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Studio SOS: Duke & Sherrie Ashton

Build Your Own Vocal Booth
By Paul White

Vocal booths aren't always the right solution to problems with live‑room acoustics, but if you do need to build one, it can be done with some DIY skills and a lot of elbow-grease...

I often to try talk people out of building stand‑alone vocal booths, because it's all too easy to end up with something that sounds boxy and horrible — but Duke and Sherrie Ashton presented a good case for installing one in their studio.

Paul White gets busy with the heavy machinery, as he cuts the timbers to size!Paul White gets busy with the heavy machinery, as he cuts the timbers to size!

Rather than record in their house, they'd chosen to set up their recording studio in an old wooden hut that had belonged to the BBC. The hut was originally used as temporary office space adjacent to the Droitwich long‑wave radio‑mast site, which was used to safeguard essential BBC work during the London blitz during the Second World War. Duke and Sherrie had reassembled the hut, and aptly renamed it 'Make Music Not War', to create a studio at the bottom of their garden on a purpose‑built solid foundation.

Although the building is of a decent size for a single‑room studio, its construction offers very limited sound isolation. Indeed, I could see daylight through some of the cracks in the walls, where the boards had shrunk! One practical solution in such situations would be to fix a layer or two of plasterboard over the entire inside of the building, and then fit a UPVC door with multi‑point locking plus double‑glazed windows, but even setting aside the cost of this approach, Duke and Sherrie had a busy production schedule, and had arranged for a singer to come over from Germany to work with them — giving them less than two weeks to find a solution! Duke said they might well add the extra plasterboard to improve the overall sound isolation at a later date, but for now a vocal booth seemed the only practical option.

While their existing 'curved absorber in front, sound‑absorbing foam behind' approach produced a perfectly viable vocal sound when recording in the studio space, the intrusion of traffic noise, lawnmowers, dogs barking — and the occasional air force practice run over the area — was causing significant spill problems. As their home, close to the Herefordshire border with Worcestershire, is only a short drive from where I live, I agreed to help out by designing and helping to build a suitable (and inexpensive) booth — so while our Technical Editor Hugh Robjohns was on holiday, I decided to tackle this one by myself. Fortunately, Sherrie agreed to take most of the photographs as the project progressed. In the end, the work took two‑and‑a‑half very hot days to complete, so it's just as well that I live within commuting distance!

Planning & Procurement

The construction of the booth was based around four timber‑framed panels, which would later be clad with plasterboard.The construction of the booth was based around four timber‑framed panels, which would later be clad with plasterboard.

The area available to install a vocal booth was a little over four feet square, and located in the rear corner of the room. Duke and Sherrie had already covered the studio gear with dust sheets in anticipation of my arrival and greeted me with lots of tea and sandwiches.

Before starting to build anything, we used mastic to fill the gaps between the wall boards — especially behind where the booth would be situated, as this would be impossible to access once the booth was built. They wanted a side window in the booth so that Sherrie could direct the singers between takes, so I suggested to Duke that he phone round all the local double‑glazing firms to see if they had a surplus window (I've found that they often have a few windows that were made up to the wrong size that they're happy to sell off cheaply), and he eventually located one that had an opening panel around the size we wanted. Less good news was that it was part of a larger window unit, so we would have to saw through the frame to liberate just the section we needed — and that's exactly what we did.

I initially recommended a UPVC door, as these usually include a multi‑point locking system that pulls the door hard against the seals when closed, making for extremely good sound isolation. However, Duke was unable to find one of the right size at the right price, so he made the decision to buy an off‑the‑shelf aluminium door instead. The model he chose had an opaque double‑glazed panel in the top half and a thick UPVC panel at the bottom. It turned out that the door opened the opposite way to how we would have preferred and was non‑reversible — but there was still plenty of room to get in and out of the booth, so Duke decided they could live with it. One advantage of double‑glazed doors is that they come complete with a frame that has seals on all four sides: whatever type of door you choose, an airtight seal is essential.

Paul and Duke start piecing together the timber frames. Note the polythene sheet that was used to slide everything into place without damaging the floor.Paul and Duke start piecing together the timber frames. Note the polythene sheet that was used to slide everything into place without damaging the floor.My 'back of a napkin' design was for a vocal booth roughly 46 x 55 x 79 inches, as measured from the outside. This would just fit the available space without extending over the window area. I felt it important to avoid having any internal dimensions that were either the same or exact multiples of each other, as that would pile up all the resonant modes at the same frequency, causing an unpleasant sound, so on the design the internal dimensions were suitably 'unrelated'.

