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:
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:
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:
View attachment 47771
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:
View attachment 47772
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:
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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:
View attachment 47776
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!
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Here is the waterfall/"CSD" graph using the same scale as I presented in my last review.
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Distortion Measurements
These are all in-room measurements at the same SPL as the spinorama measurements:
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Here is the same data but presented in the more familiar THD ratio/percentage:
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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:
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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.
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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
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