KEF R Series with MAT white paper

[jonfitch]

Ref 1 Meta:

 

[Beave]

Sorry guys but i have to do this. Since you guys are very gentle answering the questions.

Since often there is some people with the impulse response graph and saying the woofers is lagging vs the uniq, any comments about this?

A member here posted a review and also the impulse response image from the review, but the reviewer say this interesting thing:





Measurements and images from the reviewer are here:

Multitest bookshelf speakers - 2500 Euro - part 3

Intro Contents 1. Intro2. ATC SCM113. Elac Vela BS4034. KEF R3 Meta5. Monitor Audio Gold 1006. Rounding7. CommentsWe have already reached the final part of this triptych. Finally, we have […]

alpha-audio.net

Post from the member here:

KEF R3 meta Measurements

No. Again, the difference is huge, at least with KEF's excellent coaxial driver. It is not that hard to do the test yourself, with the tweeter filter. One box and is compared to the other without altering. And two or more people (ears). A "cheap" bypass cap: CORNELL DUBILIER 940C Film Capacitor...

www.audiosciencereview.com

--------------------------------


This was my question about the post from the member (same page):

KEF R3 meta Measurements

No. Again, the difference is huge, at least with KEF's excellent coaxial driver. It is not that hard to do the test yourself, with the tweeter filter. One box and is compared to the other without altering. And two or more people (ears). A "cheap" bypass cap: CORNELL DUBILIER 940C Film Capacitor...

www.audiosciencereview.com

I wouldn't give any credibility to that "review" or to that particular ASR poster.

 

[phoenixdogfan]

I wouldn't give any credibility to that "review" or to that particular ASR poster.

The only ASR member I have set to ignore.

 

[Mnyb]

It is very interesting the whole midrange driver is also redesigned and improved , it seems only the bass drivers are the same as the old series .

I also find the approach if iterating the “same” speaker over and over and making gradual progress quite endearing

R , R-meta and REF and the predecessors have a lineup of similar speakers that goes trough this process, efficient process it seems ?

 

[muad]

Is it just me or do the R Meta series have much narrower vertical axis dispersion than the Blade/Reference? It's oddly narrow for a coaxial driver, at least according to Kef's white paper measurements.

R3 dispersion:
View attachment 280350

Could likely jus the the scale. There's 5db steps between colours, very low resolution plot. It why some of the polar responses look a little funny. 1 or 3db scales are more common

 

[Vacceo]

Hi, we've only used the P-Flex so far on KC62 and LS60 Wireless, both of which use sealed cabinets and have a combination of extreme driver volume displacement and small enclosure volume, so P-Flex was not a luxury, but a technical solution to keep the surround from collapsing under pressure without using a thick and stiff surround. Big ported enclosures with less driver excursion might not benefit the same so we haven't briefed it so far for the Meta upgrades but that doesn't mean you won't see it used in some way in future speakers from us.

This said, I am super curious about what you have in the works for the subwoofer department.

I have been using a KC62 in a small room for mixed use (TV, music, radio...) combined with a pair of LS50 WII and I cannot be happier.

I guess I just have to wait, as time will give an answer to my curiosity.

That said, I can only congratulate you for years and years of outstanding designs, passion and great device. I'm still using an almost 20 year old set of IQ's on a different system, so that right there is a testament to something well done.

 

[fineMen]

Really? Were people having a hard time with this? ... it was as literally as simple as using my thumbs to gently massage the ring back in, like 1mm.

With my specimen pressing one side in makes the opposing side pop out!? Massaging it in incrementally doesn't yield in an even fit.

 

[davidbosch]

Sorry guys but i have to do this. Since you guys are very gentle answering the questions.

Since often there is some people with the impulse response graph and saying the woofers is lagging vs the uniq, any comments about this?

A member here posted a review and also the impulse response image from the review, but the reviewer say this interesting thing:





Measurements and images from the reviewer are here:

Multitest bookshelf speakers - 2500 Euro - part 3

Intro Contents 1. Intro2. ATC SCM113. Elac Vela BS4034. KEF R3 Meta5. Monitor Audio Gold 1006. Rounding7. CommentsWe have already reached the final part of this triptych. Finally, we have […]

alpha-audio.net

Post from the member here:

KEF R3 meta Measurements

No. Again, the difference is huge, at least with KEF's excellent coaxial driver. It is not that hard to do the test yourself, with the tweeter filter. One box and is compared to the other without altering. And two or more people (ears). A "cheap" bypass cap: CORNELL DUBILIER 940C Film Capacitor...

