Getting the spiral glued into the backpiece to fit into a groove on the front(unless it is quite wide) would be difficult at best. Front one should be left flat.
Need to be a very small tweeter bezel (& midbasses) to get the C-C less than a 1/4 wl at the XO.
dave
Um... I was saying foamcore is better than coroplast. I've used sheets and sheets of foamcore, building architectural models, and I think it's a good choice and have actually made small speakers with it. Isn't that your opinion? please clarify as I'm confused...
Seems to me that routing a template for use in a pin router would be expedient. Create complimentary channels in the front and back to receive the strips of foam core.
Also, why not go ahead and make an mtm using 2 Vifas and an economical tweeter? ...or 4 in a diamond mmtmm surrounding the tweeter? They are small enough that lobing shouldn't be an issue. There's no reason you full-rangers should have all the fun.
The use of fancy jigs, routers, and cutting channels and grooves is exactly what I was trying to deliberately avoid with this build as that is what kept so many people from trying to build the Cornu in the first place. Maybe if you want to go into production with a wooden channel version this is the way to do it ( and I believe this how the production version of the Cornu spiral is built). But what I found out in doing this using paper-faced foam core board was that you can build the spirals very easily simply by gluing sections at a time and curving it by hand to follow the trace of the spiral on the back. Literally, it takes 15 minutes per channel and 1 hour to glue all the channels. The key trick is to lightly score the CONCAVE side of the channels paper face with light cuts perpendicular to the bend - it not need be exact. These small cuts allow the inside paper to evenly compress the foam, the outside paper face goes into tension, and the whole thing is very smooth and sealed. Once glued in place, the curve looks very good. Also, a channel would necessitate thicker faced boards, adding weight. These speakers built with foam core channels and 1/4 in ply faces, or even foam core faces, in my case are extremely lightweight yet rigid. The light weight makes it easy to hang without requiring a stud in the wall or even a toggle bolt for drywall.
As far as using two Vifa TC9FD's and a tweeter, I find that the Vifa already has enough of a high end (it is very tweeter like). The diamond MMTMM would have lots of output, you can probably skip the tweeter given how high these drivers go. One nice thing with the MMMM (sans tweeter) is that we skip the X-over and it let's us wire the quad 8 ohm Vifa's as 2, 4, 8, 16, or 32 ohms. I would pick 4 ohms so that doubles the power my amps can drive. The CTC spacing of the Vifa's is 84 mm (plus they have squared off bezels to allow tight packing) - will this cause any comb interference effects? This now let's the Cornu handle up to 120 watts, with equivalent Vas of 5 liters (? simply additive?) and SPL levels that will be higher than a single, and the cost would still be less than a single 4 in Fostex (even in non tricked out form)!
I think this would fit if one built a slightly larger speaker box in the center but keep the spiral lengths modest as it would be pointless trying to get the little guys to push anything below 50 Hz. I like this idea....
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A round 4 inch or 3.5 in coax could work, the oval just would not look very good (imo). There is a round Pioneer 3.5 (TS A 878) that is very good.
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Cal,
I think a driver used in the Cornu should have an extra peaky high end to compensate for the mondo bass, plus it will give you more 'tweeter like' abilities to anchor the imaging compared to some of the higher frequencies that may leak out the horns. I was looking at drivers that seem to have this high end peakiness and noticed that the TB W4-1337SDF may fit this bill (it's got an extra 10 dB or so from 10 kHz to 20 kHz compared to baseline SPL). It is a nice looking titanium driver too. What do you think?
Xrk971
http://www.parts-express.com/pedocs/specs/264-916-tang-band-w4-1337sdf-specifications.pdf
Hi Mark, I must have read and responded to your post too quickly. My bad.
Agreed.
I have lowered the horn response with stuffing the throat and am hoping to take it a bit further next time I open these up.
I'm not so good at judging sound by graphs but ya, that one looks like a tweeter. I can't see this box doing any driver much harm, within reason of course.
Awesome... the cornucopy(a) goes viral.
Yeah, I can't believe the response with the views about to reach 8000 now. I think everyone likes an easy and inexpensive project that sounds great. This is what folks will see once they listen to it for the first time like Cal and I did. I like the Cornucopya name.
I was thinking FoamCornu too, but Cornucopya is better. I am an unknown on this forum but when folks hear such high praise from Cal, they jump on it. thanks for trying it Cal.If folks wouldn't mind, can I get a show of hands of how many people are actively buying foam boards or building the Cornucopya?
Thanks,
Xrk971
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For now, planning on the one cannibalized from Logitech S120's which resemble a Visaton FRS5. They are 4 ohms and rated to 5 watts according to stamp on back. Let's see how low the sound can go. Any improvement over stock enclosures would be welcome.
Although you know that I am, here is the official hand raise --
Drivers on order (actually shipping today, according to Dave) other materials will be bought once I leave the house in a 1/2 hour or so.
The straight sections and sharp corners act as low pass filters to restrict the non-bass stuff from getting out of the horn output. This would reduce the imaging if too much got out. Smooth channels with no sharp turns will let more high frequencies out but be more efficient. I made it smooth from a practical standpoint for the smaller 14 inch design as putting sharp corners in is tough given how much closer the channels are now. There is barely enough room for tip of glue gun to get in for the second and third channels, and I will say that I am approaching the small size limit of the Cornu given the need to use hot melt to secure the curves. Also, I am not as concerned about stereo imaging with the smaller one but wanted to get as much sound out as possible from the tiny driver.