RSL Speedwoofer 12S Subwoofer Review - True 16Hz Extension!

In our review of RSL’s Speedwoofer 10S MK2, we were delighted to find an outstanding combination of performance, features, and usability, and we subsequently declared it to be the most well-rounded sub in our 2023 subwoofer round-up. It packed a great punch for such a modestly sized subwoofer, and it didn’t have any significant shortcomings. Together, those factors made it a terrific value. However, its small size does give it some inevitable performance limitations, since size is a major factor in determining performance for any subwoofer. This begs the question: if RSL can squeeze that kind of performance out of an already small cabinet, what can they do when the enclosure size limitations are significantly relaxed? That brings us to today’s review of the Speedwoofer 12S. This subwoofer fully doubles the size of the 10S as well as substantially increasing the driver size (12" compared to the 10" in the Speedwoofer 10S MK II) and amplifier power. That should bring about large gains, especially in deep bass, thereby giving RSL a formidable offering for those putting together a serious home theater. The questions we will be asking in today’s review are how competitive is the Speedwoofer 12S in this segment of larger but affordable subs for deep bass, and how well does RSL’s unique subwoofer design scale for this larger size? Let’s now dig in to find out…

Packing and Appearance

     

The Speedwoofer 12S arrived at my home in a worrisome large cardboard box. I knew it would be a good-sized sub, but the box made it look like it would be huge. This was not the case, because the packing was very formidable and gave the subwoofer a lot of protection from rough shipping. Indeed, this is one of the best-packed subs I have seen at any price. It is double-boxed, and inside the inner box, the polyethylene foam packing pieces had thick edge protectors and corner protectors on every edge and corner of the unit. What is more, the polyethylene foam pieces didn’t just sandwich the top and bottom of the sub but covered the entire surface area. The top foam piece even had the letters “RSL” etched in it. The sub itself was covered with a soft foam sack to prevent it from moisture contact or getting scuffed. This packing had to have been expensive, but it shows that RSL cares about getting their product to end users in good condition. Parcel companies will have to really put in extra effort to damage this sub during transit (but I do not doubt that they will give it their best try). As someone who deals with a lot of speaker and subwoofer packing, I have to tip my hat to RSL here!

    

Once unpacked, we are faced with a fairly typical sub with a few minor stylistic flourishes. The finish is a dark textured vinyl that we often see in subwoofers and speakers in this price range. It doesn’t reflect a lot of light and doesn’t scuff or scratch easily. It also doesn’t show fingerprints like a satin or gloss finish would. With the grille on, the Speedwoofer 12S is a nearly featureless black box. The grille does round the front edges and corners which helps to soften up the appearance somewhat. It gently curves over a lower base piece that is finished in a plastic gloss and has the model name printed on it. With the grille removed, the woofer is exposed, but I think it’s a cool-looking cone. It is basically a larger version of their 10S cone, a smooth concave aluminum piece held in by a beefy half-roll surround. There is an RSL logo tooled into the bottom of the die-cast frame. There is an LED indicator meter mounted in the top left of the front baffle, and when active, its light is visible through the grille fabric. With the grille off, the edges are all hard ninety-degree turns, and the corners are hard angels too. For this reason, I think a lot of people are going to be using the grille; tripping and falling on the uncovered edges or corners of this sub could be pretty nasty. Overall, the Speedwoofer 12S doesn’t look bad but it isn’t going to win beauty contests among subs in this class either. This is very much a function-over-form design, so then let’s now talk about the design…

Design Analysis

    

The Speedwoofer 12S shares a lot of the design of the 10S albeit scaled up a bit, but it does take some engineering departures from RSL's popular 10” sub. Let’s start our analysis of the design with the driver. The 12S, as its name suggests, uses a 12” driver. The cone material of the 12S driver is the same as the 10S: a Kevlar-reinforced paper cone with an aluminum dustcap. The cone attaches to a beefy cast aluminum frame by a nitrile rubber surround and two Nomex spiders. The dual spider suspension system is interesting and is not something seen on the 10S. The spiders face each other in a mirrored configuration, and the advantage that brings is any non-linearities on one side of the spider’s travel are negated by an inverse motion, and this design should help to reduce even-order harmonic distortion products. This suspension system should offer very even motion for both inward and outward travel of the moving assembly. By using two spiders, the former should also be much more restricted to a single plane of motion, and unwanted lateral movement should be greatly reduced. The moving assembly should be much more difficult to knock out of alignment, so this driver should be more durable than typical drivers.

