I heard the B&W 800d's today

[John Ashman]

I purchased a set of 800D's in July as an upgrade to 801's I had owned for six years. The one fact that is inescapable about B&W speakers is that they ruthlessly reveal the shortcomings of all upstream components. I am driving mine with a dCS front end and Halcro monoblock amps in a room that is liberally treated with ASC tubetraps. None of the shortcomings you noticed are present in my system. They are the best value for the dollar that exists in high end speakers but..... you have to feed them with the best signal you can afford.

Cincy, I hate to say this (okay, I lie), but this is a highly escapable fact. First of all, B&Ws aren't terribly revealing speakers. Kevlar's break up modes and lack of rigidity masks a lot of detail. The whole "ruthlessly revealing" fable is based on the fact that the breakup modes make it seem like the amps are straining or the other components are distorting or are harsh, but it is, in fact, the drivers. Kevlar is a VERY problematic midrange material, especially in its FST configuration. And it has cost many, many people thousands of dollars trying to compensate for it, with mixed results.

When someone says a speaker is "ruthlessly revealing", that means that the speaks are either harsh or bright. It's just the way it is. Measure any "ruthlessly revealing" speakers properly and you will turn up warts in the upper midrange that cause the problem, which is almost always improperly blamed on ancillary components which are several orders of magnitude lower in distortion. How does a ~1% distortion component "reveal" the distortion in a .01% distortion component, anyway?

[theaudiohobby]

John,

"Ruthlessly revealing" is a suspect characteristic, revealing yes, ruthless certainly not. However adverse loads, not necessarily low impedance loads rather severe phase angle, large impedance deviations cause certain amplifiers to behave suboptimally, and this indeed may be the case here. Your critique of the FST is simply not well founded, Lynn's paper and one Revel graph just won't do. As I have mentioned over and over again, if your critique was indeed correct, why is this apparent signature behaviour not present in the 700 series, the B&W 705 is neither harsh nor bright, yet it has an acoustic crossover at about 3.7kHz, and as RGA never cease to remind us the bass rolls off very early, so the midrange and treble are very much exposed to scrutiny.

On the issue of the distortion, it is about spectrum of the distortion rather than the THD, it is a pity that THD still dominates audio specs,(because it much easier to measure, though practically useless). The distortion spectrum forms part of the signature of any audio component especially loudspeakers, their distortion spectrum still differentiates them since distortion is generally much higher than other components, apart from SET amps, across the board.

[John Ashman]

John,

"Ruthlessly revealing" is a suspect characteristic, revealing yes, ruthless certainly not.

Well, as you know, I would disagree with you hear. When someone says a speaker is "revealing", that usually means it has some upper midrange/treble issues (all speaker do, just some worse than others) that will be described by others variably as "bright", "fatiguing", "harsh" or maybe even "too detailed". When it is bumped up to "ruthlessly revealing", then the problem is fairly severe.

However adverse loads, not necessarily low impedance loads rather severe phase angle, large impedance deviations cause certain amplifiers to behave suboptimally, and this indeed may be the case here.

Possible, but not likely. Unless the speaker is being driven by a Sony receiver or something, it's not likely to be a problem. Most of the time, these 90dB+ speakers are being driven by uber amps that offer no alibis.

Your critique of the FST is simply not well founded, Lynn's paper and one Revel graph just won't do. As I have mentioned over and over again, if your critique was indeed correct, why is this apparent signature behaviour not present in the 700 series, the B&W 705 is neither harsh nor bright, yet it has an acoustic crossover at about 3.7kHz, and as RGA never cease to remind us the bass rolls off very early, so the midrange and treble are very much exposed to scrutiny.

Interesting. I have many people who tell me just how bright they are. Especially one person who LOVES brightness and he chose the 703 speakers because of that. He thinks the new D series is too warm and fuzzy. Since, as you know, most people equate brightness or harshness with detail, the new warmer D series may alienate a few B&W faithful. It is possible to have a warm tonal balance and have a lot of distortion in the midrange - this just makes the speaker sound lacking in detail. This is what is going on with the 803D which I can only decribe as very much lacking in detail and, while pleasant, it is the furthest thing I've heard from "revealing" by B&W since the Matrix 3. But if you look at the latest HT mag, they show an obvious rollof starting at 1kHz and going right through the treble. The problem is, that simply points out how lacking in detail the midrange actually is. This is usually hidden by the brighter sound that people think is detail.

On the issue of the distortion, it is about spectrum of the distortion rather than the THD, it is a pity that THD still dominates audio specs,(because it much easier to measure, though practically useless). The distortion spectrum forms part of the signature of any audio component especially loudspeakers, their distortion spectrum still differentiates them since distortion is generally much higher than other components, apart from SET amps, across the board.

You are correct. THD is simply a snapshot and gives a very low result. It's spectral decay, transient issues, IM distortion that we generally hear in the midrange.

I'm sorry that we can't agree on this whole kevlar thing, but B&W *admits* the problem in their 800D design brief. That they are "forced" to run the driver well into its breakup mode area, but they feel they have mitigated it. Well, everyone always says that. But ask any normal designer what the ideal driver is and they'll say one that is infinitely stiff with no resonance. By nature, the FST is not stiff. Worse, it has high tensile strength. Even reviewers confuse this and state how stiff the Kevlar cones are. That is incorrect. They are stiffer than denim, but not as stiff as most most plastic or paper cones and certainly not metal. The FST drivers are forced to bend in order to create the sound. Therefore, they naturally create resonances in the cone which they try to dampen, but can't really. It is definitely audible. Depending on how the speaker is voiced, it will those resonances will muddy the sound and hide detail or will add harshness and cause fatigue. Here is what B&W says on this subject:

Both the tweeter and bass drive unit diaphragms of the 800D are designed following the ‘stiff is good’ principle. However, good reproduction in the midrange has a particular requirement that precludes this approach if a single drive unit is to be used to cover the whole range.

