Dutch & Dutch 8C Quasi-Anechoic Spinorama and Measurements

[Trouble Maker]

Why doesn't, say, KEF make speakers with wide baffles? Because they want their speakers to sell.

I mean, it does visually look good from the front, but the depth is an issue for me from an efficient use of space viewpoint. Speakers that are more than a foot deep that I'm supposed to have out from the wall and my room is only 12 feet deep. What is the point of having a TV that is an inch thick mounted within an inch of the wall if I'm going to need speakers that stick out two feet into the room? And 1 of them is kind of by the front door. I guess it works for people with McMansions, but not as well in my smallish 1925 bungalow farmhouse. For me the Left/Right is not as big of a deal as the center depth.

But there is also this. I'm not offering credence to the validity of this, but simply saying they do have some technical reason behind why they say they use narrow front baffles. It seems like many, many speakers follow something along this guideline so there must be something more than just looks behind it.

https://us.kef.com/pub/media/documents/rseries/rseries2018-white-paper.pdf

It has been known for many years, and is illustrated by Leo Beranek in his book “Acoustics”, published in 1954, that the acoustic impedance of a driver (the interface between the diaphragm motion and radiated sound) is smooth when mounted both in an infinite baffle (as expected) and at the end of a long tube the same diameter as the diaphragm. This latter situation comes about because the dispersion of the driver is such that it doesn’t acoustically “see” the edges of the tube. The physics of this situation can be bent a little and it can be shown that a driver mounted in a cabinet not much wider than itself has a very low level of diffraction. It’s not perfect, but the level of diffraction is much lower than it would otherwise be.

If we look at the drivers used in the R Series systems, we can see that the bass drivers follow this requirement, but the midrange and tweeter drivers do not. Normally, the tweeter would be the most to suffer because it is much smaller than the width of the cabinet, which is determined by the diameter of the bass drivers. However, in the Uni-Q driver (more of which later), the tweeter fires into an acoustic waveguide formed by the midrange diaphragm and it is the diameter of this relative to the width of the cabinet that determines the level of diffraction.

There is more work to be done, because the diameter of the midrange (for other reasons) is smaller than that of the bass drivers, and it is here that the lateral thinking comes into play.

Around the Uni-Q driver array is what is normally called a trim ring. Not simply a decorative piece, the R Series trim ring is specially shaped and engineered. It increases the effective diameter of the waveguide such that the driver array “sees” the edges of the cabinet much less than if it were mounted normally. Hence the name “Shadow Flare”. The level of secondary radiation is decreased, resulting in less time-smearing, greater clarity and a smoother response.

 

[Deleted member 14468]

You can make great wide- and narrow-baffle speakers, but you have to know what you're doing. One thing greatly affected by baffle width is what many call the 4pi to 2pi transition, or baffle step (among other names). It's the 6dB increase in output that happens when sound stops radiating in free-space and, instead, radiates in half-space (which is what happens when the sound waves emitted from the driver "see" the baffle). Some companies use a wide baffle (Wharfedale recently) to increase sensitivity, because as the baffle gets wider, the baffle-step frequencies get lower, and you can use that to maximize the output of your upper-frequency drivers. Conversely, narrower baffles have higher baffle-step frequencies.

Diffraction can be reduced with a wide or narrow baffle, but if you look at the Vivid Audio speakers, and the KEF Blade Two series, they not only have narrow baffles, their baffles start descending to the rear of the cabinet just outside the driver. As a result, the sound waves don't travel out to the sides, but immediately behind and away. Hearing both KEF Blade Two and many of Vivid's speakers in my room, I can say that there's something to it insofar as imaging goes -- the speakers "disappear" better than any I've heard. We recently produced a video with a recording engineer in the Netherlands and he talks about the Blade Two speakers and their superior imaging. Part of that is the Uni-Q driver array, but I think part of it is also the cabinet.

Doug Schneider
SoundStage!

 

[GelbeMusik]

... there must be something more than just looks behind it.
... white-paper.pdf

Yeah, these "white papers" again. It's kind of advertising, don't You feel so, somehow?

Baffle about 1,4 times as wide as the cone: done. Reason is simple, but he "white paper" won't tell.

What's happening? In every case the wave travels first along the front baffle, originating from all over the cone or dome or whatever fancy is in there. When the wave reaches the edge, the propagation conditions suddenly change. There is more room to penetrate!

Reaction is a bounce. Yes, the void acts as an obstacle, really! Take it for granted. Parts of the wave bounces away, so changing direction.

