cone stiffness/damping plus the surround's linearity/damping play a crucial role in accuracy of the reproduced voice coil signal waveform. This is the crux of high-fidelity stereo. The surround may be resin-treated cloth, resin-treated non-wovens, polymeric foams, or thermoplastic elastomers over-molded onto the cone body. An ideal surround has a linear force-deflection curve with sufficient damping to fully absorb vibrational transmissions from the cone/surround interface, and the "toughness" to withstand long-term vibration-induced fatigue. Sometimes the conical part and the outer surround are molded in one step and are one piece as commonly used for a Guitar speaker. Other types of speakers (such as electrostatic loudspeakers) may use a thin membrane instead of a cone. Microphone Microphones can be thought of as speakers in reverse. The sound waves strike the thin diaphragm, causing it to vibrate. Microphone diaphragms, unlike speaker diaphragms, tend to be thin and flexible, since they need to absorb as much sound as possible. In a condenser microphone, the diaphragm is placed in front of a plate and is charged. In a dynamic microphone, the diaphragm is glued to a magnetic coil, similar to the one in a dynamic loudspeaker. (In fact, a dynamic speaker can be used as a rudimentary microphone, and vice versa.) The diaphragm in a microphone works similarly to the human eardrum. Other uses In a phonograph reproducer, the diaphragm is a flat disk of typically mica or isinglass that converts the mechanical vibration imparted on the buttress from the recorded groove into sound. In the case of acoustic recording the reproducer converts the sound into the motion of the needle that scribes the groove on the recording media. See also Acoustic membrane References Acoustics Loudspeakers