Sumo Samson subwoofer & Delilah crossover Measurements

Sidebar 2: Measurements

The Sumo Samson's nominal impedance is quoted as 8 ohms. In fact, I measured a minimum value of 8 ohms at 170Hz, the value below that frequency averaging about 12 ohms. This is an easy load for any amplifier, and supports Sumo's recommendation that bridged amplifiers work best with Samson. (Bridging a 4-ohm rated amplifier may double the voltage swing into the load, but it effectively turns the amp into one best suited to 8-ohm loads.) The plot of impedance with frequency (fig.1) revealed the basic box resonance to lie at 52Hz with the reflex ports tuned to 27Hz, both appearing to be of quite a high Q.

Fig.1 Sumo Samson, impedance magnitude (5 ohms/electrical div.)

Measuring Delilah's output responses with the high- and low-pass frequencies set to 80Hz and the low-pass slope to 18dB/octave revealed the outputs to be perfectly tailored, –3dB points for both outputs being 80Hz and slopes being correct. It also revealed that, as supplied, Delilah incorporates some equalization on the low-pass output. This I measured to be a boost of around 5dB centered on 27Hz—the specs state 26Hz—with the response rolling off at 12dB/octave below 25Hz (fig.2). This EQ is specifically intended for use with the Sumo Samson, said to give it a flat anechoic response to 25Hz, with then a 6th-order high-pass roll-off. If the Delilah owner wants to use the crossover with a different subwoofer model, this EQ can be switched out with an internal switch, the bass response then measuring flat below the hinge frequency but lacking the subsonic roll-off.

Fig.2 Sumo Delilah, high-pass (blue) and low-pass (red) responses (10dB/electrical div.)

Delilah's output impedance is low—I measured 108 ohms, high-pass, 1kHz, and 123 ohms, low-pass, 50Hz—implying that Delilah will not be fazed by lengthy or overly capacitative cables.—John Atkinson