www.audiosciencereview.com

--------------------------------


This was my question about the post from the member (same page):

KEF R3 meta Measurements

No. Again, the difference is huge, at least with KEF's excellent coaxial driver. It is not that hard to do the test yourself, with the tweeter filter. One box and is compared to the other without altering. And two or more people (ears). A "cheap" bypass cap: CORNELL DUBILIER 940C Film Capacitor...

www.audiosciencereview.com

Hi, it's a bit difficult to comment on subjective impressions when not being there. The measurements provided in that review are not particularly clear either and seem not to be anechoic. Like some have pointed out, there is an inherent group delay when using a crossover that is higher in a 3-way system. We wrote a little bit about this in the LS60W white paper making a case for DSP phase correction being more noticeable on a 3-way speaker.

Ported speakers as well will always be inferior in transient response due to the system order, which could be tied to the perception of bass 'timing' but their benefits (bass extension and lower displacement/lower distortion)(at least in passive speakers) tend to outperform this inherent issue. I'm not trying to sell you all the white papers! but we touch on this topic in the 2014 Reference white paper making a point about the LF alignment achieved with the longer ports, which is what we have in our speakers with fixed port lengths such as R Series. It compares the frequency response and response to a toneburst of a sealed and a ported system (close to flat).

Then it proposes modifying the ported system's alignment by choosing a particular a longer port length that yields a non-flat frequency response and then shows the response to a toneburst being closer to that of the sealed system.

We think this alignment works well enough in real rooms, provided the speakers are in decent positions.

 

[davidbosch]

I own the non-Meta Reference 5 fronts and Reference 4 center, so I'm good for a while there (I think) . I did upgrade my sides from the R3 to the R3 Meta and... My heights (6) from the Q50a to the R8 Meta. So I'm using the R8 Meta as height surround speakers, something Kef also advertises these as. I do understand that the (upfiring?) Atmos specification is very specific but I was under the impression these speakers are also fantastic as height (wall) mounted surround speakers?

While I have your attention: the R8 Meta Uni-Q driver looks like it's a bit of an outlier comparted to the other R Meta Uni-Q drivers. It actually looks similar to the LS Meta drivers. Can you shed some light (if possible) on the driver used in the R8 Meta?

I much appreciated your (and Kef's) involvement here at ASR!

"but I was under the impression these speakers are also fantastic as height (wall) mounted surround speakers?" - They are, don't get me wrong, but posting their spinorama would require posting either the two spinoramas, or more (grille, no grille, baffle angle and no baffle angle), or making a note about the grille and the angle of the front baffle, etc. so it didn't make the cut due to this.

The Uni-Q in R8 Meta is the LMF type, with the long-excursion Z-Flex surround, which is used LS50 Meta, Q Series and LSX. It doesn't have the fancy MF motor with the underhung coil and split top plate from the MF Uni-Q in the rest of the series but it is a sweet driver. I designed part of that motor and I can tell you it uses a lot of aluminium

 

[davidbosch]

Is it just me or do the R Meta series have much narrower vertical axis dispersion than the Blade/Reference? It's oddly narrow for a coaxial driver, at least according to Kef's white paper measurements.

R3 dispersion:
View attachment 280350

Hi @jonfitch , I don't blame you, they look a bit different, it's partly the interpolated data (https://www.audiosciencereview.com/...eries-with-mat-white-paper.43946/post-1563409) and the step size (and max value) chosen. And you know what, I'm thinking maybe possibly the postprocessing we do on the measured data to mirror the two hemispheres and to position the Uni-Q at the sphere origin, as there's a bit of a difference in the top end of the DI. We've been improving this system and Ref 1M was made at least one year before R3M. We'll try to improve this in the future and make visually consistent. The directivity of both Uni-Qs (R Series and Reference) is exactly the same, as they share the same geometry of diaphragms and phase plug. In the case of the tweeter, that's the tweeter dome size and profile, the horn around it made by the MF diaphragm and trim ring flaring into the baffle and the tweeter phase plug, which has an effect at high frequency.

There's an excellent paper from M. Dodd where he explains the design of the tweeter dome and waveguide geometry (available here, sorry there's a paywall: https://www.aes.org/e-lib/browse.cfm?elib=13720) and a paper from him and J.O.B. on the tangerine waveguide/phase plug (https://www.aes.org/e-lib/browse.cfm?elib=14684).

