ReadScapes


Your Room:
the Final Link

 

Originally published in IAR Hotline! Issue 39,1985 by J. Peter Moncrieff.
[1996-1999 Acoustic Sciences Corporation. All Rights Reserved.]

Versie
2018 ThingMan - met toestemming gepubliceerd



Op de praktijk- en DHZ-pagina van ReadScapes kun je een artikel vinden over
het zelf bouwen van tubes

Het Nederlandstalige artikel
"Een Luisterruimte optimaliseren met Tube Traps"
is feitelijk het meest compleet.

Dit artikel omvat
alle aanwijzingen die nodig zijn om elke akoestische situatie adequaat aan te pakken met tube traps.




Prologue:

There's a special joy and excitement in pursuing the audiophile hobby. And this excitement reaches a climax when, on that rare occasion, you make a sonic breakthrough with your audio system. We've all had that experience at least once.

Say you're installing a new phono playback component or speaker system. You spend hours and hours experimenting with aligning them to get everything optimized. Then finally you sit back and listen to music on your new updated system. Usually the sonic improvement is rewarding but nevertheless merely incremental. However, if you pursue the holy grail of your hobby diligently, then with luck perhaps once a year you achieve an improvement so striking that your system is transformed, literally born again. When you hear this, you can't believe it. And then, in an excited orgy unmindful of time or hunger, you pull out several dozen records from your collection, and play familiar snippets of each. The sound is unbelievably better. You literally rediscover the music that's on these treasured records, and later in the rest of your library. Finally, after hours that seem like minutes, at once exhausted and enervated, you can regain contact with the rest of the world.

Your audio system has once again become that magic machine that transports you to other worlds. And you have achieved this magic, by your selection of components and your work in setting them up.


I've just been through such a magic experience myself. IAR's new laboratory in Vista has several small listening rooms, typical of small apartment size rooms with low ceilings. But the main listening room for the reference system has magnificent dimensions of 25 by 30 feet, with a 14 foot cathedral ceiling. These dimensions allow the full development and propagation of very low bass waves, the wide stereo staging needed to recreate the full breadth of a symphony orchestra experience in the concert hall, and the long reverb tail that can enhance perception of the original hall ambience encoded in a good recording (a la Madsen and the subsequent delay devices that appeared on the market).

As in any listening room, the layout of the stereo system and the acoustic treatment of the surfaces needed to be optimized. And there are many acoustic parameters to juggle, as there are many desiderata to optimize. You have to optimize overall reverb time at all frequencies; control standing waves for all dimensions and at all frequencies; and control reflections from the surfaces near the speakers, near the listener, from the side walls, and between all pairs of opposite surfaces, with respect to both frequency and time delay.

These reflections affect the system's amplitude and phase response, its transient attack and decay envelope at various frequencies, the time smearing that can malform the original musical information plus obscure subsequent musical information, stereo spread and localization in all three dimensions, perception of recorded ambience, and finally the tactile coherence of the stereo image, including not only the instruments but the recorded space surrounding those instruments. You can see that all this is a tall work order, with many variables that make for many hours of experimentation for each new room you tackle. And the larger the room, the more variables there are to juggle (by at least the square of the increase in room dimensions).

The end results are worth it. After not hours but weeks of experimental work, this reference listening room and its system has now given IAR quite simply the finest stereo imaging in the world, using commercially available components. Don't take my word for it. A number of independent experts, who have heard some of the best audio systems in the world (including those of other leading reviewers), say they've never heard anything like it. Furthermore, thanks in part to the control of time smearing reflections and excess reverb, the system has given us some of the best transparency and clean purity to be heard anywhere.

The weeks of experimental research in room acoustics have taught me a lot about the subject. Most of what I've learned demonstrates that today's prevalent theories and guidelines on room acoustics and treatment are wrong and even backwards. They led me up many blind alleys, for example prescribing the use of absorbent materials on the walls around the speakers (the LEDE technique). The sonic results I obtained by following accepted guidelines ranged from mediocre to satisfactory, but none gave me the special magic I thought should be possible. So several times, after trying vainly to optimize all the above parameters following prescribed tactics, I tore everything down, stripped the giant room bare, and started again from scratch. Finally, I had to develop my own new tactics and guidelines, proceeding by ear and by the technical results gleaned up to that point.

