Guqin goose foot acoustic boundary control structure and method of using same

Abstract

The application discloses a guqin goose foot acoustic boundary control structure and a use method thereof, and belongs to the technical field of accessories of national musical instruments. The structure is provided with a silica gel elastic contact part at the bottom of a goose foot body, the contact part is in the form of a spherical cap protrusion facing the direction of a table, the Shore A hardness of the contact part is 40-60, the diameter of the bottom surface of the spherical cap is 15-20 mm, the protrusion height is 3-5 mm, the compression rate under the single foot load of 5-10 N of the guqin is 20%-30%, and the acoustic impedance is 1.5-3.0 MRayl. The acoustic impedance mismatch between the contact part and the goose foot body and the table is utilized to make the middle and high frequency overtones of the guqin body partially reflected back to the guqin body at the interface, so that the overtone energy leakage is reduced. The actually measured sound pressure level is increased by 2.1 dB at 2-4 kHz, increased by 3.4 dB at 4-8 kHz, and the reverberation time is prolonged by 20%.

Description

Technical Field

[0001] This invention relates to the field of ethnic musical instrument accessories technology, and in particular to an acoustic boundary control structure for the "goose foot" of the guqin and its usage method. Background Technology

[0002] When playing the guqin, the goose feet make direct contact with the qin table. Traditionally, the bottom of the goose feet is made of hard wood or jade, forming a rigid surface contact with the wooden qin table. The acoustic impedance of the contact surfaces is close, causing a large amount of the vibration energy of the qin body (especially the mid-to-high frequency overtones) to leak to the qin table, resulting in a dry tone and insufficient resonance.

[0003] In existing technologies, the pads placed between the guqin and the table are all designed for anti-slip purposes. Chinese Utility Model Patent CN202120895165.5 (Yangzhou Jinyun Musical Instrument Co., Ltd., 2021) discloses a silicone anti-slip pad for the guqin, comprising a rectangular silicone pad body. Two sides of the pad body contact the tabletop and the bottom of the guqin, respectively, and the surface is treated with an anti-slip coating to increase friction. The design purpose of this anti-slip pad is to prevent slipping and avoid wear and sticking to the guqin; it does not address acoustic performance, nor does it limit parameters such as the hardness or dimensions of the silicone.

[0004] In the field of audio engineering, there are hemispherical silicone isolation feet, such as the Hudson HiFi Platinum Silicone Feet (approximately 31.75mm in diameter and height, Shore A hardness 20, for audio equipment weighing 2.3-8.2kg). These products typically have a diameter of 20-50mm and a height of 20-40mm, designed for vibration isolation, i.e., reducing the transmission of equipment vibration to the support surface through damping energy dissipation. However, their hardness, size, and load capacity are incompatible with the operating conditions of the guqin's foot (a type of zither). Actual testing has shown that directly applying these products to the guqin's foot actually degrades the guqin's acoustic performance (see Example 2 in this manual for details).

[0005] In the field of stringed instruments, there are also support interface technologies aimed at improving tone. For example, the violin chin rest pad system disclosed in US Patent 6,927,328 is designed to minimize damping of vibrations; cello tailpiece anti-slip products (such as "Sound Anchor") claim to have acoustic designs that improve tone. The interfaces of the above solutions are the human-body or tailpiece-floor interface. The idea is to passively reduce vibration loss by reducing contact or damping. None of these solutions provide parameterized limits on the material hardness, geometry, compressibility, and acoustic impedance of the support interface, nor do they establish design specifications for frequency-domain selective reflection. Their application objects and load conditions are also substantially different from the interface of the guqin's foot-table.

[0006] In summary, none of the existing technologies have provided a technical solution for reducing mid-to-high frequency overtone leakage by constructing an impedance mismatch interface using a parametrically designed low-stiffness elastomer at the guqin's foot-table support interface. Summary of the Invention

[0007] To address the shortcomings of the existing technology, the present invention aims to provide an acoustic boundary control structure for the guqin's "goose feet" and its usage method. By setting a spherical crown-shaped silicone elastic contact part with specific hardness, geometric dimensions, and compression ratio at the bottom of the "goose feet," the low-stiffness interface impedance mismatch effect is utilized to partially reflect the 2-8kHz mid-to-high frequency overtones of the guqin body back to the guqin body at the support interface, reducing the leakage of overtone energy to the guqin table and improving the resonance quality of the guqin body.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: An acoustic boundary control structure for the "goose foot" (a type of guqin) includes a goose foot body and a silicone elastic contact part disposed at the bottom of the goose foot body. The silicone elastic contact part is a spherical crown-shaped protrusion facing the guqin table, with a Shore A hardness of 40-60, a bottom diameter of 15-20 mm, and a protrusion height of 3-5 mm. The silicone elastic contact part has a compression rate of 20%-30% when subjected to a normal static load of 5-10 N. The acoustic impedance of the silicone elastic contact part is 1.5-3.0 MRayl.

