Hi all,
I was wondering if a hollow cube or rectangular prism (like speaker enclosure) made of MDF or HDF walls of sufficiently high thickness, would at a certain minimum thickness show no measurable benefit from internal bracing regardless of frequency range and typical SPL requirements?
Thickness would be proportional to box size.
Assume there is a sub woofer in the enclosure.
I was wondering if a hollow cube or rectangular prism (like speaker enclosure) made of MDF or HDF walls of sufficiently high thickness, would at a certain minimum thickness show no measurable benefit from internal bracing regardless of frequency range and typical SPL requirements?
Thickness would be proportional to box size.
Assume there is a sub woofer in the enclosure.
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If I understood him correctly the OP wants to know whether there is a certain minimum wall thickness (depending on enclosure size) that makes internal stiffening/bracing obsolete.
Regards
Charles
Regards
Charles
I believe panel resonance smears soundtsge, as instead of the sound emanating from a singular source, it's radiating off the baffle / enclosure walls as well.
Since a subwoofer isnt conveying spatial information in the same way as a mid, I'm not sure what panel vibration does at those frequencies. Reduce efficiency? Ruin the frequency response via out of phase resonances?
There must be some geometries that are better than others regarding panel vibration and minimum panel thickness. An octagonal shape comes to mind - versus a similar rectangular volume. The classic barrel shape where you have curves (or appx of) in two dimensions I'd think would be even better. Imagine making something like that with only hand tools! They did. I'd need a CAD program and a CNC machine...
Since a subwoofer isnt conveying spatial information in the same way as a mid, I'm not sure what panel vibration does at those frequencies. Reduce efficiency? Ruin the frequency response via out of phase resonances?
There must be some geometries that are better than others regarding panel vibration and minimum panel thickness. An octagonal shape comes to mind - versus a similar rectangular volume. The classic barrel shape where you have curves (or appx of) in two dimensions I'd think would be even better. Imagine making something like that with only hand tools! They did. I'd need a CAD program and a CNC machine...
I made some enclosures from. Very thin material down to the cardboard. Yes, it is audible, and at some point it is so leaky and soft that only unwanted noise increases, not the SPL output. I tried bracing, and it obviously helps a lot. And it helps better than wall thickness. You want to go at least 1" to compensate for missing braces. Bracing is very powerful. I run 21" subs, and while without bracing it would be absolutely and surely unusable, with bracing it is not only usable, but borderline good!
What is the thickness and/or bracing for?
I suspect that the OP might believe that making a cabinet thicker and/or bracing it will make it radiate less unwanted sound. But he is asking for responses from engineers and those with knowledge in the areas of vibration and acoustics will know this generally won't be the case.
The reality is that there are circumstances in which targetted bracing and/or thickness will make cabinets quieter, some where it will make them noisier and some where it won't matter much.
Perhaps the bracing and/or thickness is not intended to make the cabinets quieter but to restore a little bit of output at the lowest frequencies. Or to add some mass to stop a sub jumping about the floor?
Thought experiments like this are often useful and stimulating in drawing out information and so I am certainly not knocking the OP for asking the question but it does need honing a bit. It also might not be the best forum to ask for responses from engineers though there are one or two around.
Given that stiffness is related to the cube, at some point yes. Brute force.
But i strongly suggest that your back would be much happier with a well-braced box using thinner material. And if you abandon MDF/HDF (i know in Oz that is often all you can get) and use quality plywood it can be even lighter and stiffer.
dave
I can get plywood, including marine grade. Modern standard grades are much softer than they once were so don't go too thin.
Hi all, I'm back from family duties including home schooling...not so much fun but such is life sometimes
The question was a bit of a thought bubble. I don't have access to tools or space at the moment and I cant find anyone who wants to build cabinets here so I was hoping to reduce complexity as much as possible and get it done in a day from precut slabs of MDF from Mr Plywood.
As usually happens with my thought bubbles I didn't consider how I would cut the holes...
The question was a bit of a thought bubble. I don't have access to tools or space at the moment and I cant find anyone who wants to build cabinets here so I was hoping to reduce complexity as much as possible and get it done in a day from precut slabs of MDF from Mr Plywood.
As usually happens with my thought bubbles I didn't consider how I would cut the holes...
