Kef ls50 meta demo experience

[Marc v E]

Today I went to a hifi dealer to listen to some Kef speakers. He didn't have any r series in stock so I opted for the ls50.

First impressions were that they are uncoloured in the mid and high range. A friend remarked that they imaged well too. It was easy to hear where instruments were placed in the mix. And the tonality of instruments were distinctive too.

To push it to its limits, I opted for a bass heavy track, Nadia from Nitin Sawney. This song has clear Indian vocals and a digs deep where bass is concerned. I know from experience how it sounds with a 10 inch driver and also on some Genelec speakers.

What struck me immediately is that the basslines were cut off halfway; in the song they start deep but end way deeper. The ls50 just don't translate that, which results in the song having a chorus but no undelying bassline. With that in mind I put on some rock n roll from Bryan Adams. It sounded ok, but bassguitar lines or drums didn't drive the music like I'm used to.

We asked for a sub and bingo, the basslines were there, underpinning the clear vocals. Imo there was still room for improvement in impact and timing but it was just too much to ask for such a short demo, to arrange with a suitable avr.

In short we had a very nice impression and I must say the hospitality and service from the dealer was among the best I have experienced.

 

[Purité Audio]

My experience comparing the LS50 with sub to the LS60s was that the 50s alway sounded a little less defined in the bass, perhaps their ported design?
Keith

 

[thewas]

Most compact 2-way 5" loudspeakers are limited to either deep or loud bass as the multitone distributions and compression rise there. Same for the LS50 which I own and enjoy both generations since they were respectively released. They are great for either lower listening levels or distances but highpassed with subs they can overcome also these limitations.

 

[Marc v E]

My experience comparing the LS50 with sub to the LS60s was that the 50s alway sounded a little less defined in the bass, perhaps their ported design?
Keith

It could be. From what I heard, I think I could quite easily add warmth and full range to a standmount with a sub. But and this is a big question for me, I'm not so sure I could get the bass perfectly integrated like in a well designed full range speaker if that makes sense?

I just can't get my head around it what it could be. It was low passed at 70hz, plenty of power, but I'm still missing a clear well defined bass. Maybe I'm asking for too much and should just demo the ls60.

 

[Marc v E]

I'm not critisizing the ls50 by the way. They do everything right for their size. Physics come into play when playing bass through a standmount with 2 drivers. Just trying to understand what the possibilities and limits are.

 

[ban25]

The F3 point is 79 Hz. The LS50M is bass shy, to say the least.

 

[tw 2022]

The F3 point is 79 Hz. The LS50M is bass shy, to say the least.

Yeah ,that's the trade off, I've got mini monitors in one set up and 3 way monster bookshelves in my other set up.. The difference is obvious... I can successfully fill in with a high crossover setting.. I'd venture to say you'd need a crossover around 100 Hz with the ls50s, maybe a bit higher...

 

[thewas]

The F3 point is 79 Hz. The LS50M is bass shy, to say the least.

I wouldn't call it of course a bass monster but also not bass shy especially compared to similarly sized loudspeakers, the LS50(M) like many KEF have a quite low tuned BR giving a so called bass shelving response so the -10 dB point is deeper than the -3 dB point would signalise, namely around 41 dB and its bass response is not too far from the R3(M) which also most wouldn't call bass shy:

Also according to Toole the -10 dB point correlates better to the perception of bass response then the -3 dB one.

As I wrote above its limitation is rather it multitone distortion and compression at high bass SPLs.

 

[ban25]

I wouldn't call it of course a bass monster but also not bass shy especially compared to similarly sized loudspeakers, the LS50(M) like many KEF have a quite low tuned BR giving a so called bass shelving response so the -10 dB point is deeper than the -3 dB point would signalise, namely around 41 dB and its bass response is not too far from the R3(M) which also most wouldn't call bass shy:

View attachment 412375

Also according to Toole the -10 dB point correlates better to the perception of bass response then the -3 dB one.

As I wrote above its limitation is rather it multitone distortion and compression at high bass SPLs.

Agreed the distortion at high SPL levels is significant. Once you see the mid-woofer moving, it's done.

I find the LS50M excellent for near-field use. I have a pair on my desk and I have no need for a subwoofer. Out in a room, the limitations on SPL and bass are evident.

And FWIW, I would also call the entire R line, including R3 and R11, bass shy.

 

[Old_School_Brad]

Also according to Toole the -10 dB point correlates better to the perception of bass response then the -3 dB one.

