KEF LS50 Meta Review (Speaker)

[Tangband]

A subwoofer with an external crossover can be cut at 200Hz.You need a sub available from a line input by passing the internal cross over. Neumann kh805 by example.
Without external crossover The flexbase25 by amphion can be cut until 260 Hz.

Remember that at higher crossover-frequencys, the distance between a floor-standing subwoofer and a standmounted Kef ls50 becomes critical. At 100 Hz a wavelength is 3,43 meter. At 200 Hz it is 1,71 meter.

According to Linkwitz studies, when using a fourth order crossover, you need to keep the distance between main speaker and subwoofer within a quarter of a wavelength at the crossover frequency.
Meaning: crossing over at 200 Hz = 1,71 / 4 = 43 cm .

The distance between the floorstanding subwoofer membrane should therefore be maximum 43 cm from the standmounted Kef ls50:s membrane if the crossover is at 200 Hz. Almost imposible to realize. And impossible with only one subwoofer.

Edit: using an odd-order crossover att 200 Hz is a little less dependent on exact position main-subwoofer. Meaning a 3:rd order crossover.

But at crossover frequencys as high as 200 Hz, its better to have the subwoofer in the same cabinett as the main loudspeaker.

 

[sarumbear]

The distance between the florstanding subwoofers membrane should therefore be maximum 43 cm from the standmounted Kef ls50:s membrane if the crossover is at 200 Hz. Almost imposible to realize. And impossible with only one subwoofer.

Unless you mount the LS50 on top of a tall sub

 

[Chromatischism]

Dolby will disagree.

https://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/38_LFE.pdf

Discussion starts here. Read all responses:

https://www.audiosciencereview.com/...ement-makes-my-life-tedious.23892/post-808978

 

[Spkrdctr]

This is a computed impulse from the frequency sweep. Inverse FFT is performed post computation of sound field and elimination of the room. In other words, there is a lot math involved and some accuracy may be lost causing those small wiggles. I do have an in-room, unprocessed version:
View attachment 145935

Maybe I should post these instead.

This looks better to me than the one you put in the review. Good work!

 

[sarumbear]

Discussion starts here. Read all responses:

https://www.audiosciencereview.com/...ement-makes-my-life-tedious.23892/post-808978

Typical of the music industry, total disregard of standards, unlike in film production.

That is why surround in music never grow out of the niche it is in.

 

[Tangband]

Unless you mount the LS50 on top of a tall sub

Yes thats true

 

[Spkrdctr]

What are those naked woofers doing?
I have a similar set up myself, but I use two Tequila bottle hats one under each speaker aligned with the mid-point of the driver, for that extra sweet sound.

That is his DIY Dolby Atmos set up with easy access. If they were in the ceiling it would be a pain to move them around! I like those Kenwoods. Reminds me of old car subs.

 

[Rottmannash]

My goodness, what a mess. I hope that is in your basement where nobody can see it.

Maybe he does dips while listening.

 

[MaxRockbin]

https://www.audioholics.com/subwoofer-reviews/jtr-captivator-rs1/conclusion

I didn't know Audioholics showed distortion across the spectrum. That's great.

Just for a different choice, since many people buying a smaller speaker will have a smaller sub, instead of an 18" $2600 subwoofer, how about the Monoprice Monolith 10" and 12"
https://audiosciencereview.com/forum/index.php?threads/kef-ls50-meta-review-speaker.25574/
It looks like the 10" has more than 10% distortion above something like 70hz - gradually unevenly increasing to about 150hz where the graph ends.
The 12" does a lot better, under 5% from about 35Hz - 150hz and under 10% from (? hard to read) 17Hz - 35Hz (1 of the 2 ports closed).
Pretty impressive for $500/$800 subs that are sometimes on sale. It would be reasonable to cross over high with the 12". The 10"? Probably the standard 80hz crossover would make sense.

 

[digitalfrost]

Maybe he does dips while listening.

Because of the uniform radiation pattern of the speakers, the treble will change very little while he's moving up and down. Good choices made there.

 

[Everett T]

I didn't know Audioholics showed distortion across the spectrum. That's great.

