CraigG's KhanCinema Build Thread

[CraigG]

OK, parts are ordered, so I've officially started down the road toward a set of DIY speakers. (See my "What the heck am I doing?" thread for background info.)

I've chosen to use three KhanCenters for the fronts, and In-Khan-Neatos for side and rear surrounds.

The KhanCenters aren't designed for in-wall use, but they do have less-than-typical baffle-step correction for use under a large TV. They're closer to what I need than anything else I can find, so I'm going to try them in-wall anyway. We'll see how that works out.

I have limited depth available for these in front, so my plan is to make them shallower than the original, but extend the cabinet vertically to retain the same internal volume.

Original cabinet design:



Proposed modification:



Any opinions on the change? How about bracing in the expanded lower section--do I need anything there?

I wasn't sure how important the volume in the mid chamber is, so there's a divider to keep it the same as the original. If it doesn't matter, I could simplify construction a bit by omitting it, but I may just leave in there to create a recess for terminal posts (opening up the back wall, of course).

[---k---]

Looks good. I would add some bracing in the bottom. If you put a pair of braces beneath the mid sides, I think that would be good.

I would probably leave the mid chamber as-is.

[dpc rep]

Are you going to use the design using the RS180's, or the RS225's?

[CraigG]

---k---: Thanks--that's what I'll do then.

dpc rep: RS180s. The bigger version would be tough to fit horizontally, so I would have to build them as a single 76" wide cabinet, which would then be a structural component of the wall holding up the IB sub. That alone wouldn't completely rule them out, but their full-BSC crossover also makes them less suitable for in-wall use than the KhanCenter.

[CraigG]

Revised version with bracing, and rear cut-out behind mid chamber:

[---k---]

YEAH! I think that properly maintains the spirit of overkill that we worship around here. :T

Though the big hole in the horizontal braces would have allowed you to place the crossovers down in the hole. Which I think is better than the back wall or on that brace.

[CraigG]

YEAH! I think that properly maintains the spirit of overkill that we worship around here. :T

Though the big hole in the horizontal braces would have allowed you to place the crossovers down in the hole. Which I think is better than the back wall or on that brace.

I seem to gravitate towards overkill--it's moderation I have problems with.

I was actually toying with the idea of sealing off the lower center section, and sticking the crossovers in there with their own access panel. Since the parts haven't arrived and I haven't done this before, I don't have a good sense of the size of the crossovers, so this might not be realistic. If you think they won't fit through the holes in the horizontal brace, they're probably not going to fit in the center section either.

[---k---]

It depends on how you build them. If you use NPE caps or poly caps for the woofer. Some people can make them quite small... but no matter how small they get built, I wouldn't be able to fit my hand through there.

BTW, there is still room for more overkill... but, I'll keep my mouth shut.

[CraigG]

BTW, there is still room for more overkill... but, I'll keep my mouth shut.

PLEASE don't hold back! I'd rather have as many ideas as possible on the table now, than find out later I could have done it better.

[CraigG]

Updated--sealed off the lower center compartment, and put the crossover components and terminal posts on a board which slides in from the back:



Component sizes are accurate, but the layout isn't. I just wanted to see if I could get everything into the available volume, and it looks like that won't be a problem.

[---k---]

Wow. Fancy.

[ahaik]

I have done a very similar enclosure to yours, the in wall center works very well for me.
It looks nice with my new recessed 55" LED TV in the bedroom :B

[CraigG]

Woohoo! Parts are here! Well, except for some back ordered coils.

Stupid question #1: The tweeters have stickers on them like this:



Any idea what that means? I'm guessing it's a QC test result--maybe variance from the nominal impedance?

I've got four marked "0.2", one marked "0.4", and two marked "0.6". I imagine this makes little (if any) difference, but in just case it does, should I go for symmetry (using 0.6 / 0.4 / 0.6 across the front, and 0.2 for the surrounds), or keep the low values up front and mix up the rest?



Stupid question #2: When I ordered the parts from Madisound for the In-Khans, they didn't have any of the specified 6-ohm resistors. Assuming (possibly incorrectly) these particular Eagle resistors were specified for a reason, I didn't want to substitute something completely different. I didn't see why I couldn't substitute pairs of resistors in parallel or in series, but they were out of 12-, 3-, 2-, 4-, 1-, and 5-ohm values as well. I ended up getting pairs of 3.3-ohm and 2.7-ohm resistors.

Is there any reason not to use 3.3-ohm and 2.7-ohm in series in place of a 6-ohm?



Stupid question #3: MDF or plywood? Appearance doesn't matter, as these will be concealed. I saw that Home Depot had some 3/4" maple ply on sale, making the cost nearly the same between the two. Any reason to choose one over the other?

Thanks!

[---k---]

Stupid Question #1 - the sticker indicates the sensitivity of the tweeters. I would match them up as best as possible, but don't get too hung up on it because those are pretty consistent. FWIW, I had bigger variability in a some of mine. But, when CJD measured them, he said there was a lot less variation then indicated by the sticker. We didn't do anything special with the crossover to compensate for the differences. Mast manufacturer's don't put the stickers on them (does anyone else?), they are probably causing more questions than fears alleviating.

