KEF R300 playground - measurements of raw drivers

[Zvu]

Measurements are done in room so 4,5ms gate is best i can do which translates to about 220Hz gate frequency. 1m distance. Measurements done 0-90 degrees in 10deg increments. I don't believe i'll be dragging these to the parking lot any time soon, but who knows. Until then:

Averaging them:

 

[Zvu]

I've been listening these speakers past two weeks and tweaking a bit. Nothing dramatically changed but few details for better phase matching and a bit more linearity. I'm at the stage of putting the crossovers into the cabinets so here's few screenshots:

On axis:


https://s15.postimg.cc/6xh5avkyj/Webp.net-gifmaker_1.gif


Off axis:


https://s15.postimg.cc/mvpv10mwb/Webp.net-gifmaker.gif


Simplistic crossover:


https://s15.postimg.cc/jovbh6s3v/image.png


"Exploded" view:


https://s15.postimg.cc/xvb2cfxu3/image.png

 

[Zvu]

I've made some more measurements last night to see the agreement of simulator to measured response. There is a slight upward tilt toward high frequencies but that could be due to cold (6 degrees Celsius last night). By the looks of it, if it is real, the tweeter is a 1.5-2dB hotter but final level is to be determined indoors by listening. So, without further ado...

On axis:



Off axis 10 and 20 degrees



Up to 45 degrees



The crossover work is pretty much done so for the winter i'll be doing nothing but listening music and maybe a little tweaking by ear. This was very enjoyable experience

 

[maty tinman]

KEF Q750

Q550 is so well built that i really don't know how they pull it of for that price. Woofer is similar to R300 only smaller cone. Large voice coils and large magnets, Passive radiators with double suspension to achieve better symmetry - geez

In white - they are stunning

YouTube

The KEF Q750

SoundStage! Hi-Fi | SoundStageHiFi.com - Recommended Reference Component: KEF Q750 Loudspeakers

SoundStage! Access | SoundStageAccess.com (GoodSound.com) - KEF Q750 Loudspeakers


[Polish review] KEF Q750

to English with Google: Google Translate

 

[Zvu]

Hi Maty,

I'd really like to see some measurements of q750. In the meantime, this is very good Polish site with decent measurements:

Zespoły głośnikowe | Testy w Audio.com.pl

cheers

 

[Zvu]

Here are some pics of R300's insides.

The only trace of what i presume they called constrained layer damping is this patch on the upper side of the loudspeaker, above the midrange chamber. Cabinet is upside down and i took these pics through the woofer hole.


https://i.postimg.cc/yd7vPcGt/DSC-0027.jpg


https://i.postimg.cc/SRB9ZpsR/DSC-0028.jpg


https://i.postimg.cc/vBSfVnwW/DSC-0029.jpg


Here are integrated conectors and port. Port looks good, but the -link- buttons are something i'm going to skip.


https://i.postimg.cc/rwC493Ly/DSC-0036.jpg


https://i.postimg.cc/mkzMNrTK/DSC-0034.jpg


https://i.postimg.cc/43s6kZ1h/DSC-0035.jpg

When you turn the link thingy, a metal part slides and touches small pcb and connects mid-high and woofer crossovers in parallel. I'll probably install L-pad's on that plate or i'll use some jumpers and link on - just to be sure.

Now here's the highlight of the loudspeaker, a little concentric driver. Maybe not the best pics, but one can easily spot some of the design features.


https://i.postimg.cc/t40dkFZk/DSC-0033.jpg


https://i.postimg.cc/VkjqV5X8/DSC-0030.jpg


https://i.postimg.cc/rFRC5fmz/DSC-0031.jpg


https://i.postimg.cc/76BMnc0J/DSC-0032.jpg

Oh, and grill looks quite nice too. It is made out of mdf with small Nd magnets at the corners. Cool stuff.


https://i.postimg.cc/C5qBn6Ng/DSC-0037.jpg


https://i.postimg.cc/RF8JFzwd/DSC-0038.jpg

I really like gloss Kef sign on the back. It is usually just black so it's nice that somebody thought of that.

Well that's it. I'm gonna put some bituminous coating on the outside of the midrange chamber and send the cabinets for painting.

