A loudspeaker horn with a cosine on contour and a method of manufacturing the same

Abstract

The application discloses a hyperbolic cosine contour loudspeaker horn and a manufacturing method thereof. The horn body is made of carbon fiber composite material, the cross-sectional area is expanded along the axial direction according to a hyperbolic cosine function A(x)=A0·cosh²(mx); the inner wall is provided with a spiral flow guide groove, the pitch P and the expansion rate coefficient m satisfy P=k·π / m (k is 1, 2 or 3), the rotation direction is the same as the sound wave propagation direction, the groove depth and the groove width change along the axial direction in a gradient manner; the inner wall is provided with a gradient distribution damping coating along the axial direction, and the spiral flow guide groove can be filled with a gradient distribution damping filler. The manufacturing method comprises contour parameter calculation, three-dimensional modeling, carbon fiber composite material forming, spiral flow guide groove processing and gradient coating spraying, and acoustic performance testing. The application improves the impedance characteristics of the horn throat, suppresses the standing wave and wall vibration, and reduces the harmonic distortion.

Description

Technical Field

[0001] This invention relates to the field of electroacoustic technology, and more specifically to a high-frequency horn structure for a loudspeaker, and a method for manufacturing the horn structure. Background Technology

[0002] A loudspeaker horn is an acoustic waveguide structure used to improve the radiation efficiency and control the directivity of a loudspeaker. Its basic principle is to convert the high acoustic impedance at the throat of the driver head into a low acoustic impedance at the horn outlet by gradually expanding the cross-section, thereby achieving efficient coupling of acoustic energy with air. The cross-sectional expansion law (profile curve) of the horn is the core factor determining its acoustic performance.

[0003] In the prior art, the main horn profile types include: exponential horns, whose cross-sectional area expands according to the law A(x)=A0·e^(mx), have a clear low-frequency cutoff frequency, but have a throat impedance abrupt change near the cutoff frequency; conical horns, whose cross-sectional area expands according to the law A(x)=A0·(1+kx)², have no clear cutoff frequency, have good low-frequency extension but low radiation efficiency, and poor high-frequency directivity; and Tractrix horns, which are based on the design of isotangent curves and have good wavefront consistency at the exit, but have complex profile processing.

[0004] Hyperbolic horn families have been discussed in mathematical literature. In the 1940s, Salmon proposed a generalized hyperbolic function formula for the horn cross-section: S(x) = πR0²[cosh(ax) + T·sinh(ax)]² (see US Patent US2338262), where T=0 represents a catenoidal horn. The hyperbolic cosine horn exhibits zero expansion at the throat and accelerated expansion in the middle and later sections, but its engineering applications are relatively limited.

[0005] In terms of engineering products, B&C Speakers' ME10 horn features a hyperbolic cosine profile, a throat diameter of 25.4 mm, a nominal coverage angle of 90° × 60°, a cutoff frequency of 1.5 kHz, and is injection molded from ABS plastic without any internal flow channels. Most existing commercial horns are made of aluminum alloy or plastic, and lack internal flow channels or damping structures.

[0006] Regarding the geometry of the horn's inner wall, US Patent 7686129 (Klipsch) discloses a structure with raised geometric shapes on the inner wall of the horn. These raised shapes are discretely distributed, with the surface area of ​​the central region larger than that near the throat and outlet, used to change the local expansion rate of the horn. US Patent 4685532 (Electro-Voice) discloses a structure with blades inside the horn throat, dividing the throat into several smaller pseudo-horns. US Patent 6059069 (Peavey) discloses a quadratic curve throat waveguide with straight and curved wall sections. US Patent 20180054672 (Graber, US Patent Publication No. 10405087B2) discloses a radial acoustic loudspeaker assembly including multiple segmented spiral horns, the spiral structure forming the overall shape of the horn. In the field of bass-reflex speakers, prior art discloses a structure with continuous spiral grooves on the inner wall of the bass reflex tube for guiding airflow and reducing wind noise.

[0007] Regarding horn materials, the applicant's authorized Chinese patent CN108924699B discloses a carbon fiber composite horn device, which includes a carbon fiber inner layer, a foamed material middle layer, a shock-absorbing material, and a carbon fiber outer layer, suppressing the overall resonance of the horn wall through interlayer damping of the composite material.

[0008] However, existing technologies lack coordinated design between the horn's inner wall structure and its profile: the flow guidance and damping structure of the inner wall are designed independently, without forming a structured parametric coupling relationship; the smooth throat expansion and accelerated expansion characteristics of the hyperbolic cosine profile have not been fully utilized in conjunction with the inner wall structure. Therefore, how to further suppress axial standing waves, circumferential eddies, and wall panel vibrations in hyperbolic cosine profile horns through coordinated design of the inner wall structure and profile parameters is a technical problem that needs to be solved in this field. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a hyperbolic cosine profile loudspeaker horn and its manufacturing method. By combining the hyperbolic cosine profile with the carbon fiber composite horn body and the structured coupling design between the spiral guide groove and the profile expansion parameters, the throat impedance characteristics of the horn are improved, the low-frequency response is extended, the high-frequency directivity is optimized, and wall vibration is suppressed.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A hyperbolic cosine profile loudspeaker horn includes a throat, a horn body, and an outlet. The horn body is made of carbon fiber composite material, and its cross-sectional area expands axially according to the hyperbolic cosine function A(x) = A0·cosh²(mx), where A0 is the throat cross-sectional area, m is the expansion coefficient, and x is the axial distance from the throat. The expansion coefficient m satisfies m = 2π·f_c / c, where f_c is the target low-frequency cutoff frequency and c is the speed of sound. The inner wall of the horn body is provided with a helical guide groove, and the pitch P of the helical guide groove satisfies P = k·π / m with the expansion coefficient m, where k is 1. The direction of rotation of the spiral guide channel is the same as the direction of sound wave propagation from the throat to the outlet; the depth of the spiral guide channel varies gradually along the axial direction, with the throat region depth d_throat=0.8-1.5mm, the outlet region depth d_mouth=0.2-0.5mm, and the intermediate region depth gradually changing according to a linear or exponential law; the width of the spiral guide channel varies gradually along the axial direction, with the throat region width w_throat=1.0-2.0mm, the outlet region width w_mouth=2.0-4.0mm, and the intermediate region width gradually changing according to a linear or exponential law.

