The Fi BTL subs are amazing! I don't know if it is the new head-unit I have or the new amplifiers but WOW. It is amazing how tight the sound is compared to my old setup. My old equipment had a hard time keeping up with fast bass tone - changes and sounded a little mushy. I don't know if it is because I am running a higher ohm rating and therefore the subwoofers have a little more control, or if because I am pushing with 1 amplifier and pulling (180 switch) with the other, or if it is because my source unit is just THAT much better with the signal or what but - I am truly impressed with how good musically the subwoofers are. How clean and tight the sound is. Fast or slow - the subwoofers keep in rhythm. Very clean! It seems that they need a LOT of power to make them move though. I noticed it even before I installed them - the cones were VERY tight compared to the Fosgates I had just installed. I'm sure it is to help maintain very tight control under extreme movements of the cone. They are very impressive! I did a lot of research when purchasing Fi BTL N2's and am overall satisfied with my purchase so far....but....... I have a 2005 Nissan Altima and recently have gone through a major audio overhaul. I took out my old pioneer head-unit and replaced my Rockford Fosgate T1's and T1500 amplifier. My original idea was to get 2 - T2500bd1-CP amplifiers and link them then use 2 12 T2's. Upon install of my T2's - I guess they couldn't handle the power (or because of my inexperience) I blew them literally within 30 seconds of installation. I sent the T2's in for warranty replacement and researched better subwoofers. I may have gone a little crazy with the upgrades - 3 new Kinetik 2600 batteries, 1/0 wire everywhere, 800 watt RF 4 channel for mids and highs, and the bass amplifiers, and new springs in the rear to support all the weight. After all that - I was NOT about to give up when my subs blew. After watching Steve Meade try to destroy a Fi 18 by plugging it in to a wall socket - I was SOLD! I placed my order about 3 weeks ago and about a week ago - my new subs came in! After installation and some tweaking. I noticed that one of the subwoofers made an almost mechanical noise - almost like something was hitting the cone when certain bass frequencies were being played. I thought - well...maybe I don't have a good enough seal around the basket...maybe the sub is vibrating against the box or something at certain frequencies. So I took out both subwoofers and made sure they were sealed up tight with a bit of rope caulk and very tight in the box. The next day I tested them and they sounded quite nice! Problem SOLVED!....or so I thought. It seems that whenever I play the subs for an extended period. Just enough so they kind of warm up. One of the subs makes the noise still! Even more strange is that it seems to only happen when I am playing higher frequencies - read... north of 38hz or so. I did some testing with a friend tonight.... We played a resonance test over and over and listened to both subwoofers and only the one makes the sound and only after warmed up and again only higher frequencies. It is really noticeable when playing rock when the drum beat hits - makes a nice POP noise. What the heck could be going on (gone wrong)???? What should I do? Leave it for a while and see if it gets any betteer/worse? Send it in? Am I just hearing things??? Do I have something set wrong? Believe me - I'm trying to be ever so careful with gain and distortion. It seems that with this much power - distortion is VERY unforgiving. Someone is probably going to ask so... Box is 2.00 cu/feet per sub. About 1.9 after displacement. BTL N2 12 / 2 ohm DVC / cooling option / high XMAX coils. Wired in Series (4 ohm) then parallel (2 ohm). When the amplifiers are linked they only support a 2 ohm load. Slot port - tuned to about 33hz. Crossover set to 25 hz and 80hz both high and low pass filters set at -24 db slope I think / subsonic filter is ON - I think RF has subsonic set to 27hz??? Anyway - thanks for any help. Oh and BTW - have 2 RF T2's for sale if anyone us interested LOL brand new in the sealed box.