You may or may not have given much thought to it, but your walls, floors and ceilings have a pretty significant impact on the sound you hear from your audio system. A fair number of acoustic experts generalize that when you're seated 6 to 10 feet or more from the speakers, over 50% of what you hear is actually reflected sound, not primary sound, directly from the speaker itself. The more you 

know about the effect these boundary surfaces have on your listening, the better your chances of maximizing the sound you hear.

  

Before we delve into the basics of room acoustics we'd like to review some fundamental information that will make the following easier to grasp. We are repeating some of this from past issues, so if you already know this stuff, you might just scan through it as a refresher.

 

Wavelengths - Every frequency has a specific wavelength. The lower the frequency, the longer the wavelength and vice versa. So a 20Hz wave is 56.5 feet, 60Hz is 18.33 feet, 200Hz is 5.65 feet, 10,000Hz is 1.356 inches and a 20,000Hz wave is 0.678 inches long. If you're interested, a wavelength calculator can be found here: Calculator Link: http://users.nlamerica.com/kevin/Freq.htm.

 

Hard and not so hard surfaces - Hard surfaces reflect sound waves; the stiffer the surface the better a reflector it is. Standard sheetrock on 24-inch centers will flex a lot more than a solid concrete wall or tile floor. Therefore, the sheetrock wall will actually absorb a small amount of the low frequency energy in the room while concrete or tile will reflect more of the energy back into the room.

 

Absorption and diffusion - The two most common ways to ameliorate issues with frequencies above the bass range (200Hz and up) are absorption and diffusion. Absorption is essentially "soaking up" the sound to reduce reflections back into the room. Diffusion is scattering the sound waves when they hit the diffusing surface so the reflections scatter around the room.

 

Standing waves in a square or rectangular room

Standing waves - When the length of a low frequency wave interacts with a matching (or multiples of a matching) room dimension, back and forth reflections set up that are called standing waves (also known as Eigen modes). Standing waves produce replicas of the original wave that reflect back, either in or out of phase with the original wave. As they continue to reflect across the offending dimension, large peaks or dips develop at that frequency and increasing multiples of that frequency. For example, if you have a room that's 18 feet long you'll have a standing wave at about 62Hz across that dimension. There'll also be additional standing waves at 124Hz, 248Hz and beyond. If you're unlucky enough to have a square room, say 18 feet by 18 feet you'll have the same standing wave pattern setting up in both dimensions, width and length.

 

Average rooms - Significant research has shown that the average American family room/den/living room with a mix of cloth upholstered furniture (leather is actually a reflector, not an absorber of sound), various pieces of other furniture, bookcases or shelves, etc. turns out to be fairly acceptable in terms of acoustics. However, particularly in the case of bass standing waves, just about every residential room has serious issues in the bass frequencies.

 

Locating speakers relative to the prime listening seat:

With two speaker stereo the general rule of thumb is to locate the speakers about as far apart as the distance to the center listening seat, creating a triangle between the speakers and the listening seat with 2 equal sides and 45 to 60 degree angles. Due to their exceptional horizontal dispersion, GoldenEar speakers can actually benefit from even wider spacing between, and then toed-in* towards the prime listening position. The idea is to help the speakers create a palpable phantom 

center image and a discernable "soundstage", with instruments appearing to float in position across the front. If everything falls into place, you'll not only hear instruments across the plane of the speaker positions, you'll experience a sense of depth for instrument placement within the soundstage. Toeing the speakers in, towards the listening position usually results in more specific and solidly planted imaging with optimum high frequency response at the prime seat, as well as better fidelity for off-axis listeners.

There's almost always acoustic benefit in placing the speakers with the tweeters at seated ear level. If you can't place them that way, tilt the speakers up or down as best you can, in order to aim the tweeters at seated ear level. The result will be enhanced high frequency clarity, imaging and soundstaging.

 

Locating speakers relative to boundaries (walls):

All the following recommendations must be rationalized with maintaining domestic tranquility.

 

Every wall surface adjacent to the speaker will reflect sound from the speaker out into the room, but delayed by a small amount. The most noticeable sound change from placement close to a wall will be an apparent increase in bass. That's the reason putting a subwoofer in a corner makes for so much more bass. You're hearing the reflections from the two adjacent walls and the floor combined with the direct sub output. Depending on several factors, subwoofer corner placement can be a boon or, more typically, a bust (more about this further on).

