Loudspeaker Cone: speaker diaphragm

The loudspeaker cone or speaker diaphragm is one of the major elements of the speaker with requirements of rigidity and low mass.

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The loudspeaker cone or speaker diaphragm is the main active area of the loudspeaker. When activated by the coil, it pushes the air backwards and forwards to create the sound waves.

The speaker cone design is critical to the performance of the overall loudspeaker and has requirements that are difficult to meet to obtain the optimum performance.

Speaker cone requirements

The main requirements are that the speaker cone or diaphragm should be low mass, but rigid. These requirements are not easy to achieve as rigid cones often require more mass, and low mass cones tend not to be so rigid.

Whilst the two main requirements for speaker cones appear to be mutually exclusive, clever design and the innovative use of materials can enable some very high performance loudspeakers to be designed and manufactured.

Another requirement for a speaker cone material is that it should be self damping. This helps reduce the effects of self resonances which can colour the sound.

Speaker cone materials

The materials used in loudspeaker cones can vary enormously. Tremendous developments have been made in recent years with the availability of new materials.

However the most common material used for speaker cones is a special form of paper. It has excellent self damping properties, but as can be imagined it is not particularly rigid or even not very consistent.

The paper used for speaker cones consists of wood, and rag fibres including kapok, waxes, fungicides and some resins. During manufacture the constituents are beaten together in a precise manner and for a particular time to gain the exact properties required.

If the mixture is beaten for a short period, it produces a paper with long fibres that are more flexible. These papers are good for bass cones those requiring controlled flexure as in the case of cones required for full range reproduction.

If the mixture is beaten for long periods, then the resulting paper has short fibres. This paper is suitable for loudspeakers requiring sensitive cones and for higher frequencies, although the paper is prone to producing strong resonances.

Other materials are used: polypropylene has some good self damping properties and is more rigid than paper.

Controlled flexing

Under most conditions and for most loudspeaker designs the cone is required to be rigid and free from flexure. However there are some circumstances and in some speaker designs where flexing of the cone is part of the design and this feature is t to good use.

Cone flexing can be used to enable a speaker to provide full range reproduction.

By contouring the cone and allowing flexure, it is possible for the centre of the cone to respond to high frequencies. As the frequency decreases, so a larger area of the cone becomes active until the whole cone moves for the lowest frequencies.

To achieve the full range curvilinear contours are commonly used, but hyperbolic curves also have a following with some people preferring them.

Flexure of the speaker cone can also be encouraged by placing concentric corrugations in areas of the cone.

Using controlled speaker cone flexing enables a single unit to cover the full range - typical performance figures may show the frequency range extending from around 40Hz up to 17 kHz or more.

The speaker cone determines many areas of the performance of the overall loudspeaker unit. The overall performance is governed by many aspects including he coil, magnets, frame and so forth. However the loudspeaker cone is of major importance.

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