The Listening Room - B&W electronics dm70 Instruction Manual

The listening room

The listening room
M o s t people have relatively little control over their listening room in
terms of size or shape, but as the environment in which the loudspeaker
is used plays such a big part in the quality of sound we hear, some
comments on room characteristics may be helpful before we proceed
in section 3.
There are t w o aspects of listening rooms which will most widely
influence sound reproduction : The basic dimensions of the room and
large items of furniture controlling the lower frequencies; and items of
soft furnishing together w i t h wall and other coverings affecting the
middle and upper frequencies.
All rooms have resonances, and so indeed does the concert hall, but
in the case of the latter these are so l o w in frequency, and by design,
so well spaced that they add ambience rather than colouration: The
w o r s t example in a listening room or studio would be the unlikely
event of all dimensions being the same and the room forming a cube.
The best case being a relatively large room where all dimensions are
different. Fortunately the w o r s t example is rarely, if ever, encountered
but where a choice is possible as between a square or rectangular
room the latter is to be preferred as the room resonances — k n o w n as
eigentones — occur at spaced frequencies and are therefore of lower
amplitude.
The most pronounced eigentones occur at low frequencies below
approximately 200Hz. In addition to these eigentones there is another
important influence the room has over the lower octaves of reproduced
sound. Due to the relatively small dimensions of the loudspeaker c o m -
pared w i t h wavelengths of sound in the lower octaves, the radiation
pattern or distribution of sound at these frequencies is effectively
spherical. When operating a loudspeaker in a room, this sphere of
sound is contained, to a greater or lesser degree, depending on position
within a series of plain surfaces formed by the walls, floor and ceiling.
This produces a factor k n o w n as 'room gain' and does in fact make
the lower frequencies considerably louder than if, for instance, the
loudspeaker were operated in the open air.
As a result of research carried out into the " r o o m g a i n " and how this
affects loudspeaker performance, the stand of the DM70 has been
specifically designed to give optimum results over a range of listening
conditions.
Before leaving the w a y in which the room affects the low frequency
part of the sound spectrum, a w o r d should be said on the construction