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KEF KC-62 defies physics??

ol_mcdonald

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So, tell me please, how a sub can produce 11hz @ 105 db spl with two 6.5" drivers. @amirm please test!
 

RayDunzl

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What was the measurement procedure?

I got 4.81Hz at 86.4dB just waving my hand in front of the mic.

The distortion looked kinda high, though.
 

AdamG247

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Did they really mean the KEF Unicorn? Will see one of those before we see this hit 11hz.
 
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ol_mcdonald

ol_mcdonald

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MrPeabody

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What was the measurement procedure?

I got 4.81Hz at 86.4dB just waving my hand in front of the mic.

The distortion looked kinda high, though.

I know of another way to get a similar effect, with less work. It involves the release of gas under pressure.
 

napilopez

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So, tell me please, how a sub can produce 11hz @ 105 db spl with two 6.5" drivers. @amirm please test!

FYI there are several threads on this subwoofer already. As discussed in this thread, 105dB is the max SPL at any frequency. Without graphs or more details, for all we know that's just the maximum SPL at 150 Hz =]

I asked KEF for a more specific metric, the maximum anechoic SPL achievable at 20Hz, and they said 80dB. In-room that'll be a lot louder. I still think it's impressive, but much more believable for 2x 6.5-inch woofers. Besides, it all depends on what the bass limiting curves look like. Maybe it can get to 100dB at 30Hz, for example. We'll have to get measurements to see.
 

witwald

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I asked KEF for a more specific metric, the maximum anechoic SPL achievable at 20Hz, and they said 80dB. In-room that'll be a lot louder. I still think it's impressive, but much more believable for 2x 6.5-inch woofers. Besides, it all depends on what the bass limiting curves look like. Maybe it can get to 100dB at 30Hz, for example. We'll have to get measurements to see.
If the 2x 6.5-inch woofers have an Xmax of 5 mm, then that figure of 80 dB at 20 Hz at 1 m seems to be quite reasonable and achievable. :)

With the same Xmax of 5 mm applied to a response at 30 Hz, we can get to only 87 dB, not 100 dB, unfortunately. Sound pressure goes up as the square of the frequency ratio, so we get an increase of 2*20*log10(30/20) = 7.0 dB.

Commensurately, at 11 Hz the maximum output level will be around 70 dB. By 50 Hz we get to 96 dB, and 105 dB is reached at 85 Hz.

For a subwoofer with 2x 6.5-inch drivers, to produce 105 dB SPL at 11 Hz at 1 m would require an Xmax of about 300 mm. As this is about the same order as the enclosure dimensions, then I doubt that it is feasible for it to do so. ;)
 

napilopez

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If the 2x 6.5-inch woofers have an Xmax of 5 mm, then that figure of 80 dB at 20 Hz at 1 m seems to be quite reasonable and achievable. :)

With the same Xmax of 5 mm applied to a response at 30 Hz, we can get to only 87 dB, not 100 dB, unfortunately. Sound pressure goes up as the square of the frequency ratio, so we get an increase of 2*20*log10(30/20) = 7.0 dB.

Commensurately, at 11 Hz the maximum output level will be around 70 dB. By 50 Hz we get to 96 dB, and 105 dB is reached at 85 Hz.

For a subwoofer with 2x 6.5-inch drivers, to produce 105 dB SPL at 11 Hz at 1 m would require an Xmax of about 300 mm. As this is about the same order as the enclosure dimensions, then I doubt that it is feasible for it to do so. ;)

Thanks for the reasonable analysis! I was exaggerating a bit, but everything you said makes sense. I'd actually messed a bit around with an xmax calculator myself, though didn't think of checking 30Hz.

That said, is it possible the drivers are capable of higher excursion but are DSP limited at lower frequencies to keep distortion under certain thresholds? And therefore potentially having more headroom at higher frequencies? Not saying that's likely, just a thought. Not sure if I'm misunderstanding things
 
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So, tell me please, how a sub can produce 11hz @ 105 db spl with two 6.5" drivers. @amirm please test!

Very easy! Using the calculator, you need two 6.5 inch drivers with 7.55 inches of Xmax--basically, a 15 inch stroke and done! :D

Alas, you have been a victim of smoke and mirrors--KEF never claimed it puts out 105dB at 11 Hz. No! They claimed a peak output of 105dB on one line and a frequency response on another line--they never, in any shape or form claimed the two specs are related to each other.

