The
JBL spec sheet for the 2226 H/J 15” woofer provides plenty of info. Page 1 recommends enclosure volumes ranging from 3-10 ft³ (85-285 L). Page 2 provides the Thiele/Small parameters that allow you to calculate various possible cabinet volumes and estimate their cabinet tuning and performance.
Note that the 2226 is a PA woofer designed for high volume sound, not a hifi woofer designed for low frequency response. It sacrifices clean sound for very high volume – it’s maximum SPL is high, but so is it’s distortion.
Parts Express sells the 2226H (8 ohm impedance) version and suggests two different smaller cabinets:
- A sealed cabinet of 0.87 ft³ (24.6 L) volume, which provides an F3 of 110 Hz
- A vented cabinet of 2.03 ft³ (57.5 L) volume, which provides an F3 of 69 Hz
Other cabinet volumes can also work, but they must be calculated from the Thiele/Small parameters. See
http://www.jblpro.com/pub/manuals/enclgde.pdf for a number of different suggestions. Search Google for “jbl 2226h enclosure” and you’ll see many more suggestions.
Because you are interested in using this woofer in a 2-way design, the high frequency performance of this 15” driver becomes important. At what frequency can you cross it over to a tweeter in a 2-way design? The first page of the 2226 H/J spec sheet says the highest recommended crossover is at 1200 Hz. On page 2 is a frequency response curve. It suggests to me that 1200 Hz is too high.
This curve shows two important features. It looks like this woofer is going into break-up as low as 800-900 Hz. In an ideal coned driver, the cone moves back and forth as if it were a piston – with a single surface. Break-up is the term for when this ideal piston motion fails, and the surface of the cone appears to move as multiple separate surfaces, often in opposition to each other. It can create unwanted noise, as indicated by the peaks appearing between 1 and 2 kHz. Above roughly 1.5 kHz this woofer’s performance rolls off steeply.
The second feature is the difference between the on-axis and off-axis performance. On-axis response is measured with a microphone directly in front of the driver at 1 meter distance, and off-axis response was measured, at the same distance, but with the microphone 45° off to the side. At or below 500 Hz, the two frequency response curves are the same, but above 500 Hz the off-axis response begins to drop. By roughly 800 Hz, the off-axis response drops about 3 dB below the on-axis response. Below 800 Hz this driver disperses its sound in a wide pattern, creating the possibility of a good stereo image when two speakers are used. Above 800 Hz, this driver beams its sound in a progressively narrower pattern. If you cross over at 1250 Hz, it will beam an important part the mid range. There will be a hole in the middle in the off-axis sound of this 2-way speaker, damaging its ability to create a good stereo image.
For crossover purposes, this woofer should be crossed two octaves below any break-up, roughly 900 Hz, and more importantly at least one octave below 800 Hz the frequency when off-axis performance falls more than 3 dB below the on-axis performance. This is especially true if the cross over slope is 12 dB per octave. If it were me, I’d look to cross this woofer no higher than 500 Hz.
Edit: Crossing over as high as 500 Hz might be pushing it a bit. It might only be possible with a 4th order 24 dB/octave cross over slope. A 2nd order 12 dB/octave slope would require a lower cross over frequency.
I haven't looked into the low frequency performance of the tweeter you mentioned. Is it capable of performing without distortion as low as 500 Hz?
