Once you have narrowed down your search by taking a look at several key criteria, such as the amount of output wattage, the dimensions of the loudspeakers and the cost, you are going to still have quite a few products to choose from. Now it is time to take a look at a couple of the technical specs in more detail. An important criterion of wireless speakers is the signal-to-noise ratio. To put it simply, the signal-to-noise ratio shows how much hum or hiss the speakers are going to add to the audio signal. This ratio is customarily shown in decibel or 'db' for short.
You can do a simple comparison of the cordless speaker noise by short circuiting the transmitter input, setting the loudspeaker gain to maximum and listening to the speaker. The hiss which you hear is created by the wireless loudspeaker itself. Be certain that the volume of each set of wireless speakers is set to the same amount. Otherwise you will not be able to objectively evaluate the amount of hiss between different models. The general rule is: the smaller the level of noise that you hear the higher the noise performance.
If you prefer a set of wireless loudspeakers with a small amount of hissing, you can look at the signal-to-noise ratio figure of the data sheet. Many producers will display this number. cordless loudspeakers with a large signal-to-noise ratio will output a small level of static. One of the reasons why wireless speakers generate noise is the fact that they utilize components including transistors as well as resistors that by nature create noise. As the built-in power amplifier overall noise performance is mostly determined by the performance of elements situated at the amplifier input, producers are going to try to choose low-noise elements when developing the amplifier input stage of their cordless loudspeakers.
The wireless broadcast itself also creates static that is most noticable with types which use FM transmission at 900 MHz. The level of noise is also dependent upon the level of cordless interference from other transmitters. Modern models will generally make use of digital audio transmission 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 parts which are used in addition to the resolution of the wireless protocol.
The majority of recent cordless loudspeakers use power amps which are digital, also called 'class-d amplifiers'. Class-D amps employ a switching stage which oscillates at a frequency between 300 kHz to 1 MHz. This switching noise may result in some amount of speaker distortion but is usually not included in the signal-to-noise ratio which merely considers noise between 20 Hz and 20 kHz.
The signal-to-noise ratio is measured by feeding a 1 kHz test tone 60 dB below the full scale and measuring the noise floor of the signal generated by the built-in amp. The gain of the cordless speaker is couple such that the full output wattage of the built-in amplifier can be achieved. Next the noise-floor energy is measured in the frequency range between 20 Hz and 20 kHz and compared with the full scale signal energy.
An additional convention to state the signal-to-noise ratio makes use of more subjective terms. These terms are 'dBA' or 'A weighted'. You are going to find these terms in the majority of wireless loudspeaker parameter sheets. This method was developed with the knowledge that human hearing perceives noise at different frequencies differently. Human hearing is most responsive to signals around 1 kHz. Then again, signals below 50 Hz and higher than 13 kHz are hardly heard. Thus an A-weighting filter is going to amplify the noise floor for frequencies that are easily heard and suppress the noise floor at frequencies which are hardly perceived. The majority of wireless loudspeaker will have a larger A-weighted signal-to-noise ratio than the un-weighted ratio.