☰
Whether you're making recordings, mixing, editing, mastering or simply listening for pleasure, a well designed listening space brings many rewards. Chief among these is the ability to hear beyond the room and system, all the way to the recording itself. There is a sense that the system disappears, leaving behind only the performers, their instruments and the space in which the performance took place. The space might be a real acoustic or one created by the engineers in the studio but as a listener, you are transported to that space.
An additional benefit of a well designed listening space is the ease with which changes to system components and their effects can be evaluated. This is a great help in making decisions regarding the components that will comprise the system and when considering potential upgrades. In the studio, this makes the job of accessing any audio processes faster and more reliable.
Creating such a listening space involves paying attention to a few determining factors, which is what we'll discuss in this article.
First things first. Let's look at the room itself and how it can affect what you hear. We can simplify our look at acoustics by dividing the subject in half, into those effects that occur in the bass range and those that occur in the treble.
One thing all rooms are very good at is storing bass energy. This is true regardless of the size of the room and regardless of its shape. It doesn't matter if the room is rectangular or designed without parallel surfaces as some rooms are, with walls that are closer together and a ceiling that is lower at the speaker end of the room than they are behind the listening position. Every room stores bass energy.
The frequencies where bass energy is stored are often referred to as the room's resonances or modes. There will be a primary mode for each room dimension, one for length, one for width and a third for height. As room dimensions change, the frequencies of the modes will change. The rooms that will be easiest to control will be those where the dimensions are not equal and are not multiples of each other. For example, a room that is 16 feet wide with an 8 foot ceiling will have a primary vertical resonance of approximately 140 Hz and a primary width resonance of approximately 70 Hz. There will also be resonant modes at the harmonics of these frequencies, so there will be a secondary vertical mode around 280 Hz and a secondary width mode around 140 Hz and so on for the higher harmonics of the fundamental resonance frequencies. In this particular room, the vertical and width modes will reinforce each other and these frequencies will not only sound considerably louder than other, non-mode frequencies but they will take longer to decay because the room is storing the energy.
This stored energy tends to obscure focus by smearing timing information. Low level details are covered up by remnants of the sounds that preceded them, sounds which have already finished in the record but which the room continues to hold on to. In effect, much of the silence in between notes is filled in by the room. This is exactly the reason why using an equalizer on the room (i.e. on the speakers) doesn't work. It will change the loudness of a sound in the room but it won't have any effect on the duration of that sound.
Room modes also create dips in those parts of the room where these waves bump into each other, causing cancellation. When you move around within the room, you will find some places where the bass is louder and others where it is lower in volume.
The solution is to use bass traps. Properly designed bass traps will convert some of this stored energy into heat. While they can't remove the room modes, bass traps will change the shape of the modes, smoothing them. This will flatten the peaks and dips and block the tendency of the room to hold on to certain sounds. You'll hear an increase in overall clarity as focus improves. Unencumbered by room effects, bass will have increased articulation with better pitch definition, power and dynamic "snap".
Pressure tends to build up where sound waves meet the boundaries of the room, so this is where bass traps get placed. The greatest build up occurs where boundaries meet, so corners are usually where the first traps get placed. The first harmonics of the fundamental room modes occur at the mid points of the room boundaries so additional traps here will help. The simplest room treatment will consist of bass traps in the corners behind the speakers but benefits accrue quickly as additional traps are placed in the remaining corners, the mid points of the walls and at the quarter points.
The most efficient bass traps for most rooms are the "functional sound absorbers" first proposed by Harry Olsen in the 1950's. These cylindrical traps are available as commercial products, Art Noxon's excellent Tube Traps from ASC (Acoustic Sciences Corporation) or you can build variations on the theme yourself with instructions that can be found on the Internet. Cylindrical traps can have additional benefits in the treble range, which we'll cover next.
Sound reflections from the walls and ceiling (and hard surface flooring) are the sources of room effects that occur in the treble range. Treble frequencies don't have the same power as those in the bass, so they don't have the same tendency to linger in the room. In the treble, it is the so-called "early reflections" that cause problems, obscuring detail and wreaking havoc with stereo imaging and harmonic accuracy.
