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.

∙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 DAAD’s, (more information is available at www.acusticaapplicata.com )

∙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.

∙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.

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