KEF LS50 disappointment :(

[manicm]

685s have more bass but sound boomy. Seems like speaker box also sings.

Dead wrong, they don't. I had a pair, and if you follow the manual they're very even sounding. The manual recommends 50cm away from walls, but even 30cm will do. Placed sensibly these are not 'boomy' speakers at all.

 

[Vladimir]

I can confirm Shri Kumar's experience for the B&W CM1. I own them and they are indeed boomy in the 100Hz region. I have that issue sorted to a good extent with adding internal damping and a bass trap in one boomy corner. Typical problem with boxy cabinets of that type (k).

(stole this one from Steve)

Cabasse anyone?

 

[manicm]

Shri Kumar stated the 685s were boomy. I heard the old CM1s, they were OK. And as I recall even the CM1's manual states they should be 50cm from a rear wall.

 

[Vladimir]

Shri Kumar stated the 685s were boomy. I heard the old CM1s, they were OK. And as I recall even the CM1's manual states they should be 50cm from a rear wall.

Yes indeed they really benefit from space arround them. The best sound I got from them was 1.5m from the back walls in the Cardas formation.

 

[Esra]

That´s nearly how my LS50 stand in my room too. 1.50 back and 1.10 sides and 0.7 ground.

 

[shkumar4963]

My experience was in a 2 hour session where listened to all speakers one after the other. Not sure if they were positioned accurately. But definitely PMC twenty 21 had a lot less boom then CM5 which boomed less than CM1 and 685.

Ls50 were not available for the comparison at the same shop but my recollection is that on Bother shop they had a lot less boom.

I was just comparing one feature abd not implying that one speaker us better than the other. Fir that a more complete review is needed.

Vladimir: what book did you get those curves from. May be a good book fir me to read.

 

[Vladimir]

Rectangular boxes are relatively easy to construct, relatively efficient in terms of enclosed volume, and relatively easy to live with. If you place a rectangular box on a flat surface, it won't fall over or roll away, for example! In a hi-fi application, the 'domestic manager' can place a flower vase and a photo-frame on the top to make it look less industrial, and in a studio we often place all manner of technical studio debris on top! This might be very convenient, but is not necessarily the best way of building a loudspeaker cabinet.

The acoustic effects of different shapes of loudspeaker cabinets have been known about empirically since at least the early 1940s, but it was really the academic work of HF Olson that properly documented what was going on, in a paper he published in the Journal of the AES in 1969. This work revealed very clearly that cubic and rectangular cabinets had a very damaging effect on the overall frequency response, whereas cabinets with rounded or deeply angled front-baffle edges performed considerably better. A spherical cabinet delivered an almost perfect frequency response. (The 'Cabinet shape and frequency response' diagram shows the frequency responses of various different cabinet shapes.)

The physics of the situation is essentially that the sound wave generated by a loudspeaker driver radiates outwards in a hemispherical wave, travelling sideways across the baffle surface and out into the room. However, when the sound waves reach the baffle edge of a cuboid cabinet, they encounter a pressure discontinuity. There is nothing for the sound waves to press against any more, and that step change causes severe diffraction. In effect, the sharp cabinet edge forms a secondary source of sound-wave radiation, and sound waves from that 'virtual' source interfere with those from the loudspeaker driver itself, resulting in comb filtering, directional beaming and an uneven response. The precise frequencies affected and the strength of the interference effects depend on the relative distances between the driver and the various baffle edges.

Not surprisingly, Olson's work revealed that chamfering or rounding the front baffle edges helps to reduce these interference effects by softening the transition and severity of the pressure discontinuity at the cabinet edge — and that's why most modern loudspeaker cabinets have rounded edges to varying degrees. But the best performance was obtained with a spherical cabinet, since there are obviously absolutely no hard edges, and thus no step-change discontinuities.

However, a spherical cabinet presents other practical problems, not least being how to stop the speaker from rolling off the console meter-bridge! On a more serious note, a sphere has only one dimension and thus has a very strong resonant frequency. A better compromise, combining the soft baffle edges of a sphere but with a broad spread of internal resonant frequencies, is the ovoid or egg shape. And that's where SE's new monitors enter the picture.

Source: SoundOnSound

 

[Vladimir]

Also checkout the work of Laurence Dickie, the designer of the Vivid Audio loudspeakers.

