Hybrid Audio Technologies I57-2V2 Installation & Reference Manual Download Page 19

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The first principle to understand is that below 200 Hz, acoustic treatments are rendered virtually
useless. It is Hybrid Audio’s assertion that only those frequencies above 200 Hz benefit from the
use of treatments, given that a 200 Hz waveform is about 1.7 m long; 1.7 meters is less than or
equal to most vehicle widths. This is also the frequency where we believe pure tones in the vehicle
are going to be difficult, if not impossible to localize. Finally, most vehicles exhibit a Schroeder
Frequency (Fs) between 50 at 125 Hz; the Fs (or cabin-gain frequency) is vehicle dependent, and
is the frequency at which resonances become so tightly packed in frequency and space that the
acoustical properties of the vehicle behave quite uniformly. (As an aside, one significant benefit
of car audio sound systems is that frequencies below the lowest room resonance increase at a
theoretical 12 dB/octave…it’s no wonder car audio systems have such great bass!)

Acoustic treatment can be very effective above 200 Hz, depending mostly on the polar radiation
pattern of the speaker. In the case of the Imagine midbass, the polar radiation pattern is quite large
at lower frequencies, with a narrowing of the radiation pattern (“beaming”) at frequencies into the
treble bandwidth.

Should the Imagine midbass be placed in the kick panel locations, one may find that a notable
improvement can be made by adding acoustical treatments, such as open-cell foam, into the
underside of the dashboard. Likewise, should the midbass, or in fact the I1 tweeter be placed up
high on a-pillars, or in the dashboard, where comb filtering (reflective summation and cancellation
off of a hard surface, such as a windscreen) may become an issue, a dashboard “mat” or other soft
furnishing may be a noticeable improvement. It will require trial and error to get it right, but the
learning is in the experimentation!

Advanced Installation Conclusions

Sadly, there are no rules in mobile audio, only several hypothesis and theorems that seem to work
for most vehicles. Your vehicle may be different, and defy everything we know, and everything
written in this manual. You may find that getting that rich, detailed sound that you crave may
require some experimentation and a lot of work to make it right. Or you might be fortunate to have
a vehicle that sounds excellent with minimal work. Have patience and work through the issues;
the result will be a rewarding musical experience in your vehicle! Just remember, it is critical to get
a reference, as detailed in Lesson 5. Go out and become a student of music and audio, learn, and
improve your audio system one step at a time. The journey is exciting and rewarding!

What we have included above is only a very brief primer to the world of high-end mobile audio
systems. We invite you to read more by going to our downloads page at

hybrid-audio.com

Section II • Moving Forward

Advanced Installation of the Imagine Component

Systems (Continued)

Mounting baffle dimensions

While building baffles is important, it is notable that mounting baffle size is equally important.
All mounting baffles should be kept as small as possible with respect to the size of the speaker.
The purpose of using a small baffle is to avoid the potential for low amplitude diffracted sound
waves becoming summed with the incidental waves. A narrower baffle also becomes increasingly
important as frequencies range into the Imagine midbass’ upper bandwidth, where the power
response is more uniform and incident and reflected waves are indistinguishable. In practical
terms, keep baffle dimensions small with respect to the size of the Imagine midbass, chamfer or
round sharp edges (including, in particular, the mounting hole’s rear inner edge), flush-mount
the speaker whenever possible, and use shallow, surface-mounted hardware. Also, remove all
unnecessary protrusions from the baffle surface.

Acoustic Treatment

A considerable benefit can be made to any mobile audio system with the select placement of
acoustic treatments. The purpose of using acoustic treatments is to reduce the amount of reflected
energy in the hostile automotive environment, and hear more of the direct sound being emanated
from the speaker. It is akin to the signal to noise (S/N) ratio in a piece of electronics, where the
signal could be considered the direct energy coming from the speaker, and the noise could be
considered the reflected waves off of nearby surfaces, such as windows, hard center consoles and
door panels, windscreens, and etc. A word of warning though: there is a fine line between too little
and too much acoustic treatment; just as some vehicles can benefit from some selectively applied
treatments, there is a point where the vehicle can begin to approach “semi-anechoic” conditions,
and lose its liveliness, which is not ideal. Reflections are all around us, and are a part of our
day-to-day lives. It is our opinion that some lateral reflection is a good thing; it helps to establish
stage boundaries, and gives the recoded playback and more visceral and “believable” sound.