GWN Cornscalas

[Mike Dubay]

There has been a lot of interest in Cornscalas lately. Here is my build of a pair from here in the northern Midwest, thus the Great White North (GWN) Cornscalas.

So for any big project I write down what my end goals are:

I want improved bass response from my basement listening system and the classic large format horn sound that defines Heritage Klipsch. Want good sensitivity, in the 100 db or higher range.

Cornscalas appear to fit the bill.

Project definition:

Want this to be a DIY project. I enjoy building speakers, and find the building process is a great learning tool to understanding what you are working on.

Size and SAF is really not a concern. This is for the man cave; they can take as much space as available. I have 17 feet of wall space.

I plan on building a split Cornscala, separate horns and woofer cabinets. This will allow flexibility in the future to move to MWM bass bins in the future.

I’m will be willing to try new things, but will be sticking close to the spirit of designs previous.

This is not going to be an “at all costs” project, there are always tradeoffs in a design, both cost and performance. But I expect that classic Klipsch sound when I’m done.

I plan on building my own mid range horns. There have been several detailed posts on this, and I’m ready to tackle this. This will also reduce costs, as large format high quality horns can be pricey.

I will be including pictures on the way which always seem to increase interest in the forums. This will also not be in “real time”, but more retrospective as I’m far long in the project at this moment.

So here we go…

[Mike Dubay]

So first order of business: Selecting the drivers.

Decided to go with new hardware, no surprises out of the box.

Woofers: A pretty clear winner here, based on reported superior performance and at a great price to boot, you can’t go wrong with the Crites CW1526C driver with cast frame.

Midrange: Here I’m going to depart from the usual Atlas PD-5VH. There was some positive discussions awhile back about the Selenium D250-X Phenolic Driver. I read some positive comments by a person who replaced a pair of blown Atlas drivers on his Klipschorns with these. They come in at a great cost savings compared to the Atlas drivers, so I decided to give them a try. If they don’t work out, they can be replaced with the Atlas drivers in the future.

At only 35$ each, they are worth a try.

They are 8 ohm instead of 16, SPL of 107 dB 1W/1M. With a reported frequency response of 400 to 9000Hz.

[Mike Dubay]

Tweeter: The APT line of drivers seem popular here on the forums, so going with the ATP-200, with the cool looking ‘cheeks’ horn lens.

[JohnA]

Mike,

Have a look at these, especially as a pair in each cabinet 15LF-2

Better yet, a pair of Bob's cast frame woofers in 16 ohms would be optimum.

[Mike Dubay]

Yes, went with the cast frame woofers from Bob crites. Singles for now.

[Mike Dubay]

Now for the midrange horn design.

The plan is to have the bass cabs of a similar width as the design by Cullison. http://forums.klipsch.com/forums/storage/4/1071530/cs4.pdf).

The horn will be inside a cabinet with the same width as the bass cab, so the horn will need to sit inside a 25 ¼ inch wide cabinet. The driver can stick out the back of the cabinet, so there is no depth constraint. For purely aesthetic reasons I will set the aspect ratio to be 2:1, Width to Height. Given these parameters, design a horn with the lowest frequency that will fit the above.

I went to the Volvotreter web page and down loaded the Tractrix Horn Calculator. I did several examples in which I reversed engineered several designs on the Klipsch forms so I understood the spread sheet.

http://www.volvotreter.de/dl-section.htm

I can up with the following:

Fcut off 243 Hz

Horn W:H 2.0 W/H

Throat dimension 1 inch

Horn length 21.3 inch

Width of Horn 11 inch

Height of Horn 22 inch

One of the things you need for a template for the horn is the length of the two flat horn walls. I drew a trapezoid with a 1 inch throat, and an eleven inch mouth, and a total length 21.3. This represents the inside of the horn in the vertical plane. The long side of the trapezoid was measured to be 22 inches long. For each of the distances from the horn throat, you multiply by 22/21.2 to get a ‘stretched’ length. This is a representation of the distances at the center line of the horn as it is expressed in the plane of the upper and lower walls of the horn.

I then tabulated ½ widths at the various distances from the throat. I added finer lengths when near the mouth of the horn, when the widths are changing quickly.