The FEA-optimized motor uses a large 2 3/4” diameter multi-layer copper voice coil. It is surrounded by a 6.5” diameter stack of two magnets with a combined thickness of 1 ⅝”. While the magnet dimensions don’t fully answer the question of how much magnetic force it generates, I would guess it is pretty powerful. Venting is done under the spiders as well as through the pole piece. The back plate is bumped out to allow for greater excursion distances. Altogether, this is an extremely hefty-looking driver for a sub at this price point.

The driver is powered by a 500-watt Class-D amplifier called the XDR amp (where XDR stands for eXtended Dynamic Range) with some sophisticated digital signal processing onboard. It uses a double-precision 56-bit, 50 million-instructions-per-second DSP processor that has four different preset response curves: Reference (has the least equalization), Music (places more emphasis on music-band frequencies), Movies (boosts the deep bass response), and Boundary (filters out deeper frequencies so as not to bother neighbors). Class-D amplification gives the 12S very high efficiency, and the standby power consumption is only 1 watt as well. What’s more, the amplifier of the 12S uses a new heatsink technology for greater thermal efficiency and capacity. Input connectivity consists of left and right RCA connectors, as well as speaker-level connectivity. It also has left/right RCA outputs. There is a USB power port for easier integration of a wireless receiver. The controls are fairly standard: Volume knob, variable phase knob, low-pass filter (30Hz to 250Hz with a 24dB/octave slope), and auto-on power switch. The 12S also has a chassis ground screw on the amp plate that can help those trying to get rid of a ground loop hum. 

While the 12S doesn’t have app control, it does come with a remote control that can change the DSP mode and volume level and also has a mute function. There is also a front-mounted multi-segment LED meter that can show levels for volume as well as display muting or DSP modes. This is useful because the user can easily see what adjustments are being made on the sub itself when using the remote. One quirk of the system is that the ‘auto-on’ can be overridden on the remote control so the sub is ready to reproduce any signal without needing to be activated by an amplitude threshold, but the remote is also needed to undo that to go back to ‘auto-on.’

The one non-standard control is very cool: a high-pass filter knob for the RCA outputs that have a 30Hz to 250Hz range with a 24dB/octave slope. This is very useful for simpler systems that have no bass management such as two-channel rigs with a simple stereo preamplifier. You can route the signal from the pre-amp to the sub and then to the amplifier, and the sub can do all the bass management with the user simply setting the high-pass filter at the same frequency as the low-pass filter. It does make me wish that the 12S had balanced XLR or ¼” inputs and outputs, since balanced connectivity combined with adjustable high-pass filtered outputs would be especially useful in small ‘prosumer’ studio systems.

     

The 12S has a 1” thick laminated front baffle and ¾” thick side panels. The enclosure features RSL’s ‘compression guide technology’ that divides the interior space into three different chambers where the backwave pressure from the rear of the cone can compress and expand in a manner that reduces resonances. it seems to borrow from transmission line theory, which can get quite complex. Within the sub, there is a solid diagonal piece that stretches from the lower front of the enclosure to the upper rear, so there are two larger compartments in the enclosure. The upper rear of the sub is open so that the backwave goes over it into the lower compartment. There is an opening in the front of the lower compartment that opens up to a slot port that extends to the back of the sub. The larger chambers divided by the diagonal piece are filled with a thick batting material for damping internal waves. I don’t know how well it works with respect to traditional ported enclosure designs, but it does add a lot of internal bracing to the sidewalls of the 12S. It also has two braces running along the top panel, as well as a plethora of corner bracing to reinforce the edges. This sub is very sturdy, and it feels like it in both weight and also a knock test on the panels.  

