Polyester Guqin String Trial #18

This trial is my second trial attempt, and first successful string trial, for a twisted core synthetic polyester guqin string #6. My first attempt at this string, trial #17, attempted to utilize the same string parameters as in Trial #16 for a polyester string #7, with an increase of total thread count from 30 to 36. However, through my trials and experiments, I have found that for this particular method of manufacture with these materials, to optimize the string for increased twist number and twisting tension, as the thread count increases, the number of twists needs to decrease, otherwise the string will break during the primary twisting phase. Like my string #7 trials for both nylon and polyester, it also follows the pattern for string #6 that polyester exhibits a brighter tone than nylon, with a decreased overall diameter for equivalent thread count and thread of the same diameter, as well as a stiffer string with less stretch, and higher density.

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: 1950

Twist Angle (degrees): 45

Substrand Twist Direction: Clockwise

String Twist Direction: Clockwise

Primary Twisting Tension: 3lbs

Secondary Twisting Tension: 5lbs

Starting Length (in.): 120″

Ending Length (in.): n/a


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.