[Vapor Audio]

You all remember my MTMWW's?  They're a hybrid of GR drivers, using an A/V3 top MTM section and a pair of M-165x's for the WW - they're actively crossover over between top and bottom and bi-amped.

I've been extremely happy with these speakers, but the urge to try and make them better is irresistible!  The next phase will be swapping the 16ohm M-130's for a pair of the new XBL motor M-130x's.  I've found the standard M-130's to be wonderful midrange drivers, they surprise me every day with copius amounts of honest detail, yet they never make the turn from revealing to harsh.  They're simply natural and well-behaved drivers - and from my brief experience with the M-130x I find it to be even better, capable of an even more uncolored delivery.

I also have a variety of tweeters that I'll be using with them, in a variety of different crossover applications.  So far the tweeters I have and am going to try are:

Scan Speak AirCirc 6600
Visaton KE25SC
Peerless HDS 810921
Morel Supremo 110
Dayton RS28a

Remember, the GR T2 tweeter is a 104mm flange, so only other 104mm flange tweeters will be considered - that rules out the Seas Millenium and all the other Seas Excel tweeters   But I will probably add some other tweeters to the mix as well.

The goal will be to find not only what tweeter sounds best to me, but what implementation of that tweeter sounds best, and to gain experience in how all these different domes sound.  Anybody can take measurements and tell you how the tweeters differ, but very few people can tell you how they sound. 

I'll try lower LR4 slopes, higher LR2 slopes, response shaping, zobels, minimalist approaches, and everything inbetween.  I plan on months of experimentation, and expect to have a small handful of finished designs for a M-130x MTM that I can share with anyone interested.

Any questions about what I'm doing, or something you'd like to see me do along the way, just let me know.

[Danny Richie]

If it were me, I'd leave what you have as a reference for comparison then put the M-130X woofers in an open baffle MTM arrangement.

[Vapor Audio]

If it were me, I'd leave what you have as a reference for comparison then put the M-130X woofers in an open baffle MTM arrangement.

Well it's not you 

I need these cabs for the testing, then after I'm done with this process I'm planning on building new open baffle cabs and starting all over again.  I have plenty of other speakers in the house to compare with.

[Vapor Audio]

Just an update - ScanSpeak 6600 AirCirc and Visaton KE25SC tweeters are here, so are the 4 M-130x mids.  This weekend will be taking everything out of the old cabinets and getting them ready for the new stuff.  I have a massive 45 degree chamfer bit, it'll can put a 1 3/8" bevel on the front, which models out much smoother than the current 5/8" 30 degree chamfer.  All the drivers will get wired directly to Eichman Cablepods on the rear to facilitate the external crossover testing. 

I expect I'll have some crossover suggestions ready in 2-3 weeks for those looking to do a MTM with the M-130x's.

[Hank]

Go for it Turbo.  Frankly, I think the future is Open Baffle.  Given the tremendous improvement in mid-woofs in the past few years, XBL^2 and other advancements, today's mid-woofs can move enough air while remaining pistonic, to allow use in OB's.  I would go so far as to say that within a few years the only reason to build tower cabinets is the old WAF issue - they'll tolerate cabinets veneered in fine hardwoods, but many won't stand for the open baffles with the exposed driver rears and wiring.  Of course one way out might be to do OB's with a wire frame on the back, covered with grill cloth. Hmmm...

[Vapor Audio]

Go for it Turbo.  Frankly, I think the future is Open Baffle.  Given the tremendous improvement in mid-woofs in the past few years, XBL^2 and other advancements, today's mid-woofs can move enough air while remaining pistonic, to allow use in OB's.  I would go so far as to say that within a few years the only reason to build tower cabinets is the old WAF issue - they'll tolerate cabinets veneered in fine hardwoods, but many won't stand for the open baffles with the exposed driver rears and wiring.  Of course one way out might be to do OB's with a wire frame on the back, covered with grill cloth. Hmmm...

Well, my OB2X's are my only real open baffle experience thus far.  Sure it has some strengths, but there are also weaknesses - I think the same system OB vs. boxed will deliver slightly less ultimate detail in an OB configuration.  I also think a well designed boxed system images better (more precise spatial cues) than OB.  The strengths of OB are the incredibly engaging and open midrange - it just has a sense of ease to it, and the large diffuse soundstage ... and of course simpler construction, and none of the problems with resonances and internal reflections boxes can suffer from. 

