扬声器振膜的振动和辐射分析 Vibration and Radiation Analysis of Loudspeaker Cones Wolfgang Klippel KLIPPEL GmbH 扬声器振膜的振动和辐射分析, 1 Abstract: Loudspeaker cones are more or less flexible structures performing bending and membrane modes at higher frequencies. The cone break-up is a desired mechanism giving more SPL output and a better directivity pattern than a rigid cone or piston. The measurement of the mechanical vibration by using Laser scanning techniques is the basis for getting a deeper insight into the mechanical vibration and their relationship to the acoustical radiation. Displacement sensors based on triangulation technique are an interesting alternative to cost-intensive Doppler Interferometry because not only the vibration but also the geometry of the cone is measured at high precision. This data can be used for cone design with FEA and is required for predicting the SPL output. A new vibration and radiation analysis is presented. It reveals radial and circular modes and separates vibration components which generate sound from other others which reduce the acoustical output. This technique opens new ways for loudspeaker diagnostics and cone optimization which is illustrated on woofers, tweeters, headphones and micro-speakers. 扬声器振膜的振动和辐射分析, 2
扬声器 - 一个动态系统 Loudspeaker - a dynamic system Audio band 音频范围 Frequency 振动频率 1 Hz 100 Hz 1 khz 20 khz heat transfer 热传导 Creep 蠕动变化 Resonance 共振 Cone break up 振膜分裂运动 Time constant 时间常数 1 h 1 s 10 ms 1 ms 0.05ms Length of sound wave 振动波长 3 m 30 cm 15 mm lumped model useful CRL 集合模式 扬声器振膜的振动和辐射分析, 3 distributed model required 分散模式 扬声器设计的新工具 New Tools for Loudspeaker Design 扫描设备 Scanner Hardware 致力于扬声器设计 Dedicated to loudspeakers 经济的价格 Price effective 扫描几何形状 Scanning geometry 更多其它的应用 Many other applications 软件分析 Analyzer Software 振膜振动运动可视化 Visualization of cone vibration 输出声压的预测 Prediction of sound pressure output 指向性 Directivity 可分解 Decomposition 扬声器振膜的振动和辐射分析, 4
自动化扫描过程 Automatic Scanning Process 扫描系统 SCN Scanning System z 8 分钟扫描 ( 对于轴对称振膜 ) 8 min scan (for axisymmetrical cones) 过夜扫描 Overnight scan (3000 个点 3000 points) phi r 机械扫描系统带一个转动和二个线性致动器 Mechanical scanning system with one rotational (φ) and two linear actuators (r, z) 扫描过程从外缘开始逐渐向里推进 The scanning starts at the outside rim and proceeds inwards 扬声器振膜的振动和辐射分析, 5 扫描模式 Scanning Modes 剖面扫描 Profile Scan 概况扫描 Explore Scan 细节扫描 Detailed Scan 有益于 Good for 辐射仅对于轴对称几何形状 Radiation of axial-symmetrical Geometries only 有益于 Good for 辐射所有振膜 Radiation all cones 摇摆模式 Rocking modes 扫描时间 Scanning Time 有益于 Good for 辐射 Radiation 环状模式 Circular modes 不固定性 Irregularities 8 min 1 hour 8 hours 扬声器振膜的振动和辐射分析, 6
