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Multi-Way Conventional loudspeakers with crossovers

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View Poll Results: Will MJL21193's crazy design work as proposed?
Yes 57 51.35%
No 7 6.31%
Maybe. 34 30.63%
I'll laugh when it doesn't. 13 11.71%
Voters: 111. You may not vote on this poll

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Old 19th January 2010, 10:37 PM   #11
lowpoke is offline lowpoke  Australia
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John you look like you know what you're doing. I don't see why people are doubting your curved panel technique. I'm looking forward to seeing the completed project!
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Old 19th January 2010, 10:44 PM   #12
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Thank you for the vote of confidence Jason

It's true that I do have some idea what Im doing but I have been wrong in the past about "sure" things. Like I said: we will see how it turns out. I'll do some accelerometer readings on the panel movement when they are assembled. Worse comes to worst I'm out a few hours work and maybe 30 bux worth of material - I could start again with good ole reliable MDF 4" thick.

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Old 19th January 2010, 10:47 PM   #13
SunRa is offline SunRa  Romania
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At least the experiment will be interesting . I remember seeing a cabinet design for large phy-hp fullranges which adhered to a lesser degree of stiffness of the walls. Also Nelson Pass 4way with PHY pro drivers has somehow similar principles.

So good luck with this!
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Old 19th January 2010, 10:53 PM   #14
lowpoke is offline lowpoke  Australia
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Quote:
Originally Posted by MJL21193 View Post
Thank you for the vote of confidence Jason
I'll do some accelerometer readings on the panel movement when they are assembled.
Andrew's idea of filling the void with sand sounds like an easy option to try if needs be. (Don't fancy trying to lift them afterward though!)
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Old 19th January 2010, 10:58 PM   #15
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Quote:
Originally Posted by SunRa View Post
At least the experiment will be interesting .
So good luck with this!
I think it will be too. Thanks

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Originally Posted by lowpoke View Post
Andrew's idea of filling the void with sand sounds like an easy option to try if needs be. (Don't fancy trying to lift them afterward though!)
Yes, I want these to be relatively lightweight and filling them with sand would not be a direction I'd think about taking. Also the voids will already be full of foam so I'm keeping my fingers crossed.
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Old 19th January 2010, 11:00 PM   #16
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I like the innovative approach to panel construction - hope it works well
cheers
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Old 19th January 2010, 11:02 PM   #17
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John,

I think this technique has good potential... the concept is something that hasn't escaped me in the past.

Might take some trial & error to get the tension right, and you do want to worry about the long-term stiffness of the panels -- for instance, i expect MDF would tend to become naturally relax over time.

dave
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Old 19th January 2010, 11:16 PM   #18
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Hey John. I made a mistake one time trying to build a 20" bass drum from 5-ply maple Keller shells. The shells were high quality but no matter what heads I used the drum sounded like paper. A dirt cheap mass produced basswood bass drum (with shells almost 3 times as thick) were able to kick it's butt in dynamic range and, most embarassingly, tone. I think I understand where you'd like this design to go but I think you will need more material, and unfortunately, mass. There will be flexure and resonance no matter what the construction. More mass and high damping means lower frequency, lower Q resonances.

On the bright side the way you intend to construct could actually help. You don't have a pure tensile load with cabinet pressure modulation unless the panel is a true arc segment. With one divider and converging edges you'd have a funny curve that would probably change with some more non-linear response. That would be good, but I think considerable problems will come from higher order responses and partially longitudinal waves in a hard thin medium.
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Old 19th January 2010, 11:17 PM   #19
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Quote:
Originally Posted by PeteMcK View Post
I like the innovative approach to panel construction - hope it works well
cheers
Thanks Pete

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Originally Posted by planet10 View Post
John,

I think this technique has good potential... the concept is something that hasn't escaped me in the past.

Might take some trial & error to get the tension right, and you do want to worry about the long-term stiffness of the panels -- for instance, i expect MDF would tend to become naturally relax over time.
Thanks Dave,
I want to give this every opportunity to succeed, therefore I'll proceed on the premise the it will work as expected. Filling the voids between the skins with medium density foam will go a long way to locking the structure into a permanent shape. Using a steel "backbone" will (hopefully) address the one potential weakness.
In any case, I'll start soon by cutting all of the parts for the panels. I'll see if there is a local source of the urethane foam I want to use and I'll look through my garage for the steel.
Should be barrels 'o fun.
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Old 19th January 2010, 11:37 PM   #20
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Quote:
Originally Posted by Andrew Eckhardt View Post
Hey John. I made a mistake one time trying to build a 20" bass drum from 5-ply maple Keller shells. The shells were high quality but no matter what heads I used the drum sounded like paper. A dirt cheap mass produced basswood bass drum (with shells almost 3 times as thick) were able to kick it's butt in dynamic range and, most embarassingly, tone. I think I understand where you'd like this design to go but I think you will need more material, and unfortunately, mass. There will be flexure and resonance no matter what the construction. More mass and high damping means lower frequency, lower Q resonances.

On the bright side the way you intend to construct could actually help. You don't have a pure tensile load with cabinet pressure modulation unless the panel is a true arc segment. With one divider and converging edges you'd have a funny curve that would probably change with some more non-linear response. That would be good, but I think considerable problems will come from higher order responses and partially longitudinal waves in a hard thin medium.
Hi Andrew,
Each box will have some considerable mass - there is the equivalent of more than 2 full 4' x 8' sheets of 1/4" hardboard involved plus whatever I decide to use for the baffle. Probably a few pounds of foam too. Also the skins are not as thin and frail as you think - 1/4" hardboard is very strong and tough.

I don't see enough internal pressure to be able to change the curvature of the skin, especially once it has been reinforced with foam. If the curve does not change shape, it must transfer all of the load to the rigid edges. A structure like this (shallow arch) will not do well with a point load but it will work well with distributed loads (what we find inside a speaker).

Maybe it sounds like I'm trying to convince myself as much as anyone else...
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