# Determing cabinet size for a given speaker

Discussion in 'Amps and Cabs [BG]' started by basss, Dec 3, 2003.

1. ### basssSupporting Member

Aug 27, 2001
NY
What are the basic steps for determining the size of a cabinet that a certain speaker needs? I'm not looking for an in depth analysis, I'm more just curious about how this works and would like to hear a general overview.

Oct 22, 2002
Maple Grove, MN
It is actually quite easy to calculate ideal cabinet size, given you have the Thiele-Small parameters for your speaker.

the three main variables to determine cabinet and port tuning are Vs - equivalent volume, Fs - resonant frequency, and Qts- total system Q.

I can't explaing the parameters very well, but the equations are on several web sites, some even have calculators. There's freeware to do it to.

So basically, you plug the parameters intothe equations to give you the internal volume of the cabinet (don't forget that wall thickness will add to the outer dimensions) and then plug some more numbers into another equation to get the length and diameter of your vent.

Then you can figure out the internal dimensions needed to get your volume. Then build a box, cut a few holes in it, slap your woofers/tweeters/crossover in and away you go to bass heaven.

In a nutshell.

Stay Low,

BT

3. ### Petebass

Dec 22, 2002
QLD Australia
It depends on which allignment you're using. I'll explain it as though you're using a vented cab in SBB4........ lets pretent your speaker has a
VAS of 100 litres,
QTS of 0.30,
Fs of 40Hz.

Have a look at the chart I've attached. The column on the left is QTS so follow is down to 0.30. Now move 2 colums across the find out the corresponding value in the "Alpha " column. In this case it is 2.5448.

Divide the VAS by this value. The result is the correct SBB4 cab size in litres. So 100/2.5448 = 39.30 litres.

Note that sealed cabs use a different chart, as do all the other allignments. All the charts can be found in Vance Dickasons book.