airysounds---Though you feel the SB13 has more output below 25Hz than the E15HP, the opposite is actually the case; the SB13 rolls off quite a bit more rapidly than does the E15HP (look at the graph for proof). 25Hz is not actually heard (the open bottom E string of a 4-string electric bass produces a 42Hz tone), it is felt. What you may be hearing more of with the SVS is actually second harmonic distortion, which will make low frequencies sound "fuller", more "hearable". For the sound you seem to desire, the Rythmik ported 15" sub (FV15HP) is the answer. More output than the E15HP above tuning, with a fuller, slightly thicker quality. Less lean, less clean, more pronounced and heard separately from the main speakers.
In regards to amplifier power, your comments reveal that there is something you're neglecting to take into account: Driver sensitivity/efficiency. The fact that the SB13 has a 1000W amp while the E13HP has a 600W one does NOT necessarily mean the SB13 will play louder than the E13HP, and here's why: How loud a driver will play is dependent upon (simplified for the sake of clarity) not just the amplifier power, but also the sensitivity/efficiency of the driver. A 1000W amp will produce 3dB more SPL at a given frequency from a given driver than will a 500W amp. However, the SB13 and the E15HP do NOT have the same driver. We need to know the sensitivity/efficiency of the two drivers before we can declare anything about the power advantage of the SB13. If you hook up an 85dB sensitive woofer to a 1000W amp, that combination will produce 3dB more SPL than will a 500W amp connected to the same woofer. If you hook up an 82dB sensitivity woofer (3dB less sensitive) to the 1000W amp (3dB more powerful than the 500W amp), it will produce the same SPL as the 85 dB woofer connected to the 500W amp. The 3dB advantage of the 1000W amp and the 3dB "penalty" of the 82dB woofer equal each other, and cancel out (remember your High School Algebra?!); the two combinations---1000W amp + 82dB woofer vs. 500W amp + 85dB woofer---produce the same SPL.
Does that make clear why the simple fact that the SB13 has a 1000W amp NOT tell us whether it will therefore play louder than will the E13HP with it's 600W amp? We don't know the sensitivity/efficiency of the woofer in each sub! What if the woofer in the E13HP is 3dB more sensitive/efficient than the woofer in the SB13? Well, the E13HP would then actually play louder than the SB13 (the 1000W SB13 amp being less than 3dB more powerful than the 600W E13)! Power alone tells you NOTHING about how loud a driver will play---you MUST know it's sensitivity/efficiency. MUST!
Last edited by BDP24; 09-02-2015 at 08:27 PM.