Music Without Cables? – A Look At Wireless Audio Transmitter Gadgets
Over the years a whole array of wireless audio transmitters have emerged which are supposed to eliminate the cords at home when connecting audio equipment. Can these products make good on their claim to eliminate the cable clutter? What impact has changing technology had on their performance?
The first form of wireless audio transmission was in the form of AM and FM radio stations. FM radio is still popular until now even though some new technologies such as satellite radio and digital radio formats such as HD radio and DAB radio have begun to substitute traditional FM radio. Today a variety of consumer products exist such as wireless microphones, wireless surround sound kits, Bluetooth audio transmitters, baby monitors etc which cut the cord by transmitting audio wirelessly.
One of the main application for wireless audio is distributing music all through the house and installing loudspeakers without running speaker cords which is a large difficulty in houses that are not wired for audio. The technologies used today all have pros and cons as we will examine.
One of the most traditional technologies is FM broadcasting. Audio is sent via a radio-frequency signal which is modulated (changed in frequency) with an audio signal. The technology, which is called frequency modulation (FM), is fairly simple and cost-effective to build and offers high range. Most of today’s wireless consumer products utilize FM transmission. FM, however, has serious drawbacks compared with newer technologies.
The FM signal will pick up static. Therefore there will be noticeable background noise. The amount of static will depend on the location of the transmitter and radio. The reason for the varying quality is a phenomenon known as multipath fading which is a consequence of reflected radio waves cancelling each other out. One method to deal with this problem is utilizing two antennae instead of one. Devices using this technique are known as diversity receivers. Another difficulty is that FM radios easily pick up interference from competing wireless transmitters.
Another technology which has gained popularity lately is known as Bluetooth. Bluetooth was originally designed to connect computer peripheral devices wirelessly. Before the signal is broadcast, Bluetooth transmitters will convert the audio into a digital format. Bluetooth is relatively robust in terms of interference and is well standardized. Bluetooth, on the other hand, has some pitfalls in regard to wireless audio since it was not designed for wireless audio originally. The range of the transmission is only 30 ft or less. Moreover, Bluetooth does not have enough room to send an uncompressed CD-quality audio signal. As a result the audio is compressed prior to the transmission. This compression will result in a loss of audio quality depending on the amount of compression. Another problem is that Bluetooth will cause a delay or latency to the signal during the broadcast. This delay is a particular problem for video and surround sound applications. In these applications the sound from the wireless speakers would be out of sync with the video and remaining speakers.
Satellite radio and digital terrestrial radio technologies offer high range but use extensive audio compression leading to degradation of the audio signal and have an audio delay of more than a few seconds.
Another technology transmits the audio signal without compression digitally. This technology is used in wireless audio transmitters from Amphony. By eliminating audio compression, the signal will retain the original quality. The audio latency of these products is less than 1 ms and as a result this technology is also used in wireless speaker kits for home theater setups.
This technology is quite robust against radio interference from other wireless transmitters by employing a method called forward error correction. The Amphony transmitters operate at 5.8 GHz. This frequency space is less crowded than the 900 MHz or 2.4 GHz bands thus leading to a further improvement of reliability. An advantage over Bluetooth is the ability to transmit audio to any number of wireless receivers from a single transmitter. This is important for distributing audio to multiple rooms in the home.
Wireless Surround Sound – The End Of Cable Clutter?
Recently more and more manufacturers have started to offer home theater systems with wireless speakers or a wireless surround sound kit. From a homeowners standpoint, eliminating long speaker cable runs is certainly a big plus. Multi-channel surround sound is a fairly new phenomenon and as such many older houses are not wired for rear speakers, not to mention 7.1 systems. As such a wireless solution might be the logical conclusion. But how reliable are these wireless surround sound kits in a real-world scenario and do these options really eliminate the dreaded cable clutter?
Some wireless surround sound kits, such as the LG or Rocketfish allow to connect 2 speakers to a wireless receiver unit. This eliminates the cables from the front to the back. However, still cables need to be run from the receiver to each speaker and as such the amount of cables is just reduced but not eliminated. Another wireless surround sound product from Amphony comes with separate receivers for each speaker which in comparison to the other products does reduce the cable clutter, albeit not eliminate cables completely.
Will the wireless have any effect on performance? Audio quality is a main concern. In picking a wireless system, one should choose a system where (a) the transmission itself does not pick up any noise or degradation in order to maintain the audio quality and (b) the wireless amplifier itself should be a high-quality amplifier with minimal distortion. Also, the size of the wireless speaker amplifier is a consideration as the receiver should be invisible.
In a surround sound application, such as a home theater setting, the audio from each speaker naturally should be in sync with the video and also with the audio of the other speakers. Some wireless surround sound kits, such as the product from Rocketfish, will introduce a significant delay to the signal. Therefore when choosing a wireless surround sound kit, it is important to look closely at how much latency the wireless unit will introduce. The Amphony product adds a little less than 1 ms delay which should be sufficiently low for pretty much any application.
One of the main issues with wireless devices of any sort is interference from other devices. As more and more consumer devices go wireless, the available frequency space becomes more and more limited. Especially the 900 MHz and 2.4 GHz bands are exceptionally crowded, due to WiFi hot spots, cell phones with Bluetooth etc. Picking a system that avoids these frequency bands may be the logical choice, such as systems working at 5.8 GHz.
While wireless speakers and wireless surround sound kits are suited for use in a home theater setting, their use is not limited to that application. In particular setting up speakers in another room often poses a challenge in terms of running speaker wires or using speakers outdoors. Just imagine being able to set up a speaker in your backyard in minutes. The possibilities are endless.