 

[Zvu]

The tweeter level adjusted and some more measurements made. Measurements made are 0-80 degrees. Blip at 900-1200Hz that shows on virtually all of mine previous measurements vanished. Trim ring around the midrange has very tight tolerance so when i centered it better, that aberration disappeared. I'm not saying that i could notice it while playing music (or that anyone could for that matter) but i prefer it gone if i'm to decide.

The only difference from crossover in post 42 is that series resistor on the tweeter is not 0.5 but 2 ohms.

 

[maty tinman]

KEF Q750

Hi Maty,

I'd really like to see some measurements of q750. In the meantime, this is very good Polish site with decent measurements:

cheers

Now we have the frequency graph:

[German] Test Lautsprecher Surround - KEF Q750 Atmos-Set - sehr gut - Seite 1

 

[maty tinman]

Let's remember.

SoundStage! Access | SoundStageAccess.com (GoodSound.com) - KEF Q750 Loudspeakers by Hans Wetzel

Conclusion
KEF’s Q750 is a superb loudspeaker. It’s one of the most neutral transducers I’ve ever heard, and for the money offers staggeringly transparent sound. I fed it a steady diet of male and female singer-songwriters, and was always satisfied with the authenticity of what I heard. It’s not exactly a looker, but it’s well engineered, and sounds far more expensive than its price suggests. If I had $1500 to spend on speakers, this is what I’d buy. I’m not sure I can pay KEF’s Q750 a higher compliment.

1.2 kHz?

 

[maty tinman]

Just now I have send an e-mail to Hans Wetzel, with this link.

 

[Zvu]

Just now I have send an e-mail to Hans Wetzel, with this link.

He is using R700 if i'm not mistaken.

 

[maty tinman]

But he wrote at the Q750 review. "It’s one of the most neutral transducers I’ve ever heard"

Except for the valley at 1.2-1.3 kHz.

 

[maty tinman]

Hans has confirmed and will respond in the coming days in SoundStage! Access. I have told him that I think that small valley is intentional, looking for a frequency response in soft "V".

 

[maty tinman]

Maybe the answer will be here:

SoundStage! Access | SoundStageAccess.com (GoodSound.com) - Questions and Answers

Btw, SoundStage! Access | SoundStageAccess.com (GoodSound.com) - KEF: Q350, Q750, or R500?

Regarding your question about the R500, you might have noted that I compared the Q750 to the larger R700 in my review. If the R500 is priced similarly to the Q750 in Sweden, I would spring for the R500 every day of the week. While the R500 won’t be dramatically more resolving than your Q350, you should still hear more low-level detail through the R-series model. Furthermore, the R500 is a true three-way design, which should produce deeper and more robust bass. Finally, the R500 is, to my eyes, a far better-looking speaker than any Q model, with a more solid and inert cabinet. The cumulative improvements over your Q350 should be significant. . . . Hans Wetzel

 

[maty tinman]

Hans Wetzel answered:

KEF Q750: Not So Neutral?

SoundStage! Access | SoundStageAccess.com (GoodSound.com) - KEF Q750: Not So Neutral?

[ To Hans Wetzel,

Hi from Tarragona, Spain. You wrote [in your KEF Q750 review]: “KEF’s Q750 is a superb loudspeaker. It’s one of the most neutral transducers I’ve ever heard, and for the money offers staggeringly transparent sound” [emphasis added]. But [per the measurements from www.hifitest.de‘s review, here and here], I can see a valley at 1.2kHz. I have commented about this issue in GR Research, and in DIYAudio, too. I think it is intentional, [with KEF] looking for a soft “V” response.

Maty
Spain ]

The measurements you link to do, indeed, note a roughly -3dB dip around 1.2kHz. Since you seem to be measurement-oriented, it’s worth exploring what we’re looking at. Let’s focus on the frequency-response graph. Are these measurements taken in-room, or in an anechoic chamber? Are the three curves on-axis, 15 degrees off-axis, and 30 degrees off-axis, or something else? Was it measured at 1m, 2m, or some other distance? Without any offered methodology to accompany the graph, you’re extrapolating an awful lot from three curves. That is one very narrow snapshot that is certainly better than nothing, but doesn’t offer anywhere near a complete picture of how the Q750 might sound in your average room.

