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KEF LS50 Meta Review (Speaker)

phoenixdogfan

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Interesting to note.

https://www.axiomaudio.com/blog/distortion

Particularly interesting is the finding on the audibility of low frequency distortions:

"While it is has been recognized for years that human hearing is not very sensitive to low bass frequencies, which must be reproduced with much more power and intensity in order to be heard, what these results show is that our detection threshold for noise (made up of harmonically related and non-harmonically related test tones) is practically non-existent at low frequencies. (The noise test tones are noise in the sense that they are not musically related to tones commonly found in musical instruments.) In fact, the noise tones at 20 Hz and 40 Hz had to be increased to levels louder than the music itself before we even noticed them. Put another way, our ability to hear the test frequency noise tones at frequencies of 40 Hz and below is extremely crude. Indeed, the results show we are virtually deaf to these distortions at those frequencies. Even in the mid-bass at 280 Hz and lower, the noise can be around -14 dB (20% distortion), about half as loud as the music itself, before we hear it. "
 

Helicopter

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Thanks Amir. I am impressed with the frequency response. The aesthetic is a contemporary masterpiece. It makes many other speakers look like cardboard boxes and such.

The low sensitivity, low impedance, and high distortion mean pairing it with very powerful amps or a subwoofer are necessary to get the most out of it. Since I like to play around with different amps, this is an important drawback to me. I find the distortion below 150Hz the most disapointing thing about this. It means they will never produce sound like a big floorstander, unfortunately.
 

napilopez

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On second thought, I wonder if the trim ring could be the cause for some of the variations from 1-2kHz, as with the R3. All five measurements show slightly different behavior in this region, so it could be something to take note of. It doesn't seem to be nearly as dramatic here as with the R3 though, so not a big deal overall.

The measurements are better than what I expected originally! now it seems that the LS50 WII based on the meta is something real nice to use also.
Yes, per KEF's own measurements it the LS50WII cleans up the response a fair bit, so it really just refines it that extra mile.

KEF's spin for the LS50 Meta:
LS50 Meta Spin.png


KEF's spin for the LS50 WII:
LS50 Wireless II Spin.png


The LW seems to be at neumanna and genelec levels.

Here I've compared the on-axis for both; you could use the difference between both speakers to create filter and make a DIY LS50W, at least FR-wise.

LS50M vs W KEF.png


That said, it's worth noting that curiously KEF's whitepaper measurements are all shelved down by about 2dB from all other reliable measurements, so they might be from an early prototype or simulation. Directivity is identical though.

LS50 Meta mine vs KEF.png
 

Doodski

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Thanks Amir. I am impressed with the frequency response. The aesthetic is a contemporary masterpiece. It makes many other speakers look like cardboard boxes and such.

The low sensitivity, low impedance, and high distortion mean pairing it with very powerful amps or a subwoofer are necessary to get the most out of it. Since I like to play around with different amps, this is an important drawback to me. I find the distortion below 150Hz the most disapointing thing about this. It means they will never produce sound like a big floorstander, unfortunately.
I consider these to be for a desktop or at best a small room.
 

mononoaware

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One could conclude the LS50 Meta would be much happier performance wise if it was a “satellite” speaker (rolled off above 100hz) rather than a “bookshelf speaker”.

Apparently it needs to be crossed over above 100hz at which point two or more subwoofers are needed to mask low-frequency localisation.
 

aarons915

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So we need a Kef R3 meta?

What would be the optimal sub crossover point for the LS50 meta?

I wouldn't cross them over under 100Hz if you're using a 2nd order high pass like most people, it depends on your listening levels though. If you listen into the 90db range at your listening position you might even bump that up to 120Hz or so. If you're using a 4th order high pass then I've found 80-100hz to be good. This is all based on minimizing their distortion by the way, your in-room measurements are the other variable that sometimes dictates where you want to cross your mains and your subs.
 

ROOSKIE

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Interesting to note.

https://www.axiomaudio.com/blog/distortion

Particularly interesting is the finding on the audibility of low frequency distortions:

"While it is has been recognized for years that human hearing is not very sensitive to low bass frequencies, which must be reproduced with much more power and intensity in order to be heard, what these results show is that our detection threshold for noise (made up of harmonically related and non-harmonically related test tones) is practically non-existent at low frequencies. (The noise test tones are noise in the sense that they are not musically related to tones commonly found in musical instruments.) In fact, the noise tones at 20 Hz and 40 Hz had to be increased to levels louder than the music itself before we even noticed them. Put another way, our ability to hear the test frequency noise tones at frequencies of 40 Hz and below is extremely crude. Indeed, the results show we are virtually deaf to these distortions at those frequencies. Even in the mid-bass at 280 Hz and lower, the noise can be around -14 dB (20% distortion), about half as loud as the music itself, before we hear it. "
Yes, though if the driver is distorting badly and especially if is at and beyond xmax, you are getting loads of IMD. The rest of the spectrum will be damaged during bass attack's when that little woofer is just being pounded. Especially as that distortion in the 100-200 range is quite high and below it is really high.
Plus compression - likely a lot, plus likely mechanical noises and possible port noises.
I have pretty much settled on 120hrz as the proper point for high passing just about any 5.25" driver. Even ones I have used that show low distortion below 100hrz are still getting close to xmax and a benefit is noticed. I don't find this benefit is that subtle. Plus really no 5" driver can play kick drums at scale and volume.
I would take two subs and use them as stands (or right next to)for the Meta's in stereo to create 3 ways @ 150ish hrz and then add a .1 or .2 for the really low stuff. Plus the location of stereo bass is good for some frequencies and then the additional locations of the .2/.1 subs can maximize other location benefits.
 
