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

[Sazali]

We have all been playing with the base design for some time now, with some of us willing to venture into uncharted territory. I have been thinking about how to improve the sound quality of the Cornu as it appears that a lot of mid-bass is leaking out. In a conventional BLH, the most effective way to acoustically low-pass filter this is to have a larger driver chamber with a throat. The current Cornu has a throat but a very small driver chamber volume. The ratio of the throat area to the chamber volume sets the low pass cutoff frequency. So what I think can be tried is to add a sub driver chamber either on top of the existing one in the front, or in the back next to the wall in order to expand the volume by 4x to 5x. My sims show that this will significantly reduce the mid-bass leakage and smooth out the peakiness of the main bass response. If anyone wants to try this I can post some sketches of a proposed modification to the current design. It is an easy 'after the fact' mod to your existing Cornu if you want to do some foam core surgery: cut a hole a little smaller than the existing driver chamber on the back panel, make a thin, say 1 in deep box that has 4 to 5 times the volume of the existing chamber, fill with stuffing and glue onto the back of the speaker.

hi XRK can you provide a sketch of this ? Thanks

 

[xrk971]

hi XRK can you provide a sketch of this ? Thanks

Here you go...

 

[Sazali]

Thanks xrk.. With extra volume at the rear panel this would mean a circle hole of similar size to the front panel driver hole needs to be made?

Do you think 5mm plywood would be sturdy enough for the front and rear panels?

 

[Sazali]

Also what would be the estimated dimensions of this rear box to get 4 to 5 times of the throat volume?

 

[Cal Weldon]

I would do the extra on the front or the box won't load with the wall as intended.
Plywood can be as thin as 1/4". It is well supported by the foam core.

 

[onni]

Hey x! I'm building a cornu for my sister and have access to a pair of Fountek FR88EX, can you sim them in a 50x50 cm cornu?

/Anton

 

[xrk971]

Hey x! I'm building a cornu for my sister and have access to a pair of Fountek FR88EX, can you sim them in a 50x50 cm cornu?

/Anton

I will get to it in a few days - although the 50cm cornu is quite forgiving. Typical 3in thick and adjust stuffing to taste. I am not crazy about Fountek aluminum cone drivers - very sibillant.

 

[colinegreen]

FYI - I am building a 24" cornu dipole / bipole, with drivers on both sides.

4" thick.

I have tried both flipped polarity series and normal parallel connection of both drivers. The drivers are Chinese from Ebay. I am told they are called Guide Sound 4" drivers.

The wave guides are 1/4" bendy mdf, some of which had to get a brief soak in water to bend enough.

I have not yet glued the front on, it is only clamped at the moment.

I hope things tighten up when I glue it all together.

I had to add 6"x"6" 3/4" ply baffles to move the drivers far enough apart to not touch in the middle.

I will report back when it is glued with how it sounds. So far it sounds pretty good, but not enough impact to the low frequencies.

BTW, this is my first experience with a full range driver speaker.
XRK971 has been super helpful with this and another prototype I designed but stopped working on.


Colin

 

[onni]

I will get to it in a few days - although the 50cm cornu is quite forgiving. Typical 3in thick and adjust stuffing to taste. I am not crazy about Fountek aluminum cone drivers - very sibillant.

Is it that bad? My neighbor had a pair he's not using, so I could get them quite cheap. Before that I had planned on using the FaitalPro 3fe25 which would be the same price. I kinda figured that the magnet was a little large though and the neo version is like 50 % more expensive.

/Anton

 

[xrk971]

The Faital 3FE25 is +7dB more sensitive! For a Cornu, the 3FE22 may be a better choice with a stronger motor and lower Qts, although the 3FE25 would work fine as I know a TC9FD works and has about the same high Qts. The 3FE22 is a Nd motor and comparable price range and Qts with the Fountek. I have several 3FE22 and really like their sound.

http://www.parts-express.com/pedocs/specs/294-1101-faitalpro-3fe22-8-specifications.pdf

 

[onni]

I went with the 3fe25. Here is the first spiral finished:

Too bad foamcore is so damn expensive in Sweden, the cheapest I could find was 5 usd for 50x75 cm (20x30 in).

/Anton

 

[xrk971]

Nice work Anton. The $5 a sheet is reasonable as that looks like the nicer thick stuff. In USA, thicker Elmer's brand is $5 to $6 a sheet. Only dollar store carries $1 per sheet but that stuff is very brittle and light.

