Are you considering to pick a couple of cordless speakers? You might be puzzled by all of the technical jargon used by vendors to describe the performance of their models. I will clarify one regularly used term that, nonetheless, ist often misunderstood: “total harmonic distortion” or “THD”.
Looking for the ideal model from the vast number of products, you may have a difficult time comprehending a few of the technical jargon and terms that you are going to find in the specifications of today’s wireless outdoor speakers available from Amphony Incorporated. Total harmonic distortion is generally not that well understood. Nevertheless, this term is still vital in terms of determining the quality of a specific type. Different terms, just like “output power” or “frequency response” are generally easier understood.
Briefly, “harmonic distortion” describes how much the audio signal is being degraded because of the loudspeaker or in other words how much the signal differs from the original signal. There are two common methods in order to state harmonic distortion, either in percent (%) or in decibel (dB). A -20 dB or 10% distortion means that one tenth 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 audio.
Harmonic distortion in a cordless speaker is really the result of several elements, including the power amplifier which is built into the speaker in order to drive the loudspeaker element. Amplifier distortion normally depends on the amp output power and is every now and then specified for several output power levels.
Distortion ratings for various output power levels are normally specified for several power levels or as a diagram showing distortion versus output power. Both of these methods allow to better evaluate the quality of the amplifier.Besides, please note that distortion usually is measured for a certain test tone frequency. Normally a 1 kHz sine wave tone is used during the measurement. However, amplifier distortion will usually increase with increasing frequency, in particular in digital class-D models. Another element creating distortion is the speaker element which typically works with a diaphragm that carries a coil which is suspended in a magnetic field. The magnetic field is excited by the audio signal. The variation in magnetic flux, however, is not entirely in sync with the audio signal due to core losses in addition to other factors. Also, the type of suspension of the diaphragm will bring about nonlinear movement. As such the result is distortion caused by the loudspeaker element. A lot of producers are going to display harmonic distortion depending on the power level because typically the higher the loudspeaker is driven the bigger the level of distortion.
The overall loudspeaker distortion is consequently brought about by the amplifier along with the loudspeaker element and in addition by a number of additional contributing factors. The speaker enclose is going to vibrate to some extent and therefore contribute to the distortion. To figure out the total distortion of a speaker, a signal generator is used which supplies an ultra-linear signal to the loudspeaker in addition to a measurement microphone which is attached to an audio analyzer to determine the amount of harmonics emitted by the loudspeaker. Then again, pure sine signals barely give an accurate indication of the distortion of the wireless loudspeaker with real-world signals. A better distortion analysis is the so-called intermodulation distortion analysis where a test tone which includes a number of sine waves is used. Then the number of harmonics at other frequencies is calculated.
Also, please note that many wireless speakers will experience audio distortion during the audio transmission itself. This is for the most part the case for transmitters which use analog or FM type transmission. Digital audio transmission however provides the lowest amount of signal distortion. The audio is digitized in the transmitter and not affected throughout the transmission itself. Digital wireless audio transmitters are available at 2.4 GHz plus 5.8 GHz.