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This page describes the audio system and the sound deadening efforts
in the car.
Audio System
The original Maxima sound system was quite good for its
time. It was an 8 speaker system (4 component sets)
hooked to a Clarion head unit. The modified design is
a 5 speaker setup using component sets in the front and
one sub woofer in the rear deck.
Briefly, this sound system was designed for good ears
and shallow pockets. It was also designed as a "sleeper"
audio system. Notice how each of the components are hidden
in one way or another. The system consists of all Peerless
brand drivers (two tweeters,
two
6.5" woofers,
and one 8" sub woofer), custom crossovers, and a
4 channel Hifonics Eagle amplifier. Descriptions of each
component
and it's setup are presented here. Once some of the kinks
are worked out in the sub woofer install, frequency response
and phase tests will also be presented here.
Front Component Set
The front component set uses a pair of Peerless 50mm
ring dome tweeters, a pair of Peerless 6.5" CSX woofers,
and a custom set of crossovers with a fixed crossover
point and individual speaker phase switches (0° or
180°).
Tweeters
The tweeters are Peerless 50mm ring dome tweeters number
841939 and their data sheet can be found here.
The picture to the right shows the new tweeters just before
installation.
In an effort to preserve the original mounting location,
the original Maxima tweeters were cannibalized to make
mounts for the Peerless
tweeters.
The
baskets were
fully
removed
leaving
only the
rim from original speaker. An aluminum strap
was formed and riveted to this rim and that became the
new mounting location for the new tweeters. They were
then
quite easily mounted in their original front mounting
location on the dash reflecting off the windshield.
Woofers
The woofers are Peerless 6.5" CSX woofers number
850518
and their data sheet can be found here.
The picture to the right shows the new woofer (on the left) compared to the
original woofer (on the right).
Again, to keep the original mounting location, the baskets
were cut out of the original Maxima woofers. Four custom
machined 13mm aluminum spacers were
mounted
to
the
rim
of the original
speaker, which in turn provide solid mounting locations for the 1" spacer
that is mounted on the door panel. A standard speaker grille was mounted
to help retain the boring stock look.
Crossovers
The crossovers were custom designed and [originally] fabricated
by Madisound Speaker Components, Inc. They have a crossover
frequency of 3.7Khz and built in impedance compensation
to match the woofer and tweeter. Their design, although
functional, needed to be tweaked for this application. The
picture to the right shows the final product.
The modifications were small, but quite helpful. The picture
to the left shows the modification steps taken (1 being how
they came from Madisound, and 4 being the final product). The
crossovers together originally covered an area of 9.5" x
8" (larger
than the amplifier)
and
had all
blade
type
connectors.
Some components were removed (the built in high-pass filter
since the amplifier has an adjustable one built in) and the
rest of the componets were relocated to one end of the boards.
The PCB was cut to a total size of 4" x 8" which
is less than half of their original combined size. A separate
board was
mounted on risers for screw terminals (to replace the blade
connectors) and for individual speaker phase switches (0° or
180°) to test the system with different combinations of
matching/unmatching phase.
So far the best sounding setup is with one tweeter out of phase, but the testing
is not yet complete.
Sub Woofer
The sub woofer is an 8" Peerless DVC Woofer number
831858 and its data sheet can be found here.
The picture on the right shows the woofer. It weighs in at
only 4.5 lbs and has quite some potential.
The woofer is mounted in the rear deck of the Maxima in
an infinite baffle configuration. This helps keep the added
weight down (for autocrossing) by getting rid of the need
for a box and allows for a higher output at lower power levels
(allowing the use of a smaller amplifier). The rear deck
was modified and upholstered with grille cloth to give the
illusion of a solid rear deck.
Amplifier
The amplifier is a 4 channel Hifonics Eagle amplifier. With
one pair bridged, It is rated at 2 x 45w RMS (for the components)
and 1 x 150w RMS (for the sub). It has a built in adjustable
high and low pass for the front channels and for the sub.
Currently, the sub has a highpass at 10hz and lowpass at
80hz and the highpass for the components is also set to 80hz.
The next step with the amplifier is to test the front components
full range with the sub vs. the front components highpassed
with the sub, but first the woofer mounts are being modified.
The amplifier is mounted under the passenger seat where
the original ECU was mounted. It fits in almost the
same spot, so there is plenty of clearance between the amplifier
and the seat. It is shown to the right with the front protective
cover removed for
adjustments.
Sound Deadening
Current Interior Sound Levels
A graph of the current interior sound levels can be seen below. The
MAP axis is essentially throttle position, the speed axis
is the car's speed, and the SPL axis is the sound pressure
level measured in dBA using an analog Radio Shack Sound Level
Meter. This test was taken with two passengers heading north on
I-87 in New York on a recently paved section of road from
mile marker 121 to 140. The graph is smoothed from 73 data points.
This is the baseline and test method that will be used to test after
each panel is sound deadened to see the improvements
step by step. The process will be automated using a laptop
to ensure consistent recording of data, and a test will be
done immediately before and after each modification.
Trunk Deadening
The first part of the car to get covered was the trunk to
test the liquid latex purchased from McMaster-Carr. It required
some thinning with water, and took longer than
specified to dry, but the results were good. It applied quite
well with a brush, and took two coats to get
decent coverage.
This was basically the test to see if this latex vibration dampener
should be used on the rest of the car. The decision
has been made to use it on the inside of the outer
door skins, on the roof, and some parts of the
floor. An asphalt based mastic sheet will be used
on the inner door skins, firewall, and transmission
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