Speaker Asylum: New B&W 700 Series = More of the same by layman General speaker questions for audio and home theater.

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Posted by layman on September 2, 2003 at 07:33:50

Well, I have read over the B&W "White Paper" for their new "700" series and I must say that I am disappointed.

I appreciate B&W's honesty and candor concerning their design goals, and their (honest) assessment of whether (or not) these design goals have been met. I also appreciate the accuracy and honesty of the specs and measurements that B&W has published on the speakers (B&W publish honest information about all their products). It's rare in the industry, but B&W can be relied on to publish "truthful" specs and measurements (not the more common "wishful thinking" type specs and measurements).

B&W says that they scrapped the "CDM" designation because they wanted to start over with the new series (to break completely with the prior series), but after reading the "White Paper," it's clear to me that the 700 series represents an evolution of the CDM concept rather than a revolution. The "updates" are purely cosmetic.

Here are my main gripes with the series (and with 95% of current B&W products in fact):

1. Why did B&W decide to continue to use the cheap sounding aluminum dome tweeters that they have been using for some time? The high (4 kHz) crossover frequency to the tweeter is a clue that the new tweeter does not behave any better than the old. I would have preferred to see a tweeter that could work down to a lower frequency. Such a tweeter would have exhibited better self-damping to resist ringing, break-up and distortion at the bottom of its passband. These (distortion artifacts) are all too audible with existing B&W tweeters. B&W can do better. The current tweeters do not compare well with current Scanspeak, Vifa, Seas, Morel, Dynaudio, and Audax metal and fabric domes (just to name a few).

My advice to B&W: get a better sounding, better behaving tweeter. The B&W metal dome is one of the weakest ingredients of current B&W speakers because the tweeters have a tendency to sound clinical, dry, edgy and fatiguing (which is a problem with tweeter performance i.e. self-damping, as well as voicing).

2. Why does B&W continue to use kevlar drivers? The White Paper goes on and on about the tensile strength of kevlar and its application in bulletproof vests but to me these drivers don't sound "right." Any driver that's designed to flex and break-up in band (as the kevlar drivers do) is INTRODUCING distortion artifacts into the sound. The kevlar drivers show a consistent peak at the top of their passband, which indicates that the drivers are no longer behaving as pure pistons (introducing distortion), the drivers are beaming at the top of their passband, and the drivers are being overworked (the crossover frequency needs to be lower). B&W can do better.

3. Why does B&W continue to use such a high crossover frequency (~4 kHz)? The high crossover frequency makes life easy on the tweeter but increases the stresses and strains on the bass/mid-range driver. Furthermore, the high cross ensures that the mid-range tonal balance will change as you move off the speaker's reference axis. The drivers beam at the top of their passband. The speakers produce uneven power response. Listeners positioned off the speaker's reference axis will hear a completely different (and less accurate) tonal balance than listeners positioned in the "sweet-spot." The crossover frequencies of B&W speakers are consistently too high and ensure the existence of an in-room suckout around the crossover frequency.

My advice to B&W: use a lower crossover frequency or improve your tweeters and use smaller (4-3 inch) mid-range drivers. That's the only way to prevent all the beaming and abrupt dispersion pattern changes (around the crossover frequency).

After reading the "White Paper" carefully, I can only conclude that the 700 series is a cosmetic update (more of the same) of the CDM series rather than a radical re-think. I think a radical re-think is called for given the dryness, fatigue and lack of timbral accuracy that afflicts B&W speakers. The design goals simply have not been met.

• 700 series white paper   (Open in New Window)

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