Tuesday, July 25th, 2017

James Lindenschmidt : Acoustic Design for the Project Studio

By editorJune 1, 2012

ACOUSTIC DESIGN

James Lindenschmidt, RealTraps General Manager

James Lindenschmidt is General Manager of RealTraps, where he handles the day-to-day operations outside of the factory.  He has been listening to, playing, and recording music for 30 years, since he was a child. His degree is in philosophy.

“As the number of large, commercial recording facilities grows smaller and smaller, and with the remarkable availability of affordable recording gear, the number of people producing music in project studios grows every day.  Many of us make music in spare bedrooms, basements, garages,or even office buildings – spaces that were not designed and built from the ground up to sound good, but rather were built using simple geometric shapes and standard construction techniques.

Many people working in such spaces invest in the best gear they can afford, yet overlook the importance of good room acoustics.  For instance, I speak to clients every day who are frustrated by their mixing experience.  They get their gear up and running, and then spend hours meticulously tweaking a mix to sound good in their room, only to be dejected when they play their mixes back in the car or on another system and the bass is completely wrong, either way too flabby and dominant or too anemic and thin.  Others spend a lot of time panning and doing EQ adjustments in the critical mid range frequencies, and have to make large changes such as boosting an EQ by 3dB (or even 6dB or more) in order to begin to hear a difference.  After they have spent a long time tweaking, everything sounds so much different and unnatural that a great mix seems impossible.  They get frustrated, and begin to doubt themselves and their ability to get a great mix.

However, once these clients implement an intelligent acoustic treatment strategy, they realize that the problems they experienced all along were caused by poor room acoustics.  Learning to mix is hard, and without an accurate listening environment it is nearly impossible.  At the very least it will be much more frustrating to learn how to mix – and later to get great mixes quickly and efficiently – without a decent set of monitors and a good room treatment strategy.

The same story is true for recording music in untreated rooms.  I remember years ago when I was learning how to record, getting caught up in the seemingly endless cycle of gear upgrades, thinking that was a path to a professional result.  While I am a fan of quality gear and always recommend using the best gear available to you, I quickly learned that the quality of the gear used is less important than I had thought.  The first time I installed treatment into one of my recording rooms – simple broadband absorption – and recorded drums, I knew within a few seconds of playback that I’d finally found the missing piece in my recording puzzle.  The tracks sounded more “pro” than anything I’d done in the past.  This experience showed me that the sound of the room itself is extremely important, probably even more important than the quality of the gear used (provided a basic minimum standard of low-noise, low-distortion specs common in prosumer gear nowadays).

In fact, I’d put the quality of gear 4th in the list of most important factors in producing good recordings.  The sound of the room itself and engineering technique fight it out for 2nd and 3rd place.  Knowing that the sound in the room is right, and capturing that sound in a way that flatters the song, is what these 2 aspects are about, and they go hand-in-hand.  A good engineer always takes the sound of the room into account.  Yet far and away the most important factor in making a good recording is – and will always be – a compelling performance.  Without that, one cannot create a recording that will command the listener to pay attention.

So given the importance of a good-sounding room in the recording “equation,” how does one achieve a better-sounding room?  The remainder of this article will address practical strategies for solving the acoustics problems most of us will face when producing music in small rooms built using standard construction techniques.

Room Layout

The first step is to set up the room correctly, to maximize the sonic potential of the room.  In a mixing or mastering room, it is important to make the room as symmetrical as possible, particularly from the listening position forward. Symmetry helps to ensure that you hear a balanced stereo image and soundstage, and will help with panning tracks and balancing mixes more easily.

It is also important that neither the listening position nor the speakers are placed in a null point in the room.  All rooms will show a jagged frequency response, with high peaks (+6dB or more) and deep nulls (typically more than -30dB) throughout the bass region.  To make things worse, each point in the room has its own unique frequency response.  It is important to make sure you aren’t sitting in a null point, such as the exact center of the room.  If you don’t avoid a null it will make it impossible to hear the bass adequately, resulting in mixes where the low end is way off.  For details on this strategy, including the “38% rule” and how to test for peaks and nulls, I refer you to How To Set Up A Room on the RealTraps website.