Incidentally, it's truly amazing what human hearing can detect and then analyze, as minute changes in the reverb and reflection patterns of the room cause the subtlest variations in the music and in the stereo imaging. The ear/brain gradually learns what to listen for, how to interpret it, and then what adjustments to make where in the room's acoustic treatment. The new tactics and guidelines I learned form a gold mine of material for a series of articles we'll run in IAR, on how you can acoustically treat your room for better stereo imaging and clearer sound. And the series starts here, with our review below of the ASC Tube Traps.

When all the experimental research into system arrangement and room treatment finally jelled, and IAR's new reference listening room gave me that spectacular breakthrough in stereo imaging, I went into one of those exhilarating audiophile orgies. For days, I kept pulling recordings with good imaging out of the library, and being blown away by the spectacular imaging discoveries on each new disc. I was rediscovering the music in the lab's collection, with symphony orchestras and choruses palpably spread before me in 3D space. With over 6000 records plus hundreds of pre-recorded tapes and now CDs in IAR's library, I still have a lot of rediscovering musical joy ahead.

Of course, this spectacular stereo imaging breakthrough in IAR's new reference listening room serves not only my musical enjoyment, but also yours. This room and system setup can do justice to the finest stereo components being evaluated and compared for review. It puts to the test not only their stereo imaging capabilities, but also their transparency, resolution, clean purity, and even phase behavior -- since all these contribute to the preservation of subtle musical information that is required to yield the best imaging. Also, this superior imaging, together with the low mud factor obtained by controlling room reverb, allows us to hear better into the inner textures of music (especially on complex material), which allows us to better evaluate how well components under review are preserving musical textures, subtle detail, intertransient silence, etc.











ASC TUBE TRAPS
&
D.I.Y Tubes


Even the manufacturer doesn't know how good these are. He modestly recommends that you merely use one in each corner of your listening room, to control the room's low bass standing wave modes. But they are so powerful and flexible that you should use them every 3 feet or so, along every surface, to control reflections as well, if your budget and wife's sense of decor will allow.

Your listening room is the final link in your audio system, the final link in the recording/reproduction chain. Your room's acoustics, with its many variables, have a profound effect on the sound of the music you'll hear, in many ways. Yet the treatment of listening room acoustics is still an untamed wilderness, the most primitive area of today's music reproduction systems. ASC Tube Traps are the most powerful tool yet developed, to help you come to grips with this vital problem and successfully tame this wilderness.

What are Tube Traps? Essentially, cylindrical sound absorbers. Each cylindrical module is about 3 feet long, and there are two models, 9 inches and 11 inches in diameter. The 3 foot long cylinders may be stacked end to end, to form columns that are 6 feet or 9 feet long. These columns should then be stood vertically, in the corners of your room and around its perimeter, every 3 feet or so. The columns (or individual 3 foot long modules) should also be placed horizontally on your ceiling, hung by convenient eye screws. There are also half cylinder models for midwall placement, and other variations we'll get into below.





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Tube Traps vs. Flat Panels

What's the functional difference between ASC Tube Traps and the hordes of flat panel or foam acoustic absorbers on the market? The most important is frequency range. Flat panels of sculptured foam or fiberglass can only absorb acoustic energy from the midrange upward in frequency. They are useless in the bass and warmth regions, and even in the lower midrange. That's like having speaker systems with no woofers. In contrast, manufacturer's measurements of the ASC Tube Traps show uniform acoustic absorption down into the warmth region for the 9 inch diameter model, and down through the upper bass for the 11 inch model.


This contrast has some crucial sonic consequences for you. If you employ flat acoustic absorbers, you'll have to put up enough along the walls to take care of bright reflections from hard surfaces, audible echoes, and lowering excess reverb decay time in the upper frequencies. But this can cause your room to be too dead in the midranges and trebles, which gives a lifeless sound with poor imaging and ambience. And it can cause a skewed tonal balance, with your system sounding too warm, since those absorbers soak up only higher frequencies while leaving the warmth and bass at full level.


