Microphones. Microphones. The variety of directional patterns are often characterized by the arc within which they pick up at least half the peak value. In decibels, a drop of 3 dB represents half the power and 6 dB down is one fourth the power. With any of the microphone mechanisms, different directional patterns of response can be produced. Common directional patterns are called cardiod (for heart shaped) and omnidirectional. There are also "figure-eight" patterns which accept sound from front and rear. One directional technique used is the "stereo microphone" which may be constructed from two condenser microphones attached to each other so that their peak response directions are 90° apart.
Impedance Matching of Audio Components. In the early days of high fidelity music systems, it was crucial to pay attention to the impedance matching of devices since loudspeakers were driven by output transformers and the input power of microphones to preamps was something that had to be optimized. The integrated solid state circuits of modern amplifiers have largely removed that problem, so this section just seeks to establish some perspective about when impedance matching is a valid concern. As a general rule, the maximum power transfer from an active device like an amplifier or antenna driver to an external device occurs when the impedance of the external device matches that of the source. That optimum power is 50% of the total power when the impedance of the amplifier is matched to that of the speaker. Improper impedance matching can lead to excessive power use, distortion, and noise problems.
Loudspeakers. Audio Amplifiers. A common type of amplifier distortion is called harmonic distortion. It can arise if any component in the amplifer clips the peaks of the waveform. A common specification for high fidelity amplifiers is the total harmonic distortion. This distortion may be less than 1%, or even less than 0.5% from 20-20,000 Hz for high quality amplifiers.
In the diagram, the input is a single frequency (pure sine wave), but the output waveform is clipped by the amplifier. The result is that harmonic frequencies not present in the original signal are produced at the output (harmonic distortion). An amplifier can be said to be linear if the output voltage is strictly proportional to the input signal. Plots of frequency spectra such as those illustrated here can be important diagnostic and research tools.
Sound Amplification Systems. Feedback in Sound Amplification Systems. Increasing Potential Acoustic Gain. Equalization of Sound Systems.