[SoundStage!]Synergizing with Greg Weaver
Back Issue Article
September 1998

The Listening Room: Your Final Component - Part Two

Paradigm lost

As much as I respect and admire what Harry Pearson did for high-end audio publishing by establishing the abso!ute sound back in the early ‘70s, I am nonetheless compelled to disagree with his founding premise. His long-standing tenant has been based on the belief that the ultimate goal of any electronic music reproduction system should be to faithfully replicate the one true voice of the instrument (or instruments) creating the performance and is, unfortunately, a flawed paradigm.

To that end, it is a demonstrable law of physics that instruments themselves do not have one "fixed," or in his words, absolute, voice. The same instrument, be it stringed, brass, skinned, reed, et al., may exhibit significant differences depending upon the strings with which they are strung, the alloy of metal from which they are forged, the skins with which they are stretched, or the nature of the wood from which they are fashioned. For that matter, even the varnish upon that distinct wood has a small but signature sonic affect upon the resultant voice. Furthermore, and closer to the point for this discussion, the voice of any instrument responds differently in, thereby changing with, the venue in which it is played. Each unique instrument, combined with the reflected sound of the acoustic space in which it is played, exhibits a distinct voice in every different space in which its voice is excited into play.

So it goes with our listening room. One goal in assembling our system then should be to recreate the sound of that instrument, or group of instruments, played in the original acoustic space. But we must go one step further! We must take deliberate and often bold steps to assure we do not confuse that reproduced sound with the imposition of the sound of the room in which we have chosen to assemble our equipment. To do this effectively, we need to acquaint ourselves with the three S’s -- size, shape and symmetry.

The three S’s

Size

If your room is large, reflected sound will die out more rapidly than in a smaller room, giving it more of a "dead" attribute. Conversely, in smaller rooms, reflected sound will reverberate much longer, giving it more of a "live" sound. By the same token, the furnishings in that room will also contribute to, or detract from, those same effects. Hard wood furniture and floors, plaster walls and ceilings, large bay windows or sliding glass doors will contribute to a more lively presentation, while overstuffed furniture, tapestries, carpeting, large draperies and suspended ceilings will help absorb reflected sounds. The best rooms are neither too lively (small) nor too dead (large), but attain some semblance of balance between the two extremes.

Shape (and some symmetry) – They go hand in hand

One of the things you should be able to gather is that symmetry is typically good – but maybe not in the way you would think. Let’s say you’ve settled on a room that is 11’ 2" wide X 18’ long x 7’ 6" tall, coincidentally, the size of my room. Ideally, the room should possess strong symmetry when divided lengthwise on the centerline defined by the center point of your speakers and your listening seat. If you have glass windows in the middle of the long wall on your left, your best option would be to have them present on the right as well. If there is a doorway or archway behind the left speaker, there should be one present in the same shape and location behind the right as well. Not likely, eh?

It is also best to avoid asymmetrical room shapes, like L shapes or rooms with partial dividing walls jutting into the otherwise open space. These irregularities greatly affect the reverberant fields within the acoustic space, creating problems that may not be so easy to overcome.

In some cases, however, symmetry can be your undoing. For example, your speakers should share no common distance from any boundary. So if your speakers are two feet from the back wall, they should any distance other than two feet from the sidewall and from the floor. The reasons here are identical to those applied to the rationale behind why we don’t want any two dimensions in our sound room to be identical, reinforcement and cancellation. In this case, asymmetry is the answer.

Symmetry – on its own

Regardless of long wall or short wall orientation, your speakers should be set up at the base of an equilateral triangle, with your listening position at the apex. That triangle arrangement should then be placed symmetrically within the confines of the room itself. The main reason for this is that the arrival times of all frequencies, both directly radiated from the drivers and reflected from all boundaries, are kept nearly identical. This permits better balance of timbre, larger sound stage and more solid phantom image creation. By using unequal distances, which really translates into unequal arrival times, these all important aspects of sound reproduction get skewed and distorted quite severely and are much harder to tame or correct with secondary room correction techniques.

