We continue reviewing the groundbreaking aritcle from 1989, published by International Audiophile Review. In this section, editor J. Peter Moncrieff explains what he terms as a “basic setup” for TubeTraps in a critical listening room.

To some, this degree of TubeTrap treatment in their rooms may seem daunting, expensive, or visually overwhelming. To others, this is mandatory to wring every last ounce of quality from their exquisitely curated sound reproduction system. Ask yourself: how much did I spend on that last power amplifier upgrade?

After reading this excerpt, consider the value offered by TubeTraps for allowing you to truly hear the quality of your system instead of the artifacts of your room.

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Basic Setup

(excerpt from “Optimizing ASC TubeTraps” by J. Peter Moncrieff)

To obtain all these additional sonic benefits available from TubeTraps, the basic tactic is simplicity itself (which should be a welcome relief from the complex considerations involved above for bass control). You can accomplish reflection control, for the entire perimeter of your room, by simply placing a 9 inch TubeTrap column (the skinniest and least expensive) every 3 feet or so around the perimeter of your room (except for the locations where you have already installed bass TubeTraps for optimizing bass control).

Figure 3 shows such an installation, including the bass TubeTraps from Figure 2, plus the added 9 inch TubeTrap columns for reflection control around the perimeter of the room. If by chance you did not fill all of the locations of Figure 2 with bass TubeTraps for bass control, then these locations should be filled now with 9 inch TubeTrap columns for reflection control (that includes at least the two horizontal rows across the ceiling, which is also a surface requiring reflection control).

In fact, Figure 3 shows the general TubeTrap layout in the plan of our lab’s master listening room, which is 30 feet long (front to back) by 25 feet wide, with a 14 foot cathedral ceiling. Most other listening rooms are smaller, so they would require fewer columns of 9 inch TubeTraps for adequate perimeter control.

Basically, we recommend that you place reflection control TubeTrap columns every 3 to 4 feet around the perimeter (use whatever distance within the 3 to 4 foot range that works out to evenly divide into your room’s exact dimensions).

On the front wall, in back of the speakers, we recommend you place these columns every 2 to 3 feet; or perhaps, just in back of each speaker, place an extra column or shorten the distance between columns somewhat. The reason is that energy from the speaker going straight back to the front wall, and then reflected straight back toward the listener, is especially detrimental in terms of time smearing and degrading spatial imaging.

We use only two horizontal columns across the ceiling, because our ceiling is very high and pitched, so it does not create severe reflection problems. But a low and flat ceiling would create severe reflection problems, and so would require more horizontal rows, perhaps even a row every 3 to 4 feet, spaced to match the columns along the side walls.

In addition, we have found that it helps coherence and stereo imaging to have a pair of columns placed physically halfway between the speakers, about 6 inches from each other, as shown in Figure 3. This finding owes a debt of thanks to Monster Cable, who marketed an acoustically absorbent dividing screen for just this purpose.

Our pioneering article on ASC TubeTraps in Hotlines 39 and 40 introduced this concept of perimeter reflection control, and discussed its importance. Even the manufacturer of TubeTraps had not recognized the virtues of using his product in this manner. Since then, a number of high end listening rooms have employed this strategy, with impressive sonic results. In fact, a room so completely treated with TubeTraps for perimeter reflection control has become known in the industry as a Moncrieff room.

On a recent visit to Italy’s top high end dealer, Absolute Sound, we witnessed such a room, and with some fine tuning using our trained ears, we were able to obtain superb sonics and imaging from Goldmund’s premier system set up in this room (the room did have a low ceiling, and did not have the required horizontal rows on the ceiling to control this, but otherwise had excellent perimeter reflection control).

Placing 9 inch TubeTrap columns every 3 feet or so is necessary to control the dreaded mud factor. Why? Recall that the mud factor predominates from 100 hz to about 400 hz (where surface mounted absorbent foam or fiberglass is totally ineffective). The wavelength of 500 hz is about 2.25 feet. Thus, placing perimeter control 9 inch TubeTrap columns every 3 feet, leaving 2.25 feet of blank wall space between columns, breaks up every other half wavelength up to about 500 hz. A half wavelength is the shortest amount of an acoustic wave that can reflect, at the pertinent frequency.

It is undesirable to allow several half wavelengths to accumulate along a reflective wall; this would create a coherent reflected packet of sound from that segment of the wall (or ceiling). One example is shown as the arrow in Figure 3, coming from the left speaker and reflecting from the side wall toward the listener (such coherent reflection packets would occur from all surfaces around the perimeter, unless they are controlled). This coherent reflected packet would be heard as a distinct sound source, which smears the music signal both temporally and spatially, creating obscuring mud and degrading stereo imaging. Recall that incoherent random reflections are valuable sonic assets, but coherent directional energy packets of reflected sound are detrimental.

Is a 3 foot spacing close enough? It seems to be. Breaking up every other half wavelength seems adequate to insure that no large coherent packet of sound will be reflected from any one spot around the room’s perimeter. This spacing seems adequate to control the mud factor, between 100 and 400 hz.

Above 500 hz the wavelengths are short enough so that the blank wall space between columns would reflect some coherent packets. But two other factors come into play to alleviate potential problems above 500 hz. First, these shorter wavelengths tend naturally to bounce all over the room more randomly, hence to become randomly incoherent by themselves. Second, the round shape and 9 inch dimension of each TubeTrap column begin to aid in this random scattering of the shorter wavelengths above 400 hz, because this is the frequency where the TubeTrap’s reflective side begins to reflect, and also begins to act as a cylindrical diffuser (this diffusion takes full effect at all the frequencies above where the 9 inch diameter is itself equivalent to half a wavelength, which is 550/.75 = 733 hz). Thus, frequencies above 400 hz, and certainly above 733 hz, are randomly scattered into incoherent reverberant energy which helps the music and the stereo imaging, rather than harming them.

In sum, it is both necessary and sufficient to place TubeTraps every 3 feet or so around the room (and perhaps across the ceiling), for adequate perimeter reflection control of frequencies above 100 hz. Incidentally, we recommend leaving the room walls absolutely bare behind the TubeTraps, so they are fully reflective of higher frequencies wherever the TubeTraps aren’t. If the resulting room acoustic is too bright for your taste, with all TubeTraps in place, then you can hang some attractive soft surface absorbers on the walls between (and behind) the TubeTrap columns.

Don’t you love the phrase “necessary and sufficient”? Who wants to waste money and time on system upgrades that they cannot hear, and who wants to knowingly thwart their own goals of achieving maximum fidelity? Presumably, nobody reading this email.

Remember, everything the 9″ model used in this setup can be done even better by a Model-11 TubeTrap Isothermal. Better mud factor control, fantastic treble diffusion properties, at only a very slight size increase. And thanks to modern production techniques, the value is better as well.

Figure 6 shows a preview of upcoming excerpts, but you can start playing around any time with the TubeTrap reflector orientation to modify the sound stage properties indicated above. When Mr. Moncrieff explains how and why he chose these particular orientations, you’ll have some first hand sonic experience to remain one step ahead.

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