Soft Grilles
Soft grilles can be made from any well suited cloth, weaving, stitching, foam, fabric upholsteries and other similar materials. In general, soft grilles impose little resistance on the speaker driver because the material is free to move synchronously with the sound waves. Because the grille is capable of absorbing this vibration, softer grilles are (in general) less prone to rattling except at extremely high sound pressure levels.
Soft grilles offer protection from small, lightweight objects, and may be water resistant to some degree but could be susceptible to being torn, or even stretched enough to reach the driver.
Hard Grilles
Hard grilles can be made from many types of construction material including metal, wood or plastic. Some solid grilles are made from a board or sheet of material with holes drilled or cut for the sound to pass, while others are made with thin strips of material either crosshatched together or equally spaced in parallel.
Because hard material is not free to move with the speaker's sound like soft material, the speaker's output level must be considered when designing the grille. A grille with more holes will allow more sound to pass but will offer less protection from small objects. A speaker with too much material in front of the driver will begin to distort at higher sound pressure levels, and in severe instances could damage the speaker, resulting in unwanted rattling at the least.