Stupid question #2 - The Eagles were specified because I was getting my inductors from Madisound so I bought the Eagles there. Resistor brand doesn't matter to me much.

Not sure. I think series works that way. But, this resistor is in series with the mid and taking more voltage. When we built these, CJD was a little worried about that resistor. We ran them for a while and felt them for heat. They seemed okay, so we moved on. But, you may have saw the flaming Mini-Statement crossover. To prevent this, the best solution would be to use resistors in parallel - you can use the PE sandcast ones or whatever. Another good option would be the 25W Erse resistors. I hate to make you order more parts. You can also get a pair of 12ohm, 10W resistors cheap from Frys for a $1.

Stupid question #3 - oh boy... personal preference. MDF is technically more dense and does not resonate as much. But it is nasty to work with, heavy, and nasty to work with. Plywood is nicer to work with, but can be really expensive for the void free stuff, it is stiffer. I've used some of the stuff with voids and I don't have a problem with it, but I've never gone all out on a design like Jon's Ardents. For your first build, do the mains with Ply and the rears with MDF and see which you like to work with.

[CraigG]

Thanks, Ryan!

Stupid Question #1 - the sticker indicates the sensitivity of the tweeters. I would match them up as best as possible, but don't get too hung up on it because those are pretty consistent. FWIW, I had bigger variability in a some of mine. But, when CJD measured them, he said there was a lot less variation then indicated by the sticker. We didn't do anything special with the crossover to compensate for the differences. Mast manufacturer's don't put the stickers on them (does anyone else?), they are probably causing more questions than fears alleviating.

I'm glad I asked! I'll put the higher values in the front, then--they'll be behind a screen, so a little extra sensitivity in the tweeters won't hurt, and might even help a tiny bit.

Stupid question #2 - The Eagles were specified because I was getting my inductors from Madisound so I bought the Eagles there. Resistor brand doesn't matter to me much.

Not sure. I think series works that way. But, this resistor is in series with the mid and taking more voltage. When we built these, CJD was a little worried about that resistor. We ran them for a while and felt them for heat. They seemed okay, so we moved on. But, you may have saw the flaming Mini-Statement crossover. To prevent this, the best solution would be to use resistors in parallel - you can use the PE sandcast ones or whatever. Another good option would be the 25W Erse resistors. I hate to make you order more parts. You can also get a pair of 12ohm, 10W resistors cheap from Frys for a $1.

I know that there are reasons not to substitute inductors, but I wasn't sure if there were similar reasons for resistors. Good to know I don't need to worry about it in the future.

I should be fine in terms of power handling, as the dissipated power will be split between the resistors (45% / 55% in this case). If one 10W was OK but a little questionable, two 10W should be more than sufficient. Probably no need to consider adding a fire-suppression system.

Stupid question #3 - oh boy... personal preference. MDF is technically more dense and does not resonate as much. But it is nasty to work with, heavy, and nasty to work with. Plywood is nicer to work with, but can be really expensive for the void free stuff, it is stiffer. I've used some of the stuff with voids and I don't have a problem with it, but I've never gone all out on a design like Jon's Ardents. For your first build, do the mains with Ply and the rears with MDF and see which you like to work with.

I've built two different IB sub manifolds and some other stuff with MDF, and I don't mind working with it. If there's not a really compelling reason to go with ply, I'll probably stick with MDF here. The Home Depot maple didn't say anything about being void-free, but if the gaps I saw on the edges are any indication, it's not.

[CraigG]

More revisions...

Center, now with the binding posts in a recess, and crossover on a separate board:






In-Khan-Neato, similarly modified:






I picked up four sheets of MDF today, so if it's not still over 100 degrees here tomorrow, I'll be ready to do some cutting!

[CraigG]

Some progress...

[CraigG]

EDIT: The voices in my head have calmed down, so I'm withdrawing my crazy idea. Back to the original plan! 8)

[cjd]

Ooh, what'd we miss?

[CraigG]

Ooh, what'd we miss?

I had an idea to tear out my IB sub, split it into two sections, and build the entire screen wall as a speaker baffle incorporating the subs (still IB, vented to the attic) and a set of KhanSpires:

Image not available

On further consideration, it's probably not worth the extra effort and expense, and might not even be an improvement at all over the current plan.

[cjd]

I had an idea to tear out my IB sub, split it into two sections, and build the entire screen wall as a speaker baffle incorporating the subs (still IB, vented to the attic) and a set of KhanSpires:



On further consideration, it's probably not worth the extra effort and expense, and might not even be an improvement at all over the current plan.

I'd considered that and came to the same conclusion.

[nk215]

Am I missing something here? The original design of the In-Khan-neato does not have a separate compartment for the tweeter.

[cjd]

no, but it doesn't hurt.

[---k---]

The back of the RS28 is totally sealed. So, it doesn't need to be sealed off. But, perfectionist may seal the back with wood. JonMarsh does this with his ModulaMTM. I think it mostly helps to add to baffle strength. It will also keep the woofer backwaves off the back of the tweeter... don't know if this helps. I haven't bothered and am happy.

