|The CARA Test-CD for Room Acoustics is a terrific tool for helping
you understand the characteristic sound colorations of your room and properly
identify deficiencies in sound quality you may have already noticed.
"My new loudspeaker has no bass response!"
With this CD, you will be able to wander the room and hear the variations
in sound quality. You can use this information to find better listening
positions and improve the placement of your loudspeakers.
The CARA Test-CD for Room Acoustics contains 59 test signals, with a
duration of 70 seconds each. These digital signals were computer-generated
and captured to CD using top-of-the-line mastering techniques to create
the best audio signals obtainable from a CD source.
28 pure sine wave tones from 16 to 200 Hz (distortion < -80 dB)
27 narrow band pink noise signals (bandwidth about 1/18 octave) within
the range of 20 to 200 Hz. The center frequencies equal those for the pure
sine wave tones mentioned above (except 16 Hz)
4 special bandwidth limited pink noise signals, 2 * "CARA-Noise" (to analyze
midrange sound colorations), "Polarity-Noise", and a standard pink noise
signal flat between 20 and 20,000 Hz.
The test signals are subdivided into three groups:
Room acoustics describes how room shape, size, and contents influence
the sound experienced by a listener within that room. A sound source
produces frequency-dependent sound waves travelling from the source to
the listener. These waves are reflected and absorbed by the furniture
and walls of the room. The reflecting waves interact with subsequent
oncoming waves, resulting in interference patterns greatly modifying the
sound the listener actually experiences.
A surprising fact in room acoustics is that the size of the room greatly
changes the importance of certain acoustic phenomena. Large rooms
such as churches, theaters, or conference centers, are characterized by
long reverberation times. This effect may considerably deteriorate
speech intelligibility and syllable articulation if not corrected by manipulation
of the room elements. Things such as loudspeaker positioning, delayed
signal lines, addition of absorptive materials, and general room shape
are examples of techniques used to improve the listener's perceptions in
By contrast small rooms suffer from too many reflections. The
frequency dependence of the interaction between direct and reflected sound
waves adds undesired sound coloration. These sound colorations depend not
only on frequency, but also on the actual position within the room.
In small closed rooms, the sound field forms standing sound waves characterized
by nodes (sound cancellation) and antinodes (sound multiplication) which
may have as much as a 1000 times (30 dB) volume difference between them.
Because these standing waves occur over small frequency ranges, the difference
in volumes is not noticable as a whole, but rather as if some vital part
of the sound is unbalanced (e.g. - the piccolo is too loud while the bass
drum is barely heard).