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KEF Reference 1 META Bookshelf Speaker Review by Erin's Audio Corner

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thewas

thewas

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Is there a list without marketing stuff? For example, "reduction of distortion through the use of meta materials" isn't something that makes sense to me. They put a dampened labyrinth behind the tweeter so the sound emitted to that side doesn't get reflected back to the membrane, that makes sense to me.

Would like to avoid that wall of text if they had just a list of items in technical terms. :)
In the end of course its a paper made for marketing and not a peer reviewed paper for a scientific publication (even those sometimes are of questionable quality :p), but for that it is on a very high level and the shown measurements of many improvements can be a guide for the reader to see which are the significant ones and which rather not.
 

fluid

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It is diffraction but not the "ripply" cabinet edge kind that is seen at higher frequencies. This is the baffle step. At around 150 degrees you can see the nulls that are formed when sound wraps around the speakers and cancels out near the back corners.

400Hz200mmTD.png


Changing the edge rounding can have an influence on this low in frequency too.

Edge Rounding TD.png
 

Tangband

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Those have their place, sure, but you can't reasonably expect to boost the lowest 30Hz and below frequencies by >6dB with DSP, like the long port does. How much amplifier power are you planning to spend on overdriving low frequencies to achieve that effect?
Ofcorse, there is never a free lunch…
 

Tangband

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Although I cannot state whether or not the fancy baffle actually makes a difference in the performance, as I am not KEF's engineering team, I will definitely say that MDF (or most wood in general) is already good enough, or else why would literally everyone else use wood in their enclosures and baffles? (See: Revel Salon 2, JBL M2, etc). Genelec uses fancy metal enclosures but I think the reason they do that is to reduce material / labor costs. Despite all this, we have normal-enclosure-d speakers with as good as or better performance than the Reference series. So while the metal may look nice, and may subjectively work as a placebo to "improve" sound, it really isn't showing up on measurements when you consider measurement error.

Also, consider that while yes, the metal may be stiffer, it may also be heavier / denser. This will in turn push the resonances down in frequency. Additionally, just because a resonance is higher in frequency doesn't necessarily mean that it is lower in amplitude. If the driver is imparting more force on the baffle at that frequency, then the resonance could be worse.

So basically, I would have to agree that the fancy baffle is probably just for looks and to differentiate the Reference line from the R-line. It may make a very small difference to the sound, but looking at the R3, we can see that the Reference 1 really doesn't need anything that it would get from a metal baffle.

And lastly, keep in mind that KEF is moving more towards "lifestyle" designs. Basically, they want to increase the WAF of their speakers so that more people are able to buy them. I mean, look at the LS50 Wireless, it's one of their flagship speakers, that they then made a wireless version of. You don't see Klipsch making a wireless version of their top line. So KEF is definitely trying to break into a larger market, one which is interested in looks, and the fancy metal baffle makes it look nicer, and that's about it from an engineering standpoint.
They use MDF mainly because its cheap . Much cheaper than steel or aluminium. MDF has, in nearly every box thats been reviewed in stereophile, resonanse problems between 120-400 Hz , as you can see with John Atkinssons measurements. And yes - those resonanses can be VERY audible.


”I found a very high-level, high-Q resonant mode at 188Hz that was present on all surfaces but highest in level on the side panels (fig.2). As HR wrote of the sound through the B6es of a recording of male voice and double bass, "I heard that vibrating box—not a little, but a lot. . . . [The speakers] were vibrating like sex toys!" There are also some high-level resonant modes present in the midrange.”

Kef R1 meta has a aluminium baffle sandwich with mdf behind, which is probably a very good idea.
 
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windwolf447

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What a fine speaker (and review)!

One thing I think is interesting is the evolution of thinking on cabinet diffraction by the more technically competent speaker companies over the last ~15 years or so. If you look at the speakers that represented top-tier engineering back then - e.g. KEF 20x/2, Revel Ultima, Vivid, TAD and Pioneer EX, NHT xD, GedLee, Grimm, JBL LSR 6-series studio monitors - they were all quite curvy or often had big roundovers or highly sculpted baffles.

