B&W John Bowers Silver Signature loudspeaker Measurements

Sidebar 4: Measurements

The Silver Signature's impedance magnitude and phase, measured using the magazine's Audio Precision System One, are shown in fig.1. Though the impedance magnitude is off the scale at 800Hz, a slight wrinkle in the phase trace can be seen between 700 and 800Hz, indicative of some sort of resonant problem in this region. The port tuning is revealed by the saddle between the two bass humps as lying at a low 35Hz, more than an octave below that of the similar-sized Velodyne. This is one easy speaker for an amplifier to drive, the impedance not dropping below 6 ohms and remaining above 10 ohms for much of the audio band. Coupled with a highish sensitivity—86.5dB/W/m, B-weighted—the Silver Signature will produce highish spls with even modestly powered amplifiers.

Fig.1 B&W Silver Signature, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

The Silver Signature's open architecture allowed me to take a look at the raw drive-unit responses without any crossover filters in the signal path. The basic tweeter response is shown in fig.2: It both rolls out below 2kHz and shelves down by 4dB or so in the top audio octave before peaking at 27kHz. The midrange and treble response of the unfiltered woofer is shown in fig.3. A hint of a rising trend can be seen in the midrange, with then an impressively flat treble. The steep rolloff above 7kHz is broken by peaks due to cone breakup modes.

Fig.2 B&W Silver Signature, quasi-anechoic response of raw tweeter (no crossover) on tweeter axis at 45" and corrected for microphone response.

Fig.3 B&W Silver Signature, quasi-anechoic response of raw woofer (no crossover) on tweeter axis at 45" and corrected for microphone response.

This can be seen in the cumulative spectral-decay, or waterfall, plot for the raw woofer (fig.4). Resonant modes emerge from the drive-unit's decay picture at 3kHz, 5kHz, 6.5kHz, and 15kHz. A ridge of decayed energy is also associated with the dip in the woofer's output at 800Hz, this perhaps associated with the impedance phase wrinkle noted earlier.

Fig.4 B&W Silver Signature, raw woofer cumulative spectral-decay plot at 45" (0.15ms risetime).

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