Loudspeaker Design & Measurement

Transcription

1 Loudspeaker Design & Measurement Keith Larson Smith & Larson Audio Presentation to the Lone Star Audio Fest 5/3/2008

2 Overview Bass Enclosure Design (WT2, ST or WTPro) Thiele Small Measurements Designing the Enclosure Verifying the Enclosure: Electrical Measurement -> Simulator Auto Alignment Introduction to In Air Response Interactive Crossover Design (ST or WTPro) Tweeter Protection Acoustic Distance at XO point Schematic Entry (LT-Spice, OrCad...) ICD Simulate! Build & Test a Physical Crossover (RESULTS!) Q&A 2

3 Bass Enclosure Design Measure the driver, or begin with the manufacturers specifications. Is the simulation plausible? Box Volume and Tuning are the most important parameters. Box ratios, port location.. Important, but not most If a one box build,make it slightly large 3

4 In Box Electrical Measurement Reveals Box volume, Loss Box Tuning, Port Loss Refines Cms (Vas) Overlay Simulated & Measured Electrical Data Interactive Parameter Adjust Box Auto-Align Vented, Passive, Sealed 4

5 In-Air Response Comparison Phase Accurate! Response Error < 0.5dB Simulator Auto-Alignment Reveals Actual Response Identifies Driver Port and Box Interactions Identifies Build Errors 5

6 In-Air Acoustic Response MLS, Noise, Impulse and Chirp: Real-Time response Sine and Pulsed Sine: THD, IMD, SINAD, Sweep and collect Reject Room reflections (all RT modes) Cumulative Spectral Decay and Waterfall Plots usec accurate acoustic Time of Arrival (fractions of mm) Dual Microphone alignment to further reduce room reflections Impulse Window Real Time Overlay CSD &Waterfall Setup Control Real-Time Meter 6

7 Interactive Crossover Design Real-Time Simulated RLC Crossover Testing Accuracy to Fractions of a db Simple Tweeter Protection Circuit Measure and Time Shift Drivers with mm Accuracy New XVR Format for Specifying an Arbitrary Crossover using Attenuation and Phase 7

8 Interactive Crossover Design Use a Schematic Capture Program (LT-Spice, OrCad) to Generate SPICE Or, Enter Netlist Directly Indicate Tweeter Protection Circuit Series Resistance SPICE Netlist LT-SPICE Simulate! 8

9 Interactive Crossover Design Custom Built In Circuit Analysis Module Allows Crossover Circuit to Interact with a Measured Driver Impedance (ZMA format) Same Capability Allows a Simple Resistor and Snubber for Tweeter Protection 9

10 Interactive Crossover Design db Accurate Actual Simulated vs Physical Crossover Phase Accurate 10

11 Thiele Small Parameters vs. AC Drive Level Continuum of Thiele Small Parameters from µw to 200W Compare Compression Response in Simulator Constant Current or Constant Voltage Power is Limited by External Amp and Sense Resistor (HiZP port) XY Plot for any Parameter Pair Vas (Liters) versus AC Current Drive BL versus Xmm Displacement 11

12 AC & DC Thiele Small Model Compression Full TS Model at Each DC Bias Point or AC Drive Level Reveals Suspension and Motor Mechanical Offsets XY Plot for any Parameter Pair Cms versus Xmm Displacement BL versus Xmm Displacement 12

13 Distortion Analysis Capabilities Advanced DSP Filters provide Lock-On Band Pass Filtering with greater resolution than an FFT alone (But you can use the FFT) Pick Distortion Mode Results Show up Here THD and SINAD Can Also Be Captured to Data Buffers 13

14 Crossover Component and Cable Measurement Measure Resistance, Inductance and Capacitance Impedance and Phase from 1 to 20 khz 3 ma (low power) and 4 Amp (high power) Port Ranges 5 Digit Accuracy at Full Scale Easily Measures Speaker Cables 100 pf to 1000 uf, 100 nh to 10 H, 10 milliohm to 100 kohm range Δ Inductance of 36 Leads Open/Closed 50 mω/div 10 ohm cal resistor: 1 mω/div, 1-20 khz 14

15 About Smith & Larson Audio Smith & Larson Audio is based in the USA and is the home of the original Woofer Tester, which was introduced in It was redesigned in 2005 and is in use by over 1000 customers worldwide. In 2006, the product line and our test capabilities expanded and now include the Speaker Tester and Woofer Tester Pro. Smith & Larson has over 40 years of combined experience in audio design and digital signal processing. Woofer Tester 2 $ Speaker Tester $ Woofer Tester Pro $