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.