Design and Construction of a High-Fidelity Audio Loudspeaker System

1
Design and Construction of a High-Fidelity Audio
Loudspeaker System
2
The Goal Accurate reproduction of an audio
recording
Tweeter Box
Tweeter Driver
X-over
Mid Box
Mid Driver
Amp
Woofer Driver
Woofer Box
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 Q0.69, 0.63
Q.5 Best Transient
Measured Bass Q0.65, 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
Sidewalls w/ epoxied steel reinforcement
Back Baffle
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

• 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
DMM
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
Low DCR 12 gauge inductors
Cement anchored copper pads
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.