 

The grille is a thick frame with fabric stretched over it. It is held on by some sturdy plastic pegs that squeeze into rubber-lined grille guides. It’s a stout grille and wouldn’t be easy to break. The feet are some rubber cylinders that thankfully give fingers enough clearance to lift and lower the sub by hand. Some heavy subs just don’t leave enough clearance to safely lower the unit to a carpeted floor without the risk of crushing some fingers. RSL provides two sets of furniture sliders for both hard surfaces and soft surfaces. The hard surface furniture sliders have a soft, slippery bottom that enables the 12S to be slid over hard flooring without the risk of scratching it. The soft surface furniture slider enables the 12S to be slid over carpeted surfaces easily. It’s a big and heavy sub, but RSL has provided means of moving it into position without needing to strain back muscles. 

Overall, it looks like the 12S is going after deeper bass extension and a bit more overall output than the 10S from comparing the size of the driver versus the enclosure size. The ingredients are there to make it happen. Let’s see how it pans out in practice…

Listening Sessions

The best placement for a single sub in my room gives me a relatively flat response for an un-EQ’d single subwoofer, with a window of +/- 4 dB from 25 Hz to 100 Hz with no broad dips in important ranges. This location trades low-end room gain for a relatively flat response, a worthwhile trade for my tastes. The processor used was a Marantz AV7705. The crossover was set to 80Hz. The speakers used were some Philharmonic BMR HT Towers powered by a Monoprice Monolith 5x200-watt amplifier.

As always, I will note here that since room acoustics have a huge effect on low frequencies, the way these subwoofers sound in my room at my listening position is not necessarily going to be the way they sound anywhere else for anyone else, so readers would do well to keep that in mind, and not just for this subwoofer in this review but for any subwoofer in any review.

Music Listening

As always, I spin up a pipe organ album with some strong deep bass, since it is one of the few acoustic instruments that can really take advantage of subwoofer-band frequencies. Toward this end, I selected “The American Symphonic Organ,” a 2013 release from the Brilliant Classics label. This recording features an epic instrument in the form of the EM Skinner Symphonic Organ of the Cincinnati Museum Center. This colossus has 5,000 pipes capped off by 32’ stops that can dig down to 16Hz with serious muscle. The music program is a spread of traditional pieces selected by Jean Baptiste-Robin, a talented young organist who studied under some of the most prominent modern organists. While this album doesn’t dwell on the deeper registers constantly, it is not afraid of deep bass and so serves as a great test for the low-frequency ability in audio systems. I streamed this album from Qobuz.

The first track, “La cathedrale engloutie,” set the stage for the rest of the album, at least in the use of low frequencies. Deep bass notes serve as the background for a gentle melody giving the composition a quiet sense of grandeur, and the 12S was able to project the immensity of the organ and its acoustic environment. The second track, another by Debussy, is more energetic and punctuates a playful melody with counterpoints of deep bass seriousness which were dispensed with a solemn weight by the 12S. I could hear that the performance space was a very large one through the lingering reverb, and the 12S relayed this acoustic effect with a subtle but lengthy decay. Act II of Bizet’s “Carmen” showed that the 12S could affect a light touch as opposed to beating the listener over the head with powerful bass. Barber’s “Adagio for Strings” was beautifully rendered by both speakers and sub. Most people probably associate “Adagio for Strings” with Oliver Stone’s “Platoon,” but I think its best use to date remains in “The Elephant Man.” The spell left by the serene resolution of “Adagio” was shattered by the bombastic opening from Rachmaninoff’s “5 morceaux de fantaisie, Op.3: No.2,” with the 12S delivering a startling wallop coming out of a moment of stillness. By the album’s end, I could be certain that the 12S was a subwoofer that pipe organ enthusiasts would enjoy a great deal.

    

Hans Zimmer can be counted on to deliver orchestral music with lots of bass, and his new release, “Hans Zimmer Live,” is a testament to that fact. Zimmer and a group of artists he liked to term the ‘Disruptive Collective’ went on tour in 2022 and filled huge venues to capacity. They played rearrangements of many of Zimmer’s most popular themes from movies like “Wonder Woman,” “Dune,” “The Lion King,” and “Interstellar.” This album is a recording of one of these performances, and it’s a good chance to show what a subwoofer can do with large-scale music.

