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

What Duke said  :)

Another option to consider is open baffle, if you have the room. I am really enjoying the bass from my open baffle subs, and prefer the bass quality compared to the sealed and ported subs I have had in the past. To me, it sounds much more natural than box subs - smooth, clean and dynamic, without pressurizing the room and without the boxy resonances that many box subs have. 

Open baffle subs have cancellation on the sides of the speaker, so fewer room modes are excited resulting in smoother in-room response. Also, since they don't pressurize the room, less bass energy escapes the room. 

The downside is that the drivers have to work harder to compensate for the cancellation between the front and back wave. If you like to play loud and/or have a large space, you'll need multiple drivers to play deep. They also have to be placed at least 3 feet from the front wall (although they can be very close to the side walls).

I use a stereo pair, each with four 12" drivers in a tower configuration. This is overkill, but results in lower distortion and smoother response. 

I've heard it stated that you can't get deep bass from an open baffle woofer. This just isn't the case. With Room EQ Wizard and a little bit of PEQ adjustment on the sub amps, I've measured flat response (within a couple DB) to below 20Hz, with the -3db point in the mid-teens. They can easily play WAY louder than I'd every want to play them. 

Porting main speakers is a much different proposition than subwoofers with ported enclosures.  

Biggest reason is the x-max is much less (distance a driver piston is allowed to travel) on main speakers and is easier to to control the motion with the driver's suspension.  

Lack of control of driver excursion whether main woofer or subwoofer causes distortion. 

Most main speakers are ported because they are more efficient and extend deeper and the slight additional distortion is a worthwhile tradeoff and not audible.

The main reason I prefer sealed subwoofers for music is that they have significantly less distortion than their ported counterparts, especially where it matters most in the critical 25 to 80 Hz region.  That distortion can cause coloration that can veil the midrange frequencies- not good if you love vocals and clarity.  

Ported subs work well for home theater because the additional distortion is not so noticeable in a typical effects sound track and the additional efficiency and extension is more useable.  Also midrange clarity is not very high on the list of home theater system users.  

Again, distortion at critical audible frequencies that can veil the midrange with ported subs is the main reason to avoid them for music.  

@joekras25 Wrote:

Subwoofers: Ported or sealed?

Ported! 😎