Incorporating Natalie P MTM into 3 way tower

[linguistisch]

Greetings everyone, I've been lurking for a while but now I'm working on my first serious home audio build (have built many basic builds and also complex car audio designs).

I'm in the middle of trying to solve the riddle of incorporating the Nat P design MTM into a 3 way floorstanding tower that I've drawn out in CAD. I am planning on purchasing the RS180-8 and have a pair of SB29RDC tweeters already in shipping from Madisound. The idea being that I will build a crossover around the MTM RS180-8s and SB29RDC tweeter, but with the exact internal 1ft3 vented dimensions and driver spacing of the original Dr. K's/Natalie P/Modula MTM designs. In this way I can always swap the SB29RDC for the RS28f and have access to many proven crossover designs with all else already in place to match their design and output.

The MTM on top will be electronically crossed between 60hz-80hz from the receiver, the subwoofer portion below is mounted to the side of the cabinet and is a sealed 12" 8ohm RSS315HFA-8 powered by a Dayton SPA500 amplifier in each tower. This style of design has been done before (using only outboard amps/receivers without the subwoofer plate amps I believe), but the way I have drawn it out makes it one tower and not two different shaped cabinets mounted together. All speakers will be recessed and flush with the baffles.

So my question is, in the conventional Nat P/Dr. K's/RJB designs the MTM cabinets are 9"w x 22"h x 13.5"d. I would have these exact internal dimensions of this enclosure, but my question is, if my tower is 12" wide on the outside from bottom to top, what happens when all else stays the same internally (drivers, dampening, crossovers, port, etc.) but the baffle is 12" wide and not 9" as is called for? In all my reading in the lead up to finally building I keep reading that the baffles cannot exceed 1" wider than the original design. My tower would also be 3/4" higher from the center of the top midwoofer to the TDC of the tower due to a second layer of 3/4" MDF.

William

[studiotech]

Post this on HTGuide where the NatP design came from. Jon Marsh will set you on the right course. But in short, yes some subtle things will change in BSC and diffraction effects. May not a big issue, but pass it by the HTGuide guys first.

Greg

[AllenB]

The internal dimensions can make a difference but for the most part (when implemented sensibly), they are not critical. The outside dimensions will have a more significant effect.

An inch may not make much of a difference. A wider baffle will not necessarily be wrong, either, and some may prefer this for one reason or another. The issue is probably more of how the original crossover will become incorrect with a wider baffle.

[Einric]

You could always side mount the subs and keep the baffle width a proper 9".
Definitive Tech does side subs with plate amps and I know I have seen others do it.
You could go with the BASH 300W and stand it on its side that way it could fit on the back.
If you go with the RSS315HF-4 you can squeak the 300W from the Bash and use a smaller sealed enclosure (about .75cuft smaller).

[Jay1111]

Why dont you just keep the MTM portion the proper 9" width, and make the cabinet directly below the MTM portion as wide as you want?

Changing the width will alter the baffle step frequency, and alter the diffraction effects of the drivers. Depending on where these changes fall, there can be some serious damage done to the SQ.

[Einric]

I think what Jay is speaking of would look something like this.
The Totem Acoustic Shaman was built this way.
You could even maybe add an inboard super tweeter if you ever felt the need and have a 4-Way.

[Jay1111]

That can work too. I was thinking more along the lines of a Polk Lsi 25. The side panels make the speaker about 2" wider below the mtm.

[linguistisch]

All this is helpful. I've started a thread at HTGuide and will get some help there, but naturally the more responses I get the better. I think I understand now about the BSC and the differences it will make. It sounds like it wouldn't be hard to correct necessarily, but it would mean that I couldn't do what I intended to do which is purchase the crossover components based on the other designs and install them in there without having to alter/redesign anything.

Well, towers like the TAS setup were what I've seen around and what I was thinking of when I mentioned I didn't want to stack cabinets, that's the look I was trying to avoid (forward firing subwoofer, and a stacked blocks look). I've always liked the look of the LSi25, Polk managed to make this look like it's one tall and slim tower without the hard shoulders and separate block appearance of a cubed subwoofer cabinet. I think the best way to go forward would be to have something similar to this idea and keep the 9" width at the top, but 12" wide on the bottom half. I know that sounds exactly like what I said I don't like, and it is in a sense, but I can slant the shoulders a bit with a chamfer and it might come off ok like the LSi25. I have to have that 12" width for the sub because my walls are double thick at 1.5", and the plate amps I already have are two Dayton SPA500s which themselves are nearly 12" square; the Bash would be a good idea considering its size and the fact that I could purchase a 4 ohm subwoofer instead of 8 to get the same power output.

[linguistisch]

All this is helpful. I've started a thread at HTGuide and will get some help there, but naturally the more responses I get the better. I think I understand now about the BSC and the differences it will make. It sounds like it wouldn't be hard to correct necessarily, but it would mean that I couldn't do what I intended to do which is purchase the crossover components based on the other designs and install them in there without having to alter anything or redesign anything.q2

Well, towers like the TAS setup was what I've seen around and what I was thinking of when I mentioned I didn't want to stack cabinets, that's the look I was trying to avoid (forward firing subwoofer, and stacked blocks look). I've always liked the look of the LSi25, Polk managed to make this look like it's one tall and slim tower without the hard shoulders and separate block appearance of a wide subwoofer cabinet. I think the best way to go forward would be to have something similar to this idea and keep the 9" width at the top, but 12" wide on the bottom half. I know that sounds exactly like what I said I didn't want but the subwoofer cabinet portion is double lined (1.5" thick) and I have the Dayton SPA500 plate amp that also needs to fit below as well, so as long as it doesn't look like two different blocks stacked on top of each other (like stage gear) it might be ok. I can slant the shoulders a bit with a chamfer and it might come off ok like the LSi25. Slim, tall with a subtle flair to the bottom half. Under normal circumstances the Bash would probably be a good idea considering its size, but I already own two of the Dayton SPA500 amplifiers so I need to use them. But I might take your suggestion and go with the 4 ohm RSHF instead and get the maximum 500 out of the plate amps.