Wharfedale Pacific surround speaker system Measurements
The Pi-40's ported cabinet is tuned to approximately 36Hz, and its minimum impedance through the lows and midrange is 4.4ohms at 123Hz. A reasonable rating for the nominal impedance would be 6ohms, and though the impedance drops at high frequencies to a minimum of 3.3ohms at 6.3Hz, the small amount of power required in the treble should make the speaker, overall, a relatively benign load for a good amplifier. A significant discontinuity in the impedance plot at about 500Hz indicates a possible cabinet resonance at that frequency. The Pi-40's sensitivity is approximately 88dB/W/m.
The pseudo-anechoic response of the Pi-40 at tweeter height, averaged over a 30° forward horizontal angle and combined with the nearfield responses of the woofer and port, is shown in Fig.1 (violet). The bass holds up well to 31Hz (–10dB relative to the output level at 1kHz). The overall response is quite smooth, the only notable exceptions being a small suckout at about 400Hz and a gently rising response from that point to about 4kHz. The upper treble is down a little, but the speaker should be free of edginess, as JJG found. The high-frequency rolloff typical of most speakers as you move off-axis is well-controlled, and the off-axis response remains smooth.
Fig.2 shows the same averaged horizontal front response (violet), plus the vertical responses taken at +15° (red) and –15° (blue) relative to the tweeter. Both show a significant suckout at about 4kHz, suggesting that the speaker should be listened to with its tweeter axis as close to ear height as possible.
The Pi-Center's cabinet is tuned to about 56Hz, with a minimum impedance in the bass and midrange of 8ohms at 270Hz. (A reasonable nominal impedance in this range would be 10ohms.) But the impedance drops significantly at high frequencies, with a minimum value of 2.7ohms at 4.5kHz. However, as with the Pi-40, this should cause no problems for any reasonably competent amplifier, because there is little energy in most program material at very high frequencies. The Pi-Center should therefore not be a difficult load to drive. Its sensitivity measured about 88dB/W/m.
The measured front horizontal response of the Pi-Center, taken on the tweeter axis and averaged in the same manner as described above for the Pi-40, is shown in Fig.3 (violet). The effective bass extension is approximately 50Hz (–10dB). There is a significant response dip centered at about 3kHz that might produce a little softening of the sound. Interestingly, however, this dip disappears when you move 15° below the tweeter axis (not shown), suggesting that the Pi-Center would be at its best atop a big-screen TV and not tilted down. Off the horizontal axis, however (Fig.3), and despite the unusual driver configuration described by JJG, the Pi-Center's performance is typical of most three-driver center-channel designs in that it has an off-axis suckout in the midrange that grows progressively worse as you move farther off to the side.—TJN