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RTJ Audio 18Sub Subwoofer Review

by November 18, 2023
RTJ Audio 18Sub

RTJ Audio 18Sub

  • Product Name: 18Sub
  • Manufacturer: RTJ Audio
  • Performance Rating: StarStarStarStarStar
  • Value Rating: StarStarStarStar
  • Review Date: November 18, 2023 00:00
  • MSRP: $ 6,998 - Single, $10,998 - Double, $16,998 - Quadruple
  • Buy Now
RTJ Modular Loudspeaker System Review
  • Driver: 18” cone
  • Amplifier: 2400W RMS
  • Frequency Response: 10Hz - 200Hz (in-room)
  • Enclosure Type: Sealed
  • Enclosure Material: Baltic Birch
  • Dimensions HxWxD: 22.5” x 22.5” x 15”
  • Weight: approx: 120 lbs.


  • Massive mid-bass output
  • Real deep bass extension with a true sealed 12dB/octave roll-off
  • Relatively small size
  • Ideal for baffle wall applications
  • Superb time-domain performance


  • Higher value isn’t realized until multi-sub system purchase


18SubRTJ 18Sub Introduction

RTJ Audio blew us away when they paid a visit to the Audioholics Smarthome with a pair of their 410 modular towers. It had a monster dynamic range but not at the expense of fidelity, and it was a speaker that could tackle any high-end private cinema with ease no matter how large. Sadly, we only had time to play with the 410s for one weekend, but that might have been for the best since it made loud sound so good that we might have ended up with hearing damage if we had them for a longer period. We found many of the design details intriguing, and so we leaped at the chance to review one of the subwoofer modules that RTJ calls the 18Sub. While the subwoofer modules can be had as a part of the complete 410 tower system, they can also be had separately, and there are a lot of interesting aspects of their design that warrant the 18Subs for serious consideration as an individual subwoofer system. Let’s now get into what makes the 18Sub worth the attention of subwoofer shoppers in its price range…

Appearance of RTJ 18Sub

This is going to be a short section because the 18Sub was meant to be hidden behind a baffle wall. In other words, appearance wasn’t a very large part of the design criteria. Nonetheless, it doesn’t look terrible, and if it had to be out in the room, it wouldn’t be that off-putting if placed in a corner. One of its charms in this respect is that it is a relatively shallow sub, having only a 15” depth, which perhaps makes it the most shallow 18” home audio sub on the market today. So it will not jut out very far into any space that it is placed in. The finish is a rough matte black that is made for durability rather than ravishing good looks. The 18Sub has circular notches at the top that is made to stack either the 410 speaker or other 18Subs on top. All of the edges and corners are rounded so there are no hard edges. Visually, the high point of the 18Sub is the cone, which has a smooth texture that leads into a carbon fiber-esque dustcap. The surround is an imposing large half-roll of rubber that makes this sub look like it means business. There is no included grille, since the screen or wall material is expected to fill that role.

18Sub plus amp 5 

The 18Sub is powered by an outboard amplifier that does look surprisingly stylish, so at least it gives you a neat-looking piece in your equipment rack. It is a black amp with a front vent hole pattern that looks like two bursts coming from the sides of the unit. There is a cast metal plaque with the RTJ name in a brushed aluminum texture on the front that looks quite nice. There is a similar plaque mounted on the back of the subwoofer enclosure above the binding posts - it is an attractive piece but why put it in a location that it will seldom be seen? Either way, it is a nice touch and attention to detail.

Design Analysis

The RTJ 18Sub is not an overly complex design on the surface: it is merely a long-throw 18” driver in a small sealed enclosure that is powered by an outboard amplifier. This simplicity is a bit deceiving, however. The heart of this sub, the driver, is a state-of-the-art powerhouse of transducer engineering. It combines two advantageous elements that are rarely seen together: long-throw/high power-handling combined with low inductance. The reason why these two traits so seldom go together is that drivers that have a long throw and high power-handling need a lot of voice coil in order to achieve that end. However, lots of voice coil usually creates a lot of inductance. Inductance is when the motion of the voice coil within the fixed magnetic field generates a current that itself produces a magnetic field that has an opposing polarity with respect to the original magnetic field. The induced magnetic field degrades the linear travel of the voice coil, and what typically occurs is greatly diminished bandwidth that reduces upper and lower frequency output but increases some sympathetic resonance frequency. The result is a very peakish frequency response with greatly increased distortion as the frequencies move further away from the peak. In other words, high inductance means low fidelity.

