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”.

THD is expressed either in percent or in decibel and shows how much the signal which the speaker outputs differs from the audio signal which is fed into the speaker. A -20 dB or 10% distortion means that one tenth of the radiated sound 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.

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.

Distortion specs for different power levels are usually given 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 amp.Normally distortion is measured with a 1 kHz test tone. However, amplifier distortion will usually increase with increasing frequency, especially in digital class-D models.

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.

To find out the overall distortion of a loudspeaker, a signal generator is used which provides an ultra-linear signal to the speaker as well as a measurement microphone which is connected to an audio analyzer to determine the amount of harmonics emitted by the speaker. Another distortion measurement technique which gives a better analysis of the speaker performance with real-world signals is called interharmonic distortion. This method outputs two signals at different frequencies and measures the amount of harmonics at different frequencies.

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.

You can get further details about wireless outdoor speakers as well as wireless surround sound products at Amphony’s web page.

Technorati Tags: audio, computers, hardware, Music, Music & Music Players, product reviews, Radio, Satellite Radio, satellite tv, shopping, speakers, technology, tv, video