I still think it's a personal preference, and that neither design is superior.

What I'm doing here is phase 1, building the MTM with various tweeters in a boxed configuration ... and then phase 2, move the entire set of drivers to a new pair of Open Baffle cabs.  After that I'll chose an ultimate winner.

[gooberdude]

I get the feeling that as time goes on, and more and people go OB, that the differences between OB & boxed speakers are going to melt away.

i've been tinkering a lot with my OB set-up lately, and have precise imaging that only a few other systems i've demo'd can compare too...actual palpable & accurate 3-D craziness.

As more $, time, energy and R&D go into driver technology, the future is definitely OB.

[Danny Richie]

Placement and setup as well as how they interact in a room can give a different presentation that can be large and diffuse with less focus. I think all that has to do with the room interaction though. I have also had great pin point imaging from them as well and just as focused and locked in as any other designs that I have worked on.

[poseidonsvoice]

Danny,

Can you give us some tips and pointers regarding room treatment with respect to OB's? I'm planning on building Jon Risch's bass traps for the corners, but I am really confused. Would room treatment with properties of absorption or  diffusion be more appropriate for the front wall and side walls (1st reflection points) ? I remember Siegfried Linkwitz recommending room treatment with the front walls having diffusion properties instead of absorption in dipole based systems like his Orion, so as to preserve the characteristics of a dipole in midrange on up. In addition, I figure corner bass traps have less of an effect with loudspeakers systems that employ a dipole subwoofer design (hence the advantage of dipole, H-frame and U-frame subs with regards to exciting room nodes).

Thanks,
Anand.

[Daygloworange]

Anand,

I use quite a bit of diffusion on my front and rear walls. My room is small, about 11" deep and 16" wide. One side is open to another room, and the speakers are far from the side wall on the other side, so first relection points are not a serious issue. Speakers are about 2' into the room, away from the wall.

With the OB 5 (bass reflex design) bass trapping was seriously needed. Al from RAW Acoustics convinced me to go out an get 2 bats of R-12 insulation and just plop them down in the corners. I did, and the results were drastic. The bass tightened up a lot, and reduced the ringing in the room. It aided the imaging in that room ringing has a similar effect as adding noisefloor.

With the GR Research A/V 3's I had before, there was not a bass problem at all. The transmission line design of those makes them a breeze to set up in a room.

I haven't had the OB 7's (sealed woofer section) in my room yet, so I can't comment, but I'm interested in how those will sound in the same room.

Cheers

[Danny Richie]

From 200Hz and down our OB-5 and OB-7's need to be treated just as any other speaker.

Side wall reflections will be minimized in the 200Hz range and up.

First reflection points need to be treated just as you would with most any other speaker as the tweeter behaves the same regardless.

The closer you are to the rear wall (wall behind the speakers) the more treatment you'll need. If you get to close to the rear wall then the rear wall reflections will get mixed in with the on axis response and cause some smearing.

If the speakers are further out into the room then less rear wall attention will be needed. A long enough delay from the rear wall will not interfere with the on axis response just as noted by SL. 

[Vapor Audio]

Hey guys, quit bogarting my thread!

[Vapor Audio]

Update - making progress now

Cabinets have been extensively re-worked.  I cut a much deeper 45 degree chamfer on the front baffle, simulations showed it would have significantly better diffraction control.  I also did quite bit of veneer and finishing work, including a high gloss tung finish that looks MUCH better

But the real star of the show is the new GR M-130x woofers and Visaton KE25SC ceramic dome tweeter.  Tonight I'm going to start measuring the drivers on the baffle and use that data to model some crossover ideas.  Based on preliminary data I've taken from these tweeters, I can probably go as low as 2000hz LR4 crossover, but the final curve will be based on many revisions and lots of listening. 

The bottom two woofers will remain as GR M-165x, but more volume has been added to the cabinet so that I can now port the bass section.  They really need about another full cu/ft to be ported, but this will work

[Vapor Audio]

Todays measurements are in this gallery

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=1183

Among them, this FR graph from a 2 component crossover   I try to add good verbage with my images, check them out and ask questions here.



For those wondering, the KE25SC is an excellent sounding tweeter!  I listened for about an hour today in mono using this simple crossover, I'm impressed with it.