Controlling early reflections is as simple as putting absorbent material at the points where the reflections occur. There are two such points, one for each speaker, on each wall as well as on the ceiling (and uncovered, hard flooring). Imagine the walls and ceiling of the room are mirrors. From the listening position, you'd see a reflection of each speaker on each of the walls and on the ceiling. If the floor is not covered with a carpet or rug, you'd see a reflection of each speaker here too. An easy way of finding these points is to enlist the aid of an assistant who will hold a mirror up against each wall while you sit in the listening position. With the mirror at your (seated) eye level, the assistant moves the mirror along the wall until you can see the reflection of one of the speakers. When you can see one of the speakers in the mirror, you've found the point on the wall to place the absorbent material. Have the assistant continue moving the mirror until you see the other speaker. Now you'll have the second place on that wall that will need the absorbent material. Do this for each wall as well as the ceiling if possible. A carpet or rug will work well to prevent early reflections from the floor.
While there are many types of foam sold for this purpose (and they are better than nothing at all), a much better solution lies with the modern iteration of the "functional" traps mentioned above. The best commercial designs as well as the better DIY (do it yourself) variety will be cylinders that have half their surfaces covered with a material that is reflective in the treble while the other half is fully absorbent. Too often, the use of foam to control reflections results in a dead feeling in the listening space that is neither natural sounding or comfortable. The common mistake is in the perception that if a little is good, more must be better. In fact, what is needed is absorption of the early reflections without affecting the later ones. Further, diffusing or scattering these later reflections contributes to the naturalness and comfort of the room. Cylinders with reflective halves allow the sound to be tailored as each cylinder is rotated. When placed at the early reflection points, the absorbent half can be oriented toward the speaker it is nearest, while the reflective half will help diffuse the sounds arriving later in time, in this way maintaining the natural ambience of the listening space.
So what have we learned in Acoustics 101? We've learned that room effects can be divided into those that occur in the bass range (modes) and those that occur in the treble (reflections). We know room modes can be addressed with properly positioned bass traps and that the cylindrical "functional sound absorber" variety of these can also bring the added benefits of absorbing early reflections. Modern iterations of these cylinders can also supply the requisite diffusion that helps preserve the room's natural ambience.
Now that we've treated the listening space, it's time to introduce the monitors.
In the old days, most folks thought they'd achieve stereo by placing their speakers on opposite sides of the room, often in the front corners. "Separation" was the goal and the reward was hearing those records that featured a marching band appearing to move from one speaker to the other. Or folks would marvel at recordings of small ensembles where the guitar was "on the left" and the piano was "on the right". While this was entertaining, it wasn't stereo.
With the old speaker arrangement, sound tended to localize at each speaker with the sound appearing to come "from the speakers". Close proximity of the speakers to the front and side walls allowed early reflections to blend with the direct sound, smearing detail and altering harmonic balances. Further, the corner placement was very effective at stimulating every mode the room had, resulting in boomy bass and a loss of overall clarity.
As early as 1954, the English journal Wireless World published an article by Peter Walker that spoke about speaker placement for stereo reproduction but it took another three decades for the concept to really catch on. Walker found he could maximize the performance of his speakers by placing them 1/3 of the way along the room diagonals. And so was born what has come to be known as "The Rule of Thirds".
Another strategy for speaker placement, from George Cardas, is based on the mathematical "golden ratio", also called a "golden section" or "golden mean", which Webster defines as "a proportion (as one involving a line divided into two segments or the length and width of a rectangle and their sum) in which the ratio of the whole to the larger part is the same as the ratio of the larger part to the smaller". This can be expressed as a number equal to half the sum of 1 + the square root of 5, which would be 1.618.
Applied to speaker placement, the golden ratio dictates that the distance of a speaker from the nearer side wall would differ from its distance to the wall behind it by a ratio of 1.618. In other words, take the distance from the center of the speaker to the nearest side wall and multiply it by 1.618 to get the distance it should be placed from the wall behind it. Now take that number and multiply it by 1.618 and you should get the distance from the center of that speaker to the opposite side wall. That would give you one possible speaker arrangement. You could arrive at another possible placement by taking the distance from one speaker to the wall behind it and multiplying that by 1.618 to get the distance from the center of that speaker to the near side wall.
