KEF R Series with MAT white paper

[davidbosch]

Hi folks, I'd like to share with you the white paper for the new KEF R Series with MAT (the newly released Meta models).

Big apologies for the delay we've had in publishing it, as I know some of you have been awaiting it since the market launch of the series. We've been a bit busy in R&D but I've made sure to include lots of interesting data and figures.

We've tried to go into as much detail as possible on the new technology in this iteration as well as adding new explanations on existing technology, so that you can have a global view of what we've achieved.

I sincerely hope you'll find it an interesting read and enjoy flicking through the pages.

 

[staticV3]

Hi David! Welcome to ASR.

Thank you so much for providing the community with such data. That's awesome!

On ASR, industry insiders have to register as such to avoid manipulation.
No big deal though, I'll just tag some mods to get this sorted out.
(@AdamG247 @BDWoody)

 

[Purité Audio]

Thanks David excellent, does any other manufacturer provide this depth of information?
Super.
Keith

 

[sarumbear]

Hi folks, I'd like to share with you the white paper for the new KEF R Series with MAT (the newly released Meta models).

Big apologies for the delay we've had in publishing it, as I know some of you have been awaiting it since the market launch of the series. We've been a bit busy in R&D but I've made sure to include lots of interesting data and figures.

We've tried to go into as much detail as possible on the new technology in this iteration as well as adding new explanations on existing technology, so that you can have a global view of what we've achieved.

I sincerely hope you'll find it an interesting read and enjoy flicking through the pages.

So Meta is many micro Helmholtz resonators side by side to absorb the unwanted resonances?

Now, where have I seen multiple resonators, though in a much bigger size?

 

[abdo123]

I think the KEF R6 is the star of the show. perfect radiation.

 

[jackocleebrown]

So Meta is many micro Helmholtz resonators side by side to absorb the unwanted resonances?

Now, where have I seen multiple resonators, though in a much bigger size?

Quarter wavelength resonators, not Helmholtz. The resonator fundamentals and harmonics are used to give broadband absorption. Loads of technical info here: https://www.aes.org/e-lib/online/browse.cfm?elib=20758

 

[davidbosch]

I think the KEF R6 is the star of the show. perfect radiation.

Hi @abdo123 thank you for spotting that! That's actually a mistake! I have now corrected it and reuploaded the file with the correct Spinorama for R6 Meta. This is a bit embarrassing. The LF response for R6 Meta is that of a sealed cabinet (acoustic 2nd order) and it has less bass extension than R7 Meta, which was the Spinorama put in its place before by mistake.

R6 Meta Spinorama:

 

[Jukebox]

Thanks David and Jack! Amazing work! Truly appreciated!

 

[Matias]

Amazing, this is pure ASR p0rn lol.

 

[AdamG]

Hi David! Welcome to ASR.

Thank you so much for providing the community with such data. That's awesome!

On ASR, industry insiders have to register as such to avoid manipulation.
No big deal though, I'll just tag some mods to get this sorted out.
(@AdamG247 @BDWoody)

Thank you for the Tag. Registration process has begun.

 

[fineMen]

Hi folks, I'd like to share with you the white paper for the new KEF R Series with MAT (the newly released Meta models).

Do you at KEF really think that internal cavity resonances contribute to the enclosure panels' acceleration (p/ 16)? Did you change your mind on this recently?

When will you stop optimizing the drivers? I'm serious, the tech you invest is overwhelming with unprecedented success eliminating nearly every problem associated with the dynamic driver. You kept the 2kHz dip from the baffle edges me thinks, and eventually, wouldn't a four-way suit the driver material better?

 

[staticV3]

@pierre if you'd like, I can digitize the data for spinorama.org.
Or do you usually get the raw data from KEF?

 

[jackocleebrown]

Do you at KEF really think that internal cavity resonances contribute to the enclosure panels' acceleration (p/ 16)? Did you change your mind on this recently?

Typically the force directly from the driver motor excites the cabinet more strongly than the acoustical pressure load on the interior walls. For example, the AES paper on the LS50 (link, sorry it's paywalled) shows a comparison in figure 7. However, we've made serious efforts to reduce this direct mechanical excitation and so the acoustical excitation becomes easier to see in measurement. Also keep in mind that Fig 39 from the white paper shows (in black) the velocity with a totally empty MF enclosure and the acoustical internal cavity resonances will be extremely high amplitude in this situation.

 

[abdo123]

Hi @abdo123 thank you for spotting that! That's actually a mistake! I have now corrected it and reuploaded the file with the correct Spinorama for R6 Meta. This is a bit embarrassing. The LF response for R6 Meta is that of a sealed cabinet (acoustic 2nd order) and it has less bass extension than R7 Meta, which was the Spinorama put in its place before by mistake.

R6 Meta Spinorama:
View attachment 280103

Now that’s PERFECTION.

I was more focused on the polar patterns because you guys aimed at a flat response everywhere anyway.

Is there a reason why high frequencies are struggling (lobes) a bit in other models in the vertical radiation?

 

[jackocleebrown]

When will you stop optimizing the drivers? I'm serious, the tech you invest is overwhelming with unprecedented success eliminating nearly every problem associated with the dynamic driver. You kept the 2kHz dip from the baffle edges me thinks, and eventually, wouldn't a four-way suit the driver material better?

There's always more that can be improved on the drivers to make them more ideal. With good measurement and analysis equipment it's pretty easy to find flaws in their behaviour and it's our passion to find these, try and understand them and fix them. In my opinion there are audible gains to be had by continuing with this.

To completely avoid on-axis diffraction ripple requires a cabinet with extremely smooth surfaces. If you look through the measured data that we publish you will see how far you need to go (hint: take a look at Blade). We strongly prioritise off-axis average responses because it's our experience that this is more important than the on-axis, so it does rather stand out in the data. One thing to mention is that a standing wave or driver resonance can cause a flaw that will be present on all responses in every direction (and every Spinorama curve) and hence be very audible. Four-way would be nice in many ways, but it's really hard to find a system layout for a four-way that can match the directivity behaviour of a three-way.

 

[sarumbear]

Quarter wavelength resonators, not Helmholtz. The resonator fundamentals and harmonics are used to give broadband absorption. Loads of technical info here: https://www.aes.org/e-lib/online/browse.cfm?elib=20758

I agree that the correct term I should have used is quarter wavelength resonator as Meta has multiple tube resonator with open and closed ends. However, quarter wavelength are a variation of Helmholtz resonators. 1/3 of tube near the open inlet acts as the neck of Helmholtz resonator, and the 2/3 of the tube length acts as the cavity.

I like the name Helmholtz, hence prefer to use it. In fact my own (room) resonators are in fact quarter wavelength

 

[fineMen]

Four-way would be nice in many ways, but it's really hard to find a system layout for a four-way that can match the directivity behaviour of a three-way.

A new challenge indeed. But you're right, for home use it won't be necessary. But then again, further perfectionizing the drivers neither? Nevertheless, I'm impressed how good ol' KEF picked up a problem and got it finally (I think so) solved. Bravo!

 

[davidbosch]

Sorry but i have a question to you kef guys…

Why do you guys never launch the R, reference and blades with the unicore and p-flex surround thing?
At least all models with p-flex surround (?)
Thank you and sorry for the question, but it will bring more LFE to these speakers, or nope?

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.

 

[pierre]

@pierre if you'd like, I can digitize the data for spinorama.org.
Or do you usually get the raw data from KEF?

I asked David and he sent me the data. I will merge them end of this week.

 

[nerdstrike]

I'd like to add my thanks, this white paper is more extensive than the previous non-meta R-series one. Really interesting to read.