The max SPL (CEA-2010) deltas between the discontinued 13-Ultra and the 4000 series is (as I have mentioned previously and Mike stated above) about 0.5-1.0 dB on average (depending on the test frequency). This is with both amps set to 0 dB, and is consistent with the 1000W vs 1200W rated power difference between the two amp platforms.
The FR sweeps shown on the website are not all taken at the same exact drive level. We adjust the drive level of the FR sweep to obtain an adequate S/N ratio for good data acquisition (some test days simply have higher ambient noise levels than others). Naturally the FR sweep level doesn't reflect the maximum output capability of the subwoofer - and we state that below the FR graphs.
I just did a quick check of the Standard Tune PC13-Ultra vs Standard Tune PC-4000 CEA-2010 test data (these models were specifically mentioned above) and the deltas (in favor of the PC-4000) are:
20 Hz 1.0 dB
25 Hz 1.1 dB
31.5 Hz 0.2 dB
40 Hz 0.8 dB
50 Hz 1.2 dB
63 Hz 1.3 dB
80 Hz 0.7 dB
Again no real surprises here - typical/expected gains given the 1000W/1200W power level differences between the two platforms.
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