subject: A Peek At Some Of The Most Recent Wireless Audio Toys [print this page] 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.
These products fall into 2 categories. The first type of products already has wireless built in. Second-category products, such as some streaming audio products, have optional wireless capability. Typically they have a slot to add a wireless LAN card. Newer cell phones and MP3 players already come with support for wireless. iPhones and touch-screen iPods, for example, have Bluetooth and WiFi.
The Bluetooth protocol is a fairly low-cost solution. However, its drawbacks have an impact on high-quality audio applications and are often overlooked.
1) Short range
The range of Bluetooth devices is typically only 30 ft. This excludes Bluetooth from multi-room applications.
2) Limited data transmission capacity
Bluetooth offers a maximum reliable data rate of around 1 Mbps only. This rate is not high enough to transmit uncompressed CD-quality audio. Therefore Bluetooth wireless devices use audio compression. The audio will be degraded to some extent due to the audio compression. For this reason higher-end audio equipment normally does not use Bluetooth wireless audio.
3) Audio latency
The signal transmitted via Bluetooth will undergo a slight delay of at least 10 ms. This is mostly due to the audio compression. While being uncritical for MP3 players, this delay may be a problem for video and other real-time applications.
4) No support of multiple headphones
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.
Uncompressed audio streaming is supported by WiFi. WiFi is a very common protocol. However, WiFi also has limitations in regard to simultaneous transmission to several receivers. Due to the high availability, WiFi is convenient for streaming audio from a PC. However, WiFi products have fairly high power consumption. For this reason wireless headphones typically do not use this technology.
Home wireless speaker products and wireless amplifiers normally use proprietary protocols. These protocols are specially designed for real-time audio applications. However, entry-level wireless speakers and headphones still use FM transmission. FM transmission suffers from fairly high audio distortion and hiss / static.
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 such as Amphony's line of wireless audio 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.
Wireless amplifiers are available with different levels of audio quality, power consumption and standby power. Having a high-quality low-distortion amplifier is vital for good sound quality. Digital Class-D amplifiers offer high power efficiency of at least 80%. They also have low standby power, typically less than 5 Watts. This reduces heat and keeps them cool during operation. Some digital amplifiers, however, have fairly high harmonic distortion. It is important to select a wireless amplifier with low audio distortion. This will ensure good sound quality. High-quality amplifiers have audio distortion of 0.05% or less.
