© Hybrid Audio Technologies, 2010
Page 17 of 22
change. The ITD, which results from the absolute difference in path length from the source to
the ears, remains approximately constant as distance decreases. From this we learn:
•
ITD is the dominant factor for frequencies below about 500 Hz;
•
A combination of ITD and IID are dominant for frequencies between approximately 500 Hz
and 2,000 Hz; and
•
IID, in concert with HRTF, are dominant above about 2,000 Hz.
These are generalizations, and are subject to the size and shape of one’s head and torso, and
size and shape of the outer ear (the folds and ridges of the ear), but in general, the above is a
good guideline for establishing ITD, IID and HRTF thresholds for the human auditory system.
Because the I5 midbass’ ability to play into the sub-200 Hz range, an effect clearly dominated
by ITD, up to and including frequencies exceeding 6,000 Hz, an effect clearly dominated by
IID and HRTF, placement of this driver is extremely important. The driver should be placed as
far forward as possible in the vehicle to optimize ITD. Lateral (forward to back) placement is
much more important than horizontal placement (up and down). This is because of the brain’s
ability to process sounds such as spectral envelope cues, and use a phenomenon known as
the “precedence effect”; the brain can be easily “fooled” into thinking a sound stage is high
with kick panel or floor-mounted speakers (a word to the wise: the best place to put a set of
speakers is not always “up high”, as most vehicles do not offer an amicable location in the
dashboard or a-pillars for good image placement for both seated passengers, especially in the
critical frequencies sub-500 Hz). In addition to the time equalized placement of the drivers,
the end-user must also consider that above approximately 2,000 Hz, intensity plays a key role
in good sound staging and imaging. Therefore, the Imagine midbass’ should be placed in an
area where intensity differences can be equalized, either mechanically or electronically, to
ensure good imaging and sound staging.
The lesson to be learned is that, like Lesson Two, the Imagine midbass should be placed as far
forward from your listening position as possible, and every effort should be made to optimize
time and intensity domain characteristics of the installation.
Lesson Four: Point-Sourcing
The term “point-sourcing” is often used to describe the technique of having a single pair of
speakers in an installation cover the majority of the critical middle band frequencies. In many
installation scenarios, the Imagine midbass could be considered a point-source speaker driver,
because it has the ability to reproduce six octaves of tones. Point-sourcing, if done correctly,
can lend itself to a variety of valuable attributes, including precise image definition and stable
sound staging character. By applying Lessons 1-3 above, the Imagine I5 can be used as a
point-source midbass driver to achieve excellent staging and imaging results.
The lesson to be learned here is that the I5, given its wide-bandwidth design, can faithfully
reproduce as much as six octaves of tones, and would make a valuable addition to any sound
system as a point-source driver for the spectrum comprising vocal imaging cues.
