Application Spotlight – Plastic Films for Hi-Fi Speaker Diaphragms

Material Stiffness and Density Properties Are Critical to Sound Quality

Audio fidelity in speaker applications is defined as the degree of exactness with which an original recording is copied or reproduced. There are many contributing factors that go into accurately replicating the intent of an original recording, but the quality of the equipment and its component parts plays a key role. One such component part directly responsible for the accuracy of sound reproduction is the diaphragm of the speaker. Often referred to as the cone, the diaphragm is a thin, semi-rigid membrane responsible for converting mechanical vibrations into sound. Due to their semi-rigid properties, plastic films for speaker diaphragms are frequently used as the base material in designs.

However, a crucial variable impacting accurate, hi-fi sound reproduction in these applications is the material’s stiffness-to-density ratio, or specific modulus. An ideal speaker diaphragm material for hi-fi systems is stiff but lightweight, allowing it to react with quick precision to subtle changes in the mechanical vibrations it receives. This high level of sensitivity prevents output distortion that leads to poorer sound quality.

Plastic Films for Speaker Diaphragms in Outdoor and Indoor End Uses

While the term speaker cone is used interchangeably with diaphragm, not all speaker diaphragms are cone-shaped. Designs can vary among different applications such as home audio loudspeakers, headphones, earbuds, and outdoor, automotive, or marine end uses. As is the case in many applications, the choice of plastic film used in speaker diaphragms is heavily dependent on design, quality, and cost requirements:

For the highest quality sound systems, polyester PEN films have an ideal stiffness-to-density ratio for pristine sound fidelity. PEN films also have excellent dimensional stability under varying temperature and humidity conditions, tensile strength to withstand the mechanical stress of heavy loudspeaker vibrations, and inherent resistance to UV radiation, moisture, and chemicals for potential outdoor use. While PEN films are more expensive than PET or polycarbonate alternatives, they offer higher fidelity for best-in-class speaker systems as well as excellent longevity for outdoor applications like boats, patio sound systems, and more. Tekra offers both Kaladex® and Teonex® PEN film products for hi-fi speaker applications.
Mylar® and Melinex® brand polyester PET films offer a lower specific modulus and are less equipped for harsh environments comparatively, but they still provide good stiffness, durability, and dimensional stability at a lower cost than PEN films. PET films are recommended for standard indoor or portable speaker applications that do not require the level of fidelity or environmental protection as PEN film speaker diaphragm designs. These products are sourced from Mylar® Specialty Films, formerly known as DuPont Teijin Films™.
Polycarbonate films can also be used as plastic film for speaker diaphragms, sacrificing some stiffness and environmental resistance properties for improved malleability and flexibility of design for specialized requirements. Polycarbonate films would be recommended for applications prioritizing the film’s formability over its specific modulus, such as thermoformed parts. Tekra supplies LEXAN™ polycarbonate films for such applications.