EgglestonWorks Andra loudspeaker Measurements
The EgglestonWorks Andra is moderately sensitive, my estimated 87dB/2.83V/m (B-weighted) reading agreeing with the specified figure. Its impedance plot (fig.1) suggests that the speaker appears to be an easy load for an amplifier to drive, the magnitude dropping below 10 ohms only in the high treble and below 130Hz, and the phase angle generally remaining low. However, it does reach 4 ohms in the low bass, around the tuning of the twin ports. There is a very slight wrinkle in the impedance traces between 300 and 400Hz, this generally indicative of a cabinet resonance of some kind. However, as might be expected from its massively constructed cabinet, the Andra is impressively inert. About the only resonant mode I could find was on the woofer enclosure wall (fig.2) at 350Hz. This is well down in level, however.
Fig.1 EgglestonWorks Andra, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
Fig.2 EgglestonWorks Andra, cumulative spectral-decay plot of accelerometer output fastened to woofer cabinet sidewall. (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz.)
In his interview with Wes, Bill Eggleston mentioned the acoustic overlap between the woofers and midrange units. This can be seen in fig.3, which shows the individual nearfield responses of the front woofer, one of the ports, and one of the midrange drivers. The latter can be seen to start to roll out below 120Hz or so, but it still contributes to the speaker's output an octave lower, in the midbass. The woofer's output is the trace that peaks around 30Hz and again between 60Hz and 80Hz, before gradually tapering off. It is still only 10dB down from the midrange level at 500Hz. The ports cover a broad region from 20Hz to 70Hz, with then an irregular rolloff.
Fig.3 EgglestonWorks Andra, nearfield midrange, woofer and port responses plotted below 700Hz.