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

Founder of XSA-Labs
Joined 2012
Paid Member
George,
I meant passive radiator as in similar to guitar body, not like actual non powered woofers tuned to enhance bass from driver. Yes, the vibrational modes are very complex, but can be modeled with FEA, especially if one has the Cornu in Solidworks model already. Not that I want to do this though... I have sandwiched a dense non drying putty ( plumbers' putty) between the foam core sheets and it is very quiet. Your tri-ply cardboard with silicone sounds good too. I took apart a hard disk drive once and noticed casing for the platters was a sandwich of stainless steel/sorbothane/stainless steel. You could tap it and only hear a dull thud. Earlier in the foam core thread I asked a question about using Dow Corning silicone dilatant (Silly Putty) as a smart material sandwiched between sheets of speaker cabinet walls but no one replied. I actually have a 2 lb chunk of that putty to play with...
 
Last edited:
Administrator
Joined 2004
Paid Member
I suppose I should get the other one built today - busy week ahead. Want to hear the little fellows in stereo.

One thing I will NOT be doing is using Gorilla Glue again. The gorillas can take their damn glue and go back to the Belgian Congo, for all I care. What a mess! Got all over everything, including the speaker face and my hands. Fortunately I had a can of carburetor cleaner handy which takes it off my sticky hands. Only thing I've found that does.

Anyway. It sounds pretty good, if definitely mid-bass heavy. I'm guessing a big peak circa 100Hz, but will measure to be sure. It's a cool design, but I think needs some tweaking to get a good tonal balance.
 
Founder of XSA-Labs
Joined 2012
Paid Member
Thanks for the warning with Gorilla glue.:eek: Congrats on getting first sound. :cheers: Which size did you make and what driver are you using? The stuffing is real important. Need dense pack in main driver cavity. I have some in the throats but loosely applied there. Cal noticed peak at 120 Hz too I think.

Oh, and please post sounds when you get a chance. I know you know how to do this Pano... ;)
 
Last edited:
Administrator
Joined 2004
Paid Member
I did the 20" size with the 3.5" Vifa.

Gorilla glue is OK (but messy) for small jobs. I regularly use it for gluing plastic to metal - works great. My problem with this big job yesterday was that the G.G. had thickened up in the bottle and completely clogged the nozzle. Nothing I could do would make it flow thru the nozzle. As I was already into the process, I had to remove the nozzle and dish it out with a stick. What a mess! Got all into the stuffing, as well. Yuck. G.G. does foam and fill gaps, bit it also runs down the sides no matter how you apply it. I have never used the new white gorilla glue.

I lightly stuffed the beginnings of the spiral and did some stuffing behind the driver. Sounds like more is called for. I will experiment. I have pillow stuffing, which is not very good for speakers. Might try fiberglass or cotton rags.

Yes, I'll post recordings and measurements.
 
frugal-phile™
Joined 2001
Paid Member
Looks very similar, in a simpler way. :checked:

It is a TL thou. Close to straight, A halfwave with driver mounted at ~50%.

attachment.php


dave
 

Attachments

  • Bose-spiral.gif
    Bose-spiral.gif
    14 KB · Views: 6,928
Work in progress

Ok, last tuesday I've finally found the foamcore board (not so cheap as at Dollar Tree) and last week-end I started the built.
I've scaled down to 50x50 cm the Cornu design (@planet10: thanks for the pdf) tracing a 14x14 grid, marking relevant points and joining them by hand.
Baffle and back are in poplar plywood (8 mm), 50x50 cm (20"), inner depth is 7,5 cm (foamcore strip height).
Can't wait to hear them... :D
 

Attachments

  • image.jpg
    image.jpg
    713.1 KB · Views: 3,210
  • image(2).jpg
    image(2).jpg
    875.5 KB · Views: 3,122
  • image(3).jpg
    image(3).jpg
    485.5 KB · Views: 3,040

Perfect, this is what i did.

If you find that it is too tight, trim some excess off to get the throat area opened up, I had to do that on my micro cornucopya after the hot melt glue hardened before I had a chance to set throat in correct location. I am glad folks are enjoying this build. :)
Really enjoying. First time I used a hot glue gun.
To scale down the Cornu design to 50x50 cm I had to remove the initial segment (4-5 cm) of the spirals to get a 2 cm throat.

Thanks again ;)
 
Founder of XSA-Labs
Joined 2012
Paid Member
Switters,
I like how you did it the manly way: triangle, dividers, ruler, pencil, and steady hands! :) I drew mine by hand using the grid method too. There is just something cool about laying down the spirals into a path that you drew yourself rather than a printout.
Looking forward to hearing your impressions of first sound. I forgot or did not see in your earlier post - what driver are you using?
 
Founder of XSA-Labs
Joined 2012
Paid Member
Micro Cornucopya (14 in) sound clips

I have been listening to the micro's for almost 5 days now (they are left on continuously when I am not listening) in the smaller bedroom, and I believe they are breaking in more, if that is possible with cheap no-name 2 in drivers. The sound has improved and the tonal balance, bass, and overall musical experience is now very rewarding to listen to. So much so, that I feel compelled to report how much I really like the micros and post a sound clip for folks to hear. The micro Cornucopya project has perhaps been the most bang for the buck and I can whole heartedly recommend it for those not wanting to make the bigger brothers. It is very cost effective and I would suggest ordering a set of Logitech S120's to take apart. I am actually using it with the Logitech's built in amplifier which according to specs is rated at 1.15 watts per channel. Even at this low power, the cornu horn expands the sound volume to fill the room and it is quite loud. One of the best things about the Cornucopya is its ability to sound good even at low volumes - the bass is still there. On some speakers the bass is only present at higher volumes, not so here. The speakers are about 4 ft apart and 4 ft high off the floor. The measurement was taken with a digital recorder with XY mic at about 6 ft away. For this sound clip, I am playing the amp at about 70% of max setting - quite loud. This is definitely the best sounding $10 set of speakers and amplifier that I have ever heard. When listening to the clip keep in mind that you are hearing tiny 2 inch drivers mounted in a paper faced foam box. I did not have a convenient project box to mount the Logitech amplifier in so I used an old baby wipes container with a terminal strip mounted on top,
 

Attachments

  • micro-cornu-clip.zip
    963.4 KB · Views: 697
  • a microcornucopya 05.jpg
    a microcornucopya 05.jpg
    124.3 KB · Views: 2,048
  • a-microcornu-amp-02.jpg
    a-microcornu-amp-02.jpg
    103.3 KB · Views: 1,618
Last edited: