Are you looking to get a pair of wireless surround sound speakers? You might be confused by all of the technical jargon used by the manufacturers to describe the performance of their products. I will clarify one commonly used term which, however, ist often misunderstood: "total harmonic distortion" or "THD".
Looking for the perfect model from the huge amount of products, you may have a hard time understanding some of the technical language and terms that you will find in the specifications of today's wireless speakers. THD is usually not as easily understood as some other commonly used terms such as "signal-to-noise ratio" or "frequency response".
In a nutshell, THD shows the difference between the sound that is produced by the speaker versus the audio signal with which the speaker is driven. The most common ways to express distortion are percent and decibel. These two conventions can be translated into one another. The percentage shown as THD describes which amount of energy that is radiated by the speaker are higher harmonics versus the original signal. 10% would mean that one tenth is distortion. 1% would mean one hundredth etc. 10% equals -20 dB while 1% equals -40 dB.
Harmonic distortion inside a wireless speaker is actually the result of several components, including the power amplifier which is built into the speaker to drive the speaker element. Amplifier distortion usually depends on the amplifier output power and is sometimes specified for several power levels.
Harmonic distortion measurements are usually made by 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 usually 1 kHz. Distortion, however, is usually dependent on the signal frequency. Most amplifiers will show increasing distortion with increasing frequency. In particular digital class-D amplifiers will have fairly high distortion at frequencies above 5 kHz.
Distortion is also caused by the loudspeaker driver itself. Most speakers make use of a driver which carries a voicecoil. This coil is placed in a magnetic field. The magnetic field is excited by the audio signal. The change in magnetic flux, however, is not perfectly in ync with the audio signal due to core losses and other factory. Also, the type of suspension of the diaphragm will cause nonlinear movement. As such the will be speaker element distortion which also depends on the amount of power with which the speaker is driven.
The overall distortion of the speaker thus is the sum of the amplifier distortion and the speaker element distortion. In addition, there are other contributing factors. The enclosure of the speaker will vibrate to some extend depending on the sound pressure level. These vibrations will also be non-linear in nature and contribute to distortion.
The overall distortion of the speaker is usually determined by a measurement which includes a low-distortion audio generator and a microphone which is connected to an audio analyzer. The audio analyzer will determine the amount of higher harmonics and compare these with the main signal to compute the distortion. However, pure sine signals hardly 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 which consists of several sine waves is used. Then the number of harmonics at other frequencies is measured.
Wireless speakers will also have some amount of distortion during the audio transmission. The amount of distortion will depend on the type of wireless transmission method as well as the quality of components. Usually 900 MHz FM transmitters have among the highest amount of distortion. Digital audio transmission on the other hand offers the least amount of audio distortion. The signal is digitized inside the transmitter and not affected during the transmission itself. Digital wireless audio transmitters are available at 2.4 GHz and 5.8 GHz.
Looking for the perfect model from the huge amount of products, you may have a hard time understanding some of the technical language and terms that you will find in the specifications of today's wireless speakers. THD is usually not as easily understood as some other commonly used terms such as "signal-to-noise ratio" or "frequency response".
In a nutshell, THD shows the difference between the sound that is produced by the speaker versus the audio signal with which the speaker is driven. The most common ways to express distortion are percent and decibel. These two conventions can be translated into one another. The percentage shown as THD describes which amount of energy that is radiated by the speaker are higher harmonics versus the original signal. 10% would mean that one tenth is distortion. 1% would mean one hundredth etc. 10% equals -20 dB while 1% equals -40 dB.
Harmonic distortion inside a wireless speaker is actually the result of several components, including the power amplifier which is built into the speaker to drive the speaker element. Amplifier distortion usually depends on the amplifier output power and is sometimes specified for several power levels.
Harmonic distortion measurements are usually made by 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 usually 1 kHz. Distortion, however, is usually dependent on the signal frequency. Most amplifiers will show increasing distortion with increasing frequency. In particular digital class-D amplifiers will have fairly high distortion at frequencies above 5 kHz.
Distortion is also caused by the loudspeaker driver itself. Most speakers make use of a driver which carries a voicecoil. This coil is placed in a magnetic field. The magnetic field is excited by the audio signal. The change in magnetic flux, however, is not perfectly in ync with the audio signal due to core losses and other factory. Also, the type of suspension of the diaphragm will cause nonlinear movement. As such the will be speaker element distortion which also depends on the amount of power with which the speaker is driven.
The overall distortion of the speaker thus is the sum of the amplifier distortion and the speaker element distortion. In addition, there are other contributing factors. The enclosure of the speaker will vibrate to some extend depending on the sound pressure level. These vibrations will also be non-linear in nature and contribute to distortion.
The overall distortion of the speaker is usually determined by a measurement which includes a low-distortion audio generator and a microphone which is connected to an audio analyzer. The audio analyzer will determine the amount of higher harmonics and compare these with the main signal to compute the distortion. However, pure sine signals hardly 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 which consists of several sine waves is used. Then the number of harmonics at other frequencies is measured.
Wireless speakers will also have some amount of distortion during the audio transmission. The amount of distortion will depend on the type of wireless transmission method as well as the quality of components. Usually 900 MHz FM transmitters have among the highest amount of distortion. Digital audio transmission on the other hand offers the least amount of audio distortion. The signal is digitized inside the transmitter and not affected during the transmission itself. Digital wireless audio transmitters are available at 2.4 GHz and 5.8 GHz.
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You can find further details about outdoor wireless speakers as well as wireless surround sound products at Amphony's web page.
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