As far as isolation was concerned, the door was clearly going to be the weakest link in the design, but I still opted for a two‑inch‑thick wooden‑frame construction for the booth, with two layers of 12mm plasterboard on either side, and loft insulation stuffed into the spaces to give us plenty of mass and some internal damping, with an adequate distance between the inner and outer skins. Thicker plasterboard, more layers, or a layer of barrier matt in between the boards would improve the low-frequency isolation of the design, as would a wider gap — but there's no point going overboard in one area of the design if the doors and windows don't offer the same degree of isolation as the walls.

Blobs of adhesive, applied using a mastic gun, would be used between the plasterboard layers to avoid rattles, while mastic would be used to seal all the joints and corners. Obviously, a plasterboard‑lined box would sound pretty dreadful without some carefully considered acoustic treatment, but our design left space to deal with this later. Leaving adequate internal space is vitally important, as it seems many people fall into the trap of designing a booth without allowing enough space for the internal acoustic treatment — so they then make the mistake of choosing a treatment that is too thin.

Construction

Paul stands inside the part‑constructed vocal booth.Paul stands inside the part‑constructed vocal booth.

Most of the timber we had available was cut in imperial sizes, so we decided to work in feet and inches where possible. Each of the four sides was assembled using reclaimed 4x2‑inch timber left over from the BBC hut reassembly project, so that meant pulling out nails and rejecting excessively twisted pieces. The joints were diagonally nailed, and we tacked temporary struts across two of the corners of each side‑frame, to keep it square while we assembled the booth. These were removed once the first outer plasterboard skin was added, as the plasterboard then held the frames square. The two walls that would face into the corner had to have their outer skin of plasterboard fixed before we started to assemble the booth, as there would be no access afterwards — a booth built this way is definitely not a mobile structure! To keep things moving quickly, I had Duke cut the plasterboard to size, while I handled the construction work.

With the plasterboard glued and screwed in place, the two walls facing the corner were very rigid, and also pretty heavy, so Duke and I lugged them into the studio and joined them at the corner, using long nails banged in at an angle ('dovetail nailing', as my old woodwork teacher used to call it!). We then slid the pair into place, using heavy polythene sheet on the floor to reduce friction, right up against the corner skirting-board. The remaining sides were easier to fix, as they had no plasterboard at this stage, which meant that the frames were more accessible for nailing.

Rigid Rockwool tiles were used in the roof space, as they're easier to fit than the cheaper non‑rigid variety.Rigid Rockwool tiles were used in the roof space, as they're easier to fit than the cheaper non‑rigid variety.Next, we skinned the insides and outsides with two layers of 12mm plasterboard, ensuring that any gaps were staggered to prevent air leakage. Again, all joints were sealed with mastic and adhesive was applied to the frame and blobbed between the plasterboard sheets. Most of the plasterboard was held in place using plasterboard screws, as these are less likely to crack the board than flat‑head nails.

The roof was built from 3/4‑inch chipboard sitting directly on top of the four walls, with a two‑inch deep frame screwed to the bottom, extending down inside the top of the booth — rather like a plug. This was fixed in place using more gap‑filling adhesive, and also pinned using my trusty nail gun. Before fitting the inner plasterboard skin to the roof, the frame was filled with 30mm high‑density Rockwool slab, as this was easier to fix in place than the loose insulation we'd stuffed into the walls. A couple of plasterboard screws through each slab held it up while I fixed the plasterboard ceiling. I'd arranged the door sill to be deep enough to allow us to fit a shallow, inner floating floor, if I thought it necessary: the thick studio carpet and its generous layer of underlay (atop the heavy wooden floor) sealed perfectly well with the weight of the booth walls pressing onto it, but I wanted to try to cut down floor resonance as much as possible. After some deliberation I fitted a very simple, lightweight floating floor, comprising a half‑inch plywood platform resting on a bed of 30mm Rockwool slab, and cut slightly undersized, so that it didn't quite touch the sides. More carpet was eventually glued to this using spray adhesive.

