I've been going crazy with bicycle projects lately*, and I've discovered a lot of 'neat' composites which would be fantastic for loudspeakers. My reference speakers** are made of a carbon fiber / MDF composite, and I believe the cabinet construction has a LOT to do with their good sound.
The thing that's a bummer about carbon fiber is that it's ridiculously expensive. I've done some experiments with aluminum/fibreglass composites, but it's tough to get anything to 'stick' to aluminum. It delaminates very easily; you can literally peel it off with a plastic knife if you don't prep it right.
So this afternoon I stumbled across a construction method which I think is a real home run for the DIYer 😀
It's plain ol' cardboard, but in a honeycomb. This is how Ingvar Kamprad made $36,000,000,000 selling furniture. The paper honeycomb allows Ikea to sell furniture which is stronger, lighter, and cheaper than the competition. For instance, if you made an Expedit shelf out of MDF, the shelf would likely weigh over 200 pounds! And it would cost more of course.
For our speaker projects, the honeycomb has a lot of attractive features:
The only real drawback to the cardboard honeycomb that I can see is that it takes up a lot of volume, and it's not as strong as an aluminum honeycomb. But to put this in perspection, a 4'x8' sheet of aluminum honeycomb costs about $500, and delivery is expensive. A 4'x8' sheet of cardboard honeycomb is $26 in quantity!***
Now a lot of you might prefer MDF or plywood, but the honeycomb composite, as used by Ikea, has some advantages that are particularly attractive for audio. In a loudspeaker, panel flex re-radiates sound. This destroys imaging cues, changes the frequency response, and reduces efficiency. The typical approach to panel flex is simply to use moar wood. But that approach has diminishing returns; even if you double the thickness, the panel will still vibrate. The honeycomb composite is VERY directional. According to the vendor's site, the panel can sustain 2500 pounds before collapsing. Unless you have a very very very big subwoofer, I doubt you're applying 2500 pounds of pressure to the sidewall. And that figure doesn't even include the added strength that we get when we use a composite, like Ikea does. Very similar construction is used for the floors of airplanes, where you have thousands of pounds of pressure applied as people enter the plane.
* If you're curious about my bike projects, I post them at my own forum (audiopsychosis) and bentrideronline, using the same alias I use here.
** My reference speakers are Gedlee Summas.
*** Honeycomb Packaging, Honeycomb Cardboard in Stock - ULINE
The thing that's a bummer about carbon fiber is that it's ridiculously expensive. I've done some experiments with aluminum/fibreglass composites, but it's tough to get anything to 'stick' to aluminum. It delaminates very easily; you can literally peel it off with a plastic knife if you don't prep it right.
So this afternoon I stumbled across a construction method which I think is a real home run for the DIYer 😀
An externally hosted image should be here but it was not working when we last tested it.
It's plain ol' cardboard, but in a honeycomb. This is how Ingvar Kamprad made $36,000,000,000 selling furniture. The paper honeycomb allows Ikea to sell furniture which is stronger, lighter, and cheaper than the competition. For instance, if you made an Expedit shelf out of MDF, the shelf would likely weigh over 200 pounds! And it would cost more of course.
For our speaker projects, the honeycomb has a lot of attractive features:
- It's cheaper than wood
- It's easy to work with - you can cut the honeycomb with a box cutter
- it's lighter than wood
- it's directional. This is very important. For instance, we can orient the honeycomb to resist flex in a specific direction. This is the secret to it's strength. In the Ikea furniture, if you oriented the honeycomb in the other direction, the furniture's strength would be greatly diminished. In this respect, it's actually a lot like directional carbon fiber!