18Sub driver motor   18Sub driver

18Sub dustcapInductance is measured by units of henries, termed “H”, which is the ratio of the voltage to the rate of change of current. Loudspeaker drivers term the amount of inductance as “Le” and have inductance values in the milliHenry range - mH. RTJ claims that the driver used in the 18Sub has is less than 1mH. To put that into perspective, most long-throw, high power-handling drivers would normally have Le values of around 4mH, give or take a milliHenry. Higher inductance drivers in this category might have Le values of up to 8mH, and lower inductance drivers of this type might have 2mH. For a driver that has 36mm of Xmax (one-way linear travel) and over 2,000 watts of power-handling such as the RTJ 18”, a 1mH Le is astoundingly good. That should yield a very flat response with extremely low even-order harmonic distortion. The RTJ 18” driver should have excellent fidelity characteristics along with tremendous output potential.

The driver itself weighs about 60 lbs. which is mostly motor. The motor has a 3” diameter voice coil that hangs in a gigantic magnet structure that uses three 1” thick discs that have an 8” diameter. The moving assembly is attached to the heavy-duty cast aluminum basket by a 10” diameter spider and a bulbous half-roll surround that has a 2” width and 1” height. That caliber of suspension ought to enable the cone a tremendous amount of throw, and, as was mentioned before, a 36mm Xmax gives the 18Sub driver one of the longest linear excursions from any commercial subwoofer available today.

18Sub amp front 


18Sub amp rear

The driver is given 2,400 watts RMS courtesy of an outboard class-D amplifier. The amp itself is not exactly feature-rich and expects the system to be fine-tuned from an exterior processor. It only has controls for gain, low-frequency boost, crossover frequency, and a delay up to 20ms. There is also a switch for always-on, auto-on, and off/12V trigger. The front panel has a traditional on/off switch. For connectivity, it has RCA and XLR inputs as well as a 12V trigger input and output. 2,400 watts is a lot of power and thus potential for heat generation, so the amplifier is well-ventilated and has two active fan exhausts on the rear. Heat dispersion is one of the major advantages of outboard amplifiers and is a real benefit for an amp with so much power output potential. In typical subs with plate amplifiers, much of the heat produced by the amp can become trapped in the subwoofer enclosure along with heat produced by the driver, but with an outboard amplifier, heat dispersion can be much better managed by placing the amp in an area with good ventilation. Of course, heat is the enemy of long-term reliability in electronics, so using an outboard amp should prolong the life of the system.

18Sub binding posts  18Sub interior

The enclosure is a simple sealed box with the aforementioned attribute of a relatively shallow depth of 15”. This was done so it could better fit behind more baffle walls in installs with acoustically transparent screens. As was said before, this is a subwoofer that was meant to be heard and not seen. The cabinet is a rugged affair that uses baltic birch which is much stronger than the standard MDF used in sub cabinets. It has a 2” thick front mounting frame and 1” thick paneling and braces. Four lengthwise braces run from front to back of the enclosure. The cabinet is packed with denim insulation which is one of the most effective acoustic damping fills available. It uses thick rubber rings for feet. This is a very heavy-duty cabinet, but it has to be since it has to contain the tremendous amount of backwave pressure from such a powerful driver. It needs to stop any significant cabinet vibration, especially since this enclosure is meant to have other modules stacked on it.

