Material Technology for Speakers

Development of Materials in Acoustic Equipment

Speakers and other sound and music reproduction equipment are used in a variety of situations, and a certain level of sound quality is required for each situation.For example, in audio speakers, flat, low-distortion sound quality is often preferred, whereas in speakers used for electronic pianos, response and sound clarity might be more important. In order to meet the various sound quality requirements that vary from scene to scene, we focus not only on the diaphragm, which is the component that radiates sound, but also on the surround that supports its periphery, the magnetic circuit components involved in converting electrical signals to mechanical vibrations, and all speaker components that have a significant impact on sound quality.

Development of Materials Based on Scientific Evidence

In order to manipulate the sound quality of a speaker, it is important to understand the principles of how the material properties of the components used affect vibration and sound. We conduct a series of evaluations, from measurements of various material properties, to vibration and acoustic measurements of speakers, to sound quality evaluation based on KANSEI engineering methods, in order to scientifically unravel the relationship between material properties and sound quality while promoting the development of materials.

Diaphragm made of Composite Material

In general, materials used for diaphragms should have both a high specific elastic modulus (elastic modulus/density) and a high internal loss. However, these two indices are in a trade-off relationship, and the key to the development of diaphragm materials is to create sound by achieving balance between the two.
In this regard, we are taking the approach of compositing hard filler into resin with high internal loss to advance the design of material properties that are suitable for diaphragms.

Furthermore, in recent years, we have gone beyond controlling physical properties through the shape and amount of filler added, to designing sound quality from a more microscopic perspective, such as the crystallinity and crystal orientation of the resin material and interfacial adhesion between the filler and resin. In order to stably manufacture the diaphragm that has been designed, it is necessary to use kneading technology to uniformly disperse the filler and precision molding technology to form thin diaphragms.By establishing these elemental technologies in-house, we have succeeded in creating our own unique diaphragm material.

Advanced Vibration-Damping Surround Rubber

The surround around the diaphragm must be able to follow the piston motion*1 of the diaphragm. It also has a damping function that suppresses the divided vibration*2 of the diaphragm and plays an important role in preventing frequency response distortion in the divided vibration band.
In order to realize these functions, viscoelastic properties (hardness and damping properties) are important indicators of material properties. In particular, damping properties have been found to have a significant impact on speaker sound quality. Based on the results of Yamaha’s research to date, through which we have formulated the base material (rubber and functional additives) for the surround, we have developed an advanced vibration-damping rubber for the surround that can control viscoelastic properties and suppress disturbances in frequency response.

Responding to Diversifying Needs

In the past, music was enjoyed in an audio room with large speakers. Today, music content can be easily carried around, and the environment for enjoying music and the required sound quality are becoming increasingly diverse.We will continue to conduct research on materials based on scientific evidence in order to respond flexibly to the ever-changing needs of the world.