Building La Scala cabinets

[djk]

Three beer lunch.

[Marvel]

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On 3/28/2005 6:04:13 PM djk wrote:

Three beer lunch.

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One can only "Hope"! Or is that, Only in Hope!

Marvel

[D-MAN]

Believe it or not, due to the small size of the splitting wedge in the La Scala, it probably doesn't matter if its there or not.

The splitter should be sized more along the lines of the Khorn splitter in order to use Huegen's theory of the reflectivity of waves turning 90 degrees when reflecting off of a 45 degree angle without distortions.

The prob I see with the LS splitter is that it is not "deep" enough to present a consistant 45 deg. angle to the throat opening, leaving a large portion of the waveform propagating from the opening to reflect back off of the back board (i.e., directly back to the opening). It needs to be expanded in its dimensions towards the opening and therefore also needs to be wider in order to be effective as a tool to turn the waveform into a channel, that is, present a 45 degree angle in equal proportion to the throat opening width in as much as possible, like the Khorn does.

I suspect that the MAIN purposes behind the LS small splitter size is to:

1) act as a structural reinforcement to the back panel and/or an attachment point for the angled throat baffles

2) to turn the waveform in a somewhat less effective manner than a correctly sized splitting wedge would as being better than a block of wood would be in the same position

Has anyone ever stopped to think that this particular piece is made from some other scrap of wood (probably used in some other Klipsch horn speaker) that is available and would be roughly the right size? And we fanatics meticulously COPY it in its exact dimensions?

Do yourself a favor and make one the appropriate size for the job of turning the waveform FIRST, it will act as a structural brace on its own.

DM

[Marvel]

You can make the base the 3" like I said. Then do the 45 degree cuts. The 'peak' won't be more than 3", and will still easily fit in the channel space (only 1 1/2 " tall). If you want it to be 3" tall to meet the 3x13" opening, the base needs to be 6". I realize that Andy had it at 2 1/4" as did Jim on his pdf set of plans.

That piece barely touches the four wing pieces, so it wouldn't help much with the attachment of them

[Tom Mobley]

The wings are attached to the back of the motor board, the splitter is attached to the front side of the back. That's the way I did it anyway. I think it would be very difficult to do the physical assembly otherwise.

[cueman]

That's a good point. I thought about making it bigger like Marvel said. The bigger it gets though, the smaller the opening will be for the sound wave to pass through. Would that be bad? One thing it is not though, is a structural piece. That little stick isn't going to help 3/4" plywood in the least.

Here's an idea, why not the 45 degree wedges on the inner rear corners too. I mean if it needs one wedge to bounce 90 degrees, it still has to make another 90 degrees right?

I have all of my pieces cut. Except for the 60 degree cuts on the doghouse roof part. That one is going to be tricky. Still need to cut holes in the motorboards and baffles. I am taking pictures as I go, so I might post the whole deal in a new thread when I am done.

Thanks for all the advice !!!

Todd

[Tom Mobley]

The 60* cuts are tricky. You either run the wood thru vertical against a 30* blade or build some kind of sled to hold it at 30* and run it past the vertical saw blade. Either way it's hard to get it perfectly parallel to the other side. Probably best to cut the pieces big, make a 60* cut and locate off that side to do the other side. Of course, the 60* cuts still need to be perpendicular to the top and bottom. What fun....

[D-MAN]

Here's a short explanation of the splitting wedge, sort of.

Basically my opinion of it, anyway...

An interesting point in the Khorn is that although the "slot" size was changed in 1962 for use of the K33, the splitting wedges were not changed to accomodate the narrower slot width. More food for thought....

DM

[Marvel]

Dana,

You aren't showing that correctly for a 3x13 slot. It should look like below. Then, even with a 3" base on the splitter, you aren't going to be constricting the wave as it turns the corner. With a 3" base, the full width of the slot is covered.

Marvel

[D-MAN]

Thanks, Marvel! I know it ain't EXACTLY correct! I'm using MS Paint! That alone is enough to make it "incorrect"...

But hopefully, everyone gets the point. It is that a wider and "deeper" wedge is entirely appropriate for the job of turning a waveform 90 degrees and what LOOKS like a constriction of the throat channel really ISN'T as far was the waveform is concerned.

The Khorn uses EXACTLY the same slot with EXACTLY the same throat area YET it's splitting wedge is MUCH larger in depth and width than the LS or BELLE splitter. I am stressing that point.

But I would add, that the wedge in question (on the Khorn is 4" or so wide) is too narrow, it should be bigger and wider than the 3" slot. It CAN even come out all the way to the baffle board without causing any ill effects.

BTW, got wood yet? (you're gonna really like em).

DM

[D-MAN]

Found a cool acoustics link:

http://www.kettering.edu/~drussell/Demos.html

Dan Russell's link

DM

[D-MAN]

Marvel, I hacked on your picture to better describe what I mean.

DM

[Marvel]

Got no wood yet

Got $900 my dealer wants to fix the airconditioning in my car?

I am NOT going to fix the air yet. Or I'll put a new compressor on myself.

Marvel

[D-MAN]

Bummer, dude. But as long as we keep the flame burning...

You'll get there.

DM

[cueman]

Holy crap, these plans are really flawed in the sense that 3/4" plywood is not truly 3/4" thick. It is 11/16" It doesn't sound like a big deal, but a lot of the measurements take into account the 3/4" thickness, and so some things I need to trim down by 1/8" of an inch. All the parts of the doghouse that are 22-1/4" high will come up 1/8" short if the back is not trimmed down by 1/8" Good thing I didn't start gluing things up first. Setbacks, setbacks.

Todd

[D-MAN]

I wouldn't get too worried about it. 1/8" internally won't effect the operation of the horn.

The main concern would be that everything lines up externally, like you said. It's the plywood's fault, technically, because it expands and contracts based on its water content.

It is produced at a width that is ESTIMATED to shrink down to the supposed value at a certain point as it dries. It's RARELY the thickness that its "supposed" to be.

Now MDF, on the other hand, should be the thickness expected. But then, it has some other "issues".

DM

[cueman]

I got it figured out. Basically I had to trim down the back side a little, so that the doghouse, being 22-1/4" will touch the top of the chmaber roof. I also had to shave a little off the top of the sides. I did a dry fit with clamps just now and I am happy with the way everything is fitting together. I hope to be done in about a week. I am taking pics as I go, and will post a La Scala cabinet 'pictorial' when I am done.

Thanks !!

Todd

[cueman]

OK, the cabs are done. I need to choose a finish. I am not too experienced with finishing. I was thinking Watco Danish oil. It comes in several different shades. Attached is a pic of the color I am going after. Just a light color. This is raw birch, never before finished.

Thanks, Todd

[D-MAN]

I saw a pair of stock 2003 LS's in clear poly'd birch ply, and I thought they looked cool, except for the unstained putty over the nail holes. If I had them, I would just cover the open ply on the front with some veneer so it wasn't apparent that it was plywood, and hey, right in the living room with them!

DM