[0009] Preferably, the silicone material is addition-cured liquid silicone rubber (LSR) or high-temperature vulcanized silicone rubber (HTV), with a resilience of not less than 60%.

[0010] Preferably, the material of the goose foot body is sandalwood, rosewood, or jade.

[0011] Preferably, the bottom of the goose-foot body is provided with a circular nesting groove, and the silicone elastic contact part is bonded to the nesting groove by silicone adhesive or mechanically nested and fixed in the nesting groove; the inner diameter of the nesting groove is adapted to the diameter of the bottom surface of the spherical crown.

[0012] Preferably, the outer surface of the spherical crown protrusion of the silicone elastic contact part is provided with radial microgrooves, the groove depth is 0.2-0.5mm and the width is 0.3-0.8mm, which are used to enhance friction and moisture removal.

[0013] Accordingly, the present invention also provides a method for controlling the acoustic boundary of the guqin's "goose foot" (a type of zither), comprising the following steps: S1: Based on the guqin's weight of 2-3 kg, the material of the guqin table, and the target frequency band of 2-8 kHz, select a silicone elastic contact part with a Shore A hardness of 40-60, a dome bottom diameter of 15-20 mm, and a protrusion height of 3-5 mm, so that its compression rate is 20%-30% under a single-foot load of 5-10 N on the guqin; S2: Fix the silicone elastic contact part to the bottom of the goose foot body with a pre-compression amount of 0.5-1.5 mm; S3: Place the guqin on the guqin table, so that the silicone elastic contact part forms elastic contact with the surface of the guqin table; S4: During the performance, utilize the acoustic impedance mismatch between the silicone elastic contact part, the goose foot body, and the guqin table to partially reflect the 2-8 kHz mid-to-high frequency overtones back to the guqin body at the interface, reducing the leakage of overtone energy to the guqin table.

[0014] Preferably, the hardness of the silicone is selected according to the material of the piano table: Shore A 50-60 is selected for hard mahogany piano tables; Shore A 40-50 is selected for soft cedar piano tables; and Shore A 55-60 is selected for lacquered piano tables.

[0015] Preferably, the silicone elastic contact portion is replaced after 6-12 months of use to maintain a stable elastic modulus.

[0016] The basis for limiting the Shore A hardness to 40-60 is as follows: When the hardness is below 40, the storage modulus G' of silicone is less than 0.3 MPa. Under the conditions of a single-leg load of 5-10 N and a contact area of ​​about 2-4 cm² (corresponding to a compressive stress of about 12.5-50 kPa on the contact surface), the compression ratio exceeds 50%, entering the high-strain densification region. The equivalent stiffness increases sharply, the low impedance characteristics are lost, and the support stability is insufficient. As the hardness increases, the storage modulus and characteristic impedance of silicone increase accordingly, the impedance mismatch with wood decreases, and the reflection coefficient decreases accordingly. When the hardness reaches 70, the characteristic impedance ρc increases to 0.18 × 10⁻⁶. 6 The above is related to wood (1.5×10). 6 As the impedance mismatch M decreases from 10 to below 8, the reflection coefficient |R|² decreases from 0.67 to 0.58, and the acoustic boundary effect is significantly reduced. Considering both the amplitude of the effect and the engineering margin, the upper limit of stiffness is determined to be 60. Therefore, Shore A 40-60 is the preferred window for acoustic boundary effects: below 40, stability fails, and near 70, the acoustic effect is significantly reduced.

[0017] The rationale for limiting the diameter of the dome's base to 15-20mm is as follows: a diameter less than 15mm results in excessive stress concentration, making the silicone prone to tearing; a diameter greater than 20mm results in excessively high equivalent stiffness, limiting dynamic response and potentially exceeding the installation space at the bottom of the feet. The rationale for limiting the protrusion height to 3-5mm is as follows: a height less than 3mm results in excessively high equivalent stiffness, making the silicone layer resemble a rigid gasket; a height greater than 5mm causes the instrument to be raised too much, affecting the player's fingering posture, and increasing internal dissipation within the silicone layer, reducing energy efficiency.

