• 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

Joined
Jul 10, 2020
Messages
11
Likes
10
Location
Wits End
Long time owner here (since 2013) and surprisingly I'm still in love with these speakers after all these years.

Mr. Dallas is right, they're not 'airy' speakers in the treble department, they're clinically detailed. Not everyone's cup of Java.

But I have found that if more power is applied, the more expansive they sound and the treble comes more into focus, relieving some of the harshness.
I have them paired with Yammy RX-A2040 with a puny Velodyne 8" sub in a off-kilter 20'x20's room (one end of the room has a cathedral ceiling) and yet I think they sound great and so do many of the people I've demoed them for, to the point 3 of them have bought 'em and they've had no regrets.

Thank god, I would have never heard the end of it. :)

The mistake that I've seen most often with the LS50's is people pairing them with a less than robust power plant and they complain of tinniness in the sound when they try to play them loud for a party or something.

One of my friends who bought them after he demoed mine, came back to me to complain about this. I dragged up my old Yammy RX-V3900 to his house and all I'll I heard was tumbleweeds out of him.

Another satisfied, if light in the wallet, customer.
 

whazzup

Active Member
Joined
Feb 19, 2020
Messages
147
Likes
64
The mistake that I've seen most often with the LS50's is people pairing them with a less than robust power plant and they complain of tinniness in the sound when they try to play them loud for a party or something.
Do you know which amplifier they were using that led to tinniness in the sound? For example?
 
Joined
Jul 10, 2020
Messages
11
Likes
10
Location
Wits End
Do you know which amplifier they were using that led to tinniness in the sound? For example?
It was a Denon AVR, 75 WPC if I remember correctly. It's been a while now. Did a quick intergoogle check and I believe it was the AVR-1800. Once he jumped up to the AVR-X4200 model he was much happier.
 

whazzup

Active Member
Joined
Feb 19, 2020
Messages
147
Likes
64
It was a Denon AVR, 75 WPC if I remember correctly. It's been a while now. Did a quick intergoogle check and I believe it was the AVR-1800. Once he jumped up to the AVR-X4200 model he was much happier.
Thanks! Maybe instead of rounding up the amplifiers that pushes the LS50 'adequately', a list of amplifiers that DID NOT push LS50 well (anecdotally) could be useful to see whether they have any commonalities....
 
Joined
Jul 10, 2020
Messages
11
Likes
10
Location
Wits End
Don't suppose you recorded any room measurements of the two setups?
Don't know if this directed to me but I've never measured anything. Strictly going by my Dumbo's (ears).

When I purchased the LS50's initially I had them paired with a Yamaha RX-A3030 before moving them to my bedroom and hooked them up to the Yamaha RX-A2040 and there was a difference, a slight downgrade in the SQ (sound quality). Of course there were other factors too; room size (14'x14'), going from 2 subs to a single sub, so ...
 
Joined
Jul 10, 2020
Messages
11
Likes
10
Location
Wits End
Thanks! Maybe instead of rounding up the amplifiers that pushes the LS50 'adequately', a list of amplifiers that DID NOT push LS50 well (anecdotally) could be useful to see whether they have any commonalities....
Definitely something to consider no doubt.
 
Joined
Oct 9, 2019
Messages
26
Likes
0
I really would like to get these but I don't have room for a big amp on my desk where I would have them nearfield. I am down to a Yamaha WXA-50 or Sonos AMP for where I have room. Might be able to get a Emotiva AMP with a MINI DSP for Sub crossover I guess also. Just can't go anywhere to hear them for a demo before buying where I live.
 

Angsty

Active Member
Forum Donor
Joined
Apr 11, 2020
Messages
125
Likes
143
Location
Southeastern U.S.
I really would like to get these but I don't have room for a big amp on my desk where I would have them nearfield.
You could consider the wireless, powered version, but it is a lot more expensive. The wireless version does also accept usb, toslink and RCA inputs.
 

whazzup

Active Member
Joined
Feb 19, 2020
Messages
147
Likes
64
Listing published specs of the 2 Denon models mentioned by Ponzi as well as the CXA60 mentioned by Steve below. Of course, there're too much variables still, like size of room, differing definition of loudness, and accuracy of published specs, but maybe a general picture can still be painted.


Denon AVR-1800 (manual link) - couldn't drive LS50 'loud'
Power amp rated output (2ch driven)
  • 75W + 75W (8 ohms, 20 Hz - 20 kHz 0.05% THD)
  • 110W + 110W (6 ohms, 1 kHz 0.7% THD)
Dynamic power
  • 100W x 2ch (8 ohms)
  • 145W x 2ch (4 ohms)
  • 170W x 2ch (2 ohms)
D/A output
  • Rated output - 2V (at 0 dB playback)
  • Total harmonic distortion - 0.008% (1 kHz, at 0 dB)
  • S/N ratio - 102 dB
  • Dynamic range - 96 dB


