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Sealed vs Ported Subwoofers: Wrap Up

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While the simulations above do a reasonable job of characterizing the differences between sealed and ported subwoofers, the real work begins when we make the leap from simulated / outdoor performance to performance in real rooms, as well as take human hearing into consideration. Approaching sealed subwoofers first, their shallow roll off profile can make them quite suitable for smaller spaces thanks to a phenomenon known as room gain. Below a certain frequency (nominally denoted as F=(speed of sound / (2 x Longest Room Dimension)), the room naturally boosts the low end at a theoretical rate of 12dB/octave (less in the real world, as real walls are lossy barriers). This means that in spite of the fact that they may roll off earlier in simulations or outdoors relative to their ported counterparts, sealed subwoofers have the potential to offer extension down to 10Hz and below in the right room. In addition, their small size (excluding huge overdamped enclosures) makes them much more at home in smaller spaces. 

Sealed in room vs outdoors

Outdoor (purple) vs potential indoor (blue) frequency response of the SVS SB-2000 (image courtesy of SVS).

As you might guess, where sealed subwoofers are a natural fit for smaller rooms, big, deeply-tuned ported subwoofers are right at home in larger spaces where room gain is minimal (though they can work well in smaller spaces with a bit of EQ). But what about all that nasty group delay / ringing business we talked about; surely that must affect music performance? That’s where the realities of human hearing -come into play. .

Group Delay Ported

Group delay for driver X modeled in a maximally flat ported alignment as well as a “deep tune” one-port mode.

Looking at the graphs above, you might be concerned by the spike in group delay relative to a sealed enclosure (the simulations of which don’t break 15ms regardless of Q). However, because of the relatively deep tuning points involved, the frequencies where group delay becomes a problem are areas where human hearing isn’t terribly sensitive to the issue; moreover, they’re frequencies that just aren’t particularly relevant to the vast majority of music. As such, when put in appropriate rooms and/or EQed to scrub off a rising low end resulting from room gain to achieve relatively flat in room response, it’s possible for ported subwoofers to be very capable performers, both for music and movies.

Bottom Line

Small sealed subwoofers are a natural fit for smaller rooms: their size combined with their shallow roll-off mean easy placement and deep extension in small spaces (say under 2,500 cubic feet). Conversely, large, deeply-tuned ported subwoofers offer a real competitive advantage against their sealed brethren in larger spaces where the room doesn’t boost low-end output. In addition, when designed properly, problems in the time domain are pushed low enough in frequency to be non-factors, meaning they can perform well for music as well as movies.

Conclusion

Subwoofers play an important role in today’s A/V systems, shouldering the burden of reproducing the low end in music and movies. The two most common styles utilize sealed enclosures and ported boxes; naturally, since their development people have been debating which one is better. When approaching the question from a balanced point of view, the answer that they both have their strengths and drawbacks. As such, the question of which is right for you depends on your situation, specifically, the room you’re putting it in. Happy hunting!

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Recent Forum Posts:

Verdinut posts on January 25, 2017 17:23
Back spring pressure affects ported configurations too, but to a much lower extent than is the case with a sealed box.
shadyJ posts on January 25, 2017 17:10
Verdinut, post: 1168948, member: 80194
However, I have never heard of anyone questioning the linear response in a sealed cabinet. This phenomenon definitely must exist due to the air compression and decompression effect caused by the cone displacement. Probably, our hearing is not sensitive enough to notice this phenomenon which nevertheless cannot escape the laws of physics. This is one of the reasons why I always built bass reflex enclosures.

I wonder if anyone ever attempted to measure such non-linear displacement, and if so, what were the results.
Any comments anyone?
The effects of back spring pressure would be manifest as even-order harmonic distortion products. Backspring pressure also effects ported alignments as well. Even-order harmonics have to be severe in low frequencies to be audible, especially second-order harmonics.
Verdinut posts on January 25, 2017 16:19
Bear123, post: 1026954, member: 66726
There are two advantages to sealed subs: they are smaller than ported, and have a shallower rolloff for lower extension. I don't think the servo has any impact on those two things.

As far as the sealed versus ported question goes, as long as one can acommodate the size of the ported sub, I think it is generally the better design. Most people use their subs for both movies and music to some extent or another, and ported offer vastly superior output for movies, while being equally suited for music. The only reason to go sealed imo is if you have to have the small size.

Having said that, I have a sealed sub. But, it took two 15“ drivers to match the output of a 12” ported sub in the same size box. But, since that was the biggest size box I could fit, the two larger drivers kept my output for movies the same, but double my mid bass output.
Greetings!
You installed the two 15 inch woofers in the sealed box. Did you ever explore the feasibility of rather using them in an isobaric configuration in the same cabinet for better low frequency performance?
Verdinut posts on January 25, 2017 15:42
Sealed vs Ported:
There are several reasons why many audiophiles prefer the sealed enclosure. Of course, sealed boxes are usually more compact and there is also the spouse acceptance factor, as everyone knows.
However, the ported enclosure allows a more efficient rendition and, provided IMHO that you use a subwoofer with a Qts of between 0.38 and 0.5 and a very low Fs, you should be able to obtain a smooth and strong response to a lower frequency than with a sealed box, provided it is of adequate size and properly tuned. Also, transient response should not be a problem under these conditions.

I have heard of several comments with regard to ported enclosures with poor transient response as opposed to that with sealed cabinets. Driver and box have to be properly, not married, but matched to obtain successful results.

However, I have never heard of anyone questioning the linear response in a sealed cabinet. This phenomenon definitely must exist due to the air compression and decompression effect caused by the cone displacement. Probably, our hearing is not sensitive enough to notice this phenomenon which nevertheless cannot escape the laws of physics. This is one of the reasons why I always built bass reflex enclosures.

I wonder if anyone ever attempted to measure such non-linear displacement, and if so, what were the results.
Any comments anyone?
crossedover posts on April 14, 2014 16:49
mychaelp, post: 1028032
Thanks for the article.
Subs play such an important role that most people don't realize and it's important to understand the differences between options.
My SVS has a “phase” dial of which when I turn it, there are changes in the bass sound, but I always thought Phase would be either one way or another and not a dial adjustment. I just turned it until I had a good mix of loudness and depth bass which is tight but not boomy as it was on the other end of the dial. I may never know how to really adjust that dial.
I've always seemed to notice that to get the best sound and deepest bass from a sealed enclosure, you have to spend more than a ported version. SVS is a good example of how sealed cost more to get the same “on paper” response. I had found a site that listed some layman's information but can't find it now, might post later if I find it then.

Engineering a small enclosure to play loud,low and good involves a an exceptional driver, higher power and EQ. If you want a 15" cube to compete with a large enclosure it takes more Rd and money for the most part.
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