yeah rl-p are about s quality and great outut and they recomend to tune ur box to 18 hz too but if ur going for sql the maximun tunin freqenzy will be 34 hz so if u pass 34 hz the subwoofer will act like a spl woofer so i said tune it to 32hz or 28 hz will be ok for sq or tune it even lower for more sound quiality
I WOULD LISTEN TO MIKE AT SS SINCE HE IS THE ONE WHO PLANNED THE WHOLE THING OUT AND HE'S SS. 28HZ WILL GIVE IT THE BEST RESULTS FOR SQ AND SPL. TUNING IT HIGHER LIKE 32HZ WILL GIVE IT GOOD SPL BUT MISS SOME OF THE SQ. AND SORRY THIS IS CAPS, I'M AT WORK.