?

I am going to use 3/4" pe sound dampening stuff on the inside walls, is that ok? I also read in the main thread that you should put a small wad of polyfill behind the woofers. Any idea how much? I have some left over from my sub.

One part that I dislike about college is the fact that I am away from my shop. I used to be able to come home after work and school and work on what ever projects I had. It was so nice to do. Luckily my school is only a hour and a half from home so I can come home on the weekends.

[rob17]

Today I got a third coat of polyurethane on the boxes. Last night I got the binding post cup holes cut and the woofer holes cut. I have to cut a chamfer on the back of those now.

Here are some pics:







Now my current issue is that the layout given for the baffles in the main thread is that the tweeters overlap the woofers by 1/2". Can I move the tweeter up a bit or over? The dimensions I went by where that the woofer was to be 1" below center and the tweeter is 4" above center and offset 1". How far can I adjust the tweeter without and adverse affects?

Edit: Sorry for the double post, can an admin merge it?

[ThomasW]

I don't know what you want merged?

[rob17]

I don't know what you want merged?

Just the two posts, or you can just keep it the way it is. I just figured you guys where strict around here about double posting.

[ThomasW]

Throw me a bone here, I'm not psychic, I don't know what 2 posts you're referring to or where they are??

[JonP]

Now my current issue is that the layout given for the baffles in the main thread is that the tweeters overlap the woofers by 1/2". Can I move the tweeter up a bit or over? The dimensions I went by where that the woofer was to be 1" below center and the tweeter is 4" above center and offset 1". How far can I adjust the tweeter without and adverse affects?

Uh... dosen't sound right. There may be a couple of dimensions, one of which might not be right. This is sounding vaugely familiar, but if you find the "official" dimensions, you should end up with 1/8 - 1/4" of space between the woofer and tweeter. And, that's where I ended up...

[rob17]

I was going by the dimensions that Jon Marsh had given,

The tweeter center if 4.5" from the top, offset 1" from the center (for the EM; the Modula is offset 3/4" ).

Woofer is centered laterally; center is up 7" from bottom edge.

The baffle dimesions are 17" tall by 10" wide. PE enlcousre is 12.5" deep.

I moved the tweeter up 3/4" so now there is a 1/4" gap between the two. On the next page of that thread Jon says there should be no more then a 1/4" to a 1/2" gap between the two.

Here is the chamfer on the back of the woofer:



The driver layout:



And the cutout of the tweeter with a recess for the terminals.



Finally, Madisound has been out of the 8ohm Eagle resistors for awhile now. Can I go ahead and substitute those with the 8.2ohm Mundorf mox ones? They also have the sand cast ones.

[JonP]

Ah, that's looking familiar....

You could series a pair of 4's, or parallel a pair of 16's, if available. Not sure how much difference a 8.2 would be, I'd have to look at the crossover. It might be not a big difference, or it could be sensitive.

Too bad Jon isn't visiting on a regular basis to give a quick answer.

[ThomasW]

Too bad Jon isn't visiting on a regular basis to give a quick answer.

The answer is the same as it is every time this question is posted.

All parts are made to certain tolerances. Look at the tolerance of the component listed. If what's needed is within the normal tolerances use the substitute part.

[rob17]

I just ordered the Mundorf ones. They are 8.2 with a 2% tolerance. The eagles have a 5% tolerance. So the eagles would be between 7.6 and 8.4 while the Mundorf ones are between 8.36 and 8.04 so I am withing the tolerances of the listed components. Thanks Thomas!

[JonP]

The answer is the same as it is every time this question is posted.

Sorry I didn't further the discussion by stopping to make that calculation myself.
It was late and I was lazy... I'm even in the electronics industry and do these kinds of assessments all the time, so I do deserve some embarassment... ops:

Tom is entirely correct... no need to buy 4 resistors for 2...

[rob17]

This past weekend I got the holes for the ports cut, another coat of polyurethane on, painted the bottom and the cutouts in the back black and got the crossovers wired. Wiring took longer then I would have hoped, most of the evening on Saturday.



With the port in



Painted the bottom with a rust-oleum flat black



and one of the crossovers, tested them both and they worked the first time around!

[dawg1161]

Looking good, You will love the sound of these.....I am going to build new cabinets so that they will be towers and maybe buy more parts and use original cabinets as rear surrounds ?

Keep up the good work.....