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YSC

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One could conclude the LS50 Meta would be much happier performance wise if it was a “satellite” speaker (rolled off above 100hz) rather than a “bookshelf speaker”.

Apparently it needs to be crossed over above 100hz at which point two or more subwoofers are needed to mask low-frequency localisation.
I would say for normal use as a stereo pair the distortion should be much lower at common listening level of 75-85db and at 85hz “normal” cross over to sub. Unless you intend to use them at high spl in a large living room at far field where floor-standers should be used instead
 

BrokenEnglishGuy

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Yes, though if the driver is distorting badly and especially if is at and beyond xmax, you are getting loads of IMD. The rest of the spectrum will be damaged during bass attack's when that little woofer is just being pounded. Especially as that distortion in the 100-200 range is quite high and below it is really high.
I have pretty much settled on 120hrz as the proper point for high passing just about any 5.25" driver. Even ones I have used that show low distortion below 100hrz are still getting close to xmax and a benefit is noticed. I don't find this benefit is that subtle. Plus really no 5" driver can play kick drums at scale and volume.
I would take two subs and use them as stands (or right next to)for the Meta's in stereo to create 3 ways @ 150ish hrz and then add a .1 or .2 for the really low stuff. Plus the location of stereo bass is good for some frequencies and then the additional locations of the .2/.1 subs can maximize other location benefits.

New kef incoming
1628313253980.png


1628310740132.png
1628310740132.png
 
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ROOSKIE

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Vahidhm

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I just bought them a few weeks ago as my first pair of speakers. Honestly bought Elac DBR62 and these LS50 metas at the same time and after a few days listening returned the Elacs. Kef sound was a tiny bit more robust and with a personality that I liked better. The cost difference can only be justified with aesthetics I think. I am absolutely happy with the speakers and so relieved that I see your measurements and review. Thank you. Forgot to mention that my subwoofer, svs sb2000 pro arrived a few days earlier than the speakers and they really needed that to become satisfying.
 

phoenixdogfan

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Yes, though if the driver is distorting badly and especially if is at and beyond xmax, you are getting loads of IMD. The rest of the spectrum will be damaged during bass attack's when that little woofer is just being pounded. Especially as that distortion in the 100-200 range is quite high and below it is really high.
Plus compression - likely a lot, plus likely mechanical noises and possible port noises.
I have pretty much settled on 120hrz as the proper point for high passing just about any 5.25" driver. Even ones I have used that show low distortion below 100hrz are still getting close to xmax and a benefit is noticed. I don't find this benefit is that subtle. Plus really no 5" driver can play kick drums at scale and volume.
I would take two subs and use them as stands (or right next to)for the Meta's in stereo to create 3 ways @ 150ish hrz and then add a .1 or .2 for the really low stuff. Plus the location of stereo bass is good for some frequencies and then the additional locations of the .2/.1 subs can maximize other location benefits.
I currently have a single SB2000 which I cross over at 80hz and pair with my Metas. I'll probably add a second SB2000 soon and raise the xover point to 150 hz. The SB 2000 is virtually flat from 25 hz to 140 hz, so it should be a near ideal pairing.
 

mononoaware

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I would say for normal use as a stereo pair the distortion should be much lower at common listening level of 75-85db and at 85hz “normal” cross over to sub. Unless you intend to use them at high spl in a large living room at far field where floor-standers should be used instead

In comments on a previous LS50 Meta topic, they started around 80hz cross-over and ended up with 100hz+ cross-over using 2 subwoofers to achieve optimum results and integration.

Some comments here in this thread seem to be hinting at a similar direction.
 

restorer-john

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@amirm What are we seeing with the impulse response? A single cycle? Is this supplied by the Klippel's DAC and amplified? Because there's a bunch of cycles in 3 distinct (pre-ringing-like) groups in the leadup to the impulse itself. Is it a series of impulses where you have just captured one or a single one?

Also, what is the cabinet made of- moulded plastic?
 
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Zvu

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I consider these to be for a desktop or at best a small room.

In Europe average apartment size is 50m2. Size vary from 35-75m2 in over 90%. Houses are rare in cities that exist for 600-700 years or more. With apartment of 75m2, you get living room about 25m2 at best. Kef LS50 meta is quite enough. If you add a sub, you will easily rattle neighbours glassware.
 
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