To help you select a couple of cordless speakers, I am going to clarify the expression “signal-to-noise ratio” that is usually utilized to depict the performance of wireless speakers. Once you have chosen a range of wireless speakers, it is time to investigate a few of the specs in more detail to help you narrow down your search to one model. The signal-to-noise ratio is a fairly vital spec and explains how much noise or hiss the cordless speaker makes. A way to perform a simple test of the noise performance of a set of wireless loudspeakers is to short circuit the transmitter audio input and then to crank up the cordless loudspeaker to its utmost. After that listen to the speaker. You are going to hear some amount of hissing and/or hum coming from the loudspeaker. This hiss is produced by the cordless speaker itself. Then compare several sets of cordless loudspeakers according to the next rule: the smaller the amount of noise, the higher the noise performance of the cordless speaker. On the other hand, bear in mind that you have to set all sets of wireless speakers to amplify by the same amount in order to evaluate different models.
When looking at the wireless loudspeaker spec sheet, you want to look for a set of wireless loudspeaker with a high signal-to-noise ratio figure which indicates that the cordless loudspeakers output a low amount of hiss. Noise is generated due to several reasons. One reason is that today’s cordless loudspeakers all employ elements such as transistors as well as resistors. These components will generate some amount of hiss. The overall noise is dependent on how much hiss each element produces. Yet, the location of those components is also important. Components that are part of the loudspeaker built-in amp input stage will usually contribute the majority of the noise. An additional cause of noise is the wireless audio transmission itself. Usually types which make use of FM type broadcast at 900 MHz are going to have a rather large level of hiss. Other cordless transmitters are going to interfer with FM type transmitters and bring about further static. As a result the signal-to-noise ratio of FM type cordless loudspeakers (Read this article about wireless speakers) varies depending on the distance of the loudspeakers from the transmitter plus the amount of interference. To steer clear of these problems, newer transmitters make use of digital audio broadcast and usually broadcast at 2.4 GHz or 5.8 GHz. This kind of audio transmission offers larger signal-to-noise ratio than analog type transmitters. The level of noise is dependent on the resolution of the analog-to-digital converters and the quality of other parts. Many of recent wireless loudspeaker use amplifiers which are based on a digital switching architecture. These amplifiers are referred to as “class-D” or “class-T” amps. Switching amps incorporate a power stage that is continuously switched at a frequency of around 400 kHz. This switching noise may result in some level of speaker distortion but is typically not included in the signal-to-noise ratio which only considers noise in the range of 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 wireless speaker is pair such that the full output wattage of the built-in amp can be achieved. After that, only the hiss between 20 Hz and 20 kHz is considered. The noise at different frequencies is eliminated through a filter. Subsequently the level of the noise energy in relation to the full-scale output power is computed and shown in decibel. Frequently you will discover the term “dBA” or “a-weighted” in your wireless loudspeaker specification sheet. A weighting is a method of expressing the noise floor in a more subjective way. This technique was designed 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 above 13 kHz are hardly heard. Consequently an A-weighting filter is going to magnify the noise floor for frequencies which are easily heard and suppress the noise floor at frequencies which are hardly noticed. The majority of cordless speaker will have a larger A-weighted signal-to-noise ratio than the un-weighted ratio. In addition, check out http://www.dmzforum.org/zbxe/zbxe/?mid=DMZPublications&page=528&document_srl=516294 to get a lot more details.