[0011] The mathematical relationship between the pitch P of the helical guide channel and the expansion coefficient m, P=k·π / m, is determined based on the following structural coordination mechanism: the cross-sectional area of ​​the hyperbolic cosine profile expands along the axial direction according to the law A(x)=A0·cosh²(mx), and its expansion rate dA / dx=2mA0·sinh(mx)·cosh(mx), exhibiting a periodic change in characteristic scale related to 1 / m; the axial displacement corresponding to each π radian (half a turn) of the helical guide channel is P / 2. When the pitch P is k·π / m (k is an integer of 1, 2 or 3), P / 2=k·π / (2m), which has a definite proportional relationship with the characteristic scale 1 / m of the profile expansion. The helical period of the helical channel matches the characteristic scale of the profile expansion, so that the guiding effect of the helical channel on the boundary layer is synchronized with the sound field change caused by the profile expansion, thereby suppressing the formation of axial standing waves.

[0012] The direction of rotation of the spiral guide channel is the same as the direction of sound wave propagation from the throat to the outlet. Its determination is based on the following structural coordination mechanism: when the sound wave propagates from the throat to the outlet along the horn axis, if the direction of rotation of the spiral guide channel is the same as the direction of sound wave propagation, the sound wave is guided in the same direction when it hits the spiral channel wall, the airflow in the channel is in the same direction as the mainstream, and the boundary layer eddies are guided and dissipated in an orderly manner; if the direction of rotation is opposite, the sound wave will generate a reverse collision at the channel wall, resulting in additional turbulent pulsation and phase distortion.

[0013] The determination of the gradient variation of the spiral guide channel depth along the axial direction is based on the following structural synergy mechanism: the expansion rate dA / dx of the hyperbolic cosine profile is zero at the throat (x=0), and increases monotonically with increasing x, i.e., the expansion accelerates in the middle and rear sections. In the throat region, the cross-sectional expansion is slow, the acoustic streamlines tend to be parallel, and the boundary layer easily separates to form vortices; a deeper channel can provide stronger vortex guidance. In the outlet region, the cross-sectional expansion is fast, and the proportion of reflected acoustic energy is large; a shallower channel can reduce acoustic scattering.

[0014] The determination of the gradient variation of the spiral guide channel width along the axial direction is based on the following structural synergy mechanism: the cross-sectional radius r(x) = r0·cosh(mx) of the hyperbolic cosine horn is minimum at the throat and monotonically increases with x. In the throat region, a smaller cross-sectional radius and a narrower channel width can avoid excessive encroachment on the effective flow area, thus preventing acoustic scattering; in the outlet region, a larger cross-sectional radius and a wider channel width can enhance the vortex guiding effect.

[0015] Preferably, k=1, that is, P=π / m.

[0016] Preferably, the carbon fiber composite material adopts a multi-layer prepreg layup with alternating layup angles of 0° / ±45° / 90°, a total thickness of 2-8 mm, a density of 1400-1700 kg / m³, and an elastic modulus of 60-100 GPa; the inner wall of the horn body is provided with a damping coating, which is a polyurethane-ceramic composite coating with a loss factor tanδ≥0.3; the thickness t of the damping coating satisfies t=(0.5-1.0)·t0 with the thickness t0 of a single layer of prepreg in the carbon fiber composite material, and the total thickness of the ±45° layup accounts for 40%-60% of the total thickness of the horn body; and the damping coating is distributed in a gradient along the horn axis, with the coating thickness t_throat=(0.3-0.6)·t0 in the throat area, the coating thickness t_mouth=(1.0-1.5)·t0 in the outlet area, and the coating thickness in the middle area gradually changing according to a linear or exponential law.

[0017] The determination of the axial gradient distribution of the damping coating is based on the following structural synergy mechanism: the sound pressure is highest at the throat of the hyperbolic cosine horn, and the wall vibration is mainly in bending mode; a thinner coating can avoid mass load and maintain high-frequency response. The sound pressure is lower at the outlet, and the proportion of reflected sound energy is large; a thicker coating can fully absorb reflected sound energy. The depth gradient of the spiral guide channel and the damping coating gradient are matched in opposite directions along the axial direction: the throat region has a deep groove and a thin coating, while the outlet region has a shallow groove and a thick coating.

[0018] Preferably, the spiral guide channel is filled with damping filler, which consists of alumina or silicon carbide particles with a particle size of 10-100 μm. The filling height is 30%-70% of the channel depth, and the filling density varies gradually along the axial direction, with a filling density of 60%-80% in the throat region and 20%-40% in the outlet region. Furthermore, the particle size of the damping filler varies gradually along the axial direction, with a particle size D_throat of 60-100 μm in the throat region and D_mouth of 10-40 μm in the outlet region. The damping filler in the channel increases the contact area between the sound waves and the damping material, and the micro-vibration of the particles generates additional energy dissipation. The throat region has high sound pressure and high flow velocity, and larger particle sizes can enhance the micro-vibration amplitude and energy dissipation efficiency. The outlet region has low sound pressure and low flow velocity, and smaller particle sizes can enhance surface energy absorption.

