Listed above are key speaker specifications and their definitions. Sound pressure level, SPL, is the deviation from atmospheric pressure caused by the sound wave expressed in decibels. Max input is the maximum power expressed in watts that can be used for a very short period of time without permanently damaging the speaker. The nominal input wattage is the amount of power the speaker can safely handle during long-term use. Electrical impedance is the ratio of applied voltage to current. It is important to match the speaker impedance to the system impedance. Resonant frequency is the frequency at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. Frequency range is determined by the size of the speaker, tension of the cone and weight of cone. Smaller speakers will generally operate better at higher frequencies, while larger speakers will operate better at lower frequency ranges. Low frequencies are used to create deep bass sounds while mid-range frequencies are used for voice reproductions.