Worst of all, these flat absorbers do nothing to lower and control excess reverb decay time in the bass, warmth, and even lower midrange regions. This leaves your system sounding muddy and boomy.


The ASC Tube Traps, on the other hand, don't have these drawbacks.
Because of their cylindrical shape, they can be set to absorb more unwanted upper frequency energy from the room as a whole, while taking up less wall surface area than flat absorbers would. This allows you to leave bare wall areas all around the room, which, as we'll discuss later, is crucial to obtaining good imaging and ambience, while avoiding a too dead sound. Because they have flat frequency response of absorption down through the warmth region and into the bass, they leave your room's tonal balance sounding pretty neutral, instead of too warm, dull, and bass heavy.

Most important, only ASC Tube Traps address, and conquer, the dreaded mud factor.









zelfbouw tubes

The Mud Factor

What is the mud factor?

It's hard for you to hear its pernicious presence, but you sure can appreciate the sonic improvement when it's gone. The mud factor is caused by excessive and excessively long lasting room reverberation in the warmth region, with the adjacent upper bass and lower midrange contributing somewhat. If your room has distinct echoes, excess reflections, or excessively long reverb decay in the upper frequencies, you can easily hear their sonic effects. At upper frequencies, the human ear/brain is very sensitive to timing and directionality, so it can easily detect the objectionable time smearing caused by upper frequency reflections and excess reverb, as well as the distracting directions they come from. But at lower frequencies, the ear/brain is less sensitive to timing and directionality. So it is not actively irritated by lower frequency reflections and excess reverb. Nevertheless, this delayed lower frequency information, ricocheting around your room, is a sea of lingering acoustic mud that does make it much more difficult for you to hear succeeding new musical information coming out of your speakers. As a result of this mud factor, your system will sound muddy and untransparent, throughout the frequency range, but you won't be able to figure out why, because you don't really hear anything wrong with your listening room's acoustics.

Virtually every listening room has this mud factor. Stuffed furniture, carpeting, drapes, etc. are just like the flat absorbent wall treatments, in that they absorb only upper frequencies, so they don't help the mud factor. When your room has this mud factor, you may find yourself constantly turning the volume level up, hoping in vain to hear the music more clearly. But of course, as you turn up the volume level of musical information from the speakers, the sea of mud also rises, so you gain nothing. Finally you run into power amp clipping and emotional frustration. ASC Tube Traps soak up this sea of mud. Suddenly your system sounds much more transparent, at all frequencies, because now your can hear the new musical information coming out of your speakers. And, with your system sounding much more transparent, you'll find that you can enjoy clearly hearing all the music at much lower volume levels. Also, transients will sound louder and more dynamic, since their full amplitude will appear against a background of silence, instead of being half buried in a sea of unperceived acoustic mud.

Note that this finding from our research contradicts conventional wisdom about absorbent acoustic treatment, which has always taught that you need to turn up your volume control and use more amplifier power when you put more absorbent material in your room. Using the ASC Tube Traps to absorb the mud factor not only improves the transparency of the final component link of your playback system, your listening room. It also allows you to use less amplifier power and a more transparent amplifier, while avoiding the blurring distortion of running your power amp into clipping, and giving you better loudness and dynamics.