This part interferes with the original wave. Below some wavelength the bounce happily reunites with the originating wave. Only constructive interference, frequency response looks fine. Above a certain transition frequency the bounce wouldn't unite as smooth. It interferes destructively. That gives a suckout towards the listener, and a bump to the sides. With increasing frequency a pattern forms of suck outs and bumps: comb filter effect by time delay.

The 1,4 rule is after the inherent directivity of the cone/dome. If the cone starts to beam just before the said pattern starts, the comb filter is avoided.

In consequence, following the said rule, to round over the edges doesn't make any considerable difference. It only effectively narrows the edge--visually and acoustically.

For example, this works as good as it gets:

https://heissmann-acoustics.de/disco-m/

 

[tuga]

Baffle about 1,4 times as wide as the cone: done. Reason is simple, but he "white paper" won't tell.

Baffle step frequency depending on baffle width?

 

[Trouble Maker]

It's kind of advertising, don't You feel so, somehow?

A little bit, then isn't any publicly released information about a product some is selling advertisement at some level?
I found a point someone in another thread made interesting. Maybe it was the thread about 'why are AVRs so bad' or the one where someone was proposing a push for more quantitative (FR or spins) info from speakers makers. Someone said that releasing too much technical info would just confuse most customers. The counterpoint is that they could release basic info on the web page or print materiel for a shop and then have a separate piece with more technical info for those interested. This seems like exactly what KEF is doing with these 'white papers'. I do believe they have sound engineering behind their decisions and they have no reason to lie in the white paper so it's probably true to their design decisions. You can disagree with the technical content, but I don't believe they are putting out any false info (marketing speak) about their design decisions.

 

[Trouble Maker]

...their baffles start descending to the rear of the cabinet just outside the driver. As a result, the sound waves don't travel out to the sides, but immediately behind and away.

In the paragraph proceeding what I posted above. I find this most interesting because they are fully admitting here that even at R series prices there are design (cost/performance) compromises. Emotionally, probably not many people want to read that there were design compromises when they are spending $5~$10k on a system, or even 'just' a few grand for a stereo pair. That is a lot of money no matter which way you slice it.
I can imagine the cabinets in the Blade series are quiet expensive to make.

The classic way of dealing with this effect is to round the sharp corners of the cabinet. In simple terms, this can be regarded as creating a multitude of edges, each with much lower levels of secondary radiation. The total level is much lower with the result that the time smearing becomes inaudible and the driver’s response smoother. However, the radius of curvature must be of the same order as the wavelength of the sound, the overall width of the cabinet increases, making it more visually intrusive, and the cost of manufacture increases considerably. So, whilst this technique is often found on the most expensive systems, it is not appropriate to the R Series.

 

[GelbeMusik]

... sound engineering behind their decisions and they have no reason to lie in the white paper ...

A technique that is not considered lying is to make up a problem, were no is. Only to sell the solution. With technical stuff it becomes a bit bothersome, though.

I can imagine the cabinets in the Blade series are quiet expensive to make.

Not so much as to justify the considerable markup. It's more like making a surf board, which in the making costs so and so. At least less than the retail price. And then one has to substract the cost of the wooden cabinet.

Doug got it wrong, I dare to say. Your quote of KEF on the topic corrects his perspective, I think. It is as simple explained as it is right. Only that they don't say, in roaring silence, how much the round-off improves. Not too much. I like the BLADE visually, that's for sure.

 

[Deleted member 14468]

Doug got it wrong, I dare to say.

It's OK to say -- but why do you say that? I've actually had KEF Reference 1, Blade Two, and R-series speakers in my room. I've also talked to Jack O'Clee Brown at length about this topic. In fact, many people don't know this -- the Reference 5 and Blade Two are more or less the same speaker in terms of cabinet volume and driver configuration. I've never compared the two back to back, but at KEF they have and I was told that they both win out in certain ways to each other. And in that regard, Jack told me the Blade Two sounds a little more open than the Reference 5. I asked him specifically about the baffle shape contributing to that and he thinks it does, but Jack is reserved, scientific, and not prone to just proclaim things without knowing 100%. He told me they need to do more experiments to know for sure, which I'm OK with. It's not necessarily "wrong" though.

As for who Jack is and how much we talk about this stuff, I interviewed him at KEF just two months ago:

Doug Schneider
SoundStage!

 

[Deleted member 14468]

I find this most interesting because they are fully admitting here that even at R series prices there are design (cost/performance) compromises. Emotionally, probably not many people want to read that there were design compromises when they are spending $5~$10k on a system, or even 'just' a few grand for a stereo pair. That is a lot of money no matter which way you slice it. I can imagine the cabinets in the Blade series are quiet expensive to make.