Window & Door

Using different materials layered together can help damping, as well as providing broader range absorption in a small space. The mass of the heavy matting is good at attenuating lower frequencies, while the material used in front works more effectively at higher frequencies, which the matting would otherwise reflect.Using different materials layered together can help damping, as well as providing broader range absorption in a small space. The mass of the heavy matting is good at attenuating lower frequencies, while the material used in front works more effectively at higher frequencies, which the matting would otherwise reflect.

With the plasterboard work complete, it was time to fit the window and door in the frame — in which I'd left just a few millimetres to spare, to allow for squaring up and sealing with mastic. Using carpet as an acoustic treatment on the inside of a booth (or any live space) is definitely not advisable, but we decided to use it as a cosmetic finish for the two visible walls of the outside of the box, as it would cover any plasterboard joins and add a little further damping to the structure.

Sherrie phoned around for the cheapest, thinnest contractor's cord carpet she could find, and I fixed this in place using spray carpet‑adhesive, with a few tacks along the top edge to hold it to the side the roof. Standard wooden architrave was fitted around the doors and windows, both inside and out, and was sealed with a generous amount of decorator's caulk. Skirting board was also fitted both inside and out. Sherrie painted much of the woodwork before we fitted it, so that it would only need a final touch-up when the job was complete. The cord carpet was very easy to work with, and providing you use fresh utility‑knife blades, it cuts easily and neatly.

After adjusting the door frame and hinges to get the door closing evenly, I found that we needed to block up the keyhole to prevent sound leakage from that quarter, and I also decided to stick some thin plastic strip to the top and bottom faces of the inside of the door to improve the seal. The reason for doing this was that the door uprights stood a millimetre or two proud of the door cross‑members, so the top and bottom seals weren't quite as tight‑fitting as at the sides. By fixing the plastic trim strip using double‑sided adhesive tape, we built up the top and bottom edges of the cross members level with the verticals, so the seal was much improved.

Acoustics

Paul used carpet for the outside of the vocal booth — but not the inside, where it would have an undesirable acoustic impact.Paul used carpet for the outside of the vocal booth — but not the inside, where it would have an undesirable acoustic impact.

At this stage, we had a Tardis‑shaped booth that offered a useful (albeit not perfect) degree of sound isolation, but now we had to treat the inside to stop it sounding like a box.

Just sticking foam to all the surfaces would not have been the best solution, as its effectiveness falls off at lower frequencies, (unless the foam is unfeasibly thick!), which can leave the booth sounding boxy in the lower-mid range, and dull at the high end. To improve this situation, I decided to combine traditional foam with a wide‑range trap design that we've used before on our Studio SOS visits. This simply comprised a free‑hanging sheet of barrier mat (mineral‑loaded vinyl), behind a sheet of old‑style thick carpet‑felt underlay, with an air gap behind. The idea is that the felt absorbs the higher frequencies, while the barrier matt works on the lower ones that make it through the felt. The barrier mat was tacked to one side of a wooden batten, and the felt to the other, and this was then hung from the top of the booth, about four inches out from the wall.

A larger spacing would have further improved the low‑frequency performance of the trap, but when space is at a premium, it's necessary to compromise. Few vocalists produce very deep bass anyway, and not only has this type of construction proven quite effective across the normal vocal range, it can also be hidden behind a breathable fabric sheet — which, in this instance, was a white cotton/polyester single bed sheet, cut to size and then stapled to a wooden frame with some wooden trim strip hiding the edges. A few wooden crossbars were then fixed across the frame to prevent visiting vocalists from leaning on the fabric. Only one wall needed to be treated in this way, as this type of trap generally provides enough low-end trapping for vocal work.

Paul fits the architrave around the aluminium door.Paul fits the architrave around the aluminium door.

For the other walls and on the ceiling, we used Burgundy Auralex foam around two inches thick, just to tame the reflections. As you can see from the photos, we didn't cover all the surfaces, because some high‑frequency reflection is always needed to balance the tonality of a space. The untreated plasterboard, along with the door and window, added sufficient reflection to keep the sound reasonably bright, while our hanging absorber and foam panels took care of the original boxy resonance.

