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Briefly, the interaction of the dispersion pattern of the speaker with the reflective surfaces in the room (and the
variation of both with frequency) creates an in-room frequency response that may vary markedly from the
anechoic response.
9.4 Listening Qualities
We have seen how many speaker systems store resonant bass energy, resulting in ringing and poor transient
accuracy. Now we will turn our attention to the listening experience, and describe how these measurable
properties correlate with our subjective impressions.
There are two main factors which affect subjective low-frequency accuracy, frequency response and transient
response. At low frequencies, these two descriptions are different aspects of the same event.(5) Nevertheless, for
the purposes of this discussion, we will treat these two topics separately as much as is possible.
Frequency Response Effects
As you listen to music, images of the instruments that created the sounds are elicited. For instance, one can tell
the approximate size of a drum from the sound it produces. On a high-resolution playback system, finer details
can be heard; i.e., is the head made of plastic or calfskin? Is the player using light sticks or heavy ones?
A relatively broad-band emphasis (or de-emphasis) of a given frequency range can tend to exaggerate (or
diminish) the relative size of the instruments playing in that range. A useful tool for evaluating these distortions
of size is a recording of a small group of unamplified acoustic instruments made with a simple microphone set-up.
Listening for Size Distortions
Play a recording of this type, with the volume adjusted to achieve a natural playback level. As you listen, create a
mental image of the players based on sounds being recreated. Then ask yourself, "Does this sonic image
correspond to the musical instruments that generated these sounds?"
Is the portrait a natural one, or are certain elements distorted? Does a stand-up bass sound like the correct size, or
is it exaggerated, sounding like it is ten feet tall, or as if the strings are the size of ropes? A speaker with
excessive in-room bass response can create these effects. On the other hand, a speaker system with rolled-off
bass can shrink the size of instruments, turning the same stand-up bass into a cello-sized instrument.
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5 Below about 200 Hz, virtually every woofer operates as a minimum-phase device. This means that the
responses in the time-domain and the frequency-domain are inextricably linked, and that the one generates the