 

[onni]

Nice work Anton. The $5 a sheet is reasonable as that looks like the nicer thick stuff. In USA, thicker Elmer's brand is $5 to $6 a sheet. Only dollar store carries $1 per sheet but that stuff is very brittle and light.

Oh, alright 😊 That's a huge price difference though...

Is this a good amount of stuffing?

/Anton

 

[xrk971]

I only put it in main chamber. If you want to put in channels - tie some string to it so you can pull it out if too much.

 

[programer79]

Hey guys
Well first of all let me apologize to all for late posting , especially all the the best dudes with all the great help you provided through this forum.
Well here the pictures of my cornus.
I must say i'm surprised with the quality of sound an the amount of bass coming from a 100mm driver.
They are placed in the bathroom on the ceiling and there was a noticeable drop in sound quality when they were placed in the place where they are now.
So placement and room are playing quite an important role in quality of the sound of these speakers.
If anyone has any questions about my build, do not hesitate to ask.

Greetings
Aleš

 

[xrk971]

Hey guys
Well first of all let me apologize to all for late posting , especially all the the best dudes with all the great help you provided through this forum.
Well here the pictures of my cornus.
I must say i'm surprised with the quality of sound an the amount of bass coming from a 100mm driver.
They are placed in the bathroom on the ceiling and there was a noticeable drop in sound quality when they were placed in the place where they are now.
So placement and room are playing quite an important role in quality of the sound of these speakers.
If anyone has any questions about my build, do not hesitate to ask.

Greetings
Aleš

Very nice work! The first ceiling Cornu I have seen so far

Is that a 4FE35 or 4FE32? What are the dimensions (width and depth)? Did you do the decorative millwork for the front baffle cover?

Thanks for sharing.

 

[programer79]

Very nice work! The first ceiling Cornu I have seen so far

Is that a 4FE35 or 4FE32? What are the dimensions (width and depth)? Did you do the decorative millwork for the front baffle cover?

Thanks for sharing.

Thanks for the compliments.
The drivers are the Faital Pro FP4FE32A.
the depth of the horns is 100mm (4"). The dimensions of the bafle are 740mmx740mm. The dimensions and the choice for drivers are made by following your advice a few month ago.
Thanks man.

Yes, I did the milling.
The speakers still need decorative stickers on some bolts, so the project is not closed yet ha,ha,ha.

 

[jurjenh]

Ok, so call me crazy or sacrilegious, but I think I'm going to experiment with these. Here in NZ it's not easy to find drivers in shops (unless you get prebuilt speakers, but where's the fun in that?) so I had some time to kill and bought some car speakers to experiment with. The current idea is to build some cornu spirals and potentially use them in a greenhouse running from a solar panel/12v battery, but depending on results, this may change.

Drivers are JVC CS-V628, 6.5" 2-way. Did some initial tests to get ts params, quick push/pull on the cones to loosen suspension, Fs around 120hz, Re 3.37, Qt 1.64 Qes 1.96 Qms 10.17, Vas 2.67l, Sd 113.1cm2, BL 4.411, Lp 89dB. Haven't checked freq response yet, but can find one graph in the odd flier from JVC. I bought them because a) cheapish at $44, b) best sounding speakers on the display board at supercheap autos (so mounted in a box in a big room rather than a car) and c) experience gained will be worthwhile for something...

Now I'm thinking a cornu of 75cm or even going to around 90cm and prob 10 to 12mm deep. Would scaling up the plan work, or should I go down the calculation road, also has anyone done bigger than 75cm? Or 6" driver?

Another option for these drivers is experimentation with removing the centre tweeter, shoving in a phase plug and seeing what I can get it to do...


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[xrk971]

6.5in driver is pretty big and the magnet and basket may not fit in the chamber of a 75cm scaled Cornu. Print out just the central driver chamber to-scale and see if your driver fits. My guess is you need to scale it 6.5/4 x 75cm = 121cm or 48in. 4ft x 4ft x 5in deep should work. That is a big speaker.

Good luck! Cal says the bigger the better with Cornus.

 

[jurjenh]

I may just do that, I'm a cabinet maker so have access to cheap cover sheets so 2 sheets of 16mm and some 3mm msg for the spirals... May end up becoming "doors" at that size though, maybe I need a good 4" woofer in a kleinhorn for the bass just to complete it...

With the high fs and Qts I'm just trying to extend the bass somewhat. I've done high qts high fs speakers in ml tqwt before with reasonable results, so that may be another option. And possibly a blh or fly? The cornu has just been on my todo list for a while...

I may need to do some sims to see... What's the best way to sim cornus?


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