Just for a different choice, since many people buying a smaller speaker will have a smaller sub, instead of an 18" $2600 subwoofer, how about the Monoprice Monolith 10" and 12"
https://audiosciencereview.com/forum/index.php?threads/kef-ls50-meta-review-speaker.25574/
It looks like the 10" has more than 10% distortion above something like 70hz - gradually unevenly increasing to about 150hz where the graph ends.
The 12" does a lot better, under 5% from about 35Hz - 150hz and under 10% from (? hard to read) 17Hz - 35Hz (1 of the 2 ports closed).
Pretty impressive for $500/$800 subs that are sometimes on sale. It would be reasonable to cross over high with the 12". The 10"? Probably the standard 80hz crossover would make sense.

The THX subs will definitely hit low distortion numbers. I spaced the monoprice units, as well a few others that are probably too expensive for this application.

 

[Mauro]

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:

View attachment 145854

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

Even the back panel oozes beauty and custom design:

View attachment 145855

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:

View attachment 145856

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:

View attachment 145857

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:

View attachment 145858

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

View attachment 145859

We can see the well managed directivity control better in beam width and horizontal directivity:
View attachment 145861

View attachment 145860

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:

View attachment 145862

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):
View attachment 145866

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:

View attachment 145863

View attachment 145864

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:
View attachment 145865

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:

View attachment 145867

View attachment 145868

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.

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

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Out of curiosity: what about intermodulation distortion? might this speaker be the first to be analyzed on this regard? That could be interesting from a technical point of view..

 

[Steve Dallas]

If you look at the distortion chart in the review you will see that distortion increases fast below 150Hz and at 90Hz it reaches 10%.

If the speaker is not straining to try to reproduce the frequencies between 20Hz and 89Hz, its distortion qualities will improve. Quantifying that requires setting a high pass filter and re-measuring.

 

[kniff]

Was contemplating LS50 Metas when i purchased new speakers a few weeks ago.. interestingly they perform similar to the Revel M16s that i ended up with.

I'm happy i didn't spend twice as much to get these! They do look good, but the Revels are no slouches in that regard either.

 

[sarumbear]

If the speaker is not straining to try to reproduce the frequencies between 20Hz and 89Hz, its distortion qualities will improve. Quantifying that requires setting a high pass filter and re-measuring.

A filter just reduces the signal level. Look at the chart, distortion is already very high from around 150Hz. A filter at 90Hz will make no difference as signal level seen by the driver at that frequency will be the same as unfiltered.

 

[AudioJester]

You do not necessarily need to cross it that high. Reducing low frequency demand on the speaker also reduces the distortion from the woofer. Crossing it at 80Hz may clean it up enough to play clean and loud. I believe I used 90Hz on my non-Meta LS50s with good results.

I see this theory quoted a lot for many speakers. Curious if there are any measurements to back it up?

 

[Sancus]

If the speaker is not straining to try to reproduce the frequencies between 20Hz and 89Hz, its distortion qualities will improve. Quantifying that requires setting a high pass filter and re-measuring.

Distortion measurements are performed with a sweep, so while this might be true ~in general~, it doesn't apply to the measurements. Multiple frequencies aren't being played.

I see this theory quoted a lot for many speakers. Curious if there are any measurements to back it up?

I haven't seen this specific issue examined, as THD measurements do not involve multi-tone signals. However, IMD measurements do, and they do tend to show reduced IMD as you go from 2-way to 3-way and 3-way to 4-way. But it's not magic and it won't fix the mid-bass limitations of this small woofer.

E: Actually I forgot the Neumann test(pg15) did do subwoofer + 3-way and showed reduced IMD.

Spoiler

 

[Pearljam5000]

 

[sarumbear]

Distortion measurements are performed with a sweep, so while this might be true ~in general~, it doesn't apply to the measurements. Multiple frequencies aren't being played.

That’s because we are talking about and measuring THD, which is the distortion of a single frequency signal.

There’s not even a standard on how to measure IMD on speakers. Besides, when you have +5% THD why would you even care on IMD?

 

[Sancus]

That’s because we are talking about and measuring THD, which is the distortion of a single frequency signal.

There’s not even a standard on how to measure IMD on speakers. Besides, when you have +5% THD why would you even care on IMD?

It's quite possible IMD on this is worse and more audible than THD. But I agree with you. I don't think everyone understands that THD measurements don't involve multiple frequencies, that's what I was saying.