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I have hear this phrase used a lot and I think I have a theory of what the trait of "fast bass" actually represents. If there was such a thing as a "fast", "quick", "tight" subwoofer, what exactly does that entail? The discussions I have seen seem to refute the idea that such a trait really exists.

I have owned:
-no subwoofer and B&W 802 nautilus speakers alone (capable of decent bass)
-a single SVS subwoofer coupled to B&W 802 nautilus speakers
-a single SVS subwoofer coupled to B&W 802D speakers
-Avantgarde acoustics duo omega main speakers (with built in powered subwoofer, mid bass) coupled with BG-Radia in-wall 4 room corners THX speakers (48 small drivers arranged opposed to cause vibration cancellation), Audyssey processing
-Avantgarde acoustics duo omega main speakers (with built in powered subwoofer, mid bass) coupled with BG-Radia in-wall 4 room corners THX speakers (48 small drivers arranged opposed to cause vibration cancellation), Audyssey processing, additionally JL Audio Fathom F212 x2
-Avantgarde acoustics duo omega main speakers (with built in powered subwoofer, mid bass) coupled with 4 subwoofers, 2 drivers each, Dayton Audio ultimax 15" drivers powered by a Lab Gruppen PLM 10000Q with PEQ.

currently: Avantgarde acoustics Trio omega main speakers (with built in powered subwoofer, mid bass) coupled with 4 sealed subwoofers, 2 drivers each, Dayton Audio ultimax 15" drivers powered by a Lab Gruppen PLM 10000Q with PEQ.

Along the way I was using REW since I had the B&W 802D speakers (almost 10 years). I wasn't meticulous enough to save all the tracings however.

The features that I have found most consistent with "best bass":
1. Sufficient driver surface area and other characteristics to produce higher volumes for my large room. Smaller subs simply feel anemic and bottom out too easily when driven hard. I was bottoming out JL audio fathom 212's easily on higher volume movie bass. In fact "reference" volume bass was out of the question for my 5500cu ft room with anything but the DIY subs.
2. Four subs have been consistently better than two subs, two subs were consistently better than one sub.
3. Four corner subs in a rectangular room gives very predictable results with room boundary gain (will need PEQ for sure).
4. Elimination of "one-note-bass" with multiple subs, careful placement, plus addition of PEQ is very important. eliminating peaks and nulls really has subjective benefits which can be described as "tight" or "fast" or whatever adjective you want.
5. The 4 mid-wall positions or 4 ceiling subs has been talked about by THX and Harmon but I don't have specific experience with these configurations.
6. timing aligning the subwoofer delays to all hit you at the same moment
7. doing subs in-wall or behind a baffle so that don't see them will helps with the psychoacoustics of localization. I find the immersiveness to be subjectively better.
8. With more drivers, each driver doesn't have to move that much... so low distortion is an obvious benefit.

So based on room size and desired volume response, you need to figure out what subwoofer drivers will suit your needs. 4 corner subs is almost always going to give you a good in-room response that can be further corrected with PEQ and delay settings.

If you are going DIY, my preference is to build the in absolute largest drivers, best xmax, and the most number of drivers possible based on your space constraints.

If I were building a 5500cu ft again theater today. I would do at least 4 subwoofer boxes. Each box would go just about floor to ceiling and simply completed by a trim carpenter to my specifications. I would do 4 18" drivers per box and power each box with around 7000 watts per channel. It is cheap enough during house framing to build boxes that I would likely add a couple of boxes at the mid-side walls just for good measure (more options for tuning for linearity). Along with this I would place a couple of 30-40 amp / 240 volt wall receptacles near the amps.

World class bass is simply not out of reach if you desire it. You certainly can do better with DIY than with almost any commercial boxes out there... especially if you can plan ahead for very large subs.

Reasonably achievable goal: Measured in-room Linear response down to 15hz at reference volume levels with no bottoming out or distortion ... "fast" and "tight" as you can imagine.
 
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Fast bass for small sub and the belife that large subs can't produce bass as quick is an old myth. Larger subs have larger motors, don't have to move the cones as much, ect. I have subs ranging from 8 in. to 18 in. and they all can sound great when setup correctly.
 

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Its whats outside the box and not inside that leads to good or bad sounding LF. Peaky or bloated bass leads to us concluding that the bass is sloppy or"slow" when its in fact room modals, sub placement, size and shape of room and room construction are the cause. Subs are perfect in the sense that they pretty much perform as the software tells us it will. Its not that an 8" sub can go 100mph and an 18" will only do 50mph:rolleyes: because its so big. Its more about the 18 producing far more output and if its peaky output, do to the room, it gives the illusion of being slower. You have to match the output of both then compare. So unless a box has real shoddy construction, the sub won't be the cause of "slow or fast" LF. With the exception of the SPL at certain freqs and slopes, vented and sealed sound the same.
 

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I know I will get people telling me this is just a myth, and maybe you cant really hear the difference in a blind test with modern subs anymore, but if you research subs it always says sealed subs will react faster due to internal pressure. But I'm just going by all I have read. So anyone wants to argue then argue with the speaker engineers that writes this stuff.
Also, for movies you don't really need a really fast reacting sub as you do for music. Well........... unless its a musical movie. :)


Sealed Enclosure: Originally this design was pioneered by companies like Acoustic Research. It consists of a driver mounted on one side of a sealed box. The air tight enclosure completely isolates the back wave of the driver from the front.

The sealed enclosure system is characterized by excellent transient response, excellent power handling at low frequencies, easy to design and build, smaller box size, and lower sensitivity to misaligned parameters when compared to port enclosure. However, sealed designs have a higher cutoff point and lower sensitivity than ported systems.

Because of excellent transient response (i.e., no boomy sound), when designed and build properly, some audiophiles prefer these type of subwoofers. There are others who completely dispute that sealed boxes have better transient response. They claim that the perception of transient is really a function of perceived sound quality and not the type of enclosure. According to these critics, what does improve transient response (or perceived quality) is usually more headroom, more drivers, larger boxes (depending on the driver), better efficiency, and very low distortion.

Ported Design: Some subwoofer enclosures may add an additional open port (sometimes called duct, vent, or tunnel) which allows the passage of air in and out of the box. At low frequencies, the port contributes up to +3dB to the output and makes the system more efficient and thus increases the bass response. A ported enclosure system consists of a driver mounted on one side of a box that has an open port (duct, vent, tunnel).



The ported subwoofers are characterized by lower distortion and higher power handling in the operating range, and lower cutoff frequency than a sealed enclosure system using the same driver. Distortion rapidly increases below the cutoff frequency however as the driver unloads and loses damping. Due to this, ported enclosures require a low frequency filter. The transient response of a ported enclosure is usually worse than a sealed enclosure system using the same driver. Ported enclosure systems are much more sensitive to misaligned parameters than sealed enclosure systems, which makes their construction more difficult.
 
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