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Musings about diaphragm materials
Musings about diaphragm materials
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Old 12th December 2019, 06:17 PM   #1
Sebastian K is offline Sebastian K  Europe
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Default Musings about diaphragm materials

Hello everyone,

I'm wondering how we ended up with the materials for diaphragms that we have today.

To paraphrase Wikipedia Loudspeaker - Wikipedia:

The diaphragm is usually manufactured with a cone- or dome-shaped profile. A variety of different materials may be used, but the most common are paper, plastic, and metal. The ideal material would 1) be rigid, to prevent uncontrolled cone motions; 2) have low mass, to minimize starting force requirements and energy storage issues; 3) be well damped, to reduce vibrations continuing after the signal has stopped with little or no audible ringing due to its resonance frequency as determined by its usage. In practice, all three of these criteria cannot be met simultaneously using existing materials; thus, driver design involves trade-offs. For example, paper is light and typically well damped, but is not stiff; metal may be stiff and light, but it usually has poor damping; plastic can be light, but typically, the stiffer it is made, the poorer the damping. As a result, many cones are made of some sort of composite material. For example, a cone might be made of cellulose paper, into which some carbon fiber, Kevlar, glass, hemp or bamboo fibers have been added; or it might use a honeycomb sandwich construction; or a coating might be applied to it so as to provide additional stiffening or damping.
The plastic cones or domes I see today are mostly made out of Polypropylene (PP), sometimes mixed with 10 to 30% mineral powder such as talc. The latter increases stiffness by some degree, but it also increases weight.

AFAIK, the plastic used for cones before PP came to light was Polystyrene (PS, also called "Bextrene").

PS and PP, also PET ("Mylar") are not materials with any remarkable mechanical properties. They are very cheap and some of them are certified "food safe", so they are commonly found in food packaging. (My personal recommendation: Stay away from this sh*t were possible. But that is a entirely different topic.)

One does not have to go far as for aerospace materials. In fields such as consumer goods and automotive, a variety of plastics I've never seen used for speakers (PA, PC, PEEK...) and mixtures of different grades are used for injection molding, often reinforced with (short) glass or carbon fibers to improve them. No rocket science involved.

I see no such more advanced plastic stuff in the loudspeaker industry, and I wonder why.
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Old 12th December 2019, 07:22 PM   #2
Douglas Blake is offline Douglas Blake  Canada
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True enough ... speakers now are pretty much what they were in the 1970s. Not that I think that is a bad thing, but very little change has taken place.

I would imagine there could be several reasons why it's stagnant...

Cost would be a big one, exotic materials can be quite expensive.

Manufacturing some exotics is quite difficult and it's not always easy to form them appropriately.

Then, I suppose, with the move to mobile devices and smaller bluetooth devices, there really isn't much to motivate new innovations in home audio right now.

The only really different speakers I've seen in recent years are the flat panel woofers from Tangband. But IIRC, Sony did this years and years ago...
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Old 12th December 2019, 08:20 PM   #3
jzagaja is offline jzagaja  Poland
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Musings about diaphragm materials
Self reinforced thermoplastic material can be interesting - biaxially oriented fiber core has high tensile strength while melted outer shell forming matrix provide damping. It was back in 2006 I was making self reinforced PP at 158 deg and wrote master thesis.

There are new class of printed acoustic materials - metamaterials.
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Old 12th December 2019, 10:40 PM   #4
turboyam is offline turboyam  Canada
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I think plastics (and metals), are not used in loudspeakers for the same reasons, they are not used in violins (musical instruments), they just dont have their place here. Don't you think that there are enough plasticssssssssssss everywhere???
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Old 12th December 2019, 11:00 PM   #5
Galu is offline Galu  Scotland
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I'm a fan of paper pulp cones.

Pulps might be from Douglas fir or exotic blends which include eucalyptus from Brazil or Australia (very stiff), other specialty pulps from New Zealand, or the hemp family (Fostex and Dai-Ichi like banana leaves), kapok seed fibers (poor man’s Kevlar).
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Old Yesterday, 01:34 AM   #6
PeteMcK is offline PeteMcK
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Old Yesterday, 02:34 AM   #7
audiogod66 is offline audiogod66
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The great Japanese audio companies of the 1970,1980 period were very innovative and had research budgets to be able to use and develop state of the art materials for loudspeaker diaphragms etc. Just comb through the Vintage Knob website and you will see amazing state of the art materials for loudspeaker diaphragms used during this golden age of audio. And if you have heard some of these in their prime (not old faulty worn out,modded etc) then you would maybe think we haven't come that far . What Audio company today has the research budget to develop Sony's Bio cellular drivers, Boron drivers, Beryllium etc
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Old Yesterday, 03:15 AM   #8
bentoronto is offline bentoronto  Canada
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Musings about diaphragm materials
Ho, ho, ho.... never heard of electrostatic speakers? That's the way to go for good sound instead of trivial fixes to cones, edge diffraction, etc. The Wikipedia writer is correct.

With the emphasis today on power handling, the coils are so heavy that the mass of the cone just doesn't matter.... nor does sound quality.

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Old Yesterday, 06:35 AM   #9
celef is offline celef
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Can someone please point out some really bad drivers due to their cone materials?
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Old Yesterday, 09:48 AM   #10
Bill poster is offline Bill poster  Thailand
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Originally Posted by celef View Post
Can someone please point out some really bad drivers due to their cone materials?
Early aluminium dome tweeters.
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