I find that a bit backwards, considering the equal loudness contour. What's his reasoning for this?

 

[thewas]

I find that a bit backwards, considering the equal loudness contour. What's his reasoning for this?

For example such a low shelf behaviour can show well why it usually correlates better. About the equal loudness contour we shouldn't forget the room gain which can give a large increase at the low frequencies which is also the reason that flat in the bass loudspeakers like for example large Genelec monitors need quite some EQ there to not have a boost at the listening position.

 

[thewas]

I find the LS50M excellent for near-field use. I have a pair on my desk and I have no need for a subwoofer. Out in a room, the limitations on SPL and bass are evident.

Yes, although I use my LS50M even at my desktop with a sub, on the other hand

And FWIW, I would also call the entire R line, including R3 and R11, bass shy.

if you call these too bass shy then probably almost any loudspeaker in that size is that too for you.
By the way my couch listening place is also very bass absorbent so most loudspeakers seem there without EQ or subs bass shy too but that is a property of the room.

 

[kyuu]

Were the LS50s placed near a boundary (wall)? Their bass shelving is definitely tuned with the expectation that there will be reinforcement.

 

[thewas]

Were the LS50s placed near a boundary (wall)? Their bass shelving is definitely tuned with the expectation that there will be reinforcement.

Exactly, I generally tend to place loudspeakers without subwoofers close to the front wall to avoid having the first SBIR dip in the bass:

Source of above images: https://www.genelec.com/monitor-placement

 

[phoenixdogfan]

I have them and cross over at 150 hz to my twin SB 2000's using DLBC for the crossover. I think they sound fine. I do have REW and I'm interested in measuring to see what multitone will look like at 96 db and whether that higher crossover point reduces distortion further than what Erin measured with the 80 hz filter. I'm thinking it might just do that and make the 1000-3000 hz region have better looking IMD as reflected in the multitone measurements. Maybe I'll figure out how to get that measurement done after New Year.

 

[terryforsythe]

My experience comparing the LS50 with sub to the LS60s was that the 50s alway sounded a little less defined in the bass, perhaps their ported design?

I think there are multiple factors that may explain the improved bass of the LS60 in comparison to the LS50:

1. Each LS60 has 4 x 135mm woofers. They are not even breaking a sweat where the LS50's single woofer starts to struggle (compression/response linearity and distortion).

2. The LS60 is all active with the amplifier output stage connected directly to the drivers with relatively short wires. That configuration provides for a high damping factor (assuming the amplifier has a low output impedance), resulting in very good control of the amplifier over the woofers. The LS50, on the other hand, has a passive crossover, including an inductor in series with the woofer. I don't know what is the series resistance of that inductor, but it may be high enough to have a noticable negative impact on the damping factor.

3. The LS60 is a sealed design, whereas the LS50 is ported, as you mentioned.

In my family room speakers I removed the passive crossovers and went all active. I also sealed the ports. Those changes significantly improved my bass response - much tighter bass. They don't extend as low with the ports plugged, but they don't need to since I have a subwoofer handling everything below 90Hz.

 

[Old_School_Brad]

I think there are multiple factors that may explain the improved bass of the LS60 in comparison to the LS50:

1. Each LS60 has 4 x 135mm woofers. They are not even breaking a sweat where the LS50's single woofer starts to struggle (compression/response linearity and distortion).

2. The LS60 is all active with the amplifier output stage connected directly to the drivers with relatively short wires. That configuration provides for a high damping factor (assuming the amplifier has a low output impedance), resulting in very good control of the amplifier over the woofers. The LS50, on the other hand, has a passive crossover, including an inductor in series with the woofer. I don't know what is the series resistance of that inductor, but it may be high enough to have a noticable negative impact on the damping factor.

3. The LS60 is a sealed design, whereas the LS50 is ported, as you mentioned.

In my family room speakers I removed the passive crossovers and went all active. I also sealed the ports. Those changes significantly improved my bass response - much tighter bass. They don't extend as low with the ports plugged, but they don't need to since I have a subwoofer handling everything below 90Hz.

Hi Terry,
It's interesting that you mention the increased damping factor as being audible. The general consensus on this scientific forum seems to be that, beyond a certain (relatively low) threshold, it doesn't have much impact. However, on professional audio forums, damping factor used to be a significant consideration, particularly for bass bins.
That said, the damping factor is often drastically reduced by the crossover. Even if it’s high at the amplifier's output, it diminishes considerably when the crossover is in the circuit.
I’m curious why the higher damping factor in active setups is now being promoted as an advantage, especially when, before the rise of active setups, it wasn’t considered particularly important.

