Are KEF LS50 Meta speakers power hungry and inefficient ?

[Amarendra]

I had been pondering over this question for the past one year or so since the time I acquired a pair of LS50 Meta. My current pairing is with the trusted Rotel RA 10 (pairing recommended by Darko). The Rotel talks of just 40W per channel at 8 Ohms and 4 ohms rating is not mentioned.
KEF website itself mentions that the ideal amp power for the speakers is 40-100W and impedance could dip to 3.5 Ohms.

I was always wondering if I was missing anything and was contemplating buying a power amp to connect to the Rotel- what with people recommending amps boasting of atleast 100W pc supply for the KEFs.

To understand the actual power consumption I took out the Sonoff Smart Plug out of its retirement and connected the Rotel through it. Volume knob on Rotel was kept at 9 o'clock at which it is fairly loud at a seating distance of 10-12 feet from the speakers. I did not measure how much dB was being belted out but played songs at the level at which I feel its on borderline of "loudness"- disturbing my neighbours.

The real time power consumption results stumped me. For a song like Mission Impossible title track or Heer Asmani from Fighter, the peak consumption (both channels) was 26 watts, for guitar solos from Marcin it was around 20W and for old hindi songs (Kishore/Mukesh) it dipped to 14 W Attached screen shots.
Did some more testing with songs like Kavaala from Jailor - again the consumption during peaks was around 24 W.

Is something missing in the testing? If you have any suggestions on the above do let me know.

Thanks for reading.

 

[mbhangui]

What is the worry you have? If you think your amp is not capable, this test using sonoff cannot prove it.

The wattage that sonoff is telling you is the RMS value. This is the power being cosumed by the AMP which includes the following
1. Power wasted in the form of heat
2. Power to do useless non-music stuff (like lighting up the display, bulbs, vu meter, etc)
3. Power actually converted to sound. This is going to be of an extremely transient nature. Sometimes during a drum beat, this will rise to a high value. During quiet moments it will drop to a very low value. You cannot expect to measure this with something like sonoff switch.

 

[rwnano]

Darko is praising the combination

Happy accidents will happen: Rotel's RA-10 integrated amplifier | Darko.Audio

A knockout punch (and award) that I just didn't see coming.

darko.audio

 

[ajuvignesh]

Kef LS 50 meta is rated at a sensitivity of 85 dB at 1m. That means, 1 watt of the amp is enough to produce the SPL of 85 dB. double the power and you will have a 3 dB increase in level. 1 feet away from the speaker will reduce the sound intensity by 1 db. So, at 1 W, with 10 feet away, you will have 78 dB already. 2 dB wound produce 81 db. I assume the loudness you had was about 90 dB and it would only take 16 Watts to produce on average. This changes on transients. The rest of the wattage is your amps spend on heat and required power for other components to function. On high efficiency speakers, even 1 W is enough to be so loud. Hence we get Tube amps in 3 W or so in power. So, I guess your measurements are normal.

 

[rwnano]

Op. Try buying a second hand mid 2000s AVR with high current capacity. It will be cheap and good. Key differentiation would be the heaviness in the amplifier indicating heavy transformer.

 

[square_wave]

A loudspeaker with 85 db sensitivity definitely need an amp with a lot of power reserves to bring the best out of them. If I get into specifics, people will jump all over me with statements like "doubling power will only give you 3db more volume" and all that. An easier way to do this is to borrow ( or home demo) a powerful amplifier at your home. You will be surprised. I would suggest anything around 100 watts RMS at 8 ohms with a lot of power reserves. Such amps usually weigh a lot too. Unless you are going the class d route. I have used many types of amps with varying wattage. The Loudspeaker - Amp synergy is critical. I used to own a horn speaker at 90 db that worked extremely well with a 20 watt SET tube amp. The same amp could not handle a 90 db speaker from another brand well. Horses for courses. Trial and error is the best way forward.

 

[ajuvignesh]

If I get into specifics, people will jump all over me with statements like "doubling power will only give you 3db more volume" and all that.

Is it not? This is what we studied in theory. Please explain to us how it is different.

 

[Phew]

Kef LS 50 meta is rated at a sensitivity of 85 dB at 1m. That means, 1 watt of the amp is enough to produce the SPL of 85 dB. double the power and you will have a 3 dB increase in level. 1 feet away from the speaker will reduce the sound intensity by 1 db. So, at 1 W, with 10 feet away, you will have 78 dB already. 2 dB wound produce 81 db. I assume the loudness you had was about 90 dB and it would only take 16 Watts to produce on average. This changes on transients. The rest of the wattage is your amps spend on heat and required power for other components to function. On high efficiency speakers, even 1 W is enough to be so loud. Hence we get Tube amps in 3 W or so in power. So, I guess your measurements are normal.

