# Thiele's Alignment based on Qt

 Alignment Box design Thiele's method is to choose an alignment based on QT. Order No Type Ripple(dB) f3/fs fB/fs VB/VAS QT Quasi Third Order 1 QB3 --- 2.68 2.000 0.0954 0.180 2 QB3 --- 2.28 1.730 0.1337 0.209 3 QB3 --- 1.77 1.420 0.2242 0.259 4 QB3 --- 1.45 1.230 0.3390 0.303 Fourth Order 5 B4 --- 1.000 1.000 0.7072 0.383 optimally flat 6 C4 --- 0.867 0.927 0.9479 0.415 7 C4 0.13 0.729 0.829 1.372 0.446 8 C4 0.25 0.641 0.757 1.790 0.518 9 C4 0.55 0.600 0.716 2.062 0.557 9.5 C4 1.52 0.520 0.638 2.60 0.625

Example:
• fs = 30.4 Hz

• Vas = 125.9 liters

• Qe = 0.249

• Qm = 3.9934

• Rs = 7.4 ohm
EBP = fs/Qe = 122 --> vented

With 0.5 Rext external, QT = 0.249

Looking at the table, this QT suggests
alignment No3 ( QB3 ), giving:

 Vb = 28.23 liters fb = 43.2 Hz f3 = 53.8 Hz

## Calculator:

fs [Hz] :
Vas [liters] : Vas [cu.ft.] :
Qe [] :
Qm [] :
Re [ohms] :
Rext [ohms] :

## Calculations:

EBP [] :
QT [] :
Vb [liters] : Vb [cu.ft] :
fb [Hz] :
f3 [Hz] :

Port calculations

 Dv : [cm] Lv : [cm] Pa : [cm2] Dv : [inches] Lv : [inches] Pa : [sq.inches] If you change the pipe diameter [Dv], click on 'Port' to recalculate Port length.

 GLOSSARY OF SYMBOLS fs - resonance frequency of driver in free air Vas - volume of air having same acoustic compliance as driver suspension Qe - Q of driver at Fs considering system electrical resistance only Qm - Q of driver at Fs considering system nonelec-trical resistances only Re - dc resistance of driver voice coil Rext - dc resistance of crossover-filter-coil and speakercable EBP - efficiency bandwidth product QT - total Q of driver at fs including all system resistances Vb - net internal volume of enclosure fb - Helmholtz resonance frequency of vented box f3 - alignment (-3dB) cutoff frequency Dv - Diameter of the bass reflex pipe Lv - Length of the bass reflex pipe Pa - Area of the bass reflex pipe

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