KEF KF92 2x9" drivers Sub - anyone heard it?

[killdozzer]

Two drivers instead of one. As I understand two drivers can achieve a higher (SPL) output from the same box (but it's never literally two folds).

How about evening the response across the room? Any benefit there, when having two drivers? Synchronizing the drivers properly allow them to dig deeper with less distortion, right?

Is it easier or harder to achieve seamless integration with this type of sub? It is closed box, but it states it goes incredibly deep (11Hz at -3dB and a maximum of 110dB???).

The driver is what is expensive parts-wise, so it makes sense that 2 driver sub is significantly more expensive than single, would you say KEF KF92 is bordering overpriced or would you say the price is right? It would be nice to have a test of this model.

Has anyone heard this sub? What are your opinions on performance?

 

[mazersteven]

It is closed box, but it states it goes incredibly deep (11Hz at -3dB and a maximum of 110dB???).

That's pretty deep for small drivers (9") in a small enclosure 14"×13"×14" ???

 

[killdozzer]

That's pretty deep for small drivers (9") in a small enclosure 14"×13"×14" ???

Indeed. That's what made me wonder. I don't think KEF overstates their numbers, but this is quite amazing.

 

[NINaudio]

I agree with Mazer, that f3 spec seems quite suspect to me.

In regards to your question about it evening out room modes because it has 2 drivers, the answer is no it won't do that. When the drivers are that close together it essentially acts as one source for frequencies in that range.

edited to add a review (I know, it's whathifi!) with frequency measurements, which states f3 is 14 Hz, which is still mighty impressive for 2 9" drivers:

https://www.whathifi.com/us/reviews/kef-kf92

 

[killdozzer]

Thank you both. I'm still not writing it off as there seems to be some cunning solutions built into this speaker.

In the menatime:

"Below the LFE/line-level inputs is a pair of line-level outputs. These can be set so the signals that appears there are simply a ‘loop-through’ from the line-level inputs, or you can route the audio signals through a high-pass filter to remove low frequencies before they appear at this output. "

Yaaaayoooo!!! This is one for the KEF team as it would seem buying this sub would make the miniDSP unnecessary.

But it's pricey.... damn!! I have to sell more gear. Anyone interested in Hitachi Dynaharmony HMA-8300/HCA-8300?

 

[killdozzer]

I don't have some deep respect of What Hi-Fi reviews, but this time with graphs, I'm linking it for pros here to decide are the numbers really bloated?

KEF KF92 review

Awesome low-end from a cute, compact cube

www.whathifi.com

 

[kini]

I don't have some deep respect of What Hi-Fi reviews, but this time with graphs, I'm linking it for pros here to decide are the numbers really bloated?

KEF KF92 review

Awesome low-end from a cute, compact cube

www.whathifi.com

No measurements but I enjoy his reviews

 

[killdozzer]

No measurements but I enjoy his reviews

Thank you. These YouTube reviews are of very limited benefit. You're usually left only with what reviewer felt and said. Even if you had the exact same room to play this video, it wouldn't be a faithful representation.

Although that one graph was very interesting and would support a very low low-end spec from this sub. Even if it's not 11, let it be 18, it is still very good for a 2x9".

 

[Steve81]

FWIW, in terms of effective cone area, you’re looking at the equivalent to a single 12-13” woofer. -3db at 11Hz isn’t happening in a small sealed box without a lot of internal EQ. Given the basic limitations of such a design, I wouldn’t expect huge output below 30hz or so either way, but it could be satisfactory in a smaller room depending on one’s expectations.

 

[killdozzer]

FWIW, in terms of effective cone area, you’re looking at the equivalent to a single 12-13” woofer. -3db at 11Hz isn’t happening in a small sealed box without a lot of internal EQ. Given the basic limitations of such a design, I wouldn’t expect huge output below 30hz or so either way, but it could be satisfactory in a smaller room depending on one’s expectations.

Hey Steve81, long time no see. How have you been? (It was you actually that told me long time ago I can connect the sub using pre-out/main-in).

Thank you for your input. There has, in fact been a lot of internal EQ and a lot of other useful tinkering inside this box. However, I'm not saying it is as they say, I'm still waiting to read about it. (I just didn't write it off, that's all)

Most of the things members mentioned here, they seem to approached... I've linked a review that even has some measurements (a rarity for modern day What Hi-Fi), you could at least scroll down to graph and see if they make sense.

