RS180 MTM wt Waveguide

[mayhem13]

I picked up four of the RS180s while on sale to work on over this winter but impatience has bitten me. I'm considering an MTM using the MCM waveguides and the Seas 27TDFC. Any thoughts on the crossover? I'm planning ported and tuned to 45Hz floorstanding and for the baffle, i'm going to reduce driver spacing by overlapping the Waveguide with the woofers by first mounting the guide and then routing the baffle for the woofers, the flange of the RS180 overlapping by about .25" as not to disturb the profile of the guide.

[ThomasW]

Nope not a good idea....

The reason Zaph makes a 2.5 way with his waveguide design, is a function of the woofer center-to-center spacing of a MTM with a waveguide being problematic

[Mudjock]

SP Tech does the waveguide MTM, but they claim a crossover point of 700 Hz (LR-4 acoustic slope). Something like that might be a good application for the RS-180, but I'm not sure how low you could reasonably take the 27 TDFC in an MCM waveguide.

Zaph's design really didn't test this, since his crossover point was over 2 kHz. Given that crossover frequency, Thomas is right that the center-to-center spacing issue effectively eliminates an MTM layout from consideration for that design.

[JJones]

Nope not a good idea....

The reason Zaph makes a 2.5 way with his waveguide design, is a function of the woofer center-to-center spacing of a MTM with a waveguide being problematic

What if you put a capacitor in parallel with one of the woofers, "2.5 MTM"?
I guess it should be called WTM instead then?

Of course, I don't see much point to doing it that way (instead of putting both woofers below the tweeter), but you could?

If you combined the routed overlap with a smaller waveguide, such as the DXT, then you wouldn't have to roll off the 2nd woofer quite so high...

[mayhem13]

Is there a problem with a 2.5 MTM ??

[owdi]

How about angling the mids in so their cone becomes part of the waveguide? Just a thought...

Dan

[augerpro]

Is there a problem with a 2.5 MTM ??

Depends what frequencies will be covered by both woofers. Typically you want drivers that share frequencies to be close to each other, which is why most 2.5 ways are TMM.

[Mudjock]

An RS180 MTM 2.5 way has been tried by Roman Bednarek. He also does a pretty comprehensive review of the various RS180 MTM variants currently out there. I think you would find it interesting. Roman seems to like the 2.5 way variant, but your center-to-center spacing would be a lot higher and you would obviously need a completely different crossover due to that and the different tweeter, waveguide, etc.... From what I can tell, if you are willing to put some work into the crossover, the approach has good potential.

RS180 MTM Crossover Comparison

[mayhem13]

Most MTMs using the RS180s have a center to center spacing of between 12 and 12.5 inches. By overlaying each woofer onto the guide by .25 inches, on center i'll have 13" on center and if i move the guide of center by .5 inches, i can reduce the center to center spacing to 12.5 inches. Is this really too much, especially considering the off axis response of the tweeter in the guide ??

[eyekode]

I like the basic idea a lot. Especially if you could reduce the complexity of the crossover due to the recessed tweeter.

I was thinking of something like: Seas 27TDFC + waveguide + 2x Tang Band W6-1721. Speaking of which I haven't seen any DIY designs with this woofer yet...

[augerpro]

Another thing to consider is that with a TMM it's easier to place the tweeter at or just above ear height. But really, there is no *major* reason why you can't do an MTM 2.5. Is there some reason why MTM is so important to you?

[mayhem13]

Yeah-same here. Zaph has a single cap on his Seas in the TMM waveguide design. I'll have to rework the RS180's quite a bit. Have the waveguides and 180s, no Seas tweeters yet. I think i'll work some baffle designs this weekend and see just how close i can actually get the center to center spacing without interfering with the guide profile. Might be able to modify the RS180 flange a little as well.

[Jed]

I like the basic idea a lot. Especially if you could reduce the complexity of the crossover due to the recessed tweeter.

I was thinking of something like: Seas 27TDFC + waveguide + 2x Tang Band W6-1721. Speaking of which I haven't seen any DIY designs with this woofer yet...

I'm sure someone will test those eventually. Just the woofers aren't in stock till mid July. By the way welcome to the forum!

[augerpro]

Well if you do go with 2.5 then don't try to cram the woofers too close by cutting into the waveguide. You don't want an edge causing diffraction just to gain a 1/4"