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Old 18th May 2012, 10:49 PM   #1
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Default Ikea Loudspeakers

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

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

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
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Old 18th May 2012, 11:04 PM   #2
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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
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Old 18th May 2012, 11:25 PM   #3
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Click the image to open in full size.
Click the image to open in full size.

This is the same stuff they use in steel doors!

Click the image to open in full size.

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.

Click the image to open in full size.

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.
[img]
Basically a cube within a cube.
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Old 18th May 2012, 11:50 PM   #4
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Quote:
Originally Posted by Patrick Bateman View Post
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
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Old 18th May 2012, 11:57 PM   #5
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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.
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Old 19th May 2012, 02:49 AM   #6
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Quote:
Originally Posted by Patrick Bateman View Post
...
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. ...
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.

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... you do something to prevent the walls from vibrating ...
There's the problem, right there. Honeycomb cardboard isn't rigid enough, as the tap test will show.
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Old 19th May 2012, 04:30 AM   #7
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Originally Posted by Patrick Bateman View Post
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.
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)!


Quote:
Originally Posted by Patrick Bateman View Post
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.
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
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Old 19th May 2012, 08:11 AM   #8
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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.

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Old 19th May 2012, 08:35 AM   #9
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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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Last edited by mondogenerator; 19th May 2012 at 08:48 AM.
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Old 19th May 2012, 09:45 AM   #10
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... 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. ...
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.
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