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Studio SOS: Carpeted Walls!

Brett Taylor-Holmes
Published August 2005
By Paul White

Studio SOS

Sorting out the monitoring in a studio with carpeted walls is the challenge for the SOS team this month.

Brett Taylor-Holmes called SOS because he'd just finished building a studio in a single-floor extension to his Herefordshire home and had discovered that the monitoring acoustics weren't all he'd hoped for. He'd also bought a Mackie Control to go with his Apple Logic/G5 setup and had problems getting it to work. We arrived at Brett's rather nice period house near Malvern, which adjoins the local cricket green, and were served tea and Hobnobs while we asked more about Brett and his studio, which he wants to use mainly for composing film and TV music, as well as for video editing. Brett is currently taking a master's degree in film making and is also a performing drummer and drum teacher.

Too Much Carpet!

As soon as we entered the studio, we could see some of the potential trouble spots. The monitors, which were Mackie HR824s, were set directly on top of a large, flat desk and were positioned well back in the corners where they were bound to generate strong reflections from the surface of the desk. Perhaps more seriously, Brett had used thin carpet to line the walls of his studio in the hope of providing a less reflective environment. In small areas carpet can be useful, but because it is so thin it only absorbs high frequencies with any degree of efficiency. Low and mid-range sound simply passes through it to the walls behind and then bounces back into the room, the result being a dry top end with a boxy mid-range.

He'd treated his live room in the same way with much the same result, and the door between the live room and control room was a lightweight interior door which didn't seal all the way around, so isolation between the two rooms wasn't great. This wasn't a problem when recording drums, as Brett uses his Roland V-Drum kit for that, but when recording vocals he'd had trouble with spill from the control-room monitors getting onto the recording. This was clearly going to take lots of Hobnobs!

To get better response from Brett's Mackie HR824s, Paul & Hugh moved them away from the corners of the room, and placed them on some Auralex foam isolator pads. Acoustic foam was then placed on either side of the monitoring position to reduce reflections which were muddying the stereo image — although on the left side the panel was only fixed temporarily so that it wouldn't obstruct the sight line into the live room when tracking.To get better response from Brett's Mackie HR824s, Paul & Hugh moved them away from the corners of the room, and placed them on some Auralex foam isolator pads. Acoustic foam was then placed on either side of the monitoring position to reduce reflections which were muddying the stereo image — although on the left side the panel was only fixed temporarily so that it wouldn't obstruct the sight line into the live room when tracking.

Before looking at how to improve the acoustics, Hugh and I both felt the monitors should be brought much further forward to move them out of the room corners, bringing them in front of the computer monitor screens and helping to reduce the significance of desk reflections. We also positioned them on resilient pads to stop vibrations getting through into the desktop.

Listening to some pre-recorded Donald Fagen tracks from CD quickly confirmed that something needed to be done. Amongst the bits and pieces kindly provided by Auralex, we had a set of foam speaker pads which we used with their extra wedge pieces inserted to get the speakers roughly parallel to the desktop, as this gave the best tweeter height to match Brett's normal seating position. We brought the speakers forward to reduce the amount of desk area in front of them as well as to prevent diffraction from the LCD monitors. In doing so we had also moved them away from the corners, so we looked around the back of the HR824s to see what EQ switch settings had been used.

Brett had the monitors set up for 'quarter space' which was correct for working close to corners, but we switched them to 'half space' now that they were much further into the room. He'd also left the bass extension at maximum, which provided too much low end for such a small room — especially one with no real bass trapping. Switching to the middle 47Hz setting improved things, and listening to the same record produced a tighter, more even bass end, but with very muddled stereo imaging and still some residual lumpiness in the bass. We also noticed that the bass tended to disappear as you moved back from the listening position, something we've noticed in a lot of small rooms. Careful trapping can help, but in most cases you simply have to identify the rogue areas and keep away from them when mixing.

