Are you looking to get a couple of wireless outdoor speakers highlighted at amphony.com/products/wireless-speaker.htm? You might be bewildered by all of the technical jargon used by manufacturers in order to describe the quality of their products. I will highlight a regularly utilized term that, however, ist often misunderstood: “total harmonic distortion” or “THD”.
It is often tricky to select a suitable set of wireless loudspeakers given the huge number of models. Aside from looks, you will often be faced with having to review a few of the technical specifications. THD is typically not as easily understood as several other commonly used specs including “signal-to-noise ratio” or “frequency response”. In short, “harmonic distortion” describes how much the audio signal is being deteriorated as a result of the speaker or in other words how much the signal deviates from the original signal. There are 2 common ways in order to express harmonic distortion, either in percent (%) or in decibel (dB). If a speaker states a distortion of 10% for example then one tenth of the energy radiated by the speaker is distortion. A distortion of 10% can also be shown as -20 dB. 1% distortion is equal to -40dB. A wireless loudspeaker really has numerous components which add to harmonic distortion. One of those is the built-in power amp. This power amplifier is driving the speaker element. The amplifier itself will have a specific level of distortion. Normally the distortion of the amplifier will be bigger the more output power it supplies to the speaker. In general makers will show amp distortion depending on a specific level of output power, by and large a lot less than the rated maximum amplifier output power.
Having amplifier distortion specifications for a few output power levels provides a better indication of the amplifier distortion performance.Harmonic distortion measurements are typically done via feeding a test tone into the speaker. This tone is a pure sine wave signal with minimum distortion. The frequency of this test tone is typically 1 kHz. However, amplifier distortion is going to generally increase with rising frequency, particularly in digital class-D models.
The second contributing factor is the loudspeaker element itself. The majority of speakers use a diaphragm kind driver that is driven by a coil that is suspended in a magnetic field. The coil is moving in accordance to the variation in the magnetic field that is excited by the audio signal but does not correlate fully with the signal as a result of core losses along with various factors. As such the result is distortion brought about by the speaker element. A lot of suppliers will show harmonic distortion depending on the power level as typically the higher the speaker is driven the higher the level of distortion. The overall loudspeaker distortion is as a result brought about by the amplifier and the speaker element and in addition by a series of further contributing factors. The enclosure of the speaker is going to vibrate to some extent depending on the sound pressure level. These vibrations are going to also be non-linear in nature and add to distortion. The total distortion of the loudspeaker is generally determined by a measurement which consists of a low-distortion audio generator as well as a microphone that is attached to an audio analyzer. The audio analyzer will determine the amount of higher harmonics and compare these with the main signal in order to compute the distortion. Intermodulation distortion analysis is another technique which gives a better picture of the loudspeaker distortion performance with real-world signals by utilizing a test signal with 2 harmonics and measuring how many harmonics at other frequencies are produced by the loudspeaker.
One more factor adding to distortion is the audio transmission of wireless speakers, particularly with products which broadcast an analog signal at 900 MHz. More sophisticated models use digital audio transmission. Typically these transmitters operate at 2.4 GHz or 5.8 GHz.
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