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KEF LS50 Meta Review (Speaker)

amirm

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This is a review and detailed measurements of the KEF LS50 Meta bookshelf coaxial speaker. It was kindly purchased new by a member and drop shipped to me and costs US $1,500 for a pair.

The LS50 Meta comes in different colors and I must say, it looks stunning in white:

KEF LS50 Meta Review  Bookshelf Coaxial Speaker.jpg


You could sell it as a decoration piece and it would still sell strongly!

Even the back panel oozes beauty and custom design:

KEF LS50 Meta Review back panel Bookshelf Coaxial Speaker.jpg


Love the wide apart binding posts that are easy to tighten and loosen.

Speaker also feels quite dense and solid which is good.

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in ordinary rooms yet results that can be more accurate than an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

I performed over 1000 measurement which resulted in error rate of about 1%. Clear high frequency response is responsible for ease of measurement in this regard.

Reference axis is approximately the center of the tweeter.

KEF LS50 Meta Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker is and how it can be used in a room. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:

KEF LS50 Meta Measurements Frequency Response Bookshelf Coaxial Speaker.png


Ah, close to perfection. The only issue is the roughness in the crossover region with some hills and valleys. Directivity which is a metric of how close off-axis sounds are to direct on-axis (what hits your ears first), is very good as well.

The above is substantially better than older LS50 which had an uneven frequency response.

Sensitivity is low at around 83 dB or so.

With both drivers co-located, I could not separate their response but could provide the port/cabinet contributions:

KEF LS50 Meta Measurements Driver and port Frequency Response Bookshelf Coaxial Speaker.png


I can't figure out that bump around 1.5 to 2 kHz. Could be resonance from the woofer that we can't see.

Back to our spin measurements, here are the off-axis responses:

KEF LS50 Meta Measurements Early Window Frequency Response Bookshelf Coaxial Speaker.png


Put that together with on-axis and we get one well behaved speaker:

KEF LS50 Meta Measurements Predicted in-room Frequency Response Bookshelf Coaxial Speaker.png


We can see the well managed directivity control better in beam width and horizontal directivity:
KEF LS50 Meta Measurements Horizontal beamwidth Bookshelf Coaxial Speaker.png


KEF LS50 Meta Measurements Horizontal Directivity Bookshelf Coaxial Speaker.png


The price you pay for this is slightly narrow directivity of ± 50 degrees instead of the usual ±60 degrees. So I suggest pointing the speaker at you.

Vertically the coaxial driver cleans the clocks of any standard 2-way speaker:

KEF LS50 Meta Measurements Vertical Directivity Bookshelf Coaxial Speaker.png


So not very critical if you sit at the level of the tweeter or not.

Looking at the mid frequency 3-D directivity balloon, we see the best response since I started showing it (which hasn't been long as of this writing):
KEF LS50 Meta Measurements Horizontal 3-D ballon Bookshelf Coaxial Speaker.png


The globes are not very deformed and nicely project energy forward.

Company touts lower distortion for this speaker versus the old KEF LS50. Let's look at that:

KEF LS50 Meta Measurements relative THD vs Frequency Response Bookshelf Coaxial Speaker.png


KEF LS50 Meta Measurements THD vs Frequency Response Bookshelf Coaxial Speaker.png


Looks like distortion in from 200 Hz and up is excellent but down low, even at 86 dBSPL, we hit 100% THD. Unfortunately I don't have comparable measurements for LS50 as that was a long time ago before I standardized this way.

Impedance is quite low at 3.7 ohm and stays there for good bit of the spectrum:
KEF LS50 Meta Measurements Impedance and phase vs Frequency Response Bookshelf Coaxial Speaker.png


Combined with low sensitivity, you need to have a beefy amplifier to drive them.

Finally, for the fans of timing graphs, here are the impulse and waterfall responses:

KEF LS50 Meta Measurements Impulse  Bookshelf Coaxial Speaker.png


KEF LS50 Meta Measurements CSD waterfall Response Bookshelf Coaxial Speaker.png


KEF LS50 Meta Speaker Listening Tests
I always test speakers with the same set of tracks and in the same order. Usually the first few seconds of the first track tells me most of what I need to know about the sound of the speaker and this situation was no different. The sound was "right" and very nice. For confirm I went through the rest of my test playlist and the answer stayed the same.

Wanting to see the effect of the dips in 1 to 3 kHz, I developed a single filter at 1189 Hz. Getting it to fill that gap requires a Q of something like 7. At that level, turning it on and off showed such basically non-existent difference as predicted by psychoacoustics. We just don't have that kind of disorientation in frequency in that range. I suppose if you wanted to be anal about it, you could fill the holes. It wouldn't make things worse and maybe the combination would make more of a difference. For me, it wasn't worth the time. :) I was happy with the speaker as is.

