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View Full Version : bendable plywood any good for cabs?



scorpio
08-23-2007, 05:04 AM
I'm building new bass enclosures and would like to give them a rounded shape similar to the B&W 800 series type. I would plan to use 3 or 4 layers of bendable plywood (sorry, I don't know if this is the correct technical term in English, it's direct translation from French). I would glue the sheets together using a very strong adhesive for floorboards that maintin some elastomeric quality when dried. Thing is, I don't know if this would make a 'good' cab or not, I don't see why it should not, but has anyone here attempted to make sharply curved cabinets, and if so, what did you use?

Thanks,

richluvsound
08-23-2007, 05:57 AM
Hi Scorpio,

the only flex ply I would use is designed for boat building . 3 x 6mm layers. Use epoxy or polyester resin.Use a cotton based filler powder with the resin to create a gap filling paste. You don't want any flex to the cabinet , too hard to tune ! . You will need stiffeners every 150mm , 200mm max.

I will start making curved panels next week .I will start a thread. I dont think there is one yet. A JIG is a must.

Rich

Hoerninger
08-23-2007, 07:00 AM
... , but has anyone here attempted to make sharply curved cabinets, and if so, what did you use?

My local dealer has MDF with cuts from the back which can be bend easily.
___________
Peter

scorpio
08-23-2007, 09:08 AM
Hi Hoerninger, I can get this type of MDF as well, do you know how sharp a radius you can make with this material? The plywood can make an 80 mm radius minimum, it's really very flexible. I was wondering if the MDF would not break along the kerf if bent too tight?

It's going to be applied as several skins over a matrix-type frame, I have little concern about flex in the cabinet when done. I'll shoot pics as I go along, maybe someday will post them

Cheers

Robh3606
08-23-2007, 09:15 AM
You might want to PM Widget. He has used a similar material and may be able to help you out.

Rob:)

grumpy
08-23-2007, 09:27 AM
some good reading here too:

http://www.neatconcepts.com/

4-6" minimum radius (1/4" Neatform) - MDF
6-8" min rad (3/8" Neatform) - MDF
12" min radius (3/4 Neatflex) MDF + bending birch plywood

hjames
08-23-2007, 09:42 AM
Buncha folks have done work with this concept in the past -
John W, Widget and a couple of other projects I read about but can't find right away ...

Search this site for "bondo", "kerf", and other similar keywords to see what floats up from a few years ago!

Some of the work looks similar to the danish style TiK series - very cool!


http://audioheritage.org/vbulletin/showthread.php?t=5951&highlight=bondo&page=3

Cyclotronguy
08-23-2007, 11:01 AM
And some information on how a commercial product with curved sides was made can be read on the TAD / Pioneer website (M1 reference monitor) and in the owners manual / literature cut sheet for Pass Labs "Rushmore" loudspeaker.

TAD did a a very nice translam and Pass Labs a laminar bend. From the text, Nelson Pass used 17 layers of an engineering grade wood like aircraft / marine spruce in building his cabinets. TAD stacked up piles of Baltic Ply with generous through bolts and hard glue.

From personal experience the TAD cabinet was more sonically "dead" via the knuckle test.

Cyclotronuy

edgewound
08-23-2007, 11:25 AM
The latest TAD Reference One is made up of layers of thin MDF to build up the enclosure.

The designer, Andrew Jones, told me that they had problems with the stacked laminated plywood.

Zilch
08-23-2007, 01:19 PM
The key to making the kerfed MDF work is filling in the voids. That's what I concluded from Mr. Widget's experiments with building curved cabinets.

My own approach would be to fill them with structural adhesive as part of the forming process.

I agree its elastomeric properties would be a significant resonance-dampening element in this.

subwoof
08-23-2007, 05:56 PM
There is a type of plywood that is Luan ( generic mahogany ) that all the layers are grained in the *same* direction. I used some for a customers project and even the 3/4 inch stuff was bendable within reason.

But it was a real pain to transport + shuffle around the shop ( floppy ) and that stuff smells like a wet fart when sawed......you would need to seal both sides very well..

