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Old 6th November 2012, 09:34 AM   #11
tvrgeek is offline tvrgeek  United States
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Like everything, the correct answer is "it depends"
Adding to the above mentioned types of braces, is size. All materials have their advantages. I usually will use scraps of oak from furniture projects for my surface glued braces. I will use cutout plywood for shelf type braces, and a softer wood or MDF for panel to panel braces. Properties selected for flex, compression, and resonance.

MDF is just a material. It may be great for one cabinet and poor for another. My best sub efforts are plywood/ceramic laminate, by best small monitors are MDF/HDF, my best desktops are plywood. I have an idea for a plywood/HDF laminate I want to try and was looking at all kinds of exotic materials in Granger for the baffle which is for me, the toughest problem.
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Old 6th November 2012, 09:27 PM   #12
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Quote:
Originally Posted by Kooshball View Post
MDF does not seem too resistant to bending
Have you ever tried to bend 16 mm MDF?

MDF is very stiff. There are stiffer materials, of course, but at which cost?

Also you have to consider what is achievable with bracing:

- in sub-modal region (i. e. when the panel does not resonate, that's in the bass frequencies) the panel bends due to the pressure inside of the cabinet. Moderate bracing with MDF deals with it sufficiently

- in modal region bracing does NOT reduce bending, but shifting the resonant modes to higher frequencies, where they are more audible. Mechanical panel damping is much better.

- another point are the acoustical resonances inside the cabinet, which can excite the panels quite heavily. Bracing helps here, but more does stuffing the cabinet's volume with damping material and intelligent placement of the drivers (to avoid resonances).

Thinking about these 3 points, the best solution is a cabinet with moderate bracing (small 2-ways don't need bracing), built from quite thin material (9-12 mm ply or MDF), stuff it with damping material, and apply mechanical damping (bitumen, thickness comparable to thickness of wood) to the walls.
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Old 6th November 2012, 09:43 PM   #13
tvrgeek is offline tvrgeek  United States
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Don't know what "small" means, but my 16L's made form 3/4 inch MDF absolutely do need a bit of bracing to push the resonances up out of trouble range. Even in 3L desktops do, but then again I used 5/16 5 ply for them. Both heavily stuffed with wool or Daycron. Siegfried's 4 inch square rule is not a bad starting place.

Myself, I would not add 12mm of tar to a 12mm panel. I'd start with 20mm of wood and 2 mm of no-name clone Dynamat.
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Old 6th November 2012, 10:01 PM   #14
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16 liters is small. Of course it always depends on the panel size. Check the old BBC monitors, they're good examples how to build such a small 2-way.

If you use 20 mm wood, you'll need 20 mm of damping material (simple estimation). 2 mm does nothing. It is always important that the stiffness and mass of the damping material is not small compared to that of the base material (in engineering terms: the mechanical impedances must match). Mass is directly proportional to thickness d, stiffness of thin* sheets is proportional to d^3. The density of bitumen is higher than that of wood, so mass is no problem, but stiffness is. That's why it must be of reasonable thickness.

*thin means the thickness is small compared to width and length
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Old 6th November 2012, 10:38 PM   #15
pski is offline pski  United States
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Quote:
Originally Posted by planet10 View Post
MDF does not make good braces.It doesn't make all that great a speaker box either.

Quality ply or hardwoods make good braces.

dave
Normally, I would agree. I helped my son make some MDF woofer cabs years ago. He and his friends did not understand the need for square edges and liberal glue for that matter.

Last year, I made two pairs with 1" (25.4mm) MDF I got from my neighbor who is a cabinet maker. This weighs 128 lbs per sheet and does not at all compare to the flake-prone 3/4" (19mm) sold at DIY home centers like Lowes and Home Depot.

P

Last edited by pski; 6th November 2012 at 10:44 PM.
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Old 7th November 2012, 12:40 AM   #16
tvrgeek is offline tvrgeek  United States
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Everything is a tradeoff. There are reasons/times where you can afford a 20 mm total thickness and not a 40. In a smaller box, that makes a big difference. Times you can.

This thread has a lot of "it depends" in it. Brace material, panel material, size, method, all are nothing but parameters each needs to evaluate and decide what fits their specific build. There is no right answer; no "must" here at all. I have had very good results with Home Despot 3/4 MDF, oak cross braces and my clone dampening material with wool stuffing. A friend is convinced sand in paint is the best. Others believe MDF is evil and only use ply. All just materials. The only mistake here is to look for a simple answer. PROTOTYPE and decide for yourself for your specific build.

