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My goal is to have a speaker inside a PLA casing to produce a nice hearable sound from a submersible item.

I intended to produce that sound from a Piezo buzzer stuck on a membrane held tight in hollow place between two pieces, but the result is unsatisfactory as the sound gets muffled to inaudible levels.

Is there any known 3D printable methods to permit for a sound to be heard from PLA?

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  • $\begingroup$ Welcome to 3DPrinting.SE! $\endgroup$
    – 0scar ♦
    Commented Oct 2, 2020 at 7:11
  • $\begingroup$ Thank you! I love Stack Exchange it's really helped me over the course of the years. $\endgroup$
    – B7th
    Commented Oct 3, 2020 at 2:22
  • $\begingroup$ This will be a problem, but it's not the material. I've seen recorders, trumpets, and even trombones made from pla. The problem is the shape. $\endgroup$
    – Joel Coehoorn
    Commented Oct 8, 2020 at 12:58

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In space, no one can hear you scream. That's because there's no air to be vibrated, which is part of the definition of sound.

In the case of your model, the described diaphragm will generate sound because it is surrounded by air. The vibrations in the air will transfer (and reflect) from the PLA shell you've created.

In order to hear as much sound as possible, you have to have as thin a shell as possible and only one of them. It would be more effective if you could incorporate the membrane into the shell, which eliminates the sound damping effect of the plastic sphere.

Barring that option, one layer (vase mode, but probably not) would present the created sound with a much less massive amount of plastic to vibrate.

Additionally, PLA is not known for being water tight. One can apply epoxy or other sealants to make it so, but that will add mass to the overall equation.

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    $\begingroup$ And in space if you try to scream you're out of air very quickly ^^" Thanks that's pretty much what I thought. What about using the shell as the vibrating membrane? $\endgroup$
    – B7th
    Commented Oct 1, 2020 at 22:38
  • $\begingroup$ Yes, if you can thin the shell sufficiently, attaching the transducer directly will give you quite a good start. Additionally, consider that you don't have to thin the entire shell, only the portion at which the buzzer attaches. Realistically, you can then reduce most of the assembly. $\endgroup$
    – fred_dot_u
    Commented Oct 1, 2020 at 23:44
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You are asking about acoustics (see Sound, Acoustics). The main parameters you are dealing with can be seen in the simple harmonic model: flexibility (spring) and mass. Thinner walls give you more spring and less mass. Different filament materials will also change these parameters. One thing to consider is PLA becomes more brittle as it absorbs moisture. Someone who designs acoustical musical instruments could probably help you.

However, note that the ideal acoustics is different for a person speaking versus music, such as orchestra or band. Thus, application is essential. For example, if you are building earphones, you want to dampen external sound.

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  • $\begingroup$ Very useful link I'm reading through and will see what can be done. Actually this is for an electronic instrument that has a fast decay and I am starting to think that a piezo buzzer may or may not be the best choice. $\endgroup$
    – B7th
    Commented Oct 3, 2020 at 2:25
  • $\begingroup$ The acoustics of you sound box will greatly affect the sound of your instrument. $\endgroup$
    – Perry Webb
    Commented Oct 3, 2020 at 12:19
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I did a lot of experimentation in this a couple years ago. The limitation on the sound is the amount of energy you can apply to the plastic, and the ability of the plastic to respond (move to) that energy. I ended up using epoxy to fasten a transducer directly to the plastic wall, and while the sound quality was not great (I could not have used it for speech or music) it was adequate to make the alarm sound, 50% PWM @ 3.3V and I controlled the frequency using the Arduino 'tone' library to control the frequency. I printed that side solid (no infill) and a bit thinner than the other sides (2mm instead of 4mm), printed it separately and then used epoxy to glue in (and its attached transducer) to the cube I was using for the rest of the circuitry.

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  • $\begingroup$ Hi Joseph! Thanks that does make quite a lot of sense. And I guess the separate print and glue helped separate the amplifying surface from its sound box, like a diaphragm. $\endgroup$
    – B7th
    Commented Oct 6, 2020 at 18:04
  • $\begingroup$ No. The extra print and gluing the piece to the box compensated for the inability to say to the 3D slicing software, "Use 100% infill on this wall, and this wall only". It would not have changed the sound quality at all had I been able to do selective infill instead. I just needed a thin, flexible surface. The honeycomb infill made a more rigid surface which transmitted the sound less efficiently. $\endgroup$
    – flounder
    Commented Oct 12, 2020 at 22:28
  • $\begingroup$ I see! This makes a lot of sense. Thank you! Will check if it's possible to play on different infilling. Where was the honeycomb filling I'm not sure I follow you on that one though? $\endgroup$
    – B7th
    Commented Oct 13, 2020 at 10:07

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