Here's the funny thing. There's no reason they can't use dual midrange drivers as other companies do. Even the real Nautilus speaker is a 4-way. By the time you hit $5K or so you can build essentially the best 3-way you can build (unless you want to make the cabinet ultra fancy) and you need to move to a 4-way to improve distortion, dispersion, accuracy, etc. The 800 series are 3-ways simply because that is their tradition. Even if they feel that a speaker shouldn't have a crossover above 350Hz, using a 6" midbass from ~75Hz-350Hz and a 4.5" driver above would have done a far better job, improving midbass quality by taking it from the bass drivers and allowing for a more pistonic, wider dispersion midrange without all the coloration.

With stiff diaphragms, the dispersion progressively narrows as the frequency increases and the wavelength becomes similar to or smaller than the diameter of the diaphragm. At 4kHz, the wavelength is 86mm (3.4 in) and so with any drive unit of a size large enough to give high output levels with low distortion at the bass-to-midrange crossover frequency, beaming is likely to be a problem. Off centre listeners are going to hear a sound with a significantly different balance from that on axis, and image precision will suffer. Having established that we do want to achieve high sound levels and do not want to use more than one drive unit, the best option is to use a drive unit with a more flexible cone material.

Here is where they box themselves into having only one solution and therefore "must" use Kevlar. It is simply a rationalization of Kevlar. "We had to do it". No, you didn't. There are other better options, but you can bet that the establishment at B&W told the engineering department "do anything you want but it a) has to be a 3-way and b) has to use Kevlar". And so they have to try to engineer their way out of the box that they've been put into.

That does mean that the cone is virtually certain to be operating in its break-up region for much of its usable range, but the usual deleterious effect of this (delayed resonances colouring the sound) is ameliorated greatly if the correct material is chosen."

That one pretty much speaks for itself. I can't add much there.

[theaudiohobby]

That one pretty much speaks for itself. I can't add much there.

John,

Why not quote the full text of the paragraph in question, afterall the answer to the smoking gun is second part that you glaringly omitted.

[John Ashman]

Feel free to post away. All they say is that an FST cone can produce wider dispersion than a standard 6" cone, which isn't saying much. The problem with this is that it causes more ON AXIS distortion of the sound in order to increase the quality of OFF AXIS sound. If you really want to take the discussion in this direction, that's fine with me, but it's not good for B&W. There are several *better* solutions to the dispersion problem, but none of those are an excuse to use kevlar.

[theaudiohobby]

Its all about trade offs, your comments previously where about cone-breakup...

The break-up pattern of woven Kevlar® has proved beneficial for use in midrange and
bass/midrange units, being superior to many other materials, not only because of
the inherent properties of Kevlar, but also because the woven cone is not axi-symmetric.

Any comments why B&W and many others use "woven" kevlar?

PS: I am not sure of the specific white paper you are quoting from, which of the white papers will it be?

[John Ashman]

Its all about trade offs, your comments previously where about cone-breakup...

Yes, but, remember, the upper management has boxed the engineers into a) using a 3-way, b) using only one midrange and c) using kevlar, at least for now. If your boss pays you to make a bridge out of paper, you get creative, but that doesn't make it as good as using steel and concrete. Remember also, when *freed* from constraints, the solution was the genune Nautilus speaker which used metal drivers in a 4-way design with a wide dispersion dome midrange. The advantages? Wider dispersion, lower distortion, less "shouty" sound (the upper midrange of a kevlar cone behave as if in a horn, because it is), higher output. All of the advantages B&W claims to desire, but can't produce because they are "boxed in" by management. One might say "but a 4-way design like the Nautilus is too expensive", but NHT is shipping an $1800/pr 4-way speaker with all metal drivers and far more in common with Nautilus than any current B&W product. It is possible to do. There is no excuse except for the fact that Kevlar is popular and they want to roll with that until it isn't popular. Which is why I predict that the next gen midrange in the 800 series will be some form of proprietary ceramic or other composite that "solves" their problems. Watch for it. And then it will trickle down from there.

Any comments why B&W and many others use "woven" kevlar?

Yes, it breaks up some of the modes (not all) on the cone. It is critical to do that or the sound would be truly and obviously awful. It simply creates discontinuities in the resonances of the cones which helps break them up a bit and dampen them down.

I worked at a B&W dealer when the 600 series was replacing the 500 series and Kevlar was trickling down to the 600s for the first time. It wasn't pretty. The 630's poly midrange was *far* superior* to the 640's kevlar midrange. It was when I learned to dislike the sound because I could actually hear two different solutions from the same company and the poly solution was obviously superior. I like a lot of B&W's old speakers, especially the Matrix 3, so it has nothing to do with the company itself.

PS: I am not sure of the specific white paper you are quoting from, which of the white papers will it be?

The 800D development paper. They are actually quite honest in the obstacles they face and how the (somewhat) overcome them. The problem is that there are *better* solutions to the ones they used, but they are prevented from using them. They don't say "management made us do this", but it is implied that they have boundaries - high output, wide dispersion, but with only one midrange whereas most companies would either do dual 5" drivers (as in the Matrix 800) or a mid/midbass combo as in the actual Nautilus, most NHTs, Energy Veritas, etc.