Reverse Engineering a Double Chamber Bass Reflex

[kelleysislander]

All,

I have successfully built a DCR in the past, the one from the Weems book using the 8" woofer, and I just loved it. I knew all my params and was able to utilize the T-S math to calc the ports, volume, etc, and they sounded great, especially on the LOW end!

Fast forward 15 years and I have become the proud owner of 2 large cabinets of approx 9.1 cu ft interior volume. They have two 12" Musical Instrument / PA-style drivers in each, which I will not be using. I have a vintage Pioneer 3-way crossover rated at 270 watts, and I have my choice of 2 different bass drivers:

a. 12" CTS (very little I can find out about these, mags approx 6" x 6" x 1.5")
b. 12" Wharfedale (one has a stiffer surround than the other, butyl rubber it appears, mags same size as the CTS, above)

I know absolutely nothing about the params of the drivers except their dimensions, so my problem is to determine, through experimentation, educated guessing, etc, the correct size and length of the 3 ports needed. I will divide the inner volume into a 6 cu ft and a 3 cu ft space and place the driver into the larger of the two.

Does anyone have any ideas on how to approach this situation? I want to make the ports "stackable" so that I can start with a shorter length and add segments to them (1/2" increments???) until I get the tuning I want.

I am looking for a starting point and any help would be greatly appreciated!

Thanks,

Bill