JBL GTiAutomotive owner manual Vehicle Acoustics, JBL SpeakerShop

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-

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.

Normalized Amplitude Response (dB/Hz) JBL SpeakerShop 1.0

dB			Vehicle Transfer Function
6	In Car Response Curve
0
–6
–12
–18		Enclosure-only response
–24		Transfer Function
		Compensated Tuning (33Hz)
–30
–36
5 Hz	10	50	100	500	1000	2000
			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) JBL SpeakerShop 1.0

dB	Vehicle Transfer Function
6
0
–6	In Car Response Curve
–12
–18	Enclosure-only response with
–24
	Standard “Optimum” Tuning (42Hz)

–30

–36

5 Hz	10	50	100	500	1000	2000
			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.

	Normalized Amplitude Response (dB/Hz)		JBL SpeakerShop 1.0
dB
		In Car Response with Transfer
6		Function Compensated Tuning

0

–6

–12

–18			In Car Response with
–24			Standard Tuning
–30
–36
	5 Hz	10	50	100		500	1000	2000
					Frequency

This is a comparison of in-car response curves with and without transfer function compensated tuning.

4