Subwoofers: Ported or sealed?

@tvrgeek wrote: "For music, I much prefer low Q sealed. The roll-off much better matches the room gain so flatter to start with..."

@erik_squires responded: "This is a subject I don't think most audiophiles understand.  You have no idea what in-room bass response will be until you get the speaker in place.  In many cases the problem is too much bass and exaggerated room modes."

A couple of different researchers, Martin Colloms and Dan Wiggins, have written to the effect that "typical" room gain from boundary reinforcement is about 3 dB per octave across the bottom couple of octaves.   Now obviously this is going vary significantly from one room to the next, as well as with speaker and/or listener position within a given room, and this general bass-boosting trend does not predict the inevitable room-induced peaks and dips within the bass region.  But the general trend is that rooms introduce some rise in frequency response in the bass region

In general rooms tend to boost the low end by less than the typical rolloff of a sealed box system, which is often given as 12 dB per octave, although a very low-Q sealed box can have an effective rolloff closer to 6 dB per octave.  Therefore very low-Q sealed box systems often synergize quite well with the room, as long as their rolloff doesn't start too high.

On the other hand vented boxes are usually tuned to remain "flat" down to a considerably lower frequency than a comparable sealed box, rolling off rapidly below the port tuning frequency.  This inherent response PLUS room gain can result in the "too much bass and exaggerated room modes" Eric mentions. 

Going back to our hypothetical "typical" room gain of 3 dB per octave in the bass region, it's really not feasible to build a sealed box with a Q low enough that its inherent rolloff is the approximate inverse of this room gain. 

However it IS possible to build a vented box whose inherent response slopes downward by about 3 dB per octave across the bass region, accelerating to 4th order (24 dB per octave) rolloff below the port tuning frequency.  If the port tuning frequency is sufficiently low (say 20 Hz ballpark), then the system's inherent response starts outs "in the ballpark" as far as synergy with room gain goes.

So while I agree that in general sealed boxes interact with the room better than vented boxes, imo there is a type of vented box tuning that can usually interact with the room even better than an unequalized sealed box.  My marketing department calls it "room gain compensation" tuning. 

Duke

vented box subwoofer manufacturer

@jaytor wrote: "[Open baffle subs] don’t pressurize the room like a conventional sub - the bass is there in the room. For music from traditional instruments like double bass or kick drums, this sounds very natural. These instruments don’t pressurize the room either.

"But if you are looking for that kick-in-the-chest sound, this type of sub is probably not for you."

Imo the advantage of an open-baffle, dipole sub is better room-interaction than monopole (omnidirectional) subs, resulting in smoother in-room bass. And smooth bass is "fast" bass, perceptually, because it is the in-room peaks which take longer to decay into inaudibility and therefore muddy up the bass. The result includes superb pitch definition in the bass region. But one trade-off is, good dipole bass doesn’t kick you in the chest like good monopole bass does. I say this as a long-time dealer for dipole speakers (SoundLabs).

Imo there is a technique which can combine in-room bass smoothness with kick-in-the-chest sound, and that is to use multiple monopole subs intelligently distributed. As the number of distributed bass sources increases, the in-room frequency response smoothness increases, and the variation in that frequency response from one location to another within the room decreases.

Disclaimer: I manufacture a distributed multisub system, BUT the concept can be implemented just by using multiple subs and spreading them around the room, and the subs do not have to match.

Imo the room’s effects in the bass region are roughly an order of magnitude more significant than the differences between comparably high-quality subs, so arguably HOW MANY subs you use (and how you use them) can matter more than WHICH sub(s) you use.

Duke