More and Better Bass

Similarly, using the 11 inch diameter Tube Traps to absorb bass gives you not only better quality bass but also, surprisingly and again contrary to conventional wisdom, more impactive and louder bass. ASC Tube Traps can be used to address and solve a number of bass problems, and thus accomplish a number of types of improvements in bass quality and quantity. The most obvious problem is bass standing waves, the acoustic resonances of your listening room due to its dimensions between opposing pairs of surfaces. This resonant bass ringing of your room sounds just like the ringing bass boom of some speakers and amplifiers. Since IAR Journal 3 we've shown how even a single overshoot in an amplifier's bass transient response can produce boomy, undefined, heavy, and muddy bass. Ringing, such as seen in the bass transient response of some speakers (especially vented bass systems) sounds even worse. Most listening rooms have prolonged ringing at their bass resonant frequencies (and harmonics), so they are the worst offenders of all, completely negating the work you put into the rest of your system to get deep, accurate bass. Again, note that other acoustic absorbent treatments, from flat panels to stuffed furniture, only absorb upper frequencies, and do nothing to solve lower frequency room resonances (indeed, they make the resonances sound worse, by thrusting the lower frequencies into greater prominence as they absorb the upper frequencies only). Some sound studios use very large moving diaphragm panel absorbers (equivalent to a flexible wall or floor) to quell the room's acoustic bass resonances, but these panels are clumsy and expensive, and they have resonances of their own, so they solve one problem but contribute others. The 11 inch ASC Tube Traps, placed at the pressure antinodes of the room's several fundamental resonances plus their low order harmonics, are a compact, convenient, relatively attractive and inexpensive alternative. They are also nonresonant, so they don't add colorations. And they are effective down into and through the upper bass (down to about 50 hz). ASC also makes, to custom order, even larger diameter Tube Traps, which absorb unwanted resonant energy down to 10 hz (a 15 inch diameter model is forthcoming as standard).

The other bass problems are less well known. It is no longer popular to place your speakers in room corners, nor even right against the wall, since this excites the room's resonances worse and also does not give the best stereo imaging. But nowadays, with your speakers placed away from the walls, the distance from the speaker to the nearby wall surfaces corrupts the bass (and warmth region) in various ways. Regardless of their mid and high frequency forward dispersion patterns, virtually all loudspeakers radiate omnidirectionally in the bass and warmth regions (dipoles radiate all frequencies to the rear, but virtuously do not radiate any energy to their sides). Thus, virtually all speakers radiate full energy at the nearby wall, floor, and ceiling surfaces.

For simplicity here, let's consider just the energy directed toward the wall at the rear of the speaker. That acoustic energy will reflect from the wall back toward the listener. So you'll hear a double version of the music, the original which came directly from the speaker and the time delayed reflection from the rear wall. The result is time smeared music (but see below on LEDE). Furthermore, as this reflected acoustic energy passes the speaker on the way to the listener, it combines with whatever new acoustic information is then coming out of the speaker on its direct path to the listener. At the frequency where the distance to the rear wall equals one wavelength, and st all multiples of that frequency, the acoustic energy will be reinforced, giving not only tonal coloration from too much amplitude at those frequencies, but also a boomy overhang (similar to resonant ringing) to the bass quality at those frequencies. Then, at half that fundamental frequency, farther down into the bass, the distance will be half a wavelength, and there will be almost complete acoustic cancellation of your bass by the wall reflection at that frequency, and all multiples of it. If you use ASC Tube Traps to absorb all that low frequency energy when it arrives at the rear wall, it won't reflect back toward the speaker and listener. So you won't get those phony boomy peaks at the full wavelength frequencies. And you won't get those cancellations at the half wavelength frequencies. You'll get a flatter tonal balance with less coloration, and better quality transient information in the bass and warmth regions. Note that the lowest frequency aberration caused by the rear wall reflection was a cancellation, not a peak, and that it was at a bass frequency. Getting rid of this lowest frequency aberration, by using absorbent Tube Traps, will therefore increase the amount and impact of bass energy from your system. Once again, this finding contradicts the conventional wisdom that absorbent room treatment soaks up and diminishes the loudness or power you'll hear from your system st the absorbed frequencies.

The obvious bass application of bass absorbers may be to reduce the room's standing wave resonances, a phenomenon that takes place between pairs of the room's Surfaces. In this role they improve the quality of bass transients and reduce the mud factor by eliminating ringing overhang, while reducing excess bass amplitude (and reverb decay time) at the room's resonant frequencies. But in this more subtle application, the absorber treats a phenomenon that takes place between a single room surface and the speaker. And here it serves not only to again improve the quality of bass transients and lower tonal colorations, but also to increase the amplitude of bass, that bass formerly lost to cancellation interaction between the speaker and a single nearby surface.

Obviously, you should use bass absorbers on not just the rear wall, but also the side walls and ceiling near the speakers. These other single surfaces also cause bass cancellation at other frequencies, so you'll hear your system's bass increased to its correct amplitude at these several frequencies which were being cancelled.

