KEF Blade Two Meta loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system, a calibrated DPA 4006 microphone, and an Earthworks microphone preamplifier to measure the KEF Blade Two Meta's frequency response in the farfield. I used an Earthworks QTC-40 mike for the nearfield measurements. Because I perform the quasi-anechoic response measurements in-room, I usually place a loudspeaker's tweeter midway between the floor and ceiling, which equalizes the timing of the reflections from those boundaries. But because of the speaker's bulk, I wasn't able to lift it as high as I prefer. The presence of an early reflection from the floor of the Uni-Q's output therefore reduced the anechoic time window I used for FFT analysis, which in turn reduced the farfield response measurements' resolution in the midrange.

KEF specifies the Blade Two Meta's voltage sensitivity as 86dB/2.83V/m. My B-weighted estimate was slightly higher, at 86.7dB(B)/2.83V/m. The Blade Two Meta's impedance is specified as 4 ohms, with a minimum value of 3.2 ohms. The impedance magnitude, measured with Dayton Audio's DATS V2 system, is shown as the solid trace in fig.1. It varied between 3 ohms and 5 ohms over most of the audioband, with an increase in the low treble to 16 ohms due to the crossover between the Uni-Q's tweeter and midrange sections. The minimum-magnitude saddle of 2.8 ohms at 37Hz in the magnitude trace reveals that this is the tuning frequency of the twin ports on the rear panel.

822kef.KEFB2Mfig1

Fig.1 KEF Blade Two Meta, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

The electrical phase angle (dotted trace) is generally benign, but the effective resistance, or EPDR (footnote 1), lies below 2 ohms between 30Hz and 39Hz and between 813Hz and 881Hz, and below 3 ohms between 3.9kHz and 14kHz. With minimum EPDR values of 1.23 ohms at 34Hz and 1.64 ohms between 813Hz and 881Hz, the Blade Two Meta presents amplifiers with a somewhat demanding load.

I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer. Although the sidewalls emitted an audible "bonk" when I rapped them with my knuckles, especially in the region behind the twin woofers, I didn't find any significant resonant modes on these walls. This is a testament to the effectiveness of the Blade Two Meta's use of opposed and mechanically connected woofers on the two sidewalls. A couple of modes between 400Hz and 600Hz were present on the front baffle (fig.2), but these modes were very low in level and should not have audible consequences.

822kef.KEFB2Mfig2

Fig.2 KEF Blade Two Meta, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of front baffle below Uni-Q drive-unit (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The red trace in fig.3 shows the response of the ports, measured in the nearfield. (Both ports behaved identically.) The output peaks slightly below the tuning frequency, and the upper-frequency rollout is clean, other than a couple of low-level peaks in the midrange. Both the low level and the fact that the ports face to the speaker's rear will minimize the audibility of this behavior. The four woofers also behaved identically. Their summed nearfield output (fig.3, blue trace) has the expected notch in its output at the tuning frequency of the ports. The woofers' farfield output crosses over to the midrange section of the Uni-Q driver at 400Hz, slightly and inconsequentially lower than the specified frequency of 450Hz. The filter slopes appear to be lower order than those of the original Blade Two (footnote 2), but the Uni-Q unit's farfield response (green trace above 500Hz) is superbly flat and even.

822kef.KEFB2Mfig3

Fig.3 KEF Blade Two Meta, acoustic crossover on tweeter axis at 50", corrected for microphone response, with the nearfield response of the midrange unit (green), woofers (blue), and ports (red), respectively plotted below 500Hz, 450Hz, and 700Hz.

The complex sum of the woofer and port responses is shown as the black trace below 300Hz in fig.4. The peak at low frequencies will be entirely due to the nearfield measurement technique, which assumes that the drive units are mounted in a true infinite baffle, ie, one that extends to infinity in both planes. The woofers' reflex alignment is maximally flat. The black trace above 300Hz in fig.4 shows the Blade Two Meta's quasi-anechoic farfield response, averaged across a 30° horizontal window centered on the tweeter axis. The astonishingly even on-axis response—even flatter than that of the original Blade Two—is maintained over this wide measurement window.

822kef.KEFB2Mfig4

Fig.4 KEF Blade Two Meta, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield woofer and port responses (black trace below 300Hz).

Fig.5 shows the Blade Two Meta's horizontal dispersion, normalized to the response on the tweeter axis, which thus appears as a straight line. The contour lines in this graph are commendably even up to 80° off-axis, when the higher-frequency output from the side-mounted woofers introduces some irrelevant unevenness. The KEF's vertical dispersion is shown in fig.6. The tweeter-axis response is maintained over a wide window.