[0019] Preferably, the throat has a rounded transition with a radius of 0.2-0.5 times the characteristic size of the throat; and the outlet has an edge flange with a flange height of 5-15mm and a flange angle of 15°-30°.

[0020] Preferably, the horn body is a rotationally symmetric structure or a linear sound source structure. The width of the linear sound source structure expands according to a hyperbolic cosine function, and the height expands constantly or slowly. A gradual transition section is provided between the throat and the compression drive head. The length of the transition section is 10-30mm, and the cross-section gradually changes from the shape of the drive head outlet to the shape of the horn throat. The transition curve is a circular arc or an elliptical arc.

[0021] This invention also provides a method for manufacturing a hyperbolic cosine profile loudspeaker horn, comprising the following steps: S1: Calculate the expansion coefficient m = 2π·f_c / c and the horn length L = (1 / m)·arccosh(√(A_mouth / A0)) based on the target low-frequency cutoff frequency f_c and the horn outlet area A_mouth; S2: Calculate the cross-sectional dimensions of each axial position of the horn according to A(x) = A0·cosh²(mx) to generate a three-dimensional CAD model; S3: Manufacture the horn body using a carbon fiber prepreg layup heated pressure molding process or a carbon fiber continuous fiber 3D printing process; S4: Process a spiral guide groove on the inner wall of the horn body according to the above parameter relationship and spray a gradient-distributed damping coating; S5: Connect the throat transition section to the compression drive head and measure the frequency response curve, directivity pattern, and total harmonic distortion of the horn.

[0022] Preferably, the autoclave molding process in step S3 includes: laying carbon fiber prepreg at angles of 0° / ±45° / 90° on the surface of the horn mold, with 6-16 layers and a thickness of 0.125-0.25mm for each layer; placing the mold after laying into a vacuum bag and then into an autoclave, curing it for 60-120 minutes at a temperature of 130-180°C and a pressure of 0.3-0.8MPa; and after demolding, grinding the inner wall until the surface roughness Ra≤3.2μm.

[0023] Preferably, the continuous carbon fiber 3D printing process in step S3 includes: using thermoplastic carbon fiber composite material as raw material, and stacking it layer by layer according to the CAD model of hyperbolic cosine contour through a continuous fiber 3D printing equipment. The printing parameters are: nozzle temperature 380-420°C, printing speed 10-30mm / s, and layer thickness 0.125-0.2mm. After printing, the inner wall is precision machined by five-axis CNC to Ra≤3.2μm, and the outer wall retains the printing texture to increase damping.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The hyperbolic cosine function A(x)=A0·cosh²(mx) is used as the horn profile. The cross-sectional expansion rate dA / dx=0 at the throat (x=0) is smooth, and the acoustic impedance changes smoothly, avoiding the impedance abrupt change of the exponential horn near the cutoff frequency. The frequency response curve has no dip near f_c. At the same time, as x increases, the growth rate of cosh²(mx) gradually exceeds that of the exponential function. The expansion of the middle and rear section of the horn is accelerated, which is conducive to the uniform radiation and directivity control of high frequency sound waves. Moreover, the horn length is shorter under the same exit area. (2) The carbon fiber composite horn body is 40%-50% lighter than the traditional aluminum horn, while its stiffness is increased. Combined with the inner wall damping coating, the vibration amplitude of the horn wall is significantly reduced. (3) The spiral guide groove pitch P and expansion coefficient m satisfy the structural coupling relationship P=k·π / m. Combined with the spiral direction consistency, groove depth gradient and groove width gradient, the guiding effect of the spiral guide groove on the boundary layer is synchronized with the acoustic field change caused by the contour expansion, and the axial standing wave and circumferential eddy current are effectively suppressed. (4) The matching relationship between the damping coating thickness t and the carbon fiber single layer thickness t0 is t=(0.5-1.0)·t0 and the limitation of ±45° layup ratio of 40%-60%, so that the damping coating and carbon fiber layup form a structural synergy; the gradient distribution of the coating along the axial direction matches the groove depth gradient in the opposite direction, avoiding excessive mass load in the high vibration area of ​​the throat and fully absorbing reflected sound energy in the outlet area; (5) The spiral guide channel is filled with damping filler and distributed along the axial gradient, which further increases the contact area between the sound wave and the damping material and the dissipation of particle micro-vibration, reducing wall vibration and sound staining. (6) The manufacturing method can be directly adapted to the existing carbon fiber composite material manufacturing process. It only requires customizing molds or CNC programs according to the hyperbolic cosine profile and processing according to the relationship P=k·π / m and the requirements of each gradient. The process has good feasibility. Attached Figure Description

[0025] Figure 1 This is a schematic axial cross-sectional view of the hyperbolic cosine profile loudspeaker horn of the present invention; Figure 2 Comparison of horn section expansion curves (hyperbolic cosine, exponential, conical); Figure 3 This is a schematic diagram comparing the throat impedance frequency characteristics of the hyperbolic cosine horn and the exponential horn of the present invention. Figure 4 This is a schematic diagram of the ply structure of the carbon fiber composite horn body of the present invention; Figure 5 This is a partially enlarged schematic diagram of the inner wall spiral guide groove of the present invention, showing the coupling relationship between the pitch P and the expansion coefficient m, the gradient change of groove depth, the gradient change of groove width, and the filling structure inside the groove; Figure 6 This is a flowchart of the manufacturing method of the present invention; Figure 7 This is a comparison chart of the frequency response curves of the present invention and the exponential horn. Figure 8 This is a comparison diagram of the directional patterns of the present invention and the index horn (10kHz horizontal plane). Figure 9 This is a cross-sectional schematic diagram showing the axial gradient distribution of the damping coating of the present invention.

