Perhaps the most critical component of a top-performing loudspeaker is its cone, also known as the diaphragm. While all parts of the system play an essential role in creating the highest quality sound reproduction, the cone is the element that directly produces what we hear.
In a loudspeaker, the cone is a thin, semi-rigid membrane that vibrates to produce sound. Its purpose, technically speaking, is to reproduce the voice coil signal waveform accurately. A poor reproduction means acoustic distortion of the intended sound.
What Does a Speaker Cone in a Loudspeaker Do?
An electromechanical motor drives a loudspeaker. However, it operates differently than a typical motor in that it converts electrical energy to mechanical energy by generating a reciprocating motion caused by a stationary permanent magnetic field.
The motion of the voice coil causes the cone to vibrate, creating variable air pressures around the cone. The cone then converts the vibrations into a signal. That acoustic energy emitted from the cone is sound.
The human eardrum works almost the same way.
For the cone to operate effectively and produce clear and accurate sound, it must be held securely in place by the surrounding support or “surround” yet still be able to move freely in a back-and-forth motion.
The cone should also have self-damping attributes that minimize unwanted self-resonance and distortion.
Principal Attributes of Loudspeaker Cones
Speaker cones must possess low mass yet remain rigid while in operation to be effective. Designing and configuring a lightweight material that could maintain a high degree of rigidity was the fundamental challenge for speaker designers since these two qualities seem to be contradictory.
The cone shape offered the best solution for rigidity, while early flat diaphragms turned out to be too unstable, flex too much, and create distortion. The cone shape, having geometric rigidity, moves as a single unit, much like a piston.
What are High-Quality Speaker Cones Made Of?
Since the invention of the speaker cone, the most common material to make one with has been a specially designed paper product. It’s created from wood and rag fibers and combined with specific strengthening components. The blending and “beating” of the mixture during manufacturing will produce differing fiber lengths that will determine the flexibility of the cone.
Shorter fiber lengths in the cone material may be more beneficial for loudspeaker applications that accommodate higher frequency sounds. Paper cone material with longer fibers tends to support a greater range with more flexibility.
However, some sophisticated cone materials have emerged in recent years. Polypropylene cones (a kind of plastic) which feature a soft edge, are more rigid than paper, and have superior damping capability. These are most effective in outdoor settings because they can hold up to the weather.
Carbon fiber cones and acrylic-coated cloth materials are also in use. Each has specific advantages for specific sound production applications and durability requirements.
What is the Cone “Surround”?
The speaker cone is supported within a specially designed surround or support. The ideal surround has a linear force-deflection curve with damping capability sufficient to absorb all vibrations within the unit. Also, this component must be strong enough to withstand the long-term stress of millions of vibrations without damage.
Surrounds for speaker cones can be made from resin-treated cloth or non-woven material and frequently consist of polymeric foams or thermoplastic elastomers.
The speaker cone and its surround element are generally molded as a single unit prior to the speaker assembly. This provides for minimal acoustical breakup and ensures accurate sound reproduction.
Download our Loudspeaker 101 Guide to learn even more about the inner workings of speakers.