Compare:

kef_2012_angled.jpg
1006piosex.1.jpg


1222005142525.jpg
AREVGEM2M.jpg

JBL_LSR6328P_PAK_LSR6328P_8_2_Way_1259602377_307466.jpg


I'm not sure there's a 90 degree angle or for that matter even a flat plane on our Revel Gem2's! But today everyone except Genelec and Vivid seem to have gone boxy: 201/2 to Ref1/Ref1M, Revel Studio2 to F328Be, JBL 6328 to 708, and so on. While fashion, production costs, and bass efficiency (cabinet volume) play into that, what's notable to me here is this boring box shape with nothing but a slight waveguide around the concentric driver does not seem to suffer notable from diffraction effects.

SPL%20Horizontal.png


201/2 is still IMO the prettiest speaker KEF has made to date though. My wife would probably prefer this one, albeit with a full-face grille.

The slight waveguide (Shadowflare) around the Uni-Q in combination with the midrange cone forms a large waveguide for the tweeter. When a waveguide is almost as large as the width of the baffle, you could get directivity control down to the first baffle diffraction frequency to a degree depending on how deep the waveguide is. This design seems to work well both aesthetically and performance-wise.
 

Tangband

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The slight waveguide (Shadowflare) around the Uni-Q in combination with the midrange cone forms a large waveguide for the tweeter. When a waveguide is almost as large as the width of the baffle, you could get directivity control down to the first baffle diffraction frequency to a degree depending on how deep the waveguide is. This design seems to work well both aesthetically and performance-wise.
In Kef R1 Meta the crossover is way below the wavelengt of the wideness of the cabinet , at 450 Hz , - You dont need rounded sides in this construction.
The wavelength of 1 kHz is 34,3 cm . 500 Hz is the double - 68,6 cm.
 
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bigjacko

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Where are you getting 7" waveguide from?
The width is 205 cm, the waveguide is just a bit less then that, so I guess it is around 7 inch, it is not precise but it does not matter that much.
 
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thewas

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They use MDF mainly because its cheap . Much cheaper than steel or aluminium. MDF has, in nearly every box thats been reviewed in stereophile, resonanse problems between 120-400 Hz , as you can see with John Atkinssons measurements. And yes - those resonanses can be VERY audible.
As I had showed you in the past such generalisations are not expedient, the material is secondary, the engineering is what counts, you can have an acoustically very dead MDF enclosure and a ringing metal one: https://www.audiosciencereview.com/...iew-powered-monitor.28039/page-26#post-973727
Look which one has the problematic resonances in the 120-400 Hz region you mention, it is not the MDF one.
 

tuga

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Is there a list without marketing stuff? For example, "reduction of distortion through the use of meta materials" isn't something that makes sense to me. They put a dampened labyrinth behind the tweeter so the sound emitted to that side doesn't get reflected back to the membrane, that makes sense to me.

Would like to avoid that wall of text if they had just a list of items in technical terms. :)

Would you not call "the sound emitted to that side which gets reflected back to the membrane" distortion?
 

Everett T

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The width is 205 cm, the waveguide is just a bit less then that, so I guess it is around 7 inch, it is not precise but it does not matter that much.
Just didn't know if I was missing some spec. How does that translate from the midrange driver to the recess around it? Trying to understand if the surround edge or the recess denotes the diameter?
 

changer

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Those have their place, sure, but you can't reasonably expect to boost the lowest 30Hz and below frequencies by >6dB with DSP, like the long port does. How much amplifier power are you planning to spend on overdriving low frequencies to achieve that effect?

Power ist not a limitation and group delay a function of actual acoustic slopes. So why not use the cheap power, if the driver can work it?
 

