• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

KEF LS50 Bookshelf Speaker Review

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
27,553
Likes
67,502
Location
Seattle Area
#1
This is a review and detailed measurements of the famous KEF LS50 speaker. It was kindly loaned to me by a local member. The LS50 costs US $1,500 but seems to be on sale for US $1,300 on Amazon and elsewhere.

The LS50 nails the look of the speaker with the bright color and shape of the concentric driver:

KEF LS50 Bookshelf Speaker Review.jpg

80% of the success of a speaker in this super crowded market is the industrial design and KEF nails that. The enclosure itself feels like it is solid all the way to its core!

Not much exciting on the back other than nice sized speaker terminals and a port that has benefited from good simulations:

KEF LS50 Bookshelf Speaker Back Panel Port Review.jpg

My company became a KEF dealer for a short period of time when the LS50 had just come out. We set it up with a Revel sub optimized for the room with DSP and it sounded good in our little room. Since then I have heard it at shows but no opportunity for careful analysis of it.

Of course there are tons of reviews and measurements of the LS50. The idea of us testing it is to have a reference set of measurements using the same system (Klippel NFS) and graphics as I present for other speakers.

Measurements were performed at around 57 degrees at elevation of 14 feet above sea level. All scents were neutralized in the lab as to eliminate their effect on measurements (had to take a shower myself). To make sure the system was ready for precise results, a five axis laser convolvometer was used to determine the acoustic center of the speaker. Independent lab data is available for the calibration system on request.

Spinorama Speaker Measurements
Our "bible" for how a speaker may sound based on measurements it the spinorama as standardized in CEA/CTA-2034 standard:
KEF LS50 Bookshelf Speaker CEA-2034 spinorama Audio Measurements.png


Focusing on the on-axis graph (in black) and its close relative, the listening window (dashed green line), we see that there is a good sized drop in bass frequencies between 50 and 150 Hz. Post crossover there is a boost in mid-frequencies starting at 2.2 kHz. The ideal here is a flat line and unfortunately we don't have it.

Good news is that the reflections as represented by the dashed blue line has less variation in it so be sure to let those play out instead of covering your walls with absorbers.

Predicted in-room response assuming you let the reflections be therefore looks like this:

KEF LS50 Bookshelf Speaker CEA-2034 spinorama Estimated-in-room Response Audio Measurements.png


Doesn't look too bad other than the droop in low bass.

In summary, you are going to have somewhat anemic bass with some exaggerations of frequencies.

Basic Speaker Measurements
The impedance chart is presented to figure out if the amplifier is "difficult" to drive and hence requires beefy amplification:

Speaker Impedance (red) and Phase (blue).png


Lowest impedance above 20 Hz is at 216 Hz. Phase angle is high at the same time so that is a difficult load although music energy is also rather low there.

At 40 Hz where a lot of music peaks are the impedance is higher to above 10 Ohm (good). Below it though we dip back down to 5 ohms or less.

Sensitivity is specified at 85 dB at 1 meter/2.83 volts. We get:

KEF LS50 Bookshelf Speaker Sensitivity Efficiency Audio Measurements.png


At mid-frequencies we get there. But in bass, you drop way down to some 75 dB. So don't go running standard calculators online on how loud a speaker gets based on the 85 dB one. Bass is where it is at and there, you need tons more power than 85 dB would indicate.

Advanced Speaker Measurements
For people who like to spend hours on measurements, here is all you need to pass that time.

Let's start with contour plots. In previous measurements, I showed them at 5 degree resolution. If we are going to measurebate, might as well go out with 1 degree granularity to put to shame anyone measuring speakers at 10 degree increments manually! :D

KEF LS50 Bookshelf Speaker Horizontal Contour Audio Measurements.png


KEF LS50 Bookshelf Speaker Vertical Contour Audio Measurements.png



KEF LS50 Bookshelf Speaker CEA-2034 spinorama Vertical and Horizontal Reflections Audio Measur...png


KEF LS50 Bookshelf Speaker CEA-2034 spinorama Full Vertical and Horizontal Directivty Audio Me...png

Here is the waterfall/"CSD" graph using the same scale as I presented in my last review.
KEF LS50 Bookshelf Speaker CSD waterfall Audio Measurements.png


Distortion Measurements
These are all in-room measurements at the same SPL as the spinorama measurements:

KEF LS50 Bookshelf Speaker Distortion Audio Measurements.png


Here is the same data but presented in the more familiar THD ratio/percentage:

KEF LS50 Bookshelf Speaker Relative Distortion Audio Measurements.png


High frequency polar plot
I went up and down the frequency range to find anything interesting to find but there wasn't any. The coaxial driver nicely generates a balloon of sound even around crossover region. I thought we must have some eye candy though so I thought I present this plot at 20 kHz:

KEF LS50 Bookshelf Speaker Soundfield at 20 kHz Audio Measurements.png


Science can be beautiful! Unlike the typical measurements performed, we have a full 3-D scan of the speaker radiation so we can present graphs like this with high resolution to show all their details.

A bit on the useful side, the same info plotted in 2-D (inset) shows that our acoustic center (tweeter) matches the measured acoustic center.

Really, really informal listening tests
I had just listened to the Harbeth M30 speakers so I thought I swap the two and listen to the same tracks. Well, this was a let down. There was no bass to speak of. Turning up the volume resulted in distortion as I could visibly see the little woofer trying to keep up. Definitely not a good choice for a large space. A subwoofer with proper EQ is well advised. Overall, I could not get excited over the sound I was getting.


