2008+ Subaru WRX/STI Performance Air Intake Part 5: Sound Testing
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Subaru WRX/STi Performance Cold-Air Intake
Finally, we come to the sound improvements that the Mishimoto intake provides. Everyone loves a nice throaty intake sound, almost as much as the intoxicating burble from a set of unequal-length headers. During our many dyno pulls, collection of data for decibel strength was something we wanted to explore and compare between the factory design and our design.
From the lead engineer on this project:
“The recorded sounds were analyzed to compare the relative decibel strengths across the entire bandwidth of frequencies. The red and blue lines in the graph below (<i>Figure 3</i>) represent the maximum volume achieved for each frequency band during the entire dyno pull.
A note about frequencies: The range of human hearing is typically about 20 Hz to 20 kHz. The majority of the fundamental frequencies fall between 20 Hz and 5 kHz. As a point of reference, some common sounds and their approximate frequency ranges are listed below.
Thunder: 0 Hz to 200 Hz Female singer: 300 Hz to 1 kHz
Lowest note of a bass guitar: 100 Hz Jingling keys: 1 kHz to 5 kHz
Male singer: 100 Hz to 500 Hz
The Mishimoto cold air intake had the most notable volume gain in the 40 to 160 Hz range, which provided the intake with the additional ‘growl’ that was missing from the stock intake. Substantial volume increases also occurred at 125 Hz and 250 Hz, providing the intake with some additional low-end resonant tones and contributing to the ‘throaty’ quality of the sound.”
The tones provided by the Mishmoto intake are a substantial improvement over the factory intake. The added intake growl really adds to the driving experience. Check back tomorrow for the completion of this project and images of the final product!