Bad Ass Port Calculator

[Sampsonite]

This calculator REALLY helped me out! Maybe it can help you out too.

http://www.carstereo.com/help2/Articles.cfm?id=31

[uhoh_45]

bad ass bandpass calc

http://www.carstereo.com/help/Articles.cfm?id=27

[Gotloud555]

I have use that calculator many time before and the subwoofertools.com too for desgning boxes. I would prefer using the pencils and paper to understand better on building enclosures.

[amazinblazin10]

i used the car stereo on my first box but i made a mistake by tuning it hella high.. were talking mid 40's

[andym85]

anybody know of a 6th order calc...lol

i know...probably doesnt exist...but im about to try and design one soon for a teammate of mine

for those of you interested here is the insanely long way of going about figuring a 6th order

HOPE YOU LIKE TO READ...LOL

The 6th order bandpass system is similar to the 4th order bandpass system , except in this case both the front and the rear volumes are tuned via vents. The power handling of the 6th order bandpass system ranges from excellent within its passband to poor for frequencies lower than its passband.

The transient performance of 6th order bandpass systems is usually worse than the sealed, ported and 4th order bandpass systems, making it more suitable for sound reinforcement, multimedia and other less critical applications, rather than high-end audio. Like ported systems, the driver becomes unloaded at frequencies lower than the passband.

As all of the output of the 6th order bandpass system is via the two ports, the largest port diameter possible for each volume should be used in order to minimize port noises.

As with the 4th order system, the 6th order bandpass system rarely exhibits a perfect bandpass response - there is usually some out-of-band noise present in its output. A simple notch filter can be used to reduce this noise if it is audible. Alternatively, a low-pass filter may be used, but the in-band performance may be affected

Due to the considerable design flexibility of 6th order bandpass systems, a hand-calculator 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)

To calculate the frequency response of a 6th order bandpass system,you will need to know the following:

Vas = equivalent air compliance (litres)

Vf = net front volume (litres)

Ff = front volume tuning frequency (Hz)

Vr = net rear volume (litres)

Fr = rear volume tuning frequency (Hz)

Fs = driver resonance frequency (Hz)

Qts = driver Q at system resonance

Ql = box losses (Ql=infinite (10000) can

be assumed for most cases)

Then at frequency F,

a = abs(Ff^2-Fr^2)*F^4

b = F^6

c = (Fr^2/Ff/Ql+Fs/Qts+Ff/Ql)*F^5

d = (Ff^2+Fr^2+Fs*(Fr^2/Ff/Qts/Ql+Ff/Qts/Ql)+

Fs^2*(Vas/Vf+Vas/Vr+1))*F^4

e = (Fs^2*(Ff/Ql*(Vas/Vr+1)+Fr^2/Ff/Ql*(Vas/Vf+1))+

Fs/Qts*(Fr^2+Ff^2)+2*Fr^2*Ff/Ql)*F^3

f = (Fs^2*(Fr^2*(Vas/Vf+1)+Ff^2*(Vas/Vr+1))+

2*Fr^2*Ff*Fs/Qts/Ql+ Fr^2*Ff^2)*F^2

g = (Fr^2*Ff*(Ff*Fs/Qts+2*Fs^2/Ql))*F

h = Fs^2*Fr^2*Ff^2

i = -b+d-f+h

j = c-e+g

dBmag = 20*log(a/(i^2+j^2)^.5)

Choosing an alignment

Be careful when choosing a 6th order bandpass alignment for your driver. An ultra-large box with an ultra-low cutoff frequency may not produce the best results, because of the reduced power handling and lower efficiency. Examine carefully the cutoff frequency and box size and tradeoff in efficiency to determine whether or not this alignment lives up to your expectations.

Where should I put the ports?

Ports should be placed at least one diameter away from any adjacent walls. If this is not possible to do this, the tuning frequency for a given port length will be lower than that predicted by the equations, and this may adversely affect the results.

Lining the box

One layer of lining on every wall for each section will generally give better results, as the lining will help to reduce the out of band noise. Ensure that no lining obstructs the ports. Fiberglass will work here, but make sure that none's located near the port entrance, as air turbulence can rip chunks of it off the walls and eject it through the port. Any change in the tuning frequency introduced by lining the enclosure can be adjusting by shortening the port(s) slightly.

Port size

Use the largest ports possible for your design. This will reduce power compression effects and port noise caused by turbulence. Flaring the ends of the port will also produce better results.

[andym85]

and all the shit for a 4th order...if you actually feel like number crunching...

The 4th order or sealed rear chamber bandpass system is basically a sealed enclosure system with the addition of an acoustic filter in front of the driver. The resulting system usually provides a lower cutoff frequency, the tradeoff being a larger enclosure. The enclosure can be reduced in size by using two drivers in an isobaric configuration.

4th order bandpass systems usually demonstrate better power handling characteristics than the other main systems considered here. Its transient response is second only to the sealed enclosure systems, making it a good choice for subwoofer applications.

As all of the output of the 4th order bandpass system is via the port, the largest port diameter possible for the enclosure should be used in order to minimize port noises. The ports should be flared whenever possible, for the same reasons.

The 4th order bandpass system rarely exhibits a perfect bandpass response - there is usually some out-of-band noise present in its output. A simple notch filter can be used to reduce this noise if it is audible. Alternatively, a low-pass filter can be used in series with the driver, but the in-band response of the system may also be affected if this approach is taken.