I've toured more audio companies than I believe any reviewer in the world has. Believe me, this stuff isn't often cheap to manufacture in the volumes they're manufacturing (this isn't mass production). When you see a rectangular box, it's to cut costs. As simple as that. When a company has a rounded cabinet and a reasonable price, usually they're made in China. But even Chinese manufacturers are having trouble with that. It's not easy -- it's not cheap.

Doug Schneider
SoundStage!

 

[GelbeMusik]

It's OK to say -- but why do you say that?
Doug Schneider
SoundStage!

O/k, I only read the quote: "... baffles start descending to the rear of the cabinet just outside the driver. As a result, the sound waves don't travel out to the sides, but immediately behind and away."

That's not exactly correct. To a layman it reads like aerodynamics, fluid flow or such. Acoustics and aerodynamics as engineering fields only share common grounds at the sound barrier. Not here.

In principle sound waves, how to say, they are static, they form a specific pattern. Especially they don't "travel". Too hard to explain to an anonymous audience. It is only so, that an edge, and a rounded edge in the same way act as a second sound source. What comes out is, that the primary source, namely the driver and the edge eventually form a combined generator. And naturally the two sources interfere.

The shape of the interference pattern depends on many variables. First of all it is about the distance of primary source, the driver, and the edge of whatever making as the second. The inherent directivity of the driver, the particular shape of the rounding etc.

Taking all this into account, there is an easier solution. If the baffle is not more than 1,4 times wider than the diameter of the cone/dome, then the interference pattern can be considered smooth, hence the round over can be omitted. I think that was the very idea of some B&W designs, most prominently realized with the Nautilus--compared to the wavelengths the edges are rather sharp

With a coaxial driver this is not a viable solution. But, to the rescue, the tweeter sits in kind of a waveguide, namely the hosting cone. In case that beams the tweets enough, again the particular form of the edge vanishes in the resulting sound field.

 

[Deleted member 14468]

Especially they don't "travel"... Taking all this into account, there is an easier solution. If the baffle is not more than 1,4 times wider than the diameter of the cone/dome, then the interference pattern can be considered smooth, hence the round over can be omitted. I think that was the very idea of some B&W designs, most prominently realized with the Nautilus--compared to the wavelengths the edges are rather sharp

Travel isn't the best choice, but I'm not sure what is. If you drop a stone in water and watch the rings form, they "travel" outward. That said, it's true that you can do decent enough with a cabinet that takes care of a lot of it by just concerning itself with the width, but you can also do more. I know in previous posts that you seem to like things cheap and, I think your words were "good enough." For those who like "better," however, it's a different story.

The points about baffle shape are not just for marketing purposes. They're real and easy to measure acoustically. In fact, in the 2000s, Revel, one of the most measurement- and research-oriented companies out there, did a lot of work to "sculpt" their baffles just right on the Salon2 series of speakers, with measurable and audible benefits. It's real, it works, it's measurable, it can benefit.

Doug Schneider
SoundStage!

 

[GelbeMusik]

If you drop a stone in water ...

That's not the right, not the analytical picture. The example deals not with just "a" wave, but it is an overlay of an infinite number of individual waves. For the human eye and common understanding it makes sense to speak of one wave, sure. But once a question shall be addressed, mathematics chimes in quickly. It has proven to be the most practical view, to deal with the infinite number instead. Because infinity is nothing to be scared of.

So far the "No". What about the "Yes"?

Take one frequency ( f ) at a time. Logically it is not the single drop to take, but steadily moving the wave-generator back and forth forever. That will bring up a pattern of lines witch may depict the many regularly arranged ridges of the wave (singular!). The ridges are moving outward. But the pattern remains the same. All the time, it is steady. Look later at a time t + 1/f -- exactly the same, forever.

If one places an obstacle into this wave field, the obstacle would appear as another generator, now of secondary waves. These secondaries mix with the primaries, and that is called interference. But again, the result is a fixed pattern. The pattern doesn't evolve in any way.

... you seem to like things cheap and, I think your words were "good enough." For those who like "better," however, it's a different story.

You may find beauty in an organic shape, even if it was a loudspeaker and, say, light blue. But for a knowledgable engineer or even scientist the truth and beauty lies deeper. Once one understands some stuff exemplified above, the view changes. A lot! "Good enough" is a reasonal rational. Whenever people go for perfect, desaster lurks around. So, the "good enough" may appear as even "better" than an optimum which would, if at all, only aproximately be achieved. In Your lifetime ... . Who knows, how chaotically the inference (!) of opposing ideas behaves close to "optimum"?

It's not about "cheap", it's about elegant beauty to the eye of an educated beholder.