This single surface cancellation effect, correctable by ASC Tube Traps, applies not only to speakers. It also applies to live instruments. Bass viols and 'cellos have some of their natural warmth and bass cancelled by interfering reflections from the nearby floor, with tonal colorations and time smearing caused by additive reflections at other frequencies. So ASC Tube Traps, lying horizontally on the floor, could be used to make live instruments sound more natural. And indeed, the world premiere concert using ASC Tube Traps has already taken place -- and everyone marveled at the more powerful bass they heard from live instruments.

Single surface interference problems also occur between you the listener and the surfaces near you, for the same reasons and in the same ways. So for better bass you should also treat the surfaces around your listening position.

So far, we've spoken of this single surface interference only in terms of complete cancellation and reinforcement (which effectively double the amplitude). But in between these extremes, and at all the frequencies lying between those frequencies where these extreme phenomena occur, there is still unwanted interference from single surface reflections, and there is still some corruption of what should be the correct amplitude level at all these other frequencies, either a gain or loss. You can think of this interference, between direct and reflected acoustic energy, as two sine waves combining, not at their maxima or minima (giving complete cancellation or reinforcement), but rather at some other points during their cycles. Furthermore, as Henning Moller has pointed out, the resultant of these .two sine waves combining, at all those frequencies where their maxima and minima are not synchronized, is a new wave whose phase is all screwed up relative to what it should be, and relative to either the direct or reflected signal. Here you are paying attention to your system's absolute phase polarity, having your subwoofer in the correct polarity, and even phase aligning your subwoofer (which we found to be audibly important in testing the Spica subwoofer) --but then the reflections from nearby surfaces totally screw up the phase of your bass. Absorbing the bass energy at the surfaces with ASC Tube Traps cures all these problems too, and Henning has found that the improvement in bass phase response is audible. This corroborates the work done recently by KEF, in improving the bass phase response of speakers, which also found that correct bass phase response is audibly important (see our report in Hotline 37).


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Flexible Upper Frequency Absorption

As you see, your room has a myriad of acoustic problems in the bass and warmth regions, which are uniquely solved by the ability of the ASC Tube Traps to absorb these frequencies. Now, what about the midrange and treble regions, which are also absorbable by the various flat panel materials. Here the ASC Tube Traps again win out, this time due to their flexibility. After you place all the Tube Trap columns in your room to optimally deal with the various problems above requiring bass and warmth absorption, you can then individually adjust each Tube Trap as to the amount of upper frequency absorption, and as to the direction of upper frequency absorption. One half of the cylinder's circumference has a sheet of material that reflects midrange frequencies (some trebles are still absorbed by the decorative outer material), while the other half absorbs all frequencies. You adjust how much upper frequency energy is to be absorbed, and from which direction, simply by rotating the entire cylinder in its installed location. This user adjustment turns out to be a crucial tool for modifying the upper frequency reflection patterns and time delays reaching your ears, as well as the overall room reverberation decay time at these upper frequencies. The precise reflection patterns from different portions of your room's surfaces, their direction, and their time delay are critical parameters affecting the stereo imaging of your system Once again, the Tube Traps' manufacturer doesn't realize how powerful his product is with respect to this flexible upper frequency adjustment.

There's an interesting story to document this finding of our research in evaluating this product. While optimizing the stereo imaging of our reference system, we sought to determine how sensitive and powerful the positioning and rotation of the ASC Tube Traps were in achieving the best imaging. We had Tube Trap columns set up every 3 feet or so around the perimeter of our reference listening room, each column reaching up close to the ceiling. Note that, because of the huge room dimensions of 25 by 30 feet with a 14 foot cathedral ceiling, a given movement of a Tube Trap column or rotation of it would have proportionately far less effect upon the room and its stereo image than that same displacement or rotational movement in a smaller worn. Therefore, the following findings are conservatively large for smaller listening rooms. We found that, if we moved any Tube Trap column by a displacement of merely one quarter inch in its location, we could hear the difference in the quality of the stereo imaging. And, if we rotated some columns, to change the amount and direction of upper frequency absorption, by as little as 1.5 degrees, We could hear the difference in the quality of the stereo imaging. That's how potent and flexible these ASC Tube Traps are in handling upper frequency reflections!

