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The latest series of wireless audio transmitter devices promises streaming of music throughout the home without limits. We will look at various products and technologies to find out in how far these devices are effective for whole-house audio applications and what to look out for when buying a wireless system.

Infrared wireless audio devices are restricted to line-of-sight applications, i.e. only function within a single room because the signal is sent as infrared light which can’t penetrate walls. This technology is often found in wireless speaker kit products.

RF wireless music devices broadcast the music signal via radio waves. These radio wave signals can without difficulty go through walls. The signal is broadcast either by utilizing FM transmission or digital transmission. FM transmission is cheap but quite prone to static, audio distortion and susceptible to interference.

Digital wireless audio transmitter devices, such as products from Amphony, make use of a digital protocol. The audio is first converted to digital data before being broadcast. This method guarantees that the audio quality is fully preserved. Some transmitters utilize some form of audio compression, such as Bluetooth transmitters, which will degrade the audio to some degree. Transmitters which send the audio data uncompressed will achieve the highest fidelity.

Wireless LAN (WLAN) products are practical when streaming from a PC but will add some amount of latency or delay to the signal because wireless LAN was not originally designed for real-time audio streaming. WLAN receivers ordinarily require buying a separate LAN card to be plugged into every receiver.

Powerline products send the audio via the power mains and offer great range. They run into problems in homes where there are individual mains circuits in terms of being able to cross over into another circuit. Also, these products build in a delay of a number of seconds to safeguard against transmission errors during power surges and spikes which prevents their use in applications where the audio from wireless loudspeakers has to be in sync with other non-wireless speakers or video.

Here are some recommendations for picking the optimum wireless audio system: Try to find a system that can run several wireless receivers from a single transmitter. Ideally an unlimited number of receivers should be supported. That way you don’t need to buy extra transmitters when you start adding receivers in several rooms of your house. Some devices have some form of error correction built in which will help guard against dropouts in case of strong wireless interference. Choose a digital RF audio transmitter to guarantee that the audio quality is preserved. Make sure the audio delay is smaller than 10 ms if you have a real-time application such as video.

Select a transmitter that has all of the audio inputs you need, e.g. speaker inputs, RCA inputs etc. Get a wireless system where you can buy separate receivers later on. You should confirm that you can get receivers for all the different applications you have. Such receivers may include amplified receivers for passive speakers or line-level receivers for active speakers. Select a transmitter that can regulate the audio volume of the input stage. This will give you the flexibility to connect the transmitter to any kind of equipment with different signal levels. Otherwise the audio may get clipped inside the transmitter converter stage or the dynamic range is not fully utilized.

Check that the system provides amplified receivers with a digital amplifier to ensure high power efficiency. This will help keep the receiver cool during operation. Also, make sure the amplifier provides low audio distortion. This is vital for good sound quality. Verify that the amplified receiver is able to drive speakers with the preferred Ohm rating and that it is small and easily mountable for simple installation. Products using the less crowded 5.8 GHz frequency band will normally have less trouble with wireless interference than 900 MHz or 2.4 GHz products.

A transformer is an electrical device that allows an AC input signal to produce a related AC output signal without the input and output being physically connected together. The transformer offers several advantages in coupling signals from one circuit to another. A transformer is considered large, heavy, and expensive but it continues to be the most effective solution in many audio applications. Audio transformers improve sound quality by removing interference from audio signals. Audio transformer is generally encased in a magnetic shield which is filled with an epoxy resin that provides insulation, protects the windings, and prevents vibration of the core material. Some audio transformers do not have a center tap, while other devices have a center tap in only the primary side, only the secondary side, or in both the primary and secondary sides. Transformers can be manufactured with multiple primary or secondary windings.

The two types of audio transformers are step up/ step down transformers and unity 1.1 transformers. The basic use of step up transformer is signal level compatibility, and impedance compatibility. Use of unity1.1 transformers are DC blocking, radio frequency interference and ground lift. In step up transformer, the primary and secondary have a different number of windings, thus they have different impedances. A unity transformer allows an audio signal to pass unmodified from the primary to the secondary while blocking DC voltage and radio frequency interference (RFI). Pros of audio transformer is to match impedances, to increase or decrease signal level by up to 25 db. While unity 1:1 transformer is used to increase signal level by more than 25 db. Audio transformer is used in audio devices like microphones, speakers, tape drives to transmit voice and sound signals. The transformers have wide frequency bandwidth, low distortion and noise suppression.

Audio transformers are recognized as wide band transformers. The services that are related to audio transformers are current sense transformers, gate drive transformers, RF transformers, signal transformers, switch mode transformers and telecom transformers. Current sense transformers are used to detect and measure current. Gate drive transformers are used in applications such as switching power supplies. RF transformers transfer energy from one circuit to another by electromagnetic induction. Signal transformers transfer information from one circuit to another by electromagnetic induction. Switch mode transformers are generally used mainly in switching power supplies and DC-DC converters. Telecom transformers are used in applications which require high bandwidths and fast switching speeds.