Calculating Enclosure Frequency

[Exscathe]

Hey guys and girls,

I am curious as to how to calculate the frequency that the enclosure will be tuned to when ported, So some kind of formulae relating the size of port and box I am assuming

Any help very much appreciated!

[mmets]

Download Torres Tuning Calculator. It will do it for you and also towards the bottom there is an equation that you can use I believe. I have always used calculators of some sort just because I'm not the brightest and its so much easier lol

[bbeljefe]

Girls? They got girls in here? These bastards always hide the fun stuff from me. :-)

What are you doing? Porting an existing box or building a box? There are a number of online port calculators but it would be nice to know a few more things about what you're doing.

[RooTxBeeR]

Download Torres Tuning Calculator. It will do it for you and also towards the bottom there is an equation that you can use I believe. I have always used calculators of some sort just because I'm not the brightest and its so much easier lol

He wants the formula not a program to punch numbers into. In for info

[Exscathe]

I am building a box for 2 15" drivers, I drive a hatchback so I do have a decent amount of space and I do plan on removing the rear seats. Leave some trunk space for a battery or maybe my amp depending on how it all turns out. I have built a box before for two 12's and used RE Box calculator. I just want to know how to do it myself because you are limited to a side slot port on that software. I am seeing what my options can be with the space I have considering it is a small car. I have come to two solutions so far and thats remove the rear seat belt harnesses giving me an extra 3 inches on each side but this may prove difficult. Or have a slot port going along the bottom of the box however my box would have to be tall and not very deep or I end up with 9 cubic feet lol.

[Exscathe]

Still have a few months to figure it out, buying everything throughout the winter and starting the build in early spring / late winter!! Both of the stated above options are for drivers and port facing into the cab, that's how I like to ride, look back and see my excursion!

[bbeljefe]

You don't have to build the box the exact same shape that a calculator tells you. You just have to maintain the same volumes and port lengths it reports. That said, there are some dos and don'ts with respect to port and driver placement but there is no rule that says "X volume boxes must have vertical slot ports on the left side".

I suggest doing some due diligence here as well as some other audio related sites like:

http://www.bcae1.com/

http://www.the12volt.com/

http://www.diysubwoofers.org/

Formulas and calculators can be found there, as well as in depth information about how to design and build loudspeaker enclosures.

[Exscathe]

Well I was looking for something like this:

To calculate the frequency response of a ported enclosure system, you will need to know the following: Vb = net box volume (litres)
Fs = driver resonance frequency (Hz)
Qts = driver Q at system resonance
Fb = box tuning frequency (Hz)
Ql = box losses (Ql=7 can be assumed for most cases)

then,

Fn2 = (F/Fs)^2
Fn4 = Fn2^2
A = (Fb/Fs)^2
B = A/Qts+Fb/(Fs*Ql)
C = 1+A+(Vas/Vb)+Fb/(Fs*Qts*Ql)
D = 1/Qts+Fb/(Fs*Ql)
dBmag = 10*LOG(Fn4^2/((Fn4-C*Fn2+A)^2+Fn2*(D*Fn2-^2))

Found this browsing through http://www.diysubwoofers.org/

Let's start some calculations! Lol

[Exscathe]

And this:

To determine the optimum box size and tuning for a ported enclosure system, you will need to know the following Theile/Small parameters for the driver:

Vas = Equivalent air compliance (litres)
Qts = total Q of the driver at its resonant frequency
Fs = resonance frequency of the driver (Hz)
Dv = internal diameter of port (cm)

then,

Vb = 20*Qts^3.3*Vas
Fb = (Vas/Vb)^0.31*Fs
F3 = (Vas/Vb)^0.44*Fs
dBpeak = 20*LOG(Qts*(Vas/Vb)^0.3/0.4)

where,

Vb = net box volume (litres)
Fb = box resonant frequency (Hz)
F3 = -3dB frequency (Hz)
dBpeak = maximum peak or dip in system response

Note that this is only one of many possible alignments for a ported system with a given driver. Many types of alignments exist, each with its own particular advantages and disadvantages. This particular alignment will give you a maximally flat response within the system's passband, but it won't necessarily produce the best results with every driver, particularly those with very low Qts values (EBS alignments may work better with low-Qts drivers). You can use the "comparisons" section of the PORTED.XLS file provided on this page to derive a ported alignment that best suits your needs.

From: http://www.diysubwoofers.org/

[Krakin]

If you really want to see straight up formulas and what not (not very sciency choice of wording) you can look at the documents from Thiele and Small here:

http://www.readresearch.co.uk/articles.php

I'm not sure where everything is exactly that you are looking for, but it should all be there.