In this commentary, I am going to explain the spec “total harmonic distortion”, often also referred to as “THD” which is often used in order to show the quality of wireless speakers shown at this hyperlink.
Wireless loudspeakers are available in all different shapes and sizes. Selecting the right type may often be difficult . I will shed some light on a frequently used spec which is utilized to publish the technical quality of the speaker: “total harmonic distortion” or “THD”. THD is generally not as easily understood as a few other commonly utilized specs including “signal-to-noise ratio” or “frequency response”. Briefly, “harmonic distortion” shows how much the music signal is being degraded as a result of the speaker or in other words how much the signal differs from the original signal. There are two common methods in order to articulate harmonic distortion, either in percent (%) or in decibel (dB). A -20 dB or 10% distortion means that one 10th of the radiated audio is a consequence of distortion whilst -40 dB or 1% would mean that one percent of the energy are harmonic products of the original signal. Though, be careful because there are in fact several elements which cause harmonic distortion. Cordless loudspeakers along with any type of active loudspeaker or active subwoofer all have built-in power amplifiers in order to drive the loudspeaker element. The amp itself will have a specific level of distortion. Typically the distortion of the amplifier will be bigger the more output power it supplies to the loudspeaker. In general producers are going to publish amplifier distortion based on a specific level of output power, normally a lot less than the rated highest amp output power.
Distortion ratings for various power levels are usually specified for a few output power levels or as a diagram listing distortion versus output power. Both of these methods allow to better evaluate the quality of the amplifier.Furthermore, please note that distortion generally is measured for a certain test tone frequency. Commonly a 1 kHz sine wave tone is utilized during the measurement. This allows comparing equipment from various vendors. However, distortion normally varies with different frequencies. Many digital amps are going to exhibit growing distortion amid higher frequency which can not easily be discovered through glancing at the specification sheet.
One more component causing distortion is the speaker element that generally works with a diaphragm that carries a voicecoil that is suspended in a magnetic field. The voicecoil will track the magnetic field which is controlled by the audio signal in order to move the diaphragm. Yet, this movement is not completely linear. As such there will be speaker element distortion which additionally depends on the amount of power with which the speaker is driven.
The total distortion of the speaker thus is the sum of the amp distortion along with the speaker element distortion. Moreover, there are other contributing factors. The loudspeaker enclose will vibrate to some extent and thus add to the distortion.
To figure out the overall distortion of a speaker, a signal generator is utilized which provides an ultra-linear signal to the loudspeaker and also a measurement microphone that is attached to an audio analyzer to calculate the amount of harmonics radiated by the loudspeaker. However, pure sine signals barely give an accurate picture of the distortion of the wireless speaker with real-world signals. A better distortion analysis is the so-called intermodulation distortion analysis where a test tone that includes several sine waves is used. Next the level of harmonics at different frequencies is measured.
One more factor contributing to distortion is the signal transmission of wireless loudspeakers, particularly with products which broadcast an analog signal at 900 MHz. Digital audio transmission on the other hand has the least level of audio distortion. The signal is digitized in the transmitter and not affected throughout the transmission itself. Digital cordless audio transmitters are available at 2.4 GHz plus 5.8 GHz.