There are xylophone-like instruments with bars made of wood (xylophone), metal (glockenspiel), glass (crystallophone) and rock (lithophone).

If I wanted to make a xylophone with bars made of plastic, what plastic would be best?

Or to put it another way, which plastic has the best acoustic properties (eg. low attenuation)? And how could I make bars out of that plastic?

Or to put it one more way, which plastic (noun) is the least plastic (verb)?

Q I guess, quality factor that keeps it ringing a little bit, related springiness, and not sure about many plastics qualifying, into mid audio to higher frequencies anyway, and there’d be temperature drift too, resonance shift, given how plastics soften with heat.

thinking

transition said:

Q I guess, quality factor that keeps it ringing a little bit, related springiness, and not sure about many plastics qualifying, into mid audio to higher frequencies anyway, and there’d be temperature drift too, resonance shift, given how plastics soften with heat.

thinking

High Q rules out 3-D printing for starters.
I can live with temperature drift and resonance shift. Perhaps curing it in the oven before first use might temper it.

I’m not even sure if I want thermoplastics or thermosets, and that’s about as basic a question as you can get when it comes to plastics. Thermosets have higher melting points. I did find this website. I can immediately discard anything with an attenuation greater than 10 dB/cm.

http://www.ndt.net/links/proper.htm

That suggests possibly one of polystyrene, polyethylene or nylon.
Rejecting ABS, polycarbonate, PETG, vinyl, Styrene Butadiene and possibly PVC.

But that website knows nothing about polyester, polyurethane, viscose, PET and epoxy, for starters.

I can’t rely on strength as a guide to good acoustics, nylon can contain vesicles of liquid lubricant that would interfere with acoustics.

mollwollfumble said:

transition said:

Q I guess, quality factor that keeps it ringing a little bit, related springiness, and not sure about many plastics qualifying, into mid audio to higher frequencies anyway, and there’d be temperature drift too, resonance shift, given how plastics soften with heat.

thinking

High Q rules out 3-D printing for starters.
I can live with temperature drift and resonance shift. Perhaps curing it in the oven before first use might temper it.

I’m not even sure if I want thermoplastics or thermosets, and that’s about as basic a question as you can get when it comes to plastics. Thermosets have higher melting points. I did find this website. I can immediately discard anything with an attenuation greater than 10 dB/cm.

http://www.ndt.net/links/proper.htm

That suggests possibly one of polystyrene, polyethylene or nylon.
Rejecting ABS, polycarbonate, PETG, vinyl, Styrene Butadiene and possibly PVC.

But that website knows nothing about polyester, polyurethane, viscose, PET and epoxy, for starters.

I can’t rely on strength as a guide to good acoustics, nylon can contain vesicles of liquid lubricant that would interfere with acoustics.

There’s this website, gives attenuation of a large number of materials in neper/metre. Divide by 11.5 to get dB/cm. (Is that correct?)

http://www.kayelaby.npl.co.uk/general_physics/2_4/2_4_1.html

Material, dB/cm
Butyl rubber/carbon (100/40), 11.6
Cellulose acetate butyrate, 9.0
Crown glass, 0.17
Neoprene, 20
Nylon, 1.13
Perspex, 5.0
Polycarbonate, 21
Polyethylene, 9 to 26
Polyethylene terephthalate (Mylar), 175
Polystyrene, 2.0
Polyvinyl chloride, 0.30
Polyvinyl chloride acetate, 110
Polyvinyl formal, 10.0
Polyvinylidene chloride, 18
Polyvinylidene fluoride, 96
Rubber (natural), 1.30
Rubber/carbon (100/40), 3.2
Teflon, 37

Nothing beats glass, of course, but natural rubber, polystyrene, nylon and PVC are surprisingly good.
PVC here is 0.3 dB/cm, on previous link it was 11.2 dB/cm. They can’t both be right.

As before, reject anything with an attenuation above 10.

>and PVC are surprisingly good

I thought that one earlier when looking around the room, then went had a look at what musical instruments are made from plastic

transition said:

>and PVC are surprisingly good

I thought that one earlier when looking around the room, then went had a look at what musical instruments are made from plastic

Turns out that a place called http://www.plasticcenter.com.au/ is almost within walking distance of my house. Perhaps I ought to toodle (or is the correct word tootle?) up there and hit all their pieces of plastic to find out. They supply:

ABS
Acrylic (Perspex) Sheet
Acetal Sheet and Rod
Paper Bakelite Sheet
Canvas Bakelite Sheet and Rod
HDPE (High Density Polyetheylene) rod and Sheet
Nylon Sheet and Rod
PETG Sheet
Polycarbonate Sheet and Tube
PVC (Poly Vinyl Chloride) Rigid Rod and Flexible Sheet
Polypropylene Sheet and Rod
Polyurethane Sheet and Rod
HIPS Sheet
PTFE (Polytetraflourine) Sheet Rod
UHMWPE (Ultra High Molecular Weight Polyethylene) – Sheet and Rod

Yamaha plastic recorders are made from ABS, apparently. I don’t have any idea what they sound like if struck.

https://www.ozwinds.com.au/recorders-soprano-descant-recorders-c-322_291_90.html

https://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene

Stumpy_seahorse said:

transition said:

>and PVC are surprisingly good

I thought that one earlier when looking around the room, then went had a look at what musical instruments are made from plastic

Yamaha makes its recorders and fife of ABS plastic. The piccolo is usually made of ABS resin. Clarinets are often made of ABS. “Like clarinets and oboes a bassoon may also be constructed of ABS resin.”

