Originally Posted by desertdome
Regardless of box size, if you have enough power for the low end won't the top end "never reach its potential for lack of available power"? At data-bass.com all the passive subs are power limited from 50 Hz and up - and that is with a Powersoft Digam K10!
Of course you never have enough amp to reach Xmax at the top end. You instead have thermal limits. The test results for long term compression of the UXL-18, for example, show thermal compression, not lack of amplifier power. Nevertheless, the sweeps continued to that point because the air spring of the small box prevented early over excursion.
Run the same test with the driver in a box large enough to approximate an IB and there's little chance it will reach 118dB before the driver fails.
I haven't found this to be a real world issue with my IB with actual content. Perhaps it is due to the low FS of my AE IB15 drivers, their impedance in the low frequency ranges, and the content played. The low FS combined with room gain gives me a rising bass response. I pull down my sub system by 10 dB at 10 Hz. Regarding content, the bass usually reaches its peak output at about 40-50 Hz and trails off from there. For example, in The Incredible Hulk the highest bass output is at 45 Hz using measuring software such as REW.
Perhaps it's the signal chain. When you measure in-room FR, you correct for the measurement rigs shortcomings down low, but when you play actual content, you are at the mercy of the signal chain.
Remember, excursion must quadruple for equal output for each octave lower in frequency. That's why THD increases as frequency drops, same excursion = lower output by -12dB/octave.
Hulk is a perfect example. The most difficult scene in the movie to accurately reproduce has most energy from 9-18 Hz.
Maybe someone can show similar results using IB?