Interpreting Subwoofer Technical Data
Each box/driver design on our website has accompanying graphs of the system's performance. Knowing how to "read" the graphs will help guide you to the right system. And impress your friends!
Out of Car Response
This graph shows the frequency response of a woofer and enclosure outside of the vehicle in a "Free-Air" or open space condition. This response graph is pretty close to the measured performance in a showroom.
In Car Response
This graph shows the frequency response of the woofer and the enclosure inside a typical vehicle. The reason for the increase in bass performance is due to "Room Gain" (sometimes called Transfer Function). The woofer, enclosure, and the vehicle's interior interact to produce the bass response you will actually hear. The Room Gain is different from car to car so we can only show you an approximation of the response in an average vehicle interior. Most vehicles will increase bass frequencies 3db at 50 Hz and rising up to 12 dB at 20 hertz. This is why the subwoofer will sound better inside the vehicle than in a store showroom.
We have reproduced three examples of in-car response graphs to help you understand the relationship between the graphs and the kind of sound you will hear.
Example 1 is of a bandpass enclosure. The slight peak at 48Hz will give you good "gut punch." The extended deep bass response makes this a good design for "Bass-CD's" and hip-hop. This is not a great choice for people looking for "tight" and "accurate" bass.
This graph is an example of a ported enclosure. The large peak at 40Hz makes this very "punchy" sounding, perfect for Hard Rock lovers. The quick roll-off after the peak means this system will not be great for "Extreme Bass" CDs.
This graph is an example of a sealed enclosure system. Notice that the response curve is very flat and accurate with excellent deep bass extension. For some listeners, that is a good thing, but many car stereo listeners are not looking for accurate bass but "dramatic" bass.
This graph shows how far the woofer cone moves (measured in millimeters) at various frequencies at the woofer's continuous power rating. Woofers with high cone displacement at low bass frequencies are not recommended for ultra high volume use. The woofer's suspension and voice coil may be damaged. The example below is a 10-inch driver in a bandpass enclosure. This driver has a maximum linear excursion (X-max Linear) of 9mm so this box design keeps the driver within its limits. Driver/enclosure systems that allow excursions higher than the "X-max Linear" rating of the driver will have limited power handling and will be prone to making bad noises or breaking when played loud.
Vent Air Velocity
This graph shows how fast the air inside the port or vent is moving at various frequencies, measured in "Meters Per Second". The lower the number, the less turbulence and noise generated by the port. Figures that exceed 18 to 20 can be noisy at higher listening levels. Obviously, this is not a concern on sealed enclosures. Above 20 can be audible at high levels
This article was last modified Apr 23, 2014