If I am not mistaken that reading is taken playing 1khz sine wave, when playing the complete spectrum there will be greater variation.

@Amarendra One way of doing this can be as shown in the video, you can set the desired volume level in the spl meter(avoid mobile apps) and check in the multimeter the max voltage which should give you the idea of the watts being consumed. This goes without saying that it will change with each song.

Op. Try buying a second hand mid 2000s AVR with high current capacity. It will be cheap and good. Key differentiation would be the heaviness in the amplifier indicating heavy transformer.

It is best to stick to what something is designed for incase of AVR's Home theatre it is. If transformer was the one and only component used in the amplifier then that statement might be of some use but with the plethora of components inside the amplifier varying in quality and quantity weight of the transformer alone is not a deciding factor.

 

[Amarendra]

What is the worry you have? If you think your amp is not capable, this test using sonoff cannot prove it.

The wattage that sonoff is telling you is the RMS value. This is the power being cosumed by the AMP which includes the following
1. Power wasted in the form of heat
2. Power to do useless non-music stuff (like lighting up the display, bulbs, vu meter, etc)
3. Power actually converted to sound. This is going to be of an extremely transient nature. Sometimes during a drum beat, this will rise to a high value. During quiet moments it will drop to a very low value. You cannot expect to measure this with something like sonoff switch.

All I m trying to understand is that if a power amp is needed.
My assumption was that if an amp is consistently working at 14-15 watts both channels with peaks at let’s say 30w both channels then is an external power amp needed when the stated capacity is 40W x2 ? Rotel usually gives very conservative power ratings of its amps.

Last evening I was playing “Sugar” on Apple TV and at the peak of a action scene the power consumption jumped to 34 W both channels (17 W each?). So the question is that Is there enough head room between 17 W per channel vs claimed 40 W per channel ? Also the 40W per channel is at 8 ohms where as the KEFs could be dipping to 4 ohms.

 

[Shinto]

I had been pondering over this question for the past one year or so since the time I acquired a pair of LS50 Meta. My current pairing is with the trusted Rotel RA 10 (pairing recommended by Darko). The Rotel talks of just 40W per channel at 8 Ohms and 4 ohms rating is not mentioned.
KEF website itself mentions that the ideal amp power for the speakers is 40-100W and impedance could dip to 3.5 Ohms.

I was always wondering if I was missing anything and was contemplating buying a power amp to connect to the Rotel- what with people recommending amps boasting of atleast 100W pc supply for the KEFs.

To understand the actual power consumption I took out the Sonoff Smart Plug out of its retirement and connected the Rotel through it. Volume knob on Rotel was kept at 9 o'clock at which it is fairly loud at a seating distance of 10-12 feet from the speakers. I did not measure how much dB was being belted out but played songs at the level at which I feel its on borderline of "loudness"- disturbing my neighbours.

The real time power consumption results stumped me. For a song like Mission Impossible title track or Heer Asmani from Fighter, the peak consumption (both channels) was 26 watts, for guitar solos from Marcin it was around 20W and for old hindi songs (Kishore/Mukesh) it dipped to 14 W Attached screen shots.
Did some more testing with songs like Kavaala from Jailor - again the consumption during peaks was around 24 W.

Is something missing in the testing? If you have any suggestions on the above do let me know.

Thanks for reading.
View attachment 84652View attachment 84653View attachment 84654

If the idea behind this exercise is to find the power consumption by LS50's, then doing the same test with another set of speaker with the same setup and same songs will give you a comparison on how much of this is speaker contributed.Still there will be unknowns like the time stamps on the songs at the time of measurement etc. So may be it is better to play the full song , and measure the energy consumed( if the meter can do it) for each pair of speakers.Still this could be approximate only and not accurate considering that fact that the sampling interval of the meter may not be matched in each case .But you still get a high level comparison I guess.

 

[Analogous]

Weird question: When testing a pair of speakers is the 1 meter distance calculated from each driver? (triangle arrangement?) or two mikes perpendicular to each driver? Or are they tested one at a time and never together as a pair?
Trying to understand the OPs question and some of the responses in this thread led me to this:

Understanding Speaker Sensitivity - Geoff the Grey Geek

A simple explanation on how to understand and use Speaker Sensitivity specifications. Includes calculators to determine how loud your speakers will be.

geoffthegreygeek.com

 

[Yelamanchili manohar]

I had been pondering over this question for the past one year or so since the time I acquired a pair of LS50 Meta. My current pairing is with the trusted Rotel RA 10 (pairing recommended by Darko). The Rotel talks of just 40W per channel at 8 Ohms and 4 ohms rating is not mentioned.
KEF website itself mentions that the ideal amp power for the speakers is 40-100W and impedance could dip to 3.5 Ohms.

