lABoRAToRy TEsT REPoRT
Newport Test Labs measured the frequency response of the B&W 702 S2 speakers as 38Hz to 38kHz ±3.5dB, which is an excellent result. A smaller section of this response (between 20Hz and 10kHz) is shown in Graph 1, and you can see that in addition to the superb linearity, there’s also no spectral skew, which if there had been would have resulted in incorrect sound balance, irrespective of the ±dB variation. The graph shows a very slight suckout in the response between 1.5kHz and 3.5kHz that I suspect is more related to a microphone positioning issue than to the speakers themselves, but it’s so minor it would not be audible. The low-frequency roll-off that starts at 100Hz is controlled, even and extended, suggesting superior bass response.
An expanded view of the high-frequency response of the B&W 702 S2 showing performance from 500Hz all the way up to 40kHz is shown in Graph 2. It was measured using a gating technique that simulates the response that would be obtained if the speakers had been measured in an anechoic chamber, and allows extremely precise frequency vs. level measurements. You can see that the response is quite ‘lumpy’ with the aforementioned dip between 1.5kHz and 3.5kHz followed by another response dip between 5kHz and 8kHz, then another shallow dip above 12kHz that also includes the natural high-frequency roll-off of the tweeter. This response was measured with the grille off, but another measurement with the grille on (not shown) proved that B&W’s grille is acoustically transparent, so the speakers will sound the same irrespective of whether you use them with their grilles on or off, so I’d recommend leaving the grilles on. Note that despite the ‘lumpy’ appearance of the trace, all the variations in the response are within a ±3.5dB envelope, as you can see from looking at the dB scale at the left of the graph.
Graph 3 shows the low-frequency response of the B&W 702 S2 as measured by Newport Test Labs. The output of the port (red trace) is at its maximum at around 22Hz, but there’s good output from the
port all the way from 14Hz all the way up to 80Hz. The output of the three bass driver(s) is shown by the black and blue traces on the graph. The black trace shows the response when the bass reflex port is completely blocked by the foam bungs. It rolls off steadily below 120Hz at around 12dB/octave. The blue trace shows the output of the bass driver when the port completely open. The roll-off is much steeper, at around 18dB/octave, but of course the output of the port compensates for the loss.
The overall system impedance of the B&W 702 S2 is shown in Graph 4 for both the bass reflex configuration (black dashed trace), and totally sealed configuration (solid black trace). You can see that in both configurations the minimum impedance is just 3Ω at around 120Hz and the impedance dips below 4Ω between 90Hz and 190Hz, 500 and 850Hz and from 13kHz to more than 40kHz. This means that the B&W 702 S2 only just scrapes in as being able to be classified as ‘nominally 4Ω’ under IEC 60268-5. I would definitely recommend using an amplifier that was completely comfortable driving 4Ω loads, not least because of the current it will draw, particularly at 80Hz, where you can see a 4.7Ω impedance combined with a –68 degree phase angle (phase angle is light blue trace). The electrical crossover between the ‘LF’ and ‘HF’ parts of the crossover network takes place at around 420Hz, as you can see from the pink and green traces on Graph 4.
Graph 5 is a composite response plot where the red trace shows the output of bass reflex port and the dark blue trace the anechoic response of the bass driver(s). The light blue trace shows the frequency response of the midrange driver which rolls off below 550Hz and above 1.3kHz. The solid black trace is the averaged in-room pink noise response (from Graph 1) and the dashed black trace is the anechoic high-frequency response (from Graph 2).
Newport Test Labs measured the sensitivity of the B&W 702 S2 as being 90dBSPL at 1m for 2.83Veq under its standard test conditions, which means this design has well above average sensitivity and also confirms B&W’s own specification of 90dBSPL for this parameter.
Although its frequency response is not as flat as some B&W speakers Newport Test Labs has measured in the past, the B&W 702 S2’s frequency response is still admirably flat and linear and Newport Test Labs’ measurement of it exceeded B&W’s own specification by a good margin. The B&W 702 S2 also met its specification for sensitivity, which is a rare achievement for any loudspeaker.
Graph 1. Averaged frequency response using pink noise test stimulus with capture unsmoothed. Trace is are the averaged results of nine individual frequency sweeps measured at three metres, with the central grid point midway between tweeter and midrange.Graph 2. High-frequency response, expanded view. Test stimulus gated sine. Microphone placed at three metres midway between midrange and tweeter. Lower measurement limit 500Hz.Graph 3. Low frequency response of front-firing bass reflex port (red trace) and woofer with no bung (blue trace) and with port completely blocked (black trace). Nearfield acquisition. Port/woofer levels not compensated for differences in radiating areas.Graph 4. Impedance modulus showing phase (blue), high-pass section (green), low-pass section (pink), port open (black dashed), port blocked (black solid)Graph 5. Composite response plot. Red trace is output of bass reflex port. Dark blue trace is anechoic response of bass driver. Light blue trace is sine response of midrange driver. Black trace is averaged in-room pink noise response (from Graph 1) Dashed black trace is high-frequency response (from Graph 2).