Recently a large number of wireless audio products have emerged such as latest-generation wireless headphones, iPods, cell phones and wireless amplifier products which promise to cut the cord. I will take a look at if these products keep their claim to deliver perfect-quality audio. Moreover, I will take a look at the underlying technologies.

These products fall into 2 categories. The first sort of products already has wireless built in. Second-category products, such as a number of streaming audio products, have optional wireless functionality. Normally they have a slot to insert a wireless LAN card. Modern cell phones and MP3 players already come with support for wireless. iPhones and touch-screen iPods, for instance, have Bluetooth and WiFi.

The Bluetooth protocol is a fairly low-cost solution. Still, its limitations have an influence on high-quality audio applications and are often ignored.

1) Short range

The range of Bluetooth devices is normally merely 30 ft. This excludes Bluetooth from multi-room applications.

2) Small data rate - audio compression

Bluetooth offers a maximum reliable data rate of approximately 1 Mbps only. This rate is not high enough to send uncompressed CD-quality audio. As a result Bluetooth wireless devices use audio compression. This is less critical however for compressed audio such as MP3 audio but excludes Bluetooth from use in high-quality audio applications.

3) Audio latency

The audio will experience a delay of at least 10 ms for the most part due to the audio compression which is a dilemma for real-time audio applications but less critical for MP3 players.

4) No multiple headphone support

Bluetooth does not support any quantity of headphones which may be a problem if you have a larger number of people who want to listen to headphones from a single transmitter device.

WiFi is another commonly used wireless protocol that is also suitable for audio streaming. WiFi does support uncompressed audio but will have problems broadcasting to a high number of wireless receivers at the same time. As a consequence of the relatively high power consumption it is hardly ever used in wireless headphones though. WiFi is suitable for streaming audio from a PC however because nearly all PCs have WiFi access.

While newest-generation wireless speakers and wireless amplifier products utilize proprietary digital technologies, low-cost products frequently still rely on FM transmission which is noisy and has high audio distortion and high susceptibility to radio interference.

More advanced wireless protocols are based on digital formats which avoid audio degradation and incorporate sophisticated features including error correction to deal with interference from competing wireless devices.

Sophisticated wireless amplifier devices support uncompressed digital audio streaming to maintain the original audio quality. Some of these protocols permit streaming to an unlimited number of wireless amplifiers which is convenient for whole-house audio distribution.

Some of these protocols support low-latency audio transmission which assures that the audio of all speakers will be in sync in a multi-channel application. Typically newer generation wireless audio transmitters will operate at 2.4 GHz. Some transmitter devices, including Amphony's line of devices, work at the less crowded 5.8 GHz frequency band.

Wireless amplifiers offer different levels of audio quality, output power and standby power. Digital Class-D amplifiers offer high power efficiency of no less than 80%. They also have low standby power, normally less than 5 Watts. This minimizes heat and keeps them cool during operation. Some digital amplifiers, however, have fairly high harmonic distortion. Choosing a low-distortion amplifier is crucial. Good-quality wireless amplifiers have audio distortion of less than 0.05%.


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