The baffle is slightly larger on Ref 1M but that should not affect directivity by much and should be lower in frequency than where you're pointing out.

 

[alex-z]

Kudos on the manufacturer transparency, not often that big names in the audio space even interact with forums.

I do have a tangential question, will the Q series ever get the meta-material and tweeter gap damper?

I ask because I currently use a Q100 driver as part of a DIY 3 way centre channel, and would love to get my hands on some of the newer KEF tech without paying R series prices. There was a french shop called setelec that sold KEF drivers standalone but they seem to have stopped.

 

[Soniclife]

The directivity of both Uni-Qs (R Series and Reference) is exactly the same, as they share the same geometry of diaphragms and phase plug.

Does this make the new R slightly wider directivity than the old R?

Thanks for the quality of your answers, it's rare to get such clear and understandable answers,

 

[Vacceo]

Hi, it's a bit difficult to comment on subjective impressions when not being there. The measurements provided in that review are not particularly clear either and seem not to be anechoic. Like some have pointed out, there is an inherent group delay when using a crossover that is higher in a 3-way system. We wrote a little bit about this in the LS60W white paper making a case for DSP phase correction being more noticeable on a 3-way speaker.

View attachment 280382View attachment 280383

Ported speakers as well will always be inferior in transient response due to the system order, which could be tied to the perception of bass 'timing' but their benefits (bass extension and lower displacement/lower distortion)(at least in passive speakers) tend to outperform this inherent issue. I'm not trying to sell you all the white papers! but we touch on this topic in the 2014 Reference white paper making a point about the LF alignment achieved with the longer ports, which is what we have in our speakers with fixed port lengths such as R Series. It compares the frequency response and response to a toneburst of a sealed and a ported system (close to flat).

View attachment 280384

Then it proposes modifying the ported system's alignment by choosing a particular a longer port length that yields a non-flat frequency response and then shows the response to a toneburst being closer to that of the sealed system.

View attachment 280385
View attachment 280386

We think this alignment works well enough in real rooms, provided the speakers are in decent positions.

Hi Mr.Bosch. I'd like to ask something technical.

In my experience, KEF sound has been quite consistent over the generations. From my old IQ's, to newer LS50 WII, to Blade Meta, the radiation pattern is relatively similar; the differences are in SPL, frequency extension and the clarity of reproduction.

To me, that is a demonstration that similar results can be archived with a multitude of approaches. My question is, all things equal (motor, speaker, waveguide, cabinet...), would you rather use a passive crossover or a DSP?

I was quite surprised to notice how the LS50 meta and the Wireless II sound surprisingly similar.

 

[feitaishi]

Hi Mr.Bosch. I'd like to ask something technical.

In my experience, KEF sound has been quite consistent over the generations. From my old IQ's, to newer LS50 WII, to Blade Meta, the radiation pattern is relatively similar; the differences are in SPL, frequency extension and the clarity of reproduction.

To me, that is a demonstration that similar results can be archived with a multitude of approaches. My question is, all things equal (motor, speaker, waveguide, cabinet...), would you rather use a passive crossover or a DSP?

I was quite surprised to notice how the LS50 meta and the Wireless II sound surprisingly similar.

what amp do you use for ls50 meta?

 

[exm]

"but I was under the impression these speakers are also fantastic as height (wall) mounted surround speakers?" - They are, don't get me wrong, but posting their spinorama would require posting either the two spinoramas, or more (grille, no grille, baffle angle and no baffle angle), or making a note about the grille and the angle of the front baffle, etc. so it didn't make the cut due to this.

The Uni-Q in R8 Meta is the LMF type, with the long-excursion Z-Flex surround, which is used LS50 Meta, Q Series and LSX. It doesn't have the fancy MF motor with the underhung coil and split top plate from the MF Uni-Q in the rest of the series but it is a sweet driver. I designed part of that motor and I can tell you it uses a lot of aluminium

Thanks again, and this is excellent information. So far I have been very happy with the R8 Meta (compared to the Q50a's). I assume when wall-mounted the grilles don't really matter? I have them off (like the looks better).

