Bass cancellation in sedans vehicles

• Loss or reduction of bass?

• Where is the bass?

• Why is my car louder with the trunk open?

This is a very common problem in sedans.

Here is the explanation:

Automobile manufactures strive to "dampen" or quiet the interiors of their cars by eliminating road noise, and other sounds. Automobile trunks are designed so that any noise transferred into it from the rear axles will not enter the passenger compartment out of phase with the noise from the front axles. Unfortunately, road noise has a similar frequency range to bass. If an enclosure is placed in the trunk with the woofers facing the back of the rear seats, the primary wave from the speaker passes through the rear seat and enters the passenger compartment. At the same time waves get reflected into the trunk, they then exit out of phase from the primary wave, causing bass robbing cancellation. 

Opening the trunk allows the out of phase (reflected) waves to escape and no longer cancel the primary wave resulting in an increase in bass with the trunk open, or loss or reduction of bass. by facing the enclosure towards the rear of the car helps eliminate the cancellation by sending all bass into the trunk before it enters the passenger compartment, however this can cause the trunk to rattle and vibrate.

If you want the best performance, then the example in fig.4 is the way to go. First, a baffle needs to be built to seal the trunk completely (this baffle should have a hole that the speakers will fit through). Slide the box up to the baffle and screw in place ,if done correctly this should eliminate any bass from entering the trunk.

While the system is playing, have someone sit in the car and open and close the trunk, there should be no difference in bass response. If opening and closing the trunk still makes a difference, then you will need to create a better seal.