Koeitje

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Yes, they are a "premium series" product where you pay a high sucharge for the design, cabinet materials, image/statuts, hand assembly in UK, small production batches etc. In such series the price is also more dictated by the market prices (also of the competition) than just of the costs, for example if it would be much cheaper than its competitors many people and unfortunately also today's audiophile press would consciously or subconsciously place/grade it to a lower class, this is unfortunately how the market works.
Compared to some competitors the Reference series pricing is pretty good. I see tons of loudspeakers that cost more than the Reference series and perform less.
 

hmt

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Power ist not a limitation and group delay a function of actual acoustic slopes. So why not use the cheap power, if the driver can work it?
Because the driver will need a 4x higher excursion to make up for the 6 db of the low port tuning
 

changer

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Because the driver will need a 4x higher excursion to make up for the 6 db of the low port tuning

If one wanted to tinker with the r3, and what the issue from Erin's subjective listening impression is is that anechoic bass is shelved, to achieve a passive room correction, inserting a shorter port would probably the first step. I find it to be a good consideration to EQ r3 and change the bass alignment, if possible. It is much cheaper, why not try. Linear distortion is king, if directivity allows, if drivers allow, than work it. It can make all the difference.

The second part of your assertion: this is heavily dependent on the driver. Look in the Neumann KH 150 thread. I posted a video that shows the action of a ten inch driver, the diaphragm is not moving at all, the levels are already quite elevated. There is a +4 dB PEQ, Q=1.7, fc=48, and +2.2 dB, Q=1.6, fc=74, and also a Low Shelf for baffle step compensation, +5 dB, Q=0,7, fc=150. The driver is less sensitive than my previous, so I opted for a boost instead of shelving down the higher frequencies. I have not noted an issue with the sound. Probably the voice coil is moving a fair bit, I have not asked WinISD what it assumes, but this driver has +-8mm of linear excursion. And power is not a problem.
 

jhaider

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The slight waveguide (Shadowflare) around the Uni-Q in combination with the midrange cone forms a large waveguide for the tweeter. When a waveguide is almost as large as the width of the baffle, you could get directivity control down to the first baffle diffraction frequency to a degree depending on how deep the waveguide is. This design seems to work well both aesthetically and performance-wise.

Dr. Earl Geddes and others at the time argued that edge diffraction was still a problem on speakers with large waveguides. For example, here is a picture of a GedLee Summa by @Patrick Bateman. To give you a sense of scale, that's a 15" woofer, and a Danley PA horn (I think model SH50) next it. As you can see there's very little flat area between the WG termination and the cabinet edge roundover.

IMG_0661.JPG


I'm not convinced the little extra flare is the whole answer. I suspect the difference is more computing power to model cabinet effects and design around them by playing with relative dimensions, features, and even the crossover. Obviously KEF's waveguide stub came from that, but more likely than not so did the cabinet dimensions for late model Revels and so on as well. Keep in mind that the current JBL waveguides (M2, 4367, 7-series, SCL) are, as I understand them, diffraction managing shapes rather than minimum diffraction shapes such as the GedLee oblate-spheroid waveguide.
 

Ilkless

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Keep in mind that the current JBL waveguides (M2, 4367, 7-series, SCL) are, as I understand them, diffraction managing shapes rather than minimum diffraction shapes such as the GedLee oblate-spheroid waveguide.

That is my understanding too, per Charles Sprinkle in a Mixonline interview.

“The second thing we did was use a blending geometry—there are no straight lines, you’ll notice—that has a generally decreasing radius,” he continues, “forming an infinite number of reflections, and the net effect is that it smears the reflections coming back down the horn and negates them.

Seems like low-level diffraction spread throughout the passband. In some ways like the SEAS DXT is for direct radiators?
 

changer

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This box is certainly just a box, and it introduces diffraction as every other. There is diffraction, not only the usual around baffled width that was already identified, you can even see it in reference axis measurement. You must not look at PIR for this, where diffraction ripple is averaged out. Cabinet depth can lessen the big dip introduced by the baffle, but no miracles. The rather calm ripple is probably due to the three way.
Also, bringing the waveguide to the edge is not enough, in a two way, there is a huge area below. And the wavefront is not one horizontal, another vertical. It is one wavefront and what happens on the vertical will leave traces in the horizontal response too.
 
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pierre

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Erin sent me his data.