 

[shkumar4963]

You wrote:

On a more serious note, a sphere has only one dimension and thus has a very strong resonant frequency.

I did not see that one frequency peak in "a" above that was for the sphere. Why?

 

[shkumar4963]

I was wondering if there are other reasonsfor it. Even with Nautilus speakers, the sphere is used only for tweeters and that too probably for asthetic design reasons. From the curves given, it will seem that mid bass will be helped more by having an spherical cabinet shape.

 

[Vladimir]

If you reinforce a sphere shaped cabinet well, there won't be any resonances, just like on the graph. If you don't, it will be much worse than a typical box cabinet.

 

[Vladimir]

Box is much much cheaper to manufacture and if you are after a large cabinet volume, the size of the sphere becomes impractical.

The Nautilus solves many things in a more genious ways than just using a simple sphere. Did you look at the Nautilus video I linked?

 

[shkumar4963]

Box is much much cheaper to manufacture and if you are after a large cabinet volume, the size of the sphere becomes impractical.

The Nautilus solves many things in a more genious ways than just using a simple sphere. Did you look at the Nautilus video I linked? 

Just saw the link. Did not know it was there. Thanks.

 

[jackocleebrown]

I was wondering if there are other reasonsfor it. Even with Nautilus speakers, the sphere is used only for tweeters and that too probably for asthetic design reasons. From the curves given, it will seem that mid bass will be helped more by having an spherical cabinet shape.

The effect in the curves is normally know as the diffraction effect. The frequency that you get the ripples on the response depend on the enclosure dimensions. For a very samll enclosure, like a pod tweeter, the ripples are at high frequencies. For a typical speaker width of around 20cm the ripples are in the upper midrange (above 1kHz) so it is not really a issue for the bass region unless the speaker is very large.

This data is from Olsen's experimental work where he has tried to isolate just the diffraction effect, this is why you don't see any other features on the responses, such as dips/peaks from cabinet resonance.

The directivity of the driver also changes the diffraction effect, a more directional driver has less diffraction ripple than one with wide dispersion (all other things being equal).

shkumar4963, you seem to be interested to learn more about how loudspeakers work and acoustics in general. This is a really nice intro to acoustics fundamentals: http://resource.isvr.soton.ac.uk/spcg/tutorial/tutorial/StartCD.htm

It is not directly about loudspeaker but I think that you might find it interesting.

Kind regards, Jack.

 

[Vladimir]

Welcome to the discussion Jack. I hope you don't mind doing a round of Q&A with us here, considering you are the authority to consult with regarding KEF loudspeakers ATM.

I am a fan of the budget dual concentrics Tannoy and KEF made and owned the Tannoy DC1000 and KEF Q60 in my student days. When The Q100 was born and consequently the LS50, I saw an evolution of design and engineering improvements and as a life long KEF fanboy I was happy the dual concentric lived on today. But when I saw the sudden BBC LS3/5a labeling over this series I got completely annoyed with it and I simply do not see any resemblance between the BBC broadcasting van monitor and the LS50.

Can you shed some light on the matter where the engineering DNA of the LS50 comes from?

Cheers

 

[unsleepable]

Can you shed some light on the matter where the engineering DNA of the LS50 comes from?

Cheers

The thing about the DNA is probably marketing BS. But come on, there is so much marketing BS in this sector… I hardly think that Kef will make it to the top list. In my opinion, it's mostly a very sensible brand with sensible products.

On the other hand, I find it nice that they decided to commemorate old speakers with such a beautiful design. In all fairness, I think the LS50 would have been equally successful even if they had not commemorated anything. But introducing a new product with a nice story behind it's just… Well, nice.

