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8.5 Summary of Recommendations
Now that we have looked at some of the common problems of listening rooms, as well as
their cures, let us summarize our findings and recommendations.
Flutter Echo and Standing Waves
These situations are the result of the room having parallel, reflective surfaces. The potential
problems are independent of the audio system, and need to be addressed at the source. This
means that at least one surface in an opposing pair of surfaces needs to be made less reflective
and/or non-parallel.
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Low Frequency Absorption
If a problem exists with standing waves, it is the low frequencies that will need to be
addressed. Remember that the absorption spectrum of different materials and objects is not
uniform. That is, some items will absorb only high frequencies, and some objects may only
absorb the middle frequencies. At low frequencies, about the only common item that can
absorb a meaningful amount of energy is heavily upholstered furniture. Another effective
means of absorption is the use of Tube-Traps, from Acoustic Sciences Corporation.
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High Frequency Absorption and Room Symmetry
Since flutter echo is a high-frequency effect, it becomes much easier to manage potential
problems in this area. Almost any item attached to the walls will be less reflective at high
frequencies than the bare walls themselves. Draperies, wall hangings, paintings, bookshelves
and other items will normally be present in the room, and will usually eliminate any possible
problems. If flutter echo is still audible, a fabric wall hanging provides an effective and
attractive cure.
Additionally, it is desirable to maintain a degree of left/right symmetry in the room to
preserve a balanced acoustic "space". For example, if your listening room has full length
draperies along the right wall, and the left wall is bare, slap echo will not be a problem.
Nonetheless, the sound-stage may be somewhat distorted, and it could be beneficial to place a
fabric hanging or tapestry on the wall opposite the draperies.
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Parallel Surfaces
Although it is not generally possible to make the walls non-parallel, the same effect is
achieved by breaking up the large, flat surfaces with furniture and shelving.