The US Federal Communication Commission (FCC) regulation now permits operation of Wireless Multichannel Audio Systems (WMAS) in the United States. WMAS is an advanced wireless microphone technology designed to meet the challenges of highly demanding live performance and studio applications.

WMAS offers higher spectral efficiency than conventional wireless microphone systems – the ability to transmit more audio channels within a limited block of radio frequency (RF) spectrum – as well as greater interference protection to other wireless services that share the same spectrum.

In her statement during the Open Commission Meeting, Chairwoman Jessica Rosenworcel sais: ‘Unless you’re in video and audio production, the odds are you haven’t thought much about wireless microphones but they’re everywhere. So when a new technology comes along with the potential to improve the efficiency of wireless microphone operations, we’re going to take a second look. That’s why a few years ago we issued a rulemaking to explore Multichannel Wireless Audio Systems or WMAS.’

Sennheiser began development of its WMAS more than ten years ago and, in August 2018, filed a Petition for Rulemaking with the FCC requesting a modification in the bandwidth limit specified for wireless microphones by the Commission. At that time, Sennheiser demonstrated a prototype system to the Commission’s Office of Engineering & Technology (OET). During the past five-and-a-half years, the FCC monitored further developments of WMAS technology and concluded that it justified the requested rule change.

‘We especially thank OET, who carefully studied our claims and supporting evidence,’ says Sennheiser Director of Spectrum & Innovation, Joe Ciaudelli. ‘WMAS will revolutionise the professional audio industry as well as fulfil the Commission’s goals of greater spectrum efficiency and sharing compatibility.’

‘We applaud the FCC for its adoption of WMAS technology,’ says Head of Spectrum Policy and Standards, Dr Andreas Wilzeck. ‘In particular, the alignment with EN 300 422, which was developed by ETSI, is a milestone for manufacturers and users of wireless microphones and in-ear monitors (IEMs). It is an important signal for the harmonisation of regulatory conditions for these important global applications.’

Today, conventional wireless microphones are narrowband, – limited to an RF bandwidth of 200kHz. Each audio channel uses a dedicated, mono-directional transmitter-receiver pair tuned to a unique RF carrier. Each transmitter continuously outputs power, typically 50mW, which raises the RF noise floor with each channel that’s added to the configuration. These multiple carriers are also prone to generating non-harmonic distortion products, known as intermodulation (IM), which can interfere with wanted signals.

The benefits of WMAS technology are accomplished by multiplexing audio channels onto a wideband RF channel, which is 6MHz for the US in the case of Sennheiser’s WMAS technology. In this space, portable bidirectional transceivers will be able to communicate with a base station at an extremely low power spectral density. This will provide superior protection to nearby operators of other wireless devices.

Since WMAS uses a single RF carrier, the possibility of IM products is eliminated. For the first time, in-ear monitor channels will be able to use, in parallel, the same block of RF spectrum as wireless microphones, further enhancing spectral efficiency.

‘For years customers have been asking for a single pack that is both a transmitter and an in-ear monitor receiver,’ Ciaudelli says. ‘This will finally become possible with Sennheiser’s WMAS.’

See also: 
Interview: Sennheiser WMAS