I find this hysterically funny--a sealed subwoofer is the easiest sub to calculate output--it is the most basic air pump you can have as there is not horns, no bandpass, no ports or anything to calculate. It is purely bore X stroke that produces liters of air (or less than a liter) Liters of air movement directly result in specific SPL at specific frequencies.

Look at the drivers, they are conventional with spiders and the frames have an angle which limits the diameter of the spider. The smaller the spider, the less Xmax is available so you want to stuff in the largest diameter spider in you can, use a deep surround to allow more cone movement and so on. No LOOK at that driver! The spider is not the largest you can stuff inside AND the surround is not deep. I looked at Sundown, they make very long travel drivers for car audio, they have a 6.5 with vertical sides to cram in the largest spider they can, very large magnet and a larger surround than the KEF. The specs at 70% BL is 10mm of Xmax and an Xmech of 20mm. Xmech is when the voice coils slams into the magnet and you break things.

TangBand has a 6.5 inch that has 12mm of Xmax and a Neo motor and there is a 6.5 incher that uses an XBL2 motor to punch 12.5mm. That is about your limit because of the natural limit of the diameter of the spider. You might have noticed this because a Dayton UM8 8 incher has an Xmax of 16mm, some 10 inch subs have an Xmax of 19mm and a CSS SDX12 has an Xmax of 28mm. As subwoofer frames get larger, you can have longer Xmax or stroke because the spiders become larger to allow this.

A good example of the "magical DSP" is a design from around 9 or 10 years ago called the "VBSS sub" Basically, it is a 18" PA woofer in a 6.75 cubic foot box two 4" flared ports tuned to 20Hz (or 19 Hz, 18 Hz or one port plugged for 14.5 Hz) The woofer runs $90 to $98 in price, and is limited to about 9mm of Xmax. The "magic" in it is simple, the parametric EQ has a boost of +12dB at 20Hz so you get even response up to around 105dB. To protect the driver from such massive boost, it uses dynamic limiting which limits the power allowed at specific frequencies to protect the woofer. Basically, the woofer is only allowed to move 9mm of Xmax before the power is limited. A certain amount of power is allowed at 20Hz, more power is allowed at 25Hz, even more power at 31.5Hz and no limits at 40Hz. For example, at 40 or 50Hz that sub can punch out higher than 120dB because the limiter now becomes the amp limiter.

The magical amp is called a Behringer iNuke 3000DSP which costs less than $300 (now called NX3000D) Into the 8 ohm load of the woofer it will punch out 300 watts into 8 ohms. Strap two of those VBSS subs to each channel and it jumps to 600 watts X 2 into 4 ohms. Total cost to build four of those VBSS subs is $90 X 4 or $360 for the drivers, $60 or so for the eight flared ports and four sheets of plywood--maybe $279 for the amp. $600 in parts and four sheets of 3/4" plywood--throw in some Duratex and we are talking $800 for four 18" subwoofers, 1,200 watts of total power, many bands of parametric EQ, delays, adjustable limiters and so on. If you have four of them in a typical room (generaly basement theaters) you will get room gain down around 20Hz and the subs will start to couple with each other at low frequencies (depending on distance) so very easy to get 115dB at 20Hz or "reference levels" Output at 30 or 40Hz is well into the 120+dB range and the dynamic limiters will protect the driver down low but allow full power up higher to go completely rockstar with drums and bass guitars.

Anyone can build/design such a thing--hell, I've done it! No, I don't have the VBSS but helped a friend build one and it works very well. There is nothing physics defying about it, no magic, no messiah has come down from the clouds to alter Hoffman's Iron Law--just parametric EQ boost and dynamic frequency limiters available in an amplifier for under $300. If you like, get a Eminence 21" stadium sub, slap it in a 16 cubic foot box tuned for 18Hz, throw 2,000 watts at it and apply dynamic limiting and EQ boost to get 120 to 130dB depending on frequency. It is not hard, no EE degree required, just a working knowledge how speakers work, how EQ and dynamic frequency limiters operate--a bit of software to model how to do proper setup and done. Yep, one guy and a weekend and you can do it start to finish. If a fool like me can do it--as long as you have opposable thumbs, can read and won't cut your hands off with a power saw all is well.