Room Taming 201 – Primary reflections and corners

The first malady we will seek to minimize with room treatment will be the first, or primary, reflection – that contributed by sound bouncing off the boundary of closest proximity to our speaker – from the side wall. This can be done by placing absorptive and/or diffractive materials on the walls at the point where the angle from the tweeter to the wall and then to the listening position is discovered. Remember your physics? Angle of incidence equals the angle of reflectance. Determining these points in the room can be done easily with the help of a friend, a concentrated beam flashlight or laser pointer, and a small, hand held mirror.

Position your accomplice first at the left speaker with the light or pointer. Have them aim the beam at the wall to the outside of the speaker and pointed along a line which is on center with the tweeter. You now move along the side wall with the mirror, moving it forward and backward along the wall, adjusting the light until the beam hits dead center at your listening position. Once you’ve found that point, mark the spot with a piece of blue tack or a pencil (so you can remove the mark later). Tada! You’ve found the point of the most significant primary reflection for the left speaker. Do the same for the right side and you are ready to move on.

Many companies make products to place at this spot on your wall. There are myriad’s of wonderfully executed, aesthetically pleasing - and fairly expensive - products from the likes of ASC and RPG, all of which are above reproach for this job. If you are like me, you’d rather spend your money on music. Michael Green of Room Tunes makes the TuneStrip, a 8" wide, 48" tall, 3" thick open weave covered "pillow" specially designed for this application, and a set of four go for about $180. There is the very cool Whisper Wedge from Cascade Audio Engineering, an open cell foam application measuring 24" by 48" by 3", which goes for about $100 for four. There is the absolutely staggering array of cost effective products from Auralex, which will solve ANY acoustic problem. The site is also leaden with information about acoustics and room taming. The better students will all do research at this site for extra credit.

The loyal readers among you will have guessed that I have a more frugal answer. Though not as aesthetically pleasing, and in some cases, given the particular product, not quite as effective, one can successfully substitute that funky egg crate foam bedding material sold in the bedding department of fine discount stores everywhere! A twin-sized sheet (75" tall, 38" wide, and 1.5" thick) will set you back all of $8. But, the Full sized unit (75" tall, 53" wide, 1.5" thick - $12), the Queen sized unit (80" tall, 60" wide, 1.5" thick - $15), or the King sized unit (80" tall, 75" wide, 1.5" thick), may represent better values, as you will likely find lots of places to utilize the material.

If the look of the stuff just doesn’t do it for you (it usually comes in a rather nauseating yellow color), you can make a cover for the foam with an open weave cloth (like burlap). Such martial is usually found in abundance in sewing supply stores. If that is too much for your, you can even use a simple wall hanging. Thick wall hangings will have a very desirable effect, and likely be more pleasurable to the eye. You can use comforters, quilts, or thick draperies, too. If you can use them in a pleated fashion, both the pleats and the air space created behind them will increase the effectiveness of their application. Decorate to taste!

Some of the bedding foam I’ve run across has been perforated every inch and a half with a 3/16" hole, which allows nicely for the use of push pins to hang the units on the walls. If the units you find do not have such an amenity, no worries! Just use pushpins in the depressed areas of the foam and you are set. Place a piece at least two feet wide by four feet tall (or the prefabricated application of your choice) on your marked primary reflection point, centered horizontally on your wall mark and vertically on your tweeter height, and you should have a very effective primary reflection taming device.

One of the liveliest areas in your room will be any point where all three planes of the room intersect, i.e., the corners. I am using the excellent and affordable Corner Tech from Cascade Audio Engineering. HAL is using the LENRD (Low End Node Reduction Device) Bass Traps from Auralex, which retail for about $28 each or $240 for a set of eight. The Corner Tech and the LENRD are similar in that each is a two foot tall, one foot long (per each wall mount side) triangular wedge of open cell polyurethane foam. Both snug up to the ceiling and seat on both sidewalls, offering an irregular, angled pattern cut into the front face. There are many others, like the RPG B.A.S.S. Traps, but the cost starts to get pretty steep. They have a serious effect on frequencies from about 125 Hz and up.

HAL has also used the Room Tunes Corner Tunes quite successfully, priced at about $90 for a set of four. They differ from the two previous products in that they are equilateral triangular cloth "pillows" measuring about 14" on a side and about an inch and a half thick. They are filled with a batting type material and one side has a foil reflector while the other does not. Depending on the side you place outward into the room, you can absorb or reflect, depending on your needs. These are also applied, via the provided tabs, with tacks or perhaps Velcro.