剖面扫描是很有用的! A Profile Scan is already useful! 剖面扫描 Profile Scan 细节扫描 Detailed Scan 8 分钟 8 min 8 小时 8 hours 扬声器振膜的振动和辐射分析, 7 测量几何形状 Measurement of Geometry 扬声器扫描仪 Loudspeaker 高精确性 High Precision Scanner < 10 µm for 0 < z< 300 mm < 2.5 µm for 5 mm < z < 5 mm 双有关联测量 Dual Measurement with correlation 自动检测光学误差 Automatic detection of optical errors 报告以常见格式输出 Export in common formats ( 如 such as *.txt, *.dxf) 扬声器振膜的振动和辐射分析, 8
Demo 扬声器振膜的振动和辐射分析, 9 振动数据可视化 Visualization of Vibration Data 三维动画 3D Animation 横断面削减 Cross-sectional Cut 相位分布 Phase Distribution 扬声器振膜的振动和辐射分析, 10 振幅分布 Amplitude Distribution
分解为辐射波分量及环形波分量 Decomposition into radial and circular components x = x + total rad x circ At 580 Hz Radial vibration mode 辐射振动模式 扬声器振膜的振动和辐射分析, 11 Circular vibration mode 环状振动模式 摇摆模式在 350 赫兹处 Rocking mode at 350 Hz Microspeaker 13 mm 扬声器振膜的振动和辐射分析, 12
声压的预测 Prediction of Sound Pressure Rayleigh 积分公式 Rayleigh Integral Equation 单体位于无限障板中 driver in infinite baffle 很多角度都可有良好的逼近 good approximation for most angles 计算时间短 short calculation time 扬声器振膜的振动和辐射分析, 13 指向性的计算 Calculation of Directivity 330 0 30 300 60 270-15 -10-5 90 240 120 210 180 150 指向性图 directivity pattern 扬声器振膜的振动和辐射分析, 14
平面振膜低音扬声器 ( 直径 5 英寸 ) flat diaphragm woofer 5 inch 12 ribs 扬声器振膜的振动和辐射分析, 15 平面振膜低音扬声器 ( 直径 5 英寸 ) 辐射在 1 千赫兹处 flat diaphragm Radiation at 1kHz 0 330 30 300 60 270-15 -10-5 90 240 120 相位 phase 振幅 amplitude 210 150 180 Total Sound Pressure Level 80 70 SPL [db] 60 50 40 30 102 103 104 Frequency [Hz] 扬声器振膜的振动和辐射分析, 16
平面振膜低音扬声器 - 振动在 1 千赫兹处 flat diaphragm 1 khz flat diaphragm vibration 1 khz 扬声器振膜的振动和辐射分析, 17 声压级相关分量 SPL related Decomposition x generates sound 产生音压 total = xin + xanti + xout quadrature of Reduces sound 降低音压 no sound 相抵音压 扬声器振膜的振动和辐射分析, 18
什么导致了明显的峰值 What causes significant peaks? Total Sound Pressure Level SPL [db] 85 80 75 70 65 60 55 50 45 40 35 10 3 10 4 Frequency [Hz] 通常是好 Usually ok 第一个振膜环反共振 ( 弯曲模式 )First ring anti-resonance (bending mode) 纵向共振 ( 膜片振动模式 ) Longitudinal resonance (membrane mode) 通常是坏 Usually bad 扬声器振膜的振动和辐射分析, 19 振膜环反共振 Ring Anti-Resonance f ra =1.1 khz 扬声器振膜的振动和辐射分析, 20
什么是膜片振动模式 What is a Membrane mode? 纵向刚度产生恢复力 F l longitudinal stiffness generates the restoring force F l 弯曲内力小 bending forces are small F l 膜片振动模式占用了很大的振膜面积 A membrane mode occupies a large area of the cone 扬声器振膜的振动和辐射分析, 21 什么在支持膜片振动模式? What supports membrane modes? 平坦的振膜几何形状 flat cone geometry 低纵向刚度 low longitudinal stiffness 高弯曲刚度 high bending stiffness honeycomb 芳纶 kevlar 扬声器振膜的振动和辐射分析, 22
什么导致了明显的谷值? What causes significant dips? Total Sound Pressure Level 80 70 SPL [db] 60 50 40 30 102 103 104 Frequency [Hz] 声学对消效应 Acoustical cancellation effect Causes 振膜的几何形状 Geometry of The cone 振膜上的弯曲模式定位 Location of bending modes on the cone 膜片振动模式 membrane modes 扬声器振膜的振动和辐射分析, 23 80 把纸盆做得越硬越好 Making the cone as stiff as possible Total Sound Pressure Level 75 SPL [db] 70 65 60 55 Piston range goes up to 4 khz 扬声器振膜的振动和辐射分析, 24 10 3 104 Frequency [Hz] + q -q 在 6 千赫兹处的辐射问题 Radiation problem at 6 khz 振膜分裂成 2 个部分来生成相同量级下正向的及反向的体积流速 Cone breaks-up in two areas producing positive and negative volume velocity of equal magnitude 对消效应 Cancellation effect
