Ever think of building a Cornu Spiral horn? Now you can!

[xrk971]

Originally Posted by kambule

Mr. xrk, I got some spare HiVi B3s. Are they good for your 20 inch design ? I shall keep the
throat 3 x 1.2 inch. Since they are heavier, I guess double foam core board for the panels is
required.

Another question, what is the major difference between the foam board used in the cartoon boxes and
the foam core board ?? Can I strengthen the foam board by sticking the self-sticking wall paper ??

Kambule,
The HiVi B3s should work just fine, I would reduce throat a bit to match 30 cm square Sd.
Two layer foam will be strong, not sure if needed. Can always add if you do. Wallpaper won't really add strength unless it is thick and adhesive is strong.

[kambule]

thanks xrk and hajj.

still wants to know the difference between packing type foam board and the foam core board in audio application.

[Cal Weldon]

If you are talking about the stuff I am familiar with, the packing stuff is expanded bead polystyrene in sheet form and the 'foam board' is paper faced extruded polystyrene. They are not interchangeable.

[xrk971]

The foam used to pack things in boxes is typically expanded polystyrene beads (little white balls) that are fused together into a shape with a mold. It is also used to make insulation panels, as I learned, from Bob Brines and Cal, and is called "bead board". The foam core boards that I use is a closed cell foam that is formed between two sheets of paper to give thickness and strength to the paper face. I think this foam is formed by a chemical process that generates gas bubbles to expand the polymer (rigid polyurethane) rather than beads fused together. Here is an example of the type of foam boards that I use: Elmer's White Foam Board | White Foam Core Board 20" x 30"

[recurve99]

I picked up my foam core today and plan to start this weekend. My build will be a 24 inch, 3 deep, Vital Tc9, and wood front/back.

One thing that strikes me since stuffing is so important...why not use a Zip-it to pull out the stuffing if you have too much? Those things pull amazing hair balls out of a drain...

[xrk971]

Recurve,
Good idea, we have discussed attaching string to the stuffing in a mesh bag to enable removal. A foam core back also allows surgery to cut small windows to adjust foam. I found that contact paper works as great temporary seal tape for foam core to allow stuffing test before final glue.

[kimbo1]

Carried over from my thread (Boat/full range) stupid me carrying on over there....XRK971/ Cal.......i've taken your advice and it of course, makes perfect sense!!
Thank you both for your replies, but, here's the thing; without measuring i can't give specifics but let's just say i'm thinking 'saloon' is 6' H/10'W/maybe 8' long.

Can just about do 20" but, they'll be placed no more than 12" or so from hull sides/ maybe same from deck. The only saving grace is that the 'room' isn't square in any way, bar the flat bulkhead where they'll be placed.
So, maybe 14" baffle is the way forward with 2" driver??

I've got the pdf (blue/red traces) but can't remember whos it is, think it's the original layout? Comes out at circa 7" on a piece of A4. 1" square graph paper seemingly.

Some really cheap 3" driver folded horns just about go loud enough for me in there so, given the assumed better spl from this design i'm thinking it may not be too much of a loss at 'mini' size?

However, i don't want to have NO bass at all ! Catch 22 it seems.

[xrk971]

Kimbo,
The size room you describe is probably too small for a 20 inch cornu. I have the 14 inchers in a room almost same size as your boat but with higher ceiling (9ft) and they sound great. I am using cheapo no name drivers, if you get the Vifa TC6FD 2.5 in driver, I think it will sound better. I get bass down to 100 Hz with the 2 in drivers, it is not hip hop deep by any means but what you do have is Very room filling, and works great for jazz and vocals, pop. There is a sound clip of the 14 inch cornus back in this thread (post #60).

[zayne742]

Originally Posted by xrk971

I got a reply to my PM to Hersh (Sebastien Pitkanen). He said that when he did the cornu, he talked to Daniel and the double layer plan with the semi-curved design was supposed to be the final optimized design. Apparently there is supposed to be something to that design and having 8 flow channels or horns that makes a difference. It would be interesting for somebody to make an exact copy with two layer horn in foam core in the full 70 cm size and use recommended driver (Monacor or FE108Esigma) and do a measurement. Anyone have a FE108ESigma handy?

Just to clarify, this was essentially the same as the current cornru dimensions, just with the addition of the divider and the math to adjust accordingly? It is not double the depth, correct?

Only wish I had the 108, however, I do do have 3 pairs of the Pioneer A11 needing cabinets. One pair is in my favorite BIB's. They work so nice for a cheap driver.

[xrk971]

Zayne,
The commercial Cornu uses the same plan as posted by Hersh and later redrawn by Planet10. The depth is 5.5 inches I think for both layers but there is a 0.4 in thick divider. So the actual flowpath height for each channel is 2.56 in deep. So it is like building two 27.5 in horns with a 2.56 in deep set of channels per side then capping with two facers. Of course the middle board has to have a big hole in it.