Was it all perfect? No. As I turned up bass heavy track, the low bass notes change their tonality and quickly become distorted. Notch the volume even higher and you are greeted with scary crackle. You can visually see this in the driver. It separates from the tweeter which is kind of disconcerting but that is how the coaxial driver works. By the time you see any significant separation/movement of the woofer, the bass starts to change. Push it to move more and you are in distortion territory. The driver is simply too small/lacks the excursion for high dynamic range.

That said, I had no trouble getting usable volume out of one speaker. With two speakers, it would be plenty for most people. Problem is, I am not most people. :) I don't want to know limits of equipment I use.

Conclusions
KEF moves the bar it set with the LS50 with the Meta revision. I was not a fan of the original but they have won me over with near perfect measurements and listening test results. Make this speaker handle more dynamics in bass and I would kiss the ground it walks on. But that is not there so a notch lower for me. But really, this is an excellent speaker. No doubt about that.

I am happy to recommend the KEF LS50 Meta. Suggest pairing it with a subwoofer if you want to play loud bass though.

Edit: video review posted as well:


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As always, questions, comments, recommendations, etc. are welcome.

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MZKM

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amirm

amirm

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Matias

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df00

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"I was not a fan of the original..."

I purchased the LS50 after reading all the rave reviews people gave it on the internet and was thoroughly disappoint with it. Nice to see that I wasn't the only one that was not a fan. Wish I had returned them within the return period, but missed it. Oh well, have since added EQ and now they sound much better to me.

Speaker Toni did an excellent video comparing the LS50 to the LS3/5a. This comparison is accurate. Use headphones. His LS50 had the same tonal character as mine do. With the miniDSP 2x4HD I made my LS50 sound like the LS3/5a in the video by reducing the mids a bit and boosting the top end a bit. Here is a link to the video.
 

Sancus

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With such a nice directivity EQ will save the day here. And high passing it with a KC62 subwoofer then the tiny woofer should be happy.

At low levels, yeah. 96dB distortion is still quite bad up until 200hz, especially with 3rd harmonic above 50dB.
 

napilopez

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Another one who, while I wouldn't say I was "disappointed" with the original, I wasn't blown away by it either (The LS50 Wireless 1, however, I did love). The LS50 Meta tweaks things just enough to move to great terriroty, and I personally enjoyed it a bit more than the R3, with a sub. How much of that has to do with the 'meta' aspect of things (which does seem to reduce distortion) is hard to say, but the FR improvements over the original are obvious. Here''s the listening window compared.

LS50M vs original.png


My measurements agree nicely (mine are dashed):

Me vs asr ls50m.png


That said, the resonances between 1-2kHz are curious. It's not in my data, warkyns, or soundstage networks, so it could be a qurik with this particular speaker. Not trying to start a measurement war :), just pointing out that discrepancy, as it may be something the owner may want to take note of.

We're lucky to live in an age with so many reliable sources of measurements. Here's the on-axis for the speakers from 5 sources(not including stereophile as JA technically uses a listening window, but it's similar too):

LS50M OA Comp.png


Ironically, KEF's own measurement is the worst. My guess is because they are aligning the microphone perfectly with a laser or something and the diffraction dip only shows up with 100% perfect alignment, as it disappears in their listening window.

Clearly it's best to listen a little off axis to smooth out that little bit of on-axis brightness.
 
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amirm

amirm

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That said, the resonances between 1-2kHz are curious. It's not in my data, warkyns, or soundstage networks, so it could be a qurik with this particular speaker. Not trying to start a measurement war :), just pointing out that discrepancy, as it may be something the owner may want to take note of.
I forgot Workwyn had measured it:

20210630203429_Figure5-KEFLS50Meta-Measurements.png


They show such a shelving up for the tweeter making me think we have different axis or something was off in their sample. The bass response appears to be close to their closed port measurements earlier.
 

napilopez

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I forgot Workwyn had measured it:

20210630203429_Figure5-KEFLS50Meta-Measurements.png


They show such a shelving up for the tweeter making me think we have different axis or something was off in their sample. The bass response appears to be close to their closed port measurements earlier.

Yes, the bass response matches nicely with the port open:

LS50M OA ASR Warkynpng.png


As for the shelving, In this case I think it's probably very slightly different axis or mic calibration. Warkyn, NRC and mine show similar shelving. Yours is actually only about a dB lower aboe 4khz, certainly no big deal. It's probably just a little less noticeable in your measurements due to the different scaling. Here are those four on-axis measurements overlayed:

LS50M jumble.png



If I take the average of all 5 measurement sources we get the Ultimate LS50 Meta Metameasurement :D:

LS50M metameasurement.png
 

YSC

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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.
 
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