I have looked at a Cornu with a large driver chamber. This can be implemented with a secondary chamber larger than the main one abd locared underneath the main one on the back. The Cornu is quite forgiving of driver selection in general. The added volume will help the reduce the mids leaking out by settin g the high cutoff freq lower as that is proportional to throat area divided by chamber volume. It's easy enough to simulate it. Do you have a particular driver in mind?
Think about it as an expanding line with an opening that's horn loaded with 3 horns....
Well, I'll try to model something up on MJK worksheets and see how good it might behave with different drivers.
I actually did some modelling for the cornu a few months ago, but forgot to post the results, I'll try to dig them up later tonight and post them.
But the models were made with double similar length horns, as this is one of the limitations of MJK's worksheets. IIRC, I modeled two different lengths so as to see each pair of horns contribution to the output, the downside being that the interaction between the differing length horns is not taken into account.
On the other hand, I think that modelling the BVR with equal length horn might be interesting, specifically because of the fact that the upper corner frequency of the horn will be lower, meaning less mids going through the horn which in turn will mean less stuffing. But this is all speculation for now. Let's see how it'll turn out..
More to come later today (hopefully)
well i finished my second speaker today, as you can see i had a professional helping me this time 
and i absolutely love how these sound.. i never expected something i made (out of foamboard even) to sound this good!
All of this is already in earlier posts but to help out anyone who is considering to build these themselves:
I used the scaleable pdf from post #30, if you print it with adobe reader x or higher you can select poster, then it will print over multiple pages and you can tape them together quite easy.
If you want to scale it to another size, mind the 74x74, that's the size of the red line, the black lines are 70x70 in that pdf
After sticking them together i made holes along the lines to create a stencil, then just go over it with a marker and connect all the dots.
After cutting the strips i used a ruler to bend them, place the ruler on the place you want to bend it, press down on it, then bend the foamboard around it, move the ruler a bit and repeat. Gives you much cleaner bends then folding it by hand.
I hot glued the strips to the bottom and used a polyurethane glue for the top.
Well that about covers it can't wait to start building the next pair!
ps.
Big thanks to xrk971 and Cal!! couldn't have done it without your help.
and i absolutely love how these sound.. i never expected something i made (out of foamboard even) to sound this good! All of this is already in earlier posts but to help out anyone who is considering to build these themselves:
I used the scaleable pdf from post #30, if you print it with adobe reader x or higher you can select poster, then it will print over multiple pages and you can tape them together quite easy.
If you want to scale it to another size, mind the 74x74, that's the size of the red line, the black lines are 70x70 in that pdf
After sticking them together i made holes along the lines to create a stencil, then just go over it with a marker and connect all the dots.
After cutting the strips i used a ruler to bend them, place the ruler on the place you want to bend it, press down on it, then bend the foamboard around it, move the ruler a bit and repeat. Gives you much cleaner bends then folding it by hand.
I hot glued the strips to the bottom and used a polyurethane glue for the top.
Well that about covers it
can't wait to start building the next pair!ps.
Big thanks to xrk971 and Cal!! couldn't have done it without your help.
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Coen,
Glad they worked out! They do sound fantastic don't they? Good tip on using a ruler to bend the channels. In case you missed it, the way we did the bending and curves is to score a light cut on the concave side of the channel. Just enough to pierce the paper skin and have lines about 1/4 in apart for tight bends and 1/2 inch apart for gentle bends. This way ensures that the convex side never gets creased or buckled by accident.
Nice work.
What kind of music have you played in them and what kind of amp are you driving them with? In case you don't have way to hang on wall: I use a small piece of flat sheet metal with a hole or a washer works. Tie wire or heavy twine to that and then hot melt glue that to the back to have a wire like a picture hanger on back of a frame. Hot glue a piece of foam core over the metal washer so it doesn't rub or buzz on wall.
Glad they worked out! They do sound fantastic don't they? Good tip on using a ruler to bend the channels. In case you missed it, the way we did the bending and curves is to score a light cut on the concave side of the channel. Just enough to pierce the paper skin and have lines about 1/4 in apart for tight bends and 1/2 inch apart for gentle bends. This way ensures that the convex side never gets creased or buckled by accident.
Nice work.
What kind of music have you played in them and what kind of amp are you driving them with? In case you don't have way to hang on wall: I use a small piece of flat sheet metal with a hole or a washer works. Tie wire or heavy twine to that and then hot melt glue that to the back to have a wire like a picture hanger on back of a frame. Hot glue a piece of foam core over the metal washer so it doesn't rub or buzz on wall.