Duke bored a hole in the side of the booth large enough to take a short section of plastic waste pipe, so that he could thread the necessary mic, line and 'phones cables into the booth. Once his cables are all in place, he will be able to seal them by jamming foam offcuts into the pipe. He also fitted a mains socket to the inside of the booth so that he could power guitar amplifiers. I suggested that he consider installing a couple of LED lights inside, if he had the time, as these would give adequate illumination without heat.

The location of the booth's door and window meant that vocalists would normally stand with their back to the rear corner, and this left space for a Reflection Filter or similar acoustic shield to be placed behind the mic if necessary, to further reduce reflections from the door and window.

Though there was sufficient space in the booth for a mic stand, I also floated the idea of fitting a movable mic arm, mounted to a wall or to the ceiling, to allow the mic to be freely positioned without the need for a floor stand. These mic arms — which are not unlike the mechanism of an Anglepoise lamp — can be sourced from many studio supply companies and are a really good option when you're working in a confined space.

A Good Outcome?

Duke and Sherrie Ashton, in their studio building, with the completed vocal booth in the corner behind them.Duke and Sherrie Ashton, in their studio building, with the completed vocal booth in the corner behind them.

Although a heavy UPVC door would certainly have provided better isolation, the booth did the job of keeping spill from the outside world down to an acceptable level, while the internal treatment maintained a sensibly neutral tonality for recording with a cardioid‑pattern mic. As with any structure of this type, the isolation becomes less effective at lower frequencies, and there's some quite low‑frequency structural resonance if the singer insists on stamping their foot, but when working with vocals, really low frequencies can easily be excluded by using the low‑cut switch on the mic or mic preamp (and by confiscating shoes!) if necessary.

This type of booth can also be used to record guitar amplifiers, which is just as well, as both Duke and Sherrie are guitar players, hence the need for jack tie-lines as well as XLR mic lines and headphone feeds.

Adding quiet air‑conditioning to a vocal booth is expensive, and a cheaper, more pragmatic approach is simply to open the door between takes. LED lighting helps in this respect, because it runs cool: halogen spotlights can turn a vocal booth into an oven, but LED replacements for mains powered GU20 bulbs are readily obtainable and dissipate only around 1W of heat each.

Lessons Learned

Sherrie, in the vocal booth, with an SE Reflexion Filter helping to further improve the recordings.Sherrie, in the vocal booth, with an SE Reflexion Filter helping to further improve the recordings.

As always, I managed to learn something from this project. Ideally, we'd have sourced more barrier matt to put between the plasterboard layers, to further damp the structural resonances. Although this would have added significantly to both the cost and the weight, a sandwich construction of this type really helps to improve the panel damping. We could have used thicker plasterboard, too, although a better door would have been needed to take advantage of this. I also think that, although the booth seems to be of a generous size when viewed from the outside, the internal size we ended up with was around the absolute minimum we could have got away with.

Given the time and resources, I'd still have preferred to improve the isolation of the building as a whole — and to carry on recording vocals out on the studio floor — but as a pragmatic solution to an immediate problem, the booth worked out well and it could potentially be further improved at a later date by swapping the aluminium door for a more sophisticated UPVC design.

If you find yourself in a similar position, I'd strongly advise that you first try to find a solution that doesn't involve building a separate vocal booth, if that's at all possible — but where a booth is the best solution, don't be tempted to make it any smaller than this one, as you really do need to leave enough room for the internal acoustic treatment, as well as the not‑inconsiderable wall thickness. Also, don't underestimate the amount of work involved in building a booth, or the weight of the materials, which is very important, particularly if you're not building it on a solid or well‑supported floor. This little project used 12 sheets of 8 x 4-feet plasterboard and over 20 metres of 2x4‑inch timber, so despite its size, the end result probably weighs as much as a small car!

Reader Reaction

Duke Ashton: "Paul's timely help has met an urgent need to achieve better isolation on a tight budget and within an even tighter time-frame. The reduction in extraneous noise when entering the booth is very noticeable: a 'duelling chain saws' duet being played out by some neighbouring farmers was immediately shut out. Similarly, children playing in nearby gardens can no longer be heard.

At vocal frequencies, the booth has a reasonably neutral sound, and although there's more glass than usual involved in its construction, at our request, continued use of the mic shield adequately tames any high‑end reflections. The use of reclaimed materials for much of the booth structure has kept the project economical and green, and the booth is a credit to the design skills, practical application and ingenuity of the SOS team.”

Published September 2010