Have you ever wondered what some of the technical jargon means that manufacturers use to specify the performance of wireless speakers? In this article, I will explain one frequently used term: THD or "total harmonic distortion".
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.
However, be careful that there are actually several components which cause harmonic distortion. Wireless speakers as well as any kind of active speaker or active subwoofer all have built-in power amplifiers to drive the speaker element. The amplifier 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 manufacturers will specify amplifier distortion based on a certain amount of power, usually a lot less than the rated maximum amplifier output power.
Having amplifier distortion specs for several output power levels gives a better indication of the amplifier distortion performance.Also, please note that distortion typically is measured for a specific test tone frequency. Typically a 1 kHz sine wave tone is used during the measurement. This allows comparing equipment from different manufacturers. However, distortion usually varies with different frequencies. Many digital amplifiers will show increasing distortion with higher frequency which cannot easily be discovered by looking at the spec sheet.
The second contributing factor is the loudspeaker element itself. Most speakers use a diaphragm type driver which is driven by a coil that is suspended in a magnetic field. The coil will follow the magnetic field which is controlled by the audio signal to move the diaphragm. However, this movement is not perfectly linear. This results in the signal being distorted by the speaker element itself. Also, the larger to power level with which the speaker is driven, the larger the distortion. Often speaker manufacturers will show distortion for small to moderate power levels only.
The overall speaker distortion is thus caused by the amplifier as well as the speaker element and in addition by a number of additional contributing factors. The speaker enclose will vibrate to some extend and thus contribute to the 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.
Also, please note that many wireless speakers will experience signal distortion during the audio transmission itself. This is mostly the case for transmitters that use analog or FM type transmission. Better models will use digital transmission and transmit at 2.4 GHz or 5.8 GHz to minimize signal distortion.
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.
However, be careful that there are actually several components which cause harmonic distortion. Wireless speakers as well as any kind of active speaker or active subwoofer all have built-in power amplifiers to drive the speaker element. The amplifier 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 manufacturers will specify amplifier distortion based on a certain amount of power, usually a lot less than the rated maximum amplifier output power.
Having amplifier distortion specs for several output power levels gives a better indication of the amplifier distortion performance.Also, please note that distortion typically is measured for a specific test tone frequency. Typically a 1 kHz sine wave tone is used during the measurement. This allows comparing equipment from different manufacturers. However, distortion usually varies with different frequencies. Many digital amplifiers will show increasing distortion with higher frequency which cannot easily be discovered by looking at the spec sheet.
The second contributing factor is the loudspeaker element itself. Most speakers use a diaphragm type driver which is driven by a coil that is suspended in a magnetic field. The coil will follow the magnetic field which is controlled by the audio signal to move the diaphragm. However, this movement is not perfectly linear. This results in the signal being distorted by the speaker element itself. Also, the larger to power level with which the speaker is driven, the larger the distortion. Often speaker manufacturers will show distortion for small to moderate power levels only.
The overall speaker distortion is thus caused by the amplifier as well as the speaker element and in addition by a number of additional contributing factors. The speaker enclose will vibrate to some extend and thus contribute to the 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.
Also, please note that many wireless speakers will experience signal distortion during the audio transmission itself. This is mostly the case for transmitters that use analog or FM type transmission. Better models will use digital transmission and transmit at 2.4 GHz or 5.8 GHz to minimize signal distortion.
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You can get further details about outdoor wireless speakers as well as wireless surround sound products at Amphony's website.
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