Listening Sessions of RTJ Sub18

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 receiver used was a Pioneer Elite SC-55 and the crossover was used mostly at 80 Hz. As always, I will note here that since room acoustics have a huge effect on low frequencies, the way this subwoofer 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

The conventional music instrument that digs into the deepest bass frequencies is the pipe organ, of course, and I always start subwoofer evaluation with a pipe organ recording for this reason. The album I turned to for this subwoofer is “South German Organ Music from the Late Romantic Period,” a 2016 recording of the then brand new Goll organ in the parish church of St. Martin Munich-Moosach. As the title indicates, this album tries to give more exposure to the work of German composers from the late nineteenth century to the early twentieth century, a fertile era of organ composition that has faded into obscurity. The music on this album has a good spectral balance of the organ and does not shy away from its deep bass capabilities. The bass here is not overbearing as some overly enthusiastic pipe organ albums can get, nor is it too dry as in other pipe organ recordings. How would the 18Sub handle this pipe organ mix?

The 18Sub gave each pluck and kick drum a jab that I could feel through my sofa...

Not much tweaking was needed to get the 18Sub to blend in well with the speakers, and once it was blended in it made for a seamless sound from the recording itself. The bass was powerful when it needed to be but could also retreat into subtlety. It was difficult to tell where the subwoofer stopped and the speakers started, and the only way I knew for sure that the sub was active was when notes were being played that I knew were much deeper than the main L/R speakers were capable of reproducing. The reverberant deep bass produced by the 18Sub made my room seem much larger than it actually was. In fact, the large sound made my room seem positively cavernous, as though it were a cathedral. When those low notes hit with force, their presence could be felt as much as heard, and it gave the pipe organ a physical sensation as much as an aural one. The resultant sound was utterly towering, much like the instrument that originally produced it. I didn’t think that the 18Sub would have difficulty in realistically reproducing the pipe organ and so was not surprised that it could tackle this recording with such aplomb. Pipe organ music enthusiasts wouldn’t make a mistake in choosing the 18Sub, because it truly delivers the goods that can be had from this majestic instrument.

South German Organ Music   Bass Extremes

Another acoustic recording that I listened to that has a healthy amount of deep bass was “Bass Extremes: Just Add Water.” Bass Extremes is a project by Victor Wooten and Steve Bailey, two bass guitar maestros, and they are joined by a bevy of other accomplished percussionists and bassists. This is a lively jazz album with a heavy inflection of funk and rock, thus its classification as “fusion jazz.” The clean recording combined with the rapid playing of the bassists and drums makes this a good test of any sound system’s low-frequency transient behavior. The plucks and mutes of the guitar strings require a system with fast attacks and accurate decays to sound correct, or the overhang will risk smearing the notes and blurring the performance. If you want a good album to evaluate the time-domain behavior of your subwoofers, “Just Add Water” is a terrific demonstration of that. 

The 18Sub gave each pluck and kick drum a jab that I could feel through my sofa, much like how soundwaves have that physical quality in a live musical performance. The tactile sensation for different pitches was noticeably different, as though the music found differing resonances in the human anatomy through the 18Sub. If I had to communicate a musical experience to a profoundly deaf person, I might use this recording with this sub. However, this is not to say that the visceral aspects were all the 18Sub had to offer; quite the contrary. The pitch definition expressed by the 18Sub was excellent, and the fundamental frequencies of the slides, strumming, and slapping were all precisely rendered in combination with the speakers. There was no noticeably lingering sound from the sub, and all low-frequency sounds started and stopped on a dime. The sub followed the brisk basslines with as sharp delineation as anyone could ask for. Anyone looking for a sub that can handle complex bass notation would surely find a lot to like in the RTJ 18Sub.   

The pitch definition expressed by the 18Sub was excellent...

For a 180-degree turn in music, I once again looked to the dark ambient genre where low frequencies can see extensive use in a number of ways. My album of choice for this instance was “Leviathan Device” by Triangular Ascension (although given the naming conventions of this genre, if the title and artist name were reversed, no one would be the wiser). If Hollywood produced an H.P. Lovecraft movie set in outer space, this would be the perfect music score. Bass in “Leviathan Device” can hang back as a steady drone or come to the forefront as an industrial pounding sound as well as manifest in all kinds of otherworldly sounds in between. On some tracks, it dips into true infrasonic territory with bass so deep it is just barely audible, yet its presence looms unmistakably. I set out to see if the 18Sub be able to make sense out of the complex bass in this surreal album.

