02/09/2011 Wedemark

High-End goes wireless

With its RS 220 wireless headphones, audio specialist Sennheiser is opening up a new class of wireless listening enjoyment. Due to their uncompressed transmission technology, the digital headphones combine high-end quality with absolute freedom of movement.

"Reproducing music as naturally as possible and therefore as closely as possible to the original has always been the dream of audio engineers and audiophiles alike," explained Maurice Quarré, Director Product Lifecycle Management at Sennheiser Consumer Electronics. “The conventional means of transmission for reproduced sound is the cable. It conducts the analogue signal directly and with no delay from the audio source to the transducer in the headphones." The disadvantage of wired transmission, no matter how expensive the cable is, is that the listener’s freedom of movement is restricted.

In the high-end segment, Sennheiser is now offering the RS 220, the first wireless headphones model that fulfils the demands of the most discerning audiophile. “The Sennheiser RS 220 opens up a master class in wireless audio transmission," said Maurice Quarré. "It is a pioneer of wireless high-end headphones."

From infrared to uncompressed digital wireless transmission

As long ago as the mid-1970s, audio engineers began working on systems that can transfer sound even without cables. For licensing reasons, the first technology that was used for this purpose was transmission using an infrared signal. This type of transmission requires a direct visual link between the transmitter and the receiver. In 1993, Sennheiser presented the world's first infrared headphones with digital transmission, the IS 850. The system used PCM infrared transmission and also fulfilled the demanding requirements of classical music lovers.

The first wireless headphones were launched onto the market in Germany in 1995. They transmitted their analogue signals via radio waves instead of infrared light. For users, this meant that it was no longer necessary to maintain visual contact between the transmitter and the receiver, allowing them to move freely even in the next room without interrupting their enjoyment of the music.

In 2008, Sennheiser for the first time introduced a set of earphones with digital wireless transmission, the MX W1, which utilised Kleer™ technology to receive the audio data without compression. This avoidance of data compression ensures that transmission takes place without losses, with the added benefit that the system is extremely resistant to interference and has very low latency. “The great advantage of digital transmission is that there is no longer any signal noise, and the output of digital sound sources is transmitted with very low interference," explained Axel Grell, Senior Acoustical Engineer at Sennheiser. "This, however, requires sophisticated technology, as the system’s digital audio transmission utilises the 2.4 GHz frequency range, which is also used by mobile telephones, microwaves, WLAN and Bluetooth devices.”

Wireless transmission at the highest level

The transmitter for the new RS 220 wireless headphones also transmits the digital signals to the headphones without compression via a stable 2.4 GHz connection. The wireless system makes use of what is called Direct Sequence Spread Spectrum (DSSS) technology. "This is a frequency spreading process in which the output signal is spread to a width of 22 MHz by means of a specified bit sequence. If interference occurs at one point within this frequency range, the output signal experiences no interference, as the data are transmitted with redundancy, in other words, several times. As a result, the overall sound quality is fully maintained," explained Axel Grell. A further advantage of the process is its low latency.

Choice of input sources

“Due to our many years of experience, we are well familiar with the demands in the high-end segment," said Senior Acoustic Engineer Grell. "The RS 220 can be connected to various outputs: analogue, coaxial digital and optical digital. Discerning users can therefore decide themselves on the type and quality of the audio signal being fed in." If a digital input is used, for example, the conversion step from an analogue to a digital signal is no longer necessary. With an analogue input, the quality of the audio signal can be influenced by the choice of cable.

Loop-through mode

Several audio sources can be connected to the transmitter of the RS 220 at the same time. Signal loop-through is also possible, allowing the transmitter to be integrated into an existing connection between an audio source and a further device. In this loop-through mode, the signals are passed on even when the transmitter is switched off. Sensor buttons on the transmitter or directly on the headphones enable users to switch back and forth between the sources.

Dynamic range fully maintained

An important means of creating a musical effect is the gradual transition between quiet and loud passages, as can be heard, for example, in Ravel’s Bolero. Conventional digital data transmission sometimes reduces this dynamic range, as an optimum signal volume for the entire data package is often assigned to the information when the analogue signal is converted into a digital data package.

This challenge has been resolved in the further development of Sennheiser's wireless digital headphones system by completely dispensing with the automatic level control function. The data of the digital sources are transmitted unchanged, and the user can manually adjust the reference volume for the analogue inputs. The RS 220 therefore comes very close to the audiophile ideal: a lifelike, completely unrestricted sound experience.

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Mareike Oer

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