In my experience, a simplified placement approach that combines elements of both the Rule of Thirds and the golden ratio has worked successfully in every room in which I've heard it. Please keep in mind that your particular situation may well require some adjustments to what you're about to read. What follows however, should provide you with a good starting point. First, decide which wall you want behind the speakers. Some prefer using the short wall, so the speakers fire down the length of the room. Others will use the long wall, which allows for more space between each speaker and the side wall it is closest to. Once you've decided which it will be, place the speakers so the space between them equals 1/3 of this wall's length. Note we're not using the center of the speaker as the reference here but its inside edge instead. Now measure the dimension of the room along which the speakers are firing (i.e. in the direction from the speakers to the listening position). Move the speakers forward (or backward) until the front of the speaker is 1/3 the length of this dimension from the wall behind it.
For example, let's say you've decided to have your speakers fire down the long dimension of the room. This means the short wall will be behind the speakers. If your room measures 12' by 19', you'll leave 4' (i.e. 12' divided by 3) between the inside edges of the speakers. If your speakers happen to be 1' wide, this puts their centers 5' apart, with 3' from the outside edge of each speaker to the nearest side wall. The 19' dimension divided by 3 will point to having the front edge of each speaker 6'4" from the wall behind the speakers.
Let's try another example, this time where the speakers are arranged against the long wall of the same room. In this case, we'd have 6'4" (i.e. 19' divided by 3) between the inside edges of the speakers. With our 1' wide speakers, there would be 5'4" from the outside edge of each speaker to the nearest side wall. Distance from the front edge of each speaker to the wall behind it would be 4' (i.e. 12' divided by 3).
Another approach uses the center of the driver element(s) in the speaker, the point(s) from which the speaker generates sound. Here, we'll aim for the 29% points in the room, where excitation of room resonances will be minimized. The end result will not differ appreciably from the method outlined above.
However, there is a caveat. I personally prefer the method outlined above as it tends to place the listener a bit further from the wall behind them, particularly when using the long wall behind the speakers. In order to keep the listener well away from the nearest room boundary, I would always want to keep the listening position no closer than 24" from the wall behind it. If necessary, I would move the speakers closer to each other in order to keep the listening position a minimum of 24" from the wall behind the listener.
Going back to the first example above, using the short wall behind the speakers, we'll measure 29% of 12', which gives us 41.76" (144" * .29 = 41.76"). If desired, for convenience we can call this 41.75" or 41 3/4". Place the speakers so the centers of their drivers (or the center of the total driver area, if the drivers are offset from each other) are 41 3/4" from each respective side wall. To find the distance from the wall behind the speakers, multiply 19' by 29%, which gives us 66.12" (228" * .29 = 66.12"). Again, for convenience, we can call this 66". Place the speakers so the center of each one's drive area is 66" from the wall behind it.
Applying this 29% approach to our second example, where the long wall is behind the speakers, we'd have the center of the drive area 66" (29% of 19') from each respective side wall and 41 3/4" (29% of 12') from the wall behind the speakers.
The final adjustment in either of these arrangements, will be to aim the speakers, sometimes called adjusting the "toe-in". While making sure the front, inside edge of each speaker remains where we have place it (at the 1/3 points if using the first method or where it ended up in the above procedure if using the 29% method), rotate each speaker around this point until it aims at the center of the wall behind the listening position. In other words, you'll be bringing the outside front edge of each speaker toward the listening position while leaving the inside front edge where we've already placed it. Note that the speakers will not be pointing directly at you but instead will converge at a point behind you.
The optimal listening position will be just outside of an equilateral triangle, meaning there will be slightly more distance from either speaker to the listening position than the speakers' centers are from each other.
The arrangement described here will put both you and the speakers at a good distance from the room's walls, ensuring you'll hear the direct sound from the speakers before any possible influence from the room will make its contribution. Although similar benefits are derived from what has come to be known as "near field" listening (i.e. sitting very close to the speakers), there are significant differences, the primary ones being this arrangement allows full bass response and stereo imaging to develop.
