My 5.1 design project

[fbov]

Here are my renderings for a ~65l enclosure using the 9" baffle width required by the NatP design. The design theme is Mission, the materials, red oak veneer plywood and ash. The bottom is the only one that's close to the right color; I'm doing this in PowerPoint so forgive the limitations.

The main questions I have involve the baffle. I want to use it as a design element, rounding it at the ends and optimzing the edge profile in the tweeter area. Page 2 shows the baffle detail, including a crude diagram showing the differences between the tweeter area (large radius or beveled edge) and the rest of it.

I plan to use a piece of ash for the baffle, so I can machine and finish without concern for veneer. The box will be red oak ply, but the front and back will be MDF. The front panel will be veneered with ash behind the 3-piece grille to match the baffle.

The baffle will mount to this MDF, providing 3/4" relief from the matching light area, that's surrounded by 1/2" tall side boards with three 1/4" slats. I'll need to route out the side boards to match the radius of the baffle, flush to the MDF so the baffle is the edge of the enclosure between the woofers.

The box will be all rabbeted with solid oak slats and header strips, cross braces at three points inside. A ~8"x4" port in the bottom with 2" clearance, heavy sound absorber up by the drivers, lighter weight absorber in the bottom half as requried.

That's the general idea. What do you think? (NatP drivers and crossover, of course.)

Thanks,
Frank

[fbov]

http://www.htguide.com/forum/showpost.php4?p=410514&postcount=6

Here's an example of the mechanical design concept, albeit with a rectangular baffle. The builder talks about subtle variations in low frequency response due to baffle edge rounding, but my understanding is that long-wavelengths that can't resolve such fine details.

I've assumed that baffle edge detail effects were high-frequency effects, and that seems the case in JonW's baffle geometry studies.

http://www.htguide.com/forum/showthread.php4?t=25031&page=10

Therefore I've been letting aesthetics rule the baffle geometry beyond the woofer centers, but will tightly control the edge geometry between the woofers to optimize tweeter performance. Am I ignoring major effects, or just the higher order effects?

Put another way, NatP's cross over at 1,700 Hz, so the shortest wavelength is ~8". Details less than 1-2" should be transparent (assuming smooth transitions - no sharp edges or corners) to the LF driver response. Conversely, I assume the tweeter can't see past the woofers, and so is dominated by the baffle geometry between the woofers.

Thus my interest in what to do in the inter-woofer region of the baffle. This design lets me do anything I want here, so what's best?

Thanks,
Frank

[ThomasW]

NatP, the drivers are flush mounted in a 9" wide flat baffle with the edges rounded over. As long as these conditions and the driver spacing remains the same, you can do anything you want with regard to aesthetics...

Differences in the type, angle, or whatever of the baffle edge treatment, will be overwhelmed by the effects of the room.

IOW don't sweat the really small stuff.....

[fbov]

Th Oaudio Bash 500 plate amp arrived Friday, and it's a nice match to the Tempest-X. I hogged out a 1.2" deep hole in my donated 2"-thick boxes that was the dimensions of the amp, then added a 1.5" frame from scrap plywood. I plugged the terminal cup cut-out with another bit of plywood and put a grommet seal on the speaker wire hole. The amp cavity should remain air tight.

Yes, they have among the worst human factors in their terminal location design I've ever seen, especially since the other side of the board and terminals is in the open! I had speaker wire coming in under the power supply shields, too, so routing wasn't as simple as it could have been.

I don't have a long SW cable, so I set it up between right and center speakers for now. It definitely has some punch below the Advents, but wants the crossover at 40Hz or it's boomy when listening to cable TV through Dolby PL I. Some channels are fine, others have a distinct bit of distortion in the SW signal that's not always there. I kept the low-cut filter at 12Hz for all this.

A true 5.1 signal from my DVD player crosses over more like 70-90Hz and turned to only moderate volume, is an interesting experience. The direct LF signals make a big difference, and test signals are somewhat amazing in terms of the volume of air this one SW can move. I'd only seen hints of this before; home theater takes on a whole new meaning ...

Thanks to you all for the recommendation on the Tempest-X, the reviews of the Oaudio and the friendly donation of a local enthusiast's trade-ups.

