As is ASR dogma, the best way to get good bass in a room is to use multiple subwoofers, which will generally have a shallow, low pass filter of perhaps 80hz 2nd or first order. There's no standard - some people advocate lower or higher or shallower or steeper. Bass management isn't really the issue I want to discuss here, however.
Ideally, your main speakers would have a complimentary high pass filter on them. This is much more uncommon, but that is a shame. Here's why:
This is a graph of a Rival woofer in a typical bass reflex enclosure. It has an f3 of 43hz in a small box. This is a high quality 7" woofer similar to what you get from ScanSpeak or Wavecor. This graph shows excursion in a vented box, and it shows that at only 39.5 watts, you are at the limit of excursion (6mm or so) at 60hz. If your content has any low bass, it will run out of excursion with much less power. Speakers tend to produce a lot of distortion as they near their limits and at a certain point it will just stop producing more sound.
In the past I've always advocated for plugging a bass reflex port. This essentially turns your speaker into a sealed alignment. I never really thought about this, but I assumed you would get more excursion and be able to play louder. However, this is what happens (blue line):
Yes, the over-excursion no longer happens at 60hz, but you still are dealing with the fact that at below the tuning frequency you run out of excursion fairly fast. Here, you run out of output at 14.4 W at 30hz.
It's clear that these midwoofers, while quite capable of producing pleasant bass at low levels, are not really made for higher output levels. Simply plugging your speaker results in a low, extended response that will run into excursion issues and have limited output at low frequencies.
But what if your preamp/DAC had a high pass filter on it?
This is what happens if you add a 2nd order high pass filter to your vented speaker. This ends up being what looks like a 3rd order ish response when combined with the roll-off from your vented speaker. F3 is now 80hz, which is a conventional crossover frequency. However, look at your excursion now:
Now you're running into xmax at 121.6 W! This woofer has a fairly typical IEC power handling of 70W, but still, it's nice to have that extra excursion for momentary signals. At this (maximum) power level, we are realizing the full output potential of this woofer, which is around 105db/1m.
The moral of the story - the ubiquitous hifi midwoofer is a limited full-range performer. Even next generation designs like the illuminators/purifi/anarchy woofers are not going to give you crazy output levels at low frequencies. However, they are capable of significant output if you relieve them of bass duties. Plugging a port doesn't really do much for you - a high pass filter is the way to go.
The woofer in this simulation is a full 180mm model with a pretty hefty magnet and xmax. When you consider how many people have bookshelf speakers with far less capable woofers (like a KEF LS50, almost any affordable passive speaker, even the Revels use 17cm models) it becomes clear how advantageous line level high pass filters could be for them. Indeed, the addition of subwoofers wouldn't simply 'fill out' the lower octave, it would allow for much greater dynamics as well, in a system that is visually unobtrusive and affordable.
Ideally, your main speakers would have a complimentary high pass filter on them. This is much more uncommon, but that is a shame. Here's why:
This is a graph of a Rival woofer in a typical bass reflex enclosure. It has an f3 of 43hz in a small box. This is a high quality 7" woofer similar to what you get from ScanSpeak or Wavecor. This graph shows excursion in a vented box, and it shows that at only 39.5 watts, you are at the limit of excursion (6mm or so) at 60hz. If your content has any low bass, it will run out of excursion with much less power. Speakers tend to produce a lot of distortion as they near their limits and at a certain point it will just stop producing more sound.
In the past I've always advocated for plugging a bass reflex port. This essentially turns your speaker into a sealed alignment. I never really thought about this, but I assumed you would get more excursion and be able to play louder. However, this is what happens (blue line):
Yes, the over-excursion no longer happens at 60hz, but you still are dealing with the fact that at below the tuning frequency you run out of excursion fairly fast. Here, you run out of output at 14.4 W at 30hz.
It's clear that these midwoofers, while quite capable of producing pleasant bass at low levels, are not really made for higher output levels. Simply plugging your speaker results in a low, extended response that will run into excursion issues and have limited output at low frequencies.
But what if your preamp/DAC had a high pass filter on it?
This is what happens if you add a 2nd order high pass filter to your vented speaker. This ends up being what looks like a 3rd order ish response when combined with the roll-off from your vented speaker. F3 is now 80hz, which is a conventional crossover frequency. However, look at your excursion now:
Now you're running into xmax at 121.6 W! This woofer has a fairly typical IEC power handling of 70W, but still, it's nice to have that extra excursion for momentary signals. At this (maximum) power level, we are realizing the full output potential of this woofer, which is around 105db/1m.
The moral of the story - the ubiquitous hifi midwoofer is a limited full-range performer. Even next generation designs like the illuminators/purifi/anarchy woofers are not going to give you crazy output levels at low frequencies. However, they are capable of significant output if you relieve them of bass duties. Plugging a port doesn't really do much for you - a high pass filter is the way to go.
The woofer in this simulation is a full 180mm model with a pretty hefty magnet and xmax. When you consider how many people have bookshelf speakers with far less capable woofers (like a KEF LS50, almost any affordable passive speaker, even the Revels use 17cm models) it becomes clear how advantageous line level high pass filters could be for them. Indeed, the addition of subwoofers wouldn't simply 'fill out' the lower octave, it would allow for much greater dynamics as well, in a system that is visually unobtrusive and affordable.