Effect of dimo membrane on woodwinds (dizi)

World/Folk Flutes & Winds
1

I know I asked about dizi flutes in the other forum, but I had some more general questions about dimo membranes, and I figured here would be the best place to ask them.

My fiancee has a dizi flute, and I’m fascinated by it and have some questions. Is there a good resource that explains what a dimo actually does to the sound of a flute? Specifically, I’m wondering:

  1. How is the ideal placement of the dimo and its hole determined?

  2. Does the dimo simply vibrate and add “noise” to the sound of the flute, or does it somehow enhance the existing sound by adding/subtracting overtones?

  3. Which notes are most affected by the dimo? It seems to me that the lower notes are more affected than the higher notes. Is this the case? If so, the dimo would seem to even out the volume of the octaves a bit by making the lower octave stronger.

2

I actually made dizi for a bit, so I had a chance to mess around with some of the variable related to the dimo. I’m not an expert, but I’ll share my impressions.

Placement and size of the mo kong (the hole that the dimo covers) does seem to have some importance, but I got good results from a few variations, so I don’t think it’s super critical to follow an exact template. A serious, traditional maker might easily contradict that, however! In general, I made the mo kong about the size of one of the finger holes, and I placed it about midway between the embouchure hole and the topmost finger hole. It did occur to me that the chamber that is created by adding an extra hole in that location has the potential to mess with the tuning, but I didn’t really notice any problem.

The buzzing of the dimo is highly resonant, but I don’t know that it actually changes the harmonic profile of the flute. Never measured it, however–running the audio through a spectrum analyzer might be worthwhile (programs like Audacity have one built in). One can replace the dimo with a piece of tape for a non-buzzing evaluation.

The application of the dimo can have a significant effect on the sound you get. It’s a bit of an art form, actually, and takes some practice. There are probably YouTube videos demonstrating it, but my friend Ron Korb is a skilled dizi player and he showed me the ropes a bit, and the dimo is pretty fussy. When you get it on just right you really hear the difference.