The only real drawback to the cardboard honeycomb that I can see is that it takes up a lot of volume, and it's not as strong as an aluminum honeycomb. But to put this in perspection, a 4'x8' sheet of aluminum honeycomb costs about $500, and delivery is expensive. A 4'x8' sheet of cardboard honeycomb is $26 in quantity!***
Now a lot of you might prefer MDF or plywood, but the honeycomb composite, as used by Ikea, has some advantages that are particularly attractive for audio. In a loudspeaker, panel flex re-radiates sound. This destroys imaging cues, changes the frequency response, and reduces efficiency. The typical approach to panel flex is simply to use moar wood. But that approach has diminishing returns; even if you double the thickness, the panel will still vibrate. The honeycomb composite is VERY directional. According to the vendor's site, the panel can sustain 2500 pounds before collapsing. Unless you have a very very very big subwoofer, I doubt you're applying 2500 pounds of pressure to the sidewall. And that figure doesn't even include the added strength that we get when we use a composite, like Ikea does. Very similar construction is used for the floors of airplanes, where you have thousands of pounds of pressure applied as people enter the plane.
* If you're curious about my bike projects, I post them at my own forum (audiopsychosis) and bentrideronline, using the same alias I use here.
** My reference speakers are Gedlee Summas.
*** Honeycomb Packaging, Honeycomb Cardboard in Stock - ULINE
The IKEA honeycomb panels you show aren't great for speakers. They leak (acoustically) like a sieve, and are really, really heavy, too.
Keeping with the idea of using IKEA materials for speakers, I think you might find this thread of interest:
How to make IKEA baffleXchange speaker cabinets - Techtalk Speaker Building, Audio, Video, and Electronics Customer Discussion Forum From Parts-Express.com
The frames that are used to build these speakers are essentially a skin+core+skin composite. They are pretty stiff, strong, and not bad acoustically.
I have two sizes built now, and have a third "monkey coffin" sized enclosure yet to build. Presentable enough for the wife, yet completely DIY and you can easily replace the baffles to make a totally new speaker.
I developed this method out of the lack of tools, woodworking talent, space, and a host of other issues that have prevented me from making decent cabinets. Now I can concentrate on the speakers!
-Charlie
Keeping with the idea of using IKEA materials for speakers, I think you might find this thread of interest:
How to make IKEA baffleXchange speaker cabinets - Techtalk Speaker Building, Audio, Video, and Electronics Customer Discussion Forum From Parts-Express.com
The frames that are used to build these speakers are essentially a skin+core+skin composite. They are pretty stiff, strong, and not bad acoustically.
I have two sizes built now, and have a third "monkey coffin" sized enclosure yet to build. Presentable enough for the wife, yet completely DIY and you can easily replace the baffles to make a totally new speaker.
I developed this method out of the lack of tools, woodworking talent, space, and a host of other issues that have prevented me from making decent cabinets. Now I can concentrate on the speakers!
-Charlie
An externally hosted image should be here but it was not working when we last tested it.
This is the same stuff they use in steel doors!
An externally hosted image should be here but it was not working when we last tested it.
It's also used to hold up pallets.
I gotta think that if it's strong enough to hold up a pallet, it's strong enough to keep a loudspeaker wall from flexing. (again, the manufacturer claims it can hold up over a ton(!))
As far as 'leaking like a sieve', that's why you have to make a composite.
Just like the Ikea Lack shelves, for a loudsepaker we would use a thin layer of wood, then cardboard honeycomb, and then another layer of wood.
I am aware of Ikea's LACK and EXPEDIT series panels, and these are the ones I am referring to my post as "acoustically transparent" and "heavy". OK, basically I am saying that they suck for speakers. Don't get me wrong here, I am not saying that all honeycomb constructions are bad! Just because something is stiff and strong enough to hold a pallet of freight does not mean it makes for the ideal speaker box construction material. There is a lot more to it than stiffness (e.g. damping). Trust me, I have made my share of cabinets with "acoustically transparent" walls and believe me they went into the garbage quickly.
If you can fill up the void space with something that damps sound transmission (sand fill?) then you might have something, er... something even heavier! Seriously, in my honest opinion I don't think that the paper products (pallet spacers) or the IKEA honeycomb panels are really any good for speakers.
-Charlie
If a loudspeaker is airtight, the only way that sound can radiate through the panel is via vibration. That's it.
There's no need to fill with sand - it just has to be stiff enough not to re-radiate sound.
