Auralex - Big Sound Small Room

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sweet spot Getting a big sound from a small room You can get a big sound from a small room by employing SpaceCoupler panels to achieve loosely coupled spaces, according to Auralex Acoustics chief acoustical engineer JEFF D SZYMANSKI. He takes us through the principles and applications of this interesting new product. A DESIRE OF MANY STUDIO folks is to have a great sounding ‘live’ room for instrument and vocal recordings. Unfortunately, inherent space limitations prevent many project studio o
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  45 November/December 2005 resolution A DESIRE OF MANY STUDIO folks is to havea great sounding ‘live’ room for instrument and vocal recordings. Unfortunately, inherent space limitations prevent many project studio ownersfrom achieving anything close to a ‘live’ room in thetrue sense of a well-controlled space with a usefulreverberant tail.That is about to change. The next generation of acoustical treatment from Auralex is the pArtScienceline of products and the focus of this article is to look at one of these new products, the SpaceCoupler (Figure1). The many acoustical uses of the SpaceCoupler andits high-quality construction and appearance combineto provide many options to the user. Stripped downto the basic science, the SpaceCoupler is nothing newbut nothing like it has ever been offered to the proaudio market.Loosely coupling spaces is a design technique that was developed by Russ Berger, the designer of theSpaceCoupler, to sculpt high quality live recording spaces out of rooms with otherwise small — somewould say almost unusable — footprints. Berger has been using the technique for nearly 20 years tocreate unique acoustical environments in his studiodesigns.The loosely coupled space approach starts, for example, with a small room, often just cosy enoughto fit a drummer and a kit. For the example shownin Figure 2, the room is, say, 14ft long by 12ft widewith a 15ft high ceiling. All the surfaces of the roomare hard including the floor. The lower portions of thewalls — say up to about 8ft high — are treated witha good broadband absorber. The absorber coverageis typically as close to 100% as can be achieved.Above the absorbers the walls are left alone, but can optionally be treated with diffusors as shown inFigure 2. The ceiling above is treated with absorbersto remove any flutter echo effects between the hardfloor and hard ceiling.To get the full effect of a space like this — for example, to get that ‘fat’ drum sound — the boundarybetween the dead portion of the room and the liveportion needs a well-controlled aperture. Enter theSpaceCoupler. SpaceCouplers placed horizontally at  just above the 8ft high mark separate the two areaswith a controlled aperture. The actual aperture size issmaller than the overall footprint of the room, whichis usually around 70-80% of the floor area. The exact aperture size will vary depending on the application.The SpaceCouplers in the aperture redirect soundenergy into the upper portion of the room where it is diffused. Sound then returns — again redirectedby the SpaceCouplers — to provide a ‘big room’reverberation tail that sounds exceptional.Scientifically, the SpaceCouplers maximise the initialtime gap (ITG — Figure 3). Psychoacoustically, this‘pushes’ the reverberation tail out in time by severalmilliseconds without altering its length. The qualityof the resulting tail is smooth, without any acousticalartefacts or anomalies that would be difficult to work with in the postprocessing and mixing phases. Thesubjective assessment of loosely coupled spaces isthat ‘big room’ recordings are a reality. Even in smallspaces where the reverberation time of the looselycoupled space is less than 1.0 second, processing the sound with conventional postprocessing leads tovery musical sounding reverb effects. The net result is a recording that is more aurally convincing thanapplying digital reverb to an otherwise dry signal.There are alternatives to the setup shown inFigure 2. First, the SpaceCouplers can be angled suchthat they are not parallel to the ceiling. This wouldeliminate the need for absorbers on the ceiling andwould increase the length of the reverberant tail. If the floor is carpeted — not advisable, but a reality insome rooms nonetheless — absorbers on the ceiling would probably not be needed. If a high ceiling is not a reality, but there is some extra length to the room,this entire application can be turned on its side i.e. the Getting a big sound from a small room  You can get a big sound from a small room by employing SpaceCoupler panels to achieve loosely coupled spaces, according to Auralex Acoustics chief acoustical engineer JEFF D SZYMANSKI. He takes us through the principles and applications of this interesting new product. sweet spot  Figure 1Figure 2Figure 3ETC showing loosely coupled space effect Absorbers on ceiling aboveSpaceCouplers to control flutterOptional diffuserson walls aboveSpaceCouplersAbsorbers on walls belowSpaceCouplers  46 resolution November/December 2005 reverberant space can be 6ft to 8ft of a 20-something foot long room. The SpaceCouplers would then bea false ‘wall’ between a dry area and a reverberant area.The possibilities for miking instruments and voicesin a loosely coupled space are endless. Close miking an instrument or voice would provide a high levelof direct sound with just a hint of reverberant tail.Placing overheads above a drum kit, for example, but below the SpaceCouplers would provide a great blendof direct and reverberant energy (The aforementioned‘fat’ drum sound!) Miking