Sealed Vs Ported
Sealed vs. Ported Subwoofers - A Comparison
Which subwoofer type is better – sealed or ported? An evergreen discussion topic on the forums and blogs, there is no shortage of opinions on the subject. Add in a few die-hard myths and generalizations, and it’s no surprise this is one of the most common questions asked of SVS Customer Service. At the risk of sounding ambiguous, the answer is ‘it depends’. The strengths of each subwoofer type are discussed below, along with the recommended applications and listening environments which will result in optimal performance.
Compact Form Factor
Sealed subwoofers typically have a smaller overall cabinet size and footprint, allowing easier integration into the listening environment with minimal visual impact to the décor. This makes the sealed subwoofer a natural choice in mixed media (movies, music, gaming) entertainment systems so common in today’s living rooms.
Best for Critical Music Applications
A properly designed sealed subwoofer will typically exhibit less phase rotation, lower group delay, and reduced ringing in the time domain. These characteristics make the sealed subwoofer a natural choice for critical music applications, and are typically described by enthusiasts as sounding tighter and more articulate, with less perceived overhang.
Ultra Deep Extension - A Natural Complement to Room Gain
A sealed subwoofer naturally has a shallower roll-off slope than a ported subwoofer. SVS takes this concept one step further by employing sophisticated DSP equalization to tailor the overall shape of the frequency response and roll-off slope, in order to take maximum advantage of available ‘room gain’ so common in small to mid-size rooms.
The end result is much deeper in-room extension than the quasi-anechoic frequency response would otherwise suggest. Below is a graph showing the SVS SB-2000 quasi-anechoic frequency response compared to the in-room frequency response with 7 dB/octave of room gain starting at 40 Hz (common for a small to mid-size enclosed room).
Dynamic Output Limits in the Deepest Octaves
With each successively deeper octave, cone excursion quadruples in a sealed subwoofer in order to maintain the same sound pressure level. In addition, the equalization required to tailor and optimize the quasi-anechoic frequency response consumes amplifier power. As a result, a sealed subwoofer will typically have considerably lower dynamic output limits than a ported subwoofer in the same family/price range.
This doesn’t necessarily mean a sealed subwoofer can’t perform well on action movies (which are quite demanding in the 18-36 Hz octave). Remember, a smaller room will greatly augment low frequency extension/output, and not everyone listens to movies at IMAX theater levels. So if the dynamic limits of the sealed subwoofer are well-matched to the room size and playback level, the result can be excellent performance on movies too.
Size Matters - No Replacement for Displacement
In a ported subwoofer design, a relatively large enclosure size is required in order to achieve both a deep system tuning frequency, and sufficient port area to minimize chuffing artifacts at high drive levels. A larger enclosure also greatly enhances system efficiency in the deeper octaves, with no need for additional EQ boost to achieve naturally deep extension.
The result is 2-4X more peak dynamic output in the 18-36 Hz octave as compared to a sealed subwoofer in the same family/price range. This makes the larger ported SVS subs a natural choice for system applications with larger rooms (where less room gain is present) and IMAX-like playback levels, particularly on demanding Blu-ray action and sci-fi movies with strong LFE tracks.
But What About Music?
One of the most persistent myths in the audio industry is that ported subwoofers perform poorly on music. This reputation was largely earned by the public suffering through decades of small, ported boom boxes so common in HTIB systems and brick/mortar retail outlets. These subwoofers don’t sound bad on music because they are ported; they sound bad on music (and movies too) simply because they are bad subwoofers.
SVS ported subwoofers have a flat frequency response, low distortion, excellent bandwidth linearity and a very deep tuning frequency (typically 20 Hz or deeper). The deep system tuning frequency shifts port-induced phase rotation and associated group delay below the typical music bandwidth, where we are relatively insensitive to it.
Below is a graph of the SVS PB13-Ultra group delay curves for the 20 Hz ported, 16 Hz ported and Sealed operating modes. Note the group delay curves for all three modes are coincident from 120 Hz-30 Hz (which covers the typical music bandwidth), only diverging at the very deepest frequencies. While Sealed mode unquestionably has the lowest overall group delay, the two ported modes also have exemplary time domain behavior >30 Hz and can deliver excellent sound on music, as well as stellar movie performance.
Summary:Both sealed and ported alignments have strengths and advantages, and which type of subwoofer is best for a given customer application depends on several variables. Room size, system usage, playback level, décor and aesthetic considerations, available floor space and limitations on overall subwoofer size - all factor into the selection process. In the end, both types of subwoofers can deliver an outstanding, no-compromise listening experience on both music and movies, provided the selected subwoofer model is a great match to the customer’s specific performance requirements and application.
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