I was always wondering if I was missing anything and was contemplating buying a power amp to connect to the Rotel- what with people recommending amps boasting of atleast 100W pc supply for the KEFs.

To understand the actual power consumption I took out the Sonoff Smart Plug out of its retirement and connected the Rotel through it. Volume knob on Rotel was kept at 9 o'clock at which it is fairly loud at a seating distance of 10-12 feet from the speakers. I did not measure how much dB was being belted out but played songs at the level at which I feel its on borderline of "loudness"- disturbing my neighbours.

The real time power consumption results stumped me. For a song like Mission Impossible title track or Heer Asmani from Fighter, the peak consumption (both channels) was 26 watts, for guitar solos from Marcin it was around 20W and for old hindi songs (Kishore/Mukesh) it dipped to 14 W Attached screen shots.
Did some more testing with songs like Kavaala from Jailor - again the consumption during peaks was around 24 W.

Is something missing in the testing? If you have any suggestions on the above do let me know.

Thanks for reading.
View attachment 84652View attachment 84653View attachment 84654

I have a pair of the LS50 meta's which have seen very limited use. Probably only have 10 hrs on them. I bought them from our FM @ravindrads when he was selling due to his relocation abroad. So I dont know how well they are broken in.

I have run them with 60 tube watts and found them to sound very good. I also briefly tried some high powered SS watts at 250 and 295 watts, and found a slight improvement in bass control and frequency extension both at the top and the bottom. But the biggest gain was a sense of ease to the flow, which probably improved the sense of rhythm and timing just that wee bit, where EDM, trance and techno etc sounded more fun and foot tapping.

So in my opinion, if you listen to vocals, jazz, blues, bollywood etc then the gains with a higher power amp are minimal, and in my opinion not worth it, unless you seek a different presentation. But if you listen to fast paced head slamming music, then I feel a higher power amp might deliver benefits. I say might, because Iam not familiar with the Rotel amp, and my comparison has only been between low powered tubed amps and high powered SS amps. So not exactly an apples to apples comparison.

 

[square_wave]

I have a pair of the LS50 meta's which have seen very limited use. Probably only have 10 hrs on them. I bought them from our FM @ravindrads when he was selling due to his relocation abroad. So I dont know how well they are broken in.

I have run them with 60 tube watts and found them to sound very good. I also briefly tried some high powered SS watts at 250 and 295 watts, and found a slight improvement in bass control and frequency extension both at the top and the bottom. But the biggest gain was a sense of ease to the flow, which probably improved the sense of rhythm and timing just that wee bit, where EDM, trance and techno etc sounded more fun and foot tapping.

So in my opinion, if you listen to vocals, jazz, blues, bollywood etc then the gains with a higher power amp are minimal, and in my opinion not worth it, unless you seek a different presentation. But if you listen to fast paced head slamming music, then I feel a higher power amp might deliver benefits. I say might, because Iam not familiar with the Rotel amp, and my comparison has only been between low powered tubed amps and high powered SS amps. So not exactly an apples to apples comparison.

Finally a post by someone who has experimented. A good 60 watts tube amp is a very different animal than a typical 60 watts solid state amp. If it is 60 tube watts per channel it should ideally drive better than a typical 100 watts solid state amp.

@ajuvignesh , some speakers are hard to drive through the entire frequency spectrum. It is a design feature. They have sacrificed "overall sensitivity" to achieve a gain for many other parameters in the design goal. The sensitivity at 1khz does not tell you anything apart from being academic . If you drive them with a low power amp, you are missing the whole point of the design. I have encountered many such speakers. Manufacturers always suggest you drive them with higher powered amps with very good power reserves. ATC, Dynaudio, Salk sound, some sonus faber models, also.... many designs that use expensive scanspeak / seas drivers. Unless you go MTM, those drivers are hard to drive. Especially as you go lower in the freq range. You really need to try and see what works for your speakers.

If one really likes lower powered amps ( but good sounding amps - there are many stellar examples ), one needs to carefully shop for speakers designed to work well with such amps.

 

[ajuvignesh]

Finally a post by someone who has experimented. A good 60 watts tube amp is a very different animal than a typical 60 watts solid state amp. If it is 60 tube watts per channel it should ideally drive better than a typical 100 watts solid state amp.