From wiki: “Acrylonitrile butadiene styrene (ABS) is a common thermoplastic polymer. Its glass transition temperature is approximately 105 °C. ABS is amorphous and therefore has no true melting point. The proportions can vary from 15 to 35% acrylonitrile, 5 to 30% butadiene and 40 to 60% styrene. ABS is stronger than pure styrene. While the cost of producing ABS is roughly twice the cost of producing polystyrene, it is considered superior for its hardness, gloss and toughness. ABS’s light weight and ability to be injection molded and extruded make it useful in manufacturing products such as musical instruments (recorders, plastic clarinets, and piano movements), golf club heads (because of its good shock absorbance), bumper bars, protective headgear, whitewater canoes, Lego and Keyboard keycaps.”

“These plastic recorders are made from tough ABS resin, the same polymer used in car bumpers.”

So could I melt down a second hand car bumper bar and use it to produce musical instruments?

Some places claim that their polycarbonate looks and feels like glass.

“We absolutely guarantee all our polycarbonate glasses are:
Virtually unbreakable
Looks like and feels like glass”

Could that mean good acoustic properties like glass as well?

Can you find any information, any at all, about sound transmission (other than ultrasonic) in any of the following plastics?

Polyester
Epoxy
Polyurethane.

Am asking because my first attempt at making the front of an oversized viola failed today (the varnish didn’t set properly) and I’ve found the name of a supply store for professional artists that stocks a range of resins and hardeners for all three of these plastics – and no others.

while i’m looking around

https://en.wikipedia.org/wiki/Engineering_plastic

Engineering plastics are a group of plastic materials that have better mechanical and/or thermal properties than the more widely used commodity plastics (such as polystyrene, PVC, polypropylene and polyethylene).

transition said:

while i’m looking around

https://en.wikipedia.org/wiki/Engineering_plastic

Engineering plastics are a group of plastic materials that have better mechanical and/or thermal properties than the more widely used commodity plastics (such as polystyrene, PVC, polypropylene and polyethylene).

Thanks for spotting that.

“The term usually refers to thermoplastic materials rather than thermosetting ones.”

I wish I knew why. When playing around with rocket motors I noticed that the only plastics with good high temperature performance are the thermosetting plastics such a phenolics, formaldehydes and similar.

The highest temperature thermoplastics such as Teflon and high temperature silicone fail by being too easily scratched and also having too low a melting point. Teflon melts at only 367 degrees and high temperature silicone at only 343 degrees or less. Nowhere near the melting point of aluminium at 660 degrees.

I found it was quite easy to buy tubes, sheets or rods made of thermoplastic and virtually inpossible to locally buy tubes, sheets or rods of thermosetting plastics.

I went around tapping plastic objects today at two plastic manufacturers to ascertain their acoustic properties. Results, on a scale of 0 to 4.

Epoxy 0/4 = acoustically dead.

Polyurethane 2/4 = sounds and feels like rubber (low pitch), but surprisingly not bad impedance. The more rigid grades are not necessarily better.

Polyester 4/4 = Better than commercially available drum skins. Rigid.

ABS 3/4 = OK and a bit drum-like, but not too bad.

High impact poly-something-or-other (polystyrene/polycarbonate/polyethene?) 2/4 = higher pitch than ABS but worse impedance.

PETG 2/4 = similar to above.

Acrylic 1/4 = bad even for a thermoplastic.

So I’ve settled on the following:

Top and bottom of viola – polyester reinforced polyester (because I use the sag of woven polyester fabric to get the shape).
Sides of viola – ABS (because the sample I got free is just big enough to make the sides from)

For later xylophone with plastic bars. Only polyester, ABS and Polyurethane are worth considering so far. These would be suitable for high, middle and low pitch respectively.

Other plastics are still to try, later.

Now not using ABS, using polyester instead. It has a nicer tone than both ABS and wood.

PET may be even better, but I can’t check that.

mollwollfumble said:

Now not using ABS, using polyester instead. It has a nicer tone than both ABS and wood.

PET may be even better, but I can’t check that.

PET is recyclable – plastic drink bottles. Plenty of them around.

Michael V said:

mollwollfumble said:

Now not using ABS, using polyester instead. It has a nicer tone than both ABS and wood.

PET may be even better, but I can’t check that.

PET is recyclable – plastic drink bottles. Plenty of them around.

They also can sideline as impromptu ballistic silencers?

roughbarked said:

Michael V said:

mollwollfumble said:

Now not using ABS, using polyester instead. It has a nicer tone than both ABS and wood.

PET may be even better, but I can’t check that.

PET is recyclable – plastic drink bottles. Plenty of them around.

They also can sideline as impromptu ballistic silencers?

I have no idea about that notion.

Michael V said:

roughbarked said:

Michael V said:

PET is recyclable – plastic drink bottles. Plenty of them around.

They also can sideline as impromptu ballistic silencers?

I have no idea about that notion.

I’ve never tried it either. It was only a whisper that I heard.

Michael V said:

mollwollfumble said:

Now not using ABS, using polyester instead. It has a nicer tone than both ABS and wood.

PET may be even better, but I can’t check that.

PET is recyclable – plastic drink bottles. Plenty of them around.

I’ve heard that PET requires an oxygen-free environment to work on, and I don’t have an oxygen-free environment handy.

Not only is the acoustic tone of polyester more pleasant than wood. It also sounds startlingly like the tone of wood.