Technical Specification:

This is Bowers & Wilkins official technical specification for the B&W 685 loudspeaker. Let’s see how correct it is.

Technical features: Nautilus tube-loaded aluminium dome tweeter, Kevlar fibre cone mid-woofer and flowport.

Description: 2-way vented-box system

Drive units: 1x 25mm aluminium dome tweeter, 1x 165mm woven Kevlar cone mid-woofer

Frequency response: -6dB @ 42Hz – 50kHz

Dispersion: Within 2dB of reference response

Sensitivity: 88dB @ 2.83v/1m

Harmonic distortion: 2nd and 3rd harmonics @ 90dB/1m, <1% 110Hz – 22kHz, <0.5% 150Hz – 20kHz

Nominal impdedance: 8Ω

Cross-over frequency: 4kHz

Dimensions (HxWxD): 340x198x331mm

Net weight: 7.0Kg

Impedance measurements:

(click on picture to zoom)

Blue: Left loudspeaker

Green: Right loudspeaker

Excellent consistency between the left and right loudspeaker. It doesn’t get better than this.

Impedance minimum of 4.79Ω @ 197Hz and 3.59Ω @ 20kHz.

The impedance plot shows a bass-reflex and port tuning frequency of 48Hz, which is slightly higher than normal for a medium sized stand-mount loudspeaker. Using two 4Ω drivers, I would consider this loudspeaker a 4Ω system rather than an 8Ω system according to the official specification.

Frequency measurements:

If nothing else is noted in the comments, the following frequency measurements of the B&W 685 loudspeaker are made at a 2m distance at tweeter height.

All frequency response charts are presented in a 50db scale with 1/24 octave smoothing and the measurements are valid down to 375Hz.

Frequency response on-axis: Frequency response 15deg off-axis:

Blue: Left Loudspeaker @ 2m

Red: Right Loudspeaker @ 2m

Minor differences between left and right loudspeaker.

(click on picture to zoom)

Upper left: On-axis frequency response.

Lower left: On-axis frequency response, tweeter reverse polarity.

Upper right: 15deg off-axis frequency response.

Lower left: 15deg off-axis frequency response, tweeter reverse polarity.

Here we can see a cross-over frequency of 4kHz which is true to the official specification. We can also see that the loudspeaker uses a shallow sloped cross-over topology where the drivers initially rolls-off at roughly 6dB per octave.

On the other hand we can see approximately a 5dB boost at the cross-over point compared to the frequency response above and below the cross-over point.

We can also see from the reverse polarity test that we have an unsymmetrical null, which indicates less than optimal individual phase tracking between the driver units below and above the cross-over point. The tweeter response is boosted about 4-6dB above 10kHz.

(click on picture to zoom)

Upper left: On-axis, 15 and 22.5deg off-axis frequency response.

Upper right: 30, 45 and 60deg off-axis frequency response.

Bottom: On-axis frequency response. Blue = Front cover off. Red = Front cover on.

The peak at the cross-over frequency smooths out from 30deg off-axis and above as well as the boosted tweeter level.

The front covers should be off when listening to this loudspeaker. In order to achieve the flattest and smoothest frequency response, the loudspeaker shouldn’t be toed-in. Instead let it as a starting point straight forward and toe-in until the tweeter level is according to personal taste.

Distortion measurements:

Measurement setup:

Tweeter-axis near-field measurement at 20cm

Frequency Range: 200-10000Hz

Baffle size WxH: 19,8×34,0cm

The distortion measurements are done in near-field and the amplifier output level was adjusted so that the fundamental is 90dB and 95dB at 1m. This setting simulates medium-high and high listening levels.

(click on picture to zoom)

90dB @ 1m

Left: = Left loudspeaker

Right: = Right loudspeaker

(click on picture to zoom)

90dB @ 1m

Left: = Left loudspeaker

Right: = Right loudspeaker

The B&W 685 has an excellent distortion profile and is true to the official specification. We have a 2nd order distortion spike around 0.9-1kHz, which could indicate a cone edge resonance caused by the mid-woofer, but is nothing to worry about.

Both the tweeter and the mid-woofer seem to be of high quality regarding their distortion profile and performance. I would say this is better than usual in this price range.

Measurement summary:

The B&W 685 measurements show an excellent impedance and frequency conformity between the left and right loudspeaker. It also has a great distortion profile performance for a loudspeaker in this price range.

The frequency measurements confirm my initial listening impression and it shows an elevated upper treble as well as a peak in the lower treble at the cross-over frequency. This could explain the too energetic treble and the rawness I could perceive when listening to some recordings.

The next review part contains the individual tweeter and mid-woofer impedance, frequency and distortion measurements as well as an analyze of the B&W 685 original cross-over.

Go to Bowers & Wilkins 685 review part 3.