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Studio SOS: Adam Dengel

Fixing a 'dead' live room
By Hugh Robjohns & Paul White

A dead live room, a live control room and faulty monitors... sounds like a job for the Studio SOS team!

On completing his music technology education, Adam Dengel rented a property with the aim of setting up a rehearsal room and recording studio (DC Studio). The rehearsal part of his business seems to be ticking over just fine, but the studio he built for his own recording projects (and with the aim of attracting some commercial work) hasn't been performing as expected — and acoustics problems seemed to be to blame. Adam's studio is tucked away right in the centre of Barnsley in Yorkshire, and as I was born and educated there (but left because I couldn't learn the language!), I was keen to have a look around and see what had changed.

There was too much foam — and not all of the right sort — in the live room, which resulted in a sound that was dominated by lower-mid frequencies.There was too much foam — and not all of the right sort — in the live room, which resulted in a sound that was dominated by lower-mid frequencies.Clearly Adam's studio building has been there a long time: it's made from Yorkshire stone, with the familiar black coating that accumulated during the industrial and coal-mining boom. He has lined the walls of the live room with plasterboard on batten and then glued foam over every surface apart from around half the ceiling and the floor, which is carpeted. The end wall behind the drum kit is covered with Studiospares foam (around two inches thick) as is his approximately 2m x 2m vocal booth. I estimated that the half-inch industrial flat foam used on the rest of the room would have little effect below 1kHz or so. The control room was, by contrast, completely untreated when we arrived, and sounded distinctly live, so we were going to need to apply some treatment there to kill the worst of the reflections around the monitoring area.

Adam's Studio is based around Pro Tools M-Powered running on a PC, with a Project Mix I/O interface and a pair of Tannoy Mercury M2 passive monitors. These are fed from the powered sub of an M-Audio LX4 system and Adam also has the original LX4 satellite speakers, though one of the tweeters had been been damaged, so he replaced this with a similarly sized unit from the local Maplin store. He'd also bought a switching box for his speakers, hoping to be able to switch between the M-Audio and Tannoy monitors, but he hadn't been able to get it to work.

Keep Music Live

I'd already been in touch with Adam via email to discuss his live-room problems, and from his description it was evident that his over-enthusiastic foam treatment was killing all the high end but leaving lower frequencies effectively untreated, which meant that the sound in there was boxy and lifeless. As luck would have it, the panelling he'd built over the original walls was providing some accidental low-frequency trapping, but the room was still dominated by the lower-mid range. Short of ripping out all his hard work and starting again, it wasn't possible to come up with a perfect solution, but as the room was to be used mainly for recording drums and electric instruments we felt that a practical compromise could bring about a significant improvement for very little outlay. Our strategy was to put some high-frequency reflection back into the room to balance the low end.

Using a combination of plastic sheets and MDF panels, some high-frequency reflections were added back to the live room, without compromising the absorption of mid and low frequencies.Using a combination of plastic sheets and MDF panels, some high-frequency reflections were added back to the live room, without compromising the absorption of mid and low frequencies.This was all very well in theory, but we needed to find something to use for this. At home I had a partly-used pack of rigid plastic foam sheets designed to go under laminate flooring. They were a couple of millimetres thick, and I reasoned that if these were glued on top of the foam they'd bounce some high-frequency energy back into the room, while still allowing lower frequencies to be absorbed by the flexing action of the panel on the foam. I brought along half a dozen of these sheets, which measured roughly 1200 x 600mm each, and we pinned them up to test their effectiveness in this role. Happily, they did exactly as we'd hoped, so we glued them to the foam on one of the side walls using Auralex spray adhesive, spacing them apart to help randomise the effect. The windows and untreated doors in the room also supplied some useful reflection. We didn't have enough panels to treat the opposite wall, and we weren't able to source any more at the local Wickes DIY store, so after dragging Hugh out of the electrical section (where he was buying some mains flex for use as speaker cable — because it's cheaper but just as good as dedicated speaker cable!) we decided to buy four 1200 x 600mm sheets of the thinnest MDF we could find and try that. Adam also bought a can of matte black paint to make them look less like boring sheets of MDF but, as he only had one can, we didn't have enough to paint them properly and ended up settling for a textured pattern. Adam said his girlfriend was an artist and could fill in the panels with something more interesting later! We stuck these panels directly to the foam (again, using the Auralex spray adhesive) and the difference in the feel of the room when speaking became noticeably less oppressive.