No doubt at this juncture some tin ears of the ABX double blind switch box persuasion are shaking their heads, muttering that here's another golden eared tweak just imagining that he's hearing some phenomenon that sensitively. Sorry, Charlie. We got proof. We couldn't believe that these ASC Tube Traps could so powerfully and sensitively affect stereo imaging in such a huge room that a mere 1.5 degree rotation would audibly affect stereo imaging. So we set up an experiment to prove it to ourselves. We set up a 6 foot long (2 unit) column on its side, at the junction of ceiling and wall in back of the listener, at a distance of about 10 feet from the listener. In rotating this column for optimum imaging, we found that the front stage was markedly degraded if the Tube Traps were rotated one eighth inch at their circumference from the sonic optimum, which translates into 1.5 degrees with the 9 inch diameter column. Repeated tries at rotational optimization by ear always came up with the same alignment. These two units were centered in back of the listener.

Then, as a further challenge, we added a third unit off to one side. The sonic effect of this third unit was drastically decreased compared to the first two. First because the first two units were already aligned in place, so the third unit could at most have contributed a further third of the total effect upon imaging from this ceiling/back wall junction. Second because this third unit was farther away from the listener, so its sonic effect would be less perceptible at the listening seat (and it wasn't close enough to the side wall to start causing any effects there). Now, with this third unit installed, came the challenge of aligning its rotation by ear. Could an optimum rotation point be heard? Would it seem to be sensitive to this mere one eighth inch rotation? And, most crucially, would this be provable, by the chosen alignment point physically matching the alignment point already chosen and fixed in place on the first two units already aligned? Yes, yes, yes. The outer fabric seam along the length of each Tube Trap indicates the center of the upper frequency absorbent side. After the third unit was aligned by ear to its seeming optimum for best front stage imaging, its alignment was visually checked against the first two units, by inspecting how closely the seams lined up (these seams were out of sight during the optimization by ear, since they pointed upward toward the ceiling). Did the seam of the third unit line up with the seam of the first two units? Yes it did. Within one sixteenth of one inch (about 44 minutes of arc)!










boven:
tube traps & "acoustic lenses"



Upper Frequency Diffusion

You've seen many, many room problems in the lower and upper frequencies that are addressed by the ASC Tube Traps' absorbent capabilities. But the Tube Traps do more than absorb sound. Their round cross section is also perfect for diffusing sound. The half of the cylinder which reflects upper frequency energy will diffuse the sound it reflects, as opposed to flat surfaces such as your room's walls.

What is diffusion, and what do flat walls do that is different? Simply speaking, flat walls reflect an incoming coherent acoustic wavefront straight back out, as a still coherent acoustic wavefront. This helps the ear/brain to identify the flat wall as a source of secondary radiated sound, to hear the colorations introduced both by the time delayed path from that wall and by the nature of that wall's material, and also to hear the time delayed energy itself as a coherent packet that smears the original music.

You don't want the ear/brain to hear where your room's wall is, because that distracts from the correct imaging of the original stage and hall as it was recorded. You don't want the colorations of the wall's reflected energy corrupting your neutral playback system And you don't want delayed energy arriving in tightly bunched coherent packets that the ear/brain can pick out as information, which contradicts the original direct arrival information from the speakers and so confuses the perception of music. But if, instead of being reflected as a coherent unit, that wavefront could be scattered in all directions as it is reflected, these sonic problems would be minimized. If the sound is scattered in all directions as it is reflected, very little of it will come directly from that reflecting wall to you. Most of it will be scattered to other parts of the room, and this acoustic energy will eventually reach you at scattered times, from scattered directions, and with a wide variety of colorations acquired from its subsequent reflections. This is known as a diffuse sound field.

