3.4. PROBLEM OF FREQUENCY RANGES

You can imagine for sure, that a railway engine for example cannot “oscillate” (to move to and for) ten times a second, while a leaf of a tree can do that easily. The difference between both is obviously their mass. This consideration shows: mechanical devices are very limited in the range of oscillations they can follow. This problem forces the designer of a communicationsystem first to find out what range of oscillations will be required within that system. From now on we will call the oscillations FREQUENCIES and the range required will be called the FREQUENCY SPECTRUM. During the last chapter we have been talking about the translation of sound into electric signals. When we are deciding which material should be used for the diaphragm. It is obviously very important to know the highest and the lowest frequency of sound. This frequency range is called SPECTRUM OF AUDIO FREQUENCIES. If we connect a loudspeaker to a Low-frequency-generator and if we listen to the sound produced by the speaker we will find, that we start to hear sound at a minimum frequency of about 50 Hz and most of us will not hear any sound anymore, if the frequency reaches values above 18 kHz. Therefore the audio frequency spectrum is defined as the range between 50 and 20 kHz.