Anatomically, the erhu has a vertical post without a fingerboard which goes through the sides of the resonator at the base. This resonator, made or various woods, is covered with python-skin which gives this instrument its unique "whining" tone color. Said to be the closest instrument in sound to the human voice, its tone is mellow and expressive. The player usually sits, resting the erhu on one leg, pulling the horse hair bow horizontally between the two vertical strings. The bow is never played outside the strings.
The erhu's range is about three octaves. Its two strings are typically tuned a fifth apart to d and a, but can also be tuned much lower. In the Chinese orchestra, modeled loosely on the Western orchestra, erhu are divided into first and second erhu. A "piccolo" version of the erhu, traditionally used in opera from Guangzhou (Canton), is called the panhu or yuehu and is usually tuned about one octave higher than the erhu to g and d. Only one is used in the Chinese orchestra and it is played by the principal erhu player when required. The gaohu sounds a fourth higher than the erhu, while the zhonghu, available in three sizes, plays the role of the viola. In some Chinese orchestras, such as in Malaysia, the bass parts are often played by the western cello and double bass. The modern Chinese versions, the gehu and the beidagehu are used in others.
Another relation to the erhu is the jinghu, the main accompaniment to singing in Beijing opera. It is similar in structure to the erhu but has a quite different character due to its smaller size and the fact that it is made of bamboo (traditionally a variety found in Fujian province). Despite its small size and lightweight characteristics the sound is loud and piercing. There are almost an endless list of erhu relations not only in China such as the zhuiqin, datong, "horse bone" hu, but as mentioned in Korea, the hyegûm, in Japan, the kokyu, the Mongolian morin khuur, and in India and all over Central Asia and the Middle East, relations can be found.
Text compiled loosely from the following sites: http://www.clarionmusic.com/instruments/silk/silk.html --Text Copyright (C) 1996 By Michael Santoro. All Rights Reserved Site Copyright (C) 1996, Clarion Music Center; http://power.beijing.cn.net/bikeserver/CultureC/CultureC10; http://www.music.upm.edu.my/malaysia/instruments/erhu.html - (Tan 1983). Copyright © 1997 Minni Ang; http://www.hku.hk/linguist/staff/huqin.html; http://www.students.uiuc.edu/~kejimli/erhu.html