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

Bought on rack to store speakers on. Felt good for a few hours until this morning when half a dozen new and huge boxes arrived! Have to buy another rack to store them! Needless to say, I am not happy spending money on anything I can't eat. So please help make me happy by donating food money using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Attachments

Last edited:

Matias

Addicted to Fun and Learning
Forum Donor
Joined
Jan 1, 2019
Messages
974
Likes
1,175
Location
São Paulo, Brazil
#3

Karu

Member
Forum Donor
Joined
Dec 23, 2019
Messages
87
Likes
74
#4
So, I have these and a Rhythmic sub. And I am getting the minidsp balanced (waiting for it to arrive). Where should I put the crossover for the sub - in the 100-150 hz range based on the above?
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
27,553
Likes
67,502
Location
Seattle Area
Thread Starter #5
So, I have these and a Rhythmic sub. And I am getting the minidsp balanced (waiting for it to arrive). Where should I put the crossover for the sub - in the 100-150 hz range based on the above?
No, you have to measure because your room heavily changes the response there. In general, it is best to set the crossover at 80 Hz so that the sub can't be located (by ear). Then measure and correct the overall response.
 

MZKM

Major Contributor
Forum Donor
Joined
Dec 1, 2018
Messages
2,141
Likes
4,376
Location
Land O’ Lakes, Florida
#6
So, I have these and a Rhythmic sub. And I am getting the minidsp balanced (waiting for it to arrive). Where should I put the crossover for the sub - in the 100-150 hz range based on the above?
Nah, anything >60Hz would be fine, the -6dB point is ~45Hz, so accounting for compression and roll-off slope, >60Hz would be fine; though the best for your room would need experimenting.
 

mhardy6647

Major Contributor
Joined
Dec 12, 2019
Messages
1,104
Likes
1,573
#7
Wow, that was quick! Kudos.
My impression - FWIW - is that KEF did design these fairly deliberately; I get the feeling that the performance measured above was deliberately baked in to these loudspeakers. I didn't get that impression for some of the earlier (and cheaper) loudspeakers measured here to date. :oops:

My sense of the low(er) frequency response - and again, stricely FWIW - is a little bump in the range of ca. 100 to 400 Hz, with a little, "low Q" peak ca. 150 Hz.

Nicely done and beautifully presented. Thank you.
 

MZKM

Major Contributor
Forum Donor
Joined
Dec 1, 2018
Messages
2,141
Likes
4,376
Location
Land O’ Lakes, Florida
#10
@amirm Please! The $22 Dayton B652 AIR for contrast!

Looking for the Bookshelf $9 apple DAC equivalent!
Not a fair comparison, the Apple dongle is arguably transparent and powerful enough for most IEMs.
The Dayton may or may not sound good, but a clear distinction will be obviously heard if compared to say Amir's Salon2's.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
27,553
Likes
67,502
Location
Seattle Area
Thread Starter #12
Preference Rating
SCORE: 4.49
SCORE ignore LFX: 6.61
Thanks for doing this. A suggestion: let's drop off at least one decimal point (4.5 instead of 4.49). And state the maximum any speaker can get.
 

napilopez

Major Contributor
Joined
Oct 17, 2018
Messages
1,169
Likes
3,494
Location
NYC
#13
Thanks for this! Lines up nicely with other LS50 measurements. I hope you get the chance to check out the active LS50W sometime - curious to see what the measured differences are. Mine showed both flatter on-axis and more controlled off-axis than measurements fo the passive versions I've seen, but I've not had the passive LS50 in-house to compare myself. Relatively Smooth DI curve should mean decent EQ-ability, as expected from a KEF coax.
 

MZKM

Major Contributor
Forum Donor
Joined
Dec 1, 2018
Messages
2,141
Likes
4,376
Location
Land O’ Lakes, Florida
#14
Let's start with contour plots. In previous measurements, I showed them at 5 degree resolution. If we are going to measurebate, might as well go out with 1 degree granularity to put to shame anyone measuring speakers at 10 degree increments manually! :D



You double posted the horizontal plot instead of vertical one.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
27,553
Likes
67,502
Location
Seattle Area
Thread Starter #15

MZKM

Major Contributor
Forum Donor
Joined
Dec 1, 2018
Messages
2,141
Likes
4,376
Location
Land O’ Lakes, Florida
#17
Thanks for doing this. A suggestion: let's drop off at least one decimal point (4.5 instead of 4.49). And state the maximum any speaker can get.
Precise measurements should have precise scores;). I'll round them more when I state it here, but leave the extra decimal for the comparison charts.

Sean Olive did not state the max score, a -6dB of 1Hz for bass gives ~15, and the paper you shared with me shows really poor speakers getting even negative scores (and they used 2 decimals). I am working on the assumption that it is a max of 10 though for the score ignoring bass as well as the radar chart.
 
Last edited:
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
27,553
Likes
67,502
Location
Seattle Area
Thread Starter #18
You double posted the horizontal plot instead of vertical one.
No. They are very much alike due to concentric driver. Look at the fine detail and you see the difference.
 

aarons915

Senior Member
Forum Donor
Joined
Oct 20, 2019
Messages
324
Likes
469
Location
Cincinnati, OH
#19
Doesn't look too bad other than the droop in low bass.

In summary, you are going to have somewhat anemic bass with some exaggerations of frequencies.
Sorry if I missed this somewhere but I've been meaning to ask does the Klippel take into account port output in any way or are these graphs purely from the woofer? Thanks.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
27,553
Likes
67,502
Location
Seattle Area
Thread Starter #20
Precise measurements should have precise scores. I'll round them more when I state it here, but leave the extra decimal for the comparison charts.
The calculations are precise but that doesn't mean the accuracy is there. We are trying to estimate listener preference. We will be lucky if the whole digit works let alone two decimal places.
 

Similar threads

Top Bottom