Sealed vs. Ported Subwoofers

Sealed Subwoofers:

Compact Form Factor

Which type of subwoofer cabinet design is better – sealed or ported? An evergreen discussion topic on the home audio 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 the SVS Sound Experts team. 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.

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. Sealed cabinet subwoofers are generally more accurate in frequency response and better at rendering instrumentals in a convincing way. 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 or musical, 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 rated low frequency response would otherwise suggest. Below is a graph showing the SVS SB-2000 Pro quasi-anechoic frequency response compared to the in-room frequency response with 7 dB/octave of room gain starting at 60 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 as a ported subwoofer. 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.

Ported Subwoofers:

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 (aka port noise) 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 bass 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 reference-level playback levels, particularly on demanding Blu-ray action and sci-fi movies with demanding LFE tracks.

Simply put, if you want to most room-energizing, gut-punching, floor-trembling cinematic experience possible, a ported subwoofer will deliver greater dynamic output at the lowest frequencies vs. comparable sealed models.

But What About Music?

Green Line = Sealed Group Delay Curve • Black Line = 20 Hz Ported Group Delay Curve • Purple Line = 16 Hz Ported Group Delay CurveBlue Line = 1 Cycle of Group Delay (inaudible) • Red Line = 1.5 Cycles Group Delay (commonly accepted perception threshold)Courtesy Audioholics PB13-Ultra Review (used with permission)

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 5.1 home-theater-in-a-box systems and brick/mortar retail outlets. At SVS, we call these imposter subs. 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. By doing this, SVS subwoofers remain accurate in frequency response and maintain crisp speed in transients so you don’t experience the “bloat” or “boominess” found in lesser ported subwoofers.

The graph shows group delay curves for a variable tune ported subwoofer in 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.