If your room is smaller than ours, you won’t need as many TubeTraps for a complete perimeter reflection control system. But even this might be out of reach of some of your budgets. If so, don’t give up. Some TubeTraps are better than none. But which are the most essential TubeTraps for a minimalist economy system? Our recommendations are shown in Figure 4.
Let’s start again with controlling the bass fundamental. The three bass TubeTrap columns shown at the back of the room (bottom of Figure 4) accomplish this. These should probably be 16 inch models, depending on your room length, with the center rear being perhaps a Super 16.
We’ve shown 16 inch quarter round models in the rear corners; they are much less expensive, while still offering good absorption down to low frequencies. You can save more money by using only a single TubeTrap at each location instead of a stacked set making a full floor-to-ceiling column, but of course this will not absorb as much energy (which might sound better for your taste in low bass).
Bear in mind that the more economical half and quarter round TubeTrap models come only in 5 foot high sections, while the full round models (preferable because they offer rotational control of perimeter reflections) come in your choice of 2 or 3 foot high sections.
If your taste or circumstances suggest that you do not want to control the lowest bass resonance fundamental at all, then you can eliminate these three back wall bass TubeTrap columns entirely. But then you should still retain some absorption directly in back of the listener for the warmth region and higher frequencies. The most economical model for this would be the 9 inch half round, which is a single 5 foot high unit (however, you might still want to retain a bass TubeTrap at this center rear position for controlling the upper bass boom of the room’s second harmonic side to side mode; see below). Note that the half round models are available in three versions: with the high frequency reflective strip in the center, or offset to one side, or none at all. In this back wall location, use the version with no reflective strip.
Figure 4 also shows bass TubeTrap columns at the midpoints of the side walls. These are to offer additional control of upper bass boom, beyond that afforded by the three bass columns at the back of the room. These columns can be a step down from the models at the back of the room, since they absorb the second harmonic rather than the fundamental of the front to back room mode (on the other hand, you might want to use these side columns also for more control of the fundamental of the room’s side to side mode, in which case you should select the TubeTrap model with a bass cutoff low enough to include the frequency of the room’s side to side fundamental). If you don’t want more control of upper bass boom beyond that accomplished by the three bass columns at the rear, then these midpoint columns can be changed to the more economical 9 inch half round model (use the version with the offset reflective strip, and orient the Trap so the reflective strip points toward the back of the room).
If you have decided to eliminate control of the front to back fundamental, by deleting the three bass TubeTraps at the rear, then it will surely be important to retain these side midpoint TubeTrap columns as bass units, in order to control the upper bass boom of the second harmonic of the front to back mode. Similarly, it would then also be important to retain the center rear column as a bass TubeTrap, in order to control the upper bass boom of the second harmonic of the side to side mode (you might even want to add a bass TubeTrap column at the center front wall of the room to help in this; such help may be needed because you have eliminated the rear corner bass TubeTraps, which worked to control the side to side second ham1onic as well as the fundamental).
So much for bass control; now, on to reflection control. It’s important to provide reflection control directly in back of the listener (as already discussed) and also the speakers. These are straight reflection paths which would degrade temporal coherence of the music, ruin imaging, cause tonal colorations, and contribute to the mud factor. These reflective paths should be short circuited for the full spectrum, from the warmth region up. To accomplish this, use 9 inch half round models (preferably full ceiling height columns, but it would suffice to use single 5 foot high units, which are as tall as the speakers in front and as the seated listener’s ears in back). Use the version with no reflective strip.
As we saw in the measurements above, it’s also important to control the angled primary reflection paths from the speaker to the side wall to the listener. This is accomplished by using two half round 9 inch models per side, as shown in Figure 4. Use the version with the offset reflective strip, and orient the TubeTraps so that the reflective strip points toward the back of the room (bottom of the picture). The reason for this orientation is that we want these reflection control TubeTraps to fully intercept and break up the sound coming directly from the speaker, which will arrive at the front side of the half round. But the rear side of the half round encounters random incoherent reverberant energy (Damaske effect) that has already been around the room and so is significantly delayed (Haas effect); this energy we want to encourage, by diffusing and reflecting it further. Note again that, if you have chosen to eliminate the bass TubeTraps at the midpoint of the side walls, then these too should be converted to the 9 inch half round model, with the offset reflective strip pointed toward the back of the room. This would make three half rounds along each side wall, unless you have a small room, in which case two on each side might do (a handy rule of thumb is this: start just forward of the speakers along the side walls as shown, then space them every 3 feet or so, and stop before you get to the side of the listener, as shown).
Figure 4 does not show any TubeTraps hung horizontally across the ceiling. If your ceiling is flat, it may be important to also include some rows across the ceiling. The model you select depends upon the problem being addressed. If there is some upper bass boom from the floor to ceiling mode, then a row of bass TubeTraps hung across the center of the room will help. If there is still too much mud factor, then some half round rows across the room should help; mount them to the ceiling just where you’ve placed the half rounds along the side walls (with their reflective side also pointed towards the back of the room).
This economy TubeTrap setup won’t sound nearly as subtly refined as the full fledged setup of Figure 3, but it will provide most of the basic sonic benefits to some degree. That’s a lot better than the typically seen setup of just four TubeTrap columns in the corners.
