Before we start it's important to note that many typical US dens/great rooms/living rooms are acoustically acceptable. Maybe not great, but at least OK. But that doesn't mean they couldn't be improved through the judicious use of acoustic room treatments. As we've pointed out in the past however, bass standing waves exist in pretty much every domestic space creating serious peaks and nulls throughout the area. Before we get down to standing wave issues, let's look at room treatments for midrange and high frequencies.

Treating for midrange and high frequency reflections - Treating midrqange and high frequency reflections typically results in smoother overall sound and more precise imaging. The two ways to treat reflections are absorption and diffusion. One of the most efficient absorbers of acoustic energy is fiberglass. Many commercially available acoustic panels use some form of fiberglass as their main absorptive element. It's important to understand that the thickness of any absorbent panel and their distance from the wall behind them significantly affects the lowest frequencies that they will absorb. If you were to simply use 1-inch thick panels and mount them directly to the wall you would effectively be absorbing most of the tweeter's output but little energy in the midrange or "presence" range. Assuming that you'd like to get down into the mids or a little below you would be much better off to use 2-inch thick panels and stand them off the wall.

Studio control room treatment. Much of what's here applies to your listening space as well. Image from www.soundonsound.com

Ideally, you'd want to stand absorbent panels off the wall by ¼ of the lowest frequency wavelength that you wish to absorb. If we assume that 500Hz (wavelength of 26.7-inches) is a good frequency to start with, then ¼ of the wavelength equals standing the panels off the wall by 6.75-inches. As always, domestic tranquility trumps acoustic concerns in most cases so compromise will most likely be necessary.

When you're listening, every sound that arrives at your ears within an 80 millisecond "window" is summed by your brain into a unified whole. Sound travels about 90 feet in 80 milliseconds so effectively every reflected sound in the average room is summed into one by your brain, making it impossible for you to distinguish between direct and reflected sounds. Beyond 80 milliseconds we start to hear reflected sounds as echos.

The most basic yet fruitful treatment available to you is to reduce the first or primary acoustic reflections. Note that we're not talking about bass and bass standing waves right now, just midrange to high frequencies. Also note that this isn't soundproofing; it won't prevent sound from traveling to other areas in the home. OK, so if you want to treat first reflections how do you find them? The simplest way is to sit in the prime listening seat while another person walks along the front and side walls holding a decent size mirror pointed directly forward, level and straight out into the room. As you watch them walk, every location where you see one of the speakers reflected in the mirror as it moves along constitutes a first reflection point. Those locations are good places to position an acoustic absorber or diffusing panel. You don't have to put in a panel from floor to ceiling; a 2-foot high panel centered on your seated ear height is adequate. If you can't or won't use the mirror method, a good place to start is treating the side walls precisely half way between the speakers and your listening position.

An untreated listening space. Images from www.primeacoustics.com.

The same room, but treated.

Placing absorbent panels on the wall directly behind the speakers can also enhance your system's performance. Note that if you do install absorbent and/or diffusive panels there almost assuredly will be a change to the overall sonic balance from your speakers (bass to mids to highs) as you're absorbing some of the midrange and high frequency energy that you're used to hearing. Take some time to acclimate to the new balance. If you haven't over-damped the room it should start to sound natural and well balanced in pretty short order.

Several acoustic treatment supply companies sell pre-made absorbent panels wrapped with various kinds of cloth. Some sell "art" versions that sport photos or artwork printed on the panel coverings. A few will even let you supply your own artwork for printing on the panels. Panels like these should make it easier to get room treatment buy-in from those you live with. Oh, and if you want to jump into room treatments with both feet (ears?) the room's floor should be carpeted, at least in front of the main speakers and several feet in front of them. And you'll want fairly thick carpeting with heavy duty padding beneath. Want to go completely over the top (pun intended)? Consider treating the ceiling as well!

