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

Hi Guys,

Here are some mostly finished speaker pics taken during auditioning in my basement this morning. I still need to put a few more coats of poly on then and I want to put some thin black edge trim on the edges to give them a more finished look. I put stick on rubber feet on the back to protect the wall, and used a mirror hanging kit with thick wire so they can be hung safely. I had first listened to them using a cheap DVD player, but today I hooked them up to some decent gear, even better, very very nice, those little TB's are certainly overachievers in this box.

Paul
 

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Hi X,

I based the size on the 74 cm x 74 cm drawing that I saw in this thread, that's ~ 29 inches, I increased the driver chamber diameter by 2" and increased the depth by 1/2" in an effort to reduce mids getting out of the horn. I put a good amount of stuffing in the driver chamber. I followed the expansions as shown in the original sketch. The base is deep and resolute, but not boomy. Low piano notes sound very real.

Paul
 
Final pics and build thoughts :

I finished off my cornu build by adding edge trim for a finished look. I used cheap 3/4" x 3/4" pine corner trim from Home depot. I painted them black before cutting to fit and attached using gorilla glue and brads edge nailed to keep things in place while glue set. Finish is boiled linseed oil cut with turpentine (2 coats to seal), them some poly on cheap home depot Luan underlayment. The edging is also caulked in on the inside of the sides and horn mouths using black siliconized latex caulk and really stiffened up the whole build. Rubber feet on the back to protect the walls and heavy duty picture hangers secured with both screws and gorilla glue so they can be easily hung on the wall. The speakers don't weight that much so they can safely be hung.

Tuning : tried using a zobel, didn't like it or need it with the amp (LM3886 dual mono) it will be used with. Tried a notch filter to tame the supposed 7K breakup from the alum cone, didn't like it, certainly don't need any BSC, so there is no filtering or any kind. I found that even though I made the chamber behind the driver larger than the original design and stuffed it generously there was still some midrange bleed coming from the horn mouths. This could be heard by putting your ear at the horn mouth and has the effect of confusing vocals and mids a bit. I was able to clear this up nicely by stuffing the horn paths. I started by using a softball sized amount of stuffing for each horn mouth, stuffed and reauditioned until I was satisfied, I found that in this build I needed 5 softball sized bits of stuffing per mouth. Using the ear test at the mouth also showed mid leakage was managed. The net result is a very balanced speaker with great base response that needs no filtering. They make the W4-657S tangbands that I used sound terrific and for the typical non audioholic layman listener border on HiFi. Their weakness is that I used W4-657S and for the trained ear the high frequency response and detail could be better. All in all a fun project and a great gift to give a young stud for his first apartment. Here are a couple finished pics.

PJN
 

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Almost done. All that remains is to attach the face to the spiral. The face is 4 mm plywood and the spirals are foam core.
Driver is Tang Band 871S, an old model that was popular a few years ago and I still have a few of them unused.
I'm still deciding on the glue to fix the face to the core baffle, because only the face is wood and the rest is foam core. Would white carpenter's glue enought? Or perhaps silicone sealant would be better? Which one would give better sealing for the spiral channels? Not a clue on this choice.This is my first foam core project! Any suggestions? Thanks.

is the foam spiral enough to withstand the weight of the plywood front that has the speaker?
 
Final pics and build thoughts :

I finished off my cornu build by adding edge trim for a finished look. I used cheap 3/4" x 3/4" pine corner trim from Home depot. I painted them black before cutting to fit and attached using gorilla glue and brads edge nailed to keep things in place while glue set. Finish is boiled linseed oil cut with turpentine (2 coats to seal), them some poly on cheap home depot Luan underlayment. The edging is also caulked in on the inside of the sides and horn mouths using black siliconized latex caulk and really stiffened up the whole build. Rubber feet on the back to protect the walls and heavy duty picture hangers secured with both screws and gorilla glue so they can be easily hung on the wall. The speakers don't weight that much so they can safely be hung.

PJN

looks good, did u pain the foam on the sides (exposed) black also?, makes it look classy. Did u use the plywood front?, what thickness?