[0026] In the figure: 1-throat, 2-horn body, 3-outlet, 4-spiral guide channel, 5-damping coating, 6-damping filler, 7-throat rounded transition, 8-outlet flange, 9-compression drive head, 21-carbon fiber layup. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention. All the following tests were conducted in an anechoic chamber conforming to GB / T 12060.5-2011 "Acoustic System Equipment - Part 5: Main Performance Test Methods for Loudspeakers" and IEC 60268-5 standards, with a background noise level in the anechoic chamber not exceeding 20 dB(A).

[0028] Example 1 This embodiment provides a rotationally symmetric hyperbolic cosine horn suitable for a 1-inch compression drive head.

[0029] Target parameters: Low-frequency cutoff frequency f_c=800Hz, throat diameter 25.4mm (1 inch), outlet diameter 200mm, horizontal / vertical coverage angle 90°×90°.

[0030] Calculation of hyperbolic cosine horn parameters: Expansion coefficient m = 2π·f_c / c = 2π×800 / 344 ≈ 14.6m⁻¹; Throat cross-sectional area A0 = π×(0.0127)² ≈ 5.07×10⁻ 4 m²; Exit cross-sectional area A_mouth=π×(0.1)²≈3.14×10⁻²m²; Horn length L=(1 / m)·arccosh(√(A_mouth / A0))=(1 / 14.6)·arccosh(√61.9)≈0.0685×2.75≈0.188m=188mm.

[0031] like Figure 1 As shown, the horn includes a throat 1, a horn body 2, and an outlet 3. The throat 1 is connected upstream to a compression drive head 9. Figure 2 As shown, the hyperbolic cosine profile has zero expansion at the throat, and the throat impedance is smooth. Figure 3 A rounded transition 7 is provided at the throat 1, with a rounded radius of 5mm (0.39 times the throat diameter); an edge flange 8 is provided at the outlet 3, with a flange height of 10mm and a flange angle of 20°.

[0032] The spiral guide groove has four parameters: Based on P=k·π / m, k=1, P=π / 14.6≈215mm; the horn length is 188mm, and the actual machining is 0.9 turns of continuous spiral groove. The groove depth varies gradually along the axial direction: in the throat region (x=0-30mm), the groove depth d_throat=0.8mm; in the middle region (x=30-120mm), it gradually changes from 0.8mm to 0.4mm according to a linear law; and in the outlet region (x=120-188mm), the groove depth d_mouth=0.3mm. The groove width varies gradually along the axial direction: in the throat region, the groove width w_throat=1.5mm; in the middle region, it gradually changes to 2.5mm; and in the outlet region, the groove width w_mouth=3.0mm. It is machined using five-axis CNC milling. The rotation direction is right-handed, the same as the direction of sound wave propagation from the throat to the outlet (clockwise when viewed from the throat end face). The structure of the spiral guide groove is as follows... Figure 5 As shown.

[0033] The spiral guide channel is filled with damping filler 6: particle size gradient distribution, with particle size D_throat=80μm in the throat region, linearly decreasing to 40μm in the middle region, and particle size D_mouth=20μm in the outlet region; the filling height is 50% of the channel depth; the filling density gradient is: 70% in the throat region, linearly decreasing to 35% in the middle region, and 30% in the outlet region. Filling process: Before spraying the damping coating, alumina particles and polyurethane matrix are mixed in a volume ratio of 1:1 to form a paste, which is injected into the spiral channel using a precision syringe. After curing, it is integrally formed with the coating.

[0034] like Figure 4 As shown, the horn body 2 is made of carbon fiber / epoxy resin composite material. The carbon fiber layup 21 has a layup scheme of 0° / 90° / +45° / -45° / -45° / +45° / 90° / 0° (a total of 8 layers, each layer is 0.2 mm, and the total thickness is 1.6 mm), with a single layer thickness t0=0.2 mm.

[0035] The damping coating 5 consists of a polyurethane matrix and alumina nanoparticles (50 nm in diameter, 20% by mass), with a loss factor tanδ = 0.35. The coating exhibits a gradient distribution along the axial direction: the thickness t_throat in the throat region is 0.1 mm = 0.5 t0, linearly decreasing to 0.2 mm in the middle region, and the thickness t_mouth in the outlet region is 0.2 mm = 1.0 t0. Figure 9 As shown. There are 4 layers with a ±45° ply, with a total thickness of 0.8mm, accounting for 50% of the total thickness of the horn body (1.6mm).

[0036] Manufacturing process such as Figure 6 As shown: S1-S2: Calculate and build a SolidWorks 3D model according to the above parameters; S3: Autoclave molding, lay-up on the surface of a steel male mold, vacuum bag sealing, curing at 150°C / 0.5MPa / 90min, and polish the inner wall to Ra=2.0μm after demolding; S4: Five-axis CNC machining of spiral guide grooves (P=215mm, k=1, right-handed), injection of alumina particle-polyurethane mixture paste, and spraying of damping coating according to gradient distribution; S5: Connect a 1-inch compression drive head and test in an anechoic chamber.

[0037] Measured results: The frequency response curve has a flatness of ±2dB within the range of 800Hz-20kHz. Figure 7 No frequency response dip at 800Hz; 90° horizontal coverage angle at 10kHz (-6dB) Figure 8 Vertical coverage angle 88°; THD (5kHz / 1W) 0.10%; total horn mass 0.45kg; axial sound pressure non-uniformity ±3%; horn wall vibration amplitude (Polytec PSV-500 laser vibration measurement, 5kHz / 1W) is 1 / 3 of that of aluminum index horns.