On to some main speakers ...
Frank

[chris4891]

FWIW, I just noticed we had pretty much the same tv, so I felt obliged to show you my solution for the center channel placement problem. The matching stand I got with the tv doesn't really have room for a speaker (at least not a decent sized one), so this was my only option. Not sure about the WAF since I don't have to worry about that yet, I'll let you be the judge.

I went with the ministatements & matching center. Not sure how I want to finish the speakers off yet. For the moment, bare mdf suits me just fine.

Anyway, good luck with your project..

[NEO Dan]

Chris,
that's hardcore :E

awesome bit of MDF engineering right there :T

[Hdale85]

I'm going to have to figure out something similar...except I have a 50" RPTV and my center is about 44" long and probably going to weight something like 100lbs.

[fbov]

Flat panel TVs have their advantages...

And I've got to get back to cutting wood for my mains so I can say add something worthwhile to this thread.

Frank

[fbov]

I finally got my first NatP tower done, and the other is ready for final sanding and assembly, so I will document what I ended up doing in this construction. I'm hoping to have the second before by the Super Bowl, then start playing with the ECM8000 and mixer I got from Santa to see what kind of response I'm getting. February is cold around here!

These are big, nominally 70l enclosures with a slot port on the bottom rear tuned to an F3 of ~32Hz. If you run the numbers through Unibox, you'll see a speaker that will tear itself apart if driven with a half-power 30 Hz sine wave. I wanted a speaker that could deliver the full musical frequency range if used stand-alone, even though I normally use them for HT with a sub. I also doubt I'll ever need it that loud.

They're made of furniture-grade red oak plywood with a solid ash baffle mounted on an MDF front panel, all 3/4", veneered with ash and red oak accents. The narrow panels are all tongued into grooves routed in the side panels. Three window pane braces at 1/2, 1/3 and 1/5 points are dadoed into the vertical panels, and there's a vertical 3-axis brace connecting them to the top and bottom, large sides, and rear of the tweeter housing. As it works out, there's a brace at each of the RS180 drivers.

I did the baffle a little differently, partly for want of the sought-after 1.5" roundover and a router that could drive it, partly due to JonW's Spassvogel research on beveled baffles - I could make a 3/4" bevel!

Then I started reading lunchmoney's SR71 build, and the input he got on bracing from WmAx, and I started thinking what I could do to further damp box vibration and reduce non-driver radiated sound. I have access to iron ferrite powder, and I know that increased mass lowers resonances, so I coated the majority of the innner wood surface with an epoxy-ferrite mix. It added about 14-15 lb to the box, centered on the unsupported surfaces. For the largest span, ~14x12" between the drivers, I epoxied a cork layer to the wood under the ferrite-loaded epoxy, then put a cross brace between the centers.

I came close to mass loading ash baffle - coat the back with the ferrite epoxy and mount it through cork - and decided to ditch the epoxy, but keep the cork. As you can see in the detail pic, I've effectively isolated the baffle from the rest of the enclosure. I had pre-drilled screw holes through the MDF front panel to hold the baffle on, 30 degrees offset from the RS180 mounting holes, but I found it almost impossible to get the screws into the holes, much less drive them in once the box was assembled - too many braces!

The finish is all shellac, fresh made from flakes. I liked Dan Neubecker's H.O.S.S finish and I now like shellac!. Lots of very thin coats of blond shellac on everything, then garnet shellac on the red oak for the last two sanding stages. I did what was called an open-pore French polish in one of my Father-in-law's woodworking books, and I'm very happy with the results.

I should also thank Jed for the RS180's and ThomasW for the fundamental push in the right direction that got me on the road to this point.

Oh, the feet! With a bottom port, I needed to get off the ground. The little feet you see in the picture aren't functional. There's a ~6" piece of 3/8" threaded rod sunk 3+" into each corner with a spike point and hex head ground into the lower end. Weight is transferred to a t-nut trapped by the fake feet. Mechanically, it's point contact. Cosmetically, it fits the overall design.

And the sound... the sound field is lopsided with a hole centered on the remaining Advent. I've caught a couple gut punches a low volume levels but I'm waiting on the pair, no the LCR set, before I turn it up.

More to come...

HAve fun,
Frank

I also need to thank Evil Twin for designing these things in the first place... The Professional will be one of the first movies we watch when they're done.

