Hi, New 123A based project

[badman]

Hi:

New user got interested in vintage JBL 12"s, and picked up a minty set of 123As and a set of 122As needing foam.

Right now I'm working on a design with the 123A woofer and a 3" midtweet, series first order XO at 500 specs out really nicely (well damped Fs for the mid/tweet due to series XO), and should be a good balance between divers. The 123A having the powerful motor and low Fs but higher Qts makes it well suited to a modest size Open Baffle, a use not widely explored with JBL drivers. The huge Vas of these monster AlNiCo motors (the 122A is even more powerful with a lower Fs but too damped for this purpose).

Anyway, hello all!

[Zilch]

Look also to how 123A performs closed-box....

[badman]

The closed box usage is great, except for one thing: It needs to be huge! Even a max flat alignment (which is higher Qtc than I like to shoot for) is 8 ft^3! One could, of course, go to an aperiodic box and save SOME of the volume, but it's still gonna be pretty serious in terms of size.

My sims, with the driver low down on a wide but short baffle (tilted back) show pretty impressive low frequency extension - f6 around 28 (with room interaction of course).

Not too shabby! There's of course the potential for excessive excursion, with the woofer having no enclosure based damping, and such a low Fs (for this type of app, anyway), but I don't need 110dB @ 20Hz from a speaker like this.

This limited excursion ability will probably show up in the midrange as well, when this unit starts getting towards the end of its abilities, and the power throughput needs to be lowish anyway due to the AlNiCo motor.

Should be a fun game to play

[Zilch]

BB6P suggested closed-box alignment for 123A with Qtc = 0.707 is 3.22 cuft.

With heavy fill:

F3 = 45.33 Hz

F10 = 25.99 Hz


For 2213H (123A-3) it's a bit better in an even smaller box, 2.246 cuft.

F3 = 43.96 Hz

F10 = 25.50 Hz

[badman]

BB6P suggested closed-box alignment for 123A with Qtc = 0.707 is 3.22 cuft.

"Bass Box 6 Pro" is what you're referring to I assume? I mathed it out in my head at first, but several other calculators including winISD Pro calc a max flat volume of 8ft^3. What Vas value are you using for the 123A? I'm using 235L.

[Zilch]

BB6P uses 235 L per the JBL spec.