I am open to the idea that it is just an exaggeration, don't worry! I don't want to jump to conclusions.

 

[Steve81]

I’m getting by alright, though the past 12 months haven’t exactly been the happiest times.

The measurements done at What Hi-Fi aren’t complete enough for me to say a whole lot. The sub appears to be nice and linear; obviously the anechoic measurements don’t show anything close to -3db at 11Hz, but that’s just as well considering it’s just be a waste of amp power here. Out of the box extension / roll off is good, though how well it can maintain that at higher output levels with respect to distortion and compression isn’t shown. From what data there is, it doesn’t appear to be an irredeemable crapbox, but whether it’s worth the asking price vs say a SVS SB3000 is another story.

 

[killdozzer]

I’m getting by alright, though the past 12 months haven’t exactly been the happiest times.

The measurements done at What Hi-Fi aren’t complete enough for me to say a whole lot. The sub appears to be nice and linear; obviously the anechoic measurements don’t show anything close to -3db at 11Hz, but that’s just as well considering it’s just be a waste of amp power here. Out of the box extension / roll off is good, though how well it can maintain that at higher output levels with respect to distortion and compression isn’t shown. From what data there is, it doesn’t appear to be an irredeemable crapbox, but whether it’s worth the asking price vs say a SVS SB3000 is another story.

A heck!!! Now I have to admit to myself I don't know how to read a graph!!!

I was sure this meant that there is a lot of audible activity below 20Hz and that the roll-off is not steep:

 

[Steve81]

A heck!!! Now I have to admit to myself I don't know how to read a graph!!!
View attachment 39056

I was sure this meant that there is a lot of audible activity below 20Hz and that the roll-off is not steep:
View attachment 39057

You read the graph itself ok, but that’s an in-room measurement, not anechoic.

 

[killdozzer]

But anechoic looks even better.

I mean, more SPL - 95-96dB arround 20Hz and 17-18Hz is still at 93dB.

 

[Steve81]

But anechoic looks even better.

I mean, more SPL - 95-96dB arround 20Hz and 17-18Hz is still at 93dB.

Unfortunately there’s at least one key detail missing to put those numbers into perspective: distance.

 

[Verdinut]

The reported specs seem a little bit exaggerated. KEF publish a frequency response of from 11 to 200 Hz ± 3 dB, whereas their Reference 8b sub that also uses two 9" drivers and which sells for $7.000, would only have a frequency response to 24 Hz at -3 dB:

Reference 8b Ultimate Subwoofer | KEF

Twin 9 inches driver 'force-cancelling' subwoofer Delivering exceptional bass precision and control with zero distortion, Reference 8b is a truly extraordinary subwoofer.

us.kef.com

 

[lovinthehd]

Looks like a nice, altho fairly expensive at $2k, dual opposed 9" sub. I don't know that the expense is just in an additional driver in the box, but also has separate amps for each driver. Doubt it's an spl monster in any case. The f3 is valid up to what spl with what levels of distortion, tho?

 

[killdozzer]

Few notes from the designer:

He insists.

LATER EDIT: ah, no, Sharkey is marketing (how appropriate), well then anything goes.

 

[killdozzer]

Let me try and approach this from a different angle. I'm still thinking about this sub because it's small and this is important to me.

So, let's just take it for what it is. Let's not expect the 11Hz at all. Here's a quote:

Although KEF rates the driver with a diameter of 230mm, the design of the driver is such that the Thiele/Small diameter is 175mm, which gives an effective cone area (Sd) of 240cm² per driver, or 480cm² for the system.

This means that had KEF wanted to move the same amount of air with a single cone, rather than with two, it would have had to have had a Thiele/Small diameter 247mm, which would have translated to a specified diameter of 332mm.

Looking at it this way it's close to a single 13" driver with some advantage from good DSP and force-canceling design.

Do you think there's a sub this small that performs equally good or better? Do you still think a single 13" would do better and if yes, why and how so?

Don't you think this is a good way of packing a 13 into a box of 9? (I know it is more expensive, but if the price is not an issue and you're looking for as small as possible).

 

[killdozzer]

If anyone stumbled upon any update on this, I'm still interested. I can't find any...