[0018] Actual measurements show that, after adopting the structure of this invention, the sound pressure level of the guqin in the 2-4kHz frequency band is increased by 2.1dB, the sound pressure level in the 4-8kHz frequency band is increased by 3.4dB, the reverberation time in the 2-8kHz frequency band is extended by 20%, and the acceleration of the goose foot vibration is reduced by 8.5dB (see Example 2 for details). Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the acoustic boundary control structure for the guqin (a seven-stringed zither) of the present invention. Figure 2 A schematic diagram of the mechanical structure of a cross-section of a goose-foot-silicone spherical cap-piano table; Figure 3 This is a schematic diagram of the acoustic boundary control principle (impedance mismatch reflection). Figure 4 A diagram illustrating the installation and usage of the goose-foot feet for the guqin. Figure 5 A comparison chart of sound pressure level changes in the 2-4kHz and 4-8kHz frequency bands under six support conditions (based on measured data).

[0020] In the diagram: 1-Goose foot body; 2-Silicone elastic contact part; 3-Nested groove; 4-Micro groove; 5-Qin table; 6-Guqin body. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below with reference to the accompanying drawings.

[0022]

Example 1: Standard Silicone Spherical Goose Feather

[0023] [Example 2: Control Experiment and Acoustic Performance Comparison] Experimental conditions: The same Zhongni-style guqin (soundboard made of cedar, backboard made of catalpa, silk strings, approximately 5 years old), a standard practice room (volume approximately 30m³, RT60 approximately 1.2s, background noise less than 30dBA, temperature 20±2°C, relative humidity 50%±10%). Measurement equipment: B&K 4191 free-field microphone (placed 1.0m in front of the instrument, at the same height as the soundboard), B&K 3560C multi-analyzer, Polytec PSV-500 laser Doppler vibrometer.

[0024] Six support conditions: A. Hard boundary: The goose feet are placed directly on a standard hardwood piano table (elm, density approximately 0.75g / cm³); B. Commercially available guqin silicone anti-slip mat (similar to CN202120895165.5, rectangular flat mat, Shore A 50, 2mm thick, smooth / rough surface); C. Audio hemispherical silicone feet (Shore A 20, diameter 31.75mm, height 31.75mm, for audio equipment); D. Rubber anti-slip mat (Shore A 70, diameter 20mm, thickness 4mm); E. Silicone spherical crown boundary: The goose feet are covered with the silicone elastic contact part of this application (Shore A 50, spherical crown bottom diameter 18mm, protrusion height 4mm); F. Magnetic repulsion load reduction composite boundary: The goose feet have built-in dual permanent magnets (N35, diameter 10mm×4mm, same pole self-repulsion) plus a silicone spherical crown (Shore A... 50, with a base diameter of 18mm and a protrusion height of 4mm.

[0025] The same performer (Master of Guqin with 15 years of playing experience) played excerpts from "Flowing Water," "Three Variations on Plum Blossom," and "Guangling San" in sequence, three times for each condition, 60 seconds each time, with a 5-minute rest between each performance to avoid fatigue. A microphone continuously recorded the sound pressure signal, and a laser vibrometer simultaneously scanned the vibration velocity field on the surface of the instrument. The results are shown in Table 1. Table 1. Comparison of acoustic performance under six support conditions (based on condition A) A. Hard boundary 0dB (baseline) 0dB (baseline) 0% (benchmark) 0dB (baseline) B. Commercially available silicone anti-slip mats +0.1dB -0.3dB -2% +0.5dB C. Speaker hemispherical feet -0.8dB -1.5dB -12% +4.8dB D. Rubber anti-slip mat -0.5dB -1.2dB -8% +3.2dB E. Silicone spherical crown of this application +2.1dB +3.4dB +20% -8.5dB F. Magnetic unloading composite boundary +2.8dB +4.1dB +26% -10.2dB Statistical tests (one-way ANOVA) showed significant differences among the six conditions in the 2-4kHz and 4-8kHz frequency bands (p<0.01). Post-hoc tests (Tukey HSD) showed that conditions E and F were significantly better than condition A (p<0.05), conditions C and D were significantly worse than condition A (p<0.05), and conditions B had no significant difference from condition A (p>0.05).