 

On the other hand, midrange and high frequency corner reflections will unquestionably "color" what you hear at the listening position. Experts generally agree that placing full or wide range speakers (i.e. not subs) in a corner has a negative impact on their sound. If you can keep the midrange/tweeter speakers out, away from the walls behind and to their sides you'll achieve enhanced clarity, detail, and imaging. It's also a good idea to place the speakers different distances from the wall behind them and the wall to their sides. And it's better to have both the left and right speakers in identical acoustic spaces. For example, good would be having both speakers 3 feet out from the wall behind them and 2 feet from the walls to their sides. To optimize imaging, you should have the speakers located within 1-inch distance of each other relative to the prime listening position. Seriously, get out that tape measure and check those distances. Some folks mark the speaker locations on the floor using a small piece or two of low adhesion tape.

 

The Place for Bass:

Standing waves as defined above can wreak havoc with bass in your room. Potential problems include boomy bass, lack of bass, one note bass - all caused by the nulls and peaks. These problems typically occur at different locations in the room, you can hear this for yourself by playing bass heavy music or bass test tones from a test disc and walking around the room. You're sure to hear at least a few of the above issues scattered throughout the space.

 

Click here to read the placement recommendations for GoldenEar Triton series speakers from "Sandy's Setup Tips" on the GoldenEar web site.

 

Here are some tips on how to deal with standing waves in general, particularly if you're using a separate subwoofer:

1. Should you be using a smaller, less powerful single subwoofer you might initially try using corner placement to maximize its output. GoldenEar ForceField subs are all high power subwoofers and generally don't need nor will they positively benefit from corner placement. Be aware that corner placement has the potential to create powerful room modes and locations where the bass will be particularly boomy and indistinct. If you have chosen corner placement the bass is poor at your listening position try shifting the sub and/or the listening position slightly. Remember that each wall surface is a bass reflector so try moving the sub out of the corner 6 to 8 inches at a time and possibly away from the walls altogether. Shifting the listening position can be more domestically problematic but if you can, give it a go.
    
2. Locating the sub between or directly adjacent to one of the stereo speakers can work well. Once again, the closer it is to the wall behind it, the more apparent bass you'll hear in the room.
    
3. A good way to find single subwoofer locations is to use a long connecting cable and place the subwoofer in the listening seat. Not next to it or in front of it, but physically lift the sub and put it in the seat. Be careful to remove any spikes, and protect the chair or couch. Then play that bass-heavy content or those test tones and crawl around the room slowly, listening for a good balance of bass quality and quantity. Wherever you find that good bass balance would be a good place to locate the sub. Remember, you're listening for quality, not quantity. Clearly defined bass notes, tight, punchy bass guitar sounds, etc. are the goal here.
    
4. Research has proven that using multiple subwoofers can dramatically enhance in-room bass performance. That's one of the major benefits of the Triton series. If you're not using Triton models however, two or more subs can be a real ear opener. With two subwoofers, locations to try include one sub adjacent or close to each front speaker. Other good potential locations for multiple subs include opposite room corners (this may seem inconsistent with what we said about corner placement above but using two subs makes corner placement potentially beneficial), one each in the center of the front and rear walls, one each in the center of the side walls or one each at the one quarter way points of the long walls of the room. Should you have the luxury of trying multiple locations we would suggest you give them all a shot. You'll be amazed at the difference placement can make to bass performance.
    
5. Note that if you're using satellite speakers which are crossed over above 100Hz avoid rear room subwoofer locations because you run the risk of having lower mid-range sound coming from the subs. In this case, front of the room placement is generally the best choice and directly adjacent to the L/R speakers is ideal.
   
   
   If you're using full range speakers that have the capability to generate high quality deep bass, like GoldenEar's Triton series, there's still the potential for standing wave issues. A few further guidelines may help:
    
6. Avoid sitting (listening) in room corners. This can have the same detrimental "boom inducing" effect as placing speakers in the corners.
    
7. Avoid sitting directly up against a wall. Bass pressure waves tend to "pile up" along room boundaries (walls) and make for more boomy, indistinct bass. There are also issues with reflections of the midrange and high frequency waves coming back to your ears almost immediately after they came by the first time. If you must have the prime seat right near a wall, try to move it out from the wall at least 2 to 3 feet.
    
8. Avoid sitting at the exact center of the room's length. If you look at our standing wave illustration above you'll see why.
    
9. Try to avoid sitting at any ¼, ½ or ¾ point in the room's width or length. Ditto about the illustration above.

If you have any GoldenEar set up questions please send them to support@goldenear.com 

 

Next issue we'll discuss some mid and high frequency room treatment options.