This album started off with a rumbling sound that I hadn’t really noticed as much before listening to other sound systems, and it felt like standing near a passing freight train. My sofa vibrated as though I was experiencing a mild but continuous earthquake, and I have to feel bad for any seismologists who work anywhere near a system that uses 18Subs - they would end up getting a lot of false positives in their instrumentation. The different layers of bass did not get confused on reproducing this album on the 18Sub. Rumbles, drones, thuds, and booms were presented with distinction, whereas a lesser sub might have smeared them all together in a muddy blur. It is often said that bass is the foundation of sound in music, but this takes that idea to another level. At times the bass was so thick that you could almost stand on it. But this bass was heavily textured, which was vital to the sonic image that was painted by the artist, and the 18Sub managed to translate these textures with exceptional clarity. This kind of music requires tight control over low-frequency playback as well as headroom and real extension to deliver the artist’s intentions. The 18Sub was more than sufficient in all of those categories to realize the elaborate soundscape of “Leviathan Device.”

Leviathan Device  Sub Pressure

the RTJ 18Sub managed to translate textures with exceptional clarity.

Turning to bass music of a much more brazen nature, I found a killer dubstep compilation album on Qobuz titled “Sub Pressure Volume 3.” This 2013 release falls on the more minimal side of dubstep with the exception of bass, which is used lavishly. At high enough amplitude levels, this music will present a daunting load for any subwoofer, so it makes for a great stress test to see how much the sub can dish out. I have no doubt a subwoofer with the specs of the RTJ 18Sub can get loud, so the question is would it get as loud as I can stand or would I be able to take its best shot and not go down? I queued the album and cranked the volume to see what the answer would be.

It wasn’t long after starting this album that I knew I would have to back down but not because the subwoofer couldn’t handle it. On the contrary, the 18Sub had no problem blasting out the bass here, and I could not discern a hint of distortion or compression. The bass was so powerful that it was concussive, and there was no way I was going to survive the entire 90-minute album at such high levels. Extremely loud bass is fun in small doses, but it can be fatiguing after long durations. I could feel my spine vibrating. I was also worried about stuff in my house that wasn’t bolted down. What’s more, I had a cockatiel at the other side of my home who surely wasn’t enjoying his cage getting rattled. It was me versus the 18Sub, and the 18Sub won by TKO. Needless to say, if rocking out to hard bass is your thing, the 18Sub will certainly oblige you. The sound it could produce on “Sub Pressure Volume 3” was pretty spectacular but also a bit scary. It was more than I thought I could handle.

Movie Watching

The 18Sub could reproduce epic destruction with a vivid intensity.

To see how the 18Sub would do with a large-scale Hollywood action movie, I watched “Pacific Rim: Uprising,” the sequel to the 2013 mega-monster bass-fest original. I had not previously seen the sequel, but I did enjoy the original, so I figured what better way to watch it than with an 18”, 2.4kW subwoofer in-house. “Pacific Rim: Uprising” promised to give the sub a workout if watched at a high volume level. Any movie where giant robots fight giant monsters should be a low-frequency bonanza, so how would the 18Sub sound with this clash of titans?

“Pacific Rim: Uprising” certainly delivered on the giant monster carnage, if nothing else. And the 18Sub turned that carnage into a sensory reality. “Pacific Rim: Uprising” had robots, monsters, and robot monsters, and they all sounded like they weighed the hundreds of tons that they were meant to. Memorable scenes with massive bass included the drone army attack on the Jaeger facility, the rocket thruster launch on the Jaegers, and the climactic destruction of Tokyo (naturally). These monster scenes were accompanied by monster bass supplied by the 18Sub, and it helped to make an otherwise trite movie be watchable. There are many superb demo scenes for subwoofer use, which is perhaps how this film is best viewed, and it did do a good job of demonstrating the 18Sub’s low-frequency prowess. The explosions, building collapses, giants’ stomping, and myriad other effects noises could be made to audibly vibrate the ceiling of my room. The visceral power of the sub never ceased to impress me even as the final battle didn’t seem to ever end. At the volume level that I watched it at, it was a fairly brutal experience, and when the monsters or robots took a blow, it could be felt as well as heard. The 18Sub could reproduce epic destruction with a vivid intensity, and those looking for a sub for major Hollywood movies certainly have a reliable choice here.

