Foam Core Board Speaker Enclosures?

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Cornu spiral or Fibonacci spiral for horn?

I am thinking about the next horn project. There is a cool flat panel wall hanging horn speaker called the Cornu spiral. ( 6moons audioreviews: Cornu Compact Spiral ) This would be an easy build in foamcore, or a Fibonacci sequence Spiral where the expansion ratio goes as 1:1:2:3:5:8:13 and so on. Practically it is tough to reach 13. Is there any advantage to using the magical natural expansion ratio such as used by the nautilus seashell?
 
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A quick estimate of the Cornu spiral design shown here (seb:diy:audio: Cornu Spiral Copy Horn ), re-scaled for the Vifa TC9FD will be a 20 x 20 in square (perfect for 20x30 in foamcore board stock) will result in an effective expansion ratio of about 24:1! The pathlengths (2 separate spiral lengths) will be around 1.0 and 1.36 meters for two tuning frequencies of 85 Hz and 63 Hz. The expansion ratio is huge so the bass amplification should be significant. I am thinking of modifying the design by using curves near the mouth for aesthetics and efficiency but square corners internally to act as low-pass filters.
 
OK, so the horn output is perpendicular to the output direction of the front of the driver? What driver are you using? I like how you did smooth curves, that improves efficiency but let's high frequency stuff come through. Will you use stuffing anywhere?

The design was intended to be a low-loss back loaded horn with the driver reversed (concave side facing into horn throat). Stuffing was only placed near the throat area to absorb higher freq. standing waves. The test speakers I used were Tang Band W4-1320 SJ. I gave up on the design but think it may have uses if crossed low enough.
 
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Why did you give up on the design? The bookshelf back loaded horn design I described earlier finally got tested with the Viva TC9FD drivers, they work well and have very good bass. You don't need BSC given how Much bass it produces from the front facing port. The putty damped front baffle actually works - there was almost no vibration coming through whereas the undamped panels you can feel the vibrations from the music.
 
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A quick estimate of the Cornu spiral design shown here (seb:diy:audio: Cornu Spiral Copy Horn ), re-scaled for the Vifa TC9FD will be a 20 x 20 in square (perfect for 20x30 in foamcore board stock) will result in an effective expansion ratio of about 24:1! The pathlengths (2 separate spiral lengths) will be around 1.0 and 1.36 meters for two tuning frequencies of 85 Hz and 63 Hz. The expansion ratio is huge so the bass amplification should be significant. I am thinking of modifying the design by using curves near the mouth for aesthetics and efficiency but square corners internally to act as low-pass filters.

I have already drawn out the full scale template for the 20 x 20 in Cornu spiral horn. I used a string to measure the lowest mode and it is 61 Hz. Need to get some more foam core board stock before starting. It's like how many different speakers can one make with a TC9FD? We know it works great in the Manzanita OB.
 
Why did you give up on the design?

For a couple of years I was trying some kind of different idea/prototype about every two weeks or so. I still have a closet stacked full of experimental speaker enclosures collecting dust. It was great fun and I learned something. Now I like the sound of open baffle until I find something even better.:)
 
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An interesting material called XBOARD PLUS PANELS ,has appeared recently and in its' thickest form offers a very high stiffness with a very low transmission of sound through the material.In Melbourne it is being tested in a a 650 litre vented enclosure matched to a modified Altec Lansing 15'' woofer with an ESS HEIL AMT in a two way system.The supplier of the panels is SHARP PLYWOOD in Queensland, for those who might wish to have more information.
 
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For a couple of years I was trying some kind of different idea/prototype about every two weeks or so. I still have a closet stacked full of experimental speaker enclosures collecting dust. It was great fun and I learned something. Now I like the sound of open baffle until I find something even better.:)

Ahh... OB is the Zen way.... I have an old oak tabletop sitting in my garage left there by previous Occupant that would make a great OB. The huge crossovers ($$$ coils) required are holding me back. I think you are better off with a two cheap T amps but how do you implement the crossover at line level before T amps? There are some fairly low cost woofers out there to go with the Viva TC9FD. Can OB be done for under $100? $24 for drivers, $30 for woofers, $40 for 2 T amps, just need cheap line level crossover. The thread on cheap OB was priced at $400 - hardly a cheap experiment, although they will sound fantastic.
 
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Yeah, in fact I have a Zen amp driving my OB.:)

I just am starting the work of understanding how to bi-amp using something like the First Watt B5. I would like to build the circuit myself using 2sk170 jfets.

My first OB was foam core;)

How does OB sound with foam core? I just went to dollar store and got 10 more sheets of foam core. Why can't we use cheap car audio active crossover and bi-amp rather than spending a fortune on big heavy coils and power resistors (heaters really)? I think an OB can be done for cheap as follows:
2 Viva TC9FDs $24, 2 GRS 12PF -8 12 inch woofers $32, Boss BX25 2 way active x-over $33, 2 Lepai amps $40, about $130 total not including s/h and wood or foam core boards :D.
 
I've heard that bi-amping is the way to go with OB. I tend to being a full ranger myself, but bi-amping a woofer interests me. I have parts for another class a zen for bi-amping, but I'm building one with my nephew first. I really like the way bass sounds on an OB. The beauty of foam core for me was being able to sculpt anything I could imagine quickly and on the cheap. If you like it then you can make it out of whatever you want, or can afford.
 
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I am not familiar with the term 'foam core'. Can you give me a link? I am familiar with many of the products that meet that description and they vary a lot.

Thank you.

The Elmer's brand shown here is really nice stuff but expensive $69 for 25 sheets, I use the stuff from Dollar Tree store ($1 a sheet, I guess that's obvious):eek:. Basically it is very light but stiff paper faced polystyrene foam. It cuts with an xacto, and is easy to glue with craft white glue or hot melt if you are in a hurry. Give it a try and you will be amazed at how light weight speaker cabinets can weigh and still sound good. If you have kids they love to decorate the cabinets with markers or paint.

The Elmer's brand is here: Amazon.com: Elmer's 900109 Foam Board, White Surface with White Core, 20 x30, 25 Boards/Carton: Office Products

The Dollar Tree stuff is here:Bulk Readi-Board Foam Boards at DollarTree.com