The 12S was given a chance to shine early in “Hans Zimmer Live” when a mass of percussion burst forth after a solitary vocal in “Dune: House Atreides.” The percussion was formed from both a rock drum kit as well conventional orchestral percussion, and the 12S had no problem keeping up with the attacks of the multitude of percussive instruments. Many low-frequency sounds also came from strings, brass, and synths, and Zimmer uses it all in famously bass-heavy pieces from “Interstellar,” “The Dark Knight,” and “Man of Steel,” among others. The pensive bass strings and synths from “The Dark Knight Suite” were given a solid heft by the 12S which made me want to rewatch the film. Likewise, the beefy organ sound from the second suite to “Interstellar” made me recall the Imax experience where I last saw that movie. Although not as over-the-top, the complex rhythm of bass guitar in the “No Time to Die Suite” was deftly reproduced by the 12S. The deep yet soft strings from the “Gladiator” suites were also expressed with enough finesse to be present without being overbearing. I hadn’t actually intended to listen to the full 2+ hour running time of “Hans Zimmer Live”, but the time flew by fast because of how fun it was, and the Speedwoofer 12S was an integral part of making that happen.

For something a lot less grandiose in musical style, I streamed “Mercury Mission Diaries” from Qobuz. This new release comes from the genre of dark ambient from the Cryo Chamber label and is a collaboration of many of their regular contributing artists. The tracks here form an abstract narrative and allude to the last days of a doomed spaceship mission. The music is highly atmospheric and sounds like the soundtrack for a very dark science fiction movie. Deep bass is pervasive but not in-your-face, and it is used with subtlety and nuance. It takes a competent subwoofer to hit all the notes in this music without overdoing it or underdoing it.

Bass in the first track consists of atmospheric drones underscoring an undulating arpeggiated bass line, and the 12S balances these separate elements nicely. The second track, “Caloris Crash,” calms things down to minimalist levels, and finds the subtle music of a spaceship’s engine bay. The steady rhythmic hum of machinery gives way to a build-up of mechanical stress and climaxes in a thunderous implosion. Tineidae’s “Prominence Forms” cranks things up a notch with a more conventional composition (at least by the standards of this genre) by including some actual percussion and a bassline in an urgent piece that imparts a sense of crisis. The following track, “Suspended in Emptiness,” sounds like the aftermath of a space catastrophe and is almost entirely atmospheric. Even darker ambiance is encountered in “Red Hot Harvest” by Onasander, which portrays a colossal alien landscape through cold, reverberant pads and unnerving drones. The music throughout these tracks is intended to evoke scenery for a narrative that the listener can supply if they want, and the 12S gave all of this sonic imagery a concrete foundation that made these musical scenes that much more vivid. Ominous drones, shuddering machines, and otherworldly thunderstorms are reproduced by the 12S with a physical texture that can only really be had from a high-performance subwoofer. Those who want to give their dark ambient music a cinematic quality would do well to invest in a subwoofer as good as the Speedwoofer 12S.  

    

To see how the 12S could withstand being pushed hard, I threw on “Still Contagious,” a compilation of heavy dubstep tracks from Wonk#ay Records. While the music on this particular album is on the harder end of dubstep, it is a lot more inventive and artful than the run-of-the-mill SoundCloud content in this genre, and it is a lot of fun to listen to. The bass is massive on this album, and, at high volumes, will be a tough load for any subwoofer.

With the volume cranked high on the 12S, “Still Contagious” had a club-like sound except with home audio acoustics, so I was given the best of both worlds. The beats in this album are fat to the point of being morbidly obese, and the 12S made them sound like the footsteps of Godzilla. Each kick drum hit had a visceral thump that could be felt in my chest. The rolling basslines buzzed with a palpable thickness. “Yuck Bucket” by Teniak was a low-frequency delight with a growling bassline that danced on top of some very broken breakbeats. The beats and bassline of GrymeTyme’s “36” felt like an oversized dump truck unloaded a bed full of cinder blocks on my ears. The beats in “Colossus” by Crowdad Sniper felt utterly concussive at a high volume by the 12S. The fattest beats and grimiest sound have to be awarded to ADDL’s “Also Syphilis,” which, on the 12S at a high level, could only be described as a bowel-churning experience. The Speedwoofer 12S was certainly capable of delivering the brutal bass of “Still Contagious.”

