Lately 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 some of the newest gadgets and technologies to find out how well they work and in which situations they work best.
Products can be categorized into products with built-in and those with optional wireless capability. Streaming audio products will often have a plug-in slot for adding a wireless LAN card. Latest generation iPods and cell phones already come with built-in WiFi and Bluetooth support.
Bluetooth is a fairly low-cost solution but has some drawbacks which are often overlooked.
1) Limited range
Bluetooth devices typically only have a 30-foot range which limits Bluetooth to single-room applications.
2) Low data rate – audio compression
Bluetooth reliably supports data transmission rates of around 1 Mbps only which is not enough for uncompressed CD-quality audio. Therefore Bluetooth applies audio compression. This is less critical though for compressed audio such as MP3 audio but excludes Bluetooth from use in high-quality audio applications.
3) Audio latency
Due to audio compression, Bluetooth will introduce a signal delay of at least 10 ms which will cause the audio to be slightly out of sync in case of video and real-time applications. This is again less of a problem for MP3 players.
4) No multiple headphone support
Bluetooth does not support any number 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 widely used wireless protocol that is also suitable for audio streaming. WiFi does support uncompressed audio but will have problems transmitting to a large number of wireless receivers simultaneously. Due to the fairly high power consumption it is rarely used in wireless headphones though. WiFi is convenient for streaming audio from a PC however since almost all PCs have WiFi access.
Wireless speakers and wireless amplifier products for home theater speakers typically use their own proprietary protocol. Entry-level wireless headphones and speakers typically still use FM transmission which offers low cost but is prone to noise and audio distortion.
More advanced wireless protocols are based on digital formats which eliminate audio degradation and incorporate advanced features such as error correction to cope with interference from competing wireless devices.
Advanced wireless amplifier devices support uncompressed digital audio streaming to preserve the original audio quality. Some of these protocols allow streaming to an unlimited number of wireless amplifiers which is convenient for whole-house audio distribution.
The audio latency ranges from below 1 ms to up to 20 ms. A small latency is important for wireless surround sound applications. These wireless audio transmitters typically work at 2.4 GHz. There are also some products which work at 5.8 GHz. Products that operate at 5.8 GHz have less competition from other wireless devices than those using the crowded 2.4 GHz frequency band.
These wireless amplifiers also differ in terms of amplifier output power, standby power consumption and audio quality. A high-quality audio amplifier is vital for optimum sound quality. Digital amplifiers typically offer a power efficiency of at least 80% and standby power consumption of less than 5 Watts which keeps them cool during operation and helps save energy. However, some Class-D amps have fairly high audio distortion. Audiophile wireless amplifiers offer an audio distortion of 0.05% or less.