Do-it-yourself Acoustic Absorber Panels - If you're reluctant to buy commercially available absorber panels you can make your own. We would strongly advise against using standard loose fiberglass insulation as it will "shed" particles into the air in the room, not to mention getting all over your clothing as you're working with it. We would suggest you use 1 ½- to 2-inch thick compressed fiberglass insulation which is available at most home centers and from the Internet. You can make simple wooden picture frames from straight pieces of 1x2 boards to hold the insulation and mount them to your walls. Staple or glue the insulation within the frame you've made and cover the frame with a fairly open weave cloth of your choice. You can use speaker grille cloth or any synthetic cloth that you can see through reasonably well when you hold it up to the light. Don't use cotton, wool or blends using these materials. Since you're going to wrap the cloth covering around to the back of the frame and staple it there, there's no need to miter the frame corners. These panels can be any shape you'd like to make and different sizes too, as long as in total they cover approximately 2 feet around your seated ear height, while listening.

A recent quick Internet search found companies that offer everything needed to build do-it-yourself panels except the wood for the frames themselves. These panels are fairly easy to make and effective to use. Best of all, they're affordable too. Even commercially available panels like these aren't too costly. These panels, either homemade or purchased, may well be the most effective and affordable way to dramatically enhance the performance of your system. If you'd like help with this project, contact your GoldenEar dealer for advice and assistance.

Furniture as an Adjunct or Alternative - Most upholstered furniture is sound absorbent, but not leather furniture as the leather is actually reflective.  You can try positioning some upholstered furniture at prime reflective locations as reveled by the mirror walk test. The pieces should be at least 12 inches higher than your seated ear level.  Loaded bookcases with random size books can act as efficient diffusers, scattering the acoustic reflections. These would also be a way to reduce first reflections at the listening position. You can combine acoustic panels as described above with furniture to achieve excellent result too.

Standing Waves and Bass - Since low frequency waves are so large and the vast majority of domestic rooms are comparatively small, standing wave reflections are pretty much inevitable. They cause bass peaks and nulls throughout the room and you'll typically find only a few excellent bass locations in any room. Of course, this assumes that you're listening for relatively accurate, non-boomy, musical bass response.

Once again, a search of the Internet reveals a number of companies selling ready-made bass traps and some selling the materials to make your own. Bass traps are typically fairly large and will take up more space in a room than most people are willing to give up. Some are designed to be placed in corners because the junction of multiple reflective boundaries (walls, ceilings, floors) exacerbates these low frequency reflections. Bass traps can help substantially but few people are willing to disrupt their décor to the extent required to use them. Alternatively, careful woofer placement and moving seating locations can also make a huge difference in what you hear, particularly in the bass and at specific places in the room.

Rectangles, Squares and Other Room Shapes - In rectangular and square rooms there are some locations that you should try to avoid sitting in. One quarter, one half or three quarters of the way between any two walls or the ceiling and floor are problematic. Try seated ear placements a minimum of 18-inches from any of those locations. Try not to sit up against any wall or in a corner. If your couch is up against the wall try moving it out between 18 and 24-inches. Out in the room itself, try sitting at one third or one fifth of the way between the side and the front and back walls.

NOTE: There are room mode calculators online that will show you the location of peaks and nulls in your room based upon the dimensions that you enter. Search for ROOM MODE CALCULATORS and pick one that works for you (some are very technically complex and others are simpler. Look at a few and pick one that makes sense for you.).

Unfortunately, if your room isn't square or rectangular all bets are off. Predicting acoustic results in odd shaped rooms is very complex and acoustic results are very hard to predict. By the way, square rooms represent a particular problem because they create identical standing wave patterns at the same frequencies, front to back and side to side.

Should you have boomy or indistinct bass at your listening position try shifting your seat and/or the speakers/subwoofer to make it better. Small changes in the range of 12 to 18 inches can make a substantial difference so give it a try. You can also try switching the phase control on your subwoofer if it has one. If you do, pay particular attention to the integration of the subwoofer's output to the satellite speaker's bass response. There should be a smooth transition from one to the other without any suck-outs as they transition.

Since acoustic room treatments can be as much art as science we really suggest that you discuss what you're thinking about with your GoldenEar dealer. Many of them have experience with room treatments and some can provide the materials as well as complete room treatment designs. We've also listed several suppliers of materials below. A few of these companies will also assist you with room design too. This is just a sampling as there are several more companies out there.

aaronbrownsound.com/571 - a do-it-yourself tutorial on building your own absorbent panels

Next Issue we'll discuss more about listening levels, amplifier power and loudspeakers.