Design and Construction of a High-Fidelity Audio Loudspeaker System

The Goal: Accurate reproduction of an audio recording Tweeter Box Tweeter Driver Amp X-over Mid Box Mid Driver Woofer Box Woofer Driver Achieving an excellent transient response is very important.

Driver Selection Acoustic response Impedance response Spectral decay graph Cone size vs. usable freq range & radiation pattern Cone material – polypropylene, metal, paper Spread sheet for listing drivers T/S Parameters and calculating Box size Sensitivity / efficiency Fs, F -3db Cost

Quality Factor Target Q – 0.577 Q=.707 Butterworth Q=.577 Max flat delay Measured Mid Q=0.69, 0.63 Q=.5 Best Transient Measured Bass Q=0.65, 0.67

Woofer Box Design Completely damp the back wave restricting it to the interior of a sealed cabinet Stiffness & Damping Braces Steel stiffening supports Clay interior coating Large mass Vb Qsys High Quality MDF (medium density fiberboard) Asymmetric positioning of supports

Woofer Box Construction Driver port view Brace w/ Clay Overhead view Back & Baffle Sidewalls w/ epoxied steel reinforcement

Baffle step and baffle shape Low freq radiate into a full space, high freq radiate into a half space Spherical shape produces the best acoustic baffle response

Mid Box Construction Driver Flush mounted Asymmetrically positioned brace Acoustic wave suppression T-nuts Driver offset Driver housing support Binding posts

Test and Measurement Acoustic Impedance NI LabView NI LabView Automated tests were developed to acquire 2000 data points between 10 Hz and 20 kHz. Acoustic Impedance HP Low Freq Impedance Analyzer Signal Gen Amp SPL Meter NI LabView DMM NI LabView

Impedance Plots Tweeter Mid Woofer

Woofer Impedance compensation Output Response Mag Output Response Phase Impedance Response

Acoustic Response of each tweeter

Average Acoustic Response of all 3 drivers

Tweeter Impedence & Sensitivity Compensation Output Response Mag Output Response Phase Impedance Response

Third Order X-over Individual Driver Responses Impedance Response Summed Output Response

Crossover Construction 1st and 3rd order both at 450 Hz & 2500 Hz separated by 2 DPDT switches Each impedance correction circuit can be switched in or out of the network Cement anchored copper pads Low DCR 12 gauge inductors

Inductor Quality Loose wound on plastic Tight wound on wood Loose wound on metal

Challenges & Difficulties Crack in midrange box Weak joint Experience tremendous difficulty when machining all three enclosures

Future Work Export filter output responses and multiply by the driver response yielding a more accurate simulation of the entire system response Research the quality of my x-over components measuring impedance vs. freq for the resistors, inductors, and capacitors. A deeper study of series x-overs and other minimum phase designs MEMS accelerometer glued to the driver with feedback to measure and control the behavior of the driver.