Take a look at some of our measurements on www.speakermeasurements.com, which we perform in an anechoic chamber at Canada’s National Research Council, where some of the early hi-fi pioneers did their acoustic research, including Dr. Floyd Toole (of Harman International), who quite literally wrote the book on modern loudspeaker design (see below). I’ll point you to the measurements of Revel’s Performa3 F206 loudspeaker. Numerous writers on our staff agree that the Revel (which is a division of the aforementioned Harman International) F206 is the most neutral loudspeaker at its $3500 USD price point, and its measurements are about as “textbook” as you can get for that kind of money, as evidenced by the “Listening Window,” which averages five measurements into one neat plot that is both commendably smooth and flat, with a 2-3dB tilt from left to right. There is nothing amiss between 1kHz-1.5kHz. Chart A, however, which includes on-axis, 15-degree off-axis, and 30-degree off-axis curves, shows a “valley” centered at around 1.2kHz–1.3kHz; surely not neutral!

Hi-fi measurements, like everything else in life, must be placed in context. If you were to only hear direct sound from the Revel, then a deviation like that “valley” would surely be problematic. But we don’t hear like that. What our ears hear is a combination of direct sound from the speaker drivers, along with a variety of reflections that arrive at our ears at slightly different times, which our mind interpolates into something recognizable. The takeaway is that on-axis and near-on-axis measurements like the ones you mentioned in your e-mail only paint part of the picture and have the potential to be misleading if taken in isolation. I’d encourage you to take a look at some of our other measurements, which includes several KEF models. I’ll note that the Q750 is a two-and-a-half-way design that uses passive radiators in lieu of a bass-reflex port (or two). These kind of fundamental design choices may well have contributed to idiosyncrasies in the Q750’s frequency response curve that wouldn’t appear in a two-way or three-way bass-reflex design.

We try to measure as many speakers as we can, but with writers all over North America, shipping large speakers often proves expensive and impractical, so it’s not always possible. Just so you know, I actually wanted the Q750 measured, but we couldn’t make it work logistically -- sorry about that.

To answer your question above in a terribly longwinded fashion, yes, I think KEF purposely designed the Q750 to have the “valley” around 1.2kHz in its on-axis and near-off-axis frequency response curves. I am confident, however, that KEF did not intend for that to be audible, in-room, at the listening position. I suspect that if we were to run our usual battery of measurements on the Q750, the “Listening Window” plot would bear that out, and also confirm my subjective listening impressions.

I recommend Dr. Floyd Toole’s book, Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms. I think you’ll find it highly educational. . . . Hans Wetzel

 

[Zvu]

Here are my last three quasi anechoic measurements - done indoors so not without flaws. There isn't dip that large between 1-2KHz in R300 concentric.

This is 0, 45 and 90 degrees frequency response with 2dB grid resolution.



Not too shabby with passive crossover.

 

[maty tinman]

KEF R3 test/review with Graphs

Better here too (too late to delete in the LS50 thread).

KEF R3 Review: Exemplary speakers that do almost everything right

 

[Zvu]

Not bad at all. If you take into consideration that company must handle certain tolerances in production and components values, i'd say even great.

 

[maty tinman]

Hi-Fi News: KEF R3 measurements

KEF R3 loudspeaker Lab Report | Hi-Fi News

Sensitivity (SPL/1m/2.83Vrms – Mean/IEC/Music): 86.1dB / 86.1dB / 86.1dB

Impedance modulus min/max (20Hz–20kHz): 3.1ohm @ 44Hz / 13.1ohm @ 2.4kHz

Impedance phase min/max (20Hz–20kHz): -42° @ 37Hz / 32° @ 1.3kHz

Pair matching/Response Error (200Hz–20kHz): ±0.7dB / ±2.0dB / ±2.1dB

LF/HF extension (–6dB ref 200Hz/10kHz): 40Hz / >40kHz / >40kHz

THD 100Hz/1kHz/10kHz (for 90dB SPL/1m): 0.5% / 0.2% / 0.1%

Dimensions (HWD) / Weight (Each): 421x200x312mm / 14kg

Price: £1300

 

[skif9]

Few pics of factory crossover and woofer. Few capacitors are wrapped in some sticky material. It looks like the stuff that Kef uses for CLD in LS50.

Could you please post the scheme of the factory crossover?