Fine Tuning
were wired in absolute phase (speaker positive to amplifier positive, and speaker negative to
amplifier negative), there may be acoustical anomalies in your vehicle that manifest
themselves as phasing issues. In a car, a host of things are working to interfere with the
driver's output: reflections, path length differences, arrival times, etc. The result is that,
although the drivers are moving in unison, they don't sound like they are in phase from the
listening position. By the time the sound reaches your ear, some of the waves are out of phase
to each other, creating "blurring" of the image, loss of midbass, holes in the frequency
response, etc.
To check for acoustical phase, you can use media that you are familiar with that contains a
strong center image. Does the center image seem coherent and focused, or does it seem
confused and difficult to locate? If the center image (such as a vocalist) seems confused,
blurred, or difficult to locate, the Legatia L3’s may be acoustically out of phase. If you are
unsure, you can purchase a test CD (readily available from most places) that includes an “in
phase” and “out of phase” track to quickly identify if the system’s acoustic phase is correct.
We use the International Auto Sound Challenge Association (IASCA) Set-Up and Test CD,
which divides the phasing coherency tracks into three intuitive frequency bandwidths: 20 - 200
Hz, 200 - 2,000 Hz, and 2,000+ Hz to easily check if pairs of speakers are in-phase or out of
phase.
Should you find in your testing sequence that the system appears to be acoustically out of
phase, you might be able to quickly remedy this situation by reversing one speaker’s polarity
by switching the positive and negative wires on the speaker, so that they sound in phase from
the listening position. You might find that all speakers on one side of a vehicle (midbass,
midrange, and tweeter) need to have their polarities switched to create a focused center
image. Another remedy might include the provision of acoustical treatments, as explained
earlier, to help absorb reflections, which may alter the acoustical phase of the sound. Finally,
there are higher order physical reconstructions that can be done to the listening space, such
as removing hard surfaces that create early reflections, nodes and antinodes, by changing the
interior of the vehicle to better accommodate more ideal pathlength differences and removing
obstructions to the direct sound wave.
Time Correction and Amplitude Equalization
With crossovers and acoustic phase sorted, it is now time to tune the system with some time
correction, if necessary, as well as some amplitude equalization, if you have the hardware
available in your system to do this.
There really is no science to setting time correction “in the field” without expensive test
equipment. If you have test equipment, it is much more an objective measurement function,
but alas, more often than not, it is more of an art that requires trial and error. The best
advice is to approach time correction carefully and use only the minimum to achieve the
results you desire. And it should be noted that you may find that adjusting the time correction
will effect the acoustical phase you just got done setting as well.
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