 

[jackocleebrown]

Hi Vladimir,<br>I can only really comment fully on the engineering side, not the product planning or marketing but I can give you a little bit of an idea of how the LS50 came about. I believe that our chairman was the first to put forward to idea to produce a 50th anniversary celebration model. There was a lot of discussion about what would make an appropriate product. Naturally, with this type of thing you start to look back through the product history to see what where the most significant models. There were a lot of different options but the connection between KEF and the LS3/5a is a proud tie for the company. Especially since KEF's founder, Raymond Cooke, was a former BBC engineer. The LS3/5 is one of the most successful loudspeakers of all time and, as I'm sure you know, every one used KEF drivers. For the 30th anniversary, in 1993, we produced a limited 500 pairs of KEF LS3/5as. The original discussion was to do something similar to this. However, we don't make the T27 or B110 any more so we could not make an exact LS3/5a to the BBC spec. This is where the anniversary model and the LS3/5a started to diverge. We made a few prototypes and mock ups based on an LS3/5a with modern KEF drivers. It was decided that we should use Uni-Q, rather than separate tweeter and woofer, since Uni-Q also is an important part of our history. These original prototypes retained much more of the original LS3/5a, such as the ply cabinet construction and the stepped baffle edge. Ultimately we ended up with something that was neither really one thing or another, some kind of a pastiche of the LS3/5a. Following this there was a distinct change in direction. Basically our chairman challenged the engineering team along the lines of "if the BBC were designing this today, with modern materials and technology, what would they do?". My colleague, Mark Dodd, took up the mantle on this and basically worked from scratch to come up with the final LS50 design. He focused very much on achieving the same technical goals as the original BBC designers: minimising cabinet vibration, minimising diffraction effect (in the case of the LS3/5a they used felting, the LS50 uses the shaping of the baffle) and a balance with a focus on the clarity in the midrange. Personally I think that it is just what the project needed and Mark worked like a trojan to extract every last drop of performance from the design. Mark developed a number of new technologies that we have subsequently used on other products. Nevertheless we had no idea that the LS50 would be quite as popular as it has turned out to be in the last couple of years. Hopefully knowing the development history you can more clearly understand the context of the LS3/5a mentions in the marketing literature. The white paper in particular mentions the LS3/5a a number of times because it is more or less a technical commentary comparing the methods used by the BBC designers to tackle particular acoustical challenges with those that Mark used for the LS50. This is perhaps more clear in his AES paper: http://www.aes.org/e-lib/browse.cfm?elib=16887 Kind regards, Jack.

 

[shkumar4963]

Thanks Jack. I have bookmarked the page and will go there often.

What started as a project to select a speaker for my home turned into a passion for learning what makes one speaker sound better then the other.

I listened to many speakers and fell in love with the sound of LS50. I am partial to vocals and ls50 excels in that area. Unfortunately, I did not realize that room size makes a difference and these may be too small for my room 17 by 28 by 8 ft.

Now I am planning to buy a sub or two to hopefully rectify the situation.

This group, especially Vladimir, Mark and others have been great help in my quest to understand the physics behind sound reproduction.

 

[yavor]

I have KEF Q500. Can not agree more. Useless piece of junk/rubbish. No bass at all. Very poort speakers. i regret I bought those. I also bought a Rotel CD, which in less than 150hrs of play time died completely. So unlucky. Why is all this **** on the market and in such a poor quality.

Moderator - Welcome to the forum but please take a moment to read the house rules, including the one about use of bad language.

 

[Covenanter]

I have KEF Q500. Can not agree more. Useless piece of junk/rubbish. No bass at all. Very poort speakers. i regret I bought those. I also bought a Rotel CD, which in less than 150hrs of play time died completely. So unlucky. Why is all this **** on the market and in such a poor quality.

Moderator - Welcome to the forum but please take a moment to read the house rules, including the one about use of bad language.

I used to have the Q500s and they have plenty of bass. You sure it isn't the rest of your kit? What is the rest of your kit?

Chris

 

[Vladimir]

Most likely the Rotel RA-06 SE. *unknw*

 

[shkumar4963]

Hi Jack:

I am sure you will get a lot of questions but here is a question that I wanted to ask.

If you compare the sound of best £1000 speakers 30 years back with the best £2000 speakers today, how would you compare the sound quality? What other improvements have been made in speaker quality in last 30 years?

 

[jackocleebrown]

Hi Jack:

I am sure you will get a lot of questions but here is a question that I wanted to ask.

If you compare the sound of best £1000 speakers 30 years back with the best £2000 speakers today, how would you compare the sound quality? What other improvements have been made in speaker quality in last 30 years?

Hi shkumar4963,

That is an interesting question.

Fundamentally we are still dealing with the same underlying technology and the same physical limits on what is possible. The main physical limit that we are up against when designing a loudspeaker is that to efficiently produce bass requires a large enclosure.

