As far as I know a true sub woofer is one that plays below the hearing bottom line say 18-20hz. They are the one that are FELT-but not actually heard other than room stress making noise!
I've seen many definitions for subwoofer from below 125Hz to below 30Hz, but the basic idea is that it's a dedicated driver for bass that below your normal woofer. Whether it's "needed" or not in a given system is another matter. Some speakers can play fairly full range, but that doesn't mean they can output enough air to reach the levels you may desire to play. Then there's the matter of whether you're playing movies or music and if music only, do you listen to electronic music and the like as most typical "normal" music rarely has content much below 30Hz.
I totally agree that a true full range speaker 20hz-20khz +/-3db is preferable for full range music however most of today’s home speakers and amps don’t have the muscle to get the majority of people that experience inside the budget of any blue collard workers sense of audio reason!
I'm not talking about most or many, but what's possible. If someone buys all Def Tech floor standing speakers in say a 7.1 system with built-in powered subwoofers and sets them up to reproduce LFE, I doubt they're going to need another subwoofer in their system. Now other "full range" speakers might not have enough muscle to move the air at levels desired, but then that's not really a full range speaker in that sense. My Carvers have 10" bass drivers. They're flat to 27Hz (about 25 in the actual room) and can produce pretty high SPLs down to that range, but they also have 350W going to each one of them and have high excursion. Many newer subs are designed for higher output to lower frequencies using more power. There's no reason full range towers can't do the same.
I'm not saying that's the cheapest way to go and many rooms won't support full range towers for all home theater positions (e.g. I can't fit full range front wides or side surrounds in my home theater as they would stick out from the wall too much and block the walkway or a table or whatever in at least a couple positions. For MOST people, subwoofers are the way to go and two subs are typically easier to integrate into a room for multiple seating positions than just one. I get +/- 2.5dB at the MLP for bass, but most seats are more like +/- 5dB and one seat is +/- 7dB and that is in a treated room (and room correction typically only works for a 3 foot area typically; if you have multiple rows it's not going to be a lot of help). A second sub set up properly would likely help reduce those dips/peaks. OTOH, a poorly set up second sub can do more damage than good.
Perhaps bass coming at you from multiple sources all at the same frequency and output level which by my experience isn’t possible in discrete multi channel (excluding multi sub arrangements) “may” help with room boundary interference but it definitely doesn’t simplify a very difficult in room frequency band to integrate smoothly.
I should have saved the article I read on this subject. The gist was the more bass sources you have reproducing the same frequencies (i.e. all doing LFE),the more even the overall room response tends to become. With only a couple or a few sources, you might get more destructive interference depending on room placement, but by the time you get to 5-7 bass producers around the room, it tends to help far more than hurt even without careful placement (i.e. a set of 5 full range towers in a 5-speaker home theater would likely have more even room response than a single subwoofer or 5.1 system using bandwidth limited 5 speakers and one subwoofer.) But then using a sub too would only add another bass source and further even the response. Now if the bass material is not LFE (mono),they might not all be producing bass at the same time and that would not apply as all sources have to be active for the mode kill effect to work.
Some say they can still locate their sub below 80hz and even lower probably because the sub levels are to high or the sub enclosure itself hasn’t been dampened well enough for the output!
It's usually the higher frequencies that give the position away, not 80Hz or below. "Some" people MIGHT be able to localize some bass below 80Hz (people have a wide variance in their individual responses; I can hear frequencies over 20kHz for instance for some odd reason, but they appear as beat frequencies below 20kHz in actual "sound" to me. In other words, if I play a 22kHz test tone, I can hear it, but it sounds more like 15kHz or something, not what I'd expect 22kHz to sound like). I think it's an ear anomaly somehow creating a beat frequency, but it's very annoying as I can often hear alarm systems and bug zapper type sounds (one family member has bug zappers and I have to unplug them when I visit as they're awful sounding. NO ONE I know that's been in the same house can hear those sounds. But I don't hear them at a 20kHz or higher pitch. I hear them in the 10-20kHz band as what I assume is a beat frequency.
Question for you is, “why would you want your low frequency bass which most of the frequency band in question here is from say 5hz-80hz localizable?”
I'm not suggesting it would be localizable in that band. I'm suggesting even a subwoofer with a 4th order crossover playing stereo music will not stop playing entirely above 80Hz. It would still be outputting sound 12dB down at 160Hz and 160Hz is able to be localized by most people. 100Hz is localized by most people as well and it would only be down 3dB at 100Hz. Similarly, it would be down 6dB at 120Hz, 9dB at 140Hz and and 12dB at 160Hz. So it should be a small wonder that people sometimes can localize their subwoofers with bass in the 100Hz-140Hz regions, especially if they have the subwoofer turned up 4-6dB above flat for extra bass kick (pretty common with home theater setups). A room with all full range speakers would not have that issue as all speakers would still produce stereo sounds from the correct location. That's all I'm saying. Once you move a subwoofer to position in the room that does not correlate with the actual sound position, you risk having at least some frequencies be able to be localized more than others. Room peaks can make that worse as can furniture and other room items vibrating in sympathy with the sub (rattles and the like),which will all tend be at higher or less controlled frequencies. It can be a PITA to get rid of those things.
Thunder is not localizable to us when it shakes our homes and there is plenty enough localized bass above the 80hz crossover point to give us directional information.
I don't know about you, but I can often tell which general direction thunder is coming from, at least the initial sound which is more than just rumble. Even if I play the Atmos "Amazing" demo which does three thunder claps, each from the front, middle or back of the room and they are all clearly easily localized as the thunder has components well above the subwoofer range that gives them away and all my ceiling speakers are bandwidth limited to 80Hz and above. It's the higher components that often give bass a location in the room. So bass guitar notes in the 40Hz-60Hz region may not be localized with their fundamental frequency, but their higher order frequencies and things like the finger noise on the strings can certainly be localized. That doesn't mean a subwoofer won't work in the room as the other speakers give the sounds the directional component. But in that crossover region, you can get some problems with direction, especially if the sub is cranked up and the sound in question is electronic in nature (less overtones to give the direction with the main speakers).