These are the first two areas to treat, especially if you are starting with limited resources or want to minimize the impact that such tuning devices will have on the appearance of the room. Their implementation will be seen to help out greatly with image specificity, tumbrel balance, clarity, micro dynamic shadings and room echo.

Room Taming 202 – Front and rear walls

The whole trick here is to have near total front wall absorption and have the rear wall slightly diffractive. What we want to do is deaden, from a reflective point of view, the rear wall, behind the loudspeakers. Keep in mind, the rear means behind your speakers, not behind you. We are dealing with the direction the sound waves are propagated, and as they are firing toward you, you are at their front and the wall behind them is the rear. Got that? Okay.

One of the most common approaches used is known as the LEDE method (Live End, Dead End), wherein the area behind the speakers is kept fairly dead and the area behind the listener is kept fairly live. The use of large curtains or tapestries on the walls behind the speakers will do wonders for deepening and sometimes heightening the stage. Absorption behind the speakers has the effect of taking the rear walls out of play, letting the sound recede far behind that physical barrier, deepening the SoundStage!

Materials from companies like Sonex and Auralex can be successfully applied here. However, several of the King sized egg crate bedding foam units, depending on your wall size, may be all that are required to completely cover the rear wall. You may choose to completely cover your rear wall, or just do some nice looking symmetrical pattern. The choice is yours, but use your ears to decide whether just a little is enough! You should cover a large portion of the very center of the rear wall at a minimum. You can again use tapestries, comforters or quits here. You will also likely wish to treat the sidewalls some several feet forward into the room as well.

Diffraction behind you has the effect of defocusing the reflected sound, letting some of the sounds reverberate behind you the way they would normally in an actual venue, yet without being overly energized. What I have done, in the efforts of maximizing the limited space currently available to me for storage of my software, is to place my entire software collection along the back wall. The irregular edges of the records serve well to diffract directly reflected sounds. You may choose to use some other method, like the Auralex T’Fusor (about $220 for a set of eight, which will cover about sixteen square feet), the RPG Abflectors (about $240 for a pair of 19.5" wide X 47.5" tall X 6" thick devices), or one of the many other applicable devices, too numerous to list here.

Many rooms overload with bass or mid-bass, depending on the room dimensions. The use of bass traps of some nature is quite useful in such cases as it provides for better low frequency support. Guess what! Bass traps come in all kinds of sizes, shapes and prices. You knew that, right? Good for you! I currently attack most of the excess LF energy in my room with the use of four of the Spiral Tech’s, again from Cascade Audio Engineering. The Spiral Tech is a four-foot tall cylinder, shaped like a rounded cog when viewed from the top, and has a 10-inch diameter. I have placed these in the rear corners and spaced two more along the back wall. They are again fabricated from open cell polyurethane foam and are VERY effective.

The ASC tube traps, while quite expensive, have a well deserved reputation for their effectiveness and are quite easy on the eye, as are many of the devices from RPG and Room Tunes. In the past, I have used a homebrew combination of the concrete forms available at building supply stores, which come in various diameters from about 6" to 12", and the ever faithful bedding foam. Take a hole saw to the cardboard concrete former, leaving just enough material intact to maintain the cylindrical form. Or, you can use chicken wire to create a round form of varying dimension on which to apply yet again some of the bedding foam. Then, after applying a layer of the foam, just stuff either of the open forms with pillow batting from the sewing store. Placing these traps into the front and rear corners, as well as along the side and/or rear walls as needed will significantly damp excess bass and mid-bass energy. You could even try to use comforters or quilts, rolled into long tubes, using string or twine to hold the shape. Typically he larger the diameter of the trap, the lower the frequency it will tame.

The use of this order of taming approach will increase stage depth, width and height, allow for tighter focus of images, provide yet truer timbre, enhance detail and clarity, and tame both excess slap type echo and bass or mid-bass energy.

Room Taming 203 – Second reflections and ceiling

With our primaries out of the way, secondary reflections can now be dealt with. These would be the reflections from the left speaker to the right (far) wall and back to the listening position - and the opposite path for the right speaker. There are two approaches to managing this particular reflection. The first is to use absorptive/diffractive materials on the sidewalls at the point of the reflection. We can determine the placement location for these secondary taming devices in the same fashion we used for finding the primary reflection points. You may again use prefabricated materials for this secondary taming, or your homebrew methodology. Yup, you can use big tapestries, quilts, comforters or draperies to your advantage here yet again.