... the Salon2 series of speakers ...

The rounding acts very much like cutting the edges more narrow. The particular profile of the edge doesn't do. Any evidence otherwise?

 

[Deleted member 14468]

The rounding acts very much like cutting the edges more narrow. The particular profile of the edge doesn't do. Any evidence otherwise?

I get the idea you like to play what we call "armchair quarterback." Second-guess design decisions without actually doing any work...

People on this forum are probably pretty familiar with Harman's work. Right now, I can't find it, but a few years ago Revel's lead designer, Mark Glazier, did a presentation at the ALMA conference (a loudspeaker-design conference) about the baffles on the Salon2 series and, yes, showed the evidence on why they did what they did. I know you'll respond from the armchair that you haven't seen it, so it's not true, but you should really try to look into what the top, well-educated, engineering-based designers are doing.

Doug Schneider
SoundStage!

 

[GelbeMusik]

I get the idea you like to play what we call "armchair quarterback." Second-guess design decisions without actually doing any work...

Ahh ja. I don't work "with" You, as the English euphemism goes, not for You, actually. But only for the fun of it, should I feel embarassed, dismissed, insulted, motivated, praised?

You didn't like the wave equation?

So, starting point was the D&D. Yes, I did a (working--he works!) cardioid 10 years back. Any questions?

 

[Deleted member 14468]

But only for the fun of it, should I feel embarassed, dismissed, insulted, motivated, praised?

Well, feel how you want. You seem to be extremely critical of everything, including very knowledgeable people who happen to do very good work.

Doug Schneider
SoundStage!

 

[tuga]

Well, feel how you want. You seem to be extremely critical of everything, including very knowledgeable people who happen to do very good work.

Very critical but not particularly demanding. Goodenough. Not great.

 

[Senior NEET Engineer]

We recently produced a video with a recording engineer in the Netherlands and he talks about the Blade Two speakers and their superior imaging. Part of that is the Uni-Q driver array, but I think part of it is also the cabinet.

Doug Schneider
SoundStage!

Part of it is the thousands of dollars he spent on cabling

 

[GelbeMusik]

You even can toe them in 45 degrees for 'extreme' toe in and get a much more spacious sound akin to a wider directivity design.

It really changes its directivy figure, gradually, with toe in. This is because the directivity is related to the reference axis. Naturally the reference axis is the direction towards the listener. In case that is changed, it makes the relations change, giving different "directivity", "early reflections" and so on.

It only needs a push on the button to re-compile the data e/g from the NFS. The wider the radiation, the smaller the effect, of course. I doubt, that such should be considerd a beneficial feature, though.

 

[napilopez]

I mentioned this in another thread, but thought I might as well post it here as well. As the early reflections curve - especially after the early reflections fix - includes a substantial weighting to the vertical data, it somewhat obscures the cardioid nature of the 8C. If we calculate a 'Horizontal DI' curve using the only horizontal portion of the early reflections curves -- the Total Horizontal Reflections curve, which is part of CTA-2034A -- we get this:

It was apparent already in the polar maps, but I personally prefer SPL plots. If we wanted to boil down horizontal directivity to a single curve, this makes 'constant directivity' nature of the speaker much more apparent.

Breaking down the total horizontal reflections into its three component curves (front, side, and rear), you can see how the 8C simply radiates way less energy to the back. For reference, here's how these curves look on a more typical speaker, the Q Acoustics 3030i:

It is the typical response; the speaker approaches omnidirectionality at lower frequencies.

And here is the D&D 8C:

It is the region below roughly 1K that is notable. From 200 to 1K, rear radiated sound is roughly 13-16dB down from the direct sound.

The net effect is, of course, the intended goal: rear radiation will have minimal interference with the rest of the sound, especially in the bass and low mids, where the room is normally such a problem.

P.S. As a side note, one nice thing about taking extensive measurements is that you can always go back and make new/better observations

 

[Balle Clorin]

By the way, just in case anyone doubts whether indoors quasi-anechoic measurements can approximate the real thing, there's quite good agreement between my measurements and the NRC's, even off-axis. Different degree intervals, but on-axis, 30, and 60 degrees track very well.

View attachment 54888

You can do a whole lot with a Umik-1 and a lazy susan if you have a bit of open space in your home.

Of course, you lose resolution at the low end and splicing the bass gets complicated, but with enough measurements at different distances you can get a pretty complete picture. I think I'll write up a guide one of these days if anyone else wants to get started taking quasi-anechoic measurements who can't send speakers to Amir - which is of course usually the preferred option.

Any progress/link to the guide for quasi-anechoic measurements?