822kef.KEFB2Mfig5

Fig.5 KEF Blade Two Meta, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

822kef.KEFB2Mfig6

Fig.6 KEF Blade Two Meta, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15–5° above axis, reference response, differences in response 5–10° below axis.

Turning to the time domain, the Blade Two Meta's step response (fig.7) indicates that the tweeter and midrange sections of the Uni-Q drive unit are connected in negative acoustic polarity, the woofers in positive polarity. The decay of the tweeter's step, which arrives first at the microphone, blends smoothly with the start of the midrange step; its decay in turn smoothly blends with the start of the woofers' step. This, together with the different distances of each unit's acoustic center from the microphone, implies optimal crossover implementation. The Blade Two Meta's cumulative spectral-decay plot on the tweeter axis (fig.8) is superbly clean.

822kef.KEFB2Mfig7

Fig.7 KEF Blade Two Meta, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

822kef.KEFB2Mfig8

Fig.8 KEF Blade Two Meta, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

I've come to expect superb measured performance from Jack Oclee-Brown and his team at KEF, and the Blade Two Meta delivered. This is modern loudspeaker engineering at its best.—John Atkinson


Footnote 1: EPDR is the resistive load that gives rise to the same peak dissipation in an amplifier's output devices as the loudspeaker. See "Audio Power Amplifiers for Loudspeaker Loads," JAES, Vol.42 No.9, September 1994, and stereophile.com/reference/707heavy/index.html.

Footnote 2: See fig.3 here.

COMPANY INFO
KEF, GP Acoustics (UK) Ltd.
US distributor: GP Acoustics (US) Inc.
10 Timber Ln.
Marlboro, NJ 07746
(732) 683-2356
ARTICLE CONTENTS

COMMENTS
remlab's picture

but this is as close as I've ever seen. I know KEF has always done nonstop R&D over the decades and will continue this practice, but how on earth could they ever improve on this design? I'm sure that HD and IM distortion measurements are just as flawless as everything else. Crazy.

volvic's picture

Have heard them over the years in different iterations, improvements etc., and they never fail to amaze. They seem to do everything right and not many speakers have ever done that for me, maybe Focals, MBL and Verity Audio. Very special speakers, wish I had the space and the cash for a pair.

JRT's picture

...for another interesting, well thought out, well executed, and well written review of an interesting loudspeaker. And I also appreciate the efforts of JA1 in providing measurements and associated useful commentary.

You gentlemen do not receive enough positive feedback in the comments section for the high level of competence in all of the good work which you provide here, and the significant effort that goes into that.

Edit: I had a question about the Uni-Q coax utilized in this loudspeaker, but reading the KEF whitepaper at the link provided in footnote 2 answered my question.

Mev Dinc's picture

your excellent review moved them to the top of the list.

johnnythunder1's picture

Any time I've seen the Blade speakers I think of the ridiculous "fish fountain" from Jacques Tati's Mon Oncle. https://medium.com/@hyeoh/bong-joon-hos-parasite-and-jacques-tati-s-mon-oncle-d1b23564db93

remlab's picture

..sometimes in the near future. Trickle down technology(Kind of). I know the magazine frowns on one piece audio solutions, but it would still be a very interesting review in comparison with the Blade 2

JRT's picture

KEF's LS60 Meta wireless is a two piece (if you ignore counting the added componentry included in varied domestic IT infrastructures) consisting of a seemingly proper pair of floor-standing DSP filtered active loudspeakers with added functionality.

Compared to KEF's Blade II Meta and LS50 Meta, the LS60 Meta utilizes a smaller diameter Uni-Q coax, allowing for the narrower baffle, which may be a little more conducive to domestic harmony with a non-audio-enthusiast spousal-type weighing in with counter demands on room decor. And it will sound better than an aging Bose Lifestyle modular hideaway system.

All of that is in contrast to the one piece wireless Sonus Faber Omnia boombox audio enabled plant stand, in Stereophile's review recently posted here.

https://www.stereophile.com/content/sonus-faber-omnia-wireless-loudspeaker

rpeluso's picture

So with this review I gather that you now think the Perlisten S7t speakers are the second best you have ever heard, is this right?

Kal Rubinson's picture
Quote:

So with this review I gather that you now think the Perlisten S7t speakers are the second best you have ever heard, is this right?

Yes and I wrote a somewhat detailed and, perhaps, sophistic explanation of the situation but that did not make it into print. Bottom line is that I was not sufficiently motivated to buy the S7t and I moved on. It is still a speaker that I would recommend to anyone for serious consideration.

