
Due to the considerable design
flexibility of 6th order bandpass systems, a handcalculator method does not exist for
determining optimum box size and tuning. However, I've provided two tables below that will
allow you to design two 6th order bandpass alignments for a particular driver. These
systems will have flat (or very nearly flat) frequency responses within their passbands,
and, in most instances, the front and rear volumes will be sufficiently large to prevent
power compression from using excessively small port diameters to achieve the required
tuning. However, if you do use these tables, please examine the predicted results
CAREFULLY, to see if they match your requirements. You will likely have to measure the
frequency response of the built system and adjust the port lengths accordingly, as the
tables assume zero losses. An alternative method for designing a 6th
order bandpass system is to use the frequency response equations and some trial and error
to find a 6th order BP alignment whose frequency response matches your needs.
To use the following calculations, you will need to know the
following:
Vas = equiv. air compliance (litres)
Qts = driver Q at its resonance frequency
Fs = driver resonance frequency (Hz)
First of all, using the driver's Qts value, determine the values of Vf/Vas,
Ff/Fs, Vr/Vas, Fr/Fs, F3h/Fs, F3l/Fs and Gain from one of the tables given below:
Table #1:
Qts 
Vf/Vas 
Ff/Fs 
Vr/Vas 
Fr/Fs 
Fh/Fs 
Fl/Fs 
Gain 
0.18 
0.190 
1.950 
0.440 
1.000 
2.370 
1.052 
2.3 
0.19 
0.200 
1.960 
0.460 
1.000 
2.410 
1.013 
1.9 
0.20 
0.212 
1.960 
0.465 
1.000 
2.410 
1.070 
1.4 
0.21 
0.215 
1.980 
0.470 
1.000 
2.460 
1.076 
1.1 
0.22 
0.217 
2.020 
0.510 
1.000 
2.590 
1.060 
0.9 
0.23 
0.223 
2.032 
0.530 
1.000 
2.640 
1.060 
0.6 
0.24 
0.230 
2.040 
0.550 
1.000 
2.680 
1.060 
0.3 
0.25 
0.252 
2.010 
0.580 
1.000 
2.620 
1.060 
0.2 
0.26 
0.270 
1.988 
0.600 
1.000 
2.570 
1.060 
0.6 
0.27 
0.294 
1.960 
0.630 
1.000 
2.510 
1.064 
1.1 
0.28 
0.308 
1.950 
0.660 
1.000 
2.500 
1.060 
1.4 
Table #2:
Qts 
Vf/Vas 
Ff/Fs 
Vr/Vas 
Fr/Fs 
Fh/Fs 
Fl/Fs 
Gain 
0.25 
0.142 
2.608 
0.270 
1.000 
3.952 
1.398 
0.3 
0.26 
0.162 
2.520 
0.291 
1.000 
3.740 
1.368 
0.3 
0.27 
0.183 
2.438 
0.315 
1.000 
3.529 
1.353 
0.8 
0.28 
0.203 
2.385 
0.341 
1.000 
3.423 
1.323 
1.1 
0.29 
0.210 
2.347 
0.370 
1.000 
3.360 
1.293 
1.3 
0.30 
0.225 
2.316 
0.391 
1.000 
3.297 
1.281 
1.6 
0.31 
0.246 
2.263 
0.420 
1.000 
3.170 
1.262 
2.0 
Then, use the steps below to calculate the front and rear enclosure sizes and
tuning for the 6th order bandpass system.
1. Calculate the front volume parameters using the following
equations: Vf = (Vf/Vas)*Vas
Ff = (Ff/Fs)*Fs
Fh = (Fh/Fs)*Fs
where,
Vf = net front volume
Ff = front tuning frequency (Hz)
Fh = upper 3dB cutoff frequency (Hz)
2. Calculate the rear volume parameters using the following equations:
Vr = (Vr/Vas)*Vas
Fr = (Fr/Fs)*Fs
Fl = (Fl/Fs)*Fs
where,
Vr = net rear volume
Fr = rear tuning frequency (Hz)
Fl = lower 3dB cutoff frequency (Hz) 

