Bass trapping can go a long way towards solving low-frequency problems in small rooms — but so, too, can monitor placement, as we find out in this month's Studio SOS...
James Welch had built himself a rather nice studio in a large wooden outbuilding. He'd already kitted it out with some DIY sound‑absorbing panels, made from Rockwool and barrier mat, and this included two large, deep bass traps in the front corners of his control room, which he'd based on ideas we've explored in previous episodes of Studio SOS.
At first, all seemed to be going well for James, but when he took the time to carry out some listening tests, he found that his listening position still lacked bass when compared with the rest of the room, and he noticed that some notes seemed to be exciting room modes, producing quite obvious 'hot spot' resonances. It was at this point that James asked if we could help, and he also provided information on the room size and construction.
One clue as to the problem was the shape of the control room, which was only a hair's breadth off being a perfect square, at 3.69 x 3.64 metres. Another issue was the very low and slightly sloping ceiling, which was only a little over two metres at the highest point — and thus low enough for some of the taller clients to touch with their heads in the centre of the room!
Matt Houghton had been let out of the SOS office to fill in for Hugh, who was temporarily out of action. On arrival, we were greeted with hot drinks and the now‑obligatory Hob Nobs, while we took stock of the situation and performed some listening tests of our own. A quick burst of Massive Attack's 'Angel' confirmed that the low bass end did indeed dip at the listening position, and playing a couple of low octaves of sine waves, a semitone at a time via a Reason synth, showed up the 'hot' notes quite clearly. The tests also showed that the stereo imaging could use some improvement.
James' Studio was configured around a Mac running Pro Tools LE via a Digi 002 interface, with monitoring provided by a pair of passive Tannoy Reveal speakers, powered by a Crown power amplifier. The speakers were on stands behind a large oak desk, which James had made from recycled material. The desk included cutouts for his small TAC Bullet analogue mixer and a processor rack containing a Dbx 266 compressor and a Focusrite ISA 828 preamp. He had one DIY absorber fixed to the wall behind each speaker, both trapping and diffusing panels on the rear wall, another trap on the right‑hand side wall (but not the left, as that's where the control‑room window is) and the aforementioned corner traps fitted diagonally across the front two corners. There was also a flat 'cloud'‑type Rockwool absorber panel suspended above his listening position, and a sofa at the rear of the room for clients.
Using the mystical insight provided by the ingestion of tea and Hob Nobs, it became evident that although James had done his best to fix the room using trapping, there were still several fundamental issues that needed addressing, each of which we thought might make an incremental improvement.
The most obvious problem was that James had set up his desk some distance from the wall, so as to provide room for the speaker stands behind, and this resulted in his listening position while seated being almost bang in the centre of the room, with his head not far off midway between the floor and ceiling. As past experience has shown, in smaller rooms that are close to square in shape, no matter how much trapping you seem to throw at the problem, there's always a null spot in the centre of the room in which the bass level dips quite alarmingly. This spherical 'dead spot' is usually around 75mm in diameter, and the closer you get to its centre, the more the bass end seems to vanish.
The metal‑frame speaker stands James had were quite substantial, but they were let down by very small, lightweight wooden platforms, which meant that the speakers felt somewhat wobbly. Furthermore, the deep desk and the speaker positioning behind it meant that a significant amount of sound would reflect from the desk, giving the potential for undesirable comb‑filtering. The practical outcome of this type of scenario is that the tonality of the sound may not be accurate, as you hear both the direct and reflected sound. The stereo image may also be compromised for the same reason.
Finally, although James had put absorbers behind the speakers — always a good idea — he had left an area of bare wall between them, which meant that he was facing a nearby reflective surface while mixing. This can also mess with the stereo imaging and clarity, by reflecting sound back to the listening position.
We didn't want to do anything irreversible until we knew we could make an improvement, so our first suggestion was to move the desk back towards the wall, so that the listening position could be taken away from the centre of the room. Of course, that meant doing away with the speaker stands and placing the speakers on the desk. Because of the equipment cutouts in the desk, there wasn't room to stand the speakers on it directly, so we mocked up a bridge shelf using a couple of wooden filing boxes and a plank, standing the speakers on top of the plank at close to their original spacing. This move allowed the listening chair to be moved forward by 40cm or so, which got James out of the dead zone. Repeating our listening tests showed that he could now hear plenty of low end, although we still had those hot notes (caused by excitation of the room modes) to deal with.
Faced with this situation, it's always worth experimenting with speaker position, and my instinct here was to bring the speakers closer together to increase their distance from the side walls. It invariably helps if you randomise the wall‑to‑speaker distances between the rear and side walls, as the last thing you need in a small room is a speaker that's the same distance from the side walls as it is from the front wall. It's also helpful if you can adjust the speaker height so that the woofer isn't exactly midway between the floor and ceiling, as any symmetry in placement encourages resonances. In fact, in very small rooms we've occasionally found that instead of having the monitors set up symmetrically about the centre‑line of the room, as theory dictates, it can help to offset the whole thing slightly to one side, again to help create different reflective path lengths. In this situation, we kept a reasonable left/right symmetry, and it seemed to work, but if all else fails, offsetting is definitely worth a try.
