Latest-generation wireless audio products such as iPods, iPhones and wireless surround sound products promise to cut the cord while delivering crystal-clear audio. We will review some of the newest devices to find out which applications they work for.
These devices fall into 2 categories. The first category of products already has wireless built in. Second-category products, such as a few streaming audio devices, have optional wireless ability. Typically they have a slot to insert a wireless LAN card. Newest touch-screen iPods and iPhones already have WiFi and Bluetooth built in.
Bluetooth is a fairly low-cost solution but has some drawbacks which are frequently overlooked.
1) Inadequate operating range
Bluetooth devices generally merely have a 30-foot range which restricts Bluetooth to single-room applications.
2) Low data rate - audio compression
Bluetooth will apply audio compression because it does not reliably offer a high-enough data rate for uncompressed audio. The audio will be degraded to some degree because of the audio compression. For this reason higher-end audio equipment normally does not use Bluetooth wireless audio.
3) Audio delay
The audio will experience a delay of no less than 10 ms for the most part as a result of the audio compression which is a problem for real-time audio applications but less serious for MP3 players.
4) No support of multiple headphones
Bluetooth does not support any number of headphones which might be a problem if you have a larger number of people who want to listen to headphones from a single transmitter device.
Another common protocol is WiFi which supports uncompressed audio but also has problems simultaneously streaming to many receivers. Due to the high availability, WiFi is suitable for streaming audio from a PC. However, WiFi products have rather high power consumption. Because of this wireless headphones normally do not use this technology.
Home wireless speaker devices and wireless amplifiers generally employ proprietary protocols. These protocols are specially designed for real-time audio applications. Yet, entry-level wireless speakers and headphones still utilize FM transmission. FM transmission suffers from rather high audio degradation and hiss / static.
More recent wireless audio protocols are based on digital transmission. This avoids audio degradation. Some protocols also incorporate error correction to deal with interference from other wireless devices.
Latest-generation wireless amplifiers employ uncompressed audio transmission. New protocols also allow streaming to an infinite number of receivers. This allows whole-house audio distribution.
The audio latency of these wireless amplifiers is typically between 1 ms and 20 ms. A small-latency amplifier is vital for home theater audio. This ensures that all speakers will be in sync. Normally newer generation wireless audio transmitters will operate at 2.4 GHz. Some transmitter products, such as Amphony's line of products, 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, usually less than 5 Watts. This minimizes heat and keeps them cool during operation. Some digital amplifiers, though, have fairly high harmonic distortion. It is essential to choose a wireless amplifier with low audio distortion. This will guarantee good sound quality. High-quality amplifiers have audio distortion of 0.05% or less.
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