In one passage, I pushed it really hard, and after a certain point it didn’t get any louder, but it never audibly distorted. This was at an extremely loud level; so loud in fact that I turned off the amp to the main speakers just to get a sense of the sub’s own limits without going deaf. I would say that a single 12S would be enough for most people in any medium-sized room, or maybe even a large room if the user doesn’t need extreme loudness levels. To fill a large room, two will likely suffice for all but the most ardent bass heads. The good news is that these are so inexpensive that a multi-sub 12S system isn’t a hugely expensive proposition. Multiple subs are pretty much required to get a smooth in-room low-frequency response anyway, so long as the user has the freedom of placement to spread the subs out. Among the multiple articles that Audioholics has published on this subject: History of Multi-Sub & Sound Field Management for Small Room Acoustics and Early Reflections and Bass for Small Room Acoustics. Another advantage of a multi-sub system is that the subs will last longer if they are not driven hard frequently. A multiple Speedwoofer 12S would be a pretty killer system, especially for those who love bass-heavy music.

Movie Watching

One movie that I had not yet seen but looked like it could have a wealth of deep bass in the sound mix was the 2014 sci-fi actioner “Lucy,” helmed by the famous French action movie director Luc Besson. The plot of this movie concerns a young American student in Taiwan who is forced to become a drug carrier of high-tech designer drugs for an international cartel. She smuggles a large quantity of an experimental drug in her stomach, but when one of the cartel thugs kicks her in the abdomen, the seals for the drug break, and its effect is that her intellect radically increases thereby making her a threat to her cartel captors. The trailer promised lots of fighting and gunplay, and with a music score by Eric Serra, this movie should give the subwoofer a lot to do.

The premise for the movie ended up being quite a bit more absurd than I bargained for, but the bass quality and quantity did not disappoint. Much of the bass sound came from the music and the ‘metamorphosis’ scenes of the main title character. Lucy’s intake of the experimental drug and its effects on her physiology was kaleidoscopic brain-bending journeys, with the bass from the 12S making it sound like the listener is caught in a tornado. Much of the gunfire and fistfights weren’t mixed to be bass-heavy, but one action scene that did compel ample subwoofer usage was a lengthy car chase through the streets of Paris. Much of the chase was a car racing the wrong way against the flow of traffic, and the resultant carnage kept the sub busy with satisfying crunches and crashes of vehicles rolling over in the wake of the recklessly driven car. Most of the bass in the sound mix comes from Eric Serra’s music score. Serra is a frequent collaborator with Besson, and his scores always utilize lots of deep bass: see “La Femme Nikita,” “Leon the Professional,” and “The Fifth Element.” He brings that same sound signature to “Lucy” with a brooding, tense score. Pulsating synth bass sound drives the action, and massive koto-esque drums punctuate plot developments with thunderous declaration. The Speedwoofer 12S reproduced this bruising score without strain, and everything sounded larger than life and cinematic. “Lucy” was ridiculous fun, and the 12S helped to make its preposterousness bearable.

   

Another movie that looked like a bass fest which I hadn’t seen but was interested in was a newer release on Netflix titled “Day Shift.” It concerns a Los Angeles man, played by Jamie Foxx, posing as a pool cleaner as a cover for his real occupation as a unionized vampire hunter. The movie looks to be a fun blend of comedy, action, and supernatural thrills, and it promised loads of low-frequency mayhem.

"Day Shift" did indeed have its fair share of powerful bass, and that was demonstrated in the opening scene when our protagonist fought a vicious vampire with a plethora of weapons. The main character’s preference for a short-barrel pump-action shotgun as his primary weapon gave the 12S plenty to do, and it gave each blast a tactile punch. Other firearms kept the 12S busy as well, including a variety of pistols, automatic rifles, and a small chain gun. Likewise, the super-human strength of the vampires was exhibited by the subwoofer with a brawny oomph as they kicked and punched our hero through the air and against walls. There was also plenty of low-frequency carnage in a requisite car chase where the protagonist’s 60s Chevy 4x4 is chased through a run-down L.A. district (including the obligatory detour through L.A.’s canal system) by a Baja race truck, Dodge Charger, and a fleet of motorcyclists. Roaring V8s and head-on collisions were given a visceral grunt by the 12S which lent the mass and weight of these vehicles a bit more reality. The music score by Tyler Bates was mostly rock with a pinch of orchestral, and the sub was given a lot more to do with the various rap songs thrown in with tracks by Ice Cube, Snoop Dogg, and Ol’ Dirty Bastard. The 12S energized my room with hip-hop beats and bass with at least as much power as any of the action scenes. “Day Shift” was a perfect breezy movie for a Saturday afternoon matinee, and the Speedwoofer 12S helped to make it feel like a true movie-going experience.

