So I'm working on designs for my next 3-way speaker. The basic design is a floorstander with arc'd sides, flat front and back. I'm wanting to use aluminium for the front baffle, probably in an aluminium-rubber-aluminium sandwich configuration, with wood attached (glued?) to form the rest of the cabinet.
My main worries are the effects of thermal expansion/contraction of both the wood and aluminium... will the cabinet rip itself apart? and what's the best way to attach wood to aluminium anyway? has this been done successfully?
Any ideas and input would be welcome.
My main worries are the effects of thermal expansion/contraction of both the wood and aluminium... will the cabinet rip itself apart? and what's the best way to attach wood to aluminium anyway? has this been done successfully?
Any ideas and input would be welcome.
Last edited:
I was thinking of that, I haven't looked at the coeficcient of expansion for wood vs aluminium, I had guessed wood would be higher but maybe my intuition is off...
I did consider some kind of suspended mounting that would allow for expansion and contraction, as the construction will be inherently composite anyway - for audio benefits as well as physical practicality.
I guess the quesion is, do I need to acount for expansion in a baffle that's approximately 840*150mm, or will it be so minor as to never warrant worrying about (i.e. am I right to be worried about this)
I did consider some kind of suspended mounting that would allow for expansion and contraction, as the construction will be inherently composite anyway - for audio benefits as well as physical practicality.
I guess the quesion is, do I need to acount for expansion in a baffle that's approximately 840*150mm, or will it be so minor as to never warrant worrying about (i.e. am I right to be worried about this)
Seasonal wood movement is predominately driven by humidity changes and occurs at different rates tangentially and radially to the growth rings - the length dimension is generally stable. This expansion and contraction is much larger than thermal movement...an 8" width of walnut will vary by as much as 1/8" in width in typical indoor conditions. When designing wood to wood joints where the moving cross grain meets the stable long grain, the joint needs to allow for this wood movement. You will need to accommodate this movement if your design attaches cross grain wood to aluminum. It can be as simple as screwing through an oversize hole in the aluminum with a large headed fastener that lets the wood move by the difference between the ID of the hole and the OD of the fastener. I don't think thermal movement will be of any concern in comparison.
I was planning on using mdf/ply (maybe just ply) with a burr walnut veneer for the cabinet, My understanding was that I could seal the MDF and wouldn't need to worry about humidity dependent expansion, but will this also have further ramifications for the veneer? The planned design would have an aluminium front/top/base, with MDF cross sections, ply side panels and a veneer over the ply, possibly with a layer between the veneer/ply of 1mm neoprene.... or more likely use a sandwich of thin ply with neoprene in the middle, to help reduce vibrations and make it easier to bend the ply round the cross sections to form the arc's in the first place!
Plywood is significantly more dimensionally stable to humidity changes than wood slabs. The alternating plys are laid at right angles to each other and bound with adhesives so the cross grain movement is stabilized by the long grain in the adjacent plys. If your construction is high quality plywood and aluminum I don't think you will need to take any special precautions regarding wood movement...just design with good general fastening techniques.
How radical would the curved panels be?
If you can make your own vacuum bagging rig, 3-4 layers of bending (rubber) ply glued with yellow PVA can make for a pretty sturdy panel that still includes a fair amount of internal damping. It does take a fair bit of time and material to fabricate a robust jig on which to lay up the curved panels, and several hours of bagging time to allow the glue to completely cure. The very soft and coarse open grain of rubber ply face are perfectly fine for laminating with post-form grades of plastic or metal laminates ( Formica, Arborite, etc), or phenolic backed veneers, but trimming those materials for shallow recessed cutouts for drivers, ports, terminal cups etc on curved panels is a royal pain. For paper backed or raw veneer, you'd definitely need a top layer of something like 1/8" hardboard
Without getting into a debate about it, the dimensional stability that kevin mentioned is one of many good reasons to consider high quality plywood for the carcass/ skeletal framework - if not loudspeaker enclosure in general.
(too close to inciting another "religious" debate on the subject?)
If you're not concerned about ever removing the aluminum panel, sizing it slightly small and using something like a exterior grade glazing caulking ( Sikaflex , etc) for perimeter seal as well as panel adhesion would provide very durable adhesion, while also retaining some compliance to allow for heat expansion. But to be honest, unless in a sauna or getting a lot of direct sunlight in a "greenhouse" situation, at the ambient room temperatures most domestic speakers are used, thermal expansion is probably not that significant a problem.
If you can make your own vacuum bagging rig, 3-4 layers of bending (rubber) ply glued with yellow PVA can make for a pretty sturdy panel that still includes a fair amount of internal damping. It does take a fair bit of time and material to fabricate a robust jig on which to lay up the curved panels, and several hours of bagging time to allow the glue to completely cure. The very soft and coarse open grain of rubber ply face are perfectly fine for laminating with post-form grades of plastic or metal laminates ( Formica, Arborite, etc), or phenolic backed veneers, but trimming those materials for shallow recessed cutouts for drivers, ports, terminal cups etc on curved panels is a royal pain. For paper backed or raw veneer, you'd definitely need a top layer of something like 1/8" hardboard
Without getting into a debate about it, the dimensional stability that kevin mentioned is one of many good reasons to consider high quality plywood for the carcass/ skeletal framework - if not loudspeaker enclosure in general.
