Product Review - REL Stentor Subwoofer - May, 1998

By Daniel Long

REL Stentor Subwoofer - Ported 10" Downward-Firing Driver 200 Watt Amplifier Mfr. FR: 15 Hz - 120 Hz ±6 dB Size: 22"H x 23"W x 15"D Weight: 110 Pounds MSRP: $4,000 US

REL Acoustics Limited, North Road, Bridgend Industrial Estate, Bridgend, Mid Glamorgan, Wales, Great Britain CF31 3TP; Phone 44 1656 768 777; Fax 44 1656 766 093; E-Mail [email protected]; Web http://www.rel.net; USA: Sumiko, 2431 Fifth Street, Berkeley, California 94710; Phone 510-843-4500 ; Fax: 510-843-7120; E-Mail [email protected]

The Introduction to the Stentor in REL's web pages states that their subwoofers can be tuned for any room. I would disagree with the idea that you can accurately tailor, using the controls built into the sub (an impressive array, I must add), deep bass response in any room. As far as I know, you can only do this to a certain extent. If you have a null where standing waves result in almost no volume at a certain frequency, increasing the volume at that frequency won't do much of anything because the null is still there. Room treatment is a better way of attacking standing waves.

The Stentor is a 10" ported subwoofer. At first glance, this appears like a small sub. But look at the specs. The Stentor weighs in at a very robust 50kg (110lbs), and that's not just from the veneer on the bottom!

The ABC's of an ARM'ed REL

The Stentor (actually Stentor II, but from here on I shall refer to it only as Stentor) is the second model from the top of REL's line of
subwoofers. Only the monstrous Studio II (88kg/194lbs) is larger. The Stentor is a beast of a subwoofer, meaning it is rated to go below 20 Hz (- 6 dB at 15 Hz).

Though heavy, my first impressions of the Stentor was that it wasn't very large. Nor did it have an 18" or even a 15" driver. In fact, the Stentor has a high-excursion 10" driver. It is able to move large amounts of air because of the 200W rms (400W peak) MOSFET amplifier built-in. And to do this in a controlled manner, it uses what REL calls Acoustic Resistive Matrix (ARM) loading. This complex method is to have the loading cavities seen by the driver built successively smaller as they wind their way towards the small port. Along the way, there is also one special control cavity which is not explained by REL in the manual.

The powerful amplifier, high excursion driver, and ARM loading lead to better transient response at low frequencies, usually what most cheaper subs get wrong. It is often easy to play loud but not with finesse. REL's ABC or Active Bass Controller, is the circuitry incorporating the low-pass crossover used by the Stentor. It is adjustable with one Coarse and one Fine rotary switch with 4 positions each, enabling a large range of settings (16) between 25 Hz and 100 Hz.

Setup/Wiring

There are two ways you can connect the Stentor (or any REL, for that matter). The "easiest" way (I call this M1) is to simply connect its low-level input to the dedicated subwoofer output of an A/V receiver (or you can use a second set of pre-amp outs). This way, you should normally be able to set up your mains as "small" at a high-pass frequency that will have them reproducing most of the spectrum but keeping the lowest tones out. You can also connect the pre-outs of your mains (front left/right) to the line level inputs on the REL. Bear in mind that the REL does not supply high-pass line-level outputs to return high-pass signals back to your amps, so if you use pre-outs, you must have two sets or split them with a y connector. This, of course, does not reduce stress on the amplifier or the speakers, nor does it enable the system to play any louder than before unless you are able to use a high-pass in your A/V receiver to limit bass from to your mains.

You can then dial in the REL slightly higher or lower (depending on your room response/dimensions) than your main speakers' natural roll-off. The REL is one of very few subwoofers that have balanced (XLR) jacks. Use of balanced connections with long interconnects can yield less hum (a big problem with subwoofers in a system with lots of other components that cause ground loop hum).

The second way (I call this M2) is to use the high-level (or speaker-level) inputs from the speaker outputs of your power amp. This method is recommended by REL. There are no high-pass speaker level outputs to send high-pass amplified signals to the mains.