[0026] The acoustic effect of commercially available guqin silicone anti-slip pads (condition B) is almost indistinguishable from that of hard boundary pads (condition A) (2-4kHz +0.1dB, 4-8kHz -0.3dB), with a slight decrease in reverberation time (-2%). The reasons are: (1) its rectangular flat pad structure generates a large surface contact under the weight of the guqin, resulting in high equivalent stiffness and limited dynamic response; (2) its thickness is only 2mm, lower than the 3-5mm limit of this invention, and is close to a rigid pad; (3) its hardness is selected based on anti-slip requirements rather than acoustic optimization, and cannot form an effective gradient impedance layer. This comparison shows that not all combinations of "silicone + guqin" can produce acoustic boundary control effects. Only when the parameter window of the conditions described in this invention is met, such as spherical crown structure, Shore A 40-60 hardness, 15-20mm bottom diameter, 3-5mm protrusion height, and 20%-30% compression ratio, can significant reflection of mid-to-high frequency overtones be achieved.

[0027] The hemispherical silicone foot pads (condition C, Shore A 20, diameter 31.75mm, height 31.75mm) produced significant negative acoustic effects on the guqin (2-4kHz -0.8dB, 4-8kHz -1.5dB), and the acceleration of the goose foot vibration increased by 4.8dB. The reasons are: (1) The energy storage modulus of Shore A 20 silicone is only about 0.15MPa. Under a single foot load of 5-10N on the guqin, the compression rate exceeds 60%, entering the high strain densification zone, and the equivalent stiffness increases sharply; (2) Its diameter and height are much larger than the limits of this invention, resulting in excessive lifting of the guqin body, excessive equivalent mass, and change of the vibration mode of the guqin body; (3) Its design goal is to isolate the vibration of the audio equipment, dissipate the vibration energy of the instrument itself with high damping characteristics, and amplify the reverse transmission of floor vibration to the guqin body. This comparison shows that using the hemispherical silicone structure of the speaker damping pads for the feet of the guqin not only fails to produce an acoustic boundary control effect, but also causes acoustic degradation. Therefore, those skilled in the art will not gain any technical inspiration to use such products for the feet of the guqin.

[0028] The rubber anti-slip pad (condition D) has a significant negative impact on mid-to-high frequencies (-0.5 to -1.2 dB), with the goose foot vibration acceleration increasing by 3.2 dB. This indicates that the high damping characteristics not only dissipate the vibration energy of the instrument itself, but also amplify the reverse transmission of floor vibration to the instrument body.

[0029] [Example 3: Blind Auditory Experiment and Subjective Evaluation] Thirty-two participants (12 guqin players / music school teachers and 20 music enthusiasts) underwent double-blind ABX testing. All recordings were loudness normalized to ensure that the equivalent continuous sound pressure level (Leq) for the six conditions differed by less than 0.3 dB in the 1-8 kHz frequency band.

[0030] Results: The accuracy rates for distinguishing between A and E were 77.3% (p<0.01), A and F 83.1% (p<0.001), B and E 85.4% (p<0.001), C and E 91.7% (p<0.001), and D and E 89.1% (p<0.001). The Likert scale (9-point scale) showed that condition E had a 6.8 difference in overtone fullness compared to condition A (p<0.01), a 6.5 difference in sustain length compared to condition A (p<0.01), and an overall preference of 6.9 compared to condition A (p<0.01). Condition B showed no significant difference from condition A across all dimensions (p>0.05). Condition C was significantly worse than condition A across all dimensions (p<0.05). Multiple linear regression analysis (R²=0.91, p<0.001) showed that the overall preference was mainly determined by the 4-8 kHz sound pressure level (normalized β=0.52) and the 2-4 kHz reverberation time (β=0.31), with the vibration transmissibility contributing negatively (β=-0.24).

[0031] [Example 4: Compatibility with different piano table materials] Hardwood piano tables (density greater than 0.8g / cm³): Use Shore A 55-60 silicone rubber with a raised height of 4-5mm to balance coupling and reflection. Softwood piano tables (density less than 0.5g / cm³): Use Shore A 40-50 silicone rubber with a raised height of 3-4mm to avoid over-coupling. Lacquered piano tables (with a polyurethane lacquer coating): Use Shore A 55-60 silicone rubber with a raised height of 4mm. The lacquer itself increases contact rigidity, requiring slightly harder silicone rubber for compensation.

[0032] The acoustic principle behind the above material selection rules is as follows: the harder the piano table material, the higher the interface contact stiffness, requiring the use of higher-hardness silicone to maintain the contact area within the 20%-30% compression ratio range under load, preventing excessive compression of overly soft silicone into the high-strain densification zone under high-stiffness interface conditions; conversely, the softer the piano table material, the lower-hardness silicone needs to be selected to maintain the acoustic impedance gradient between the silicone and the piano table, preventing the silicone from becoming too hard and causing the interface to approach rigid contact. The target frequency band of 2-8kHz corresponds to the mid-to-high frequency overtone series. The combination of silicone hardness, bottom diameter, and protrusion height must ensure that the equivalent interface stiffness is lower than that of the foot and the piano table to form effective impedance mismatch reflection.

