Originally Posted by Decadent_Spectre
Everyone has different definitions of loud and good, and what constitutes a good sub.
Some people find 100db to be loud, others think 120db is loud, while some may think 140db is loud.
Some people like the rumble of the low end in movies, others like synthetic/electronic bass, and some like a kick drum.
Some prefer vented, others sealed, others horns.
It's all a matter of personal preference.
It also depends greatly on frequency...I have experienced a legit 130dB+ of 16Hz more than once and I would not call it loud to the ear at all, more like audible but many orders of magnitude more of a "physical" body phenomenon than any discomfort on the ear mechanism itself. In fact it makes you afraid for the surrounding structure or vehicle. Now 130dB+ 3 octaves higher at 125Hz is a whole other thing which will cause ear discomfort in most people and is accompanied by less obvious physical sensations on the rest of the body and surroundings but is many times more subjectively loud. If you increase the frequency another 3 octaves to 1000Hz this same SPL level will cause less noticeable physical sensation on the body or surroundings (No concerns for a building or car interior) but will cause severe ear pain in most people since this is an area where the ear is far more sensitive than way down in the bass.
Typically it is easy to get enough sub for more headroom than needed from 40-150Hz...Say 120dB at your headrest, which would probably be more than enough for the typical listening habits of most. But maintaining headroom gets increasingly difficult as the desired extension is lowered from 40Hz to 30 to 20 to 16 to 10 etc...Even with typical room gain this requires huge increases in total displacement, SD, power, etc...Most of the improvement in bigger sub systems is often targeted at more deep bass headroom and deeper extension. The difference in equipment needed for a sub system that can deliver 120dB to the headrest at 16Hz versus one that can only deliver that much at 32Hz is huge.
Just for reference of what an excessive multi driver DIY setup can do in a 3200 cubic foot room here is what my 8x sealed XXX 18 / 2x Powersoft K10 system will do when measured at my headrest with the CEA-2010 program. I am limited by the available amp power and tiny sealed enclosures to about 4dB less than what the drivers could theoretically do at xmax, but nonetheless doing these tests broke a door frame and 3 pictures. The CEA-2010 burst signals are less than half a second duration. I stopped after the 31.5Hz burst caused a large picture to fall off of the wall in the hallway upstairs and break on the tile foor. I decided to call it good at that point. I have a large peak at my listening position at about 45Hz so undoubtedly 40Hz would have been over 140dB. I also measured over 128dB at 7Hz with a sine wave with this system. In no way would I want to experience these levels in my home for any sort of real duration if split second signals cause such devastation already. This is a brick and concrete room on 4 out of 6 boundaries too. I'd hate to think of what it could potentially do to an older wood frame structure. I typically listen at -20dB below this systems potential so it's way overkill for me.