REL ACOUSTICS T/9x Subwoofer Review

The REL Acoustics T/9x Subwoofer is fully evaluated by Douglas Moore.

Subwoofers are a topic of much debate in the home audio world. Some people swear by them saying that their speaker system is not complete without one. Others do not like anything added or taken away from their beloved main speakers and think a subwoofer may alter or even damage the sound. I grew up in a time before powered subwoofers were a thing in the home. Large floor-standing speakers with large bass drivers were the closest thing you could get to sub-bass. If you had bass response down to the 45-hertz range you had something special.

I remember in the 80s I wanted to go audition anything new in the high-end audio stores. Harvey’s Stereo was one of the main stereo shops in Springfield at the time and my father would take me there every time we visited Springfield. Many times, I was looking at the speakers and walked into their higher-end room with the larger floor-standing speakers. But this time things were a bit different.

While listening to a particular system the salesman was telling the customer about a new product they just received. While the system was playing, he reached down and switched on a box that was on the floor. That box was a Velodyne subwoofer, and for the first time in my life I heard was true low bass was about. The room was pressurized as I have never heard, the floor felt like it flexed with each bass pulse. The other thing that seemed very strange at the time was that with the subwoofer on all other aspects of the speaker’s sound improved as well. To this day this one experience changed forever how I felt about subwoofers in high-end audio systems.

If you think about how you set up floor-standing speakers in a home audio system many times they should be placed as far away from the back wall in your room as possible.This is great for the vast majority of speakers when it comes to midrange and treble. This also helps with soundstage and imaging, but the bass is held captive to this setup because that is not where it does its best performance. The bass is less strident and will inevitably lend itself to more room problems.

Subwoofers that are designed correctly can help with this even with “cost no object “speaker systems and particularly small and bookshelf monitors. A lot of people who have auditioned subwoofers with high-end systems have heard subwoofers that were not set up correctly to optimize their sound quality. This is my opinion of course but a well-integrated and leveled subwoofer should, and will usually disappear in the system. This disappearing act will give the impression that your speakers are producing bass down to almost 20 hertz.

Another thing that adding a subwoofer can do is to improve the overall soundstage and realism of the sound within your listening room. A lot of what a subwoofer can do is show more of the venue of the event whether it is the sound of the room at the studio session or the energy of the stage at a live recording. The low-frequency energy coming through the subwoofer adds to the pressurization that matches the pressurization when the recording was made, thus giving you a more realistic experience; presuming of course that your room is pretty well balanced sonically. This effect and the added effect of lower frequency extension and bass detail are why even systems with the best speakers money can buy can arguably, be improved with the use of a good subwoofer.

REL Acoustics  is a company that does things a little differently. From the moment I first heard a REL, this was very apparent. It was the late 90s and I thought I had heard all that a sub could do since I had worked in high-end audio and had heard Velodyne, Mirage, and B&W among others. However, REL was different.

As I was browsing through a REL dealership, one of the owners asked If I had heard of REL. I kindly said no, he said you need to hear this. He took me into a room with Magnepan speakers and turned on the music. From the first listen I knew this was a different experience. The bass seemed to come directly from the speakers and had tightness and detail that I had never heard. The REL subwoofers just seemed to be in a different class. REL is very much a music-first type of subwoofer company. They do have a home theater subwoofer line now, but they have only recently ventured in that direction. They have a different philosophy about connecting a subwoofer than other companies out there.

REL T9x high level cables

As you see above the cable used with REL subwoofers is a high-level cable. This means that you hook up the subwoofer much like you do your main speakers. Using the speaker’s outputs on your power amplifier, this high-level connection then passes to the REL subwoofer through a SpeakON connector input on the subwoofer which is converted to a low-level signal. REL says that connecting their subwoofer in this fashion means the subwoofer gets the same signal and sound signature as your main speakers allowing the sub to integrate with the system better. REL uses very high-speed devices in their high-level inputs so that there is no lag in sound going through this circuit. They procured the latency down to 8 milliseconds on their design (their reference level subwoofers are 4 milliseconds!!).  

There are other subwoofer brands out there that have high-level inputs but they do not use the high-speed circuits REL uses. They are merely there for convenience and are not recommended by most subwoofer companies. This high-level circuit is just one of the stand-out features of REL subwoofers.

The subwoofer I will be reviewing today is the REL T/9x and is the first subwoofer system having been reviewed here at The Sound Advocate. The T9x represents the flagship of their entry-level line and while being a flagship of this series it still represents huge capabilities in a smaller unit.

There are 4 series of subwoofers in REL’s lineup, the Reference Series, the Serie S, the Serie T, and the Serie HT. The Reference Series is their cost no object line, S being their middle range, T being their entry-level range, and HT is their home theater line. The Reference, S, and HT/1508 subwoofers also allow you to set up six-packs on these subwoofers for unparalleled bass performance in a system.