[0038] Example 2 This embodiment provides a hyperbolic cosine horn for a line sound source suitable for a line array system.

[0039] Target parameters: Low-frequency cutoff frequency f_c=600Hz, throat size 25mm×100mm (width×height), outlet size 300mm×100mm, horizontal coverage angle 120°, vertical coverage angle 10°.

[0040] The width (horizontal) of the line source horn expands according to a hyperbolic cosine function, while the height (vertical) remains constant at 100mm. The expansion coefficient in the width direction is m_width = 2π × 600 / 344 ≈ 10.95m⁻¹; the length in the width direction is L_width = (1 / 10.95)·arccosh(√(300 / 25)) ≈ 0.0913 × 1.97 ≈ 180mm.

[0041] Spiral guide groove parameters: k=2, P=2π / 10.95≈574mm; width direction length 180mm, actually machined as 0.35 continuous spiral grooves along the width direction. Groove depth gradient: 0.9mm in the throat region, 0.35mm in the outlet region, with a linear gradient in the middle; groove width gradient: 1.8mm in the throat region, 3.2mm in the outlet region, with a linear gradient in the middle; the rotation direction is right-handed.

[0042] Damping packing: Particle size gradient, 90μm in the throat region, 25μm in the outlet region, with a linear gradient in the middle; packing height is 60% of the tank depth; packing density gradient: 75% in the throat region, 25% in the outlet region, with a linear gradient in the middle.

[0043] The horn body is printed using continuous carbon fiber 3D printing (CF / PEEK) with a nozzle temperature of 400°C, a printing speed of 20mm / s, and a layer thickness of 0.2mm. After printing, the inner wall is precision machined to Ra=3.0μm using five-axis CNC, while the outer wall retains the printed texture.

[0044] Damping coating: polyurethane + alumina, with an axial gradient distribution: 0.15 mm thickness in the throat region (t0 = 0.2 mm, 0.75·t0), 0.25 mm thickness in the outlet region (1.25·t0), and a linear gradient in the middle; ±45° layup accounts for 50%.

[0045] Measured results: frequency response curve flatness ±2.5dB in the range of 600Hz-18kHz; horizontal coverage angle 120°±5° (-6dB), vertical coverage angle 10°±2°; THD (2kHz / 1W) 0.13%; total horn mass 1.2kg; axial sound pressure non-uniformity ±4%.

[0046] Example 3 This embodiment provides a rotationally symmetric hyperbolic cosine horn suitable for large cinema bass horns.

[0047] Target parameters: Low-frequency cutoff frequency f_c=250Hz, throat diameter 50mm (2 inches), outlet diameter 600mm, coverage angle 60°×60°.

[0048] The expansion coefficient m = 2π × 250 / 344 ≈ 4.57 m⁻¹; the horn length L = (1 / 4.57)·arccosh(12) ≈ 0.219 × 3.18 ≈ 696 mm.

[0049] Spiral guide groove parameters: k=1, P=π / 4.57≈687mm; horn length 696mm, actually machined as 1.0 continuous spiral groove. Groove depth gradient: 1.2mm in the throat region, 0.4mm in the outlet region, with a linear gradient in the middle; Groove width gradient: 2.0mm in the throat region, 4.0mm in the outlet region, with a linear gradient in the middle; Rotation direction is right-handed.

[0050] Damping packing: Particle size gradient, 100μm in the throat region, 30μm in the outlet region, with a linear gradient in the middle; packing height is 40% of the tank depth; packing density gradient: 80% in the throat region, 30% in the outlet region, with a linear gradient in the middle.

[0051] The horn body has a wall thickness of 4mm (16 layers of carbon fiber prepreg, each layer is 0.25mm, t0=0.25mm); the damping coating has a gradient distribution: the thickness in the throat area is 0.1mm (0.4·t0), the thickness in the outlet area is 0.3mm (1.2·t0), and the thickness gradually changes linearly in the middle; the ±45° layup accounts for 50%.

[0052] Actual test results: frequency response curve flatness ±3dB in the range of 250Hz-8kHz; no frequency response dip at 250Hz; THD (1kHz / 1W) 0.16%; total horn mass 4.5kg; axial sound pressure non-uniformity ±3.5%.

[0053] Comparative Example To verify the contribution of each structural feature of the present invention to the technical effect, the following comparative examples were set up, and the test conditions were the same as those in Example 1.

[0054] Comparative Example 1: Same throat size, outlet size, and target f_c as Example 1, but using a conventional exponential horn profile A(x) = A0·e^(mx), with a length of 283 mm (95 mm longer than Example 1); made of 6061-T6 aluminum, with a wall thickness of 2 mm and a weight of 0.85 kg; without spiral guide grooves or damping coating. Actual measurements: Frequency response dip of 7 dB at 800 Hz; horizontal coverage angle of 75° at 10 kHz; THD (5 kHz / 1W) of 0.8%; horn wall vibration amplitude 2.8 times that of Example 1; axial sound pressure non-uniformity ±16%.

[0055] Comparative Example 2: The same hyperbolic cosine profile as Example 1, but made of ABS plastic (injection molded) with a wall thickness of 3mm; without spiral guide grooves, carbon fiber lay-up, or damping coating. Actual measurements: Three resonant peaks (Q value > 10) appeared in the 2kHz-5kHz frequency band, with a peak-to-valley difference of 8dB; THD 1.5%; the horn wall vibration amplitude was 4.2 times that of Example 1.

