In this commentary, I will explain the spec “total harmonic distortion”, often also titled “THD” which is commonly used in order to describe the performance of wireless speakers made by Amphony.
Looking for the ideal model from the enormous amount of products, you might have a hard time comprehending several of the technical jargon and specs that you will find in the specifications of modern cordless loudspeakers. Total harmonic distortion is typically not that well understood. However, this term is still significant in terms of determining the quality of a specific model. Different terms, like “output power” or “frequency response” are usually easier understood.
In brief, THD describes the difference between the sound which is produced by the loudspeaker versus the audio signal with which the speaker is driven. The most common methods to show distortion are percent and decibel. These 2 conventions can be converted into one another. The percentage shown as THD shows which amount of energy that is radiated by the speaker are higher harmonics versus the original signal. 10% would mean that one 10th is distortion. 1% would mean one hundredth and so forth. 10% is equal to -20 dB whilst 1% is equal to -40 dB.
Harmonic distortion inside a cordless loudspeaker is really the result of numerous elements, such as the power amplifier that is built into the speaker in order to drive the loudspeaker element. Generally the bigger the amplifier is driven the higher the level of amplifier distortion. For this reason, some producers will state amplifier distortion depending on amplifier output power.
Distortion specs for different power levels are generally specified for several output power levels or as a chart showing distortion versus output power. Both of these methods allow to better evaluate the quality of the amplifier.Besides, please understand that distortion typically is measured for a certain test tone frequency. Typically a 1 kHz sine wave tone is used during the measurement. This allows evaluating equipment from different producers. Though, distortion generally varies with different frequencies. A lot of digital amps are going to exhibit growing distortion with higher frequency which can not easily be discovered through looking at the specification sheet.
The second contributing factor is the loudspeaker element itself. The majority of loudspeakers employ a diaphragm kind driver that is driven by a voicecoil that is suspended in a magnetic field. The voicecoil will follow the magnetic field which is controlled by the audio signal in order to move the diaphragm. However, this movement is not entirely linear. This results in the signal being distorted by the loudspeaker element itself. Furthermore, the bigger to power level with which the loudspeaker is driven, the larger the distortion. Frequently loudspeaker manufacturers are going to publish distortion for small to moderate power levels only. The overall distortion of the loudspeaker thus is the sum of the amplifier distortion in addition to the loudspeaker element distortion. Moreover, there are other contributing factors. The enclosure of the speaker will vibrate to some extent depending on the sound pressure level. These vibrations will also be non-linear in nature and add to distortion.
To figure out the overall distortion of a speaker, a signal generator is utilized that supplies an ultra-linear signal to the loudspeaker in addition to a measurement microphone which is attached to an audio analyzer to calculate the level of harmonics radiated by the loudspeaker. Intermodulation distortion analysis is one more method which offers a better picture of the speaker distortion performance with real-world signals by using a test signal with two harmonics and measuring how many harmonics at other frequencies are generated by the loudspeaker.
A different factor contributing to distortion is the audio transmission of wireless loudspeakers, especially with models that transmit an analog signal at 900 MHz. More advanced types make use of digital audio transmission. Normally these transmitters operate at 2.4 GHz or 5.8 GHz.
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