Frequency response (at 1 meter)
S-IW571L (vert. mount) 30 Hz to 20 kHz ±4.9 dB
S-IW571L (horiz. mount) 30 Hz to 20 kHz ±5.1 dB
S-IW871LR 29 Hz to 20 kHz ±5.2 dB
Bass limits (lowest frequency and maximum SPL with limit of 10% distortion at 2 meters in a large room)
S-IW571L 40 Hz at 77.1 dB
88-dB average SPL from 40 to 80 Hz; 100-dB maximum SPL at 63 Hz; bandwidth uniformity 86%
S-IW871LR 40 Hz at 84.5 dB
93-dB average SPL from 40 to 80 Hz; 102. 3-dB maximum SPL at 63 Hz; bandwidth uniformity 90%
All of the curves in the frequency-response graph are weighted to reflect how sound arrives at a listener's ears with normal speaker placement. Measurements were made with the speakers mounted in large enclosures provided by the manufacturer; the enclosures approximated the volume of the space inside a standard wall cavity. I draped blankets around the edges of these enclosures to prevent diffraction and mimic the "infinite baffle" acoustics of mounting in a real wall. Because of the configuration of these enclosures, I had to make measurements at 1 meter instead of our usual 2 meters, but because there are no speaker cabinet edges for sound to reflect from, this closer measuring distance was adequate in this case. These tests gave quasi-anechoic results down to about 500 Hz. Response of woofers was close-miked, summed, and spliced to the quasi-anechoic response.
Because the S-IW571L will be used both horizontally and vertically, I measured it mounted both ways. (The S-IW871 has no additional drivers beyond the concentric woofer and tweeter, so it measures the same vertically and horizontally.) All tone switches were set at 0 except as noted.
Both speakers measured smoothly in the ranges where their woofers and mid/woofers dominated but got rougher in the tweeter range. The averaged response of both started to drop above 3.5 kHz, and showed a broad dip between about 7 and 12 kHz - almost certainly the reason why I perceived both speakers as treble-shy. Fortunately, for most adult listeners, this anomaly will be heard as a treble rolloff rather than as a dip because it's so high in frequency. This response pattern remained fairly consistent until the mike was moved 45º off-axis, where deep but extremely narrow dips showed up at 8.4 and 14.9 kHz for the S-IW571L, and 9 and 14.4 kHz for the S-IW871L. The S-IW571L measured almost the same vertically as it did horizontally, with only slight changes in the response. The - 3 dB bass response is approximately 30 Hz for the S-IW571L and 29 Hz for the S-IW871LR. The second sample of the S-IW571L varied by at most 1.8 dB from the first at all frequencies. The second sample of the S-IW871L varied by at most 1.5 dB except in a band between 10 and 12 kHz, where the two varied by a maximum of about 5 dB.
Above about 2.5 kHz, the +/0/- switch on the S-IW571L boosts treble by 1.5 dB or cuts it by about 4 dB. The +/0/- switch on the S-IW871LR worked the same way, although it cut by slightly less, about 3 dB. The 0/- bass switch on the S-IW871LR cut bass by about 2.5 dB in a band between approximately 60 and 150 Hz.
Mounted in the supplied enclosures, both speakers deliver 6 ohms nominal impedance, matching the manufacturer's rating. Minimum impedance is 4.3 ohms at 155 Hz for the S-IW571L and 4.7 ohms at 9.6 kHz for the S-IW871LR. Although the impedance of these speakers runs a little low, the impedance curves are relatively flat and the impedance phase shift is mild, so neither speaker should prove difficult to drive. Sensitivity of the S-IW571L measured a little low at 86.5 dB at 1 meter with a 2.83-volt signal at the speaker terminals. The S-IW871LR measured about average at 88 dB.
Bass output of these speakers will depend on the wall in which they're mounted; the larger the space behind them, the deeper the bass response will be. Mounted in the supplied enclosures, the S-IW571L's dual 5[1/4]-inch woofers average 88 dB between 40 and 80 Hz, reaching a peak of 100 dB at 63 Hz. Its useful bass extension is about 40 Hz, where it puts out 77.1 dB. The S-IW871LR's 8-inch woofer delivers a bit more bass: It averages 93 dB between 40 and 80 Hz, reaching a peak of 102.3 dB at 63 Hz. The speaker's useful bass extension is roughly 40 Hz, where it puts out 84.5 dB. Both speakers always produced distortion higher than 10% at frequencies below 40 Hz.
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