REL says they do not recommend setting up the Serie T units in a six-pack due to their small size and lighter weight being an issue with stability. While I think it would be cool to be able to build up to a Serie T six-pack I do understand their concerns.

The T9x subwoofer utilizes REL’s 10” fiber-allow cone active subwoofer driver and 10” inverted dust cap bottom-firing passive radiator. I have worked with a lot of subwoofers in my years and generally, I stay away from passive radiators because most of the time they take away from the speed of the bass. But every design that REL works on is a study in perfection and with that comes a design that uses a passive radiator and keeps the speed of a sealed design.  

The amplifier in this subwoofer is a 300-watt class A/B design that REL has used reliably for years with virtually no failures. This reliability was important to me, especially because up until now I have built my custom subwoofers. While the drivers were very good and sounded great the plate amplifiers available in the DIY market are mostly cheaply made models with limited lifespans. I was on my 3rd plate amplifier when I decided that it was time to trust in REL’s more reliable designs.

If you are on the fence about which REL subwoofer to choose they have a very helpful speaker matching app on their website with many of today’s more popular speakers and what subwoofer REL recommends for each speaker.

What Is The Best Subwoofer for Me? | REL Acoustics For many people, this app will be of great value in your decision-making.


My REL came double boxed and very well packed. They included all the cabling to get you going and a very well-written manual to help with setup. The subwoofer was wrapped in a protective cloth bag to keep from scratching the finish and was easy to come out of the box. It all felt like a very high-quality packing job.

Inspecting the subwoofer itself only confirmed the quality the REL is known for. The gloss black finish is on par with an automotive finish on a new car. And all the switches and jacks were of good quality and working order. It did not take it long for me to get this subwoofer installed.


It is very easy to get this subwoofer installed and they offer different options for such, even though they recommend high-level inputs being used for a music system. Their patented circuit for this high-level connection is the best in the business and has the fastest filter components currently available (they even put heavy epoxy around this circuit so other companies can steal their circuit design).

They also offer a low-level input RCA jack if you choose to run this directly off of your preamp output. REL is also thinking about people that will use this subwoofer with a music/home theater setup. REL offers you an LFE input as well. This input will work alongside the high-level input so that you can get the benefits from this subwoofer on both your movie LFE effects and the low end of your main speakers at the same time!! I have not seen this level of input variability in many subwoofers on the market. While I did not use the LFE input on this subwoofer since I did not use this subwoofer for movies or multichannel music I did not test this but many people I know say it works perfectly.

Another aspect of the T9x’s controls I like is that they have positive clicks for each step like some volume controls so that you are changing the controls one step at a time. This allows very precise adjustments when setting it up. Here is a picture and video link on why the high-level connection is the preferred way to connect a REL.

What is a High-Level Connection? | REL Acoustics


The one thing the REL is adamant about with their high-level connection is knowing what type of power amplifier you are using and if it is dual-deferential. If you read REL’s manual before installation they give you all the different ways to connect their subwoofer to the different amplifiers that are out there. If you take your time and learn your amplifier then the connection will go right and you will get the benefit of this connection type.

Also, REL has plenty of resources on their website and you can even call them or email them before connecting to make sure that you are doing this part right. There are not very many amplifiers out there that a REL has not been connected to at some point so they are very knowledgeable about this connection procedure and are very eager to help anyone in this endeavor.

My power amplifier is the Pass Labs X150.5 which is a dual-differential design. So I had to look at REL’s method of connection for this type of amplifier. In effect, I connected both positive leads to the right and left channel’s positive output and do not connect the ground. This worked perfectly for me on my system. REL did say that on some systems not connecting to the ground will cause a hum in the subwoofer and for those systems, there are additional steps to be taken. This includes connecting the ground to the chassis ground of the amp or hooking it to the ground of an unused input connector. I recommend talking to REL about your system before doing any of these additional steps to ensure you are doing the right thing.


After connecting the subwoofer to my system I followed the manual’s instructions on setting the crossover and level of the subwoofer to work with my speakers. This took a little bit of time and it always helps to have a friend (or wife!!) do the changing on the controls while you sit in your listening position until the sound falls into place.

Any seasoned music listener or audiophile should be able to do this because it is all about when the subwoofer disappears in the system. When the level and crossover are set perfect the sub will bring no attention to itself and will fill out the bottom octaves of your main speakers as if the speakers themselves are doing the work. For the most part, I got this right on the first try only having to go back and do micro adjustments a couple of times.