RSL Speedwoofer 12S Measurements and Conclusion

 

Testing on the RSL Speedwoofer 12S was conducted with the microphone facing the woofer at a 1-meter distance with measurements scaled back to a 2-meter distance by subtracting 6dB. The temperature was recorded at 55F degrees with 55% humidity. The subwoofer’s gain was set to maximum, phase was set to zero, and the low pass filters were set to bypass.

 

The above graph shows the measured frequency responses for the Speedwoofer 12S subwoofer. It should be kept in mind that these responses were measured with the microphone facing the woofer, and some of the port-generated output isn’t fully represented in this orientation, so this subwoofer’s frequency response does extend a bit deeper than what is shown on these graphs. Users have a variety of different tonalities to pick from. ‘Reference Mode’ holds the most neutral response and is nearly ruler flat from the low 20s to nearly 100hz. ‘Movie Mode’ tips up the bass from 20 to 40Hz, and that should give a bit more oomph to effects sounds such as explosions. ‘Music Mode’ shaves off some low-end that might alleviate room gain, and ‘Boundary Mode’ shaves off a lot of low-end so as to be less noticeable to neighboring rooms. Individual tastes should determine what mode to be used, but RSL tells me that most of their customers prefer ‘Reference Mode.’ That isn’t surprising to me as it should yield the most balanced sound, at least in a room that doesn’t get a lot of low-end gain. My room does not get much gain, so I did appreciate the “Movie Mode” to add a little bit of punch on movie night. RSL provides something for everyone here.

 

The above CEA-2010 measurements are short-term bursts that show the subwoofer’s clean peak SPL before heavy distortion sets in. Our measurements have been referenced to 2-meter RMS, which is 9dB down from the standard requirement for the measurements to be shown at 1-meter peak. However most publicly available CEA-2010 measurements are shown at 2-meter RMS, so we followed that convention.

The Speedwoofer 12S posts respectable numbers in mid-bass (which, for subwoofer-band frequencies, we will classify as 50Hz and above), but it packs a much more serious punch in deep bass. Relative to the 10S, the Speedwoofer 12S doesn’t really exceed its output at 50Hz or above, but it makes gains at lower frequencies, and the lower it goes, the larger the gains. For example, at 16Hz, the 12S can hit 100.1dB whereas the 10S hits 86.5dB. That is over a 13dB difference, and that means that you would need more than four 10S subwoofers to equal a single 12S at 16Hz. At 20Hz, the 12S more than doubles the output that the 10S can produce. At 25Hz, the 12S exceeds the 10S by nearly 70%, and at 31.5Hz, the 12S still outperforms the 10S by over 50%. By 40Hz, the 12S’s lead shrinks to a 2dB advantage, but that still constitutes a 25% output difference. Relative to other subwoofers, the 12S maintains more headroom in deep bass than in mid-bass. Many subwoofers in this class have more disparity between mid-bass and deep bass headroom. This burst test data places the 12S in Audioholics’ Bassaholic ‘Large’ Room Rating, meaning it should be able to handle a room of 3,000 cubic feet. It easily surpasses the 25Hz threshold for the large room rating, but only clears the frequency band above that by a couple of decibels. For information on how the room ratings are determined, please read our article “Bassaholic Subwoofer Room Size Rating Protocol”.

Testing for long-term output compression was done by first conducting a 20-second sweep tone where 50Hz hit 90 dB with the subwoofer 1 meter from the microphone (graph has been scaled to 2 meters for easy comparison with our other review measurements). We then conduct further 20-second sweeps by raising the gain by 5dB until no more output could be wrung out of the subwoofer. These tests show us the long-term continuous headroom that the Speedwoofer 12S is capable of. Again, we should note that the microphone orientation that this sub was tested in does not fully reflect port contribution, so it does have a bit more low-end output than what is shown here. This testing was done with the 12S set in ‘Reference’ mode, but running the subwoofer in ‘Movie’ mode would end up at the same response shape and max output when the amplifier and driver have nothing left to give. The subwoofer doesn’t really change its response shape until the last few dB and keeps a nicely flat response up to then. And even so, the differences between the nominal response shape and the maximum output response aren’t gigantic. The 12S keeps good control over its response at all drive levels and doesn’t compress as much as most subs that we push to the limit.