If this were not the case, then the sound from the rear of a loudspeaker cone would re-radiate through the cone itself.
Here's a hypothetical example. Let's say you're standing in a room made of cardboard. It would seem that the walls would be acoustically transparent. IE, you might say "these walls are made of cardboard."
But if the room is airtight, and you do something to prevent the walls from vibrating - then no sound will enter the room.
There's no need to fill with sand - it just has to be stiff enough not to re-radiate sound.
If this were not the case, then the sound from the rear of a loudspeaker cone would re-radiate through the cone itself.
Here's a hypothetical example. Let's say you're standing in a room made of cardboard. It would seem that the walls would be acoustically transparent. IE, you might say "these walls are made of cardboard."
But if the room is airtight, and you do something to prevent the walls from vibrating - then no sound will enter the room.
And it does. It reflects off the interior of the enclosure and out through the cone. You can prove it for yourself. Take a driver mounted in an enclosure and play music through it. Take an identical driver and place it face-to-face over the first driver. (Short its voice coil terminals together, or be extreme and pour glue into the voice coil gap.) Now listen.
The panel may be advertised to hold 2500 pounds. But that is if you lay it on the floor and stack 2500 pounds on it. Put a brick under each corner and try again, and it'lll crumple like... cardboard.
Or just hold one side of it up near your ear and tap on the other side...
Incidentally, interior doors for houses are usually made with the same construction - solid wooden edges, covered with 3-ply skin and cardboard honeycomb between.
There's the problem, right there. Honeycomb cardboard isn't rigid enough, as the tap test will show.
Uh, not sure what you are saying here... the sound DOES re-radiate back out the cone unless it is absorbed internally (or in the cone material itself)!
I got into a discussion with a mechanical engineer once about this topic. He illustrated to me that you can not win if you only have stiffness, and that damping in the panels is also very important. As you raise stiffness, the resonant frequency is just increased - you don't diminish transmission. Only damping can do that. So you need a panel with a balance of stiffness (just enough) and damping (as much as possible). Essentially, you can not make the structure stiff enough to raise all the possible resonances above the audio band.
-Charlie
I agree. Damping means removing energy from the system. Normally that is done because the material flexes, and the flexing dissipates energy. If you make it very stiff it can no longer flex and can not dissipate energy. That energy then manifests itself as higher frequency vibration, which is also flexing of course but less lossy at the higher frequency.
jan didden
jan didden
the LACK table i have is not honeycomb, it is recycled wood chips, somewhere between OSB and low density chipboard. It is a coffee table and may get holey soon to make a small OB project. It is rigid enough that i dont think panel flex will be a major problem. RE carbon fibre and adhesion to aluminium: i would imagine that once u sand the oxide off, then itd glue fine, IF u work quickly. With resins ive used, epoxy, its a better bond than some or many plastics. BUT I havent tried polyester resin, maybe thats the issue? Also after many years working in warehousing i can confirm that those pallets carry up to 2000kg, even when supported by 2 flt forks...they are more than rigid enough, many times that of flat sheet stock mdf or ply. BUT, they arent well damped. Filling with PU foam, flatting off, and adding damping should help that.alternatively, use some of that resin on the cardboard honeycomb, and also use it to bond and stiffen the skin panels?
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I've unpacked systems delivered on such pallets, too. Their advantage is that they can go in the cardboard recycling bin, their disadvantage is that you can't stack them on wet surfaces. But they're an order of magnitude more solid than the panels Patrick gave pictures of.
Think AC vs DC. A honeycomb without any facing or backing will support a very heavy load (DC). So the sound absorbing capability is completely down to whatever it is you laminate to the honeycomb.
Off topic, but couldn't resist since this is about speakers, honeycomb, aluminum and fiberglass...
My sub of choice... (although I only have Phase Linears and Evolutions, no Mac audio's)
My sub of choice... (although I only have Phase Linears and Evolutions, no Mac audio's)
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
thats wherd the similarity ends- the type i have experience of theyre plastic NOT woodfibre. A friend made a go-kart racer using an ABS pallet of this type.