To use the following calculations, you will need to know the following:

Vas = equivalent air compliance for the driver (litres)

Fs = driver resonance frequency

Qts = driver Q at Fs

The following equations will allow you to design a 4th order bandpass system with a desired low frequency limit or a desired gain. You will need to choose a value for "S" that suits your requirements. 4th order bandpass systems where S is less than 0.7 will have a degraded transient response, but wider bandwidth and smaller box requirements.

if S = 0.7, then b = 0.7206, passband ripple = 0.00 dB

if S = 0.6, then b = 0.9560, passband ripple = 0.35 dB

if S = 0.5, then b = 1.2712, passband ripple = 1.25 dB

4th order bandpass system with desired low frequency limit

Choose a value for Fl, the lower 3dB cutoff frequency,

then,

Fl' = (Fl*Qts)/Fs

Fh = (Fl'+*Fs/Qts

Qbp = (Fl'*(Fl'+)^0.5

Fb = Qbp*Fs/Qts

Vf = (2*S*Qts)^2*Vas

Vr = Vas/((Qbp/Qts)^2-1)

Pa = -40*LOG(1/(Qbp*2*S))

where,

Fh = upper -3dB cutoff frequency (Hz)

Qbp = Qtc of sealed chamber

Fb = resonance frequency of vented chamber(Hz)

Vf = net volume of vented chamber (litres)

Vr = net volume of sealed chamber (litres)

Pa = gain (dB)

4th order bandpass system with desired gain

Choose a value for Pa, the gain in efficiency,

then,

Qbp = ((10^(-Pa/40))*2*S)^-1

Fl = ((-b+(b^2+4*Qbp^2)^0.5)/2)*(Fs/Qts)

Fh = Fl+(b*Fs/Qts)

Fb = Qbp*Fs/Qts

Vf = (2*S*Qts)^2*Vas

Vr = Vas/((Qbp/Qts)^2-1)

where,

Fl = lower -3dB cutoff frequency (Hz)

Fh = upper -3dB cutoff frequency (Hz)

Qbp = Qtc of sealed chamber

Fb = tuning frequency of vented chamber (Hz)

Vf = net volume of vented chamber (litres)

Vr = net volume of sealed chamber (litres)

Pa = gain (dB)

To calculate the frequency response of a 4th order bandpass system, you will need to know the following:

Vf = net front volume (litres)

Ff = front volume tuning frequency

Vr = net rear volume (litres)

Fs = driver resonance frequency (Hz)

Qts = driver Q at system resonance

Ql = box losses (Ql=infinite (10000) can be assumed for most cases)

then at frequency F,

A = (1/Ff)^2*F^4

B = ((1/Ql+(Fs/Ff)/Qts)/Ff)*F^3

C = (((1+Vas/Vr+Vas/Vf)*Fs/Ff+(1/Qts)/Ql)*Fs/Ff+1)*F^2

D = ((1/Qts+(Fs/Ff)/Ql*(Vas/Vr+1))*Fs)*F

E = (Vas/Vr+1)*Fs^2

G = A-C+E

H = -B+D

dBmag = 20*log(F^2/(G^2+H^2)^.5)

Choosing an alignment

Be careful when choosing a 4th order bandpass alignment for your driver. An ultra-large box with an ultra-low cutoff frequency may not produce the best results, because of the reduced power handling and lower efficiency. Examine carefully the cutoff frequency and box size and tradeoff in efficiency to determine whether or not this alignment lives up to your expectations.

Driver orientation

For bandpass systems, you may get better results if you orient the driver so that its magnet is in the vented section. Also, locate the port so that the speaker is not visible through the port. Both of these techniques will help to reduce the out of band noise that can be a problem with bandpass systems.

The total volume of the vented section will now be given by

Vf' = Vf+Vs+Vp+Vm,

where

Vf = net vented volume given by calculations,

Vs = volume displaced by driver,

Vp = volume displaced by the port

Vm = volume displaced by any bracing and any other miscellaneous items used within this section.

High power applications

If you're designing your system for high-power applications, use a slightly lower tuning frequency. This should produce better results at higher volumes.

Car Audio applications

If you're designing a system for car-audio use, remember that the interior of the car is going to boost the bass by about 12dB/octave below 60~80 Hz. A 4th order bandpass box that sounds flat in open air may sound boomy and flabby in a vehicle. Try aiming for cutoff frequencies in the 40-50 Hz region..

Where should I put the ports?

Ports should be placed at least one diameter away from any adjacent walls. If this is not possible to do this, the tuning frequency for a given port length will be lower than that predicted by the equations, and this may adversely affect the results.

Stuffing the sealed section

If you stuff the sealed section of the enclosure, you can reduce the volume requirement. If using 100% fiberglass stuffing, you can reduce the volume requirement by about 25%, e.g. if the equations predict a 1 cu.ft. sealed volume is required, you can use a 0.75 cu.ft. sealed volume that's 100% stuffed.

Lining the vented section

One layer of lining on every wall for the vented section will generally give better results. Ensure that no lining obstructs the ports. Fiberglass will work here, but make sure that none's located near the port entrance, as air turbulence can rip chuinks of it off the walls and eject it through the port. Any change in the tuning frequency should be measured and adjusting by shortening the port(s) slightly. The lining will help to reduce the out of band noise.

Port size

Use the largest port possible for your design. This will reduce power compression effects and port noise caused by turbulence. Flaring the ends of the port will also produce better results.

[andym85]

the smiley face is a "b" ....

[Neel]

Awesome post amatt, a good read and reference for sure, maybe its time for me to start playing with different box designs..