There is a guy in Canada, the single guy engineering type that has his basement underground, fully treated with walls over 2 inches thick. He took 16 of those Dayton 18" PA woofers, built two columns with 8 woofers each (4 on each side opposed) in 24 cubic foot sealed enclosures.
Strapped them to a very stout PA amp that pushes 8,000 watts and obtained 115dB at 2 watts of power. Ran it full throttle in his room at 8 KW and exceeded 150dB (why the basment is underground and his nearest neighbor is over a mile away) He posted his distortion at 115dB and it was very low, down to a few tenths of a percent. Typically, he never goes over 130dB peaks in the bass region so content. Total cost for the 16 drivers at $85 each, a clone stadium amp at $1,000, he has audio processors for everything already and the wood/bracing to build two 24 cubic foot sealed enclosures was under $3K. Oh yeah, he has another 15 subwoofers to do the low stuff--those TC Sounds 18's with more stadium amps but such is required to get a frequency response flat down below 2 to 4 Hz. Those 16 PA woofers have no high pass filters for protection and are not EQ'd below 40Hz where the TC Sounds add in.

So yeah, I find what KEF is doing is laughable--but they need to make a profit so give incomplete, misleading specs--like audio gear on Alibaba. They specifically create magic but they know their customers better than me so they can profit from it. Yes, it makes KEF look like those flea market car amps that promise 4,000 watts and contain a single 20 amp fuse but it sells. They are selling to specific groups, the people that want a tiny, sexy little sub to match the room decor, people that are the KEF fanboys and faithful and others that use specs to determine how good they are, how large their manhood is etc. Granted, anyone that knows/understands acoustics won't buy such a thing but KEF does not make high performance subwoofers anyway so no big loss.

So when somebody actually measures ones and it is obviously weak will this hurt KEF? No, they aspire to the lifestyle market which is much larger than the performance at all costs HT/music market. The Phantom sells well, it obviously has bogus specs and KEF wants that money--honey! It has all the buzzwords for the clueless, a thousands watts! 11 Hz! 105dB! and it is expensive enough so the audiophile claim of "You are just jealous because you can't afford it" applies. Sure, they damage their rep but it's not like KEF was the engineering powerhouse of the late 70's and 80's anyway. They went coax to simplify in the 90's and now are angling to go full lifestyle. It worked for Bose! No worries, just business so for the KEF owners that will get butt hurt because they refuse to produce world class performance with lifestyle audio...just the way it is. You will adjust, plenty of KEF fans from the 70's/80's with 104.2 towers etc. saw those little coax bookshelves from the 90's and they left the church...and KEF survived so welcome to the 20's.

KEF lost its direction after making its last batch of BBC-licensed monitors, and eventually went into receivership in 1992.[6] It was acquired by GP Acoustics, a member of the Hong Kong-based Gold Peak Group.[1]

Makes sense, they went bust in 1992 and was purchased by a China based company... sooo... yeah.
 

jhaider

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Alas, you have been a victim of smoke and mirrors--KEF never claimed it puts out 105dB at 11 Hz. No! They claimed a peak output of 105dB on one line and a frequency response on another line--they never, in any shape or form claimed the two specs are related to each other.

It's not "smoke and mirrors" but rather SOP to decouple frequency response from max output capability at a given frequency. KEF is guilty of nothing here except for following industry norms. The closest real-world competitor for this subwoofer is probably the Paradigm MilenniaSub. The form factor differs, but the basic idea (compact and unobtrusive, exotic bespoke dual opposed drivers shaped by advanced DSP, failure to include grilles) is the same, and the price is about the same too. Paradigm claims 24-120Hz ±3dB. Brent Butterworth measured this subwoofer, and more than confirmed this specification (the actual HF extension was about 250% superior to Paradigm's claim). However, you can also see from the link output capability was lower down low, such that at high SPL the frequency response would no longer conform to spec.

I have a MilenniaSub. Right now I'm deploying it in a system with two of those oft-overlooked-but-shouldn't-be Technics fat-boy coaxial bookshelf speakers. The improvement in extension was instantly obvious throughout the room, not just in the seat improved by the onboard ARC Genesis correction. The output "limitations" were either masked by skillful use of limiters or simply irrelevant at the volume levels used in this system.

