Hi-Fi component loudspeakers
are the devices which interpret input signals and convert them into audible sound waves. Speakers are probably the most important part of any hi-fi system and it really is case of "you get what you pay for". A typical test for a speaker system would involve a qualitative analysis by the human ear of a wide variety of sound spectra; from the lowest frequency such as that produced by a 32' pipe organ rank, up to that of the highest notes produced by e.g. the human voice; a violin or a piccolo.
The average human ear is really only capable of 'hearing' frequencies in the range of 20Hz to 20,000Hz. In fact some of the lowest notes such as that produced by organ pipes are really more 'felt' than 'heard'. Some church organs have 64' pipes (an example is the 'Gravissima' at Worcester Cathedral) and these are designed principally to move air and resonate rather than to produce truly audible sound. In fact, just a 32' organ pipe generates sound at 16Hz which is below the 20Hz audible threshold.
Taking these factors into account, it may be readily understood that it requires loudspeakers of some quality to reproduce these frequencies faithfully and without distortion. The lower the frequency, the more air has to be displaced; and thus many hi-fi systems incorporate powered subwoofers to move air at the lower end of the frequency spectrum. These subwoofers use large and strong speaker cones. We're all familiar with speaker distortion - try listening to Widor's Toccata without a subwoofer and at best you'll hear some strained bass notes and at worst; with too much amplification, you'll 'blow' the speaker cones. The capability of a speaker is generally defined as its 'frequency response range'.
At the upper end of the sound spectrum, loudspeaker enclosures will incorporate mid-range speakers and 'tweeters'. These speakers comprise smaller cones that are more suitable for reproducing frequencies in the 10,000Hz - 20,000Hz spectrum.