TubeTrap Diffuser Alignment

This issue we share the next section of a groundbreaking article from 1989 by IAR. Editor J. Peter Moncrieff explains how one can adjust the rotational position of TubeTraps to improve the soundstaging, coherence, ambience, and depth of your finely crafted sound system.

And here’s a secret worth sharing: following these guidelines can even allow a mediocre stereo setup sound engaging, immersive, and dare we say, high-end! You may find yourself searching for that next upgrade…

Read the full PDF

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

Alignment of TubeTraps

ASC TubeTraps are designed to absorb the full frequency spectrum (down to their bass cutoff) on one side, but to reflect and diffuse most of the frequency spectrum above 400 hz from their other side. That engineering feature becomes a very pow­erful and flexible tool for precisely adjusting perimeter reflec­tion control.

Recall that we spaced TubeTrap columns about 3 feet apart to control the mud factor, between 100 hz and 400 hz. The entire spectrum above 400 hz, include fog the midrange and trebles, is a different matter entirely. It consists of short wave­lengths which are directional, and which can be directionally steered to sonic benefit, rather than simply absorbed every­where.

By simply rotating the cylindrical TubeTraps, you can de­termine how all frequencies above 400 hz will be steered in your room (with the half round model, you are more limited, and you must preselect and orient the reflective direction if any). The subtlest change in rotation of any cylindrical TubeTrap in the room can make a significant difference in truly op­timizing the sound of your system (that’s why we recommend the full round rather than half round models, if you can afford them).

Rotating TubeTraps to absorb energy (above 400 hz) on short primary reflection paths (within the Haas window) can work wonders to improve stage imaging and coherence, and eliminate glary hot spot colorations. And rotating TubeTraps to reflect and diffuse later reverberant energy on long secondary, tertiary, etc. paths can work wonders to improve imaging am­bience and depth.

The basic strategy is shown in Figure 5. The line radiat­ing from the center of each circle represents the seam sewn along the length of each TubeTrap; this is the direction of maximum high frequency absorption. The setup shown in Fig­ure 5 will give decent performance, but it really intended just as a starting point, from which you should further fine tune by ear. If you have also installed any horizontal rows across the ceiling, they should be rotated to point similarly into the room as the equivalent TubeTrap columns at that point along the side wall, and then fine tuned from that starting point.

The sets of TubeTrap columns along the side walls that are off to the side of the listener are an interesting case study. The Damaske effect says that you can best hear the hall ambi­ence in a recording when randomly diffuse incoherent informa­tion is presented at the side of the listener’s head. Thus, all TubeTrap columns along the side walls (and rows across the ceiling) are rotated to optimize the following two factors. Ab­sorb those unwanted coherent packets of energy coming along the short reflected path from the speakers to the side walls to the listener (especially those that come at the listener from his front). And meanwhile reflect and further diffuse reverberant en­ergy that has come on a long, multiple reflected path and is al­ready incoherent and delayed (especially that which will come at the listener from his side).

Meeting these two desiderata simultaneously yields the ro­tational alignments seen in Figure 5. If you look closely, you’ll notice that the seams of the TubeTraps near the speaker along the side walls point almost perpendicularly’ into the room. Then, as you go backward in the room toward the listen­er, the rotational alignment of each successive column pro­gresses toward having the seam point parallel to the side wall, and toward the front of the room.


tube trap from ascThe reflector buttons seen here are positioned opposite the seam, and indicate the midpoint of the treble-diffusing half of the TubeTrap.

This progression is in part a natural consequence of hav­ing each column point directly at the nearest speaker, for maxi­mum absorption of the short path energy. But it also serves to present to the rear part of the room. and to the side of the lis­tener, a progressively increasing amount of reflection and diffu­sion of the reverberant long path energy in the room. By the time we arrive at the column directly to the side of the listener, the seam is pointing directly into the wall, for maximum re­flection and diffusion of reverberant sound here.

A further subtlety. You’ll notice that some of the side col­umns are shown with two lines radiating from them. This indi­cates that the bottom TubeTrap is rotated to have its seam pointing more perpendicularly into the room, while the top TubeTrap has its seam pointing more parallel to the side wall, or more into the side wall. If your ceiling is tall enough so that you are using a stack of three TubeTraps per column, start off with the middle TubeTrap oriented the same as the bottom one.

Why do this varying rotation? Because the speakers and the listener’s ears are closer to the room’s floor than to the ceil­ing. Thus the unwanted short path that we want to absorb is handled by the bottom TubeTrap. Meanwhile, the top TubeTrap sees mostly long path energy that has already been through multiple reflections, which we wish to encourage. So we orient the bottom TubeTraps for more absorption, and the top TubeTraps for more reflection and diffusion. Feel free to explore the possibilities of setting other columns with different rotations for the bottom and top TubeTraps.

Now you know a bit more about how to really get the best out of your TubeTraps. And you also know what you would do if only you had another half dozen TubeTraps. Oh, the possibilities.