Please don’t take this as criticism or confrontation -it’s more of a genuine question out of curiosity. If you have any measurements to support the claim that it’s indeed audible, I’d really appreciate it.

An afterthought; Could the audible difference be due to the bass driver in an active setup receiving more power compared to a passive setup, where the crossover consumes a portion of the power before it reaches the driver? This would of course be evident by better linearity or better low frequency extension.

 

[terryforsythe]

It's interesting that you mention the increased damping factor as being audible. The general consensus on this scientific forum seems to be that, beyond a certain (relatively low) threshold, it doesn't have much impact. However, on professional audio forums, damping factor used to be a significant consideration, particularly for bass bins.
That said, the damping factor is often drastically reduced by the crossover. Even if it’s high at the amplifier's output, it diminishes considerably when the crossover is in the circuit.
I’m curious why the higher damping factor in active setups is now being promoted as an advantage, especially when, before the rise of active setups, it wasn’t considered particularly important.

Hi Brad,

I think there is much confusion about damping factor (DF). DF is defined as the ratio of the rated impedance of a loudspeaker (the actual driver) to the source impedance of the power amplifier (it's output impedance), and is calculated as DF = (ZL + ZS)/ZS, where ZL is the load impedance (of the driver) and ZS is the amplifier's output impedance. (https://en.wikipedia.org/wiki/Damping_factor). The more simple form of the equation, DF = ZL/ZS, commonly is used.

This definition is overly simplistic for passive speakers, though. It only considers, for the source impedance, the output impedance of the amplifier, without any consideration to the impact of passive filters (crossovers), speaker wire, etc., in the circuit between the driver and the amplifier. There is much confusion in the audio industry regarding these considerations.

Here is an article that explains DF pretty thoroughly: https://sound-au.com/biamp-vs-passive.htm. As explained in that article, passive filter components do need to be considered when determining DF. From the view of the driver for which DF is computed, the passive filter components add to the source impedance (ZS).

Let's do some simple calculations to see the effect with my speakers, Elac UBR62 Uni-Fi Reference. The resistance of the woofer, ZL, is 4.15 ohms. The passive crossover has two inductors in series with the woofer, one having 1.2 ohms resistance and one having 0.4 ohms resistance, for a total resistance of 1.60 ohms. Let's assume 0.04 ohms for resistance of the speaker cables. Now, let's compare the DF for a high output impedance amplifier (e.g., a tube amplifier) and a low output impedance amplifier (e.g., a good solid state amplifier), both with passive and active crossover configurations. For these calculations I will assume a 4 ohm output impedance for the tube amplifer and a 0.02 ohm output impedance for the solid state amplifier:

High output impedance amplifier with passive crossover:
DF = (4.15 + 1.60 + 0.04 + 4.00) / (1.60 + 0.40 + 4.00) = 1.74

High output impedance amplifier all active without passive crossover:
DF = (4.15 + 0.04 + 4.00) / (0.40 + 4.00) = 2.02

Low output impedance amplifier with passive crossover:
DF = (4.15 + 1.60 + 0.04 + 0.02) / (1.60 + 0.40 + 0.02) = 3.50

Low output impedance amplifier all active without passive crossover:
DF = (4.15 + 0.04 + 0.02) / (0.40 + 0.02) = 70.17

One big caveat to the above calculations is that I only computed DF using DCR and did a lot of hand waiving to make the calculations simple, but in reality the DF is determined by the actual impedances, which vary with frequency.

Still, these simple calculations show the benefit on DF when going all active and using a low output impedance amplifier.

However, if an amplifier with a high output impedance is used and/or passive crossovers with high resistance are used, the benefit is not nearly as significant. That could lead people, who do not look very deep into calculations, to reach overly simplistic conclusions.

In my setup I have a Hypex Nilai Stereo amplifier, which has very low output impedance, driving the woofers. Comparing the bass response with and without the passive crossovers, the difference is significant. The bass is much tighter, less sloppy, without the passive crossovers.

A few months back someone posted a graph showing the step response of a woofer using different damping factors. The woofer settled noticably faster using a high DF. I should have bookmarked that post, but didn't.