Adam's DIY vocal booth was a decent size and actually sounded pretty even — possibly due the panel construction beneath all the foam, and the fact that the booth was fairly large and irregularly shaped. However, as the singer faced the booth window, we felt it would be advantageous to cut down reflections from that quarter by putting an SE Reflexion Filter behind the mic. Sonic Distribution had kindly given us a few to use on our SOS visits, so we set one up after our usual rejigging of the mounting hardware to get the centre of gravity of the combined mic and filter somewhere close to the centre of the mic stand.

We Have Control

That left the control room, which we decided to deal with after a spot of lunch. This being Yorkshire, we had pork pies and corn-based synthetic pork scratchings rather than our usual feast of chocolate Hob Nobs! We'd brought four sheets of Auralex foam with us and decided to use these to kill the worst of the reflections around the plaster-walled listening area that was set up on the short wall of the rectangular room, but rather right of centre due to the location of a door. We fixed one panel to the nearest (right-hand) side wall at the main reflection point, split another panel to put next to the M-Audio monitors, which were mounted on small shelves, and used the remaining two panels above the control-room window and on the ceiling between the mixing chair and the monitors. The improvement in the stereo imaging was very noticeable and the liveness of the mixing area had been reduced, though some further absorption towards the rear of the room (which must have been six or seven metres long) would also be beneficial. A heavy curtain over the entrance doors would be an easy solution, and some slatted blinds over the left-hand windows might help to control reflections from there. A leftover piece of foam from Adam's store room was propped up in the corner to the left of the mixing position but we left it to Adam whether to fix this permanently or buy another piece of Auralex.

Paul White performs radical open-tweeter surgery on a faulty speaker.Paul White performs radical open-tweeter surgery on a faulty speaker.Having done what we could with the acoustics, Hugh set about installing the speaker switch-box using the twin-core cable we'd picked up from Wickes. This worked fine, though the subwoofer level setting was inevitably going to be a compromise, due to the significant difference in sensitivity between the Tannoy speakers and the M-Audio satellites. The sub's fixed crossover point of 140Hz was also a little too high to integrate properly with the Tannoys. The trick was not to turn the sub level up higher than strictly necessary, to fill out the lower octaves.

With everything up and running, switching between the Tannoys and the M-Audios revealed a curious out-of-phase character to the sound — not quite out of phase but definitely not in phase — and it was impossible to get a stable image from the M-Audios. Hugh checked all the wiring to make sure there wasn't a silly cable error, but everything checked out. Deliberately swapping the positive and negative wires over on one of the M-Audio satellites didn't cure the problem either.

At first we thought the replacement metal-dome tweeter Adam had installed in one of the M-Audios was the problem, as it did sound brighter than the original soft dome fitted to the other speaker. Clearly, the two speakers would have different frequency response and dispersion characteristics, but this problem seemed to be something more than that. After further listening using the white noise tracks on Hugh's BBC test disc, we thought it worth checking the tweeter to see if it was wired in the wrong phase relative to the woofer.

Unfortunately, Adam had poked the wires through the tweeter terminals before soldering them, and as soon as we got them hot enough to desolder, the plastic holding them just collapsed... so it was off down the road again to Maplin to buy another tweeter (which, at £2.99 each, wasn't too punitive). The plan was to buy two identical tweeters, so that the monitors would at least behave in the same way, but unfortunately there was only one in stock, so we had to settle for that.

Sub-standard

Before fitting the tweeter permanently, we tried wiring it in the opposite polarity to the previous arrangement, and the sound from the speaker heard in isolation was definitely better. However, it now sounded 'properly' out of phase when a mono signal was applied to both speakers. A quick examination of the woofer showed that the bass-unit wires were soldered to the driver rather than to the expected spade terminals, so rather than risk damaging it while trying to swap the wiring over, we reversed the speaker wires feeding the cabinet instead, and were rewarded by a far more satisfactory result. The left speaker was still slightly brighter, because of the replacement tweeter, but at least everything was now in phase, despite the terminals on the back of the box suggesting otherwise. Adam said he hadn't touched the woofer wiring, so there was no way he could have put it out of phase, but examining the two speakers showed that one was internally connected using spade terminals and the other using soldered joints. As the system was originally an ex-demo model it may be that some earlier repair had been carried out, resulting in the internal wiring error.

