ALK Cornscala with K401 or Trachorn

[jwc]

Bob,

Did you just squeeze the port holes closer together?

Back in the fall, my original idea was to build a tall Cornscala where the three ports openings were "stacked" and the volume of the port itself was the same. The volume of the cabinet would be the same. My cabinet width goal was about 17 inches.

I got caught up in making the port IDENTICAL. This was the reason for keeping the width of this cabinet identical to the Corn. The total heigt and depth is the same as the scala.

So maybe my tall cabinet could work? 17 inch width would just about accomidate the K401

jc

[BEC]

Coming to 24 inch width is easy. Just maintain the square inch volume of the port openings. Now when you start getting narrower than 24 inches, you have to see if you can maintain the port area. Don't think there is room to come down to a 17 inch width and mantain the port area, but haven't tried to work it out to see for sure. Might be possible to raise the shelf a bit to accomodate the port area.

I need to think about the 17 inch width a bit more. That might be an interesting experiment. Talk about really tall, you could mount the horn vertically.

Bob

[Deang]

It makes more sense to design the network around the bass bin. You have to pad the middle and top down to match it, and running the K-33 up to 600Hz leaves the signature of the Cornwall bottom intact. It also ensures that the cabinet generates the necessary 98db/w like the original, and lowering the crossover may give up some sensitivity. Leaving the crossover at 600Hz also helps out the K-400/401 a little bit. She may go down to 400, but I don't think she's always happy about it. Offloading that 200 cycles probably gives JC a much cleaner midrange, especially when jacking on the volume control.

JC, the attached schematic is a simple 1st order with a 400Hz crossover. Something for you to try if you get bored.

[BEC]

Here is what I use on mine. Works very good. Haven't tried any other crossovers.

Bob Crites

[Al Klappenberger]

jc,

The "page at a time" version of the web site works much better. It loads the pictures much faster and the scroll properly.

Al K.

[jwc]

The tall Cornwall would have the 3 port openings stacked and the port itself would be taller and narrower. SAME volume. If there is belief that the bass is dependent on volume and port size only, then this idea should work. As apposed to the shape of the bass bin making a difference.

Haven't thought about the horn being vertical. Would that sound right?

I know the Cornwall vertical worked fine but would a K401?

Thanks for the crossover plans. I hope to make my next set.

jc

[Marvel]

MS Word generates some of the worst HTML code ever. MS should really remove that 'feature' from the program.

I usually use ConTEXT, by a guy in Croatia. Great text editor, with many, many templates for syntax highlighting. It works great, allowing multiple files to be open with tabs across the top of the page. Al, you might like it too.

http://www.context.cx/

Nice looking cabinets.

Marvel

[Tom Adams]

"Any one else have Mississippi State connections?"

I too went to Miss. State.

And I worked for Ideal Acoustics (part time) in 1979-1980.

Spent most of my earnings there.

BTW - nice job JWC. I really didn't need to see this though. I'm having enough trouble getting through with my home theater project and now I see this and my brain starts thinking about another project!

Tom

[rigma]

I went to Mississippi State 1971-1974 majoring in Mechanical Eng. Now live in Nashville.

[jwc]

I was at Mississippi 1988. Transferred to Washington University 1990. Long story. I basically grew up in Starkville.

Live in Carrollton GA now.

I appreciate the input on different web page options. I could have just typed it up my self but I got lazy.

However, there three ways to get the document

http://www.jwcullison.com/csindex.htm

If you have a slow connection:

http://www.jwcullison.com/csclicktoconvert/index1.html

OR YOU CAN DOWNLOAD THE MS WORD FILE AND SAVE SOME TIME

ftp://www.jwcullison.com/Cornscala/cs/Cornwall%20mod%20description4.doc

My wheels are turnin' again on the Tall Cornscala. However, the K401 is 24" inches deep. The cabinet width goal was 17-18 inches. This would look stupid.

The trachorn is 18-19 inches deep with the driver installed. This could work. Otherwise, you are back to using small horns.

jc

[colterphoto1]

Master Carpenter JC sez:

"The tall Cornwall would have the 3 port openings stacked and the port itself would be taller and narrower. SAME volume. If there is belief that the bass is dependent on volume and port size only, then this idea should work. As apposed to the shape of the bass bin making a difference.

Haven't thought about the horn being vertical. Would that sound right?

I know the Cornwall vertical worked fine but would a K401?

Thanks for the crossover plans. I hope to make my next set.

*******

JC- thanks for the labor of love man, those are beauts and something I've often thought about building myself. Fantastic job. I don't mean to be critical in this post, but these are some of my thoughts on the CornScala project:

I like your idea of not re-engineering the cabinet volume and port. Keep it simple by keeping the volume and the port volume (not just the 2D size) identical to the original. Word was that Klipsch got it within 3% of Thiele-Small paramaters and they did the tuning by ear. So lets not tamper with volume. agreed?

I do, however think the shape of the bass bin makes a difference. Cutting the plywood sheets for a 2'x2'x2' box for maximum materials efficiency didn't matter with the LS because it wasn't the cabinet itself, just the horn. If the bottom portion of your cabinet is this shape, you are very close to the original CW volume, but there might be room for improvement.

