Vehicle Acoustics - JBL GTiAutomotive Application And Installation Manual

Vehicle Acoustics

The acoustics of your vehicle also influence
bass performance tremendously. Fortunately, the
small interior volume of most cars and trucks
boosts low bass output enough to allow for small-
er enclosure sizes while still achieving good bass
performance. As a general rule, below 50-80 Hz
(depending on interior size), bass response
increases at a rate which approaches 12dB per
octave as the frequency decreases. This adds a
significant bass reinforcement to the actual output
of the subwoofer. If this rise in bass is not
addressed in the design of your enclosure, bass
performance may be boosted to the point where it
is actually too strong for some tastes. For others,
there is never too much! The enclosure design
recommendations which appear on the specifica-
Normalized Amplitude Response (dB/Hz)
dB
Vehicle Transfer Function
6
0
In Car Response Curve
–6
–12
–18
Enclosure-only response with
–24 Standard "Optimum" Tuning (42Hz)
–30
–36
5 Hz 10 50 100
Frequency
This graph shows the effect of vehicle transfer function added to an enclosure
using "standard" tuning. Note the peak at 50Hz, with a –3dB point of
approximately 31Hz.
4
tion sheet for your particular model, were
chosen for optimum in-car performance.
You may find them to be different than the
recommendations from formulas used to
design enclosures for in-home or profes-
sional sound-reinforcement applications.
These "Transfer Function Compensated"
tuning recommendations result in small
enclosures with excellent in-car low fre-
quency performance.
JBL SpeakerShop 1.0
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Normalized Amplitude Response (dB/Hz)
Vehicle Transfer Function
dB
6
In Car Response Curve
0
–6
–12
–18
Enclosure-only response
Transfer Function
–24
Compensated Tuning (33Hz)
–30
–36
5 Hz 10 50 100
Frequency
This graph shows the result of tuning the enclosure to compensate for the effects
of the vehicle transfer function. Note that the in-car response is smoother and the
–3dB point moves down to approximately 22Hz.
Normalized Amplitude Response (dB/Hz)
dB
In Car Response with Transfer
Function Compensated Tuning
6
0
–6
–12
In Car Response with
–18
Standard Tuning
–24
–30
–36
5 Hz 10 50 100
Frequency
This is a comparison of in-car response curves with and without transfer function
compensated tuning.
JBL SpeakerShop 1.0
500 1000 2000
JBL SpeakerShop 1.0
500 1000 2000