You are surrounded by this ambient, reverberant field of diffuse acoustic energy, but no single part of it sticks out as identifiable in any parameter of time, direction, or coloration. Thus it enriches the ear/brain's perception of space and ambience on the original recording, without being distracting, confusing, or otherwise calling attention to itself. Additionally, a diffuse sound field set up in a good room has a uniformly decaying reverberation tail at all frequencies, with no gaps or severe discontinuities.

Thus, you can set up ASC Tube Traps every 3 feet or so around the perimeter of your room (and at other surface junctions, e.g. the wall/ceiling), as needed to control the room's bass and the warmth region's mud factor. Then you can micro-locate and micro-rotate each tube to deal with reflected energy in upper frequencies. By rotation, you control the amount and direction of upper frequency absorption. And, where upper frequencies aren't absorbed, they're diffused.





Available Models

Which models of the Tube Traps should you buy? The 9 inch diameter full round model is the original, and the only one available until now. We've spent months with this model, learning all the tricks it can do, and there are still aspects to explore. The 11 inch diameter model is brand new, and should be identical except that its absorptive capacity is greater (about 6 sabines across the frequency spectrum), and it extends down to lower frequencies (50 hz vs. 120 hz, according to the manufacturer's measurements). Both factors make the 11 inch model a better absorptive value than the 9 inch model, in spite of its higher cost. This new 11 inch model is also available in a 2 foot long instead of 3 foot long cylinder, which is more economical, and also allows stacking with a 3 foot long section (either 9 inch or 11 inch diameter), to give a 5 foot long instead of 6 foot long column, which might strike some as being more decor conscious. A forthcoming 15 inch diameter model will extend absorptive coverage below 50 hz, down into the low bass.

ASC has announced a third model for the near future, which is a half round section of a 9 inch diameter, 3 foot long tube. This half round cylinder model is for the room's flat surfaces (not corners or wall edge junctions), but that's just where you need the full cylinder's rotation feature, which we found so sensitive for achieving superb imaging from our room, since we could adjust the absorption and diffusion of single surface reflections. This half round model, soon coming off the assembly line, is to be used with its flat side flush against a wall surface. The half round side facing the room is fully absorbent at lower frequencies, extending down about as far (150 hz) as the 9 inch full round model, but with less absorbent capability (5 sabines less). At upper frequencies, the central third of the half round side has a reflective strip running the length of the tube, which reflects and diffuses most upper frequencies back into the room (again, the outer decorative cloth still absorbs some treble energy). Meanwhile, the outer third on each side of this central strip is fully absorbent at all upper frequencies. This makes the half round column effective at suppressing boundary layer support of upper frequencies along the bare wall surfaces, and also keeps the half round columns, spaced at say 3 foot intervals along your walls, from talking to each other with reflected energy. This half round 9 inch Tube Trap model costs just half the price of the full round 9 inch model, so it is a cost effective way of obtaining the perimeter coverage of your room we suggest. Nonetheless, its lack of adjustability for amount and direction of upper frequency absorption should limit its usefulness in tuning your room for best stereo imaging, and we found this feature very important in evaluating the full round 9 inch model. When this forthcoming half round model starts coming off the assembly line, we'll check out this aspect for you and issue a review update.











D.I.Y. tubes, ready for shipment

Where to Install Tube Traps?

Where should you install the ASC Tube Traps? For the present, let's consider doing your room using the original 9 inch full round Tube Traps with which we've had the most experience, plus the new 11 inch full round model for added bass extension.

Let's start with the corners.

A standard rectangular room has eight corners where three surfaces meet, sometimes called tri-corners. These are the four corners at floor level, plus the four corners at ceiling level. These eight tri-corners have a unique property. They are the only locations in your room where every standing wave of your room, at every frequency and in every direction or dimension, has a pressure maximum (and velocity minimum).
Consequently, placing acoustic pressure absorbers at these unique locations accomplishes more to quell your room's many standing waves (resonant modes) than would placing such pressure absorbers at any other locations. ASC Tube Traps are designed to be pressure absorbers, so the most effective place to start using them is in your room's eight tri-corners. This is also the location that the manufacturer recommends - indeed as the only place to employ his cylindrical Tube Traps.



5 februari 2018 ThingMan - met toestemming gepubliceerd



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