pacific rim uprising  Malignant

For a different type of cinematic subwoofer exercise, I watched the new release “Malignant,” the latest horror outing from director James Wan. Wan is a modern master in set-up and payoff in delivering scares, and the trailer for “Malignant” promised a bass-heavy fright-fest much like with his “Conjuring” and “Insidious” franchises. In “Malignant,” a woman has visions of ghastly murders, and matters get worse when she learns these murders are really occurring as opposed to being hallucinations. The reality-bending aspects of the story assure scenes with heavy low-frequency use, so how would the 18Sub fare with this type of content?

“Malignant” did not disappoint in the use of hard deep bass, and the 18Sub did not disappoint in recreating that bass with exuberance. While there were many bass-heavy effects sounds, the most memorable low-frequency element to me was the music score by Joseph Bishara. It was a mixture of traditional orchestral horror film strains along with synthesizer ingredients that were reminiscent of some of the slasher films of the 1980s. Through the 18Sub, the pulsating bassline of the music was physically felt. The acrobatic carnage caused by the villain was another part of the sound mix that was given a tactile sensation by the 18Sub. Every slain body that fell to the ground had a palpable thud thanks to the 18Sub. There were other effects scenes that were accompanied by deep-digging, guttural bass that shook my sofa. “Malignant” was a fun horror movie made more enjoyable by such a forceful subwoofer. Anyone looking for commercial theater-type dynamics would not make a mistake in getting the 18Sub for their home audio system.

RTJ Audio 18Sub Subwoofer Measurements


18Sub outdoor testing

Testing on the RTJ Audio 18Sub was conducted with the microphone facing the woofer at a 1-meter distance and then scaled back to 2-meters in our graphs by subtracting 6dB in output. The temperature was recorded at 62F degrees with 84% humidity. The subwoofer’s gain was set to maximum, phase was set to 0, and the low pass filters were left off.

18Sub Frequency Responses

The above graphs show the measured frequency responses for the RTJ Audio 18Sub subwoofer. Here we see a traditional sealed response shape which is unusual since most manufactured sealed subs use a high-pass filter for protection which makes for a steeper roll-off on the low end. The RTJ driver is such a robust unit that it doesn’t need as much protection from over-driving as most sealed subs. We also see a very neutral response that extends well past 600Hz. In fact, it maintains a flat response out to 600Hz- such a wide frequency band for a subwoofer that it could easily be used as the bass driver in a full-range three-way loudspeaker if desired. That is quite a feat for a long-throw 18” sub with a low resonant frequency, but it is one of the advantages of having such incredibly low inductance. Our graph shows the difference that the LF Adjust knob makes between the minimum, maximum, and mid-way settings. The minimum and mid-way settings look to change the slope of the low-end roll-off, whereas the maximum setting extends the knee of the response from 40Hz down to below 30Hz. The level of room gain should determine the level of boost that you set the LF Adjust to, as well as your preference for deep bass.

RTJ 18Subn CEA2010 Data

Bassaholic ExtremeThe 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 performance demonstrated here from the 18Sub is formidable with output exceeding 120dB through the entire mid-bass band along with great deep bass output as well. There are plenty of ported subs that can not achieve these deep bass numbers, but that is what can be had from such a high-displacement driver. This subwoofer punched with tremendous force in my listening sessions, and here we can see why. This level of performance easily earns this subwoofer our Bassaholics ‘Extreme’ room size rating making it suitable for rooms of 5,000 cubic feet.