A few final points regarding speaker placement. Aim for symmetry between the left and right sides, particularly in the part of the room where the speakers are. A large object near one speaker will skew the soundstage. Try to keep the area between and near the speakers as open as possible. This means staying away from alcoves too. The same goes for the space between you and the speakers. Having a table (or mixing desk or video monitor) in front of you will provide an early reflection surface that will confuse the stereo imaging and alter the frequency balance from the speakers. (Recording or mixing set ups with a desk in front of the listener cause midrange or presence dips that engineers will tend to "compensate" for with unnecessary midrange boosts. Better to drop the height of the desk by at least a foot or move the controls off to the side so they don't interfere with what the speakers are trying to tell you.)
The importance of proper speaker placement can't be overemphasized. While treating the room's acoustics is also of highest importance (the room is after all, part of the system), I am tempted to say I'd rather hear well placed speakers in an untreated room than poorly placed ones in a room full of traps. Of course, both are required for the best monitoring environments.
It was quite a magical experience when I first encountered this kind of speaker placement. The sound was no longer confined to the speakers, which in fact, now seemed harder to identify as the sources of what I heard. Instead, the whole front part of the room came to life, containing the sonic equivalent of a hologram. It was as though that part of the room now opened out into another space, the one occupied by the musicians. Instruments that were in the background actually seemed to originate from a point far behind the speakers. I'd been a hi-fi hobbyist as well as an audio pro for years but now I finally understood what the term "stereo" means.
Ever notice how your playback system sounds better during the late night hours? One of the reasons for this is the AC coming from the wall outlet is cleaner when there is less usage. What makes AC "dirty"? Everything that shares the power line. Computers, household appliances, audio and video gear, not just in your home but from your neighbors who share the line as well, all contribute. Additionally, the copper lines act as antennae, picking up more dirt from radio broadcasts, cell phones, etc.
Installing dedicated lines from your breaker panel and high quality outlets to feed your system will help prevent current from being drawn away by other devices like refrigerators, etc. This is a good idea for those instances when your power amp needs to pull a lot of current in response to musical peaks but these measures won't do anything to clean up the pollution on the power lines. The only ways to achieve clean AC are with either an AC regenerator, which will create new AC to feed your system or with a good power line conditioner which will filter the noise.
Most power line conditioners will include protection from power surges and spikes as well. The most elaborate ones will also regulate voltage. Avoid the power strips sold as surge protectors for computers, which can actually add noise to the power line.
Clean AC power results in much quieter backgrounds, enabling low level details to be heard more easily. The absence of power line hash allows for a cleaner midrange and treble, with purer harmonic presentation. Bass frequencies benefit too, with increased tightness and pitch definition. Musical dynamics will have more subtle gradations and when called for, more "punch". Stereo imaging is more solid and soundstage dimensions (as contained in the recording) expand in all directions. Even your video gear will provide blacker blacks, less grain, better contrast and color purity and better overall definition.
It was the early 1970s when Bob Fulton brought forth the first cables designed for use with audio equipment. At the time, most systems were wired with common lamp cord (also called "zip" cord). Today, there are hundreds of designs for speaker cables, line level interconnections, digital cables, video cables, AC cords and microphone cables.
While that old zip cord does a wonderful job of carrying AC power to your toaster and light bulbs, music (and video) have different requirements. The best modern cable designs are rightfully considered components in their own right and as such, will significantly affect system performance.
Cables can interact with each other, inducing noise, so when wiring a system, it is important to keep different types of cables apart from each other. Many audio writers in England refer to this as "dressing" the cables. Your line level interconnects should be kept away from your speaker cables. Signal carrying cables should also be kept apart from AC cords and power supplies. If you encounter a situation where different cable types (i.e. speaker, interconnect, AC) can't be separated, have them cross each other at a 90 degree angle rather than run them parallel to each other. Separating them will be better.
Remember too that cables are directional. Sometimes this is because the connections differ at each end (some designs leave "ground" unconnected at one end to minimize noise transfer). Even if the connections are the same at both ends, all cables will become directional once they've been used long enough to break-in. Some manufacturers put arrows on the cable or on the connectors to help with proper orientation. When I start using a cable without arrows, I orient it so any writing on the jacket follows the direction of signal flow.