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Charlie,
You are missing a key point. A (potential) resonance needs to be excited before the panel vibrates.
The energy to excite a resonance is inversely proportional to the square of the frequency (arguably, above a certain frequency, it is arguable that this is more like the inverse of the 4th power given that music is the source of excitation energy).
So if you can push the resonance high enuff (somewhere over 600-700 Hz i'd guess from the curves), the resonance will NEVER get excited by the music, so it is as if the resonances do not exist.
dave
Coming here a few years late, but I am a Bateman fan (I know more about his subwoofer experiments.) Patrick, if you are aware of this thread, will you comment on what, if anything further you have done with composites? In particular, I am now scouting materials for a Tapped Horn and why not honeycomb board? Probably not price-wise, as cheaper plywoods not much more expensive, but it'd be excellent to be the inventor of the ten pound subwoofer. Like many of my ideas, I'm sure someone smarter than I (and that is most people here probably) would have done it already, were it possible.
Acoustical reasons "why not" are in posts #2,4,6 and 7. In addition, edge treatment and corner glue up of honeycomb board is problematic.
Foam core with epoxy works well for building lightweight speaker cabinets (as well as boats, surfboards, and airplanes) but is very expensive, and far more work than dealing with the usual materials. Cost to benefit ratio can pay off fairly quickly in fuel savings on a boat, but not so much in a speaker cabinet.
These are in theory torsion boxes, after lugging my heavy 18mm mdf cabinets up two stories, I am considering other ways to make these and furniture lighter. And torsion boxes are perhaps the way.
I remain a skeptic, about whether sound can really travel through a composite panel. Granted, I don't know physics well, but I do know this much: sound propagates through a medium (usually air, but also...) There is no way sound can get through a barrier (such as a speaker cabinet) unless the barrier can move. So, if the material is stiff ( = resists motion), how is transmitting sound? Sorry, this just makes my ******** alarm go off 🙂
I concede with real-world materials there will always be some vibration = resonance. But if this frequency is above the range of interest, who cares? I am building a sub that will operate at most up to 100 Hz.
A more valid reason these composites are not widely used is primarily they cost "somewhat" to "a whole lot more" than plain old plywood or MDF. With the exception of the honeycomb board (even it is like only 1/2 or 1/3 the cost of standard woods). I'm still itnereested in the Sing products, but it must be at least 2x 3x cost of normal wood. Weight is a factor in (say) touring cabinets, but who cares if it justs sits in a corner of your living room and slowly makes the home's plaster crumble 🙂
A second factor that I've seen mainly on other forums is that many composites require some different techniques. For example, one of these panels may be very strong and stiff, but it's mostly hollow. Care must be taken when driving nails or screws or it may not hold as it would with wood. Also some of the panels don't have no edges at all 🙂
Some of the techniques may be cost but not time effective: DIY fiberglass looks a mess but you can make anything from a canoe to a sailboat to a subwoofer cabinet 🙂
I concede with real-world materials there will always be some vibration = resonance. But if this frequency is above the range of interest, who cares? I am building a sub that will operate at most up to 100 Hz.
A more valid reason these composites are not widely used is primarily they cost "somewhat" to "a whole lot more" than plain old plywood or MDF. With the exception of the honeycomb board (even it is like only 1/2 or 1/3 the cost of standard woods). I'm still itnereested in the Sing products, but it must be at least 2x 3x cost of normal wood. Weight is a factor in (say) touring cabinets, but who cares if it justs sits in a corner of your living room and slowly makes the home's plaster crumble 🙂
A second factor that I've seen mainly on other forums is that many composites require some different techniques. For example, one of these panels may be very strong and stiff, but it's mostly hollow. Care must be taken when driving nails or screws or it may not hold as it would with wood. Also some of the panels don't have no edges at all 🙂
Some of the techniques may be cost but not time effective: DIY fiberglass looks a mess but you can make anything from a canoe to a sailboat to a subwoofer cabinet 🙂
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