In all efforts to maximize the perceived loudness of portable devices' speakers, care must be taken to avoid damage to the speakers themselves. These small transducers can only withstand this limited volume. There are two main speaker protection aspects available -- maximum film offset and maximum voice coil temperature.
Is a typical loudspeaker profile where the physical limits of motion of the film can be clearly seen, especially in the downward direction. The audio signal is not allowed to be too strong, otherwise it will cause the vibration element to contact the fixed frame assembly or cause excessive tension of the suspension material (ring or cartridge). In addition, the RMS value of the audio signal is not allowed to be too large, otherwise it will cause the voice coil to overheat. Overheating of the voice coil will deform the circle of the coil tube, causing friction with the edge of the magnet or magnetic pole plate. Moreover, the high temperature in the voice coil will also lead to the deterioration of its electrical insulation performance, and eventually cause the turn of the voice coil to short circuit, thereby reducing the voice coil impedance and overload of the amplifier. Excessive voice coil temperature can also heat the permanent magnet, which may cause it to demagnetize.
Techniques used to prevent speaker damage include automatic gain control (AGC) for input signal amplitude and/or power supply voltage, dynamic range compression (as previously described), hard limiting, flexible tone chipping, and amplifier output overtesting. The disadvantage of these techniques is that they are feed-forward methods and do not sense the actual speaker basin offset, voice coil temperature, or speaker impedance (which varies proportionately with temperature). More complex protection mechanisms, such as thermal feedback, are expected in the future, but one or more of the above mentioned protection mechanisms are currently the norm.