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WTK: Best Material to make Speaker Box With

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carfreak1024
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WTK: Best Material to make Speaker Box With

Postby carfreak1024 » July 19th, 2009, 9:37 am

I personally always used MDF, actually one time i used some HDF, but mostly MDF.

But someone told me that the best material to use is called marine plywood, or any kind of dense core plywood, lined with fiberglass insulation.

could someone shed some light here as to why this is so.

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Postby southside connections » July 19th, 2009, 10:16 am

to be honest, there is no "best" type of material to build a box. there are many things you can use tho-


mdf
hdf
ply(everything from birch,to marine to costruction)
plastics(fibreglass ect)
paper tubes
metals
composites



well anything, once it's built solid and, is airtight you can use

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Postby carfreak1024 » July 19th, 2009, 10:26 am

what about the fiberglass bit, but nice build on the forum dey southside. I build alot of boxes myself not for customers and thing but for myself and meh cousins and close friends. I should start to post up some of my builds. But i always afraid to do so because i don't want no bandit to come and know exactly how to jack we music.

What yuh think about using laminated MDF?

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Postby noyztoyz » July 19th, 2009, 12:15 pm

i dont think much bandits browse trinituner?

southside connections
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Postby southside connections » July 19th, 2009, 3:37 pm

you would be suprised^^^ but, he has to realise that i don't show alot of things i do, just main pics

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Postby 3stagevtec » July 19th, 2009, 4:48 pm

the best material would one that would dampen sound reflections inside the box and rigid enough to prevent any panel flexing..

correct me if i'm wrong anywhere..

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Postby MonsterPower » July 19th, 2009, 5:30 pm

actually resonant frequency and light weight while holding firm with least flexing should be taken into account

dense is good but finding a dense material that is light weight is near impossible

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Postby madman.devin » July 19th, 2009, 11:37 pm

One of the best, if not the best material is Birch ply.
I'm not sure if it's available locally but it works !

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Postby southside connections » July 20th, 2009, 10:13 am

birch is avlibe locally, but the price wawwwwww

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Postby altec » July 20th, 2009, 11:18 am

some people(fanatics) actually use concrete for home use

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Postby southside connections » July 20th, 2009, 3:44 pm

^^^^ plus a lil bracing and some fibreglass coating inside makes for an extreemly strong box

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Postby sMASH » July 20th, 2009, 8:06 pm

k.i.s.s.

keep it short and simple

no, no,

keep it simple stupid

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Postby pugboy » July 20th, 2009, 8:45 pm

who sells birch ply locally ?

the regular ply sold in the hardware stores is a waste of time

I happened to be in the warehouse of peakes saw some ply today which looked good though

southside connections wrote:birch is avlibe locally, but the price wawwwwww

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Postby southside connections » July 20th, 2009, 8:53 pm

chan ramlal had last time i checked and also young sing

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Postby SR » July 20th, 2009, 9:04 pm

Birch ply vs. MDF for sub woofer enclosures
Written by Orca
Tuesday, 20 March 2007
There has been a lot of talk recently about using birch ply to construct sub woofer boxes as an alternative to MDF.

But why bother? Birch ply is expensive…

Birch ply is a stronger and stiffer material than MDF. A birch ply box will flex less than a MDF constructed box. I’ll let someone else explain why box flex is undesirable.

There are many grades of birch ply and even more grades of plywood available. Far too many to be listed here. Care must be taken when purchasing your plywood.

In general:-

Birch faced ply: -
This is plywood faced with a birch wood veneer. The internal laminates are minimum grade spruce and birch in alternate layers.

Birch ply:-
All laminates are birch. Face layers are also birch. Standard number of plies for 18mm thickness = 13

MDF:-
Chips about 20mm in length from either softwoods or hardwoods are thermally softened before being past through a machine which mechanically refines the chips into bundles of fibres or individual fibres. These fibres are mixed with a synthetic resin then pressed into a sheet. The fibres are randomly arranged within the material. This mat is then pressed again whilst subjected to elevated temperatures and pressures to cure the resin and produce a sheet of the desired thickness.


Mechanical properties:-
In laymen’s terms, strength is an indication of how much load a material will withstand before failure and stiffness is how much the material will flex, or deform, when subjected to a given load.

We are not really interested in the ultimate strength of our sub boxes as they seldom fail, so the material strength is of little use. However, we are interested in how much a box will flex. Therefore, we will concentrate on the stiffness of sub box materials.

Eb = Modulus of elasticity in bending.
Eb describes how stiff a material is under bending. The higher the number, the stiffer the material is and the less it will flex. It allows us to easily compare the stiffness of different materials.

The following properties are all based on 18mm sheet materials:

Birch faced ply:-
Eb = 2700 N/mm^2 perpendicular to grain
4600 N/mm^2 parallel to grain
Density = 11.6 kg/m^2

Birch ply:-
Eb = 3400 N/mm^2 perpendicular to grain
4600 N/mm^2 parallel to grain
Density = 12.4 kg/m^2

MDF:-
Eb = 2200 N/mm^2
Density = 10.8 kg/m^2

It can be seen from the above, that the plywood properties are directional depending on the orientation of the grain. For the purposes of this analysis, we can assume the stiffest properties as sub box panels are generally supported on all four edges. MDF is a homgeneous material and the mechanical properties are identical in any direction.

Comparing the Eb values given above it can be seen that the birch based plywood is over twice as stiff as the MDF. Therefore, if two identically sized sub boxes were fabricated, one from 18mm MDF and the other from 18mm birch ply, the MDF box would flex twice as much as the birch ply box.

That’s quite an improvement from simply using a different material for your enclosure.


Thickness vs. Material stiffness:-

Birch ply is expensive and MDF is relatively cheap.