In the last paragraph, I mentioned break-in. Cables, like speakers and all the other components that make up your system, require break-in (sometimes called "burn-in") to reveal their best. There are special burn-in CDs sold for this purpose but all you really need is a CD with some wide range music. After connecting everything and arranging all of your cables, put in a CD and set your player to "Repeat". Then just let the music play. If your speakers, speaker cables and power amplifier are already burned in, they can be left off but the rest of your components should be turned on so they'll pass the signal. Most gear will show cleaner treble and more powerful bass within the first several days. In the following days, you'll hear the soundstage open up and overall focus will improve. After about two weeks, most components will have reached their full performance potential. Many loudspeakers however, can require as much as two months to hit their stride. Keep in mind this means two weeks or two months of playing music. The time the system is turned off does not count.
The subject of vibration control is covered in detail in Vibration control for better performance. That article also contains instructions on how to build your own rudimentary vibration control devices for just a few dollars each. Here, I'll just provide a bit of background that I hope will make you curious enough to consider its application in your system.
Over the course of the last few years, I've been doing a lot of research and experimentation regarding the effects of external vibrations, more specifically, seismic vibrations, on the performance of audio components. When I speak of seismic vibrations, I'm referring to those of very low frequency (below the range of human hearing) and relatively low amplitude. In short, I found that what your audio and video components are supported by has a profound effect on their performance.
I listened to and thought about the effects produced by all sorts of equipment supports, from racks and shelving to the various "footers" (i.e. adjunct feet) being sold to audio hobbyists and pros. Among the footers, a particular type of device known as a "roller bearing" impressed me beyond expectations. Comprised simply of a set of three steel ball bearings, each in a shallow "bowl", they allow for horizontal movement of the shelf under the supported component, without transmitting that movement to the component. While all the various footer devices had some effect on the sound, more often a change rather than making things better or worse, the roller bearings made consistent and repeatable improvements.
Placing a set of roller bearings under my CD player resulted in an across the board improvement in every category used to describe its performance: frequency extension, dynamic range, soundstaging, overall clarity, etc. In short, the sound just "opened up" to a degree I wouldn't have believed had I not heard it for myself. "Floating" the loudspeakers on sets of roller bearings was equally astounding. As I added sets of roller bearings under my other components, the effect, though more subtle, was cumulative. Today, all the components in the studio, including the power conditioner, are supported by roller bearings.
After hearing what roller bearings could do for my system, I began to think about air bearings and the result was the creation of a custom designed rack that has an air bearing on each shelf. Where roller bearings worked their seismic isolation magic in the horizontal and rotational planes, the air bearing rack did so in the vertical plane (and to some degree in the horizontal as well). When I first installed the completed racks in the studio, I was not prepared for the degree to which they allowed the system to reach new heights in performance.
The first thing I noticed was the Cinerama-like expansion of the soundstage. The music sounded like it was freed from the confines of the loudspeakers to a degree I'd not heard before in the system. I began playing record after record and in every case discovered I was hearing information I was previously unaware of. The difference wasn't simply one of nuance; I was hearing instruments I'd never noticed before on recordings I'd known since childhood. It was as if every record I own had been carefully re-mastered to bring out previously hidden musical information.
It is important to remember that isolating your gear from the influence of seismic vibrations doesn't add these benefits. What it does is prevent the vibrations from compressing dynamics, shrinking the soundstage, defocusing images, hardening the treble and muddying the bass. The effects of well implemented isolation techniques provide so many performance benefits (for both audio and video), it is surprising no one has been shouting this from the rooftops.
Setting up a high performance monitoring environment involves careful consideration of room acoustics and treatment, monitor and control placement, AC power conditioning, cables and how they are oriented and routed, component burn-in and seismic vibration control. When each of these factors has been addressed, it isn't easy to describe the total result of all the performance improvements they provide. It's a bit like having a giant audio microscope. Hearing the system "disappear" and finding yourself virtually in the performance space with the musicians before you, is absolutely magical.
Happy Listening!