In this article, we consider the construction decisions taken in a dizi and explain how they affect the intonation of the instrument.
The dizi is often made of the culm (``stem'') of either bitter bamboo or purple bamboo.
Bitter bamboo (pleioblastus amarus) tends to be tan in colour and have a smooth finish, while purple bamboo (phyllostachys nigra) tends to be darker and have more prominent nodes (the joints between the longish segments).
There are other materials in which the dizi may be made of (mahogany, titanium, stainless steel to name a few), but they tend to be pricey for the amateur player. The metal versions also have a tendency to be less likely to be in tune due to the laziness of many manufacturers to tune each stamped out instrument---tuning the dizi involves carefully shaping the tone holes (校音 or xiaoyin), an extremely hard task when the material is a metal.
Tonally, the bitter bamboo is said to carry a tuning more stably than that of the purple bamboo. But the purple bamboo is said to be brighter and sharper in tone. Bitter bamboo also tends to be slightly cheaper than purple bamboo.
The density of the bamboo is an important factor on the sound quality.
Look for dizi that has some heft in it without having a very thick wall. Flick a fingernail on the walls of the dizi and listen to the sound produced. It should sound bright, like striking a porcelain bowl, instead of a dull thud sound. A dull thud may indicate that the bamboo is not dense enough, or that it has a crack in it, both of which aren't good indications.
Traditionally, it has been said that a single continuous bamboo dizi has a better overall sound quality since there is no medium change that will affect the propagation of the acoustic waves.
However, such dizi run a serious risk of being hard to tame in terms of intonation, and in the modern context of dizi playing, intonation is of prime importance.
Most dizi tend to come in two halves with a tenon (接铜 or jietong) to join the head joint and the body. Tenons tend to be made of either copper (reddish brown), brass (yellowish tinge), or white brass (silvery tinge).
The fit of the tenon should be snug and firm but not stuck---with a little bit of torque while holding the head joint and the body with a hand each, it should be possible to slide the tenon in and out gradually without the tell-tale stop-and-go high friction feel that comes from a badly constructed/maintained tenon.
It is also important that the head joint and body of the dizi should not be rocking or jiggling when connected by the tenon.
Single Inserted Tenon Joint
An early design for the tenon is commonly called the ``single inserted tenon'' (单插接铜 or dancha jietong). On one end (usually the head joint), an extruded copper pipe is fitted tight in the bore of the bamboo, while on the other end (often the body), a slightly larger diameter copper pipe is fitted tight and flush with it, acting as the socket to the extruded tenon.
While this early design is still prevalent in the cheapest dizi, it is not commonly seen for good quality dizi made recently. Stability is often an issue with the tenon-socket joint since the tenon is often not as thick or durable as the ones seen in the concert flute.
It is also common for the tenon or socket to experience oxidation to the point where it causes the whole joint to seize up.
Double Inserted Tenon Joint
A more durable design came about that reinforced the tenon with an external tubing, converting the original tenon into a part of a wall-based socket. This is commonly called the ``double inserted tenon'' (双插接铜 or shuangcha jietong). A corresponding reinforcement of the exterior circumference of the original socket is done to enable a smoother metal-to-metal contact for slipping the wall-based socket (usually the head joint) onto the wall-based tenon (usually the body).
The design lends an air of elegance to the dizi since the external metal piping ``hides'' the joint behind what appears to be a smooth and unbroken extension of the bamboo. It also stabilises the joint due to the increased number of contact surfaces.