Originally the subwoofer was placed under the desk, midway between the two speakers, but the panelled rear and sides of the desk created a resonant cavity that tended to boom. So to get the bass sounding as even as possible, we moved the sub out and stood it on the floor to the left of the desk, close to, but not exactly at, the centre of the wall. The improvement was very noticeable, with a much tighter and more even bass end. Adam had been worried about doing this, as he thought the bass might sound off-centre. With such a high crossover point that would be a risk, but the far smoother response easily outweighed any minor imaging issues, and in fact it seemed to integrate pretty well with the desktop speakers. The vibrations we could feel in the desktop were much less severe after we moved the sub, too, and we also put the Tannoy speakers on a pair of Auralex MoPads rather than the thin scraps of foam Adam had been using. The angled foam inserts were arranged to direct the tweeters up towards the engineer's head, which was another useful improvement.

Drum Recording

In contrast to the live room, the control room was largely untreated, so it was difficult to make accurate judgements about the sound.In contrast to the live room, the control room was largely untreated, so it was difficult to make accurate judgements about the sound.While we were in Maplin looking for replacement tweeters, Adam also picked up some interlocking heavy foam mats. When we returned, he assembled them to use under the house drum kit, to help prevent creep and to minimise noise getting into the structure. He was using AKG C1000 mics as drum overheads, which are less than ideal in this application, as they have quite a modest high-end response for a capacitor microphone, so he was looking at replacing these with some alternative small-diaphragm mics when his budget allowed. In the meantime, we found some foam offcuts and made holes in the middle. We could then slide them over the backs of the overhead mics, to further cut down on ceiling reflections getting back into the mics, as experience has shown that in smaller rooms the drier you can keep the overhead mics, the better your chances of producing a good, tight drum sound.

Adam's final query related to his clip-on AKG drum mics, which are back-electret models. He found that these always produced too much level, overloading his mic amps. He'd bought a pad adaptor to try — but this had a mono jack output which he'd fed into a line input, overlooking the fact that the mics need phantom power to operate. Even if they had been dynamic models, the combination of a pad and the reduced sensitivity of a line input would still have meant he got virtually no signal. What is actually needed is a balanced in-line XLR pad that still passes phantom power, or a separate bank of preamps with more headroom (or switchable pads) for use with the drum mics.

Job Satisfaction

After a few hours work, the performance of both the live room and control room had been improved to a worthwhile extent at minimal cost. The original live-room problem was due to over-treating the walls with a material that was only effective at upper-mid and high frequencies, so it threw the overall tone of the room out of balance. Normally, foam-style treatments work best if applied to no more than 25 to 30 percent of the total wall area, rather than everywhere, and the thicker the foam (or the further spaced from the wall it is), the more effective it is at lower frequencies. By reintroducing some simple high-frequency reflection we helped to reinstate some kind of spectral balance.

The control room had no treatment at all, and while a rigorously-designed solution could be quite complicated and expensive, the simple expedient of controlling the strong reflections around the monitoring position, using Auralex foam, made a big improvement. Moving the sub and putting the Tannoy monitors on MoPads also tightened up the sound and made the bass end sound more even. By way of upgrades, obtaining better active monitors as soon as possible should be a priority, closely followed by upgrading the drum overheads for small-diaphragm capacitor models that have a nominally flat response up to 20kHz or above. 

Reader's Reflections....

Adam Dengel, in his control room after the Studio SOS treatment.Adam Dengel, in his control room after the Studio SOS treatment. Adam Dengel: "As a regular reader of SOS, it was a nice suprise for me when Paul and Hugh agreed to come to the studio armed with their years of knowledge and experience: after all, this was only the studio's second year of business. I'd invested a lot of time into trying to set up a decent music facility for the Barnsley area, but I'd hit a brick wall with my limited knowledge of acoustics, and needed advice.

"The acoustic treatment in the mix room is fantastic, the monitor response is incredibly clear, and the room itself no longer sounds like a cave! I've been mixing a lot of tracks in Pro Tools this week and the difference is obvious. The bass end especially is more even, making it easier to mix. The monitor switch that Hugh installed for me has also helped my approach to mixing.

"The live room sounds brighter and it has a nicer 'feel' to it, especially when recording drums. I decided to leave the half-sprayed boards as they were, because I've had numerous positive comments on Paul's artwork!

"Finally, the SE Reflexion filter works a treat with vocal tracks, as sound bouncing off the window has been greatly reduced. Thanks again to the SOS team, Auralex and Sonic Distribution for helping and improving DC Studios."

07872 114648

dcstudios@hotmail.co.uk

www.dcstudios.org.uk

Published June 2008