To cut a long chunk of theorising short, bringing the speaker positions in by 200mm or thereabouts reduced the bass hot‑spot quite significantly, so after shuffling the speakers around a little more, to try to fine‑tune our new‑found success, we decided that this new layout was the way to go. All we needed now was a more permanent, more rigid — and more elegant — way to support the speakers in their new positions. Fortunately, there was a retail park nearby with both a Homebase and a B&Q store, where we could buy any materials we needed, and James' own tool kit included a large radial‑arm circular saw, which would make short work of any cutting.
The plan Matt and I concocted was to build a pair of simple three‑sided pine bridges to fit over each equipment pod, and to top each with a heavy tile of some kind to add mass. These would be used to support the speakers at just the right height, with the tweeters aimed pretty much directly at the engineer's head, or a point just behind it. Matt favoured granite, of the type used for kitchen worktops, but although these can be found in several supermarkets for a very reasonable price (masquerading as 'worktop savers'), granite tiles of a suitable size turned out only to be available in packs of six in the local DIY stores, and they were very expensive! It always pays to keep an eye out for the sort of DIY bargains you might be able to press into service in your studio...
We did, however, find some suitably heavy ceramic tiles that were available individually, and that measured 30mm x 60mm, which made them exactly the right size for our needs. We also bought a roll of non‑slip matting to put between the wooden bridge and the tile, with a further piece beneath each speaker. Paul carried the non‑slip matting back to the car, while Matt got lumbered with the tiles... and James somehow made all the wood, plus three grown men, fit into his VW Golf!
We used pine board 15mm thick to make the bridges, and all we had to do was slice it into suitable lengths using the radial arm saw, and then glue and pin the joints, with a further bracing piece fitted to the underside of each top, level with the rear edge. Even before the glue had dried, we had the stands in place, the speakers fitted and strips of non‑slip matting cut to sit beneath where the edges of our bridges rested on the desk.
Out came the record collection again, and as well as replicating our previous bass‑smoothing miracle, the more solid stands also had the effect of tightening up the bass slightly. Perhaps more surprising was that the stereo imaging was now also noticeably better. However, the ceiling cloud was now in the wrong place relative to the desk and speakers, so we needed to relocate that too. This turned out to be very easy, as the cloud was fitted out with hooks at the corners, and James had left plugs in the ceiling just where we needed them, as that's where he'd first tried fitting his cloud! All we had to do was screw hooks into the old plugs, but instead of using short lengths of chain to support the frame, we suggested using plastic cable ties, as these would be easier to fit and we could pull the whole assembly up tight against the roof's near‑central support beam, where people were less likely to bang their heads on it.
This move proved to be very worthwhile, but to improve listening for anyone else in the room, we thought it might also be worth sticking up a couple of foam panels on the ceiling just behind the cloud at what would be the mirror point for anyone sitting on the sofa at the rear of the room. It would also make the ceiling more comfortable for taller clients! Fortunately, we had a few Universal Acoustics panels left over from a previous Studio SOS expedition, so we glued two to the ceiling, one to the front wall between the existing traps, and one below the control‑room window on the left side wall, where there was no other treatment. Once again, we checked with a variety of known commercial material and noticed a further improvement in focus and imaging.
James then put up some drum recordings he'd done and commented that he was now hearing things that had gone unnoticed before. Matt also felt the low‑frequency balance was more even at different points around the room, and it was even acceptable — if not ideal — when sitting on the sofa against the back wall. This is worth pointing out because low‑frequency sounds always increase in level when you listen right next to a wall, due to the boundary effect, and that's exactly where the listener's head is while sitting on the sofa. As luck would have it, the resilience of the wall and the trapping qualities of the sofa seemed to go some way towards compensating for this.
By the middle of the afternoon, we were all pleased with the result, because although James had done all the hard work building the traps and creating a really comfortable working space, the new speaker stands and the positional fine‑tuning made a huge difference, as well as leaving him with quite a bit more usable floor space in his control room.
We had a play around with some of James' guitars and amps in the live room, and discussed some room‑mic placement tricks. James was also taking delivery of a number of clear plastic orchestral screens that he planned to use on a recording that evening — and they looked very interesting — but as everything in the live room seemed to be pretty well sorted, we left it well alone.
Pausing only to accept another packet of Hob Nobs for the drive home, we left James to get used to his new monitoring setup.
James: "I can't thank you enough for your help today. Your professionalism and general willingness was really appreciated. The control room sounds 100 percent better, and the additional space you have created in there is a real bonus. I'm doing the jazz session right now and it sounds great (those screens are amazing!). The band, sitting on the sofa, think it sounds great, and the whole feel of the control room is just better.”