[CraigG]

Am I missing something here? The original design of the In-Khan-neato does not have a separate compartment for the tweeter.

Like they said, it doesn't need to be sealed. I'm not doing it for any acoustic reason--I just wanted a handy spot to stick the crossover. There was a functional reason to do this for the fronts (couldn't get the crossover in through the holes in the brace), but I'm just doing it on the In-Khans because I want to.

[CraigG]

Does this look like a reasonable crossover component layout to avoid interaction between the inductors? (this is for the KhanCenters)

[---k---]

Yeah, those inductors look okay to me.

Don't glue those resistors down to the board. Don't glue them at all. Just let them float above the board so that they get maximum cooling. You shouldn't have an issue, but why not.

[numberoneoppa]

Wow, that's impressive.

[CraigG]

Wow, that's impressive.

That's a lot of work with a circular saw and a straightedge, let me tell you! It sure does make one of these look tempting.

[TacoD]

That's a lot of work with a circular saw and a straightedge, let me tell you! It sure does make one of these look tempting.

I use the Festool plunge circular saw and still it is a lot of work .

[numberoneoppa]

Festool? I suppose I could dream.

[CraigG]

More progress!

Center sections for the fronts glued up:



Also got the baffles routed for the surrounds. Here's a shot showing the front, back, and a baffle:



...and here's how the back looked before the rear panel was attached, showing how I did the binding-post recess:

[---k---]

Nice. Don't forget to drill the holes for the wiring between each chamber prior to gluing it all up. (I've made that mistake once or twice.)

[richnen]

Looking good Craig!

What kind of finish, or have you decided yet?

[CraigG]

Nice. Don't forget to drill the holes for the wiring between each chamber prior to gluing it all up. (I've made that mistake once or twice.)

:lol: Yeah, good thinking! It would be a little tough to get a drill in there through the speaker holes.

[CraigG]

Looking good Craig!

What kind of finish, or have you decided yet?

Since they're going behind a screen, they need to be black, and relatively non-reflective. I'm probably going to use DuraTex. I was thinking of using truck bed liner, but I probably don't need THAT much durability, and from what I've read, it has a tendency to collect dust in the texture. DuraTex is a little smoother, so it shouldn't have that problem. I found a great example someone did with DuraTex and a roller:



If these were going to be at all visible, I'd probably attempt what Phisch did on his KhanSpires--that black ash looks fantastic!

[cjd]

For behind an AT screen I recommend wrapping the baffle in black felt.

[---k---]

I agree with CJD. Do felt.

But, if you're going to do paint, go to Sherwin Williams and get their All Surfaces low sheen paint in black (it comes pre-mixed in white or black) and roll it on. It is what I've used. It is a very tough acrylic paint and will be much cheaper than the truckbed liner. Depending on the roller you use, whether you back roll, or what, you can get different textures, if that is what you want.

http://www.sherwin-williams.com/pro/products/all_surface_enamel_latex_base/?referringCategory=interior_paint_coatings/paint_coatings/

[CraigG]

Hmmm...felt? I hadn't thought of that, but it would probably work really well. Any tips on what kind to get, how thick, where to find it, etc.? I imagine you just stick it on there with spray adhesive, like they do with pool tables.

If I covered the face of the baffle in felt, should I route the driver holes a bit oversize and make the recesses a bit deeper, and sandwich the felt between the the drivers and the baffle? I haven't routed the holes for the fronts yet, so it wouldn't be much trouble to do that if the felt would provide a good enough seal behind the drivers. (I guess they make gaskets out of felt, so I don't see why it wouldn't work.)

I suppose I could shave enough off the edges of the baffle to account for the thickness, and wrap the felt around the edges so it would end up flush with the cabinet sides, and then just paint the rest of the cabinet.

And I guess I finally have a solution for how I could finish the rest of that wall--I could cover the sub cabinet in felt, and make up trim pieces to fit between everything, and cover those in felt, too.

[cjd]

The entire wall behind my screen is felt covered. And outside the screen is 1/4"x2" based frames with acoustic treatment in the middle, wrapped in felt. Except the IB manifold, for which I built a frame wrapped in grille-cloth that just slides into position. Even the ceiling above and walls to each side are felt treated.

I used wool felt I got at the local fabric store (JoAnne I think) and 3M spray adhesive. It isn't very thick. I suspect it seals well enough behind the drivers, but if you're paranoid roll it over the edges but not behind the drivers.

[CraigG]

Thanks for the suggestions--I picked up a gallon of the Sherwin-Williams all-surface, and enough felt to do the whole front wall. :T

I did a test run on a driver cutout, and it looks like adding 1/16" to the recess diameter is just right to get the driver in there with the felt around it.

[CraigG]

Crossovers are done:

[---k---]

Those look nice. Jammed a lot in a small space. Looks like all of your inductors are at 90 degrees to each other.

[Hdale85]

So CJD, I had PM'd you a bit about speakers, lets say instead of in walls I did something like these behind the Seymour screen, would there be a pretty big dip in the top end and would dialog suffer from it? Really have to decide what I'm going to do here lol....

[cjd]

Dougie, build a trio of Khanspires, use the silk dome version of the RS tweeter.