First let's compare KEF own data manually scanned with Erin's data generated by the Klippel NFS: clearly KEF is honest. There is a diff in the bass likely due to errors increasing in this area.
newplot (3).png


Let's look at the differences between the Ref 1 Meta and the KEF R3. Differences are not obvious:
- the 30hz-100hz has a gap which could be measurement error. Reference is better.
- top end: Reference is also better (a bit less hot).
- directivity is the same.
newplot (2).png


The speaker doesn't need an anechoic EQ but since the software compute it anyway, here it is:

Code:
         SPK auEQ
-----------------
NBD  ON 0.32 0.28
NBD  LW 0.26 0.22
NBD PIR 0.23 0.19
SM  PIR 0.94 0.98
SM   SP 0.96 0.99
LFX       37   37
LFQ     0.79 0.79
-----------------
Score    6.6  7.0
w/sub    8.4  8.7
-----------------

and the EQ itself:
Code:
EQ for KEF Reference 1 Meta computed from ErinsAudioCorner data
Preference Score 6.6 with EQ 7.0
Generated from http://github.com/pierreaubert/spinorama/generate_peqs.py v0.15
Dated: 2022-05-07-09:34:33


Preamp: -1.9 dB


Filter  1: ON PK Fc  1038 Hz Gain +1.52 dB Q 2.41
Filter  2: ON PK Fc  3855 Hz Gain +0.89 dB Q 0.86
Filter  3: ON PK Fc   552 Hz Gain -0.70 dB Q 2.58
Filter  4: ON PK Fc   283 Hz Gain -0.57 dB Q 3.00
Filter  5: ON PK Fc   824 Hz Gain +0.50 dB Q 3.00
Filter  6: ON PK Fc  8813 Hz Gain +0.50 dB Q 2.98
Filter  7: ON PK Fc  8896 Hz Gain -0.51 dB Q 2.98
Filter  8: ON PK Fc  9288 Hz Gain +0.50 dB Q 2.99
Filter  9: ON PK Fc  9241 Hz Gain -0.51 dB Q 3.00

It generates the following differences on the spinorama:
filters_eq.png
 

Vacceo

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What a fine speaker (and review)!

One thing I think is interesting is the evolution of thinking on cabinet diffraction by the more technically competent speaker companies over the last ~15 years or so. If you look at the speakers that represented top-tier engineering back then - e.g. KEF 20x/2, Revel Ultima, Vivid, TAD and Pioneer EX, NHT xD, GedLee, Grimm, JBL LSR 6-series studio monitors - they were all quite curvy or often had big roundovers or highly sculpted baffles.

Compare:

kef_2012_angled.jpg
1006piosex.1.jpg


1222005142525.jpg
AREVGEM2M.jpg

JBL_LSR6328P_PAK_LSR6328P_8_2_Way_1259602377_307466.jpg


I'm not sure there's a 90 degree angle or for that matter even a flat plane on our Revel Gem2's! But today everyone except Genelec and Vivid seem to have gone boxy: 201/2 to Ref1/Ref1M, Revel Studio2 to F328Be, JBL 6328 to 708, and so on. While fashion, production costs, and bass efficiency (cabinet volume) play into that, what's notable to me here is this boring box shape with nothing but a slight waveguide around the concentric driver does not seem to suffer notable from diffraction effects.

SPL%20Horizontal.png


201/2 is still IMO the prettiest speaker KEF has made to date though. My wife would probably prefer this one, albeit with a full-face grille.
As a user of KEF IQ speakers, I do see the same trend you point out with cabinet shapes. From an aesthetics perspective, I really wish Kef would still employ the rounded cabinets I have but with updated drivers, crossovers and so on instead of the shoebox shape they currently release. Do I think the current series are ugly? Not at all! They follow the Ikea-like style of manufacturers such as Dali.

It is also true that at the present times, considering furniture trends, euclydean shapes (squares) are easier to integrate in most living rooms, shelves and so on; so speakers can go visually unnoticed.

However, the really interesting aspect of frames is that it seems that engineering for speakers has become so good that they can be presented in a variety of shapes yet, they keep a good performance and response, no matter the shape. For that reason, it would be nice to have a bit more variety of shapes without the Sonus Faber insane prices.
 
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