By Linda Cullmann


To help you pick a set of cordless speakers, I will explain the expression "signal-to-noise ratio" which is regularly utilized to depict the performance of wireless speakers.

While searching for a couple of wireless loudspeakers, you initially are going to check the cost, power amid additional fundamental criteria. Yet, after this initial choice, you will still have several types to choose from. Next you will concentrate more on a few of the technical specs, like signal-to-noise ratio and harmonic distortion. An important parameter of cordless loudspeakers is the signal-to-noise ratio. To put it simply, the signal-to-noise ratio describes how much hum or hiss the loudspeakers are going to add to the music signal. This ratio is typically described in decibel or "db" for short.

Evaluating the noise level of different sets of wireless loudspeakers may be done quite easily. Simply collect a number of versions that you wish to compare and short circuit the transmitter audio inputs. Afterward put the cordless speaker volume to maximum and check the amount of hiss by listening to the loudspeaker. Usually you will hear 2 components. The first is hissing. In addition, you will often hear a hum at 50 or 60 Hz. Both of these are components which are produced by the cordless loudspeaker itself. Next compare several sets of wireless loudspeakers according to the following rule: the lower the level of hiss, the better the noise performance of the wireless loudspeaker. Though, keep in mind that you should set all sets of cordless loudspeakers to amplify by the same amount in order to evaluate several models.

In order to help you evaluate the noise performance, cordless speaker manufacturers show the signal-to-noise ratio in their cordless loudspeaker spec sheets. Simply put, the larger the signal-to-noise ratio, the smaller the amount of noise the cordless loudspeaker produces. Noise is produced due to a number of reasons. One reason is that today's wireless speakers all employ elements including transistors and resistors. These components are going to generate some amount of noise. As the built-in power amplifier overall noise performance is mostly determined by the performance of components located at the amp input, suppliers are going to try to select low-noise elements while designing the amp input stage of their cordless loudspeakers.

Noise is also brought on by the wireless transmission. Different styles of transmitters are available that work at different frequencies. The most inexpensive kind of transmitters employs FM transmission and usually broadcasts at 900 MHz. Other cordless transmitters will interfer with FM type transmitters and create further noise. As a result the signal-to-noise ratio of FM style cordless speakers changes depending on the distance of the speakers from the transmitter and the level of interference. To avoid these problems, modern transmitters employ digital music broadcast and typically transmit at 2.4 GHz or 5.8 GHz. The signal-to-noise ratio of digital transmitters is dependent mostly on the type of analog-to-digital converters and other components which are utilized as well as the resolution of the cordless protocol.

Most of today's wireless loudspeakers use power amplifiers which are digital, also known as "class-d amplifiers". Class-D amplifiers employ a switching stage which oscillates at a frequency between 300 kHz to 1 MHz. This switching noise may result in some level of loudspeaker distortion yet is usually not included in the signal-to-noise ratio which only considers noise between 20 Hz and 20 kHz.

The signal-to-noise ratio is measured by inputting a 1 kHz test tone 60 dB below the full scale and measuring the noise floor of the signal generated by the built-in amplifier. The volume of the cordless speaker is set such that the full output wattage of the built-in amplifier can be realized. Next, only the hiss in the range of 20 Hz and 20 kHz is considered. The noise at different frequencies is removed via a filter. Next the amount of the noise energy in relation to the full-scale output wattage is computed and shown in decibel.

Frequently you are going to discover the term "dBA" or "a-weighted" in your cordless speaker specification sheet. A weighting is a technique of showing the noise floor in a more subjective fashion. This method was developed with the knowledge that human hearing perceives noise at different frequencies differently. Human hearing is most sensitive to signals around 1 kHz. Then again, signals below 50 Hz and above 13 kHz are barely noticed. An A-weighted signal-to-noise ratio weighs the noise floor in accordance to the human hearing and is typically higher than the unweighted signal-to-noise ratio.




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