Denon AVR-X4200W (manual link) - could drive LS50 'loud'
Power amp (Front)
  • 125W + 125W (8 ohms, 20 Hz - 20 kHz 0.05% THD)
  • 165W + 165W (6 ohms, 1 kHz 0.7% THD)
Dynamic power
  • 130W x 2ch (8 ohms)
  • 190W x 2ch (4 ohms)
D/A output
  • Rated output - 2V (at 0 dB playback)
  • Total harmonic distortion - 0.008% (1 kHz, at 0 dB)
  • S/N ratio - 102 dB
  • Dynamic range - 96 dB


Cambridge Audio CXA60 (tech specs link) - could drive LS50 'adequately'
Power output
  • 60W RMS into 8 Ohms
  • 90W RMS into 4 Ohms
THD (unweighted)
  • <0.002% 1kHz at 80% of rated power
  • <0.02% 20Hz – 20kHz at 80% of rated power
 
Joined
Jul 10, 2020
Messages
11
Likes
10
Location
Wits End
I have found my LS50's work best with the crossover to the subs a little higher than 100 hz. Another forum member running a very similar system also uses 100 hz and he is considered to be an expert around here.
Wannna thank u guys for recommending crossing the LS50's at 100hz. I fiddled around a bit and set the crossover at 95.2 on my Yammy RX-A2040 and there was a noticeable improvement. I previously had them set on the default 80hz, which wasn't bad by any means but its rounded out the overall soundstage now.

Danka!
 

KaiserSoze

Active Member
Joined
Jun 8, 2020
Messages
297
Likes
158
Listing published specs of the 2 Denon models mentioned by Ponzi as well as the CXA60 mentioned by Steve below. Of course, there're too much variables still, like size of room, differing definition of loudness, and accuracy of published specs, but maybe a general picture can still be painted.


Denon AVR-1800 (manual link) - couldn't drive LS50 'loud'
Power amp rated output (2ch driven)
  • 75W + 75W (8 ohms, 20 Hz - 20 kHz 0.05% THD)
  • 110W + 110W (6 ohms, 1 kHz 0.7% THD)
Dynamic power
  • 100W x 2ch (8 ohms)
  • 145W x 2ch (4 ohms)
  • 170W x 2ch (2 ohms)
D/A output
  • Rated output - 2V (at 0 dB playback)
  • Total harmonic distortion - 0.008% (1 kHz, at 0 dB)
  • S/N ratio - 102 dB
  • Dynamic range - 96 dB


Denon AVR-X4200W (manual link) - could drive LS50 'loud'
Power amp (Front)
  • 125W + 125W (8 ohms, 20 Hz - 20 kHz 0.05% THD)
  • 165W + 165W (6 ohms, 1 kHz 0.7% THD)
Dynamic power
  • 130W x 2ch (8 ohms)
  • 190W x 2ch (4 ohms)
D/A output
  • Rated output - 2V (at 0 dB playback)
  • Total harmonic distortion - 0.008% (1 kHz, at 0 dB)
  • S/N ratio - 102 dB
  • Dynamic range - 96 dB


Cambridge Audio CXA60 (tech specs link) - could drive LS50 'adequately'
Power output
  • 60W RMS into 8 Ohms
  • 90W RMS into 4 Ohms
THD (unweighted)
  • <0.002% 1kHz at 80% of rated power
  • <0.02% 20Hz – 20kHz at 80% of rated power
The difference between the power capability of the two Denon amplifiers (at the distortion level that Denon uses for their specifications) is 2.2 dB. For some reason the word "anecdotal" is trying to find its way to the tip of my tongue.
 

whazzup

Active Member
Joined
Feb 19, 2020
Messages
147
Likes
64
The difference between the power capability of the two Denon amplifiers (at the distortion level that Denon uses for their specifications) is 2.2 dB. For some reason the word "anecdotal" is trying to find its way to the tip of my tongue.
definitely. Still too many variables. But that’s how all observations start. The real specs of the older Denon amp might not be as close to the published specs. Hopefully we can get to the next stage where we can pinpoint attributes of amplifiers that tell us how well they’re going to drive speakers...
 

KaiserSoze

Active Member
Joined
Jun 8, 2020
Messages
297
Likes
158
definitely. Still too many variables. But that’s how all observations start. The real specs of the older Denon amp might not be as close to the published specs. Hopefully we can get to the next stage where we can pinpoint attributes of amplifiers that tell us how well they’re going to drive speakers...
That's a nice ambition, but to do this properly you are going to have to conduct some very difficult double-blind tests. If a statistically significant percentage of a statistically significant number of listeners in proper testing conditions report hearing a problem when the speaker in question is paired to some particular amplifier (or a class of amplifiers that share some particular attribute by which they are distinguished from amplifiers at large), then it will be scientifically justified to report this finding. But this will be extremely difficult, and already this is looking like your garden variety audiophile "test" where some conclusion is reached and reported without the proper scientific methodology.

