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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 20th January 2010, 12:01 AM   #21
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It will be interesting to see how it actually turns out.
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Old 20th January 2010, 12:14 AM   #22
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Hello,
Quite an interesting approach you've got there, and nothing I've seen before. I shall follow this thread to see how it turns out.

I'm not entirely sure about the physical properties of hardboard, as I don't think I've ever worked with it before, but with something only 7mm thick I'd be worried about it losing it's rigidity if it's bent constantly for a long period of time, and become "soggy". Just a guess though, not sure how the tensile strength is.
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Old 20th January 2010, 02:08 AM   #23
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Quote:
Originally Posted by klankymen View Post
Hello,
Quite an interesting approach you've got there, and nothing I've seen before. I shall follow this thread to see how it turns out.

I'm not entirely sure about the physical properties of hardboard, as I don't think I've ever worked with it before, but with something only 7mm thick I'd be worried about it losing it's rigidity if it's bent constantly for a long period of time, and become "soggy". Just a guess though, not sure how the tensile strength is.
Thanks,
I don't think that it will become "soggy". Most people have had an old radio or record player with a hardboard back or bottom. I have a piece from an old organ that must be 40 years old and it still looks and feels fine.
Another thing: Maybe you fellows are discounting the effect of the foam that will fill the void. This foam will go a long way to reinforcing the structure by tying the skins together and locking the shape in place. It greatly increases the load distribution and provides some damping.
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Old 20th January 2010, 02:10 AM   #24
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Originally Posted by MJL21193 View Post
for us common folk...
John, I will never consider you common folk.
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Old 20th January 2010, 02:19 AM   #25
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I'm blushing Cal...
OR was that an mild taunt? Whatever, I can handle either.

Gee, no one has commented on my driver selection or box design...everyone is hung up on the construction.
One concern I have is the sensitivity of the drivers, in particular the mid. At 87db it is quite a bit lower than the woofers and tweeter.
I may do some more digging to find a driver that is a bit more efficient.
Suggestions are welcome but I do want a 6-7 inch driver for this.
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Old 20th January 2010, 02:32 AM   #26
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I would be interested in trying 2 different materials for your sandwich; hardwood on the outside, something else on the inside.

These are very similar to the 3 ways I'm still working on. I ran into an issue with the mid, not the woofer. I used 2" MDF. The back panel is screwed on, not glued. It resonated like crazy right at 400 Hz. Added 15 more screws and the bump was gone. Blew my mind, the panel weighs 50 lbs.

Go for it.
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Old 20th January 2010, 02:34 AM   #27
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Default I like the approach

John,

I like the approach with panels. I'd say try foam one and letting it cure a fair time and then check the stfiffness. If more is required space the panels further apart. That chart for aluminium shows a good increase until you get over an inch apart. I'd be a bit concerned with the thin corners and the connections where 3 panels meet.

Looking forward to following your work.
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Old 20th January 2010, 02:42 AM   #28
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Originally Posted by Mike Gergen View Post
I ran into an issue with the mid, not the woofer. I used 2" MDF. The back panel is screwed on, not glued. It resonated like crazy right at 400 Hz. Added 15 more screws and the bump was gone. Blew my mind, the panel weighs 50 lbs.
How big was that panel? I did a quick calc considering thickness and MDF density and came up with 833 square inches which could be something like 20 x 40 inches. That sounds pretty darn big if it is only supported at the edges. At that size the resonant frequency would be around 200 Hz.
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Old 20th January 2010, 02:54 AM   #29
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Originally Posted by MJL21193 View Post
Thanks,
I don't think that it will become "soggy". Most people have had an old radio or record player with a hardboard back or bottom. I have a piece from an old organ that must be 40 years old and it still looks and feels fine.
I'm sure you've seen pieces that have been under stress and are permanently warped as well.

You could always laminate the piece (ie make plywood), with something like plastic laminate.

dave
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Old 20th January 2010, 03:02 AM   #30
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Originally Posted by MJL21193 View Post
OR was that an mild taunt?
It was an taunt. It would be nice to see something like this with a couple 15's, a strong mid and nice horn tweeter in your plans. This business of a 1" dome tweeter just doesn't cut it when you use the word large John.
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