[0056] Comparative Example 3: Same carbon fiber composite material, throat size, outlet size, and target f_c as Example 1, but with an exponential horn profile (length 283mm); the spiral guide channel was conventionally designed (pitch P=100mm, not satisfying P=k·π / m), with a channel depth of 0.5mm uniformly across the entire length and a channel width of 2.0mm uniformly across the entire length, without any infill. Actual measurements: frequency response dip of 6.5dB at 800Hz; horizontal coverage angle of 78° at 10kHz; THD 0.42%; axial sound pressure non-uniformity ±12%. Compared with Example 1, under the same material conditions, the hyperbolic cosine profile has a significant advantage over the exponential profile.

[0057] Comparative Example 4: Same hyperbolic cosine profile, throat dimensions, and f_c target as Example 1, but made of 6061-T6 aluminum (2mm wall thickness); the spiral guide groove was machined to P=π / m=215mm, with a uniform groove depth of 0.5mm and a uniform groove width of 2.0mm, right-handed, without groove filling or damping coating. Actual measurements: no depression at 800Hz; horizontal coverage angle of 88° at 10kHz; THD 0.55%; horn wall vibration amplitude 2.5 times that of Example 1; axial sound pressure non-uniformity ±8%. Comparison with Example 1 shows that, under the same profile conditions, carbon fiber composite material has significant advantages over aluminum.

[0058] Comparative Example 5: Same as Example 1, but with a spiral guide groove pitch P=5π / m=1075mm (k=5), groove depth of 0.5mm uniformly across the entire length, groove width of 2.0mm uniformly across the entire length, no groove filling, and a damping coating of 0.2mm uniform thickness across the entire length. Actual measurements: no depression at 800Hz; horizontal coverage angle of 89° at 10kHz; THD 0.32%; axial sound pressure non-uniformity ±10%. Compared with Example 1 (THD 0.10%, non-uniformity ±3%), it shows that the coupling relationship between pitch and expansion coefficient P=k·π / m (k=1,2,3) has a significant impact on the standing wave suppression effect.

[0059] Comparative Example 6: Same as Example 1, the spiral guide groove pitch P=π / m=215mm, but the spiral direction is opposite to the sound wave propagation direction (left-handed), the groove depth is 0.5mm uniformly throughout, the groove width is 2.0mm uniformly throughout, there is no filling inside the groove, and the damping coating has a uniform thickness of 0.2mm throughout. Actual measurements: no depression at 800Hz; horizontal coverage angle of 88° at 10kHz; THD 0.27%; axial sound pressure non-uniformity ±8%. When the spiral direction is reversed, the sound waves generate reverse collisions at the groove wall, resulting in additional turbulent pulsations and phase distortion.

[0060] Comparative Example 7: Similar to Example 1, the spiral guide groove P=π / m=215mm, right-handed, with a uniform depth of 0.5mm and a uniform width of 2.0mm throughout, without any filling inside the groove; however, the damping coating has a uniform thickness of 0.2mm throughout (non-gradient distribution). Actual measurements: no depression at 800Hz; sound pressure level at 15kHz 0.6dB lower than Example 1; THD 0.23%; axial sound pressure non-uniformity ±5%. The uniformly thick coating generates excessive mass load at the throat, suppressing the high-frequency response.

[0061] Comparative Example 8: Same as Example 1, but with discrete protrusion geometry (refer to US Patent US7686129) on the inner wall of the horn instead of a continuous spiral guide groove; the protrusions are hemispherical, 3 mm in diameter, 0.5 mm in height, spaced 15 mm apart axially, and 12 evenly distributed circumferentially, without groove filling. Actual measurements: Two resonance peaks (Q value ≈ 8) appeared at 2.5 kHz and 4.8 kHz, with a peak-to-valley difference of 4 dB; THD 0.48%; axial sound pressure non-uniformity ±11%.

[0062] Comparative Example 9: Same as Example 1, but with a three-blade structure (refer to US Patent US4685532) inside the horn throat, dividing the throat into three 120° fan-shaped regions. The blades are 5 mm high, 1 mm thick, and 30 mm axially long; there are no spiral guide grooves or groove filling. Actual measurements: A distinct resonance peak appears at 3.2 kHz (Q value ≈ 12), with a peak-to-valley difference of 6 dB; THD 0.52%; axial sound pressure non-uniformity ±13%.

[0063] Comparative Example 10: Same as Example 1, with a spiral guide groove P=π / m=215mm, right-handed; however, the damping coating thickness t=2.0mm (not satisfying t=(0.5-1.0)·t0), and the ±45° layup ratio adjusted to 20% (not satisfying 40%-60%); the groove depth is 0.5mm uniformly throughout the entire length, the groove width is 2.0mm uniformly throughout the entire length, and there is no filling inside the groove. Actual measurements: no depression at 800Hz; sound pressure level at 15kHz is 1.2dB lower than in Example 1; THD 0.35%; horn wall vibration amplitude is 1.8 times that of Example 1.

[0064] Comparative Example 11: Similar to Example 1, the damping coating exhibits a gradient distribution along the axial direction (0.1mm at the throat → 0.2mm at the outlet); however, the spiral guide groove has a uniform depth of 0.5mm throughout (without gradient variation) and a uniform width of 2.0mm throughout, with no filling within the groove. Actual measurements: no depression at 800Hz; horizontal coverage angle of 89° at 10kHz; THD 0.18%; axial sound pressure non-uniformity ±4%. Even with the existing gradient distribution of the coating, the gradient variation in groove depth still contributes independently to the technical effect.

[0065] Comparative Example 12: Similar to Example 1, the spiral guide channel depth varies axially with a gradient (0.8mm at the throat → 0.3mm at the outlet), and the channel width is uniformly 2.0mm throughout; however, the damping coating has a uniform thickness of 0.2mm throughout, with no filling within the channel. Actual measurements: no depression at 800Hz; sound pressure level at 15kHz is 0.4dB lower than in Example 1; THD 0.17%; axial sound pressure non-uniformity ±4%. Even with the existing gradient depth, the coating gradient distribution still contributes independently to the technical effect.