Note also that anytime that it is reported that a certain speaker needs a certain kind of amplifier, or a certain amount of power, before it sounds right, that this is something that should always, always be viewed with skepticism, especially when the two amplifiers differ by only 2.2 dB and they are by the same manufacturer, most likely the same topology. This is not to suggest that it is impossible for their to be incompatibilities between amplifiers and speakers (beyond the obvious need for the speaker's minimum impedance to not be less than the amplifier was designed to work with), however it is likely true than vast majority of claims of this nature are fanciful. I generally disregard claims of this nature unless there has been an investigation which has determined the particular reason why the speaker didn't sound right when paired with the particular amplifier. I've come across claims of this variety on very many occasions, but I do not recall a single instance where the claim was along the lines of, "It sounded as it should at lower volume, but when turned up a little louder, the tonality changed, with an attenuation somewhere around ..." The fact that you never hear it stated this way is a red flag. It never occurred to the person making the claim that if the power capability of the amplifier were genuinely an issue, that it should only occur at higher volume, i.e., that you should be able to test this theory simply by turning the volume down a little bit (by only 2.2 dB in this case) to see if it goes away. As such, the claim that is made is that at all volume levels the given speaker sounds bad with amplifiers with power output less than X Watts. This just doesn't make sense to me, which is why I am highly skeptical of all claims of this nature. The first test of the hypothesis shouldn't be to listen to the speaker with a more powerful amplifier. The first test should be to experiment with the volume level to see if the supposed problem is sensitive to the amount of power the speaker is demanding of the amplifier. I won't say that there are no exceptions, but in a very high majority of the cases when people assert inferior and superior pairings of amplifiers and speakers and when this is not for a fundamental reason that should be obvious and trivial to identify...
 

whazzup

Active Member
Joined
Feb 19, 2020
Messages
147
Likes
64
Oh, I do know it’s more of a pipe dream than a realistic expectation that we can find those magic attributes, or expect manufacturers to give them to us. But it’s still fun to keep the conversation going, continue to shake the trees in the hope that something comes loose :D
 

KaiserSoze

Active Member
Joined
Jun 8, 2020
Messages
297
Likes
158
My understanding is that yes 0 phase like an ideal resistor is easier to drive. I think it's not that it's -6 at 216Hz but that a little lower frequency than that it's coming up from -50 degrees. 4 ohms minimum is fairly common for bookshelf speakers and that phase transfer around 200Hz is almost identical to the revel m106 that amir also said wasn't super easy to drive.

I think a lot of the reputation about the LS50's amplifier needs comes from a lot of the fluff in this industry. There have been a lot of recommendations of the LS50 as a great speaker that punches way above it's weight/price and therefore the idea is that it can make use of a better amplifier. There has been a typical idea that you must break your budget up equally between source, amp and speakers for example. If you were a typical audiophile that didn't know about the great value hypex amps then you might think you need to pay significantly more than $1500 to get a good amp. I think it also helps to deflect negative criticism from people who didn't like the ls50 - for example "you didn't feed it with a proper amp". Then couple those thoughts and ideas floating around with the ls50W version using 200W for the woofer. That then means Kef confirmed it - you *need* at least 200W to get the most out of them. However the LS50W is also using DSP to push the bass response of the driver out lower then the passive would.

So do you need a ton of power - like Steve said - well how big is your room? I drive mine with an amp rated for 80W into 4 ohm. They are obnoxiously loud in my apartment with the volume set at 1/3 (whatever that means). That equates to say 85-90dB at the listening point. However I do use a sub and room correction which could make things easier. Would the sound improve with a better amplifier? Who knows - maybe? I'm somewhat skeptical that I'd notice though. But do I still have an itch to try a hypex or purifi amp? Oh yes...
I think that your interpretation of the phase issue is almost certainly correct, i.e., that it isn't the -6 (or whatever) but the much greater phase angle (the phase offset between voltage and current) at nearby frequency. I also like what you wrote in that second paragraph. In general claims of the sort that speaker XX needs a more powerful amplifier are just "fluff" as you put it.

Anyway, even though it was someone else who raised the question of how phase angle in speaker impedance can cause difficulty for an amplifier, I thought I would attach two links to write-ups here.

https://www.stereophile.com/content/measuring-loudspeakers-part-one-page-6

https://www.audioholics.com/loudspeaker-design/understanding-impedance-electrical-phase/page-2
 

whazzup

Active Member
Joined
Feb 19, 2020
Messages
147
Likes
64
I think that your interpretation of the phase issue is almost certainly correct, i.e., that it isn't the -6 (or whatever) but the much greater phase angle (the phase offset between voltage and current) at nearby frequency. I also like what you wrote in that second paragraph. In general claims of the sort that speaker XX needs a more powerful amplifier are just "fluff" as you put it.

Anyway, even though it was someone else who raised the question of how phase angle in speaker impedance can cause difficulty for an amplifier, I thought I would attach two links to write-ups here.

https://www.stereophile.com/content/measuring-loudspeakers-part-one-page-6

https://www.audioholics.com/loudspeaker-design/understanding-impedance-electrical-phase/page-2
thanks for the links! Probably you’re referring to my questions. Not an engineer by trade, will have to digest them slowly.

another question: should one look at phase angle changes like acceleration of an moving object? Like the magnitude and steepness of the phase change graph is more important than absolute values?
 

Similar threads

Top Bottom