Do KEF Aluminum cone speakers have a serious design flaw?

[Doodski]

And we should bear this in mind when someone asks for an amp recommendation for a two way KEF. This is one case where the "you can never have too much clean power" thing is obviously a myth.

The situation where this kind of long term extreme damage can occur requires the operator ignoring very loud crackling and snapping sounds coming from the drivers while soaking the driver in very high power levels all the while. Not 2 seconds, not 10 seconds but minutes or more at extreme power levels. This is not a fast thing nor is it subtle when it occurs.

 

[Jim Taylor]

You´re old school. Younger generations seem to be proud-either by choice or ignorance-not to be ashamed to show the world how stupid they are. Social media amplifies that phenomenon.

 

[olieb]

Only a continuous and ongoing process manages to produce kinks and then cracks at this point.

This is exactly what happens when material fatigues.

This has absolutely nothing to do with aluminum and material fatigue.

Well, if you say so.

 

[antcollinet]

and those amps could cause a blowout like the ones shown at high output.

Again - that is not unique to KEF. Most speakers are not going to be able to cope with a 500W purify turned up full.

 

[Mnyb]

It's not posited as a warning though. It is given as an accusation of a "serious design flaw"

Yes hence why i suggested a better tittle that did not contained an inbuilt accusation at a serious design flaw, but OP seems predisposed at this line of inquiry ? @uwotm8 did you blow up your KEF's in an embarrassing manner are there any pictures ? I suggest "you got to fight for your right to party" by the beastie boys ..

I the tread was more neutral we could invite the KEF people on the forum to answer ( there are atleast 3 of them active ) ? they should now ?
Is this a failure mode typical of very rigid drivers ?

 

[Doodski]

Yes hence why i suggested a better tittle that did not contained an inbuilt accusation at a serious design flaw, but OP seems predisposed at this line of inquiry ? @uwotm8 did you blow up your KEF's in an embarrassing manner are there any pictures ? I suggest "you got to fight for your right to party" by the beastie boys ..

I the tread was more neutral we could invite the KEF people on the forum to answer ( there are atleast 3 of them active ) ? they should now ?
Is this a failure mode typical of very rigid drivers ?

I have used and tested aluminum alloy drivers used for subs and when they hit the stops they make a horrible amount of noise. In the case of the KEFs the noise level from the driver being destroyed and the extreme motion of the driver itself would mean the operator would need to be both deaf and blind. Think like 100% distortion at a very loud volume level.

 

[ssashton]

Again - that is not unique to KEF. Most speakers are not going to be able to cope with a 500W purify turned up full.

And a lower power amplifier that is clipping badly will probably just blow the tweeter with HF trash instead. These people need speakers with an in-line fuse, haha.

 

[jackocleebrown]

Hi Everyone,

I can understand that these pictures look dramatic and alarming to anyone that is a KEF loudspeaker owner, or that might potentially be considering purchasing KEF loudspeakers. I asked our operations team to collect some statistics for worldwide Uni-Q failures on some of our most popular 2-way speakers.

• This data is for Q150, Q350 and LS50 META.
• We've had to compile it from a few different sources but it captures the majority of global sales so I believe it is statistically significant.
• The data is for the time period 2016/1/1 to 2025/3/2.
• This includes Uni-Qs replaced for any reason, which will also include accidental and handling damage in addition to failure during use.
• This includes both repairs that were done both under- and out-of-warranty
• The number of Uni-Qs we have replaced is 0.08% of sales.
  

Here's some key info:

• All KEF loudspeakers undergo very thorough power handling and high-level performance checks during development to make sure they are suitably rugged for the market.
• With passive products, we are not able to protect the loudspeaker driver from over driving. Any passive loudspeaker will break eventually if the applied signal level is increased indefinitely.
• The current style of 2-way Uni-Q driver is now very mature and we have thousands of happy users.

 

[Mart68]

And a lower power amplifier that is clipping badly will probably just blow the tweeter with HF trash instead. These people need speakers with an in-line fuse, haha.

Or just speakers more suited to what they want to do.

Years ago I sorted out an old PA system for a friend of a friend. It suited what he wanted to spend and what he wanted to do - which was just to blast out old rock and dance music at silly levels once a month when he had the lads round to drink and play pool.

Or they can save up and buy hi-fi speakers that will go to high levels without strain. On the used market that's not mega-money.

Just following the crowd and 5 star reviews doesn't necessarily get something tailored for the individual concerned.

 

[uwotm8]

@uwotm8 did you blow up your KEF's in an embarrassing manner

Ofc not, I'm not a KEF guy. I however do like R series and LS50 look, and current Uni-Q as well. Definitely a true technical beauty.
Anyway, I don't crank volume higher than 80-85 dB with any speakers and even this is for short periods, basically it's below 75 dB (if not 65).
So if I ever wanted to buy KEF speakers I'd simply go and buy. I saw these pictures years before and they changed nothing to me. I know that I will not reach their limit even remotely. But that's me; commeting today's review of Topping B200 one person mentioned that "it has better clipping than B100", then I wondered about how loud do people go, and was told that it was made just for fun, to check its clipping. 200W seems a nice check for sure

 

[Roland68]

This is exactly what happens when material fatigues.

Well, if you say so.

Please forgive me for using industry standards here.

Normal material fatigue is assumed to be caused by repeated alternating loads during normal use, where the material fatigue eventually leads to failure. This also leads to material softening and fatigue cracks, which can also be measured with a microhardness measuring device.

