1. Design and Construction of a High-Fidelity Audio Loudspeaker System

2. 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.

3. 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

4. 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

5. 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

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

7. 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

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

9. 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

10. Impedance Plots
Tweeter
Mid
Woofer

11. Woofer Impedance compensation
Output Response Mag
Output Response Phase
Impedance Response

12. Acoustic Response of each tweeter

13. Average Acoustic Response of all 3 drivers

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

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

16. 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

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

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

19. 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.