For most speaker cabinets, if you measure more than a few, follow the same general rules that we use for room size. Go ahead, measure a few. That is to say that none of the dimensions should be numerically akin to any other. What you're trying to do in designing the box is to have dissimilar dimensions so that any standing waves that are reinforced are different in each dimension. So a cabinet of 1'x2'x4' would be equally bad because each dimension would reinforce the sound wave one octave higher. Also certain multiples are less than advantageous because they reinforce a musical fifth or third or other increment. There is that 'golden' number of 1.6something that is found in nature a lot, good number to use.

Consider the original Cornwall measurements 34 x 24x 14 interior. The various ratios of one side to another are h:w .70, d:h .41, w:d 1.7- see, very oddball ratios, this aids in breaking up any standing waves.

There are several considerations in designing the CornScala cabinet. Firstly, by design decree, it must contain the K401/K55 horn/driver combo, so there is a minimum depth of 24", (unless special consideration is made for say corner loading, so the driver could hang out the back of the box). Vertical height is also important so the horns aren't shooting at your knees, so pretty close to a seated person's ears would be ideal. Thirdly, like the original Cornwall, a large motorboard is a good thing as it gives good separation between the woofer and the ports.

I created a little XL spreadsheet to run the numbers on Cornwall vs these design parameters, and came up with this. These are exterior dimensions- 35H x 17W, x 24H. I'd be interested to see what these numbers would do if run through the room dimension calculator the Architectural guys have.

On the matter of horn orientation, the CW horn is purely exponential, I think the K400 is perhaps otherwise. PWK made mention somewhere that the CW orientation didn't seem to matter much from a dispersion standpoint, but I wonder if it's beamier one way than another.I think the K400 or K401 should be left horizontal. I've asked many times, but NEVER seen a good dispersion chart on ANY Klipsch horn aside from the K77, which should properly be oriented vertically. But we're probably best off using a K79 or one of the super EV or JBL designs if you really want to get to 20K.

Peace,

Michael

[BEC]

The practical minimum on width seems to be about 20 inches since the K-401 is about 18 inches wide. Minimum depth with that horn is about 24 inches with the driver also.

Bob

[colterphoto1]

seriously, Indy, put the power tools DOWN!

Michael

[colterphoto1]

Guys, KILL the shelf and you get to use the area around the horns for more cabinet volume. That only existed in the LS because the doghouse had to have a 'top'. Not necessary in CornScala.

Michael

[colterphoto1]

Just read the last couple of posts. If you make it all one box, try 31H x 19W x 24D. Bob, that would give 17.5 inches across the motorboard, could 401 fit in that? I guess we'd have to increase the Height a bit to allow for the volume taken up by the K401/K55 and K77 assemblies. Does anyone have the volume of these?

I guess by keeping the top section separate, you could do 28H (for bass bin only), x 20W x 24 D. Then the whole speaker would be about 40" high.

JC- do you really not like a box that is deeper than it is wide? You should see the RF15's- they're about 7" wide and 15 deep, really peculiar looking. However the narrow face does give better placement options and tall gets those horns up off the ground.

Both of these give the same volume as the original CW.

Pardon me for horning in on your engineering. Hope it's okay. Fascinating business really!

Michael

[IndyKlipschFan]

One of the major things that separates the K horn from the Belle/ or La Scala is the height. If the CornScala is taller, I do not see a problem with anyone having with this too. The overall effect will be much better at your seating arrangement at ear level. Because of this, it will seem a LOT more open in the mids and highs. (Now at some point it is too much. You can't put the high end/ mids near your ceiling and the bottoms on the floor for WAF and besides, I have a feeling it would sound terrible?) This speaker was usually on a stage in large auditoriums, it was designed origionally to be a PA Speaker on top of trains or again meeting rooms for Rockafellers political campaign.

Why not build a Cornwall speaker cabinet bottom (If we know this is a home run) just for the woofer... And put the split la Scala top... on top? (I have seen many people use this exact size Klipsch, JBL, EAW for instance, it must be really good for a 15" woofer?) If you go to the Klipsch cinema products page look at the bottom cabinets. They look a LOT like a cornwall bottom to me!

I have the split La Scalas... With foam material under the high end cabinets to tilt it up slightly and turned to my sweet spot while the bass is firing out into the room straight. It makes a HUGE difference!

[colterphoto1]

Indy, I have a set of JBL bass bins for theatre use (they might be my subs one day) that are EXACTLY this size of a Cornwall cabinet.

However, if we can utilize the space around the horns as part of cabinet volume, we can shrink the size down a bit. It's also a LOT more cabinetry to build the speaker in two boxes, to say nothing of the trapezoidal box for the LS top, then you have to put two input cups in. It does add significatly to the complexity of the project. But I do appreciate the split tops, they are soooo great for positioning.

And positioning is everything!

Michael

[jcmjrt]

JW,

Thanks for keeping track of your project so well. Those are great pics and explanations. I wish that we could ship great sound around as easily as we do great pics - I'd love to hear your Cornscalas sing.

[BS Button]

Colt,

Got any 400 horns for sale?

[PrestonTom]

Fantastic project! Very inspiring also. Thank you for photographing all the details.

Enjoy them,

-Tom