In this essay, I will explain the specification “total harmonic distortion”, often also named “THD” which is frequently used in order to show the performance of wireless loudspeakers.
It is often complicated to select a suitable set of wireless outdoor speakers highlighted at http://www.amphony.com given the great amount of models. Aside from looks, you will often be confronted with having to consider some of the technical specs. A few of those are most likely comparatively easy to comprehend like “output power” or “frequency response”. Yet, a spec which is not as easily understood is the spec relating to how much distortion the speaker has. In a nutshell, THD describes the difference between the sound which is produced by the loudspeaker versus the audio signal with which the loudspeaker is driven. The most widespread methods to state distortion are percent in addition to decibel. These 2 conventions can be translated into one another. If a loudspeaker specifies a distortion of 10% as an example then one tenth of the energy radiated by the loudspeaker is distortion. A distortion of 10% may also be expressed as -20 dB. 1% distortion equals -40dB.
A wireless speaker in fact has a few components that add to harmonic distortion. One of these is the built-in power amplifier. This audio amplifier is driving the speaker element. Customarily the larger the amp is driven the bigger the level of amplifier distortion. For this reason, a few producers will list amp distortion depending on amp output power. Distortion specifications for various output power levels are generally given for a number of power levels or as a chart showing distortion versus output power. Both of these techniques allow to better evaluate the performance of the amp.Furthermore, please understand that distortion usually is measured for a specific test tone frequency. Typically a 1 kHz sine wave tone is used during the measurement. Nevertheless, amplifier distortion will usually increase with increasing frequency, especially in digital class-D models.
Distortion is additionally caused via the loudspeaker driver itself. Many speakers use a driver which carries a coil. This coil is placed in a magnetic field. The voicecoil will follow the magnetic field that is controlled by the music signal to move the diaphragm. Nonetheless, this movement is not entirely linear. As such the result is distortion brought about by the speaker element. Most manufacturers will specify harmonic distortion based on the power level as usually the higher the loudspeaker is driven the higher the level of distortion. As such both the amp and the speaker element itself contribute to distortion. In addition, there are other factors which also contribute to distortion. The whole amount of distortion is the total of all of these factors. The enclosure of the loudspeaker will shake to some extent depending on the sound pressure level. These vibrations are going to also be non-linear in nature and contribute to distortion.
In order to figure out the overall distortion of a loudspeaker, a signal generator is used that supplies an ultra-linear signal to the speaker in addition to a measurement microphone that is attached to an audio analyzer in order to calculate the level of harmonics radiated by the loudspeaker. Intermodulation distortion analysis is a different method which offers a better picture of the loudspeaker distortion performance with real-world signals through using a test signal with 2 harmonics and measuring how many harmonics at different frequencies are produced by the loudspeaker. Wireless loudspeakers will also have some level of distortion during the audio transmission. The level of distortion is going to depend on the kind of cordless transmission technique and the quality of components. Generally 900 MHz FM transmitters have among the largest amount of distortion. Better models are going to use digital transmission and transmit at 2.4 GHz or 5.8 GHz to reduce audio distortion.