X1 SLAMM Klone

[Smilie]

Will someone please describe the advantages and disadvantages of the Wilson X1 SLAMM MTM module?

I am building an MTM to be used with a sub-woofer with RS180's and the RS28 T's. Does it makes any sense to go to the trouble of buiding an MTM box similar to Jon's X1 SLAMM Klone. Or should the box be a simple design like the Modula or Natalie P?

If there is nothing to be gained by the more complex box, the simpler box is much easier to build.

My crossovers will be active all the way.

Thanks

[JonMarsh]

The complex box is not for the faint of heart or new woodworking hobbyist.

It has potential advantages and disadvantages, in my experience. Diffraction control is more of a problem, and I'm considering retrofiting the surfaces with whispermat type foam. Having a rear ambience tweeter extends the HF power response in the room, but may not be desirable in all situations. Those cabinets are VERY rigid and uncolored (even though mine were made of MDF layered to 1-1/2" and not special phenolic materials), and mine are not adjustable to many "wrong" positions or capable of focusing the crossover lobe downwards, as are the Wilson- I think that was partially necessary for their design becuase they used such a high crossover frequency - 3 kHz- much too high for a source that tall. Creates lobing issues in the crossover region with that spread of drivers in an MTM.

OTOH, if you're planning on building your own enclosures, then if you want very stout, dead enclosures, the 1-1/2" panel thickness will do the trick. The PE cabs will get you most of the way there for a lot less hassle and expense.

~Jon

[Smilie]

Building a complex box is not a problem for me. But to tell the truth, a simple square sided box has a lot of romance due to its simplicity. The real question is whether there is good reason to go with the more complex box format.

BTW for this discussion I am assuming there will be no "fill" T's only the MTM.

The advantages I can see for the complex box are that by canting the M's the c-c spacing of the mids is reduced, the T's acoustic center is moved back relative to the M's and the MTM can be aimed like a short focused line.

The disadvantages I see are the host of diffraction and radiation anomolies the canted M's will create by overhanging the T and the added time and effort required to build the box.

So, Jon, since you have experience with the X1 MTM format I am wondering if it is worth the effort or will a simple straight sided box present the same acoustic quality as the complex box assuming all other things remain constant. In other words, both boxes are the same stiffness and non-resonant and the crossovers are optimized for each given box.

I guess another way to ask the question is, if you were to build a no-holds-barred MTM with the Modula drivers would you go for a straight sided box format or an X1 format or what?

Thanks

[JonMarsh]

No holds barred? Dipole arrangement like the Arvo...

In a box, it all depends on what you want. You can't put diffraction control on driver cones... what I did with the M8 bookshelf project was 3/8" felt, which butted flush to the edges of the gille, which had rounded edges. With a tall diamond cutout for the tweeter, that worked pretty well.

The X1 shape helps the vertical dispersion with a more conventional crossover, but with the lower crossover point and small overlap and different phase characteristic of the Modula crossover, this becomes fairly unnecesary.

What I'd suggest doing if you're working up your own enclosures is going for a 1-1/2" roundover like you can do with the router bits I have from MLCS (this takes a bit of care and multiple passes- this can be either veneered MDF or solid hardwood), and keep the flat part of the baffle similar to the Modula MTM (if you want to use that crossover as is). This will help minimize diffraction issues. If you're preapred to model, meassure, and develop your own version of the crossover, try a wider layout, say, 12", and a driver layout more like the Arvo- model using BDS to get the response as flat and smooth in the passband, then build and meausure what you get with your boxes, then model the final crossover. If you don't plan to do any modeling or measuring on your own, then stick with something close to the flat panel width.

Are you planning on using digital crossovers so you can do baffle step, driver notches, etc? Like a DEQX or DCX2496? Or something like what Linkwitz uses in analog for the Orion, or Monte Kay's new dipole project? A practical approach might be to model and develope with a DCX2496, then build an analog implementation.

~Jon

[ThomasW]

http://www.cliowin.com/FOTO/gpphoto/Hancock/slamm.htm

[Smilie]

Wish I had the room for a Dipole system. I just gave my dipole system to to a friend because I currently do not have room for it. So here I am working up a baby X1. :roll:

Your "Impossible Dream" article has been a motivator for me to examine the X1 MTM format. Nice article! Since I know you have worked with both formats, I was seeking your opinion. From what I understand from you, a simple box seems to be the way to go. :T

You are correct that I will bi-amp the MTM and that I will use a 2496 to get it going. If it all works out I will then have to decide whether to go passive or break out my photo resist and burn some analog boards. But that is so much work I may try to use some of my old home brew analog boards and add some sister boards to get the job done. On the other hand if the 2496 works well, I may just leave it alone. :roll:

As I have mentioned elsewhere, my goal is to make a floor stander MTM and cross to a bin or sub for some decent SPL at lower freqs. But for now I want to get the MTM up and running because all I have are some Focal based MTM sattelites that I don't particularly like. :cry:

I will test the RS28's I have with a three tone test centered at 1K and see how my results compare to MK's results. If they do not fare well I guess I can cash them in and try the H1212's or something similar. But I sure do like the look of the low end FR of the RS28's. I hope they make the grade. :B

One of the reasons I am so concerned about T's low end abilities is that, depending on the material played, there can be considerable energy being handled by T's in the range from 1K to 2K Hz. As an example see the attachment below which is from Audio July 1989. The graphs represent peak recorded signals vs freq. Obviously, if it is on the CD you would like to accurately reproduce the peaks on play back. And contrary to what is often commonly believed, there can be serious levels in the 1K to 2K region. 8O

In passing, take a look at the Telarc 1812. How many systems can reproduce that bass? Wow! :E

BTW if anyone is interested, I can post some more interesting graphs from that article. I think the article should be required reading for all who play in this arena.

In any event, I'm off to buy some MDF. :T

Thanks for the help. :T