A Single-Digit-Micrometer Thickness Wood Speaker

Researchers have created an audio speaker using ultra-thin wood film. The new material demonstrates high tensile strength and increased Young’s modulus, as well as acoustic properties contributing to higher resonance frequency and greater displacement amplitude compared to a commercial polypropylene diaphragm in an audio speaker.

Typically, acoustic membranes have to remain very thin (on the micron scale) and robust in order to allow for a highly sensitive frequency response and vibrational amplitude. Materials made from plastic, metal, ceramic, and carbon have been used by engineers and physicists in an attempt to enhance the quality of sound. While plastic thin films are most commonly manufactured, they have a pretty bad impact on the environment. Meanwhile, metal, ceramic, and carbon-based materials are more expensive and less attractive to manufacturers as a result.

Cellulose-based materials have been making an entrance in acoustics research with their environmentally friendly nature and natural wooden structure. Materials like bagasse, wood fibers, chitin, cotton, bacterial cellulose, and lignocellulose are all contenders for effective alternatives to parts currently produced from plastics.

The process for building the ultra-thin film involved removing lignin and hemicellulose from balsa wood, resulting in a highly porous material. The result is hot pressed for a thickness reduction of 97%. The cellulose nano-fibers remain oriented but more densely packed compared to natural wood. In addition, the fibers required higher energy to be pulled apart while remaining flexible and foldable.

At one point in time, plastics seemed to be the hottest new material, but perhaps wood is making a comeback?

[Thanks Qes for the tip!]

22 thoughts on “A Single-Digit-Micrometer Thickness Wood Speaker

    1. I see what u did there! But u know, Mike, most people would want to document this project thoroughly. Question is: take the pictures with your cell phone or with a standard SLR camera? Given that some phones’ cameras may not deliver suitable photo quality, I’d say that if you choose cell u loose!

  1. Cellulose is stable at high humidity? I don’t think is a good idea use it in such a tiny (compared to whole headphones) and critical component. Sounds like soybean-based insulation in cars wiring…

  2. 1. How long before they “biodegrade” inside my speaker cabs?

    2. If said speaker cones are indeed biodegradable, then their acoustic/mechanical parameters will not be the same six months after manufacture, let alone say six years. Or am I missing something here?

    1. biodegradable does not equal immediate breakdown. Biodegradation often involves very specific conditions (high humidity, acidity,specific microbes..yada yada). These would likely not just spontaneously break down.

    2. +1 Don’t understand the biodegradable issue as it applies to some fractional ounce component of the speaker driver. I wonder how many decent speakers ( cones, frames, capacitors, cabinets connectors; the whole thing) have wound up in the landfills because of “biodegraded” foam rubber speaker surrounds. The best way to avoid making trash is to make sure what you manufacture has long lasting durable functionality.

      1. “+1 Don’t understand the biodegradable issue as it applies to some fractional ounce component of the speaker driver.” A pretty important “fractional ounce” Methinks.

        I have at least a dozen 12″ and a couple of 15″ H|H PA speakers that are more or less, 50 years old. Complete with ‘press molded’ integral paper dampers fixed as solidly to their cages as the day they left the factory. You made a very good point in so much as “The best way to avoid making trash is to make sure what you manufacture has long lasting durable functionality.” But that obviously didn’t apply to the whoever gave us ‘foam’ speaker damping, when the wheel wasn’t broken. So it is a moot point as to what is/isn’t a decent speaker, when the design proposed above, is even less proven over time.

        My own ‘retro’ amps have needed tlc. Especially with regards to replacing decades old electrolytics (who knew back then they were biodegradable after 30+ years?) But hey, we’re ‘hackers’ that doesn’t mean the whole thing has to go into the landfill, because one or two parts didn’t get to three score and ten.

        1. Which is why I listen to a really nice pair of Norman Laboratories Model 7s that I rebuilt with a recone-ing kit. (Which are driven by a pair of 1960s McIntosh MC20s)
          None of this would be going to the landfill any time in the future.

  3. I have never heard a poly-plastic speaker that sounds good. All good speakers are already of that thickness or a little more before the that shrinking process and are made of processed (paper) wood. The cone shape is inherently strong, flat is wobbly and not phase linear. Funny it has to have a cone structure to make it work while adding non radiating mass. Not to say this stuff wouldn’t make a good mid or tweeter, just not full range.

    A lot of progress happened a hundred years ago as we went from earphone metal diaphragms and phonograph horns to cones of processed wood. There were also solid spruce horns and cones. In 10 years or so we had 2 and 3 way systems and phenomenal efficiency with horn loading.The speed of sound in good sitka spruce is Mach 10! That is how a piano “amplifies” the sound of the strings on the bridge. If velocity was less, sounds cancel as sound comes off of it in many phases instead of one linear wave. The soundboard has ribs cross grain and a crown or dome shape it is not flat. This not flat way predominates on all wood acoustic instruments.

    Lastly, very thin leather was used as a surround way before foam. I have used very thin rubber or nylon cloth used in player pianos for making a series of pie rim shaped sections with pvc-E glue and get rotten rim speakers going again.

  4. After all that processing, it’s no longer wood. Plastics like cellulloid, Tenite, and Rayon (acetate) are not wood despite being made, in part, from wood.

    “Cellulose-based materials have been making an entrance in acoustics research” That’s why so many things like lightweight metals and other exotic materials were tried before high density plastics took over for speaker cones from the cheapest to almost the most expensive speakers. Paper is *crap* for speaker cones. It has to be heavy and molded with ridges to get decent properties of stiffness but not too stiff for speaker cones.

    Plastics enabled higher manufacturing precision and more accurate audio reproduction, along with greater speaker longevity, which reduces waste. Plastic cone speakers can withstand environments that destroy paper cone speakers, environments that will destroy these “wood” speakers.

  5. “At one point in time, plastics seemed to be the hottest new material, but perhaps wood is making a comeback?”

    At one point, plastics were made of wood. Cellophane, glassine, and if you include cotton you have nitrocellulose and celluloid.

    1. Considering one of the most common failure modes of a loudspeaker is excessive power which creates heating of the voice coil, sometimes to ignition, I might recommend not using nitrocellulose (guncotton) as a speaker cone. Although it could provide interesting effects with the 1812 overture or a new dimension to Pachelbel’s “Cannons in D Minor”.
      I’ve heard people refer to a failed speaker as being blown out. Hmmm…

    1. You mean, “It’s a shame nobody has made a decent paper cone since mylar was the latest thing to separate audiophiles from money when they already had perfectly good speakers.”

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