提示 : 减少纸盆有效面积 TIP: Reduction of effective cone area 分裂始于外部 Breakup starts outside 外环面积不能辐射明显的音压 Outer ring area does not radiate significant sound 内部应辐射音压 ( 同相分量 ) Inner part should radiate sound (in-phase component) 64 khz 2 khz 1 khz r b 500 Hz 3 khz 7 khz 扬声器振膜的振动和辐射分析, 25 例样 Examples 扬声器振膜的振动和辐射分析, 26
专业 16 英寸低音扬声器全振动位于 1 千赫兹处 Professional 16 inch Woofer total vibration at 1 khz 扬声器振膜的振动和辐射分析, 27 带芳纶的芳纶的中音扬声器 7 千赫兹处振动 Midrange with Kevlar Vibration 7 khz 扬声器振膜的振动和辐射分析, 28
带芳纶的中音扬声器 7千赫兹处振动 Midrange with Kevlar Vibration 7 khz 0 330 30 300 60 270-30 -20 240-10 90 120 相位 phase 210 振幅 amplitude 150 180 Total Sound Pressure Level 90 85 SPL [db] 80 75 70 65 60 55 103 扬声器振膜的振动和辐射分析, 扬声器振膜的振动和辐射分析 29 Frequency [Hz] 104 高音扬声器 软球顶 (直径) 1 英寸 Tweeter Soft Dome 1 inch 扬声器振膜的振动和辐射分析, 扬声器振膜的振动和辐射分析 30
高音扬声器 软球顶 15 千赫兹 Tweeter Soft Dome 15 khz 弯曲模式及膜片振动模式 Bending + Membrane Modes 扬声器振膜的振动和辐射分析, 31 高音扬声器 软球顶 15 千赫兹 Tweeter Soft Dome 15 khz 330 0 30 300 60 270-15 -10-5 90 240 120 210 180 150 Total Sound Pressure Level SPL [db] 85 80 75 70 65 60 55 50 45 10 3 104 Frequency [Hz] 扬声器振膜的振动和辐射分析, 32
号筒压缩单体 Horn Compression Driver 几何形状 geometry Total Sound Pressure Level 轴声压级响应 SPL response in axis SPL [db] 85 80 75 70 65 60 55 50 45 10 3 104 Frequency [Hz] 扬声器振膜的振动和辐射分析, 33 压缩单体在 5.5 千赫兹处 Compression Driver at 5.5 khz 扬声器振膜的振动和辐射分析, 34
压缩单体在 10 千赫兹处 Compression Driver at 10 khz 扬声器振膜的振动和辐射分析, 35 压缩单体在 15 千赫兹处 Compression Driver at 15 khz 扬声器振膜的振动和辐射分析, 36
耳机 振动在 1760 赫兹处 Headphone Vibration 2760 Hz 不对称的弯曲模式 Asymmetrical Bending Mode 扬声器振膜的振动和辐射分析, 37 耳机 辐射在 2760 赫兹处 Headphone Radiation 2760 Hz 0 330 30 + - + - 270 300 ϕ -15-10 -5 60 90 ϕ 240 120 210 180 150 80 Total Sound Pressure Level 70 60 SPL [db] 50 40 30 20 10 3 104 Frequency [Hz] 扬声器振膜的振动和辐射分析, 38
SPL [db] 90 80 70 60 50 40 Total Sound Pressure Level 10 2 103 Frequency [Hz] 微型扬声器 Microspeaker 13 mm 几何形状 Geometry 扬声器振膜的振动和辐射分析, 39 测量 Measurements 材料参数 Material Parameter 振膜几何形状 Cone Geometry 音箱, 号筒, 房间 enclosure, horn, room 振动及辐射分析 Vibration and Radiation Analysis E,η 受力分析 Mechanical Analysis (FEA) 被预测的振动 predicted vibration 声学分析 Acoustical Analysis (BEA) 0 330 30 300 60 270-20-15-10-590 240 120 210 150 180 6 khz 声学输出 Acoustical Output 纸盆振动 Cone Vibration 实测振动 Measured vibration 声压级响应指向性 SPL response directivity 实测输出 Measured output 扬声器振膜的振动和辐射分析, 40
结论 Conclusion 位移传感器 + 扫描仪 + 信号处理 Displacement sensors + scanner + signal processing 成本经济的解决扬声器的动态测量 cost effective solution for loudspeaker vibrometry 几何形状 + 振动数据是分析的基础 Geometry + Vibration data is basis for analysis 振动和辐射之间的相互影响是很重要的 Interaction between vibration + radiation are important 新的分解技术 简化解读 New decomposition techniques simplifies interpretation 扬声器振膜的振动和辐射分析, 41