Loudspeakers

As I discuss in our boxout stacking two notionally identical speakers boosts output but complex reinforcement/cancellation will occur from the offset wavefronts. Three forward responses are plotted here by way of illustration [see Graph 1] – on the top bass/mid axis [red trace], top tweeter axis [green] and exactly midway between the two cabinets [black], each indicating the big variations that occur over different listening positions (vertical axes). Adding the grilles [mid axis, blue trace] adds another 'layer' of diffraction from each baffle but the upper-mid/treble-focused response trend is essentially unaltered. The 'best case' mid-position still shows errors of ±6.7dB and ±6.8dB, respectively, though separate upper/lower enclosure responses [grey trace, Graph 1] suggest the crossovers are not identical.

Note the ~3dB difference in output once the two cabinets are connected in parallel – here the impedance is halved from a minimum of just 4.3ohm/200Hz (top speaker) and 5.1ohm/100Hz (lower speaker) to 2.5ohm/180Hz although sensitivity still does not meet the rated 88dB at 82.0dB/1kHz (or 82.4dB from 500Hz-8kHz). The minimum EPDR is a tough 1.1ohm/335Hz but there are gains in bass reach if not sensitivity. The two 200mm bass/mid units have subtly different bandpasses, the top unit working over 30Hz-680Hz (–6dB), rolling off above 200Hz, and with a combined electrical/acoustical 4th-order LF roll-off following a peak at a low 40Hz [green shaded area, Graph 1]. The lower unit operates over 34Hz-250Hz (–6dB), peaking at 53Hz with a gentler roll-off. The corrected bass extension for the Grand Studio II is a creditable 33Hz (–6dB re. 200Hz). PM