The Boston Acoustics ProSeries 6.5LF Woofer is a powerful 61/2-inch driver specifically designed to handle low-
frequency and mid-bass signals down to the subwoofer crossover point. The circuit described here allows the
6.5LF to added on to existing full-range speaker systems to augment output below 300Hz.
This crossover is easily built using very few components. It is very useful in systems with limited mid-bass output
in the front stage, or systems where the mid-bass output is coming from the rear of the car and additional mid-
bass output is desired in the front of the vehicle. As you can see from the frequency output curve on the right,
there is no low-frequency cutoff in this crossover. Instead, it is preferable to use a two-way electronic crossover
between the 6.5LF woofers and the subwoofer in the system. In applications where no subwoofer is present, this
crossover also allows the 6.5LF to be the primary deep-bass driver in the system.
+5dB
0dB
-5dB
-10dB
-15dB
-20dB
20Hz
100Hz
1kHz
10kHz
20kHz
Crossover output
Woofer Installation
When installing the 6.5LF Woofer, it is important to ensure a complete seal between the front and back of the
woofer. A very small air leak anywhere near the woofer can dramatically reduce low frequency output and nega-
tively affect the frequency response of the driver. Additionally, it is very important to securely mount the woofer on
a rigid baffle. Any energy that moves or vibrates the baffle is energy that is not accurately reproducing sound. The
woofer cone should be nearly coplanar with the baffle board. Spacing the woofer off from the baffle or recessing
the woofer too far into a cavity can introduce anomalies in the frequency response of the driver.
The 6.5LF Woofer is designed for infinite baffle applications. In most installations it will be mounted in the door of
the vehicle without a separate enclosure. If it is necessary to build an enclosure to house the woofer, the enclosure
should be relatively large. For a 61/2-inch woofer, a 1/4-cubic foot or larger enclosure is sufficient. When construct-
ing an enclosure, be sure that the airspace inside is completely sealed from the outside air.
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