Not a very exciting question unfortunately. The "engineer" comment was more about people who have done some research with measurements and such, not necessarily a qualified engineer. There are plenty of people on this forum with good engineering brains.
My rule is to buy tools even for a single use (carburetor air flow gauge, for example, very helpful when I had a Lotus) rather than pay a shop. You could rent a jig saw to cut the holes - but might be cheaper to buy a second-hand one for $20.
Many elaborate sculptured bracing concepts have been posted here - some showing considerable lack of intuition about forces. But all you need is something very solid between opposite walls.
I like discarded hockey sticks (Maple?), electric conduit pipe, or a cheap piece of hardwood dowel from Home Depot. Cut crudely to length and slobber lots of epoxy gook on the joint.
There have been long discussions about the audibility of cabinets vibrations. Not feasible to actually measure audibility in any useful manner except by making cloned cabinets to compare. Too bad. My guess is that it is way down the list of problems. Even if it is easy to show the wall vibrates a minuscule amount, it is just not audible.
B.
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I had a pair of Celestion SL6 that had a honeycomb aluminum inner lining IIRC. I suppose too, they sought to make the enclosure stiffer. Honeycomb pattern is one of the strongest and lightest structures around, and has been refined over time by nature. I would start there, as I presume you want to to be manageable should you have to move your enclosure. It's good enough for aerospace, so I am pretty sure it's engineer approved (in the right application of course)... gotta respect that. They use their brain muscle, not their back muscles 😀
That should hopefully increase the number of responses.
A good engineering brain would mean understanding the engineering but when it comes to one or two topics like loudspeaker cabinets the absence of this knowledge is striking because of what has tended to take it's place. For example, the view that making cabinets thicker and/or bracing the hell out of everything makes cabinets quieter. It is interesting how this has taken hold to become a mainstream view and how it isn't shaken by evidence in the form of measurements, simulations, the products of engineering-lead manufacturers or the occassional engineer banging on about mass, stiffness and damping. Most folk seem to consider it obvious and to leave it at that.
Of course most other areas relevant to speaker DIY are fine requiring significantly less engineering knowledge to understand adequately and evidence in the form of simulations, measurements or similar are both much more readily available and aligned with expectations.
Doubling the panel thickness is similar to cutting the span in half. If you have 3/4 mdf spanning 12" with a brace in the center then you would want about 1.5" thick mdf spanning 12" with no brace.
Addressing weight; skinned sandwich or box/beam style construction will get you around 90% of the stiffness of a solid cross section. So 1/4" or even 1/8" ply over 1" rigid foam or honeycomb nomex or aluminum "should" get you the required stiffness.
Addressing weight; skinned sandwich or box/beam style construction will get you around 90% of the stiffness of a solid cross section. So 1/4" or even 1/8" ply over 1" rigid foam or honeycomb nomex or aluminum "should" get you the required stiffness.
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Are you talking about a subwoofer? This is the multiway forum. Regards a subwoofer, I shouldn't think rigidity would matter much from a sound perspective, I might be wrong. 🙂
In a subwoofer it is fairly easy to push the potemtial resonances well above the pass band where they will not be excited. More of an issue is ballooning of the box.
dave
dave
?
The major hardware chains here all sell ply. I don't remember ever seeing a shop that sells MDF but not ply.
In Australia, you can simply look at the F-rating, no word of mouth or guesswork is required to determine basic engineering properties.
Structural grading | WoodSolutions
? that's exactly what the rating system is for.
The sheets of F17 ply you buy this year will the same basic engineering properties as the sheets of F17 you bought 10 years ago.
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The simplest method might be to buy cheap used cabinets on ebay, e.g. I recently got a pair of working, cosmetically perfect 15" + 2" Yamaha boxes for $120. That's much cheaper than building!
Alternatively, buy an empty box from these guys:
etone PROFESSIONAL SOUND
If you do get sheets precut to DIY, consider this stuff (formply) instead of MDF.
Formply | Plyco
This retailer calls it "structurally similar" to premium birch - because it has the same engineering properties (F rating) at 1/3 the price.
The main catch is you need to use a non water based glue (e.g. polyurethane rather than PVA).
Both are great suggestions Hollowboy. I think Plyco is in Vic but may find the same quality formply locally. Cheers
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