Friday, May 25, 2007

Comparison of cone materials

This seems to be a common question when choosing a speaker driver: what's the best cone material? Well, I don't think there's really any such thing as a "best" material – they all have strengths and weaknesses.

One difficulty that speaker manufacturers have to contend with when designing their speakers is that they have to operate across a wide range of frequencies. At low frequencies (such as 100Hz) the cone generally has to move as a stiff, cohesive unit, while at relatively high frequencies (such as 3kHz) it's sometimes preferable if only a small, low mass section of the cone vibrates and the rest remains still. So, what should they do?

There are two popular schools of thought regarding the design of speaker cones or diaphragms:

  1. The cone should be as stiff as possible and operate like a piston throughout its usable range.
  2. The cone should be stiff enough to operate like a piston at low frequencies, but also be flexible and have enough internal damping to behave in a well-controlled manner at high frequencies.
Both varieties have drawbacks.

Stiff cones:
  1. They tend to have very little internal damping and therefore ring prominently at their resonant frequencies.
  2. The relatively large radiating area introduces "beaming" at high frequencies, whereby most of the sound is projected in a forward direction along the cone's axis of vibration.
Flexible cones:
  1. They tend to introduce distortion due to hysteresis and intermodulation effects when the cone flexes and a variety of different frequencies are reproduced simultaneously.
  2. Minor resonances occur across a wide range of frequencies due to imperfect absorption of transverse ripples that travel across the cone's surface.
Stiff cones are usually constructed of materials such as: aluminium/magnesium alloys, titanium, ceramic, and sandwiched composites. Some of the manufacturers include: Seas, Visaton, Accuton, Alcone, Eton, Aurasound, and HiVi. Manufacturers of flexible cones tend to use materials like paper, polypropylene, and a variety of composites. Some manufacturers: Vifa, Seas, Audax, and Manger.

Of course, this isn't the "be all and end all" of speaker cones. It's just the beginning! Have a look around on the 'net and you'll find lots of cool variations, techniques and alternative technologies.

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