[0033] [Example 5: Replacement and Maintenance] After prolonged use (6-12 months), the silicone elastic contact part undergoes oxidation and permanent compression deformation, leading to an increase in elastic modulus, an acoustic impedance approaching that of wood, and a decrease in reflectivity. Regular replacement is recommended. When replacing, remove residual adhesive and re-bond a new silicone elastic contact part.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A guqin (a seven-stringed zither) acoustic boundary control structure for goose feet, comprising a goose foot body (1) and a silicone elastic contact portion (2) disposed at the bottom of the goose foot body (1), characterized in that: The silicone elastic contact part (2) is a spherical crown protrusion facing the piano table (5). The Shore A hardness of the silicone elastic contact part (2) is 40-60, the diameter of the bottom surface of the spherical crown is 15-20mm, and the height of the spherical crown protrusion is 3-5mm. The compression rate of the silicone elastic contact part (2) under a normal static load of 5-10N is 20%-30%. The acoustic impedance of the silicone elastic contact part (2) is 1.5-3.0MRayl.

2. The acoustic boundary control structure for the guqin (a seven-stringed zither) according to claim 1, characterized in that: The material of the silicone elastic contact part (2) is addition-cured liquid silicone rubber or high-temperature vulcanized silicone rubber, with a resilience of not less than 60%.

3. The acoustic boundary control structure for the guqin (a seven-stringed zither) according to claim 1, characterized in that: The material of the goose foot body (1) is sandalwood, rosewood or jade.

4. The acoustic boundary control structure for the guqin (a seven-stringed zither) according to claim 1, characterized in that: The bottom of the goose foot body (1) is provided with a circular nesting groove (3). The silicone elastic contact part (2) is bonded to the nesting groove (3) by silicone adhesive or mechanically nested and fixed in the nesting groove (3). The inner diameter of the nesting groove (3) is adapted to the diameter of the bottom surface of the spherical crown.

5. The acoustic boundary control structure for the guqin (a seven-stringed zither) according to claim 1, characterized in that: The outer surface of the spherical crown protrusion of the silicone elastic contact part (2) is provided with radial microgrooves (4), the depth of the microgrooves (4) is 0.2-0.5mm and the width is 0.3-0.8mm.

6. A method for controlling the acoustic boundary of the "wild goose foot" pattern on a guqin (a seven-stringed zither), employing the acoustic boundary control structure for the "wild goose foot" pattern as described in any one of claims 1-5, characterized in that... Includes the following steps: S1: Based on the weight of the guqin (2-3kg), the material of the guqin table (5), and the target frequency band (2-8kHz), select a silicone elastic contact part (2) with a Shore A hardness of 40-60, a spherical crown bottom diameter of 15-20mm, and a protrusion height of 3-5mm, so that the compression rate of the silicone elastic contact part (2) under the single-leg load of 5-10N on the guqin is 20%-30%; S2: Fix the silicone elastic contact part (2) to the bottom of the goose foot body (1) with a pre-compression amount of 0.5-1.5mm; S3: Place the guqin on the qin table (5) so that the silicone elastic contact part (2) forms an elastic contact with the surface of the qin table (5); S4: During the performance, the acoustic impedance mismatch between the silicone elastic contact part (2), the goose foot body (1), and the piano table (5) is utilized to cause the 2-8kHz mid-to-high frequency overtones to be partially reflected back to the piano body at the interface of the silicone elastic contact part (2), thereby reducing the leakage of overtone energy to the piano table (5).

7. The acoustic boundary control method for the guqin (a seven-stringed zither) according to claim 6, characterized in that: In step S1, the Shore A hardness of the silicone elastic contact part (2) is selected according to the material of the piano table (5): Shore A 50-60 is selected for hard mahogany piano tables; Shore A 40-50 is selected for soft cedar piano tables; and Shore A 55-60 is selected for lacquered piano tables.

8. The acoustic boundary control method for the "wild goose foot" pattern of the guqin according to claim 6, characterized in that: The acoustic impedance of the silicone elastic contact part (2) is 1.5-3.0 MNayl, and the resilience is not less than 60%.

9. The acoustic boundary control method for the "wild goose foot" pattern of the guqin according to claim 6, characterized in that: The silicone elastic contact part (2) should be replaced after 6-12 months of use to maintain its elastic modulus stability.

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