In this piece of writing, I am going to clarify the term “total harmonic distortion”, often also called “THD” which is regularly used to describe the quality of cordless loudspeakers (You may get detailed resources on the subject of wireless waterproof speakers at this source).
Looking for the ideal model from the vast number of products, you might have a hard time comprehending some of the technical jargon and terms that you will see in the specifications of the latest wireless speakers. THD is typically not as easily understood as various other commonly used specs including “signal-to-noise ratio” or “frequency response”.
In a nutshell, THD describes the difference between the sound which is produced by the speaker versus the audio signal with which the loudspeaker is driven. The most widespread methods to state distortion are percent along with decibel. These two conventions can be translated into one another. A -20 dB or 10% distortion means that one tenth of the radiated audio is a result of distortion while -40 dB or 1% would mean that one percent of the energy are harmonic products of the original signal. Harmonic distortion in a cordless loudspeaker is really the consequence of a number of elements, such as the power amplifier which is built into the speaker to drive the speaker element. The amp itself will have a certain amount of distortion. Typically the distortion of the amplifier will be higher the more output power it supplies to the speaker. Normally vendors are going to publish amplifier distortion based on a specific amount of power, generally a lot less than the rated maximum amp output power.
Having amplifier distortion specifications for a few output power levels provides a better picture of the amplifier distortion performance.Usually distortion is measured with a 1 kHz test tone. However, amplifier distortion will usually increase with increasing frequency, particularly in digital class-D models. The second contributing factor is the loudspeaker element itself. Many loudspeakers utilize a diaphragm type driver which is driven by a coil that is suspended in a magnetic field. The magnetic field is excited by the audio signal. The variation in magnetic flux, though, is not completely in sync with the music signal resulting from core losses plus other factors. Also, the type of suspension of the diaphragm will cause nonlinear motion. As such there is going to be speaker element distortion that furthermore depends on the amount of output power with which the loudspeaker is driven.
As such both the amp and the loudspeaker element itself add to distortion. Furthermore, there are other factors that also contribute to distortion. The whole amount of distortion is the sum of all of these factors. The enclosure of the loudspeaker is going to 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. To find out the overall distortion of a loudspeaker, a signal generator is used which provides an ultra-linear signal to the speaker and a measurement microphone that is attached to an audio analyzer in order to calculate the amount of harmonics radiated by the speaker. Though, pure sine signals hardly give an accurate picture of the distortion of the cordless speaker with real-world signals. A better distortion analysis is the so-called intermodulation distortion analysis in which a test tone that consists of a number of sine waves is used. Next the level of harmonics at different frequencies is measured.
In addition, please note that the majority of cordless speakers will experience audio distortion during the audio transmission itself. This is mostly the case for transmitters which use analog or FM type transmission. More advanced types use digital audio transmission. Generally these transmitters work at 2.4 GHz or 5.8 GHz. On top of that, check out http://comunidade.sol.pt/blogs/withdlephal/default.aspx?p=2 to get a lot more facts.