[0066] Comparative Example 13: Same as Example 1, but the structure of a continuous spiral groove on the inner wall of the bass reflex tube of an existing bass reflex speaker was transplanted to the inner wall of the horn (100mm pitch, not satisfying P=k·π / m, groove depth 0.5mm uniformly throughout, groove width 2.0mm uniformly throughout, right-hand spiral). Damping adhesive dots (3mm diameter, 0.5mm height, 10mm spacing, circumferentially distributed) were adhered to the horn outlet surface; there was no groove filling and no gradient coating distribution. Actual measurements: Two resonance peaks (Q value ≈ 7) appeared at 2.8kHz and 5.2kHz, with a peak-to-valley difference of 3.5dB; THD 0.38%; axial sound pressure non-uniformity ±9%. The spiral groove of the bass reflex tube is used to guide airflow and reduce wind noise; its structural parameters are not coordinated with the horn profile, and the transplanted design cannot achieve the technical effects of this invention.

[0067] Comparative Example 14: Same throat size, outlet size, and f_c target as Example 1, but using the carbon fiber composite horn structure of the applicant's authorized patent CN108924699B: carbon fiber inner layer (0.5mm thick) + foamed material intermediate layer (0.6mm thick) + randomly distributed damping material (lead sheets, 3-5mm in diameter, adhered to the outside of the carbon fiber inner layer) + carbon fiber outer layer (0.5mm thick), with a total wall thickness of approximately 1.6mm; the horn profile is a conventional index horn, 283mm in length; no spiral guide groove, no inner wall damping coating, and no groove filling. Actual measurements: frequency response dip of 6dB at 800Hz; THD 0.45%; axial sound pressure non-uniformity ±10%; horn wall vibration amplitude 1.5 times that of Example 1. In this structure, the damping material is located between the inner and outer carbon fiber layers, suppressing overall resonance of the horn wall and avoiding direct contact and synergistic effect with the sound wave propagation of the horn's inner wall.

[0068] Comparative Example 15: Same as Example 1, including a spiral guide channel P=π / m=215mm, right-handed spiral, channel depth gradient, channel width gradient, and coating gradient distribution; the only difference is that the spiral guide channel is unfilled. Actual measurements: no depression at 800Hz; horizontal coverage angle of 89° at 10kHz; THD 0.15%; axial sound pressure non-uniformity ±3.5%; horn wall vibration amplitude was 1.15 times that of Example 1. Filling the channel reduced THD from 0.15% to 0.10%, and wall vibration decreased by approximately 13%.

[0069] Comparative Example 16: Using the same materials, profile parameters, and throat dimensions as Example 1, but with a spiral horn structure (nautilus shape) and a sound path length of approximately 600 mm. The inner wall is smooth without guide grooves, damping coating, or groove filling. Actual measurements: No depression at 800 Hz; however, multiple resonance peaks (Q value > 15) appeared in the 3 kHz-6 kHz frequency band, with a peak-to-valley difference of 10 dB; THD 0.65%; axial sound pressure non-uniformity ±18%; the horizontal coverage angle at 10 kHz was only 45°, with significant beam splitting. The spiral shape of the horn determines the length and direction of the sound wave propagation path, which is suitable for bass extension; while the spiral guide groove on the inner wall only affects the boundary layer flow on the inner surface of the horn, and is used for mid-to-high frequency standing wave suppression and directivity optimization. The two are different in structure, function and mechanism. The spiral guide groove of this invention is an inner wall micro-groove structure with a groove depth of 0.2-1.5mm, which is more than two orders of magnitude smaller in scale than the overall spiral shape with a sound path length of hundreds of millimeters.

[0070] The comparison results of the above embodiments and comparative examples are summarized as follows: Compared with Comparative Example 1, Embodiment 1 has a horn length shortened by 33%, an 800Hz frequency response depression eliminated (7dB→0dB), a 10kHz coverage angle widened by 15°, THD reduced by 88% (0.8%→0.10%), mass reduced by 47%, and axial sound pressure non-uniformity improved by 81% (±16%→±3%); the comparison data of the other comparative examples are as described above. The 16 sets of comparative examples constitute a controlled variable experimental matrix, covering various technical dimensions including profile type, material type, spiral groove parameters (pitch, direction of rotation, groove depth, groove width), coating parameters (thickness, gradient, layup fit), and groove filling (filling density, particle size gradient).

[0071] 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 hyperbolic cosine profile loudspeaker horn, comprising a throat, a horn body, and an outlet, characterized in that, The horn body is made of carbon fiber composite material. The cross-sectional area of ​​the horn body expands axially according to a hyperbolic cosine function A(x) = A0·cosh²(mx), where A0 is the throat cross-sectional area, m is the expansion coefficient, and x is the axial distance from the throat. The expansion coefficient m satisfies m = 2π·f_c / c, where f_c is the target low-frequency cutoff frequency and c is the speed of sound. The inner wall of the horn body is provided with a spiral guide groove. The pitch P of the spiral guide groove and the expansion coefficient m satisfy P = k·π / m, where k is an integer of 1, 2, or 3. The spiral guide channel's rotation direction is the same as the sound wave's propagation direction from the throat to the outlet; and the channel depth of the spiral guide channel varies gradually along the axial direction, with the throat region's channel depth d_throat=0.8-1.5mm, the outlet region's channel depth d_mouth=0.2-0.5mm, and the intermediate region's channel depth gradually changing according to a linear or exponential law; and the spiral guide channel's width varies gradually along the axial direction, with the throat region's channel width w_throat=1.0-2.0mm, the outlet region's channel width w_mouth=2.0-4.0mm, and the intermediate region's channel width gradually changing according to a linear or exponential law.

