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Quote:
Originally Posted by
Doctor_Electron
NOTE: If you wish to journey far beyond my primitive methodology, Read Here:
http://troelsgravesen.dk/vent_tuning.htm
I built a pair of 5 cubic foot cabs for subs using 2235s. I used two 4" PVC tubes in each. Using the old JBL Enclosure Construction Guide, I estimated a rough-in value for port lengths, with an extra 1" in case the calcs might be off a bit.
Finally used the tuning procedure in the guide which has a 1,000 ohm resistor in series with amp output, AF signal generator into the amp, and ac voltmeter across the loudspeaker terminals. Done at low power levels.
Lastly I adjusted port lengths for the double notch response.
I made the subs' low-pass network to be -3db at 125 Hz* with quality 10 mH inductor from Gold Sound in series with the driver, and a zoebel network from a JBL 3107 network (12 uf cap in series with a 10 ohm 25 watt resistor) connected across the driver.
*125 Hz recommended in a project article in Speaker Builder magazine, using the 2235 or 2245.
Hafler DH-220 amp for the subs. Alesis Matica 500 for the 4410s.
With everything above 125Hz handled with 4410 monitors, IMO the low end response and in particular superb detail from the 2235's, they could not have sounded better.
The high-pass function of -3db @ 125 Hz for the 4410's was implemented via a .022 uF polystyrene cap in series with each of the >125 Hz power amp's input RCA jacks, working into the amp's 22K ohm input impedance. Low to high range transition was seamless and first-order slopes adequate to work with the 2235 and the (now mid-bass) 127H's of the 4410s.
The sound of the system did justice to the JBL Pro brand.
Sorry for the thread divergence from just port size. The rest is just an example of what easily can be done as long as you have most excellent drivers to work with.
Regards, -de-
Thanks Doctor_Electron. I'll take some time and do the math laid out in the link you provided. I had also seen the enclosure guide and I have seen a lot of JBL 4320 that were converted to 4333's that retain both ports.
Without much else to go on, I had decided to go with the same ports that the original 4333 had since it has the same volume box. So I went from (2) 7" ports to a single 4" port - same as 4333. I blocked the other port but if I wanted to, I could just unseal it and reinstall the ports which I have still retained.
not sure how I will test how effective the single port is but I guess we'll see soon.
