Khancenter Build: On-Wall Fireplace Surround Phase I

[Thoth]

Well, here we go! This will be the first phase of the on-wall fireplace surround project that I first brought up in this thread: http://www.htguide.com/forum/showthr...n-wall-project. Many, many thanks to ---k--- and cjd for their great designs and their patient advice to a complete noob. ;x( I'm hoping for lots more feedback from them and anyone else who wants to chime in as I try to pull this off.

Here is my starting AutoCAD model for a quick sanity check and verification of my volume calculations. I have not yet modeled the braces, rabbets, etc.:



Showing the dimensions of the MT enclosure was too confusing - it measures 12.1x28.2x14.6 internally, giving me 4.98L. The outer box is 26.2x28.2x66.2 internally, which is 45.36L. Subtracting 7.3L for the outer volume of the MT box and another ~2-3L for the braces should leave me right at 35L. Looks pretty good so far based on the following from Ryan's original Khancenter thread:

Someone was asking for a small center channel again. The Khan would also most fit the bill, but was deep. I remembered that I built it deep for no other reason than I could. I guess I subscribe to the "build as big of a box as you can crowd." And was too lazy to really do more than one model.

Well, correct me if I'm wrong, but it looks like with 2 RS180-8, you can build it much shallower and not give up anything when used with a crossover to a sub. Going with the 20L sealed allows one to reduce the depth to like 14" deep.

If you agree, I'll make a note in the first post. Maybe this would open the design up to more people.

Everything look generally OK so far? Do I need to allow more volume for the drivers and XO's? I'd like to stay with the proposed height and depth, but could easily go wider.

Don

[---k---]

Metric! Argh. I can do some rough conversion in my head, but had to got the calculator out. It looks like you're going a little wider and a little taller to reduce depth and keep the volume up. I don't see any issue with that. You do need to subtract some volume for the crossover and the drivers themselves, but that isn't a lot. You should be still have plenty with that size.

I've always thought that if I build another one of these, I might try and angle the backside of the mid chamber so the reflection off the back doesn't come straight back to the driver. Theoretically, that is better. But a pain to build.

[Thoth]

Yeah, sorry about the metric - I really took to it back in school, then it just happened that my work called for it a lot over the years, so I guess it's now my default setting.

Since the overall volume looks good, next would be driver spacing. This baffle layout from the original thread looked like the most current (I converted to metric on my end, of course ):



I also seem to remember a mention in one of the posts about keeping the mid and tweeter as close as possible. I already got the drivers from PE and they threw in a truncated mounting plate for the tweeter, so I could go even closer than what is shown. Should I do that, or stick with the drawing? Routing for the truncated plate looks awkward...

I've always thought that if I build another one of these, I might try and angle the backside of the mid chamber so the reflection off the back doesn't come straight back to the driver. Theoretically, that is better. But a pain to build.

Hmmmm.... The parts are relatively small, so the sliding compound miter saw should be able to get at them. What angle are you thinking?

[Thoth]

Been looking at all of that extra hidden space in the cabinetry surrounding the speaker enclosures, and am toying with outboard crossovers. Anybody got thoughts on that?

Speaking of the crossover, there were a couple different iterations and associated BOM's in the original thread, so I thought I would combine what looks like the final version into one image for reference:



Hope this is right, 'cause I just hit the Submit button at PE! Wish the prices were still the same...

[---k---]

If the crossover was measured and designed for the truncated frame from the get go, it would be better. I'm not sure about now. I want to say that it the truncated frame could theoretically help, but I need to let CJD answer that one.

As for the mid chamber, I would say put whatever angle is easy to make work. I would probably make the back of the mid intersect with the back of the speaker and angle it up to keep the volume the same. This also benefits giving you more room behind the mid.

My personal opinion on exterior crossovers are just one more thing to build and deal with. More wires going everywhere. If you got the space to stick them inside it makes things easier.

That looks like my excel file, so you should be good. If there are others, it was people substituting parts for personal preferences. Do I even want to know what the price is up to now?

[cjd]

Keep spacing to the tweeter to spec. The truncated frame would give you more baffle surface (should I say some?) between the drivers which may prove more helpful than routing the truncated frame.

C

[Thoth]

Do I even want to know what the price is up to now?

Wasn't THAT bad - $368.01 total.

I have now managed to confuse myself (a common occurrence) about the driver spacing though. Looking back at the original thread and the Khancenter page at DA, I see two other baffle layouts that are different than the one I posted above. I probably picked that one out originally because it's the biggest image Any chance you could take a look and set me straight?

Thanks CJD. I'm going to skip the truncated frame.

Don

[---k---]

$368 isn't nearly as bad as I was expecting. I think the price of the Khans is way up over $100/ea from when I built them.

Here is the deal. I didn't make a sketch before cutting wood on that baffle. I don't think I even had calculated the box volume. I just knew everything would work and be MORE than enough. I was riding high on confidence and just started cutting. The sketch was made afterwards eyeballing the center to center measurements of the drivers. I'm a good rough carpenter, but a poor finish carpenter. My attention span doesn't allow me to measure more precisely than 1/8". There is a big red font warning on this one for a reason.

So, what you need to know to make your own baffle / box layout: The distance between the center of the tweeter and mid should be as close as the round face plate allows. You'll notice in some of mine, I get a little too close and end up with no wood between the two. I think that is too close and looks bad, but I'm too lazy to cut new. I think having 1/8" space between the mid and tweeter frames would look nice. I wouldn't worry about being +/- 1/4".

With the drives in hand, a few measurements, a few test cuts, you'll be okay.

[cjd]

^sound advice

Close enough is close enough, and 3-5mm between the driver frames will make your life ever so much easier.

C

[Thoth]

OK, think I get it now about the baffle layout. I saw your warnings but wasn't really sure how much difference was "different". Guess being new to speaker building is making me a little more anal about stuff than usual (although my wife would probably say that's not possible).

Looks like I may be ready to quit bugging you guys for a few days and go cut some wood . Thanks again, and stay tuned for progress photos!

Don