18Sub compression sweeps2

Testing for long-term output compression was done by first conducting a 20-second sweep tone where 50Hz hit 90 dB with the subwoofer 2 meters from the microphone. 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 subwoofer is capable of. Here we see more tremendous numbers from the 18Sub which achieves a continuous 115dB+ at 30Hz and above. The response shape does change a bit above 115dB, and there we can see that natural response of the driver in the cabinet, and that DSP does do some response shaping at lower drive levels. There is a small hump just under 40Hz that is probably telling us that the enclosure is just a tad smaller than optimum. However, the driver is so powerful that it isn’t badly penalized by being housed in this small enclosure, and it still has tons of headroom at all frequencies. There is hardly any frequency-specific compression at all, a rarity among subwoofers that I have tested. This sub keeps the same response no matter the drive level; nice!

18Sub THD 2D view B 

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 18Sub has so much linear excursion that it doesn’t run into significant deep bass distortion until the highest drive level. Taking the gain down by a few dB ensures that distortion will never be audible at any frequency. At that point, the subwoofer plays very clean bass, and at nominal levels, the bass was so clean I wasn’t able to capture a reliable distortion reading above the environmental noise floor that in many instances still put it at less than 1%THD. At the highest drive level, the sub is still quite comfortable above 30Hz, meaning most music can be played as loudly as you want without significant distortion. At the highest drive level, the only thing that will distort in mid-bass ranges is your hearing as your eardrums implode. This is extremely clean bass that most outrageously expensive ‘audiophile’ brand subs could only hope to aspire to.

18Sub 2nd Harmonic B 18Sub 3rd Harmonic B

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.

One of the principal causes of even-order distortion in subwoofers is inductance, and we do see some even-order distortion quantities in lower bass, even though the 18Sub has very low inductance. I would attribute the cause as being the very small enclosure. There is not a lot of space for the internal air to move which creates a lot of backpressure, especially at lower frequencies. This causes a slight imbalance of outward excursion to inward excursion thereby giving rise to even-order distortion. It isn’t a tremendous amount of distortion, and for the same drive levels, the odd-order distortion is going to be a lot more audible, so this is more of a point of academic interest. Odd-order distortions are very low until we get below 30Hz at very high drive levels where the driver is reaching the end of its linear excursion. It can move a lot of air, and even at the maximum drive level, the distortion levels aren’t massive.

18Sub Group Delay4

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 18Sub turns in an outstanding showing here, among the best group delay measurements we have ever seen. Group delay hovers at or below 10ms until we get lower than 40Hz. There is nothing even remotely audible in this set. This subwoofer is as sharp as a razor blade much as I heard in listening to it on any content. One point of academic interest is the blip at just below 20Hz in the maximum LF Adjust setting where we can see the equalization causes just a tad extra delay there, as all filters will do, but this is very mild compared to what I see from most filters or equalization on subwoofers. Overall, the time-domain behavior is nearly ideal here. Anyone who is obsessive about the transient response from their subwoofer has a real champion in the 18Sub.

Conclusion of RTJ Sub18

Before bringing this review to an end, I will briefly go over the strengths and weaknesses of the product under review, and, as usual, I will start with the weaknesses, since I am the kind of person who always wants the bad news first. Thankfully there isn’t much bad news to report with the 18Sub. One might complain that it isn’t a very pretty sub, but it is meant to be hidden behind a baffle screen, so looks don’t really count here. Likewise, there are some who would prefer that the amplifier be onboard the enclosure, but again, that wouldn’t suit this subwoofer’s application.

18Sub amp front angle

One can say it is a very pricey subwoofer at $7k, but that pricing is in line with high-performance subwoofers from more established installer brands. I would have to question how many of those brands have anything that performs as well for the same cost. You may be able to get more SPL for the dollar from high-value internet direct brands, but the buyers for this sub are turning to installers for their audio systems and aren’t out to assemble their own system. What is more, it’s likely that few buyers will only be purchasing a single 18Sub, and the discounts that can be had for multiples make them a much higher value item, even against internet direct brands. Buying four 18Subs, which is a reasonable assumption for a high-end theater, lowers the individual pricing to $4,250: Not exactly inexpensive, to be sure, but for what it can do, it is a very reasonable sum. And four of these would produce absolutely mind-boggling bass.

