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Enclosure walls construction for 3012LF Neo
Enclosure walls construction for 3012LF Neo
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Old 11th July 2018, 12:42 AM   #41
Flaxxer is offline Flaxxer  United States
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Next subject Porting the beasts. I routed a 1/2" deep by 3/4" wide recess, around the 12" x 7" square I cut across the back of my bass bins, right at the very bottom. This allows for bolt in port tuning. I can play around with different tuning set ups, to see what sounds the best to me. I made it large enough to accept a 6" PVC port But my question is this. Any reason at all to use a PVC port, instead of just making it slot loaded, since it can be either way with the modular port system?
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Old 11th July 2018, 03:01 AM   #42
hollowboy is offline hollowboy  Australia
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Quote:
Originally Posted by Bon View Post
I have not used BB since it is hard to find where I am at any reasonable cost.
If you want BB just for structural qualities (strength, consistency) and/or the nice end grain, you can buy this format for half the price of BB that has a wood veneer.
Birch Filmface Plywood (Black / White) | Plyco
Plyco are Vic based, but you might be able to get something like it in Sydney (e.g. Gunnersens sell 12mm Birch formply, and they have resellers everywhere)

Even without the veneer, Birch is still overpriced here. Local (eucalyptus) structural plywoods with similarly nice grain & the same strength rating cost about $30 less per sheet.

Quote:
Originally Posted by Bon View Post
Secondly, in the past I have laminated 5mm hardboard (masonite or similar) to the back panel of mdf
I've tried hardboard (I got a couple of packs of a really dense, high gloss flooring material for $0) as a backing for 19mm timber. It seemed good, but the weight was pretty serious! I never finished the (fridge sized) project because I thought the weight might literally kill me. Poor planning, that.

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Originally Posted by Bon View Post
This has lead to my preferred format of, glued 12 mm mdf, laminated with 5mm hardboard.
If you're making a laminate anyway, consider braceply.

Most structural plywood (including BB) that I see for sale is rated F14 to F17, so the strength:weight is roughly 4 times as good as MDF (example numbers here:
MDF vs. Spruce-pine-fir :: MakeItFrom.com)

Cheap braceply is F27, which is almost double that.
2440 x 1200mm 4mm F27 Hardwood Plybrace | Bunnings Warehouse

...this means that an 8mm layer of braceply (8^3 * 27 = 13824) would be about as stiff as a 15mm layer of MDF (15^3 * 4 = 13500).
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Old 11th July 2018, 03:21 AM   #43
hollowboy is offline hollowboy  Australia
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Originally Posted by Flaxxer View Post
But you can still hear music playing through the walls just slightly.
I once built a bass box into a structure (a corner firing quad 15" - to get the LF boost from corner loading, without the hassle of a bass horn). The 'lid' of the bass box was my bed (in a separate room to the sound system).

Original lid: pine 2x4 bracing, 18mm MDF, topped with a futon. I could clearly feel the bass rumbling through this.

Modified: added second layer of 2x4, poured concrete between them, and topped it with a layer or sheetrock. After that, I could still feel the bass, but it was damped considerably.

My take home message: brute force has diminishing returns.
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Old 11th July 2018, 03:48 AM   #44
puppet is offline puppet  United States
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Quote:
Originally Posted by Flaxxer View Post
Next subject Porting the beasts. I routed a 1/2" deep by 3/4" wide recess, around the 12" x 7" square I cut across the back of my bass bins, right at the very bottom. This allows for bolt in port tuning. I can play around with different tuning set ups, to see what sounds the best to me. I made it large enough to accept a 6" PVC port But my question is this. Any reason at all to use a PVC port, instead of just making it slot loaded, since it can be either way with the modular port system?
I'd think you'd need to run some sims in winISD to see where a good starting point may be.
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Old 11th July 2018, 05:19 AM   #45
Bon is offline Bon  Australia
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Quote:
Originally Posted by hollowboy View Post
If you're making a laminate anyway, consider braceply.
I have seen the Bunnings braceply and it is not void free. The sheets seem to warp quite easily in storage. Now formply is a totally different animal. I use it for my workbench tops (see my previous photos) and it is very stiff and remains straight. It is designed to be used as concrete formwork so it can resist high forces and humidity without deforming. Unfortunately it can't be easily glued or painted. The phenolic surface coating is designed to resist adhesion.
Quote:
Originally Posted by hollowboy View Post
Most structural plywood (including BB) that I see for sale is rated F14 to F17, so the strength:weight is roughly 4 times as good as MDF (example numbers here:
MDF vs. Spruce-pine-fir :: MakeItFrom.com)
Cheap braceply is F27, which is almost double that.
2440 x 1200mm 4mm F27 Hardwood Plybrace | Bunnings Warehouse
The stiffness properties have to be taken in context. The two other relevant properties are mass and damping. High stiffness just moves the resonances higher in frequency. They will still need to be damped. High mass means the panels move for longer when excited. The worst material I ever used was cast concrete. It was very stiff and massive but rang like a bell.
Quote:
Originally Posted by hollowboy View Post
...this means that an 8mm layer of braceply (8^3 * 27 = 13824) would be about as stiff as a 15mm layer of MDF (15^3 * 4 = 13500).
My concern would be that the braceply tendency to warp would pull the mdf out of shape. Even when glued up, the warping forces might exert an unwanted force on the box joints.
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Old 11th July 2018, 06:09 AM   #46
hollowboy is offline hollowboy  Australia
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Quote:
Originally Posted by Bon View Post
I have seen the Bunnings braceply and it is not void free. The sheets seem to warp quite easily in storage.
Maybe they've changed supplier since then?

