Selecting JBL 2213/cabinet/port tuning frequency

[slowburn]

I've been using 4312 (mid-ranges and tweeters removed) with LE85/horns and 2405 bullet tweeter combo for a year now. First order series caps and on each compression driver, L-pads to waste dBs. No iron on the woofer, ala stock 4311. Suits me, my family, and my room quite well.

Love the JBL 123A/2213 tone so I'm trying them in a little bigger cabinet than that in which they normally work. The 4310/11/12 monitors are about 1.5 cubic ft. After reading that the 4311's are tuned around 40hz, I decided, "well, without being greedy and knowing there's no free lunch, how about a little more bass."

I forget who, but someone here suggested that I aim for 2.5 ft. in the new enclosures. I aimed but constraints parked me at about 2.1 in what are now the finished cabinets.

As in the 4311's, the woofers will fly solo in these new ported boxes. JBL LE85's on stereolab round horns will rest on top and outside of the cabinet. Probably the 2405's, too, but that's irrelevant for now.

My goal is to get the woofers to sound a little deeper, a little more open and lifelike than they do in the 4311. I'll run them wide open, ala the 4311/12, with same first order series caps on the upstairs horns.

The new port tube is 4" diameter. After some cypherin', I'd arrived at about 11.75" long, which I believe theoretically tunes the whole shebang to somewhere in the 30-33 hz range.

I've built a phono stage with octal tubes and point-to-point wiring, so I know the meaning of "fine tuning." (my hagerman cornet clone works, sounds good, but I wouldn't advise anyone to follow me down that frustrating path!) I know it may take some tube tweaking but how do I decide what frequency to even aim for?

Help! And thanks in advance.

[Robh3606]

Get a copy of WinISD, it's a free box program you can do simulations in. Look up the JBL Alpha it's a bigger cabinet for them with a passive radiator, just as easily use a port or you could run them sealed in a big box.

Rob

[slowburn]

Get a copy of WinISD, it's a free box program you can do simulations in. Look up the JBL Alpha it's a bigger cabinet for them with a passive radiator, just as easily use a port or you could run them sealed in a big box.

Rob

Thanks Rob. Don't do windows, though. and cabinets are built.

Let's review the question. How does one determine the frequency at which the woofer enclosure's port is tuned? How do I decide a frequency starting point for balancing efficiency, bandwidth, and linearity?

[badman]

Thanks Rob. Don't do windows, though. and cabinets are built.

Let's review the question. How does one determine the frequency at which the woofer enclosure's port is tuned? How do I decide a frequency starting point for balancing efficiency, bandwidth, and linearity?

WinISD will do it for yah. 5-6 cubic feet, sealed, is a nice alignment for this driver.

[Robh3606]

Let's review the question. How does one determine the frequency at which the woofer enclosure's port is tuned? How do I decide a frequency starting point for balancing efficiency, bandwidth, and linearity?

You can't find freeware for Apple?? You can calculate the tuning. The equations are somewhere easier to use a simulator. The easiest approach to to start with the clasic T/S alignment which is max flat and then go from there. From there I mean start to tune the box Fb lower. So if ideal comes in at 50Hz give 40Hz a try as an example. Look at the ideal volume as well it may be smaller than you have built so adjust accordingly. You should be able to get the exact tuning frequency by entering the volume you have and changing the tuning frequency to match your duct lentgh and diameter. You also need to look at your displacement/excursion curve and power input vs excursion to see that you don't exceed the drivers x-max over your desired bandwidth. You just tune the box accordingly.

Rob