@ajuvignesh , some speakers are hard to drive through the entire frequency spectrum. It is a design feature. They have sacrificed "overall sensitivity" to achieve a gain for many other parameters in the design goal. The sensitivity at 1khz does not tell you anything apart from being academic . If you drive them with a low power amp, you are missing the whole point of the design. I have encountered many such speakers. Manufacturers always suggest you drive them with higher powered amps with very good power reserves. ATC, Dynaudio, Salk sound, some sonus faber models, also.... many designs that use expensive scanspeak / seas drivers. Unless you go MTM, those drivers are hard to drive. Especially as you go lower in the freq range. You really need to try and see what works for your speakers.

If one really likes lower powered amps ( but good sounding amps - there are many stellar examples ), one needs to carefully shop for speakers designed to work well with such amps.

I got it. Mine is a hard-to-drive speaker because the impedance goes below 4 ohms in the bass region. However, my Schiit Aegir which is a class A amp for 10 watts and class A like for the remaining 10 watts drive it without much issues. Yeah, I would need a muscular amp to bring the speaker's full potential although the speakers are rated at 90 db/W sensitivity.

 

[square_wave]

I got it. Mine is a hard-to-drive speaker because the impedance goes below 4 ohms in the bass region. However, my Schiit Aegir which is a class A amp for 10 watts and class A like for the remaining 10 watts drive it without much issues. Yeah, I would need a muscular amp to bring the speaker's full potential although the speakers are rated at 90 db/W sensitivity.

So, typically when your power reserves run out, a symptom to watch out for is bass with no strength, depth or power and the highs start getting brighter.

 

[ajuvignesh]

So, typically when your power reserves run out, a symptom to watch out for is bass with no strength, depth or power and the highs start getting brighter.

Thank you. Mine is a small room and the combination sounds beautiful. I have cranked it to the fullest of Aegir without a preamp straight from DAC. It sounded clean without any distortion. I use Minidsp shd studio as a passive preamp and I did it by cranking it to the full. Yes, I will keep the symptoms in my mind.

 

[MaSh]

LS50 Meta is really a very popular speaker. Seems to be slightly on the inefficient side of the scale.

Coming to the question, would these speakers benefit from the modern Chinese class D amps from fosi, ayima,etc? If not which other amp would be best suited to these speakers for a nice balanced output without any rolling off of the highs or thinning of the mids, etc?

MaSh

 

[Amarendra]

LS50 Meta is really a very popular speaker. Seems to be slightly on the inefficient side of the scale.

Coming to the question, would these speakers benefit from the modern Chinese class D amps from fosi, ayima,etc? If not which other amp would be best suited to these speakers for a nice balanced output without any rolling off of the highs or thinning of the mids, etc?

MaSh

I have been grappling with this question for long. Ppl like Steve Guttenberg have enjoyed these speakers even with Rega io not even Brio. Darko reviewed these with Rotel RA 10. I really don’t think you need 100s of watts unless you are playing really loud in a large room. I tried the Norge power amp with the Rotel on these speakers but honestly I feel the Rotel by itself is also good enough. Having said that the Fosi Audio V3 mono should be good with these. I got one of the monos to drive my center channel-
a Wharfedale in my HT- seems to be bursting with power.

 

[General_sound]

Rotel RA 10 may be lacking power but makes up by having good sound and tonality. A simple proven circuit design with no remote or DAC etc. I feel it is suitable for 88db + bookshelves. It drives a 4 ohm Elac BS 53 reasonably well, though bass depth is lacking vis a vis a more powerful amp like Marantz PM 7001. If you have one, retain it, as it is a classic.

 

[MaSh]

I have been grappling with this question for long. Ppl like Steve Guttenberg have enjoyed these speakers even with Rega io not even Brio. Darko reviewed these with Rotel RA 10. I really don’t think you need 100s of watts unless you are playing really loud in a large room. I tried the Norge power amp with the Rotel on these speakers but honestly I feel the Rotel by itself is also good enough. Having said that the Fosi Audio V3 mono should be good with these. I got one of the monos to drive my center channel-
a Wharfedale in my HT- seems to be bursting with power.

Yes I had tried a fellow member's rega elexr amp with my nht speakers and that amp really had lovely dynamics. He is using it as a pre.

V3 mono vs ZA3 is what gets me thinking. ZA3 has a tad bit of flexibility in my opinion, start as a stereo amp and scale up to mono if it sounds good. Maybe even do some opamp swaps.

Rotel RA 10 may be lacking power but makes up by having good sound and tonality. A simple proven circuit design with no remote or DAC etc. I feel it is suitable for 88db + bookshelves. It drives a 4 ohm Elac BS 53 reasonably well, though bass depth is lacking vis a vis a more powerful amp like Marantz PM 7001. If you have one, retain it, as it is a classic.

True, the old trusted designs can never go out of trend. However it's their cost these days that makes me cringe a bit.

MaSh