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Sub wall thinckness (1 Viewer)

ChristopherD

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Mar 28, 2002
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I built my ported 185L Tempest out of .75" MDF (1.5" baffle)and am wondering if 1.5" all the way around would result in significantly better sound quality and quantity. While I'm happy with the current product, I wonder if there is "more" to be had. Can I glue another layer of .75" MDF all the way 'round and get the same effect as building a new enclosure with 1.5" material?

Thanks.
 

Brae

Supporting Actor
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Jul 25, 2002
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Bracing is key is the wall thickness is too thin for the driver/crossover/power design being applied, but has anyone tried to come up with a Thought Example for said driver/crossover/amp(power) model between using single 3/4" MDF walling with bracing and determine the necessary wall thickness to eliminate bracing?

This, of course, assumes weight is not a problem for folks. I'd be curious. What about if you sandwich something between two layers of MDF walling, or used differing wall thicknesses?
 

Ben Ven

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Mar 6, 2002
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There was an article in Speaker Builder magazine a few years ago on this topic. If I remember correctly, the author, whose name escapes me, tested various panels and bracing techniques.
The panels were of various thicknesses. Laminate panels were also tested. Various braced panels, different location, different bracing materials, hard glue, soft glue. You name it, it was tested.
I believe the author mounted an accelerometer on the panels and derived the vibration with some software. Bottom line was that just plain old MDF (2 pieces 3/4" laminated together with I think white glue) was the winner. Braced panels didn't even come close. Bigger is better!
Less panel excitation=less coloration=better sound quality IMHO.
 

AjayM

Screenwriter
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Aug 22, 2000
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Hey if you want to get crazy going for double wall thickness and a lot of bracing will get you what you want, and a hernia as a bonus. Check out the cut-away drawings of some of the higher end subs out there like the Aeriel and you'll see big panel thickness and a ton of bracing.

I think it was Dan Wiggins awhile ago recommending the use of void-free plywood for sub boxes, the resonance's from the sub are to low of a frequency to effect the sound output, and it allows you to build a well braced enclosure without needing a forklift to move around.

Andrew
 

Brae

Supporting Actor
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Jul 25, 2002
Messages
509
And here I was thinking of using a concrete form for the 100%-static cabinet ... :D
 

ChristopherD

Stunt Coordinator
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Mar 28, 2002
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107
Points well taken. I think I braced well, but it was my first woodworking project and first go at a table saw. I will never be convinced that it is constructed as well as it should be. I think I may laminate another layer of MDF just to be sure.
 

Allen Ross

Supporting Actor
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Sep 30, 2002
Messages
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my buddy accross the hall (the same one that is modding his amps) is building two sub boxes for stereo subs, in each box he has dual 10 inch drivers he scored off of PE for dirt cheap. their only 10 but have practicly the same motor assmbly as my tempest, with the same surround. There really funnny to look at.

Anyway he is using doubled up 1 inch MDF, yes thats right he had to specail order 1 inch MDF from HD but he got it and together with his mains that he is building, they will sit ontop of his subs. He is estimating that the stacks (dual sub, and a main that is comparable to my tepest in size) will weigh in at just under 400 pounds, now he will have two of them and i beleive that, that weight isn't including his amps and other hardware
 

Allen Ross

Supporting Actor
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Sep 30, 2002
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819
yeah he is only working on them on the weekends so progress is slow,

as for the money he sold a bunch of Western Electric/Electrovoice drivers and OXs that the University had and got a third of the sales. He ended up with about 3500 bucks from the deal.
 

RichardHOS

Second Unit
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Mar 11, 2003
Messages
454
has anyone tried to come up with a Thought Example for said driver/crossover/amp(power) model between using single 3/4" MDF walling with bracing and determine the necessary wall thickness to eliminate bracing?
For simplicity, you can consider a plate with fixed supports at each end. Panels of a sub enclosure will really act as a membrane, but this will at least serve as a decent approximation of both braced and unbraced build designs, and give some idea of how they compare.

The stiffness for fixed end plates is:

k = (192EI)/L^3

Area moment of inertia for the plate is:

I = (1/12)WT^3

Thus, the stiffness would be k = (16EWT^3)/L^3

If you wanted to find out how much closer (relatively) spaced bracing would have to be if you halved the MDF thickness, simply equate the stiffness equation describing each situation and solve for the new L.

For example, let L' be the brace spacing with 3/4" MDF, and L" be the spacing for 1.5" MDF.

k = (16EWT^3)/(L')^3 = (16EW(2T)^3)/(L")^3

Simplifying the expression leaves the following result:

L" = 2L'

So, a decent first estimate would be that doubling the panel thickness allows you to span twice the length between braces and still have the same enclosure stiffness. It's interesting that this approximation works out to a perfect "double for double" ratio.

In any case, you can clearly see the effect of increasing panel thickness. It halves the number of required baffle-braces, and if you were only planning one it would eliminate that one.
 

Jack Gilvey

Senior HTF Member
Joined
Mar 13, 1999
Messages
4,948
Check out the cut-away drawings of some of the higher end subs out there like the Aeriel and you'll see big panel thickness and a ton of bracing.
Yup. ;) Certainly one way to do it, though. The fact is that no one would ever buy a sub that they felt was too light for the money, even if it was just as "dead" acoustically as a concrete tomb. Marketing 101.
 

Michael Hartwig

Stunt Coordinator
Joined
Sep 18, 2002
Messages
56
I've built my Tempest 145L sealed with the 13ply 3/4" Baltic Birch. I find the octagon shaped enclosure great for control of unwanted resonancy. With the octagon shape of this enclosure the widest panel is 8 1/4" (on inside). The body size of this cabinet requires only one octagon ring for mid bracing. With the sides having 45 degree angles (8 in total); there are no corners. The largest flat spot is the top. I use 3/4" BB topped off with 1/2" marble. The beauty of this design, is a great looking cabinet with a modest manageable weight. Plus it sounds great.
 

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