Nice going Coen, those look great. I like your expert help too.
If you hadn't heard before, we have all used the 'score the inside of the curve' before doing the bending. Also, since I have a rounded edge to my countertop, I can run it back and forth over the scores and end up with something that has almost the perfect curve. ie: I'm not fight the 'memory' of the foam in order to glue it. Made the gluing process very quick.
So glad you got the enjoyment out of them as others have.
EDIT: By the time I finished typing, two more posts ahead of me.
If you hadn't heard before, we have all used the 'score the inside of the curve' before doing the bending. Also, since I have a rounded edge to my countertop, I can run it back and forth over the scores and end up with something that has almost the perfect curve. ie: I'm not fight the 'memory' of the foam in order to glue it. Made the gluing process very quick.
So glad you got the enjoyment out of them as others have.
EDIT: By the time I finished typing, two more posts ahead of me.
I used Bison professional konstruktielijm - polyurethane
this one:
http://www.bison.nl/static/resized/products/assets/asset_9235_4.gif.270x330_q95_autocrop.png
On the first speaker i used quite a lot so it kept leaking out, then with the second speaker i made the mistake of using less glue, so i ended up with some tiny holes at the side, which i had to fill up again
so better use to much and having to clean up a few times then using to little I also had four 5kg plates on it to press it down and let it dry well over 4 hours (next time i'll probably slap on even more weights)
I did mis the scoring, guess i was to eager to get started building them. I'm using a Marantz SR7200 reciever to drive them. As for the music, i played everything i could find, from guns n' roses to david guetta, now i just have a youtube playlist running just to hear how everything sounds, but my speaker building pro is sleeping in the room next to me so i can't really get the most out of them now, if you know what i mean
Nice going Coen, those look great. I like your expert help too.
If you hadn't heard before, we have all used the 'score the inside of the curve' before doing the bending. Also, since I have a rounded edge to my countertop, I can run it back and forth over the scores and end up with something that has almost the perfect curve. ie: I'm not fight the 'memory' of the foam in order to glue it. Made the gluing process very quick.
So glad you got the enjoyment out of them as others have.
EDIT: By the time I finished typing, two more posts ahead of me.
That would probably even work better, i'll try it on the next run
Talking about that, i found some posts on a dutch forum of someone building these with flexible plywood:forum.zelfbouwaudio.nl • Toon onderwerp - spiral horn met frs8
(scroll down to the bottom) Anyone here have experience with it?
Also if you use 5.2mm, 3-ply(1/4" approx)ply that has a thick lateral (across the sheet) inner layer and two thin veneer layers on the outside lengthwise, you can plane or sand off one veneer side and the stuff will bend pretty easily. Get it wet on the remaining intact veneer side, and it will go even easier. If you have the right equipment-a big belt sander with a new 36 grit belt or a hand held power planer, it can go pretty quickly. With access to a wide belt sander you could probably do it really quickly, though you would have to use a thicker board to back up the piece as you ran it through on the conveyor. Lauan 5.2mm 3 ply-which has "Philippine mahogany" faces is often sold as underlayment, but tends to be very well mannered to work with and pretty clear on it's faces.
Can't read Dutch, but do have some experience.
There is also bending ply that is harder to find, but is kind of like the above mentioned 3-ply, but is "turned inside out"----the outer layers are thicker and the inner layer is thin. It bends without sanding or planing it because there is very little thickness to the inner layer, and you bend it across the grain of the outer layers. There is also 2 ply bending plywood, which I haven't used, but it probably bends a tighter radius than the 3 ply. With the bending ply, I think that if you were going to wet this stuff, it would be on the outside of the curve, because it is going to expand a lot across the grain.
Here is a link to one manufacturer of bending ply:
Columbia Forest Products : Radius Bending Plywood
Columbia Forest Products : Radius Bending Plywood
Another option is to use plywood on the channels only on the visible final sections near the mouth and use foam core construction on the interior. The foam core is actually quite stiff in the axis perpendicular to the bend once glued in place and provides inherent bracing for the speakers. Luaan plywood works really well for the faces and also for the visible portions of the channels at the mouth.
Thanks for the info
i was looking at aircraft plywood, it's made out of multiple very thin layers and very flexible like the bending ply.Anyone here ever compared a pair of wooden cornu's vs foamboard? i'd like to know if they're worth the trouble.