Lastly, if you do any tracking in the room you may want to find a “sweet spot” in the room for tracking.  For instance, if you are an acoustic guitarist, you can walk around the room while playing your guitar, listening for places in the room where the sound “comes alive” and is pleasing.  You can do the same while singing if you are a vocalist, or if you are a drummer you can move the floor tom (to excite the low end) and the snare around, to see where they sound good.  Later, we will look at spot treatments in the room to maximize sound quality for these recording zones, but we will begin with the single most important treatment strategy you can implement in a small room.

Bass Trapping

Corners, including wall/ceiling corners, are great places to install bass traps

As mentioned previously in the Room Layout section, most rooms have a jagged frequency response, particularly in the low end, and every point in the room as its own unique frequency response.  As a result, various peaks and nulls – as much as 20-30dB or more – are inescapable.  To understand why bass traps help solve these problems and flatten the frequency response throughout the room, we must first understand what causes these peaks and nulls in the first place.  The answer to this question is comb filtering.  As reflected sounds travel around the room, they encounter other sound waves, and these sound waves interact with one another.  At some locations and some frequencies, the sound waves reinforce one another and get louder (ie, create a peak).  At other locations and frequencies the sounds cancel each other out and get softer (ie, create a null).  You can think of this as similar to recording a single source with multiple microphones; if the mics are out-of-phase they will cancel each other out and compromise the sound quality.

By installing bass traps into the room, some of this excess, reflected sound is absorbed – and with less reflected sound energy in the room there will be less interference, less comb filtering, and the resulting frequency response will be flatter.  Many of my clients are astonished when the bass sounds louder after treatment is installed.  It is certainly counter intuitive that this is the case, until one remembers that the bass traps are reducing the destructive interference that creates the nulls in the first place.

The simplest type of bass trap is a broadband absorber of adequate thickness, using an absorbent material with adequate absorption characteristics and gas flow resistance characteristics.  For decades, a 2’x4′ absorber, at least 4” thick, made from rigid fiberglass has been the reference standard.  In recent years, rock wool of a similar density has become a lower-cost alternative that performs similarly, but may not be as nice looking as rigid fiberglass, particularly over time as the traps age.  The more of these bass traps installed in the more corners of the room, the flatter the frequency response will become.

One caution with this type of broadband absorber is to not provide too much high-frequency absorption.  Unfortunately, it remains all-too-common for people to over damp the high frequencies, resulting in a dead-sounding room.  Superior broadband bass traps will contour the absorption curve to absorb maximum bass, and less treble.  This allows one to focus most of the absorption where it is needed most – ie, the bass.  It also allows you to install enough traps to fix the bass without making the room too dead in the treble.  All RealTraps bass traps, for instance, accomplish this by using a proprietary limp mass membrane in the design.  An additional benefit of this design is that thinner panels are much more effective than they would otherwise be.  Our MiniTrap – which remains our bestselling bass trap – is only 3” thick yet is still effective to below 80Hz.

Bass traps should be placed anywhere in the room where a bass build up is audible.  Corners – including wall/ceiling and even wall/floor corners – are in most cases the best place to start.  Additionally, rooms usually benefit from bass trapping on the rear wall behind the listener, as well as the front wall directly behind each speaker.  For more on placing bass traps, including a listening test to help you find “where the bass lives” I your room, I refer you to Filtered Noise Helps Place Bass Traps on the RealTraps website.

Bass trapping in a room is in most cases the single biggest improvement that you can make, in part because it will improve the sound of everything you do in the room, whether it be recording, mixing, mastering,or listening for pleasure. Once the bass trapping strategy has accomplished all the “heavy lifting” acoustically, two more strategies are next for most rooms.

Early Reflection Management

Without treatment, early reflections from the side walls (and also the ceiling and the floor, not shown) will smear the stereo image and make it more difficult to hear details in the music

In terms of the mid- and high-frequency response of the room, the biggest problem to overcome is early reflections.  Early reflections obscure the detail of the sound, and confuse our brain’s ability to localize a sound.  To illustrate this concept, imagine a typical 2-channel stereo listening scenario.  As the speakers play, the first thing one hears is the sound traveling directly in a straight line from the speakers into your ears.  Then, a few milliseconds later (because the sound has a few feet further to travel), we will hear the first reflections bouncing off the side walls, the ceiling, and possibly the floor.  Unless you have a huge room (about 30′ wide or more) these reflections aren’t pushed back enough in time to be perceived as a distinct echo.  Rather, our brain will interpret them as essentially the same sound, coming from 4-5 different locations, thereby confusing our ability to pick out where the sound is coming from.