(too close to inciting another "religious" debate on the subject?)
If you're not concerned about ever removing the aluminum panel, sizing it slightly small and using something like a exterior grade glazing caulking ( Sikaflex , etc) for perimeter seal as well as panel adhesion would provide very durable adhesion, while also retaining some compliance to allow for heat expansion. But to be honest, unless in a sauna or getting a lot of direct sunlight in a "greenhouse" situation, at the ambient room temperatures most domestic speakers are used, thermal expansion is probably not that significant a problem.
Last edited:
Just pick up any piece of aluminum and strike it with a hammer. Try the same with a piece of wood. There is a reason folks don't use aluminum.
He did propose constrained layer damping, which along with resilient mounting and the mass of installed drivers should, I think, substantially mitigate panel resonances.
BTW there have been more than a couple of commercial products over the years that have incorporated aluminum in enclosures - Krell, Kef Muoan would be a couple of extreme examples- no doubt there many others, and the number of DIYers who've played with it is certainly greater than the implied "none"
BTW there have been more than a couple of commercial products over the years that have incorporated aluminum in enclosures - Krell, Kef Muoan would be a couple of extreme examples- no doubt there many others, and the number of DIYers who've played with it is certainly greater than the implied "none"
You can provide a damping system, but aluminum has astounding resonances. When used as a decorative foil, it is not an issue. Bonding to aluminum is not easy.
aluminium turn quite 'dead' when attached to other material
if not, it will ring like a bell, yes
but I would not glue it to anything, but only use machine screws
actually it's possible to buy such alu front baffle, ready to mount
if not, it will ring like a bell, yes
but I would not glue it to anything, but only use machine screws
actually it's possible to buy such alu front baffle, ready to mount
Yup, the bonding of aluminium to wood is a definite concern, my main reason for wanting to use aluminium was looking for as rigid a solution as possible that was non-ferrite. I was hoping that putting a layer of neoprene or something similar bonded to the back of the aluminium would control any ringing.
I'm basing most of my decisions on opinions of others and basic engineering intuition, which can of course be flawed... the more thought i put into it. the more I think that a good quality ply would be a better idea throughout... though I have read of people finding massive benefits in filling tweeter cavities with sand... has anybody else compared different cabinet techniques for the same sets of drivers?
Maybe I'm getting deep into opinion territory here, but I know my aim is to create a cabinet with minimal resonance, even if it's sympathetic to the frequencies being produced, I'm keen on the idea of a speaker design with the minimum possible distortion from original input.
I'm basing most of my decisions on opinions of others and basic engineering intuition, which can of course be flawed... the more thought i put into it. the more I think that a good quality ply would be a better idea throughout... though I have read of people finding massive benefits in filling tweeter cavities with sand... has anybody else compared different cabinet techniques for the same sets of drivers?
Maybe I'm getting deep into opinion territory here, but I know my aim is to create a cabinet with minimal resonance, even if it's sympathetic to the frequencies being produced, I'm keen on the idea of a speaker design with the minimum possible distortion from original input.
Tinitus - sorry, just read your reply, I'd like the baffle to be thinner if possible, so the option is either 5mm or 10mm aluminium, maybe with a sheet of 1mm rubber sandwiched to ply, the whole thing bolted togther?
Problem is I feel likt the ply would need to be of a decent thickness, and I'd quickly get over the target of 18mm or less for baffle thickness... that said, if I used ply I'd like the idea of two 10/12mm sheets with rubber in the middle...
Problem is I feel likt the ply would need to be of a decent thickness, and I'd quickly get over the target of 18mm or less for baffle thickness... that said, if I used ply I'd like the idea of two 10/12mm sheets with rubber in the middle...
to have a thin baffle is possibly the best reason to use alu
I would say 6-8mm for a narrow baffle
and on the outside, mount other material around driver chassies
probably no need to complicate further
much of what can be done will often be waste of time and money
not that it makes no difference, but drivers and crossover are what matters
If you look at commercial builds with aluminum baffles they often also have aluminum backs and both are just clamped onto the carcass using long thru bolts with suitable gaskets.
dave
dave
How often is a speaker under use subjected to a hammer blow? A stiff material which has a higher natural resonance is much harder to get to resonate with music. Add to that that the aluminum panelwill be clamped/afixed to a material with much higher damping. And that the OP is proposing a damped sandwich.
Using aluminum baffles is expensive compared to using wood. You do see it in commercial loudspeakers. Usually not the affordable ones. And often very highly regarded ones.
dave
- Status
- Not open for further replies.