P.S.: The LS60s are on the to-do list.

wannarock2's picture

yeah the LS60 wireless could be the bargain of the design.
(kal thinking surround sound ☀‿☀)

yyz's picture

I am curious how the Blade 2 Meta, my next speaker, would sound with overwhelming power such as with the Rotel Michi M8 monos.

About 5 years ago I heard the Blade 1 with the Hegel H30 monos which are similar power wise to the Michi M8. It was a real fun listen, but the Hegel was not very clean sounding on top. When I demoed the lower powered Michi X5 integrated, it seemed cleaner sounding than the Hegel H30 with the some new B&W speakers. As a frame of reference, the Benchmark AHB2 is as clean as it gets for my ears.

The upcoming KRELL KSA i400 uber amp is something that I think would be excellent with the Blade 2 Meta. I have owned 2 of the new KRELL XD amps and I am now considering trading one in for this uber KRELL amp.

I also have my Benchmark AHB2 monos available, which I know will be good not sure about being great with the Blade 2 Meta due to power. The single AHB2 stereo was awful with Magico A3 (not enough power) and the monos were not the best with my now sold hard to drive Thiel CS3.7 speakers.

b-baij-jo's picture

I've had the B2Ms for a month now and I am over the moon. As for amplification, I am using a Zanden 8120 (re. 100 tube watts) to drive them with excellent results. I am running a pair of subs - and using a mere 5th of their power. I am very satisfied. Amazing clarity and coherence - and add in exceptional soundstaging, imaging, and dynamism - the you have a speaker that is hard to beat. Order yours soon as the wait was loooong - but worth it.

ejlif's picture

for about 3 years. I came to slowly realize they are one of the most dull and uninspiring speakers I ever owned. I'd take a pair of Klipsch Forte over a pair for pure enjoyment of playing music. I went back and forth over and over for a year putting different speakers in and out and comparing and eventually I sold them. I thought they would be my dream speaker. I loved the looks. I was quite disappointed with the actually product in real life. Light and made of plastic. The entire base is just a piece of plastic and they aren't even heavy. I'm perplexed out how they come up with such a high price for these. Seems like they are double or triple what they should be based on the quality. Mine is a case of different strokes for different folks I ended up far preferring the sound of lower power tubes and efficient speakers over the power hungry Blade 2. I tried for 3 years to like these speakers but could never warm up to them.

Kal Rubinson's picture

Fair enough indication of an alternate perspective and your decision to move on. From my POV, I've yet to hear a Klipsch speaker that I could live with (and that includes the originals).

Jim Austin's picture

After all, your tastes are your tastes. But as to that lightweight "plastic" cabinet, someone should set the record straight. Here's what JA wrote after measuring the original Blade 2 (not the meta): "The Blade Two's enclosure is extremely inert, and the force-canceling woofer arrangement seems to work as advertised." The result with he Metas was a bit different: " Although the sidewalls emitted an audible "bonk" when I rapped them with my knuckles, especially in the region behind the twin woofers, I didn't find any significant resonant modes on these walls. This is a testament to the effectiveness of the Blade Two Meta's use of opposed and mechanically connected woofers on the two sidewalls. A couple of modes between 400Hz and 600Hz were present on the front baffle (fig.2), but these modes were very low in level and should not have audible consequences."

Another perspective: Here's an image of the larger Blade Meta, from the recent Audio Advice Live show in Raleigh. The speaker is playing loudly in a highly resonant space.

Jim Austin, Editor
Stereophile

remlab's picture

There is no law that says you have to like objective accuracy(Some people actually believe this). After all is said and done, if it doesn't move you...

steve59's picture

It would have been great if KR or JA had reviewed both speakers. Would blade 1 owners benefit more by upgrading to meta's or using equal money on better components?

I was able to get an extended audition of the perlisten s7t and found the listening window to be to small to be practical even if the effect is polarizing.

Kal Rubinson's picture

To be sure but those kinds of comparisons generally demand that the reviewer already possessed the original pair. So, we do it when we can and JA did it with the LS50s, original and Meta.

I think you are spot-on in your observation of the Perlisten S7t.

MikeP's picture

I liked the Kef Reference 5 Meta's even more! I believe they are the best kept secret in Kef's line right now ! Please review them and find out...

MikeP's picture

Compare them to Grandinote Mach 18's or Mach 36's please ! Go listen to Mitch's system in Long Island, New York. Mitch has the Grandinote Mach 36's maybe the best speakers on the planet ! Mitch's E-mail is pennpalmitch@gmail.com Anyone can go listen to Mitch's system.

Kal Rubinson's picture

To be honest, those Grandinote speakers are too tall, too large and too expensive for me and my room. I also find the design concepts difficult to accept without some objective measurements to support them. (All this is said without having heard them and, therefore, are not criticisms of the speaker, itself.)

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