			Template	Template
[in]	[in]	[in]	[in]	fractional inches
stretch			half	half
length	height	width	width	width
0.00	1.00	1.00	0.50	8/16
0.93	1.42	0.86	0.43	7/16
2.05	1.92	0.81	0.41	6/16
3.03	2.37	0.82	0.41	7/16
3.92	2.78	0.86	0.43	7/16
4.92	3.23	0.92	0.46	7/16
5.99	3.72	1.01	0.51	8/16
6.94	4.15	1.12	0.56	9/16
7.93	4.60	1.27	0.63	10/16
8.94	5.06	1.45	0.72	12/16
9.06	5.11	1.47	0.74	12/16
9.96	5.52	1.67	0.83	13/16
11.05	6.01	1.96	0.98	1
12.01	6.45	2.28	1.14	1 2/16
13.03	6.91	2.68	1.34	1 5/16
13.99	7.35	3.15	1.58	1 9/16
15.02	7.82	3.78	1.89	1 14/16
16.02	8.27	4.53	2.27	2 4/16
17.02	8.73	5.49	2.75	2 12/16
18.00	9.17	6.69	3.34	3 6/16
18.99	9.62	8.27	4.14	4 2/16
20.01	10.08	10.53	5.26	5 4/16
20.50	10.30	11.96	5.98	6
21.01	10.54	13.86	6.93	6 15/16
21.25	10.65	14.99	7.50	3 12/16
21.50	10.76	16.40	8.20	8 3/16
21.75	10.65	14.99	7.50	3 12/16
22.01	10.99	21.98	10.99	11

Then draw a full sized template, stretch length against half width.

[Mike Dubay]

I traced the half template on ¾ inch birch plywood, flipped the template over, and traced the other side. I rough cut the template and refined it to the traced line with a drum sander and hand sanders. With a full sized template, using the router table I make three other horn walls using the first as a template.

[Mike Dubay]

Now for the jig for making the horn. I made a trapezoid 11 inches at the base, 1 inch at the top, and 21 7/16 long. I inserted a screw at the top, and mounted the trapezoid vertically on a piece of scrap wood. Two of the horn walls are now set on the long side of the trapezoid and various braces and stops are attached. The side of the horn walls must be sanded even to the interior width so the next two faces will lie flat against the faces. I used 50 grit sand paper on a 3 inch pipe to sand the edges even.

[Mike Dubay]

I then glued two slightly over sized pieces of flexible plywood to the existing horn walls. The only thing I did not love about the flexible plywood is that the grain opens up when bent to a tight radius. Just some extra filling and sanding. Next time I will place a piece of birch veneer on the flexible plywood to provide a smooth finish.

[hklinker]

Nice work on the horns. Keep the posts and photos coming. Just finishing a pair myself![]

[kevinmi]

Hey Mike-I just made a pair of mid horns for my Khorns using the program you sent me. I'll be posting pics soon. I went to the local Michigan Lumber to buy some flexible luan for the horns, and they wanted $40.00 for a full sheet. As I was walking through the warehouse, I spotted some other thin luan, so I asked about it. It was door skin luan, used to put over a damaged door, and very thin. Long story short-it bent the same as the bendable luan and cost me $11.00 for a whole sheet! Hope to get an invite to listen to your GWN's when they're done! -kevin

[Mike Dubay]

Hope to get an invite to listen to your GWN's when they're done! -kevin

. Sure thing Kevin, That is one sweet looking turn table in your avitar. Who makes it?

[Mike Dubay]

Here is my first horn out of the jig.

[Mike Dubay]

Side view.

[Mike Dubay]

The base for the horns consists of a trapizoid of 3/4 inch birch plywood, a triangle down the middle, and a rectangle to mount the driver to the squawker.

[Mike Dubay]

Why just build a base for the horn, when you can instead over build the base for the horns.

[Mike Dubay]

Attaching the horns to the base. Boy are these things getting heavy, and feel very solid.

[Mike Dubay]

Almost a shame to black them out. Look sinister in black with the driver mounted. Next time I would like to have the horns stay a natural wood color. Maybe have a layer of oak veneer on top of the flexible plywood. Or mahogany lamiate as Kevin suggested. Why go to the time of building wood horns and then cover them in black to hide them.

[Mike Dubay]

Close up of the driver and adapter. To align the adapter I placed a 1" cylinder in the hole in the horn through the adapter, then marked the holes which gave good alignment.

[kevinmi]

Hope to get an invite to listen to your GWN's when they're done! -kevin

. Sure thing Kevin, That is one sweet looking turn table in your avitar. Who makes it?

Mike, that's my JVC TT installed in a plinth I made this summer. I bought another JVC TT that I'm going to build a similar plinth for out of oak to match the Khorns.-kevin