In the world of subwoofers, the REL Stadium is something different from the norm. It is self-powered by a 100watt onboard amplifier. It isn't small either, but nor was the bass! My feelings about this product moved from initial trepidation, based on past experience of subwoofers, to surprise and delight once I had got the device tuned in. The Stadium is a real house mover. At £695 it is also something of a bargain, one that opens up some very interesting possiblities for home hi-fi.
First, the possibilities. I combined the REL with two radically different types of loudspeaker. It was partnered with my own beloved Quad ESL-63 electrostatic loudspeakers, price £2072. The outcome was completely successful. Since this is a notoriously difficult loudspeaker to complement with a subwoofer, yet in great need of one, the success was unexpected but welcome.
Having overcome this problem and become acquainted with the tuning of the REL, I was confidentit would do a wonderful job with Goodmans' new Maxim 3, price just £120. This is an affordable combination; it also turned out to be practical and deeply impressive in sound quality.
So this look at the REL Stadium covers two very different set ups, yet peculiarly, both combinations share many qualities. Both are the sort of loudspeaker I would prefer to live with - namely a point source, flat response, reference monitor of exceptionly wide bandwidth and superb staging ability. It's just that the Goodmans/REL set-up takes up little room, and equally little cash. Yet it produces a sound you won't find easily elsewhere. Needless to say, most of the happy hours were spent in front of the electrostatics, so they feature first and strongest in this assessment.
REL Acoustics make two other subwoofers: the £1195 Stentor and the early, less expensive, £325 Stygian Mk1. The Stadium possesses less internal bracing than the Stentor and is a bit smaller and less embellished externally. What you get in the Stadium is a large, 72 litre floorstanding cabinet complete with bass amplifier and two high power Volt 10in (25cm) bass units. It is a mono system, like most subwoofers since at very low frequencies, directionality is lost.
Single cabinet (mono) subwoofers that auddibly degrade stereo do so because they are poorly engineered. This is one reservation I have about many systems. Those that work off the main amplifier might be cheap and simple, but their poor crossovers start to combine (mono) the two stereo channels right up to around 250Hz. At this frequency stereo can be discerned, so the degradation is audible. The Stadium has a fast, forth order, low pass filter that feeds bass to its internal power amp. The highest bass that the Stadium will reproduce is 120Hz, but the filter is switchable. This figure can be adjusted right down to 30Hz maximum - a very low value. As a result, the Stadium does not upset the stereo of the main system, as REL claim.
There's another potential problem with sub-woofers related to the upper working limit and the roll-off rate. Their resonant cabinets can colour deep male voice quite severely, making for a boomy, unnatural sound that the ear is very alert to. This can offend both Rock and Opera lovers. Because it goes no higher than 120Hz the Stadium has little effect in this respect. When switched to its upper limit, the deeper components of male speech do invariably pass through it, but such components are attenuated enough not to be audible with the main speakers working I found. In practice I set the Stadium to work only the lower octaves with the Quads, where I felt it was most successful and least intrusive. It doesn't colour the sound of the main system when properly adjusted.
The upper frequency limit of a subwoofer is important, it must not go so high as to degrade stereo (with single cabinet types at least) and it mustn't colour voice either. Yet it must be high enough to take over where small speakers leave off. My own work with loudspeakers and, in particular, development of a crossover to match Celestion SL-6000 sub-woofers into the Quad ESL-63s, showed me that around 100Hz is the wise upper limit. The Stadium's upper limit of 125Hz is just right.
Whilst my own crossover eliminates bass from the Quads, allowing them to go louder, the REL does not affect the main system at all. It's a back-up subwoofer, a feature that helps it to integrate more easily. It senses the signal on the output of the main amplifier amplifies the bass portion only. This is a simple but very effective technique I found and, although the Quads don't go louder, the system itself does.
Unpowered subwoofers are the sort commonly partnered with matching satellites are in fact ordinary bass cabinets. They don't go down low enough to be true 'sub-woofers' in the generally understood sense of the word in hi-fi circles. A proper sub-woofer should go below 40Hz, preferably to 20Hz (i.e. one octave below 40Hz), or even lower. REL claim 20Hz is the lower limit of the Stadium, so it is meant to be a true sub-woofer, something that sets it apart from many similarly named but simpler items.