The above graphs show the corresponding total harmonic distortion to the long-term output graphs. Essentially, they depict how linear the subwoofer remains for the corresponding drive level seen in the long-term sweeps. The quantity being measured is how much of the subwoofer’s output is distortion and is shown here as a percentage. The 12S puts up a very nice showing here, never surpassing 10% THD above 25Hz even at the maximum drive level. The last few decibels of its performance envelope do push it a bit above 10% THD at 20 to 25Hz, but at lower drive levels, the output is very clean. At the 90dB sweep, the 12S keeps THD below 10% at 16Hz, and at higher frequencies for the same drive level, it is vanishingly low, not even registering 1% THD. At higher drive levels than 90dB, the 12S isn’t very happy at 16Hz and below, but it isn’t producing much output in that range anyhow so any distortion products wouldn’t be terribly audible. Overall, the 12S is fairly buttoned up and is averse to producing noises that aren’t in the source signal, no matter how loud it is cranked. On this count, it separates itself from the Speedwoofer 10S again; while the 10S has about the same level of output above 50Hz, the 12S keeps output a lot cleaner in that range when driven hard. In fact, the 10S would probably be perceived as being a louder sub since the harmonics would be a lot more audible than the fundamentals. If you want a subwoofer that doesn’t lose fidelity no matter how hard it is pushed, RSL looks to have brought one to the table.

 

The above graphs depict measurements of the constituent harmonics from the long-term output sweeps and are what the total harmonic distortion measurements are composed of for the 2nd and 3rd harmonics. These individual harmonics can give us a clue as to what might be the cause of some quirk or non-linearity. We are only showing the 2nd and 3rd here because they more or less reflect the higher even-order and odd-order behaviors, although higher-order harmonics tend to be much further down as a percentage of distortion compared to the second and third.

The distortion products of the 12S look to be a mixture of even and odd-order harmonics. At around port tuning, even-order harmonics are dominant, and below that, odd-order harmonics take over. It’s possible that the back pressure from the enclosure and port is preventing the cone from oscillating as far inward as it is moving outward. The good news is that even-order products are more difficult to discern, so the higher percentage of even-order from 16Hz to 25Hz is less likely to be audible than if they were odd-order. The explosion of odd-order harmonics at 16Hz and below at the higher drive levels is inconsequential, because, as we noted before, the output is dropping like a rock at this point, so there isn’t much of a signal left to distort at such low frequencies.

 

Group delay is the measurement of how much time it takes for individual frequency bands of an input signal to be produced by the speaker. It can indicate that some frequency components are developing slower than others or are taking longer to decay. It is generally thought that 1.5 sound cycles are needed for group delay to be audible at bass frequencies, although there is an argument that group delay should remain under 20ms to be completely unnoticeable, but that is likely meant for mid and upper bass frequencies.

The 12S does well in this measurement, not surpassing 1 cycle until just above 20Hz and even then just barely. It should be noted that this group delay measurement was done in ‘Reference’ mode which is the mode least shaped by DSP equalization, according to RSL. Other modes did elevate the group delay a bit more but not by much, except for ‘Boundary’ mode which added significantly more group delay below 50Hz. I doubt many people will use Boundary mode, and RSL tells me that the vast majority of their buyers use Reference mode. The group delay seen in the above graph gives no cause for concern, and nothing there would be audible in typical use. The time domain behavior of the Speedwoofer 12S is very competent, and it makes a good choice for anyone who is looking for a sub that isn’t laggy-sounding or bloated. Something else that should be noted is that the performance seen here is a marked improvement over the group delay exhibited by the Speedwoofer 10S.

Conclusion

Before bringing this review to a close, I will briefly go over the strengths and weaknesses of the product under evaluation, and I will start with the weaknesses, since I am the kind of guy who always wants the bad news out of the way first. There aren’t many real weaknesses of the Speedwoofer 12S when pricing is considered. As we discussed before, one area in that competing subwoofers will outperform the 12S is mid-bass output. While the 12S does fine here, there are similarly priced subs that do offer more punch in this area. It is important to note that some of them also allow significantly more distortion in this range as well; RSL could probably push the woofers harder but at the cost of clean bass. The trade-off may or may not be worth it depending on the personal preferences of the listener. As I mentioned before, listeners who like their music really loud may want two of these subs rather than just one.