:cheers:

sub

merlin
08-23-2007, 06:07 PM
The latest TAD Reference One is made up of layers of thin MDF to build up the enclosure.

The designer, Andrew Jones, told me that they had problems with the stacked laminated plywood.

Hi Edgewound,

do you know if they are still building up from the ground using CNC'ed sections or have they gone to a more conventional construction following the delamination issues?

Storm
08-23-2007, 06:07 PM
Reading this thread made me think of something.

Isn't there veneer that I could get to re-do the 250TI's in like a rosewood or something?

Would it be difficult, seeing that the corners are smooth?

;)

FWIW: The 250TIs are listed for one more go around. Offers are more than welcome.

Thank you.

-Storm.

edgewound
08-23-2007, 06:19 PM
Hi Edgewound,

do you know if they are still building up from the ground using CNC'ed sections or have they gone to a more conventional construction following the delamination issues?


Hi Merlin,

They are using thin layers of MDF to build up the curved back and side profile.

The MDF layers are glue laminated together. A result of stressed panels(bent) is that they don't resonate. That's some science used by old aeroplane builders...curved wing surfaces makes a more rigid airfoil.

Cyclotronguy
08-24-2007, 12:43 PM
I've spent quite a bit of time with the original TAD M1's, most of the US pairs (no commercial affiliation or interest, just friends with the major US seller)... they did not delaminate.

When you have end-grain, and not, hard glue and not then sanding for a perfectly smooth finish across all the different surfaces is difficult at best. Sanding wears away the softer wood quickly and affects the hard glue least. As one might easily imagine this quickly leads to a washboard finish unless one is very, very careful.

OK, lets presume Andrew got the finish perfect at the factory... and I'm pretty sure he did. Now you take that cabinet, cycle it through hot and cold, damp and dry (think wood and up to 18% growth possible on something like cherry with extremes of climate, most of it in one direction btw). What you quickly discover is that the "perfect finish" is only perfect under one enviornmental condition.

Out in the real world the finish began to show stresses and the differences in enviornmental expanison could be seen... the cabinets failed in a cosmetic sense, not to the best of my knowledge a physical sense.

Cyclotronguy

JBLnsince1959
08-24-2007, 12:59 PM
Hi Merlin,

They are using thin layers of MDF to build up the curved back and side profile.

The MDF layers are glue laminated together. A result of stressed panels(bent) is that they don't resonate. That's some science used by old aeroplane builders...curved wing surfaces makes a more rigid airfoil.


how thin for the layers and how thick once glued together? ( how many layers)

Hoerninger
09-04-2007, 10:20 AM
... , do you know how sharp a radius you can make with this material? The plywood can make an 80 mm radius minimum, it's really very flexible. I was wondering if the MDF would not break along the kerf if bent too tight?

Scorpio,

sorry for the delay.
I have not found any information regarding the smallest radius. But I know it can be quite small without breaking.
The attached picture shows how the new Everest is made, consisting of 9 mm and 16 mm MDF glued together (White Paper (http://audioheritage.org/vbulletin/attachment.php?attachmentid=18595&d=1158158693)).

(http://www.soundstage2.com/lasvegas2007/showstop03.html) (http://www.soundstage2.com/lasvegas2007/showstop03.html)
____________
Peter

richluvsound
09-04-2007, 12:51 PM
What you can see is both halves of the Jig. I needed something that would last for more than one pair of speakers. I used 25mm MDF and Tulip wood. Glued and screwed as I did'nt want movement in the frame . It's strong enough to be used with a nuematic press should I get more orders for this design. :D The first panel is curing as I write this . I'll post a photo of the outcome tommorow.

Rich

grumpy
09-04-2007, 02:40 PM
Nice Jig! :) Forthcoming pics of end product?



