In order to improve sound quality and deliver a more immersive soundscape, additional speakers are now being placed around the vehicle cabin, with some brands boasting over 20 speakers in their top of the range vehicles. This is largely due to the lack of dispersion from a speaker when sitting off-axis, and adds significant costs, complexity and weight to the vehicle.
An innovative patented technology known as a Ported Cavity Tweeter solves this problem, while greatly reducing costs, complexity and weight of the sound system. This dramatic improvement in loudspeaker technology means even an entry level vehicle can be capable of very high quality sound, as detailed below.

2 WAY SPEAKER PROBLEMS
One of the main issues with a 2 way speaker system is reduced dispersion when the bass/midrange is asked to reproduce frequencies beyond its piston range, which for a 6 ½” driver is around 900 Hz. Beyond this point, the radiation pattern (or Polar Response) will progressively start to narrow and higher frequencies become quieter off-axis. Ultimately this becomes known as “Beaming”.
The Polar Response is a function of the physical dimensions of the speaker cone and the speed of sound.

This is of particular concern with car audio as the listener is seated well off-axis (around 75 degrees for the nearest speaker, and 45 degrees for the furthest).

The narrow dispersion at higher frequencies also means there are limited reflections from the vehicle surfaces around the speaker.
This results in a dull, lifeless, non-immersive soundscape.

The second problem is that at higher frequencies the speaker cone will begin to flex, creating peaks and dips in the frequency response which creates a very harsh sound. These peaks and dips vary, depending on the listening angle. Equalization can reduce these peaks, but only for a small listening area and usually at the detriment of other seating positions. This is known as Cone Break-up, and is a function of the size, shape and materials used to make the speaker cone. Over the years, the loudspeaker industry has spent billions of dollars trying to address this Cone Break-up issue. The use of different curvatures and exotic materials (plastics, aluminum, magnesium, titanium, carbon fiber, etc.) for the cone have attempted to minimize this ”break-up” effect and extend the on-axis range of the driver. While improvements have been made, the problem still exists at large.

By crossing over to a tweeter, these bass/midrange driver
problems become reduced. This is usually done around 3KHz, as a typical tweeter cannot handle lower frequencies at high volume.
First, the diaphragm will travel further than it’s design parameters, producing massive distortion. Second, the Ferrofluid and voice coil will overheat and be damaged beyond repair.
So there is a gray area from 1-3KHz in the crossover region of a typical 2 way speaker system, between a bass/midrange driver that is forced to operate beyond its piston range (reducing its
off-axis output and entering its cone break-up region), and a tweeter that can not reproduce midrange frequencies efficiently,
nor handle the power to do so at realistic sound levels. Adding a 3rd speaker to cover this region is the usual fix, but comes with its own problems as discussed below.

3 WAY SPEAKER PROBLEMS
Current best practice is to use a dedicated midrange speaker (say 3 ½”) to cover the 1-3KHz range. Having a smaller cone, the radiation pattern narrows at a higher frequency than a 6 ½” driver, and it will also enter its break up region at a higher frequency. This allows it to cross over to a traditional tweeter before the worst of its beaming and break up region.
The downsides to using a midrange speaker are the cost of the driver, its complex passive cross-over (or additional amplifier and DSP in an active design), additional wiring and assembly time, increased weight and compromised vehicle aesthetics. There is the difficulty of blending the sound from the Bass, Midrange and Tweeter accurately due to efficiency, distance and phase
differences. Midrange drivers also tend to be less efficient
than bass drivers or tweeters, and can limit the overall SPL and headroom of the system.
Overall this option adds considerable cost and complexity to the design, and increases the weight of the vehicle.

THE SOLUTION
The Ported Cavity Tweeter (Patent No. US 10,462,577 B2) utilizes tuned ports in order to dramatically increase the output level between 1.3KHz and 4KHz, thus requiring much less power over this range. The tuned ports also dramatically reduce the diaphragm travel and distortion. This allows it to cross over to the bass/midrange driver at a much lower frequency than would normally be possible, avoiding most of the bass/midrange dispersion and break-up issues. This enables a 2 way system to finally match or exceed the performance of a 3 way. Depending on the end use, a crossover frequency of 1200Hz is not unreasonable. The small diaphragm of the tweeter radiates sound evenly up to 3KHz. The compact size allows the tweeter to be placed at ear height (or higher), raising the soundscape above that of a door or dash mounted midrange driver. This results in a smoother response, and a much more immersive experience.
Below shows the in-car response of a Ported Cavity Tweeter mounted in an A-pillar (blue line) as measured from the front seat. The purple line shows the effect of closing the ports, with it now operating as a traditional tweeter. Cross-over points and EQ settings are the same for both measurements. The roll-off above 10KHz is due to the measurement being 45 degrees off axis.

The graphs below show the reduction in diaphragm travel, and power input of the Ported Cavity Tweeter for the same SPL and crossover.
As above, the blue line is with the ports open, and the purple line is with ports sealed, operating as a traditional tweeter

KEY ADVANTAGES