I have a stack of the reddish hardwood stamped F27 (which Bunnings resells from Gunnersens), and this is good: it cuts cleanly, doesn't warp, and it even looks nice - it is made for utility, but most sheets have large sections that are flawless.

Quote:
Originally Posted by Bon View Post
Now formply is a totally different animal [...] Unfortunately it can't be easily glued or painted. The phenolic surface coating is designed to resist adhesion.
I hadn't noticed that was your workbench material

Yea, it seems to be an oddly overlooked (cheap-but-good) material. Particularly for PA boxes - you can leave it in the rain ~forever.

Polyurethane glue seems to work well on it. I score the gluing surface a little, but I dunno if that's needed.

I assume PVA would work fine if you cut through the phenolic layer (e.g. in a a build that used dado joints, like your picture in post 37).
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Old 11th July 2018, 09:26 PM   #47
Flaxxer is offline Flaxxer  United States
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After starting this thread about the Kappalite woofers, I am now using the 3012LF in my new 3 way, fully active, DSP build. The ongoing build thread can be seen here:


Kappalite, B&C, Ciare, Heil Modular 3-Way build thread
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Old 11th July 2018, 09:30 PM   #48
Flaxxer is offline Flaxxer  United States
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Quote:
Originally Posted by puppet View Post
I'd think you'd need to run some sims in winISD to see where a good starting point may be.
I have already done that, and have several tuning points already selected for comparing. My question was, Any reason at all to use a PVC port, instead of just making it slot loaded, since it can be either way with the modular port system?

Slot or round ported should sound the same, if tuned identically. I was asking about differences in the two, as related to my particular build, with the slotted recess, for interchangeable ports of ANY kind. Thanks
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Old 12th July 2018, 09:33 AM   #49
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by hollowboy View Post
...this means that an 8mm layer of braceply (8^3 * 27 = 13824) would be about as stiff as a 15mm layer of MDF (15^3 * 4 = 13500).
How did you arrive at those numbers?
F27 is a nominal stress grade, 27 is not the stiffness.

Best wishes
David
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Old 13th July 2018, 03:05 AM   #50
hollowboy is offline hollowboy  Australia
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Quote:
Originally Posted by Dave Zan View Post
How did you arrive at those numbers?
F27 is a nominal stress grade, 27 is not the stiffness.
I haven't paid the ~$100 for the standards document, but I've seen it referenced in a few places. Stiffness is definitely part of the rating.

Timber Plus Toolbox, Assembling wall frames, Wall frame components, F grades and MGP grades
An F grade is a measure of the bending strength of a piece of timber. 'F' stands for force in megapascals (MPa), and is the amount of force a piece of timber can withstand without bending beyond an acceptable limit. A piece graded to F11, for example, will have a safe working stress in bending of 11 MPa.
Structural grading | WoodSolutions
For example F8 timbers have the following properties (from AS 1720.1 Table H2.1):

f 'b = 22 MPa the characteristic bending strength
f 'c = 18 MPa the characteristic compression strength (parallel to the grain)
f 't = 13 MPa the characteristic tensile strength (parallel to the grain) - hardwoods
f 's = 2.2 MPa the characteristic shear strength
E = 9100 MPa the characteristic modulus of elasticity parallel to grain
I note that:

1) Hoop pine is a standard softwood (maxes at F8 as plain timber) but is used in marine plywood (Aus standard for marine ply is F14 minimum), so stiffness must improve substantially when a wood is turned into plywood.

There must be a limit to this, because:

2) The highest F rated ply seems to be made from local species that are themselves very hard, like Spotted Gum and Ironbark.
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