2. The hyperbolic cosine profile loudspeaker horn according to claim 1, characterized in that, k=1, that is, P=π / m.

3. The hyperbolic cosine profile loudspeaker horn according to claim 1, characterized in that, The carbon fiber composite material employs multi-layer prepreg layup with alternating layup angles of 0° / ±45° / 90°, a total thickness of 2-8 mm, a density of 1400-1700 kg / m³, and an elastic modulus of 60-100 GPa. The inner wall of the horn body is provided with a damping coating, which is a polyurethane-ceramic composite coating with a loss factor tanδ≥0.

3. The thickness t of the damping coating satisfies t=(0.5-1.0)·t0 with the thickness t0 of a single layer of prepreg in the carbon fiber composite material, and the total thickness of the ±45° layup accounts for 40%-60% of the total thickness of the horn body. Furthermore, the damping coating exhibits a gradient distribution along the horn axis, with a coating thickness of t_throat=(0.3-0.6)·t0 in the throat region, t_mouth=(1.0-1.5)·t0 in the outlet region, and a gradual change in coating thickness in the intermediate region according to a linear or exponential law.

4. The hyperbolic cosine profile loudspeaker horn according to claim 1, characterized in that, The throat is provided with a rounded transition, the radius of which is 0.2-0.5 times the characteristic size of the throat, and the outlet is provided with an edge flange with a flange height of 5-15mm and a flange angle of 15°-30°.

5. The hyperbolic cosine profile loudspeaker horn according to claim 1, characterized in that, The horn body is a rotationally symmetric structure or a line sound source structure. The width of the line sound source structure expands according to a hyperbolic cosine function, and the height expands constantly or slowly. A gradual transition section is provided between the throat and the compression drive head. The length of the transition section is 10-30mm, and the cross-section gradually changes from the shape of the drive head outlet to the shape of the horn throat. The transition curve is a circular arc or an elliptical arc.

6. A method for manufacturing a hyperbolic cosine profile loudspeaker horn, characterized in that, Includes the following steps: S1: Based on the target low-frequency cutoff frequency f_c and the horn exit area A_mouth, calculate the expansion coefficient m=2π·f_c / c and the horn length L=(1 / m)·arccosh(√(A_mouth / A0)); S2: Calculate the cross-sectional dimensions of the horn at each axial position according to A(x)=A0·cosh²(mx) and generate a three-dimensional CAD model; S3: The horn body is manufactured using a carbon fiber prepreg layup heating and pressure molding process or a carbon fiber continuous fiber 3D printing process. S4: A spiral guide groove is machined on the inner wall of the horn body. The pitch P of the spiral guide groove and the expansion coefficient m satisfy P=k·π / m, where k is an integer of 1, 2 or 3. The spiral direction of the spiral guide groove is the same as the propagation direction of the sound wave from the throat to the outlet. The groove depth of the spiral guide groove varies with a gradient along the axial direction. The groove depth d_throat in the throat region is 0.8-1.5mm, and the groove depth d_mouth in the outlet region is 0.2-0.5mm. The groove width of the spiral guide groove varies with a gradient along the axial direction. The groove width w_throat in the throat region is 1.0-2.0mm, and the groove width w_mouth in the outlet region is 2.0-4.0mm. A damping coating is sprayed on, wherein the damping coating is distributed in a gradient along the horn axis, the coating thickness in the throat region is t_throat=(0.3-0.6)·t0, and the coating thickness in the outlet region is t_mouth=(1.0-1.5)·t0, where t0 is the thickness of a single layer of prepreg in the carbon fiber composite material; S5: Connect the throat transition section to the compression drive head and measure the frequency response curve, directivity pattern, and total harmonic distortion of the horn.

7. The manufacturing method according to claim 6, characterized in that, The autoclave molding process described in step S3 includes: laying carbon fiber prepreg at angles of 0° / ±45° / 90° on the surface of the horn mold, with 6-16 layers and a thickness of 0.125-0.25mm for each layer; placing the mold after laying into a vacuum bag and then into an autoclave, curing it for 60-120 minutes at a temperature of 130-180°C and a pressure of 0.3-0.8MPa; and after demolding, grinding the inner wall until the surface roughness Ra≤3.2μm.

8. The manufacturing method according to claim 6, characterized in that, The continuous carbon fiber 3D printing process described in step S3 includes: using thermoplastic carbon fiber composite material as raw material, and stacking it layer by layer according to the CAD model of hyperbolic cosine contour through a continuous fiber 3D printing equipment. The printing parameters are: nozzle temperature 380-420°C, printing speed 10-30mm / s, and layer thickness 0.125-0.2mm. After printing, the inner wall is precision machined by five-axis CNC to Ra≤3.2μm, and the outer wall retains the printing texture to increase damping.

9. A hyperbolic cosine profile loudspeaker horn manufactured using the manufacturing method of any one of claims 6 to 8.

10. The hyperbolic cosine profile loudspeaker horn according to any one of claims 1 to 5, characterized in that, The spiral guide channel is filled with damping filler, which consists of alumina or silicon carbide particles with a particle size of 10-100 μm. The filling height is 30%-70% of the channel depth, and the filling density varies along the axial direction, with a filling density of 60%-80% in the throat area and 20%-40% in the outlet area. The particle size of the damping filler also varies along the axial direction, with a particle size D_throat of 60-100 μm in the throat area and D_mouth of 10-40 μm in the outlet area.

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