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Infrared light (IR) is used throughout the world for remote controls of electronic devices such as televisions and hi-fi systems. Because infrared is accepted to have no known health risks and does not interfere with other devices, the use of infrared transmission is not limited. Typical distances of application are within a range of 1 to 50 m. The maximum distance depends partly on the technical properties of the IR radiator, such as output power and radiation angle, but also on the local conditions, such as external light sources, objects in or moving into the signal path or the varying orientation of the receiver or radiator. Systems using infrared transmission technology have to take these factors into account.

Typically, an infrared diode serves as the transmitter, which works at wavelengths of about 800 to 900 nanometers with a specific angular directivity. Theoretically, the receiver diode would be chosen in such a way that the maximum distance of speech transmission is only limited by the noise sources in relation to the signal strength received. In reality, infrared receivers are very sensitive to external disturbances such as light and reflective materials. Bright sunlight usually reduces the range, while artificial light may not affect it.

Figure 1 below shows the position of infrared light in the spectrum of electro-magnetic waves. In this definition, we speak of infrared for radiation at wavelengths of l > 770 nm. Since it is invisible light that is very close to the visible spectrum, infrared light has properties quite similar to the light visible to the human eye. It spreads evenly in all directions and is absorbed and reflected by obstacles or the walls of a room. Due to diffraction along edges and diffuse reflections, originally shaded areas can also be covered. Should the need arise, infrared relay stations can be installed in order to extend the distribution of the IR signal into spaces not directly covered.

 
Figure 1: Spectrum of electro-magnetic waves, note the small range that the human eye can actually see

Normally, an infrared radiator can only cover a limited area or small room. In order to achieve infrared wireless communication in many areas or rooms, a radiator can be placed in each area/room and a network of cables would then connect them. The distance between two radiators can be up to 40 m, but usually not more than 30 m is currently recommended.

Until now, the positioning of infrared radiators for audio transmission has been a matter of experience. In its manual, Sennheiser gives guidelines on how radiators should be mounted and directed. Furthermore, the manual recommends carrying out tests after installation. In complex rooms with complicated structures, this can reveal 

	areas where the noise is higher than the actual signal
	areas where the signal is much higher than necessary, which would be inefficient
	cancellations due to interference because of different signal travel times and cable lengths
	unconsidered effects of external light as well as reflections by walls and ceiling

Therefore, what is required is a tool that allows all the parameters of an infrared installation to be predicted. A simulation would have to take the following circumstances and conditions into account: 

	room configuration
	potential radiator locations
	areas where the infrared signal transmission is to be received
	data of suitable infrared equipment (for instance frequencies, output power and radiation pattern)
	intensity and type of interfering light sources
	reflection behavior of walls, ceiling and floor
	radiator connections and synchronization

The Sennheiser simulation tool EASE-IR 4.0 makes it possible to estimate these parameters and to verify the optimum selection of radiators. It also helps to avoid interference. The simulation helps to create installations that do not require any subsequent alterations.

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