New build - Usher 8948A / RS28F waveguide MTM

[DoubleTap]

This bad boy should be a beast! The cabinet is the same shape I've been using for my RAAL/AudioTechnology 2-way called Cirrus, but using MDF instead of Baltic Birch for cost savings. Final volume is 1.2cu/ft, ports will be on the rear. Custom stands will be made with the crossover in the base of the stand and a Speakon connector on the bottom of the cabinet. Attaching the milled MCM waveguide to the RS28F was simple. I took my first tweet measurement today and WOW, this combo will deliver ... I'll be able to cross wherever I want. I'd guess it'll be around 1200-1400hz. The 8948A is my favorite Usher woofer, having used it a couple times now it just has more ease through the midrange than the Carbon cone Ushers ... and every bit as much bottom end grunt as a 7" Revelator.

I left the stick measure by the cab so you can see just how big these are going to be, definately not some wimpy monitor. I'd guess than finished out they'll be close to 80 pounds each and completely resonance free.

My plan for finishing is to paint the cabinets an automotive Pearl White, and veneer the baffle with a bleached white Sycamore bookmatch. Of course then I'll have to refinish the whole house with Ikea to match

If there were a spot available, I could have these ready for Iowa.

[Paul Carmody]

Re: New build - Usher 8948A / RS28F waveguide MTM

Very niiiice! Two of those midwoofers ought to have quite a lot of power handling.

[Thomas Brown]

Re: New build - Usher 8948A / RS28F waveguide MTM

45- You are a sick, sick man! Those are just unbelivable...
Absoutely amazing work.

[DoubleTap]

Re: New build - Usher 8948A / RS28F waveguide MTM

Power Handling ... check! And they'll need it, I use 1000wpc amps.

I do have a sickness for sure. Originally I was going to use the Seas DXT in this design, but once I realized I had room for the 6.5" waveguide I figured that's an even better option.

Notice the top/bottom panels and front baffle are constrained layer with 1/8" mass loaded vinyl inbetween. See that channel cut in the cabinet walls? I fill that with a mix of sandblasting media and epoxy. These cabs are DEAD when done.

[Ray Tremblay]

Re: New build - Usher 8948A / RS28F waveguide MTM

Damn! Other than the fantastic workmanship, with those drivers, that has some serious potential. Good job. I'm curious to see how this turns out.

[Thomas Brown]

Re: New build - Usher 8948A / RS28F waveguide MTM

Notice the top/bottom panels and front baffle are constrained layer with 1/8" mass loaded vinyl inbetween. See that channel cut in the cabinet walls? I fill that with a mix of sandblasting media and epoxy. These cabs are DEAD when done.

I did notice the different colored layers in the cabinets, but did not see it on the baffle till you posted and I looked again.
saw the channel and guessed it would be filled with some sort of mass.

again, you are a sick, sick man! :D

[DannyT]

Re: New build - Usher 8948A / RS28F waveguide MTM

Nice cabinets
Do you mind to share the details on attaching the RS28F to the waveguide? Pictures would be great

[Dennis]

Re: New build - Usher 8948A / RS28F waveguide MTM

You must have one serious dust collection system!

[bmaupin]

Re: New build - Usher 8948A / RS28F waveguide MTM

Have you thought about doing a TMM instead? Vertical off-axis around the xover frequency is bad with a MTM and seems it would be really bad with wide spacing from the waveguide.

[DoubleTap]

Re: New build - Usher 8948A / RS28F waveguide MTM

Have you thought about doing a TMM instead? Vertical off-axis around the xover frequency is bad with a MTM and seems it would be really bad with wide spacing from the waveguide.

No, CTC spacing is about 18th on my list of considerations anyway ... and a 1200hz wave is a foot long. CTC with this configuration will be about 6 3/4", which is just barely outside the 1/2 wavelength distance.

If somebody could demonstrate to me that lobing from wider than optimal CTC spacing has significant audible impact when listening inside the 15* sweetspot window, I might change my mind. But my experience says that the impact is minor to negligible. Discussions with numerous accomplished designers have further solidified that view.

A TMM on the otherhand means 2.5way ... which means full BSC ... which almost always means imbalance from too fat a bottom end when used in real rooms.

[evilskillit]

Re: New build - Usher 8948A / RS28F waveguide MTM

Those are going to look sharp. Probably sound at least as good as they look.

[philiparcario]

Re: New build - Usher 8948A / RS28F waveguide MTM

looks like this piece of wood would make really nice baffle

http://cgi.ebay.com/6-4-WIDE-SUPER-Curly-Figured-Maple-lumber-Luthier-9961-/110582097439?pt=LH_DefaultDomain_0&hash=item19bf34e61f#ht_963wt_1139

this seller has a few pieces that could work for you.

[weinstro]

Re: New build - Usher 8948A / RS28F waveguide MTM

Interesting lam stack. What goes into the gap I can see in the 2nd photo?

Regards,

Rob

[Pete Schumacher]

Re: New build - Usher 8948A / RS28F waveguide MTM

No, CTC spacing is about 18th on my list of considerations anyway ... and a 1200hz wave is a foot long. CTC with this configuration will be about 6 3/4", which is just barely outside the 1/2 wavelength distance.

If somebody could demonstrate to me that lobing from wider than optimal CTC spacing has significant audible impact when listening inside the 15* sweetspot window, I might change my mind. But my experience says that the impact is minor to negligible. Discussions with numerous accomplished designers have further solidified that view.

A TMM on the otherhand means 2.5way ... which means full BSC ... which almost always means imbalance from too fat a bottom end when used in real rooms.

In all fairness, a 2.5-way can certainly be modified for less than 6dB baffle step. It all depends where you cut off the .5 woofer and how you shape the full range woofer's response around the XO point.

More complex than a 2-way, but the forward lobe is a little more vertically uniform.

However, I kind of like the look of MTM, and if you were to go 2.5-way, I'd make the upper woofer the .5 so the TM forward lobe is maintained. You could build up a couple XO versions and try them out. I'd be glad to help!! ;)

[BELAMP]

Re: New build - Usher 8948A / RS28F waveguide MTM

Dadgummit ! This is why I haven't received my Cirrus speakers yet ! He is just playing around in his shop :p LOL

Looks way cool bud ... Can't wait to get my waveguide design ! Breaking windows with Breaking The Law .... Oh yeah !