Something else that some people may not like about the 12S is that it is a bit plain-looking and rather boxy. The other side of this is that by eschewing fancy finishes and more elegant shapes, RSL can offer a subwoofer of high performance for a relatively low price. There are not many other 12” woofer subs with 500-watt amps that can hit 100dB at 16Hz that only sell for $800. That is a lot of sub for the money. If RSL were to curve the cabinet, round edges, or offer gloss finishes, the price would have to be hiked considerably. Nonetheless, it may be worth having an optional higher-end finish available for an additional cost, like maybe a satin white or black. That might allow the 12S to fit in better with finer interior decors.

One more nit I would like to pick is that the absence of balanced inputs is a missed opportunity by RSL. I am not sure why they have implemented speaker-level inputs but no balanced inputs. I would guess that balanced inputs would find a lot more use than speaker-level connectivity, especially since the 12S has the ability to send out a high-passed signal. It would have made the 12S easy to integrate into higher-end equipment as well as studio environments. It would also have made longer cable runs possible for those who don’t want to resort to wireless transmitters.

With those criticisms out of the way, let’s now talk about the strengths of the Speedwoofer 12S, the foremost of which is its performance in light of its cost. To reiterate, this is a subwoofer that can hit 16hz at 100dB in our burst tests, and to do so for only $800 shipped is a great service to shoppers who want serious deep bass without spending a fortune. It can exceed 105dB continuously from 30Hz to 50hz and it stays very clean all the while. In Reference mode, it has a beautifully accurate response, and its control over non-linear behavior at all drive levels is commendable. That, combined with its good time domain performance, makes it a true high-fidelity subwoofer, even if it doesn’t look like one or cost like one.

Another praiseworthy aspect relates to its performance under stress. It is very reluctant to make noises that aren’t in the original signal, and its strict limiters prevent it from over-driving or being pushed into excursions that put the driver in danger. You cannot kill the Speedwoofer 12S by playing it hard, so there is no need to worry about that.

The 12S also has some useful features that are not frequently found in its price class. The addition of high-pass filtered outputs makes simple bass management possible for basic audio systems without needing to add more components, and that can be very useful for simple two-channel systems. The 12S has a remote control that makes it easy to adjust settings without needing to pull the sub out from the wall, and a front-mounted LED meter lets you know the level of adjustment being made without needing to refer to the rear of the sub. While they don’t see much use anymore, speaker-level inputs do enable connectivity to simpler systems where users might only want to augment deep bass in a two-channel setup. RSL also makes it easy and inexpensive to add a wireless connection with their wireless audio kit when you purchase that with the 12S. The thoughtful inclusion of furniture sliders for the feet makes moving this heavy subwoofer around to find the most optimal location to be a painless ordeal.  

The build quality of the 12S is much better than average, with a plethora of bracing including the compression guide technology structure which helps to make the side walls that much more rigid. It is also tightly packed with stuffing. It is a fairly dense unit, and buyers will learn when they try to lift it into place. The packing makes it that much more daunting when buyers receive it: this packing is among the best I have seen that wasn’t palletized, and I don’t know how RSL can offer this level of packing for the price they charge for the 12S. RSL really does not want to deal with shipping damage problems, and that will be obvious to anyone when they unpack the 12S.

In the end, the Speedwoofer 12S is certainly a worthy addition to RSL’s line-up. For those who have the space and budget for a larger sub, it should definitely enter into strong consideration. Home theater enthusiasts will enjoy its deep bass prowess, and audiophiles will love its clean, linear bass. It's a significant upgrade from the Speedwoofer 10S, and it’s not just quantitatively better, it’s qualitatively better. The Speedwoofer 10S has been a major success for RSL, and I have no doubt that the Speedwoofer 12S will be another hit once enough people get to experience it.

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

• — Excellent
• — Very Good
• — Good
• — Fair
• — Poor

Metric	Rating
Bass Extension
Bass Accuracy
Build Quality
Fit and Finish
Ergonomics & Usability
Features
Dynamic Range
Performance
Value