The second method is to place a tube trap device between and somewhat in front of the speakers. Placement here is critical and the tube goes along the centerline running front to back at the intersection of the newly determined lines to the sidewall for placement of the secondary taming materials. This is quite an interesting look, as the tube will inevitably be somewhere near the center of the room. This will certainly spark a conversation or two as you bring people into your listening room and begin to explain its purpose. Both approaches combined work even better.

The fruits of this labor are yet more truthful timbre, less slap echo, further enhanced detail, and a wider and still more focused stage.

Finally, we move on to an area I’ve only explored in the past year and a half or so with superlative results, the ceiling. What you do here again is the trick with the focused beam and the mirror – though it is a bit more challenging. Shine your beam at the ceiling and move the mirror around until the beam hits your listening chair at head level. This is the ceiling’s primary reflection point. There are the ASC half tubes that are quite cool looking, expensive and labor intensive to install. There are many other devices, ranging from tubes to foam forms that can be hard mounted. There are even drop in tiles for dropped ceilings. I’ve even seen a thick blanket, draped from the ceiling in a pleated fashion, used to good effect here, but hanging it is a major chore. Take your pick!

To do it, Synergizing style, try some of the bedding foam and a large piece of cardboard, the largest piece you can get -- say like four feet by six feet. You can stop by an appliance store and see if they will let you scavenge an empty refrigerator carton. Use a can of automotive carpet spray adhesive to treat both the surface of the cardboard and the back of the foam. When dried to a tacky finish, apply the foam in an alternating, rounded wavelike pleated fashion, starting with the foam attached on the long edge of the treated cardboard, then letting it pleat up along its length, then touching down on the treated cardboard again, repeatedly. You can punch holes in the cardboard and foam (if it isn’t the pre-perforated style) and then use wire ties to anchor the foam at the points where it touches the cardboard. The result should look something like a washboard on steroids.

You can now place the completed cardboard/foam form, with the waves running parallel to the front and back walls of the room, on the ceiling, centered front to rear and left to right on your reflection mark. You can do so with thumb tacks or push pins on a normal ceiling, as the entire unit is quite light. You can hang it from a suspended ceiling, or, if you want to get really serious, you can mount hooks into the ceiling and perforate the cardboard accordingly to hang from them.

This particular taming method has a stunning effect on stage depth and clarity! Don’t rule this one out even though it promises to be a serious chore to implement.

Culmination

For those of you who want the most bang for the buck, you really should try the Auralex products. They do not employ me, nor do I have any interest in the company. They just produce very affordable, highly effective materials! The other companies all build very good materials, even if they come at a higher cost, and as I have somehow come to be seen as the "champion of the economically challenged," I am just trying to stay within that vein.

Overall, these room-taming approaches provide a glut of improvement. You will enjoy much more accurate low frequency support. You will be treated to significantly reduced (if not completely abated) slap echo. The corrected timbre that you will reveal will astonish you. There will be a refined clarity and realization of low level detail previously only hinted at. And the expansive, focused SoundStage! will leave your jaw on the floor. These approaches also provide for a more involving experience at a lower volume setting, as well as increasing the high volume threshold for you head bangers out there.

Dear readers, please believe me when I tell you that this room taming process can and likely will be quite time consuming and somewhat costly. But, YOU WILL NEVER REALIZE THE FULL POTENTIAL of your immense investment, both in terms of the cost of your equipment and all your precious time, until you take the initiative to tame the final and most critical component in your system, the room in which it is all assembled.

In next month’s third and final installment dealing with whipping your room into proper acoustic shape, I will be sharing with you some room realizations by the wonderful group of friends that I have developed here on the western shore of the Chesapeake Bay. I have referred to them many times by the frivolous but functional label, the Southern Maryland Irregulars. This will be my last installment from this part of the world, as, by the time you read this, I will be packing up my humble abode and making my way to the greater Chicago area. I am looking forward to a whole new set of audio adventures to chronicle for your enjoyment amid America’s heartland in the great Mid-West.

Until then, happy listening!

...Greg Weaver
gregw@soundstage.com

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