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Harmonic distortion refers to the presence of additional frequency components in the output audio that are multiples (harmonics) of the input signal frequency. It occurs when a loudspeaker driver introduces unintended changes to the original signal, resulting in the generation of harmonic frequencies that were not present in the source material. Harmonic distortion can degrade sound quality, introduce coloration, and affect the accuracy of sound reproduction. There are two main forms of harmonic distortion that we measure:
- Total Harmonic Distortion (THD): THD measures the total amount of harmonic distortion in a signal relative to the level of the original or fundamental frequency. It is expressed as a percentage or decibel (dB) value. The lower the THD value, the lower the level of harmonic distortion.
- Odd-Order and Even-Order Distortion: Harmonic distortion can be categorized as odd-order or even-order based on the relationship of the harmonics to the fundamental frequency. Odd-order harmonics are multiples of the fundamental frequency (e.g., 3rd, 5th, 7th), while even-order harmonics are multiples of twice the fundamental frequency (e.g., 2nd, 4th, 6th). The presence of odd-order harmonics tends to be more noticeable and objectionable to the human ear.
- Sound Quality Degradation: Harmonic distortion alters the original signal by adding unwanted frequency components. This alteration can lead to a loss of clarity, accuracy, and detail in the reproduced sound. It may introduce a harsh or "muddy" character, negatively impacting the overall sound quality.
- Coloration: Harmonic distortion can impart its own tonal character to the sound, causing coloration or changes in timbre. This coloration can significantly impact the perception of the audio, leading to inaccurate reproduction and a departure from the intended sound.
- Overloading and Damage: Excessive levels of harmonic distortion can strain the loudspeaker driver and the associated components, potentially leading to overloading and damage. The additional energy in the form of harmonics can cause increased excursion of the diaphragm, increased heat dissipation, and higher mechanical stress, potentially resulting in driver failure.
- Driver Design: Employing high-quality loudspeaker drivers with carefully designed components, using advanced materials, precise manufacturing processes, and optimized motor designs can reduce nonlinearities and unwanted resonances that contribute to distortion.
- Crossover Design: Proper crossover design and implementation ensure that each driver operates within its intended frequency range, minimizing the potential for distortion. Well-designed crossovers ensure smooth integration between drivers and maintain accurate reproduction across the frequency spectrum.
- Enclosure Design: The loudspeaker enclosure plays a significant role in controlling resonances and minimizing distortion. A well-braced and properly damped enclosure can reduce unwanted vibrations and resonances that contribute to harmonic distortion.
- Signal Processing and Feedback: Sophisticated signal processing techniques, such as digital signal processing (DSP), can be used to correct and compensate for harmonic distortion. Feedback systems, such as active control or adaptive algorithms, can continuously monitor and adjust the output to minimize distortion.
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