Frank, the sub woofer I have is flat to single digits in my room. I can easily reach 10Hz with no problem and you know when that happens
. In other, much bigger rooms, other people have also shown graphs that indicate that my sub can reach into the single digits. At those frequencies, they are felt more then heard. That is where the monster shake and rumble comes into play. As far as just getting butt kickers, or something like the Crowson(which I have) I agree %100 that they are fun. But having something like that does not automatically negate the need for a sub that goes really low. You still want that sub to fill in the bottom octaves because no matter what, you still notice it, When you watch a movie like War of the Worlds, or Inception, Unstoppable you will feel what a sub that can go that low can do for the movie watching experience,
This may get long, but let me give you a few examples. First, with myself. My previous sub, before the SubMersive, was JM Labs a SW900. That was a ported sub that had a 13.13 in driver and it had a 400 watt amp. It was a mighty fine sub. It could get loud and shake the room with no problem. I even did my own chart of it.
SW900(with EQ).png 18k .png file
As you can see, it was not a bad sub. It was fairly flat in my room. Except for the room dips at 63 Hz and around 20Hz. Now that was not a max chart, that was an Eq'ed chart. Here is a max SPL chart, I will never do this again
So, that was my previous sub. Like I said, it was a great sounding sub. But, it did not go super low. When I started talking with Mark he assured me that going from what I had, to the SubMersive would be a monumental change. Well, within the first 10 seconds of watching a movie with the SubMersive I could tell the difference. It went way lower than the SW900. That showed itself by just adding a "weight" to the soundtrack and effects. Now when I watch a movie that has serious bass it is a grand experience. With the Submersive, I know that if there is any bass on the soundtrack, I will pick it up. So I know what you are asking your self. If the SubMersive is so good, then why did you get the Crowson. Well, I don't live alone. Getting the Crowson allows me to get that great tactile feel without having to crank up my overall system too much. But again, even just the raw SubMersive was plenty for my room. I just wanted to tinker and see what would happen.
Here is what my sub looks like after all of the EQ'ing is done
Take a look at that green line. That's the sub. Look how flat it is. There is no drop off at all and that graph ends at 16Hz not because that's where the sub ends. It stops at 16Hz because Craig's gear does not go lower than that. But I have yet another graph that showed that I am virtually flat to 8hz that was done a long time ago by Mark S. Once you really experience that low powerful bass done right, it's hard to go back to any else.
Now you have 4 great subs spread about your room. No doubt about it. I am sure you have great bass all around. And I am not saying that you should get rid of them and get something else. I would never do that. All I can do is say that I did not get it either until I bought a sub that could do what mine could not. If you are satisfied with how your system sounds and feels(and I can't imagine why you would not be), then don't worry about it. I was bitten and I would not have been satisfied until I checked it out for myself.
Now I know this is long so just hang in there a bit more. Way back in the beginning of HT education, I used to go to this store all the time. It was a high end audio store. They had a lot of top notch gear. That is where I first realized that the sub I had back in the beginning(a definitive technology PF15) was really not as good as I thought it was, So, I started listening to other subs, I knew one of the salesman there pretty well so they would be just hang out and go from room to room. It was there that I heard subs that were much better then mine. One of them was a $9,999 Wilson Watch Dog sub. That sub was amazing for a 12in sub and 400 watt amp. I also heard a Dynaudio sub. But then I heard the JM Labs subs. I was really impressed. One of them was the Sub Utopia Be. That was a beast. It had a 1000 watt amp and 16in driver and was ported. It was so intense I once had it shaking their 22,000 sq ft building. But it was too much and the SW900 was way better then what I had so I bought that. Then, as I mentioned above, I started to want more. I got a hold of Mark. He assured me that the SubMersive would be worlds better then what I already had. Well, I can honestly say that for 1/3rd of the price I achieved the sonic and tactile performance of the $6,000 sub Utopia Be which up until that time, was the best sub I had EVER heard.
I just can't stress how much fun it is to watch a movie and see things shaking on the screen and get the same feeling in my room. If it is done right, there is no going back. Like I said, it's more then just shaking or rattling. It's that extra something that puts you more into the movie. That's how you have to look at it. Getting a "shaker" can be fun. But it is no substitute for a sub that can get there on it's on. I hope that explains it a little
. At least from my end.