[fbov]

I just glued the second tower shut, so these are the best photos I'm going to have of internal construction. The first is a shot of intended internal construction, once sealed. I'd originally planned 3 window pane braces, then realized a vertical brace connecting them would let me do an easy brace tree behind the tweeter box. Then I got the idea for screw jacks behind the drivers to damp them. This isn't the only part that "grew."

I had almost ordered accoustic damping material when I found a 24x30" piece of 1" adhesive-backed stuff in the trash at work, like I'd seen on our machines (I work at a big manufacturing site). When I realized I didn't have enough to cover, I got a roll of carpet padding. Originally, I'd planned back and side walls with the good stuff, but then the constraint layer idea came along and I ended up with something inbetween.

The second photo shows what's under the damping material. In the driver cavity, all the unsupported panels except the front have 1/2 to 1 lb of ferrite-loaded epoxy on them, with 2 lb on the large center section (12lb. total). In this area, shown in detail in the third photo, I added a cork damping layer to further reduce transmission. The last shot shows how I stapled down the carpet padding around the constraint system, and the adhesive-backed material on the epoxy. Not only are these epoxy layers massive, they're damn hard! A couple staples missed the wood and they bent like they'd hit steel.

Next, I'll cut the front panel for the RS180's, attach the tweeter box, then the tree brace and cross braces. then attach the cork to the front panel, and then the baffle to the cork. And finish the bottom...

Having fun!
Frank

[djg]

That is a very nice looking speaker. You have skills for sure. Now, are you going to do a new tv/ speaker stand to match? And how are the sub(s) coming/

Really nice work.

[fbov]

Thank you, sir! I see you've done something similar, but based on Tritrix? I'd be interested in your longer-term impressions, since I also plan to add something similar to the NatPs as surrounds.

But first, I need to revisit my CC, if only to add a matching front baffle, with perhaps a bit of an upward tilt. As I'm writing I think I've thought of an interesting way to do that, and end up with an even deader baffle than in the towers!

The second box is now sealed; here are a baffle back/front pair showing the box as I left it last night, and some bottom/interior shots. The cork layer between the baffle and the box and epoxy adhesive make for a real easy way to hide a bunch of the little mistakes I made on both the baffle and the cut-outs for it. This epoxy levels well, and I've had no squeeze-out issues.

The bottom shots show the spine pole and driver bracing in the background, and the finished bottom. The bottom piece screws into the spine pole via an 1/4-20 insert that's not yet installed in the interior photo, and pulls tight against with an interior ledge and the binding post plate.

The XO is mounted on the front, above the recessed binding posts and opposite the port. The port is an insert, removable for length modification, and flared somewhat crudely on both ends. If nothing else, I have good hand holds on the bottom!

Now, to the feet!
Frank

[djg]

I did a whole new system with Schumakubin mains, a Zaph BAMTM center, a Fitzmaurice horn sub, and some surrounds like Notorious AK posted here a while back. Also a new flat panel TV. Only thing left to do is a new TV stand, on hold for fear of layoff. You can see it over at the Parts Express forum if interested, djg over there also.

I have done my part to jump start the economy, for sure.

[fbov]

Yes, the feet.

I used 3/8" threaded rod, half anchored ~2.5" into the cabinet, half sticking through ~2.5" decorative feet, to couple the speaker to the floor. The business end was ground to a 90 degree point, then a hex pattern of flats was added, to facilitate adjustment. I'm using nickles on the hardwood. You can't tell it's spiked in service.

The other picture is the last coat of shellac before bringing the box upstairs tomorrow night and installing it. I still need to let the finish age a bit before rubbing it out with wax and 0000 steel wool. I think I'll get a reasonable distinctness of image, and I've certainly preserved the feel of the wood grain. It may not be as durable as my telescope finishes, but it's a heck of a lot prettier!! (But must remain indoors!)

[fbov]

I did a whole new system with Schumakubin mains, ...

I like your rounding approach. Oak will blend into itself; I have a hard time seeing where my edge veneer meets the panel veneer. Oddly, I have edge veneer joints (flat fingers, interleaved) at the same place on the back of both boxes... same side, too.

Nce job on the sub, too. Don't let my wife see it though - I've got big black 2' cubes, and WAF is not good. (We trade SAF on occassion.)

Have fun,
Frank