Matching a sub to a prebuilt ported design

[gorvann]

How do you match a sub to an already bulit ported box cabinet?
I have some old loudspeaker cabinets. A three way design that has the port already installed. I dont have the orignal drivers. I like the cabinets and want to install new drivers and crossovers.
Any help on this would be gladly accepted.

[BlueWizard]

Within certain limits, the cabinet and port are independent of the speaker. The volume of the cabinet combined with the diameter and the length of the port cause the box to resonate at a particular frequency.

There are different schools on where that resonance frequency should be, but in general, it should be roughly near the Fs resonance frequency of the speaker/driver itself. In that sense, the cabinet and driver are connected.

Measure or estimate your cabinets internal dimensions and convert it to either square feet or Liters. Next determine the ports inside diameter or dimensions and its depth.

Then use one of these port calculators to determine the resonance frequency of the box. Remember to subtract some internal volume for the space that the driver takes up.

http://www.2k4civic.com/portcalculator.html

http://www.linearteam.dk/default.asp...ventcalculator

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

Set the volume and the port information, and determine the tuning frequency.

The other factor to consider is that different drivers are optimized for different sized boxes, though there is some flexibility. This is somewhat determined by the Vas specification of the driver.

Also, you need to determine whether the driver is more suited to a seal cabinet or a vented cabinet.

To get this, you divide the Resonance Frequency (Fs) by the Electrical 'Q' factor (Qes) or (Fs/Qes). If the number is 50 or less, then a seal enclosure. While a value of 100 or more suggests a vented enclosure. Anything in between is a judgment call.

Steve/bluewizard

[901Fixer]

What is the brand of the loudspeaker cabinets? If you have the make and model it is possible you can get replacement drivers or much superior drivers based on cabinet size.

If custom made, measure the inside dimensions and post them as I'm sure the volume and port size will inspire folks here to recommend various drivers that will work in such a space. Also describe if there are seperate compartments for the mid and tweeter or if it is just one big box with everything in it.
Are you willing to modify these cabinets some if necessary? Nothing major and probably just inside which won't be seen anyway.

Oh yeah, what is your budget?

[gorvann]

Thanx Mr. Wizard. Your assistance has been very helpful.