However a lot of things have changed:

Materials have developed a lot. For example neodymium magnets allow us to build more compact motor systems and this gives more freedom for the designer. Pod tweeters and the Uni-Q tweeters both rely on nedymium in the motor systems.

30 years ago most tweeters were fabric and most woofers were paper. Today most manufacturers use other technologies to try and minimise mechanical resonance in the cone/dome.

Computer modelling is much more advanced too, this means that we can do a lot of work on the computer to optimise a design. 30 years ago there was a lot more reliance on building many prototypes. As a result it was tricky to make big leaps in performance. The computer modelling also helps to allow a deeper understanding of the behaviour of the loudspeaker, you can build up a computer model to just mimick one particular aspect of the design in isolation so that you can understand and optimise it (for example the diffraction mentioned above).

Taking a 25mm metal dome tweeter as an example. The very first 25mm metal domes gave output up just above 20k before the dome went into resonant breakup. Using computer modelling to optimise the design a 25mm metal dome can now go up to around 40kHz.

The computer modelling aspect has also transformed motor system design. Small changes to the motor system can have a bit effect on the distortion generated in the midrange of the loudspeaker. Amplifiers are also generally more powerful. This means that a modern speaker can afford to trade a little sensitivity for bass extension and output capability. The motor systems are designed with this in mind to handle the extra power and in most cases to allow more cone movement.

The other aspect that has changed it the understanding of what makes a good loudspeaker. Following research such as the Eureka project and Toole's studies we focus a great deal on the dispersion and power response of our designs. It is not enough to simply get a flat response on-axis because a large proportion of the sound reaching the listener is via reflected paths.

Understanding of loudspeaker driver behaviour has also improved, thanks to work by people such as Wolfgang Klippel. There is also a huge improvement in measurement tools.

Anyhow, getting back to your question. If you took a loudspeaker from 30 years ago and compared it to an equivalent from today I think that you would notice a much greater openness and clarity from today's loudspeaker. The ability to louder without the character of the speaker deteriorating. Assuming the speakers were roughly the same size you'd probably find today's loudspeaker was slightly harder to drive but has more bass output and less bass distortion.

Kind regards, Jack.

 

[Freddy58]

Hiya Jack, great to have you offering some input

I'm a big fan of KEFs. Some years back I had the Concorde IV's and have recently bought some R300's. Both have the quality I like, kinda laid-back but authoritative, with wonderful bass. The LS50 seems to have divided opinion here. Most seem to be favourable, but there are a few (myself included) that were disappointed. To me, it seemed to lack any character at all, something I wouldn't expect from a brand like KEF. Am I missing something?

Cheers...Freddy

 

[jackocleebrown]

Hi Freddy, The LS50 and R300 are quite different designs. Firstly the R300s are significantly larger than the LS50 but they are roughly the same sensitivity. This allows the R300 to have considerably more bass extension. Indeed, they almost have as much bass extension as the R500s. The characteristic of the bass response is also quite different. The LS50 has a bass roll off that starts comparatively high but rolls off very gently. For some rooms and tastes this works very well indeed and gives a very dry sound to the upper bass and more extension than you might expect given the box size. The R300 bass response is very flat down to the roll off, which is lower. This gives a more powerful bass sound. They will both interact a little differently with the room and depending on your setup and your preference you might well prefer one to the other. In the new Reference we supply two different port tunings effectively allowing the user to switch between an "R-series" and "LS50" style of bass response. We have noticed that optinion is very polarised on which sounds "best". The second big difference between the two speakers is that the R300 are three-way with a dedicated bass driver, whereas the LS50 is two-way. The benefit of the three-way design is that the Uni-Q is optimised for MF+HF duties and does not have to deal with the bass. The bass driver can also be optimised for bass only. Against this, it is a more complex setup, requiring more electronics in the crossover to split the signal for the three drivers. Again, some might prefer the three-way R300 due to the extra control and headroom that the three-way system provides. On the other hand there is something very nice about a good two way system, the simplicity helps to give a very cohesive sound. For both systems the Blade was used as a reference point for voicing but due to the differences in the bass response and the driver arrangement they do not sound exactly the same, particularly in the midrange. Which one you like will depend a lot on your taste as well as your setup. Very pleased to hear that you are enjoying the R300s. Kind regards, Jack.