Looking to build a 3.5 way speaker system

[dmm]

I want to first thank Jon Marsh for uniting the thread for me.

1st question. Am I out of wack with my science thinking that the directional line of intersection of the individual speakers is important? Note the curved line in the drawings.

2nd question, yes that is the port alongside the tweeter, since I planned to house the crossovers behind and within the upper cabinet for accessability, is this that bad?

3rd question, If in fact I return the port to the rear, can I end it at the absolute back of the box, effectively shortening that section inside the box, or does it have to be fully set within the interior of the cabinet itself?

I see so many different new designs from manufacturers and DIY people that at times seem to contradict each other, such as tilted up, tilted forward, straight up, set back from the woofers. Hard to know what really works.

My inclination is to build the middle side view with the front looking like it is shown. The forward tilt in the MTM is 4 degrees and the up tilt to the bottom box is 10 degrees up. Any thoughts?

I am getting very close to at least doing the front baffles for the MTM. I have in my possession 1 3/4" solid mahogany that I will glue up. This will allow me to incorporate my sliced edges very simply.

I intend to build just the MTM first, so if possible, I might be able to send them somewhere to get tested.

Jon, I have your complete thread on the Modula's, is there one crossover in particular you think I should build which would adapt better to this design out of all the changes you went through?

FYI, the MTM cabinets have a volume of 1.028646 cubic ft inside.

[dmm]

I've glued up the baffles for the MTM top boxes but have not had an opportunity to do the bevels yet. Will post pics when possible.

[---k---]

Sorry didn't see this a while ago. Not sure if you're still looking for answers.

Tilting the baffle is to time align the drivers. This is important for some crossovers. First order crossovers need time aligned drivers or a delay network so that the sound arrives at the same time. But, assymetric crossovers, like used in almost all the speakers designs found here, you do not need to time align the drivers. It is magic within the crossover design that is beyond my ability to explain. But bottom line, a good design like the ModulaMTM, the crossover fixes the problems with the driver not being time aligned.

You see differnt DIYer's doing differnt things, because there are lots of ways to skin a cat. Speakers are a collection of compromises. You'll see Jon does it one way with one speaker and a differnt way another time to meet different goals.

You do NOT want the port next to the tweeter. You can put the crossover anywhere it will fit in the box.

Not sure what your 3rd question is asking. Best thing is to have the port on back with the flare like Jon shows. Inside the box, you want the other end of the port atleast the same diameter away from all the walls.

[dmm]

Thanks for the advice on the forward tip of the MTM, saves me some further complications on the box construction.

That means that I will probably not bother to tip the bottom either.

As for the port on the front, I've already decided to return it to the rear. Since I intend to extend the box on the MTM cabinet so it is more in size with the bottom cabinet, (the interior of the cabinet will be just at 1 cubic foot) I was wondering if I can place the port on the outside of the back end of the box while maintaining the proper length of port, it would be occupying some of the space of the crossover cavity and not extend in to the MTM cabinety as far as normal.

I know the previous is convoluted, I will try to show what I mean in a drawing soon.

[ThomasW]

If the 15" is being use there's no need to use a port in the MTM module. Reason being the MTM port is tuned to frequencies that the 15" will be playing.

[dmm]

I was going to use the most recent crossover plan for the Modula's and since they have a port, I thought it was necessary.

[JonMarsh]

The port only affects the behavior below about 70-80 Hz, and does not interact with the crossover. With the configuration you're planning, the port is unnecessary.

[ThomasW]

Porting increases output at the tuning frequency (around 32Hz in the case of the Modula MTM).

In your speaker the 15" will be reproducing frequencies at and above the port tuning of the Modula MTM. So it's pointless to port the MTM section since no sound will be coming out the port.

[dmm]

One thing I had in mind, I might be using the MTM's as stand alone speakers for a while since I am building them first.

Won't the loss of the port mean an entirely new crossover for the MTM?

[---k---]

Won't the loss of the port mean an entirely new crossover for the MTM?

Nope.

[ThomasW]

Won't the loss of the port mean an entirely new crossover for the MTM?

In this instance there's no relationship between the alignment (sealed vs ported) and the MTM crossover

The manifest lack of understanding even elementary aspects of speaker design, prompts me to strongly suggest you buy and read Ray Alden's book "Speaker Building 201" before you go any further.....

[dmm]

For what ever help it might be to those who read this post, here is my research list.

"Building Speaker Systems" by Gordon McComb 2nd and 3rd editions

"Advanced Speaker Systems" by Ray Alden

"Great Sound Stereo Speaker Manual" by David B. Weems

"Designing, Building and Testing Your Own Speaker System" by David B. Weems 3rd edition

"Speaker Building 201" by Ray Alden

"Loudspeaker Design Cookbook" by Vance Dickason 7th edition

"Bullock on Boxes" by Robert M. Bullock III

In addition there are numerous websites, like this one, giving out advice and information.

You can never have too much information. Asking questions only helps clarify that which is not entirely clear.

[JonMarsh]

Sometimes it takes a bit of time and experience to connect the dots on complex topics.

[dmm]

noticed that Parts Express has a sale on plate amplifiers. Anyone care to comment on what wattage I will need for my JBL 2231-h woofers?

[dmm]

here is an update on the MTM part of the project.

I glued up the mahogany and have now beveled the faces. I did this by drawing the bevel desired, chiseling away most of the area not wanted, then taking a belt sander with 60 grit paper to grind it flat. I then hand sanded all of the face with 100, 150, then 180 grit paper. The picture shows 1 coat of jet mahogany gel stain applied.

I cut out the speaker holes with a Jasper jig and my plunge router. I ordered a bevel bit to add a bevel to the inside or back side of the woofer openings.
I decided to go in to my stock of wood for the case work and have glued together 2 half inch sheets of baltic birch plywood, for the sides. Plan to use pieces of 3/4" baltic for the top, and 2 glued up pieces of 3/4" baltic for the bottom.

will update when I cut it out.

I need to downsize my picture, it's coming.