Hi
Well, I tried Alpine, Pioneer and Sony - Alpine and Sony have similar drivers but no specs. So, time for some "engineering expediency". Freq range is given as 62-21000Hz, so I will assume that 62Hz is the Fs. Typical Vas for a 6 inch driver is about 1 cubic foot. Assuming the same mech compliance, that gives us 7 litres for the 4 inch.
Your internal volume comes to about 8 litres, which must be split across 2 drivers so it's effectively 4 litres per driver.
Now, a common rule of thumb for reflex tuning if you don't have all the info is to go for the driver Fs, in this case 62Hz. However, porting only helps if the enclosure is not too resonant to start with. I can't guess the driver's Qts and this is hard to measure.
If the drivers without porting sound thin with some tight but not very loud bass (in sealed cabinet), then they probably have a low enough Qts to be suitable for porting - in which case port at 62 Hz and enjoy louder bass.
On the other hand, if the drivers sound like they have quite full bass already (but not very deep) then they are not suitable for porting. However, you want the ports anyway for airflow reasons - a compromise in this case would be to "underport" where you tune too low, and the port has little acoustic effect, but can still pass a DC airflow. Underporting would require about 30Hz tuning freq in this case.
A simple formula for port length is (from memory) Ld = 2691 * Sd / Vb / Fb^2 - 0.88 sqrt(Sd). It's all in feet and inches I'm afraid. Your Vb (for each driver) is therefore 1/7. Trying a 1 inch port (Sd=pi/4) and Fb=62 Hz, we get Ld = 3.07 inches.
If the driver is suitable for porting then based on what I know, I recommend a 1 inch diameter, 3 inch long port for each driver. If not, I recommend you use ports 1 inch diameter and 12 inches long to underport down to about 30Hz.
In order to mono-ise the bass, I suggest something like this:
Code:
empeg L ---/\/\/\/-----+------ amp L
|
-----
-----
|
empeg R ---/\/\/\/-----+------ amp R
I.e. run the empeg's L and R outputs through resistors and then join them to each other via a cpacitor. You need to determine the amp's input imedance (should be in the specs) and use resistors of about the same value (R). The cap is then 1/(5000R) for a 300Hz cut-over (roughly). I choose 300 Hz becuse the driver seperation is about a quarter-wave at 300Hz, and so that's about where the drivers begin to act as a point source acoustically.
Now all you have to do is install the fan in the middle of the box - you should be able to build a partial baffle across the middle of the box to assist the airflow. No need to seal it from an acousticl POV becuase there will be negligable sound pressure across it.
Anyway, I hope this helps even though its all a bit vague and approximate. Do try experimenting. You could also try mailing Magnat for the driver specs just on the offchance. I'll probably not log in until next year now, so speak to you then.
Cheers, John
Edit: fixed ASCII art -wfaulk
) that can put together a box, in whatever material you favor, that houses the MkI docking sled you have (and, as you say it'll stay in the house, don't need in order to mount it in the car). That makes the whole project fairly easy - or you can get the fitting connector