However, this is a significant overload, which ends in the cracks shown due to deformation and overstretching of a relatively brittle material. Microhardness measurements in such cases show very little to no material softening. The cracks occur due to the massive overloading and deformation of the material beyond its tear strength.
That is a big difference.

 

[RickS]

Thanks @jackocleebrown for your response!

I am not a current owner but have owned KEF speakers in the past. It does not appear the OP's blogger has owned but many members here do. We now have at least 100 more responses than the original article does. She theorizes about the Uni-Q design but is pretty obvious her claims are speculative. Her article headline is clearly alarmist hype. The website does not have any speaker reviews, so the main goal appears sensational. Will see if she issues any retraction. I think she should...

KEF is on my (very) short list of reputable audio companies whose products I would purchase or recommend to friends (and I have). 

 

[Old_School_Brad]

I have used and tested aluminum alloy drivers used for subs and when they hit the stops they make a horrible amount of noise. In the case of the KEFs the noise level from the driver being destroyed and the extreme motion of the driver itself would mean the operator would need to be both deaf and blind. Think like 100% distortion at a very loud volume level.

Exactly. That dreadful "clank clank" sound is unforgettable once you've heard it. And as you mention, it's even worse with metallic cones because they have less natural damping, making the contact with the voice coil more pronounced. Unlike composite or pulp paper cones, which can absorb some of the impact, metal cones transfer the energy more sharply, resulting in a much harsher sound. Terrible (and loud) warnings that destruction is near.

 

[Svend P]

I have used and tested aluminum alloy drivers used for subs and when they hit the stops they make a horrible amount of noise. In the case of the KEFs the noise level from the driver being destroyed and the extreme motion of the driver itself would mean the operator would need to be both deaf and blind. Think like 100% distortion at a very loud volume level.

This is what happens when you feed an 18" subwoofer driver with an X-max of 47.6 mm (1.8") more power than it can handle. Nothing is above destructive behavior. The picture is not mine, but I have had mine make that noise you describe. You turn down the volume very quickly after that. They are even rated for 8000 W short term power

 

[Heinrich]

This article sniffs too much like clickbait.

It is, not the smell but substance. It is insignificant, or in some statements clearly wrong out of not being educated in the field. Or do you really want your speaker to distort proportional to the current excursion? I mean, all these defects originate in simple overexcursion. May it be due to switch-on/off plop or way, way, way too much rumble-bumble for idiots.

Even paper cones crack, or fold by the way. Polycones not, but they melt and burn - read: needs exstinguisher. Now that real guys go for diamond, a vacuum cleaner will take care in case. And with beryllium, alas. nobody ever came back, you know?
And voice coils bottom out, ending to be bent scratching all the way - resin/glass design crack, insulation burns, surrounds overstretch, lead wires break and glue joints break, screws get loose ...

Repairs don't last longer than a week, if after Covid the substitute is readily availabe. (Second hand info, though.)

 

[Doodski]

This is what happens when you feed an 18" subwoofer driver with an X-max of 47.6 mm (1.8") more power than it can handle. Nothing is above destructive behavior. The picture is not mine, but I have had mine make that noise you describe. You turn down the volume very quickly after that. They are even rated for 8000 W short term power

View attachment 432961

Impressive woofer! Out of curiosity what amp where you powering this beasty with?

 

[Svend P]

Impressive woofer! Out of curiosity what amp where you powering this beasty with?

A Crown XLS2500 bridged per subwoofer. I have mine in 125 l closed cabinets, so that might not help keeping them in check either.

 

[Mnyb]

Hi Everyone,

I can understand that these pictures look dramatic and alarming to anyone that is a KEF loudspeaker owner, or that might potentially be considering purchasing KEF loudspeakers. I asked our operations team to collect some statistics for worldwide Uni-Q failures on some of our most popular 2-way speakers.

• This data is for Q150, Q350 and LS50 META.
• We've had to compile it from a few different sources but it captures the majority of global sales so I believe it is statistically significant.
• The data is for the time period 2016/1/1 to 2025/3/2.
• This includes Uni-Qs replaced for any reason, which will also include accidental and handling damage in addition to failure during use.
• This includes both repairs that were done both under- and out-of-warranty
• The number of Uni-Qs we have replaced is 0.08% of sales.

Here's some key info:

• All KEF loudspeakers undergo very thorough power handling and high-level performance checks during development to make sure they are suitably rugged for the market.
• With passive products, we are not able to protect the loudspeaker driver from over driving. Any passive loudspeaker will break eventually if the applied signal level is increased indefinitely.
• The current style of 2-way Uni-Q driver is now very mature and we have thousands of happy users.

+1 for having actual historical data in my line of work it’s a given , but consumer electronics these days who knows what your competitors do or don’t do .

 

[PHD]

Isn't there a KEF rep in this forum with all the great reviews their speakers are getting here?

 

[Old_School_Brad]

Isn't there a KEF rep in this forum with all the great reviews their speakers are getting here?

That would be @jackocleebrown and he responded with comment #108.

Do KEF Aluminum cone speakers have a serious design flaw?

And we should bear this in mind when someone asks for an amp recommendation for a two way KEF. This is one case where the "you can never have too much clean power" thing is obviously a myth. The situation where this kind of long term extreme damage can occur requires the operator ignoring very...

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