The Theater Series four π Speaker goes deeper but has rising response in the bottom octave. Response is flat from (f3) 50Hz up, but has useful response to below 20Hz. It rises at 12dB/octave starting about 16Hz, so it can really go deep with room lift, and the slope is complementary.

Another characteristic of the Theater four π is the midwoofer's narrowing directivity making response rise 6dB in the octave just under crossover to the tweeter. When it is placed in a room corner, then the rest of the audio range is forced into approximately the same directivity pattern, and this equalizes response. Floor placement against a back wall comes close.

The JBL 2226 used in the Professional Series four π speaker does not have this kind of rising response. It has flat response on-axis, even through the region where DI begins to narrow. This is because the midwoofer has falling power response that is roughly equal to its rising DI.

The Professional Series four π speaker sounds more natural in large spaces. If it radiates into a constrained space, the bass will be a little over-emphasized. Tuning is slightly underdamped, so it doesn't sound boomy when used in smaller rooms or placed in corners, but it is best used used in larger environments radiating into quarter-space.

One more thing I should mention is the fact that the JBL 2226 uses a shorting ring. This dramatically reduces distortion, especially at midrange frequencies above 100Hz.