Polyester Guqin String Trial #22

This string trial, at this point, is the current final and best iteration for my experimental twisted core polyester guqin strings for a polyester guqin string #6. This particular set of qin strings took a surprising amount of iterations compared with some of the other trials. Each trial slightly increased a couple of parameters, mainly twist number and twist weights, to try to bring it to the maximum for these numbers just before the breaking point of the string (during the primary twisting phase.) Since this string is thicker than string 7, it is much easier to experiment on and push further without breaking. Looking at the harmonic analysis data across all of these iterations, there are only very minute, subtle changes, but overall, I have gotten the process down to a point where I can accurately reproduce the same type of string for nylon and polyester strings 5, 6, and 7 extremely consistently. Once all of the major parameters are known, then it is just a matter of experience and practice. This particular string works well for string #6, and is slightly brighter in tone and physically thinner than its nylon counterpart. This iteration for this polyester guqin string will be used as a core for thicker strings when I start experimenting on making thicker overwrapped strings for the qin.

Included in this page are all of the major string parameters that I have obtained so far for this string, as well as all relevant data I have collected and analyzed for this string, including harmonic content data, spectrograms, and autocorrelation graphs. You can enlarge the images by clicking on the thumbnails.


Material: Polyester

Thread: Barbook’s Weaverbird Polyester #15 Brown

Thread Diameter (in.): 0.0048″

Theoretical Calculated Twisted Substrand Diameter (in.): 0.0199″

Theoretical Calculated Twisted Total Diameter (in.): 0.043″

Thread Strength: 1.5lbs

# of Substrands: 3

# of Threads per Substrand: 12

Total Thread Count: 36

# of Primary Twists: 2025

Twist Angle (degrees): 45

Substrand Twist Direction: Clockwise

String Twist Direction: Clockwise

Primary Twisting Tension: 7lbs

Secondary Twisting Tension: 7lbs

Starting Length (in.): 120″

Ending Length (in.): 98.5


1. Linear Spectrum Harmonic Content Graphs


2. Autocorrelation


3. Spectrograms (Window 4096)


4. Spectrograms (Window 2048)


5. Spectrograms (Window 512)


  1. Linear Spectrum Harmonic Content Graphs – Shows the harmonic content of each string, graphed along the linear spectrum in terms of frequency to intensity. A very accurate way to easily visualize the harmonics and overtones of each string.
  2. Autocorrelation – Shows the periodic nature or trends from a given set of data. Autocorrelation can provide a unique look at data, and can reveal repeating patterns from seemingly random datapoints. For this application, it is derived from the original signal and more clearly shows the decaying oscillatory nature of the plucked string.
  3. Spectrograms (Window 4096) – Shows the spectrogram of each string, with a window setting of 4096. This setting allows one to clearly view all of the harmonics by showing the frequency, intensity, and duration of each harmonic. This graph can be most easily cross-correlated to the linear spectrum harmonic content graphs to compare durations and intensities of harmonics in a string.
  4. Spectrograms (Window 2048) –  Shows the spectrogram of each string, with a window setting of 2048. For this application, I have found that this setting is ideal in viewing the oscillatory instabilities of the guqin string more clearly, which cannot be seen as well in higher window settings. These are seen as wavering lines, which are most noticeably present in the mid-upper harmonics.
  5. Spectrograms (Window 512) – Shows the spectrogram of each string, with a window setting of 512. For this application, I have found that this setting, while having the lowest frequency band resolution of the three settings, allows one to zoom out on the entirety of the harmonic spectrum, and see how the overall power level and intensity shifts from one string to another, and where the harmonic content is overall most present for a given string.