Reproduction of sound in headphones or hearing protectors is essentially a trade-off between sound from the signal source, e.g. a cellphone, and environmental sounds. Acceptable signal to noise ratios and the useful noise level range for communication can be determined by already available measurement methods. The attenuation of surrounding noise, e.g. measured according to ISO 4869-1, can determine the signal to noise ratio, but also determine the detection threshold of surrounding sound. Speech intelligibility tests can determine the level of surrounding noise where communication with nearby people is possible. In between these limits, a product can be optimized for different situations. Examples of measured detection levels are presented and the in between performance to the speech intelligibility limit is discussed.
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