Improving The Stereo Imaging

To sort out the worst of the imaging problems, we used three panels of acoustic foam, one on either side of the listener at the 'mirror' points, and one on the ceiling. If you hold a mirror flat against the wall and mark where you can see the monitor from your normal listening position, that denotes where the centre of your acoustic foam panel needs to be. The trick works for placement of the ceiling panel too. Brett had placed a window through to the live room at the left-hand mirror point, and there was a large picture behind glass on the other, which was less than ideal! So after removing the picture, the right-wall and ceiling foam panels were fixed in place using spray adhesive, but the left-wall panel was temporarily fixed over the control room window using masking tape. Our suggestion for the long term was to glue this panel onto an MDF sheet and then hang it over the control-room window on hooks only when mixing. During tracking it could be left off to restore sight lines into the live room.

Paul constructs improvised bass traps by cutting an Auralex foam panel in half and then mounting small foam blocks to the halves to distance them from the surfaces to which they are to be fixed.Paul constructs improvised bass traps by cutting an Auralex foam panel in half and then mounting small foam blocks to the halves to distance them from the surfaces to which they are to be fixed.

The back of the room was another flat carpeted wall, so we decided to use one of the new Auralex four-inch panels that comes with thick foam spacing blocks which allow it to be used away from the wall to increase the low-frequency absorption. We put this right at the top of the rear wall, since you need to get the trapping into corners to have any impact on low end. Although we didn't have any corner bass traps with us, we told Brett that it wouldn't hurt to add some later — there was plenty of space to install something in the two rear corners of the room, which would be ideal.

The panel kit we had used comes with a pair of polystyrene diffusers which we felt might also help if we fixed them to the rear wall below the foam to scatter some high end, rather than allowing the carpet to absorb it all. The idea was tested subjectively by temporarily propping them in place and conducting more listening tests. There was a small but worthwhile increase in liveliness which further countered the tendency of the room to sound boxy, so we decided to fix them permanently using the spray adhesive again. A word of warning here — polystyrene reacts very badly to some types of glue, so check the glue on a gash piece of polystyrene first to avoid having to watch your new diffusers melt away before your eyes!

Another foam panel was placed on the rear wall of the studio, along with a (white) polystyrene diffuser designed to combat the high-frequency absorption of the carpeted studio walls.Another foam panel was placed on the rear wall of the studio, along with a (white) polystyrene diffuser designed to combat the high-frequency absorption of the carpeted studio walls.

We had one more four-inch foam panel left which we decided to cut in half and fix across the front corners of the room using the supplied spacing blocks, which happen to be cut at a 45-degree angle for exactly this purpose. We could have installed them directly behind the monitors or up against the ceiling, but we decided on the latter as it should make them more effective at low frequencies — and it also looked better.

While these little modifications weren't going to transform Brett's studio into a world-class monitoring facility, the subjective improvement was very significant. Now the stereo imaging was good and the room sounded much more neutral and far less boxy. It also looked good, which is important if you're spending long hours working in one place.

Live-room Acoustics

Turning our attention to the live room, it became clear that the dividing wall was a simple stud partition, with a single layer of MDF on either side and no insulation between them at all. So sound isolation between the control and live rooms was very poor, and only a complete rebuild of the wall would help — which wasn't practical or necessary. We felt that the best approach would be to make the best of the situation by modifying the way Brett worked when tracking, and to improve the live room acoustics to help with vocal and acoustic-guitar recordings.

We suggested creating an area where vocals could be recorded effectively by fitting a curtain rail around one corner and then hanging a heavy drape or duvet on this. Our remaining piece of two-inch Auralex foam was stuck to the ceiling with the idea that the singer would stand under that with their back to the drapes to record. The rest of the room wasn't too crucial, as the V-Drums don't care about acoustics and any guitar amps would be close-miked. Acoustic guitars could be recorded satisfactorily in the vocal position. We didn't have the time or fittings to put up the curtain rail, but Brett said he could arrange that with no problem.

The final remaining foam panel was placed on the ceiling in the live room, above where Brett was planning to set up his mic for vocal recording.The final remaining foam panel was placed on the ceiling in the live room, above where Brett was planning to set up his mic for vocal recording.

