Hermetic subwoofers or bass reflex: Which one to choose?

Audio equipment

Hermetic subwoofers or bass reflex: Which one to choose?

Which type of subwoofer is better – sealed enclosure or bass reflex? This is an always hot topic of discussion in forums and blogs, it doesn’t seem like anyone can reach an agreement on it. Add in a couple of common myths and generalizations and it’s no surprise that this is one of the most common questions asked of our customer service. Even knowing that we may be ambiguous, the answer is “it depends.” Below, we will discuss the advantages of each type of subwoofer, as well as the conditions in which they are recommended to obtain optimal performance.



In general, airtight subwoofers are smaller, allowing them to be integrated more easily into your room, with minimal visual impact on your décor. This reason makes the sealed subwoofer the most natural choice for mixed entertainment systems (movies, music, video games), quite common in today’s living rooms.


A well-designed sealed subwoofer will generally exhibit less phase rotation, less group delay, and reduced time-domain hum. These features make the sealed subwoofer the natural choice in complicated musical applications, and its proponents generally describe it as having a tighter, more articulate sound and less noticeable projection.


A sealed subwoofer generally has a less pronounced roll-off than a bass reflex subwoofer. SVS takes this concept a step further by employing sophisticated DSP equalization to tailor the overall shape of the frequency and decay response to make the most of the available “spatial gain” so common in small and medium sized rooms.

The end result is a deeper room extension than the quasi-anechoic frequency response might suggest. Below is a graph showing the quasi-anechoic frequency response of the SVS SB-200 compared to the frequency response with a spatial gain of 7bB/octave starting at 40Hz (typical in small to medium sized rooms).


In a sealed subwoofer, with each successively lower octave, the cone excursion quadruples in order to maintain the same sound pressure level. Additionally, the equalization required to adapt and optimize the quasi-anechoic frequency response consumes amplification power. As a result, a sealed subwoofer will generally have considerably lower dynamic output limits than a bass reflex subwoofer in the same family or price range. This doesn’t necessarily mean that a sealed subwoofer can’t work well for action movies (which are very demanding on the 18-36Hz octave). Remember, a smaller room will greatly increase the extension of low frequencies and not everyone listens to movies at the volume of an IMAX theater. If the dynamic limits of the sealed subwoofer are well adapted to the size of the room and the playback level, the result can be exceptional even in movies.



In a bass reflex design, it is necessary for the enclosure to be relatively large to be able to reach a low frequency and to have enough space to avoid backfiring at very high volume. A large enclosure also improves system efficiency in the lower octaves, without requiring additional EQ boost to achieve naturally deep extension.

The result is two to four times greater dynamic output in the 18-36Hz octave compared to that of a sealed subwoofer in the same family or price range. This makes larger bass reflex subwoofers the natural option for systems in large rooms (where we find less spatial gain) and IMAX-type playback volumes, with especially demanding action or science fiction films, with LFE tracks very present.


One of the most persistent urban legends in the audio industry is that bass reflex subwoofers are not good for music. This reputation is justified due to the decades we have had to suffer with small subwoofers in hypermarket home theater systems. These subwoofers don’t sound bad with music because they are bass reflex; They sound bad with music (and also with movies) because they are bad.

SVS bass reflex subwoofers have a flat frequency response, low distortion, excellent bandwidth linearity, and a very low tuning frequency (typically 20Hz or less). The bass tuning frequency of a system shifts the port-induced phase rotation and associated group delay below the typical bandwidth of music, where we don’t appreciate it as much.

Below you will see a graph of the SVS PB-13 Ultra group delay curves for the operating modes 20Hz ported, 16Hz ported and Sealed. Note that the group delay curves of the three modes coincide between 120 and 30 Hz (which covers the typical musical bandwidth), only to diverge at the lowest frequencies. While the Hermetic mode has unquestionably the lowest overall group delay, the two bass reflex modes also exhibit exceptional >30Hz time domain performance and can deliver excellent sound with music, but also stellar performance with movies. .


The two versions of subwoofers have advantages and disadvantages and which type of subwoofer is best for a specific customer depends on several variables. The size of the room, the use of the subwoofer, the playback volume, the type of decoration and other aesthetic considerations, in addition to the available space – all of these factors influence the selection process. At the end of the day, both types of subwoofers can give you an outstanding, no-compromise experience with both movies and music, as long as the subwoofer you choose suits your specific needs.

SVS manufactures a wide variety of home subwoofers, airtight and bass reflex, to suit every room, audio system and budget. Review all models and use the comparison tool to see features and specifications; This way you can choose the best subwoofer for your system.

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Simon Müller

Simon Müller is the driving force behind UMusic, embodying a lifelong passion for all things melodious. Born and raised in New York, his love for music took form at an early age and fueled his journey from an avid music enthusiast to the founder of a leading music-centered website. Simon's diverse musical tastes and intrinsic understanding of acoustic elements offer a unique perspective to the UMusic community. Sporting a dedicated commitment to aural enrichment and hearing health, his vision extends beyond just delivering news - he aspires to create a network of informed, appreciative music lovers. Spend a moment in Mueller's company, and you'd find his passion infectious – music isn’t simply his job, it’s his heartbeat.