Loudspeakers and Listening Rooms

It is not easy to audition loudspeakers or predict their behavior in a given home. Normal listening rooms differ radically in terms of their interaction with loudspeakers, and this interaction tends to increase sharply as the speaker's frequency response extends into the deep bass and in proportion to its ability to reproduce the details of the soundstage and musical dynamics. As Roy Allison pointed out, over a quarter of a century ago, given rooms can easily pro. duce 10dB swings in bass frequency response at given speaker placement positions and given power levels. More recent studies have shown that small or normal sized listening rooms can produce major shifts in the ratio of direct and reflected sound. and in the impact of the Hass effect on apparent frequency response, phase, and imaging at given points in the frequency spectrum.

For many audiophiles, room treatment is simply not practical for aesthetic or financial reasons, or simply because they live in apartments or homes where treatment would have to extend to the level of rebuilding. Even where such treatment is possible, it has limits. It is possible to after most listening rooms to make a given loudspeaker relatively, flat from about 400 Hz up and to create a balance of reflected and direct sound from a given type of speaker which will minimize room effects in terms of altering the performance of the speaker.

Finding the right mix of trade-offs to suit both your own taste and your own room is one of the rarest prizes in the sport of audio. It means actually being able to enjoy music without having to remember - at least at the subliminal level - that something is always wrong. It also means; being able to get the best out of the rest of your system and music. Being an audiophile is an inherently neurotic pastime, and security in the choice of a loudspeaker is rare indeed.

It is virtually impossible, however, to treat most home listening rooms to the point where you can avoid major swings in bass response below 80 - 100 Hz, and there is no clear consensus as to what room treatment really best minimizes room/speaker interaction in terms of soundstage, or what method of measuring frequency response in a real world listening room is really relevant at the listening position. The fact that room treatment is an increasingly measurable art form with an increasingly good theoretical underpinning does not mean it is not an art form or that respectable theorists agree.

The reader should be aware that any full-range dipole with produce bass cancellation that varies in frequency according to the room and the distance from the rear wall. According to the designer, Leo Spiegel, the Apogee Divas are mechanically tuned in the low - frequency region to provide significant output below 25 Hz. This is accomplishes by mechanically tensioning the woofer ribbon across its geometry. This produces a relatively low "Q". About 50 percent of the output of the speaker is radiated to the rear, however, and the proper balance of energy can only be preserved if the speaker is at least 36-48" from the rear wall and no more than 60". A displacement of three feet from the rear wall will produce cancellation in the area from 70-95 Hz, a four - foot displacement will produce cancellation In the 55 to 70Hz band, and a five - foot displacement will produce cancellation in the 47 to 56Hz band. This means that considerable experimentation in room placement will be needed to get the best overall performance in a given system, but that the user can also do a great deal to compensate for room effects with relatively limited speakers movements.