 

[Old_School_Brad]

Hi Brad,

I think there is much confusion about damping factor (DF). DF is defined as the ratio of the rated impedance of a loudspeaker (the actual driver) to the source impedance of the power amplifier (it's output impedance), and is calculated as DF = (ZL + ZS)/ZS, where ZL is the load impedance (of the driver) and ZS is the amplifier's output impedance. (https://en.wikipedia.org/wiki/Damping_factor). The more simple form of the equation, DF = ZL/ZS, commonly is used.

This definition is overly simplistic for passive speakers, though. It only considers, for the source impedance, the output impedance of the amplifier, without any consideration to the impact of passive filters (crossovers), speaker wire, etc., in the circuit between the driver and the amplifier. There is much confusion in the audio industry regarding these considerations.

Here is an article that explains DF pretty thoroughly: https://sound-au.com/biamp-vs-passive.htm. As explained in that article, passive filter components do need to be considered when determining DF. From the view of the driver for which DF is computed, the passive filter components add to the source impedance (ZS).

Let's do some simple calculations to see the effect with my speakers, Elac UBR62 Uni-Fi Reference. The resistance of the woofer, ZL, is 4.15 ohms. The passive crossover has two inductors in series with the woofer, one having 1.2 ohms resistance and one having 0.4 ohms resistance, for a total resistance of 1.60 ohms. Let's assume 0.04 ohms for resistance of the speaker cables. Now, let's compare the DF for a high output impedance amplifier (e.g., a tube amplifier) and a low output impedance amplifier (e.g., a good solid state amplifier), both with passive and active crossover configurations. For these calculations I will assume a 4 ohm output impedance for the tube amplifer and a 0.02 ohm output impedance for the solid state amplifier:

High output impedance amplifier with passive crossover:
DF = (4.15 + 1.60 + 0.04 + 4.00) / (1.60 + 0.40 + 4.00) = 1.74

High output impedance amplifier all active without passive crossover:
DF = (4.15 + 0.04 + 4.00) / (0.40 + 4.00) = 2.02

Low output impedance amplifier with passive crossover:
DF = (4.15 + 1.60 + 0.04 + 0.02) / (1.60 + 0.40 + 0.02) = 3.50

Low output impedance amplifier all active without passive crossover:
DF = (4.15 + 0.04 + 0.02) / (0.40 + 0.02) = 70.17

One big caveat to the above calculations is that I only computed DF using DCR and did a lot of hand waiving to make the calculations simple, but in reality the DF is determined by the actual impedances, which vary with frequency.

Still, these simple calculations show the benefit on DF when going all active and using a low output impedance amplifier.

However, if an amplifier with a high output impedance is used and/or passive crossovers with high resistance are used, the benefit is not nearly as significant. That could lead people, who do not look very deep into calculations, to reach overly simplistic conclusions.

In my setup I have a Hypex Nilai Stereo amplifier, which has very low output impedance, driving the woofers. Comparing the bass response with and without the passive crossovers, the difference is significant. The bass is much tighter, less sloppy, without the passive crossovers.

A few months back someone posted a graph showing the step response of a woofer using different damping factors. The woofer settled noticably faster using a high DF. I should have bookmarked that post, but didn't.

I’m aware of what the damping factor is and how it’s calculated. What I’m really looking for is evidence to support whether it is truly audible (active vs. passive systems). My understanding is that measurements suggest it has little to no audible impact above a certain low threshold. I came across Toole’s observation, which places this threshold at 20, described in the following way:

Even eliminating the inductor and driving the woofer directly changes things only slightly. The article (Toole, 1975) shows oscilloscope photographs of tone bursts of various frequencies and durations while the damping factor of the amplifier was varied from 0.5 to 200. At damping factors above about 20 (internal impedance less than 0.4 ohms), no change was visible in any of the transient signals, and changes in frequency response were very much less than 1 dB, and then only over a narrow frequency range.

It would be appreciated if you could find that step response you describe.

 

[terryforsythe]

I came across Toole’s observation, which places this threshold at 20

That probably is a good rule of thumb. In the examples I provided, when using a low output impedance amplifier, with a passive crossover the DF is 3.50 and is 70.17 without. The passive crossover setup has a DF well below 20 and the all active setup has a DF well above 20, and thus should reflect a visible change in the transient signals.

It would be appreciated if you could find that step response you describe.

I don't recall in which thread it was posted. You should be able to find it if you search. Nonetheless, the calculations I provided and the passage you noted "At damping factors above about 20" should answer the question.