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05 November 2013

How Much Noise Do Cordless Speakers Produce?

By Linda Cullmann


Are you searching to acquire a new a couple of cordless loudspeakers for your home? You might be dazzled by the amount of alternatives you have. In order to make an informed selection, it is best to familiarize yourself with popular terms. One of these specifications is known as "signal-to-noise ratio" and is not often understood. I am going to help clarify the meaning of this expression.

As soon as you have narrowed down your search by looking at a few key criteria, including the amount of output power, the dimensions of the speakers in addition to the cost, you will still have quite a few models 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 cordless loudspeakers 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 commonly shown in decibel or "db" for short.

You can perform a straightforward assessment of the wireless loudspeaker hiss by short circuiting the transmitter input, setting the loudspeaker volume to maximum and listening to the speaker. The hiss that you hear is created by the wireless speaker itself. Next compare different sets of wireless speakers according to the following rule: the smaller the level of static, the better the noise performance of the wireless speaker. Yet, keep in mind that you must put all sets of wireless loudspeakers to amplify by the same amount to compare different models.

In order to help you evaluate the noise performance, wireless loudspeaker makers publish the signal-to-noise ratio in their cordless loudspeaker specification sheets. Simply put, the larger the signal-to-noise ratio, the smaller the level of noise the wireless speaker generates. One of the reasons why wireless speakers produce noise is the fact that they utilize elements including transistors as well as resistors which by nature create noise. Generally the components which are located at the input stage of the built-in power amp will contribute most to the overall noise. Thus suppliers normally will choose low-noise elements whilst designing the cordless speaker amp input stage.

A further cause of noise is the cordless audio broadcast itself. Normally products that utilize FM style transmission at 900 MHz will have a comparatively high level of noise. Other cordless transmitters are going to interfer with FM type transmitters and create additional hiss. Consequently the signal-to-noise ratio of FM style cordless loudspeakers varies depending on the distance of the loudspeakers from the transmitter plus the level of interference. To steer clear of these problems, modern transmitters employ digital music broadcast and typically broadcast at 2.4 GHz or 5.8 GHz. This kind of music broadcast provides larger signal-to-noise ratio than analog style transmitters. The amount of hiss depends on the resolution of the analog-to-digital converters as well as the quality of other parts.

A lot of of modern cordless speaker use amps which are based on a digital switching architecture. These amplifiers are called "class-D" or "class-T" amps. Switching amps incorporate a power stage which is continuously switched at a frequency of approximately 400 kHz. This switching noise may cause a certain 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 most popular method for measuring the signal-to-noise ratio is to set the cordless loudspeaker to a gain which enables the maximum output swing. Next a test tone is fed into the transmitter. The frequency of this signal is generally 1 kHz. The amplitude of this tone is 60 dB underneath the full scale signal. Then, the noise floor between 20 Hz and 20 kHz is calculated and the ratio to the full-scale signal calculated. The noise signal at other frequencies is removed by a bandpass filter during this measurement.

A different convention to state the signal-to-noise ratio utilizes more subjective terms. These terms are "dBA" or "A weighted". You will find these terms in most wireless speaker spec sheets. In other words, this method tries to express how the noise is perceived by a person. Human hearing is most sensitive to signals around 1 kHz whereas signals below 50 Hz and higher than 14 kHz are barely heard. An A-weighted signal-to-noise ratio weighs the noise floor according to the human hearing and is normally higher than the unweighted signal-to-noise ratio.




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