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.
 
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...
 

Galu

Member
2018-04-17 6:50 pm

audiogod66

Member
2012-02-10 4:51 pm
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
 
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.

B.

Well if that were true, I wonder why almost nobody buy esl's anymore?
I threw my Audiostatics away last year.

And you really can't compare esl's with stiff high power cone drivers, even though they're stiff beyond absurdity and sound bad just because of it, there's no way esl's compare, nor in house nor outdoors.

I wish it were different, it's a beautifull principle and regarding materials: it's just Mylar;-)
 
Nobody, I am sure, disputes that ESLs have superior sound quality and nobody disputes there are great practical obstacles to their widespread use.

The real take-away message is that a light diaphragm (which is better matched in impedance to the air it is pushing) has inherent degenerative feedback... at least some. You might say the diaphragm is limp and it isn't making waves unless some force acts on it.

The absolutely crazy unacceptable ridiculous feature of today's cone drivers is that they are operated without feedback. With motional* or other feedback, nobody would have trouble using the 100-year-old Rice-Kellogg driver. Crazy to design something as flawed as a cone driver (run by rubber and fabric "springs" and semi-inductance) without feedback and expect good performance.

B.

* motional feedback (and some folks may know I am a big enthusiast) relates to getting the cone motion to match the signal (for example, by gluing an accelerometer to the dust cap). Actually, the real feedback ideal is feedback from your chair location, eh.
 
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zbig001

Member
2018-11-07 2:05 pm
The results can be satisfactory, even if the moving mass in a given dynamic transducer is not as low as I would like to see it.

You just have to cut the speakers suffciently high so the behavior of the moving mass is governed solely by inertia forces.
In practice, the distance where the useful section of the frequency range begins can be surprisingly far from Fs, unfortunately...
That forces the use of a software crossover, where you have steep slopes and equalization in time domain available.

You do not really need to strain your hearing to recognize the high quality of reproduction achieved in this way.
The depth of the sound stage and its detailed arrangement is striking if the room is quiet enough.
 
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...You just have to cut the speakers suffciently high so the behavior of the moving mass is governed solely by inertia forces....

And where can we buy those woofers with 5 Hz resonance?

BTW, easy to portray how perfect a vc driver can be in theory until you remember it is made of rubber, fabric, paper, and all kinds of little gremlins that shake and behave badly.

B.
 
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Thank you Pete, this is a good read. That web page is dated 2001, but apart from brand names and speaker models that have disappeared, and improved measurement systems (Klippel...) nothing has really changed.

It does not address my original question: Why aren't we seeing more recent developments of plastic and compounds in speaker designs, even when they could be drop-in replacements?:confused:

I like my current 12" prosound paper cone widebanders a lot. I have tamed them with DSP, but even without much EQ they don't sound as harsh as measurements would suggest.