Maybe you can shed some light on some other conversations that are happening in ASR of the Reference vs R Series? There are a couple of Kef YT videos explaining the different drivers that are used in the Series. I have personally (at home) compared the R11, R900 and Reference 5s and obviously the Ref 5 is night-and-day better. However, it seems like some members insist that a R3 Meta should sound equal to the non-Meta Reference Series. I did try the R3 Meta vs Reference 5s at home (with a 200Hz crossover set to mostly remove the obviously LF benefits of the 4 LF drivers) and I still found the Reference 5 Uni-Q to be clearly superior (obviously the Reference Uni-Q will bring this to yet another level, but unless the stock market explodes that's a purchase for another day/year). Also, the LF in the Reference 5 is fantastic, and comparable but more controntrolled compared to the R900 (2x8" drivers). I've always found the R11s to be lacking a bit of LF (coming from 1990s Reference Fours).

 

[pjn]

Hi @pjn that's right, on the floorstanding models the LF section is divided into two enclosures. The main reason is that you want the biggest dimension of the enclosure (the height in this case) to be shorter to move the first longitudinal acoustical resonance (standing wave) higher in frequency, since it's being excited by the asymmetrical position of the LF driver(s) along this dimension. So if say, you have a standing wave at around 400 Hz with two enclosures (happening in both), you'd have that standing wave at around 200 Hz with one enclosure. You want to move this frequency higher where the LF output is already attenuated as the crossover to the MF has begun and it will also likely be easier to damp with wadding, plus with two enclosures you'd be able to use twice the wadding on the velocity antinode of the resonance. The brace also adds stiffness to the cabinet walls, which being long, also want to resonate lower in frequency. The positions of the ports are determined so that the leakage of the standing waves is minimal. The upper and lower ports are the same, the enclosure volume is roughly the same, so the tuning of the two enclosures ends up being similar. However, you can certainly play with partially or totally closing up either or both of the ports (with the foam bungs provided) to tailor the response of the speaker in your room if the walls are more rigid and/or closer than usual. I find the lower port tends to have the biggest effect since it's loaded by the ground boundary more than the upper port.

Thanks David. A great detailed description. And it's good to know I wasn't totally wasting my time. I'm exceptionally pleased with the R7s and the R6 is great for vocals (as is the R7 as a stereo pair) - after trying a few centers it is definitely the best.

 

[Vacceo]

what amp do you use for ls50 meta?

The guy who had them used a NAD C700.

 

[voodooless]

Ported speakers as well will always be inferior in transient response due to the system order, which could be tied to the perception of bass 'timing' but their benefits (bass extension and lower displacement/lower distortion)(at least in passive speakers) tend to outperform this inherent issue. I'm not trying to sell you all the white papers! but we touch on this topic in the 2014 Reference white paper making a point about the LF alignment achieved with the longer ports, which is what we have in our speakers with fixed port lengths such as R Series. It compares the frequency response and response to a toneburst of a sealed and a ported system (close to flat).

View attachment 280384

Then it proposes modifying the ported system's alignment by choosing a particular a longer port length that yields a non-flat frequency response and then shows the response to a toneburst being closer to that of the sealed system.

View attachment 280385
View attachment 280386

We think this alignment works well enough in real rooms, provided the speakers are in decent positions.

The question is: is the difference really from the port, or is it just the difference in frequency response? What happens if you take the first example, EQ the ported version to have the same frequency response as the closed one? I bet the sine response will look very similar.

 

[jackocleebrown]

The question is: is the difference really from the port, or is it just the difference in frequency response? What happens if you take the first example, EQ the ported version to have the same frequency response as the closed one? I bet the sine response will look very similar.

You're exactly right. Since the low-frequency roll-off of a loudspeaker is minimum phase (at least to a good first order approximation) then the transient response is inextricably linked to the frequency response. If you EQ the closed box to have the same response as the ported (using minimum phase EQ) then they would have the same transient response as one another. You just need to be careful of not exceeding the available displacement, power and port velocity. Also, with a passive loudspeaker the ability to apply EQ is rather limited unfortunately.

 

[voodooless]

You're exactly right. Since the low-frequency roll-off of a loudspeaker is minimum phase (at least to a good first order approximation) then the transient response is inextricably linked to the frequency response. If you EQ the closed box to have the same response as the ported (using minimum phase EQ) then they would have the same transient response as one another. You just need to be careful of not exceeding the available displacement, power and port velocity. Also, with a passive loudspeaker the ability to apply EQ is rather limited unfortunately.

Also, note that this is all theoretical. In a real-world room, all bets are off. The room will dictate the frequency response, and therefore also the transient response. The advantage of the lower tuning that KEF does, is that it generally will favorably complement the room gain, giving more extension and better power handling. it will also give a bit more latitude for EQ down low.