Right off the bat, I will tell you that this subwoofer needs some time to break in its driver to sound its best. It sounded pretty good at first but its dynamics and lower bass output were hindered until this process was done. I am not talking about 500 hours here or anything close. A few afternoon listening sessions at moderate volumes seemed to do the trick as the subwoofer started to come alive and sing with dynamics and lower bass content. Playing songs off of Silk Sonics 2021 album An Evening With Silk sonic gave me the lower-end bass to test the sub. The song Fly As Me gave me a good dose of this bass. In the chorus of the song their a synthesized thump that comes through that shakes the room with the right setup. And the T9x delivered the goods!

As the T9x is a smaller subwoofer compared to many on the market, it hits pretty hard. Albums like Oscar Peterson’s We Get Requests are great albums to test the subwoofer’s ability with the stand-up bass since this instrument has a lot of body and deep tonality. The REL did not disappoint, giving me all the tone and body that this instrument presented and being fast enough to keep up with the drums as well. Not many subwoofers can handle both of these tasks and still keep their composure and sound true to the instrumental texture and tonality.  

For me, a subwoofer must be fast enough to present every detail in the bass with any type of music I throw at it. It must also perfectly blend and pull a chameleon act as far as disappearing into the system only to be noticed when you turn it off and hear what it adds to the sound. The T9x did this better than any subwoofer I have heard anywhere around its price. Only the higher-end REL subwoofers I have heard beat this one!! Now don’t get me wrong, there are many great subwoofers out there from many brands.

I have heard great results from JL Audio subwoofers, for example, they actually punch a little harder and deeper than the REL subwoofers do so if your mission is overall bass punch then they might be a better fit for you. What REL does well is blending the musical accuracy and real-life bass tones involved in the recording. This is bass that sounds like real instruments being played.! They do this better than any subwoofer I have heard. As you go up the REL line this just keeps improving and improving. For you home theater enthusiasts out there that care more about the movie dynamics and the utmost extension, definitely look at their Series HT line.

SERIES HT / 1510

While the REl Serie HT line gives you a satin vinyl finish instead of the nice gloss finish of their higher-end subwoofers, They give you more power and larger drivers for your money. Serie HT uses class D amplifiers instead of Serie T’s class A/B. For users of home theater receivers or lower-end mid-fi equipment, the Serie HT will most likely be a better product for you as they are made to use with low-level inputs much like many other home theater subwoofers out there. Another aspect to remember is that the Series T, S, and Reference series subwoofers are very sensitive to the equipment being connected to them and will scale with your system. Thereby, if you are using beginner-level or mid-fi equipment you most likely will not get the most out of the upper-level REL offerings.


I have installed and heard many subwoofers in my high-fi journey. Some have been good and others not so much. There are other subwoofers out there in the price class that offers great performance. SVS is one of them if you are looking for features and technology like phone apps to control the subwoofer and eq functions to dial it in they might be a better fit. Rythmik is another company that makes good servo-controlled subwoofers.

Servo subwoofers use a constant monitoring system to see how the woofer cone’s movement compares to the input sine wave. If there are any differences the servo circuits will make adjustments to compensate. While I did not have products here for direct comparison with the REL I have worked with both companies’ products before and know them well. If you are mostly a home theater person then an SVS subwoofer might give you more bang for your buck. Rythmik offers a more active approach. But to my ears and through the years I have found that REL offers the best in terms of integration with the main speakers, speed, bass texture, and tone, and REL accomplishes this through rigorous design and research.


My time with the REL T9x has been an excellent experience and I would highly recommend anyone looking for a music-first subwoofer in this price range give this unit a listen. REL offers a 60-day free trial with free returns, a 60-day price guarantee, a 3-year warranty, and free shipping if ordered directly from REL. To me, this makes trying one out in your system a no-brainer!!

Review SystemSpeakers: Spatial Audio M3 Turbo S open baffle. REL T9x subwoofer Digital: Denafrips Venus II, Modified PC-based Music server/streamer. Amplification: Hegel P20 preamp. Pass Labs X150.5 power amp. Conditioner: PS Audio Quintet. Cables: Iconoclast SPTPC speaker cables, Mogami XLR interconnects, Iconoclast BAV REL subwoofer cable

REL T/9x price: $1,449.00




Front-firing active driver, down-firing passive


10 in. FibreAlloy™, 254mm long-throw, inverted alloy dust cap, steel chassis


10 in., 254mm long-throw, inverted dust cap


-6dB at 27 Hz


High-Level Neutrik Speakon, Low-Level single RCA, LFE RCA




300 watts (RMS)


Class A/B


Arrow (Optional), Zero Compression Single Large Scale Integrated Chip

Protection System








220-240 volts, 110-120 volts for certain markets

Dimensions W X H X D 14.5 x 13.4 x 15.5 in., (370 x 340 x 393 mm)


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