I have not found any information regarding the smallest radius.

see post #6. -grumpy

Andyoz
09-04-2007, 02:48 PM
Wow, even your jigs look good Rich. What are you up to there? Making more than one hey...hmmm

richluvsound
09-04-2007, 02:54 PM
cheers Grumpy,

I wish seen that post before I started. My supplier said he could only get 9mm

so I had to double it up ££££££. I filled the gaps to with resin and . I did'nt think I should leave any voids. Ah well , it'll be bloody bomb proof atleast !

Rich

macaroonie
09-04-2007, 04:21 PM
Nice jig pretty much as we discussed. Did you go a few % beyond your ideal curve to allow for relaxation ? Are you putting a layer of glass mat in between ?:dont-know

macaroonie
09-04-2007, 04:34 PM
That these guys were just at the end of my street.
http://www.aitwood.com/default.asp

Check it out under Millwork curved PLY sheets all kinds of radiussessss

Andyoz
09-04-2007, 04:35 PM
I reckon that jig would make a nice bed for one of the "visitors", imagine the lumbar support when that thing's laying on its side.:)

grumpy
09-04-2007, 08:38 PM
I wish That these guys were just at the end of my street.

http://www.aitwood.com/default.asp

That's where I found the neatflex/neatform stuff... they almost
-are- at the end of my street. <30min away. I don't recall what
pointed me there... probably someone here :)

I have yet to make it over there in person, but rest assured, I will. -grumpy

richluvsound
09-05-2007, 12:48 AM
Hey fanny paws !

it aint pesch ! . No relaxation either. I'll measure these 2 or 3 times before I cut this small fortune. I did'nt use any glass layer. I did'nt see a reference to it in any off widget's posts- If its good enough for the master its good enough for me .:) I just wish we could get the magic goop tho !

Rich

macaroonie
09-05-2007, 03:14 AM
Hey you are the guy on the spot so what do I know.I would still be tempted to try 4 x 4mm baltic birch with glass interleaves. You have the jig now so a tryout would not be a big deal esp if you halved the sheets.
Just a suggestion -- why dont you get some steel angles and fix them along the length of both parts of your jig that way you could use bolts to crank it all together.:)
Magic goop -- at one time I worked for Ariston and we were messing about with QLN speakers from Sweden. They had a board system that derived from the bus and truck industry. in essence the sheets were laminated with a layer of visco elastic with a very lossy nature. About 1mm as I recall. Very similar to Stycobond flooring adhesive. Anyway the end result was as dead as dead can be.
There were endless tech sheets in Swedish and German to substantiate the effectiveness of the treatment.
Betcha a web rummage would turn something up.

macaroonie
09-05-2007, 03:20 AM
Oh now that I remember , at Ariston we turned out a couple of solid plinth turntables using 15mm mdf/ goo / 15mm mdf or it may have been 12/goo/12/goo/12. . At the development stage we had 'controls' in place ie non treated decks for comparison and the improvement was substantial and at low cost too ( per plinth ).
Made a rega sound pretty stupid but then that aint hard.:D

richluvsound
09-05-2007, 04:26 AM
Mac ,

good idea on the use of steel . The jig can evolve, but I have to watch the pennies at the moment . Plus, I want to get the panels done before Ian arrives. I takes up a fair bit of room and I don't want the poor Aussie bugger snorting resin fumes in his sleep.... Shame you can't make it down Mate.

Rich

Andyoz
09-05-2007, 04:32 AM
Sorry I haven't been more involved with this but I'm flat out at work and my key "dealer" is off on holidays, back tomorrow apparently.

Rich, don't worry about Ian + fumes, where I came from the lads used to sniff all sorts of things.

macaroonie
09-05-2007, 05:15 AM
Old bed frame rails cast angle. 3 quid from the scrappy.
Sorry cant make it but I have clients stacked up like a busy day at Heathrow.
I'm booked solid till Feb. And you know how it is once you get on the job there is always ' whilst you are here ' or ' do you know anyone who can..... '

Pop Alexandra
06-23-2021, 02:41 AM
I saw a couple of laminated plywood (https://revetementagro.com/en/product/agro-plast) cab casings and they looked a lot sturdier than expected. I'd try one, to be sure.