Chest voice, also called chest register, is the vocal register that corresponds to the natural speaking voice, that is, the natural disposition or mode of the vocal folds when they are at their thickest. Chest voice is characterized by mellowness, richness of tone, and darker vowel qualities, sometimes accompanied by a distinct sensation of vibration in the chest, especially in the sternum and breastbone area. However, the term is really a misnomer because an effective resonating chamber is a hollow place surrounded by hard surfaces, (such as bone), and the chest is too full of organs to be suitable for amplifying the singing tone. Since resonance occurs where there is plenty of empty space for amplification of the lower vibrations created by the vocal folds, what singers may associate with chest resonance is actually sympathetic vibration; that is, vibrations being conducted through the bones of the chest cavity. Not all singers experience sympathetic vibrations in the chest when singing in this register; some only feel it when their hands are placed on their chests.
In terms of what is happening with the vocal folds, chest voice is produced when the singer contracts both the cricothyroid (CT) and thyroarytenoid (TA) muscles at the same time, but the TA is more active, thus tending to shorten the folds and produce a lower pitch range. The fundamental frequency and lower overtones are stronger than higher overtones in chest voice, and a large amount of the vocal fold tissue is in vibration. In addition, the vocal folds are usually closed through more than half of each cycle of vibration. Compare with head voice.