Whichever method you use (both methods are possible with all conventional subwoofers), you need to make sure you don't have overlapping bass response between the subwoofer and your mains. Otherwise, it will sound boomy (too much in the 80 Hz region). On the other hand, if there is a gap between the subwoofer response (low pass) and the mains' response, your system will sound "thin". Subwoofer and mains adjustment are important, so take your time.

As the setup is detailed in the manual, and is fairly easy to understand (though not necessarily easy to achieve the desired seamless transition between the mains and the subwoofer), I shall just say that on a system with Mirage M-1090i mains driven by an NAD 208THX, it took all of 40 minutes to get a very good match. Extrensive listening will allow fine tuning.

Music and Movies

I was impressed, to say the least, with the performance of this product. When the sub was first installed, the delivery guys simply plugged the sub-out of my Marantz SR-96 THX receiver into the Stentor. I had wanted to use M2 but stayed with the line-level connection (M1) for a little while just to get a feel of the sub used in this manner as well as to form an opinion for later comparison. I could also let it break in. I switched to M2 (low-passed at 30 Hz) for most of the critical listening.

It sounded dynamic, easily played loud, but was a little boomy in the 60 - 80 Hz region. There was surprisingly good delineation of deep bass notes (Stanley Clarke's "East River Drive" CD was the test) despite this humpy response.

With movies, it was as exciting as it was boomy on music! I guess that extra reinforcement was where it matters with loud and punchy soundtracks like that on "Speed", "Air Force One" and "Crimson Tide". As it broke in (taking its time, I might add), I became aware of a subtle shift downwards in that 80 Hz hump. After three weeks, it became not only less noticeable but lower in frequency, at about 50 Hz.

So, after full break in, music was now much smoother than before. This is important, because if you listened to this sub for the first week, you might think it was just a boomy sub and take it back. Give it a good three weeks of heavy use, and then decide.

I utilized the usual bass suspects for the tough tests. One favorite of mine is on the Sheffield Drive CD. In Dave Crusin's "Keep Your Eye on the Sparrow", Ron Carter plays a potent standup bass intro which reveals subwoofer problems very well. On subs that run deep but not boomy, this track places you in the same acoustic space as Crusion and Gang (Lee Ritenour on guitar, Larry Bunker on percussion, RC on acoustic bass, Harvey Mason on drums and DC on keyboards). Brings you back to 1976. You get the idea.

Sometimes I preferred M1 and sometimes I preferred M2. When I used the sub with line-level sub-out , I could play the system louder than when I used M2. This was because the main speakers bottom out below about 34 Hz when run full-range (in M2).

On music with M2, the transition between the Mirages' and REL was indistinguishable, meaning I could never reliably tell which speaker was playing the bass. The system sounded like a cohesive unit, which is exactly what we should strive to achieve. On Michael Ruff's "Talking Like Strangers", the Stentor purred along with the bass line, and never once let a bass note go out of control (except for that 50 Hz problem previously mentioned, which could just be a room effect).

I preferred M1 somewhat with movies, however. I guess the REL has more output below 80 Hz than the Mirages. Sort of like "cranking the bass for the flicks". With this setting, the Stentor simply roared along. I took out an older DD LD, "True Lies" and watched it through. With the previous subs I've used, only the HSU HRSW12V hinted at what I got with the Stentor. Pure unadulterated power!

While the HSU seemed to lose control just a little bit (with only 150W at it's disposal) when played really loud, I could never get the Stentor to break up. Of course, the Stentor is several times the price of the HSU, so this is not a fair comparison. Nevertheless, those are my observations.

Conclusion

Although REL strongly recommends M2 (using the high-level inputs and balancing gain and low-pass carefully), I used both and have to say it depends on what a consumer does more of. Movies or music. Bear in mind, it isn't a simple matter to switch from one connection method to the other. You have to switch off, disconnect cables and reconnect some other cables. While you can get 70 - 80% of the Stentor's performance with about ½ less money, the Stentor truly is an excellent deep bass subwoofer. It's very powerful, very flexible, and very attractive too.

Daniel Long

I am grateful to my friend Jason for the loan of his REL Stentor.

© Copyright 1998 Secrets of Home Theater & High Fidelity