But building these has convinced me... i need something bigger
, so i'm looking at a new pair of drivers, these are on my short list:the one Cal is using:
Fostex FF125WK
Frame size: 117 x 117mm
Sensitivity (2.83v/1m): 89dB
Nominal impedance: 8 ohm
Frequency range: 67Hz-22kHz
Free air resonance: 67Hz
DC resistance (Re): 6.7 ohm
Voice coil inductance (Le): 0.044mH
Effective piston area (Sd): 0.0066m²
Moving Mass (Md): 5g
Force factor (BL): 5.596 Telsa/m
Qts: 0.42
Qms: 5.091
Qes: 0.464
Vas: 7.265L
or
Fostex FE126En
Frame size: 117 x 117mm
Sensitivity (2.83v/1m): 93dB
Nominal impedance: 8 ohm
Frequency range: 83Hz-25kHz
Free air resonance: 83Hz
DC resistance (Re): 7.2 ohm
Voice coil inductance (Le): 0.035mH
Effective piston area (Sd): 0.0065m²
Moving Mass (Md): 2.8g
Force factor (BL): 5.63 Telsa/m
Qts: 0.3
Qms: 4.8
Qes: 0.33
Vas: 8.5L
I'm also really curious if this one would work in a 70 / 80cm box or if i should just go with a 4/5inch one:
Fostex FE166En
Technical Data:
Frame size: 166 x 166mm
Sensitivity (2.83v/1m): 94dB
Nominal impedance: 8 ohm
Frequency range: 53Hz-22kHz
Free air resonance: 53Hz
DC resistance (Re): 7.2 ohm
Voice coil inductance (Le): 0.052mH
Effective piston area (Sd): 0.0133m²
Moving Mass (Md): 6.8g
Force factor (BL): 7.65 Telsa/m
Qts: 0.25
Qms: 3.426
Qes: 0.266
Vas: 37.02L
Excursion (lin-max): 1.00mm
Nominal power handling: 65w
Anyone who can tell me which one would be best suited?
Coen,
I did a sim for Cal's FF125WK driver a few posts back. It looks pretty good and I believe had sufficient xmax. But I think you can get better performance from the W4-1052SDF driver as it has more bass extension and costs less.
The FE126EN, has a good frequency response for a 27.55 in x 5.5 deep Cornu:
But suffers from a very small xmax which is exceeded at 1 watt, so I woud not recommend.
The FE166EN is a 6.5 in class driver and will not physically fit in the driver chamber unless you scaled up to a 40 in x 6 in deep Cornu. The Freq response looks very good and it will go all the way to high 40 Hz.
The xmax starts to run into some issues at 1 watt - but the driver can probably handle more before damage. The huge baffle is the problem - it is very big and will dominate any wall.
I think you may want to try looking for a 4 in class driver with a fairly high efficiency of close to 90 dB, xmax > 1mm, and a moderately high Qts in the 0.4 to 0.8 range as this will actually give you improved bass extension. Something like the TB W4-1052SDF can work nicely and not cost a lot.
TB W4-1052SDF in 27.55 in x 5 in deep Cornu:
Cone excursion for W4-1052SDF
I did a sim for Cal's FF125WK driver a few posts back. It looks pretty good and I believe had sufficient xmax. But I think you can get better performance from the W4-1052SDF driver as it has more bass extension and costs less.
The FE126EN, has a good frequency response for a 27.55 in x 5.5 deep Cornu:
But suffers from a very small xmax which is exceeded at 1 watt, so I woud not recommend.
The FE166EN is a 6.5 in class driver and will not physically fit in the driver chamber unless you scaled up to a 40 in x 6 in deep Cornu. The Freq response looks very good and it will go all the way to high 40 Hz.
The xmax starts to run into some issues at 1 watt - but the driver can probably handle more before damage. The huge baffle is the problem - it is very big and will dominate any wall.
I think you may want to try looking for a 4 in class driver with a fairly high efficiency of close to 90 dB, xmax > 1mm, and a moderately high Qts in the 0.4 to 0.8 range as this will actually give you improved bass extension. Something like the TB W4-1052SDF can work nicely and not cost a lot.
TB W4-1052SDF in 27.55 in x 5 in deep Cornu:
Cone excursion for W4-1052SDF
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While X is doing all the hard work, I'll tackle this one. I don't see an advantage to using wood for the spirals but definitely use it for the front and back.