A Quick Look At Exactly How Modern Technology Minimizes The Noise Of Outdoor Audio Speakers | The Communication Blog

Tuesday, November 19, 2013

A Quick Look At Exactly How Modern Technology Minimizes The Noise Of Outdoor Audio Speakers

By Linda Cullmann


To help you select a pair of wireless loudspeakers, I will describe the term "signal-to-noise ratio" that is usually utilized to express the performance of cordless speakers.

After you have narrowed down your search by looking at a few key criteria, including the amount of output wattage, the size of the speakers in addition to the cost, you will still have quite a few products to choose from. Now it is time to take a look at some of the technical specs in more detail. Every cordless loudspeaker is going to generate a certain amount of hiss and hum. The signal-to-noise ratio is going to help quantify the level of noise generated by the speaker.

Comparing the noise level of different sets of wireless speakers can be done quite simply. Just collect a number of products which you wish to evaluate and short circuit the transmitter audio inputs. After that set the wireless speaker gain to maximum and verify the level of static by listening to the loudspeaker. The static that you hear is generated by the cordless speaker itself. After that compare different sets of cordless loudspeakers according to the next rule: the smaller the amount of static, the higher the noise performance of the cordless speaker. Though, bear in mind that you must put all sets of wireless speakers to amplify by the same level to compare several models.

When glancing at the wireless loudspeaker specification sheet, you want to look for a set of wireless loudspeaker with a large signal-to-noise ratio number which indicates that the cordless loudspeakers output a low amount of static. There are a number of reasons why wireless speakers will add some form of noise or other unwanted signal. Transistors and resistors which are part of each modern cordless loudspeaker by nature generate noise. The overall noise depends on how much noise every component generates. Yet, the position of these elements is also significant. Elements which are part of the loudspeaker built-in amplifier input stage are going to in general contribute most of the noise.

An additional cause of static is the wireless music transmission itself. Normally types which make use of FM type broadcast at 900 MHz are going to have a comparatively large level of static. The amount of hiss is also dependent upon the amount of wireless interference from other transmitters. Newer types are going to generally make use of digital audio broadcast at 2.4 GHz or 5.8 GHz. This kind of audio transmission provides higher signal-to-noise ratio than analog style transmitters. The level of hiss depends on the resolution of the analog-to-digital converters along with the quality of other components.

The majority of of latest wireless speaker use amps which are based on a digital switching architecture. These amplifiers are referred to as "class-D" or "class-T" amplifiers. Switching amplifiers include a power stage which is always switched at a frequency of around 400 kHz. In consequence, the output signal of cordless loudspeaker switching amps exhibit a fairly large level of switching noise. This noise component, however, is generally inaudible since it is well above 20 kHz. However, it may still contribute to loudspeaker distortion. Signal-to-noise ratio is generally only shown within the range of 20 Hz to 20 kHz. As a result, a lowpass filter is used when measuring cordless loudspeaker amps to remove the switching noise.

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 amplifier. The volume of the wireless speaker is set such that the full output power of the built-in amplifier can be achieved. Subsequently, only the noise between 20 Hz and 20 kHz is considered. The noise at different frequencies is eliminated by a filter. Subsequently the amount of the noise energy in relation to the full-scale output power is calculated and shown in decibel.

Frequently the signal-to-noise ratio is shown in a more subjective method as "dbA" or "A weighted". This method attempts to examine in how far the cordless speaker noise is perceived by human hearing which is most sensitive to signals at frequencies at 1 kHz. For that reason an A-weighting filter will magnify the noise floor for frequencies which are easily heard and suppress the noise floor at frequencies which are barely heard. Many wireless speaker will have a higher A-weighted signal-to-noise ratio than the un-weighted ratio.




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