Genesis Technologies 500 loudspeaker Measurements

Sidebar 3: Measurements

The well-finished Genesis is quite sensitive, at an estimated 89.2dB(B)/2.83V/m. To judge from its plot of impedance magnitude and phase against frequency (fig.1), however, it needs to be driven by an amplifier capable of healthy current delivery. With an average impedance of around 3 ohms and a minimum of 1.73 ohms between 400 and 500Hz, where much of music's power is concentrated, the 500 makes extreme current demands on amplifiers.

Fig.1 Genesis 500, electrical impedance (solid) and phase (dashed) with controls at recommended positions. (2 ohms/vertical div.)

There was something odd about the electrical phase angle of the impedance in that it appeared rotated through 180 degrees. If this is not a plotting aberration, I have not seen this before. While it does not in itself add to the difficulty of the electrical load, the 500's phase angle does approach the worst case of 90 degrees in the midbass and at ultrasonic frequencies. The rising magnitude trace in the bass is due to the crossover to the active woofer section. But at 100Hz, where the magnitude has risen to 4 ohms, the phase angle is almost 90 degrees, meaning that the speaker will draw the maximum current when the voltage across its terminals approaches 0V. This is very hard for amplifiers with inadequate output stages and power supplies to cope with.

Although KR found the enclosure quite inert, I did uncover a couple of panel resonant modes on both the bass and midrange enclosures. Fig.2 shows a cumulative spectral-decay plot calculated from the output of a simple plastic-tape accelerometer fastened to the center of the midrange side panel. A strong mode can be seen at 309Hz, with some lower-level modes lower in frequency. These could also be detected on the woofer-enclosure side panels, with the lower-frequency modes higher in level.

Fig.2 Genesis 500, cumulative spectral-decay plot of accelerometer output fastened to midrange-cabinet side wall. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)

Fig.3 shows, from left to right, the nearfield responses of the woofers (set to "95"), the midbass coupler, and the midrange unit, spliced to the farfield response of the midrange unit and tweeter on the latter's axis. The woofers cover a broad bandpass (from below 20Hz to around 120Hz), with the midbass coupler filling in for an octave beneath the true midrange unit, as well as overlapping it for about another couple of octaves. The Genesis' upper-range output is basically flat, though marred by a narrow suckout between 700Hz and 1kHz.

Fig.3 Genesis 500, acoustic crossover on tweeter axis at 50", corrected for microphone response, with the nearfield woofer, midbass coupler, and midrange responses plotted below 600Hz and 355Hz, respectively.

Genesis Technologies
936 Chambers Court, Unit B3
P.O. Box 3789
Eagle, CO 81631
(970) 328-9515