Yes, HD MDS is more prone to delamination than higher quality. The best plywood from a big box store is poor at best. But if you don't have a truck and don't have access to furniture or boat quality ply, you must learn how to deal with what you can get. For years, even very expensive speakers were made from low grade particle board. It also depends on the finish. Even a melamine skin has a dramatic effect on rigidity. My sub boxes that seem to work very well are just CDX ply but have ceramic plates glued to them. The durometer of the glue matters too. They have only one shelf brace. ( 60L)
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Old 14th November 2012, 04:42 AM   #17
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I say scrap the MDF and switch to solid wood or birch or even pine ply

Say what they will but the speed of sound for plywood makes it a superior choice. I think MDF cabs have a decent sound but, they also sound dry and like the music has this limp projection. There is also a splattery, muffled effect for subs.

But, maybe those of us that prefer plywood and solid wood are completely wrong and guitars, drums, cellos, pianos will soon switch over to this super HD MDF so many "experts" insist is superior.

Ultimately, MDF DOES sound like crap and anyone that insists the voids of ply will ruin sound is...well an idiot! The voids are negligible and if they make up even 5-10% of the mass, I'll sell everything I own and go live in an igloo at the North pole. These are the people with the same train of thought that hard wood is completely unreliable and performance will vary in every single cabinet you build even when all have the same drivers.
Clearly these people have never built ANYTHING out of solid wood let alone speaker enclosures. I've built solid pine cabinets that sound excellent and suffer from none of the fantasy problems all of the self accredited experts dictate that they will. Yes I said PINE. The cheapest wood one could choose and it still performed great. I've alsu used Ash and poplar. The Ash sounds tremendous for these cheaper solid woods. You just have to seal it. Solid wood is by no means unpredictable and rarely if ever suffers from the claims of these people who have typically never built ANYTHING out of solid wood and merely parrot what they have heard.

Parroting infinite wisdom is a pandemic.
It's time people put up or shut up because they constantly argue about things they've never actually done or, done once with little or no experience, had poor results due to incompetence and joined the train of thought rather than the miracle of free will.

Yeah so to actually answer your question, get some 2-3 dollar pine 2x4's, split them into 2x2's and you have your bracing solution. MDF is pushed as superior cabinet material because it's quick, easy and cheap. The claims of it's superiority come from people who do not want sound texture. They want flat, limp, splattered, sterile, lifeless, trapped in a vacuum projection.

My real advice is, never build with MDF again!
I guarantee if your first non MDF build is even just with a 20 dollar sheet of yellow pine ply, you will permanently make the switch. If distortion is an issue, you pad it or stuff the cab with batting.
Wood is an excellent sound conductor. Internal cabinet distortion on the other hand has a million solutions.

MDF is just a lazy, cheap, quick but ultimately inferior way to build without running into any major issues.

Last edited by TestTones; 14th November 2012 at 04:45 AM.
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Old 14th November 2012, 06:04 AM   #18
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Quote:
Originally Posted by TestTones View Post
MDF is just a lazy, cheap, quick but ultimately inferior way to build without running into any major issues.


Quote:
... without running into any major issues
Except what it sounds like?

dave
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Old 14th November 2012, 07:07 AM   #19
DrBoar is offline DrBoar  Sweden
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As far as measurements goes
dämmung-und-versteifen
How this correlate to subjective results is an other kettle of fish.

TestTones I do not understand your argument with musical instruments like guitars and cellos usings solid wood. The body of the cello is an intrinsic part of the sound generation of the instrument. The box of a loudspeaker on the other hand should not be a major part of the reproduction of the sound of that cello. So the walls of a cello or a loudspeaker really have different requirements and thus solutions.
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Old 14th November 2012, 11:46 AM   #20
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Quote:
Originally Posted by planet10 View Post




Except what it sounds like?

dave
Show pics of any of your solid wood or ply builds.
I'm betting you can't.
MDF sounds dry, limp, splattered and artificial but other than that, sounds great!

Meanwhile any guitar or bass cab made out of real wood or even cheap pine ply will sound better than any MDF cab with the same speakers.
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