above the SpaceCouplers inthe reverberant area would provide a great reverberant fill recording that combines with the close-mikedsignal or signals. Different miking techniques wouldapply to different recordings. A combination of allthree of the above might work for a drum kit. A combination of a close mic and an overhead below theSpaceCouplers might be more appropriate for a voiceor an acoustic guitar. A combination of a close micand an overhead above the SpaceCouplers could yieldthat long-sought-after ‘live’ guitar amp sound.The loosely coupled space application is just thebeginning. A byproduct of the acoustically optimisedgrid of a SpaceCoupler is that it can be used over flat absorbers to increase their efficiency and providea decorative finish to what some might consider a‘ho-hum’ flat acoustical panel. Simply placed over any flat absorber, low frequency absorption can beincreased by more than 40% below 250Hz (Figure 4).Above that, the absolute absorption of the panel doesnot change, but the exact nature of the absorptionthat is occurring does change. This has to do withthe angle-dependence of absorption and is a moretypical scenario for small room applications than therandom incidence absorption normally quantified bylaboratory tests.A flat absorber (as opposed to a sculpted absorber)absorbs the most sound when the angle of incidenceis perpendicular to the panel. This is described asnormal incidence. As the angle of the sound source isincreased, the absorption decreases and reflection off the face of the panel increases. We have researchedthis quite a bit and have found that as the angleof incidence is increased, the reflected sound levelincreases as well. Figure 5 illustrates some scenarios.To improve the otherwise poor off-axis performanceof flat absorbers, a SpaceCoupler can be placed over the flat panel. Sound arriving at non-normal anglesof incidence is redirected into the absorber. Eachtime redirection occurs more energy is lost until thereflected sound emerges from the treatment reducedsignificantly in level. There is actually a threefoldbenefit to this application of the SpaceCouplers: theefficiency of the absorber is increased; the overalldepth of the absorber is increased, extending thelow frequency effectiveness; and it provides off-axisscattering. This last benefit is highly desirable as it  * (32 channel inputs, 16 aux returns all @96k/24-bit *16 busses or two 6.1 surround busses *8 aux sends** Powerful automation with 100 mm touch-sensitive motorized faders * Dedicated* EQ and dynamics on each channel** Per-channel LED ring encoders for pan, aux sends, EQ and more * 24 channels ® built in * 2 expansion slots for FireWire ® , Surround Monitoring, ADAT ® , AES/EBU, TDIF and* TASCAM Mixer Companion software (Win®XP/OSX) with driverless USB connection to computer for back-up/ sweet spot  Figure 5Figure 4 Octave Band Increase in Absorbtion using SpaceCouplerover Flat Absorber Panel50%45%40%35%30%25%20%15%10%5%0%125Hz250Hz   500Hz  47 November/December 2005 resolution can greatly improve the sound quality at listening locations behind the main mix area. Producers’areas and comfy couches are notorious for not having the same sonic quality as the sweet spot.Using SpaceCouplers over the side wall absorberscan make the sound more consistent and actuallywiden the sweet spot to encompass the other areaswhere producers and players might be sitting whenevaluating mixes.Two of my favourite applications of the SpaceCoupler are over absorbers above the mix position and over deep absorbers on the rear wall of a control room. Theformer is a very efficient, space-conserving methodof eliminating the floor-ceiling first and second order axial modes that plague basement and bedroomstudios. A relatively small area of SpaceCouplers over a few inches of absorption on the ceiling can greatlyincrease the low frequency punch in the room andallow for better mixing decisions for low frequencycontent.The second application — SpaceCouplers over deepabsorbers on the control room rear wall — is a veryaesthetically pleasing way of finishing out what might otherwise be a very dull, fabric-covered rear wall. Thisuse of deep absorption is most often found in ‘neutral’room designs. Mixing the SpaceCouplers with somediffusors can provide high frequency scattering, yet still allow the low frequency sound into the deepabsorbers to control modal build-up and cancellationin the room. Angling the SpaceCouplers over the deepabsorbers can also help facilitate the ‘waveguide’approach of the Hidley/Newell ‘non-environment’approach to control room rear wall design.Even used without an absorber underneath (bottomright of Figure 5), early (high frequency) reflectionscan be reduced by 10dB or more. Used at varying angles and depths, performance can be increasedeven more.The SpaceCoupler is handmade from solid wood.The craftsmanship is high and the musical qualitiesof the Paulownia wood (used in musical instrument construction in Asia) give a very natural feel to theroom. What Berger and others (including myself)have found is that using a high quality, natural wooddiffuser — as opposed to diffusors made of more‘manmade’ materials — can give a room a naturalsound quality that isn’t really quantifiable.The possible applications for the SpaceCoupler areincreasing daily; coupled spaces, increased absorber efficiency, well-scattered (diffused) sound, and so on.The high-end appearance makes the SpaceCoupler thenewest alternative to flat absorbers and diffusors instudios around the world. ■ sweet spot  AURALEX, US: Website: Contact 1000Hz2000Hz4000Hz
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