It’s often asked, ‘Do I use 18mm Birch ply or 25mm MDF for my new sub box?’

As discussed above, birch ply is a stiffer material than MDF. It’s just over twice as stiff. However, the thickness of the material has a far greater effect on the overall stiffness than the actual material stiffness.

Example:-

It is common to ‘double up’ on the baffle thickness of a sub box from 18mm to 36mm.

You’d imagine that by doubling the thickness, you’d double the stiffness and effectively half the flex of the baffle. However, this couldn’t be further from the truth…

By doubling the thickness from 18mm to 36mm you in fact increase the stiffness by a factor of 8. The 36mm baffle will be 8 times stiffer than the single 18mm baffle.

This is derived from the second moment of area of the section given by Ixx = (bd^3)/12

Where d is the depth, or thickness in this example. The thickness value is cubed to arrive at the section stiffness.

For the full increase in stiffness to be exploited, the baffles should be glued together so the two layers act together in unison under load.

A double 18mm baffle is 8 times stiffer than a single 18mm baffle.

A triple 18mm baffle is 27 times stiffer than a single 18mm baffle.

A quadruple 18mm baffle is 64 times stiffer than a single 18mm baffle.

And so on….

By simply increasing the thickness of the material the stiffness overall is increased dramatically. Remember that birch ply is twice as stiff as MDF. However, the original question was ‘Do I use 25mm MDF or 18mm birch ply for my box?’

In this case, the increased thickness of the 25mm MDF will far outweigh the increased material stiffness of the 18mm birch ply. The panels of the 25mm MDF box will be 28% stiffer overall than the 18mm birch ply box.

In general, the thickness of the material is king to minimise flex. The thickness will increase the stiffness far more than a stiffer material would. However, by doubling the thickness you also double the weight of the box.

For ultimate performance, the stiffer birch material should be used in multiple layers. You will then get the best of both worlds. But it is worth keeping in mind that double the layers of material and the weight of the box will also double.

As always in car audio we are faced with a compromise. Box stiffness vs. weight vs. cost.

The choice is yours.

But for someone constructing a simple 18mm thick enclosure, Birch ply will be twice as stiff and only a fraction heavier than MDF. I know which one I’d go for and I'd double the baffle too whilst I was at it.


http://www.talkaudio.co.uk/index.php?op ... &Itemid=26



MDF with proper bracing does the job for me

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Postby 3stagevtec » July 20th, 2009, 9:35 pm

very interesting.. double layers is actually 8 times stiffer! cool...

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Postby MonsterPower » July 20th, 2009, 9:38 pm

nice read up sr ....

does anyone know the different resonant freq of ply vs mdf ?

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Postby 3stagevtec » July 20th, 2009, 10:03 pm

too much variables to answer that question.. the material resonant freq would depend alot on enclosure size, shape, bracing, weight of speaker in the box, etc etc..

harder materials might have a higher resonant freq i think..

(correct me if wrong anywhere)

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Postby MonsterPower » July 20th, 2009, 10:21 pm

ever wonder why many mids boxes are made of ply and not mdf

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Postby madman.devin » July 20th, 2009, 10:29 pm

^^^^
Mids boxes need to be moved around alot and therefore need to be built with a material that could withstand weather and friction.


So far Birch seems to be the best material for a sub box, but ur buget would then have to be taken into consideration !

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Postby nervewrecker » July 21st, 2009, 8:43 am

plexi, pvc & fiberbrite.

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- Rovin's car audio -
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Postby - Rovin's car audio - » July 21st, 2009, 11:15 am

pioneer wrote:just keep life/things simple and use MDF...it's readily available at a fair price :roll:


i find so too thats y i wasnt even bothering to comment in this thread

even if birch might be better u go to ur local hardware "yall have any birch plywood" ...they = :o :? :? "what is dat ?" ...they wont even know what u talking about since nearly all d ply that comes into T&T is from brazil \ chile \ china ...fact it : we dont get d best quality materials here & even if 1 or 2 hardwares bring it in they gonna charge u considerably more for it

try even locating 1" MDF & see how hard it is to get ...last time i checked too was nearly $300+\sheet ...

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Postby nervewrecker » July 21st, 2009, 11:19 am

^^^

go in the corner shop & ask for insecticide spray nah, they will be like wtf is that? you have to ask for bop! :lol:

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Postby - Rovin's car audio - » July 21st, 2009, 11:44 am

we dont even get exact 3\4" material - they going with metric now & short changing ppl in smart


3\4" = 19.049 MM ....they sell 18mm as 3\4"



doh even talk bout RHS & other types of steel u always getting 4-6" short of a 20ft length which they advertise & u paying for ...

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Postby madman.devin » July 21st, 2009, 12:13 pm

Rovin we sell the 1" mdf for 260 a sheet

The RHS that are imported are the shorter ones, as with everything u get what u pay for !

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Postby nervewrecker » July 21st, 2009, 12:16 pm

^^^

I was waiting for you to comment :lol:

wait till rovin hear how far you live, but he could always send me to buy for him, I dont mind commin down by you :mrgreen:
if you see traffic backup in front your place I casue a few weeks back :fadein:

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Postby - Rovin's car audio - » July 21st, 2009, 12:27 pm

was willing to give him a sale but if he rel far & i have to pay over $100 transport it wont make sen$e ....

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Postby nervewrecker » July 21st, 2009, 12:32 pm

remember how you was complaining harrys far......keep driving :lol:

but I donno how much it will be for transport. you dont now anyone with a van that can go buy it for you & bring it in the tray?

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Postby infinite_RPM » July 21st, 2009, 9:32 pm

madman devin where u from??

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Postby madman.devin » July 22nd, 2009, 12:08 am

I'm from Rio Claro thats about 20 mins before Mayaro.

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