The in-room frequency resonse (see Fig.1) with my Quad '63s clearly shows that it extended bass response of the system down to 8Hz in our 16ft x 12ft listening room. That is low - very low. In practice it meant that the Stadium reproduced some joke/heart-stop tracks with deep bass very effectively. So REL are conservative in their claim of a 20Hz lower limit. The Stadium is a true subwoofer that will reproduce two octaves lower than most loudspeakers - even big ones. This is an impressive achievement.
So much for downward extension. It is in frequency response smoothness that 99% of subwoofers fall down. To get big bass from a small cabinet they are often tuned to boom, usually around 60Hz. This sounds awful in practice, giving 'one-note' bass that destroys bass lines and becomes throughly irritating after a while. REL have done a lot to avoid this problem, something that contributed greatly to my appreciation of the Stadium. It does not boom or overhang, reproducing bass cleanly andplaying a bass tune well.
However, even before measurement I suspectedthere was slight emphasis very low down, in the sub-bass region, since a very deep 'boof' occasionally made itself known, which rattled the room quite strongly at times. This was most frightening whith a live VHF radio transmission from a studio where the presenter kept thumping the table or microphone; I had to jump up and turn the volume down quickly before something got damaged or our windows fell out.
Analysis revealed a small sub-bass peak at 20Hz (just visible in Fig.1). After tuning the 'boof' disappeared; in truth I had the gain up too high. The gain control needs to be used with care I found. those kettle drum strikes at the start of Carmina Burana can be given any intensity and power, they rattled our windows and sent shudders of vibration through my body until I found that with the Quads the Stadium was best reigned right back to 43Hz maximum frequency setting (low) and zero on the gain control (this does not take the volume to zero).
Ther small 20Hz peak can get excited by one or two records. The 'heartbeats' at the start of the Floyd's 'Dark Side of the Moon' have a dominant 20Hz component. With the Stadium switched down to 'minimum everything' , the beats were still shaking the room. Luckily, few CDs have low frequency signals as loud as this.
Another track that does however is Billy Idol's 'Charmed Life' CD. On track 2 there is an interesting low frequency event - a trick played by the producer I suspect. A door closes with an enormous subsonic thump, acousticall illustrating the lyric: "I walk through you door". This sent a huge subsonic impulse through the building, better felt some 30ft away down a corridor than in the listening room. Few loudspeakers even hint at the existence of this trick. The Stadium didn't flinch from reproducing it a full level.
So much for subsonic fireworks. Although it possible to keep them down to being audible but not dominant or intrusive with the Quads, I feel REL could usefully provide lower minimum gain all the same, in order to give more variation with the ESL-63s, because of their insensitivity.
And now onto the final hurdle for a subwoofer - bass playing. thisis difficult to assess properly with an add-in subwoofer, since the main speaker does much of the work and can mask subwoofer weaknesses, such as waffle and one-note effects. With the main speakers disconnected, my ears/body told me the fundamentals from Robbie Shakespeare's bass playing on 'Language Barrier' were all there. However, I have learnt that it is better to measure this sort of thing to be sure, since hearing acuity is limited below 100Hz. the bass playing analysis (see Fig.2) shows the bass line being reproduced by the amplifier (i.e. the electrical output signal), with the output of the Stadium superimposed upon it. They are nearly identical.
This proves beyond a doubt that the Stadium is accurate in its bass reproduction - in fact it is unusually accurate. There's barely a few dB variation in reproduction of the bass line, from 50Hz up to 125Hz (above 125Hz acoustic output rolls off, as it is meant to). This subwoofer plays bass with uncanny ability in a room. I know from my own work that to get such good results in-room takes a lot of work. That's why really good subwoofers are so rare.
With the Quads working, Robbie Shakespeare's rumbling and repetitive bass riffs, which supported the earlier Grace Jones albums so manfully, really strode along. There wasn't any note slurring, nor any loss of power, nor any peakiness that favours one note over the rest. You get the tune, not a floundering representation of it. The bass power and the sense of control was superb.