Basically, it is a 18" PA woofer in a 6.75 cubic foot box

And thus, completely out of the scope of a compact subwoofer.

There is nothing physics defying about it, no magic, no messiah has come down from the clouds to alter Hoffman's Iron Law--just parametric EQ boost and dynamic frequency limiters

Is anyone claiming anything different here? The "magic" here is that KEF managed to get two voicecoils of different sizes in one motor to perform similarly enough for a dual-opposed sub, that's all. Is that worth something? Maybe. It's certainly a novel design, and one would expect further refinements as KEF iterates. However, it's also worth noting the width of the sub (and thus presumably the 2-in-1 driver) is about 10". That depth could be achieved with, for example, two Peerless XLS10's or SB Acoustics SW26's as well as and some discontinued inverted-motor drivers such as this Aurasound 8 or Peerless/Tymphany 10 would allow even less space between the drivers.

So yeah, I find what KEF is doing is laughable--but they need to make a profit so give incomplete, misleading specs--like audio gear on Alibaba.

Or Paradigm, and basically every other speaker company.

They are selling to specific groups, the people that want a tiny, sexy little sub to match the room decor,

Yes, and so what? That brings up another pet peeve of mine. Generally, people on internet forums vastly overstate the bass SPL required for most program at actual humans' listening levels. Unfortunately, that leads some readers to throw up their hands and conclude that since they can't coexist with eyesores there's no use in setting anything up at all.

Granted, anyone that knows/understands acoustics won't buy such a thing.

Or they might, when it fits a given use case, because they have a deeper understanding than expressed above.

They...now are angling to go full lifestyle.

Have you heard of the "egg" speakers? KEF has been doing the "lifestyle" thing, and very well, for decades now.

For that matter, I wonder how this subwoofer compares to their previous grille-less designer sub, the HTB2.
41ie4K3x4TL.jpg


HTB2 used a single 10" woofer with a 10" passive radiator, and an Icepower amp. I'm not aware of third party measurements of that sub. Maybe someone else has seen some?

Makes sense, they went bust in 1992 and was purchased by a China based company... sooo... yeah.

Was it really necessary to conclude with grammatically-incorrect bigotry?
 

BrokenEnglishGuy

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my kef r300s in my 2.8 * 3.3 meters small very small room give me -10dB 30hz~, i imagine something like this just destroying my room.. xd
 

Kvalsvoll

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and basically every other speaker company.

There are several brands that may disagree about this statement. I do not agree that my specifications are misleading or false. I find that even though specifications may be incomplete or in other ways makes it difficult to find relevant data, outright misleading specifications are still the exception.

Specifications that are very far from reality is bad for both customers and manufacturers. It gives the industry a bad reputation, and customers are mislead to believe that this is state-of-the-art - the best you can get, when there is so much more to experience and explore.
 

Nevi

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I bought the Kef LS 50W II, with the KC 62. Before that, I used Yamaha HS 7s with the HS 8 subwoofer. Very linear response from around 30hz and up.
When I heard the first LS 50W I thought wow. But when the new LS 50 II came, and I heard them with the KC 62 sub, I knew they would be my new speaker set up.
The sub really do dig deep. But up to a certain point. You can only fool physics so much. But to a nearfield set up (with my computer) that Kef package is nice. Have any others tried the combination?
 

ThELiZ

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I've had the LS50WII + 2x KC-62 subs on home demo and have been really impressed by the performance gains 2 subs have given me. This is the first time I've tried subs, and after a bit of time spent moving them around and measuring, got them sounding pretty decent... The main reason I'm not keeping them is that I do not like sing the Kef Connect app, the subs hum, the subs don't wake up until loud music is played... And they really really don't suit our living room. Ah well.


LS50WII - No EQ - 2 Subs vs No subs.jpg


LS50WII - 2 subs - EQ vs No EQ.jpg


Edit: Sorry. Just realised this is a super old/recently bumped thread... Might have been better putting this info in a more up to date thread.
 

Nevi

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My sub has never had hum. Wasn’t that some earlier model? I’m super impressed with my Kef set up.
 
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