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

Well, I read about a third of the way through this thread and built one speaker for an Aurasound Whisper. Let's just say it was a good learning experience learning how to make foamcore make those tight bends. :eek:

So now I'm going to build two more using what I learned. (Make shark gill slits on the inside of a bend and only glue down short pieces.) But before I do, would someone be so kind as to tell me how deep to make it and the throat area? I'm using the pattern I found here and have it drawn out on a 14" square. The first one I built 14" square by 3" deep and the throat area matched the Sd of the Whisper.

Here are the specs for the Whispers:
Thiele-Small Parameters
Resonant Frequency (Fs)250 Hz
DC Resistance (Re)6.4 ohms
Mechanical Q (Qms)4.72
Electromagnetic Q (Qes)0.80
Total Q (Qts)0.68
Compliance Equivalent Volume (Vas)0.01 ft.³
Maximum Linear Excursion (Xmax)3 mm
Surface Area of Cone (Sd)13.2 cm²

Thanks!
 
This weekend I finished reading this thread and finished my second Cornu.
Keeping in mind that I listen to primarily acoustic music (bluegrass and folk) but I'm really impressed with these. Acoustic bass is apparent enough to enjoy my music and I really like the mids and highs of these small drivers. The 3" sounded a bit hollow, but I stuffed the horns and I really can't tell much difference between the 2" and 3" deep versions.

I just finished printing and taping together the plan for a 20". I have a pair of Fountek FR89EX that need a good home....
 

Attachments

  • 20201126_193842-1 (1).jpg
    20201126_193842-1 (1).jpg
    181 KB · Views: 309
  • aurawhisper2.jpg
    aurawhisper2.jpg
    176.5 KB · Views: 566
I started laying out the 20" plans on the bottom plates and didn't feel like poking all those holes.
So I came up with another approach. I laid my plan on the bottom plate and pushed three pins in for alignment. Then I put the pattern on the second bottom plate and pushed those pins in again. Now I can remove and replace my pattern on both plates and keep the pattern aligned.

Then I cut the pattern on the outside line in 90 degree segments. I traced the pattern outline, put it on the second plate, and repeated.

Cut on the outside again in 90 degree segments. Trace again.

Repeat. Once you get past the second set of vanes you can cut in 180 degree segments.

It turned out pretty good. It's more accurate than the hole poking method I used on my first set. It may not make any practical difference, but satisifies my OCD. :D
 

Attachments

  • c1.jpg
    c1.jpg
    152.3 KB · Views: 355
  • c2.jpg
    c2.jpg
    141.6 KB · Views: 346
  • c3.jpg
    c3.jpg
    116.1 KB · Views: 329
  • c4.jpg
    c4.jpg
    159.3 KB · Views: 331