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Spiral Horn

I have recently made several spiral horn subs. I do not have the means or the power to do this experimentation for real, and I have only been playing with sound waves for 2 months. This site is where the idea came from, and I have since experimented greatly with the designs.

http://www3.ocn.ne.jp/~hanbei/eng-intro.html

I have pics, but do not know how to retrieve them from my camera with this operating system (Mandriva Linux 2006 (official))

Yes this is a true horn, My latest has an increase in distance between the walls in the spiral of +10mm every full turn. I am not however using these as ports and instead making RLH's. (rear Loaded Horn) The owner of the site Masaaki Takenaka intended his to be inside the ports of Hemholtz Resonator Cabinets. This may work very well, but not what I need for my application. (3" driver cannibalized from computer sub. Pretty Lame HUH!)

Instead I made a "basstube". There is a small ammount of volume between the speaker's magnet and the beginning of the horn and the driver in simply attached to the end of a long 2.5" ABS plastic pipe like a bass tube. The horn is tuned to a cutoff frequency of 51Hz and doesn't have much for a response above that. It has amazed me with great sound and DEEP lows it can be heard quite well with a Frequency generator (my friend at the car toys shop has one) even as low as 23hz. Any lower and the 3" driver can't handle it and just produces distortion.

The modifications I have made since I started are:
1. Longer length
2. larger throat/mouth ratio
3. cut away mouth opening for larger mouth
4. closed off end making a side firing mouth and completing the full soundwave bend.

My question is, has anyone else been able to produce great results with this horn? I have achieved a 6db increase in the low end below 45hz, and a very pleasant sound even without damping material. (I use a mangled old wool sock anyway because it eases the light coloration from the horn.)

Has anyone been able to make a "colorless" spiral horn? If so, how? I some day will begin using larger drivers and better tubes. I am totally amazed with how well this works with a 3" driver and want to see what an 8 inch is like.

Wish you could hear the difference, this thing will play all the way down to 23hz audibly! It would possibly play even lower if I had more wattage. This design doesn't need a crossover as far as I can tell because of the 51hz cutoff. (which has the do with the size of the throat.)

Thanks for any input and ideas.

HellionDarkLord
helliondarklord704f
gregm
3,405 posts
 
Actually you'd be better off using a low pass (try line level) to avoid intermodulation & straining the drive unit.

I listened to a 6,5 inch spiral. It sounded warm, not extremely articulate but, as you note, "deep" and "effortless" (i.e. the energy used was ~50W max). Unfortunately, I don;t know what the chap actually did -- as in mods to our Japanese friend's original... CHeers
eldartford
4,262 posts
 
The idea of implementing expansion of the horn by variation of the pitch of the spiral is an ingenious approach. Construction of the spiral is obviously the main problem. The spiral horn could be cast in one piece in plastic or even some mineral substance. If someone got this into production I bet you could sell a bunch of them.

I have not heard such a loudspeaker, but my concern is that a horn is a horn is a horn, and will sound like one. For music that includes a lot of horns (dixieland jazz) the result can be superb.
ultrakaz
187 posts
 
Thanks for posting your experiments. I've been visiting Mr. Takenaka's site for a couple of years and corresponded with him. Nice and helpful guy.

I too agree that if somebody casted the spiral tube and could sell inexpensively I would buy a pair or two. I think the Bose Acoustice wave implements a similar concept; as for sound quality, well, just ask Herbie.

I think there is a tradeoff where the deeper you go the less "articulation" you get. Takenaka-san must have experimented with varying lengths/diameters until he achieved a balance. Have you asked him about the likely success of your proposed plan?

Keep us posted on your progress.
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