LP201 - Accelerometer Preamp

Loudspeaker Measurements

This series of examples demonstrate how the LP201 can be used to obtain complete acceleration, velocity, and excursion data on a woofer.

For these tests a PCB 352B10 accelerometer was mounted to a 6.5" (165mm) woofer in a ported enclosure. A drop of hot melt glue was used to attach the accelerometer to the seam between the cone and dust cap as shown below.

Because of the very small size and low mass (0.7g) of the 352B10, the overall change in the effective moving mass of the driver is relatively small.

This driver had a cone mass of 28g, so adding the 352B10 only changes the mass by approximately 2-3%. Most typical production variations in drivers can be easily more than this from unit to unit.

The enclosure was driven at about 1W (2.8V) and the graphs at the right were produced for acceleration, velocity, and excursion using the LP201.

The graphs shown here demonstrate some typical results for measuring the motional behavior of a driven cone loudspeaker.

The shape of the excursion curve will show much more of the low frequency behavior, and far less of the mid/high frquency behavior. The port resonance is reducing the driver excursion at about 32Hz. The units here are milliMeters. The excursion at 10Hz reaches about 1mm. The depth of the null at the port resonance is largely a function of the losses in the port and/or enclosure. Lower port losses will produce a deeper null.