This makes the Stadium great for Reggae, all Rock - and of course for Organ works. Oh yes! The room shook - did it ever shake! - as Peter Hurford worked his way sinuously through Cesar Franck's Choral No2. The analyser showed vast levels of 30Hz being generated in the room, but my neighbours knew all about it without one. Those sustained notes got the building going - and the one next door - and the one after that.
Getting a subwoofer to reproduce this sort of thing cleanly demands huge power handling ability. I never got the Stadium to show signs of stress all the same. REL have got the problems inherent in good subwoofering beaten. I only got more and more impressed as I used it.
The Goddmans Maxim 3s are meant for wall placement to reinforce their bass. This also produces peaky bass with emphasis around 60Hz, which makes smooth matching and an even sounding bass performance of the sort I talked about earlier difficult or impossible to obtain. Whilst the Stadium worked with the Maxims against the wall, I found it better to move the Maxims out, keeping them on stands. This gives a more open sounding stereo image with firmer images as well.
After some fiddling, I found that the frequency controls were best set to maximum (i.e. highest cut off frequency of 120Hz), with gain kept right down close to minimum. Since the Maxims are sensitive, the Stadium does apear to have too much gain, meaning the control has a sudden and coarse action. Properly adjusted however, the Stadium and Maxims worked from 20kHz right down to 10Hz (-6dB) - an astonishing range. The frequency response analysis (see Fig.3) shows smooth bass. There is a narrow suckout at 50Hz and a small (+5dB) peak from the subwoofer at 20Hz. As in-room bass goes (far field), this is a very even performance in measured terms.
The Maxim 3s have wonderful imaging and staging properties. They are dynamic sounding and very forward andimmediate. With the Stadium, bass quality was smooth, seamless - and endless. I was glad to have to make the Stadium work over its entire frequency range, because this was more revealing. It stayed tight as a drum in sound quality, providing deep, clean bass and massive subsonics, when they existed on a CD of course.
The whole presentation was dramatic - and more 'out of the box' and generally more etheral than usual. These items in combination offered some of the best bass I have ever heard and, generally, a standard of performance I can honestly say is quite unusual. I have never come across a system of such enormous ability before at such a low price. The Stadium showed that, when partnered withthe right items, it is a magic ingredient, turning a small system into a giant slayer.
Now to practicalities - and blemishes. Ideally, the Stadium should be sited between the loudspeakers. It is big, measuring 575mm wide, 520mm high and 352mm deep. Being a large, black box, weighing 23kgs (50lbs) it is hardly beautiful. However, the cabinet could double as a small table. Just bear in mind that vases placed on it will have to be bolted down and coffee will exit the cup vertically, ending up in strange places - like your shoes. The cat isn't likely to sit on the cabinet, unless it is training for the nest shuttle mission.
The signal sensing wires are fragile, but the sensing arrangement, with 'earth lift', is well thought out. I experienced no difficulties. Switching between different frequencies on the coarse tuning control occasionally 'opened' the filter, allowing a short blast of programme through the box. This was more disconcerting than dangerous.
the instructions could usefully be more succinct and illustrated. The controls need to be calibrated, then the tuning-in process could be beter explained. Exactly what the Stadium does and, therefore how to tune it was not clear I felt. It takes time and alot of experimentation to get right. In fairness, however, our sample was the first of the Stadium breed; the tuning dials are said to be better calibrated in later Stadia.
Finally, potential users need to be aware that LP warps can be a problem when any subwoofer that goes below 10Hz, like this one, is partnered with a preamp lacking a warp filter. Cone flap and warp noise will result, because the Stadium is a bass reflex unit with little natural damping. I used CD alone.
The Stadium subwoofer was more successful than I could ever have imagined. It reproduces bass right down to the lowest frequencies (10Hz), it adds no colouration and it offers the tightest, smoothest bass quality available from any loudspeaker. Anyone wanting to hear smooth, yet strong bass lines, with no slur or overhang should check it out.
I suspect I will be useing one with my Quad's in future; it is more compact and practical than other arrangements and it will just 'tack onto' any system that is in use. Quad owners should be delighted with the Stadium, it matches so well. However most people I suspect will be more interested in using the stadium with good, miniature loudspeakers, like the Goodmans Maxim 3s. It's a fascinating and unique combination that is difficult to beat for both drama and fidelity.
Noel Keywood