Specifications

Woofer Design

The design goal for the woofer is good transient response, low Q,

low cutoff frequency and minimal coloration near the crossover

region.

For the cabinet size dictated by design, no available off the shelf

woofers met our design requirements. Most off the shelf woofers

are designed to operate over a much wider bandwidth than is

desirable for the LFT-8b. In a hybrid system of this type, it is

desirable to have as low a crossover frequency as possible for the

woofer. Because of these factors we chose to design our on

woofer.

An eight-inch woofer was chosen because it offered the best

balance between low frequency response, the size of the box and

blend with the mid-range driver.

The woofer cone is purposely very heavy for an eight-inch driver

(99.8 grams). Since it is Q that defines transient performance.

This mass (combined with a very complaint surround and spider)

gives a very low Q in a small sealed enclosure.

A second reason the cone is heavy is to prevent it from

responding to mid-range signals, which would cause a poor blend

with the mid-range panel. The cone material is felted paper,

which is coated with a thick emulsion. This helps to mechanically

roll off the woofer to prevent mid-range coloration. Without a

crossover, the woofer response begins to roll off above about 500

Hz and has no usable output above 1 kHz. This allowed the

crossover to be 6 dB per octave.

Since the efficiency between the mid-range and high frequency

driver is slightly lower than average and bandwidth and efficiency

and efficiency of a woofer system are inversely proportional, we

are able to extend the low frequency performance of the woofer

system.

The woofer is a true air suspension design. This means the

compliance of the air in the enclosure has a much larger effect on

low frequency performance than the compliance of the woofer

components (spider and surround).

Technical

Information