In terms of the stereo image, our ability to pick out instruments in the soundstage is compromised.  When mixing, it is much more difficult to dial in panning, subtle EQ adjustments in the mids and highs, reverb/delay tails, etc., with any sort of precision.  The solution to this problem is to install absorption at these first-reflection points on the side walls and ceiling.  For details on this strategy, including how to find your reflection points with a mirror and a helper, I refer you to Creating A Reflection-Free Zone on the RealTraps website.

The same strategy is useful in the recording zones as well.  For instance, an absorptive “cloud” installed on the ceiling above the recording zones will improve recordings immensely.  Arguably the most dramatic example of this improvement is in overhead mics on a drum kit, but this strategy is also useful for vocals, acoustic instruments, and anything else recorded with a microphone.  If there are any nearby walls that will reflect sound straight back into the mic, then these spots should also be treated with absorption.  In many one-room studios, I love to use traps on stands to do double-duty; when listening/mixing they go at first-reflection points on the side walls, but when tracking move them to reflection points near the instrument and the mics to improve the sound of the recording.

These steps alone (good setup, bass trapping, early reflection management) have already provided an astounding upgrade in the sound of your room.  For many people, these steps alone will be enough.  But for some – especially for those who need the best-sounding recordings possible, there is one last step that will take an already good-sounding room and make it great.

Ambiance Tweaks

After the above steps have been implemented with bass traps and selectively-applied high frequency absorption, the overall reverb time of the room will be shorter, and will be more consistent across the frequency spectrum.  However, a few more tweaks can help improve the sound even more.  This last step is particularly important in recording spaces, where instruments and vocals are recorded with microphones.  This means you might want to retain some ambiance in the room, so in most cases you don’t want to overdo the high frequency absorption.  Start with just the broadband bass traps in the corners and selectively-applied high-frequency absorption at reflection points, as described in the previous steps, and then take stock of where you are.

One problem that can linger even after you’ve gotten this far is flutter echo.  Flutter echo is a metallic, “boinging” sound when you clap your hands in the room, caused by two reflective parallel surfaces.  This is most common to the rear of the room since much of the existing absorption is at the front of the room, particularly the side walls at the rear of the room are often culprits.  If you have a flat ceiling, it can also be floor/ceiling related.  You can test for flutter echo using things like thick blankets hung temporarily across one of the parallel surfaces, and repeating the clap test.  If the flutter echo is reduced or removed, then you know you’ve found (one of) the culprits.  You can then permanently treat the offending spots with absorption or diffusion.In general, our take on diffusion is that it is never necessary to use diffusion to get good sound, but is often very useful in getting great sound.  Additionally, diffusers are almost never the most cost-effective improvement you can make, simply because most diffusers are very labor-intensive (read: expensive) to build.  Diffusion is a different way to deal with reflections; rather than absorbing the reflections as traps to, they scatter the reflection evenly in all directions, which removes the ability of the wave to damage the sound in the room yet keeps much of the ambiance of the sound.

Diffusion and bass trapping will really help the acoustic problems of the rear wall of a listening room

Diffusion is particularly useful on the rear wall of a listening room, and in most cases this is a great place to begin with diffusion.  The rear wall often also benefits form bass trapping, so it is useful to either use diffusers that are also bass traps or to use diffusers in conjunction with bass traps.  If budget permits, superior sound can be achieved with a lot of diffusers.  As an example, I refer you to Hearing Is Believing on the RealTraps website, where we use bass traps in the corners, absorption at reflection points, and diffusion everywhere else around the perimeter of the room, with world-class results that exceeded our already high expectations.

If all these steps are followed, then all the work you put into upgrading the acoustics of your project studio will pay off handsomely.  Everything you do in your studio – recording, mixing, mastering, rehearsing, recreational listening,or anything else – will sound better.  Perhaps more importantly in situations where budget (and therefore also time) is short, it allows you to get good results that you can be confident about much more quickly.  Things like microphone placement become much less critical, simply because the sound difference between point A and point B will be far less dramatic in a treated room, and the sound will be much more consistent throughout the room.

You will also be unwittingly help us here at RealTraps fulfill our mission: making the world sound better, one room at a time.”

James Lindenschmidt
RealTraps LLC
June 2012

 

Our thanks to James.  If you want to explore more about the RealTrap’s approach to acoustical design then we recommend you visit the excellent guide articles on their website at www.realtraps.com

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