It turned out that Brett's monitoring difficulties arose when he fed the singer a headphone mix from his MOTU 828 MkII interface and then tried to juggle the headphone and speaker monitoring level using its front-panel controls. The MOTU 828 MkII isn't really designed to do this, and both Hugh and I felt that the only satisfactory solution would be to use a monitor controller that allowed the cue headphone and speaker levels to be controlled independently. Furthermore, some monitor controllers have two headphone outputs, each with its own level control, so the vocalist can have one feed and Brett the other while tracking. This would allow him to track vocals with the monitors turned right down, thus avoiding spill into the live room. An additional benefit with a monitor controller of this type is that there's a talkback facility built in so you don't have to yell through the control-room glass. Brett agreed that this approach made a lot of sense and put in an order for a Mackie Big Knob the same week.

Troubleshooting Mackie Control

That left the Mackie Control to deal with. Brett's troubles with this had started when he bought two MIDI leads that were such a tight fit in the Mackie Control's sockets that he was almost afraid to pull them out again! I took a couple of MIDI cables along with me and they fitted fine, so I think he was probably unlucky and just happened to get a pair where the pins had been too heavily plated. Then again, this isn't the first time Brett has been unlucky with leads — when he bought his MOTU 828 MkII he couldn't get that going for ages, and the culprit turned out to be a faulty Firewire cable!Mackie Control, ready to be set up with Logic.Mackie Control, ready to be set up with Logic.

Once we'd switched on the Mackie Control, it was clear that it hadn't yet been set up to work as a Logic Control, but as I was unfamiliar with the unit I decided to break the habit of a lifetime and look in the manual. This showed which two buttons to hold down while turning the unit on to get it into the mode where you could choose what controller you wanted it to emulate. Pressing down the selection buttons on the first two channels entered the emulation mode, and then pressing the V-Pot on channel eight selected the Logic Control option, after which I configured it in Logic's Preferences. 

All seemed well, with the transport controls and faders behaving as they should, but a few more tests showed that we still had problems. The Jog wheel wouldn't jog and the pan controls would only pan to the extreme left or right with nothing in between. No amount of resetting or trashing Logic's Preferences would fix it, so I came to the conclusion that the most likely cause was a hardware or firmware fault, and the only way to prove that was with a replacement Mackie Control.

As Brett was a relative newcomer to Logic, I took some time to set up a default song for him with 24 audio tracks and 16 instrument tracks, which I thought would be more than enough for most of his projects. I showed him how to create screensets, then explained that the best way to deploy reverb plug-ins is to use them in busses, fed from post-fade aux sends, as that way all the channels can have access to the same effects.

If you simply drop a reverb plug-in into the insert point of every channel that needs reverb, you'll soon run out of CPU power, especially if you're using a power-hungry convolution reverb such as Logic's Space Designer. For most mixes, two different reverbs will provide all the variety that's needed. Hugh and I also went through the basics of compression, as this is one area that a lot of people have trouble with.

Summing Up

By the middle of the afternoon the studio was sounding much more neutral, Brett had a good idea what needed adding to his gear list and, aside from the Mackie Control problems, his system was up and running, requiring only a suitable duvet before he could begin making first-rate vocal recordings. Once again, it is demonstrable that, while it may look very nice, the overuse of carpet as an acoustic treatment can really mess up your room acoustics unless balanced by some high-frequency reflection and low-frequency trapping. Given the choice, I wouldn't have used much if any in this room, but as we were faced with a finished job we had to incorporate what was already there into the final design.

The Auralex panels mounted on blocks really seemed to do the trick in sorting out the lower mid-range, though Brett's room would benefit from more bass trapping, and a large void under his desk area was still acting as a resonator to some extent, as it was an empty space enclosed on all sides but one. Filling this with mineral wool, foam, or even old bedding would help damp it down and provide low-cost bass trapping.

Published August 2005