[Blaser]

Here are the SS Rl-p18 sub specs:

Dual 4 Ohm Measurements
Qts: 0.436 Qts: 0.493 Mounting Depth: 26 cm
Qes: 0.482 Qes: 0.554 Total Depth: 26.5 cm
Qms: 4.535 Qms: 4.500 Outside Diameter: 46.7 cm
Fs: 20.71 Hz Fs: 21.5 Hz Weight: 41 lbs
Re: 3.74 Ohm Re: 6.26 Ohm Magnet Width: 18.8 cm
Ls: 3.317 mH Ls: 4.341 mH Mounting Cutout: 43.2 cm
Rp: 7.629 Rp: 10.27 Displacement: 0.2 cu ft
Vas: 314.2 L Vas: 276 L
Mms: 376.7 g Mms: 373 g
Cms: 156.7 u Cms: 137.7 u
Bl: 19.50 T*m Bl: 24.25 T*m
SPL: 89.45 dB SPL: 89.25 dB
Sd: 0.1188 m^2 Sd: 0.1188 m^2
Xmax: 27.4 mm Xmax: 27.4 mm
500 - 1000 watts RMS range

The Maelstrom-X Pre-Production Parameters: Fs: 17.7 Hz
Le: 0.87mH
Re: 3.1 Ohms (Voice Coils wired in parallel)
Qms: 7.8
Qes: .38
Qts: 0.36
Mms: 494g
Cms: 0.17 mm/N
Vas: 324L
Sd: 1182 cm^2
Vd: 7.8L
BL: 21.17
X-max: 33mm
X-mech: 42mm
Pmax: 1500W

Prices are comparable with a bit more for the RL-p18. I have been playing with WinISD and got some shots for you below.

According to WinISD, It seems they have both quite similar performance, with the RL-P18 a bit more efficient, and slightly louder. The Maelstrom X can be tuned like 1 hz lower and could have a slightly smaller enclosure than the RL-P18

I have dual of those and you really can't go wrong with Sound Splinter. I do not know the Maelstrom X but it looks like a good sub. But the Soundsplinter would be more tempting for me.

Note: The Rl-P18 is in green, 2000 W signal applied, cone excursion and port velocities are assumed RMS (closer to realprogram material).