18Sub hero2So what does it do that commands such a premium? It packs a huge punch in a small container. If there is a commercial subwoofer out there that produces more deep bass SPL per liter, it’s difficult to imagine what it would look like. The 18Sub has monster output with only a 15” depth, so it can easily be hidden behind baffle walls. And with only a 22” height and width, they are easily stacked as subwoofer arrays for gigantic bass per footprint. Nothing out there competes for that level of output per floorspace. This makes them a great solution for no-holds-barred home theater systems and high-end private cinemas. But it isn’t just sheer output that they offer; their sound quality is also superb, and the 18Sub has both stellar distortion and time-domain performance. It is a truly high-fidelity subwoofer. A multi-sub 18Sub system would have infinitesimally low distortion as well as some of the best time-domain performance that money can buy. The operative words here are clean and powerful, If I were putting together a home theater where the subs and speakers were to be hidden behind the screen, an 18Sub system would be my first choice if it could fit the budget.

This brings me to something I would like to see from RTJ Audio: the 18Sub is using a special driver, and I think it deserves better than being hidden behind a false wall. I would love to see it implemented in a proper hi-fi subwoofer for those of us who do not mind the sight of audio equipment. Give it the traditional hi-fi glamour that it deserves such as a curved cabinet with a high gloss finish. The 18Sub enclosure does stifle the driver’s performance a bit anyway, so give it some more breathing room (a Qtc of .7 or lower would be interesting…) That would allow better deep bass performance and lessen the need for DSP response shaping. That would make for one hell of a subwoofer, and a serious threat to many of the pretty subs with middling performance from high-end speaker manufacturers.

RTJ 18Sub Versus the Competition

RBH 21-SF/R SubwooferOf course, we would be remiss in not mentioning the JTR Captivator RS1 which could also be had for a lower cost individually, and it uses the same driver in a larger enclosure with an onboard amplifier. However, it can not fit into a false baffle wall and is made to be used as a typical stand-alone subwoofer and not as part of the room’s architecture. We therefore do not see it as being directly competitive with the RTJ 18Sub, but those who can stand to have the sub visible in-room ought to give it a close look for similar performance for a lower MSRP.

The RTJ 18Sub fights in the space of high-end home theater installer brands for false-baffle and in-wall subwoofers, and there is a lot of competition such as Procella Audio, Ascendo Acoustics, Grimani Systems, and JBL Synthesis, to name a few. They are all expensive, and you are not going to get a comparable system for under five figures, so RTJ’s pricing is in line with what you can expect to pay for something in this category. For example, the JBL Synthesis SSW-1 is a passive, dual 15” vented module intended for false baffle installation, and it goes for $9k alone. We haven’t dealt much with these types of systems in full reviews, although one exception is the new RBH Sound 21-SF/R. It goes for about as much as a dual RTJ 18Sub system, and we would expect them to have comparable displacement ability. Both are excellent systems, and the particulars of the room and installation should dictate which is a better solution. We like either of these over what we see from other high-end installer brands which generally look to be more expensive while using lesser-performing drivers. When surveying the market for the most directly competitive in-wall or false-baffle subwoofers, we don’t see anything we would consider over an 18Sub system or a 21-SF/R. Competing systems look to be at least as expensive yet not as good.

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

  • StarStarStarStarStar — Excellent
  • StarStarStarStar — Very Good
  • StarStarStar — Good
  • StarStar — Fair
  • Star — Poor
Bass ExtensionStarStarStarStarStar
Bass AccuracyStarStarStarStarStar
Build QualityStarStarStarStar
Ergonomics & UsabilityStarStarStarStar
Dynamic RangeStarStarStarStarStar
Fit and FinishStarStarStar
About the author:
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James Larson is Audioholics' primary loudspeaker and subwoofer reviewer on account of his deep knowledge of loudspeaker functioning and performance and also his overall enthusiasm toward moving the state of audio science forward.

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