Kef R300 playground - measurements of raw drivers

[Zvu]

I did some measurements of Kef R300 raw drivers. Rain prevented making full set of measurements but i found quiet enough neighbourhood so yesterday at about 01:00am some sweeps were heard from the parking lot.


https://s15.postimg.cc/yu3mz4ldj/image.png (https://postimg.cc/image/yu3mz4ldj/)
https://s15.postimg.cc/5exyq4gu1/image.png


https://s15.postimg.cc/tioqef70n/image.png (https://postimg.cc/image/tioqef70n/)
https://s15.postimg.cc/ivux8zyvd/image.png


https://s15.postimg.cc/dkg0oakif/image.png (https://postimg.cc/image/dkg0oakif/)
https://s15.postimg.cc/8lsi9rgpl/image.png


This amount of quasi anechoic resolution makes it much easier to simulate the crossover between woofer and midrange.


https://s15.postimg.cc/yuvnt984n/image.png (https://postimg.cc/image/yuvnt984n/)
https://s15.postimg.cc/y5cvgw7l5/image.png


I've managed to get about 9ms of gate time. I'm quite satisfied with consistency so here are files for simulators.


https://www.dropbox.com/s/dzg8gzfclgh8h92/Kef%20R300%20sim%20files.zip?dl=0


Few words about it.


You'll find on axis and about 45deg off axis files in .zip folder. Only woofers are merged (between 100-200Hz). Mids and tweeters aren't because there's no need to. You have everything you need to derive Z axis offset. You'll find that frequency response of midrange+tweeter, that is needed to derive Z offset between them, drops bellow 300Hz. I am protecting the tweeter that way so, when deriving Z offset, look only how combined frequency response behaves over 300Hz in regard to reference. As far as X and Y offsets all you need to know is that woofer and midrange centers are 26cm apart. There are impedance files there. Just in case you don't like how i extracted my sim files i added HolmImpulse measurements .zip file that you can import into your HolmImpulse and set the gate to derive files as you see fit.


Here's Kef's crossover. I betcha you can do better than that if you try:


https://s15.postimg.cc/rueyys7on/300.png (https://postimg.cc/image/rueyys7on/)
https://s15.postimg.cc/43flgo7hn/300.png


Measurements are done in factory cabinets, gated, at 1.03 m distance mic at tweeter axis - gate is good to 100Hz. Holm-impulse, calibrated ECM8000, M-Audio Fast Track II USB interface, Dell Inspiron notebook.


Play and enjoy yourself (:

[roomcurve]

Excellent work, thank you very much for providing it freely! :cool:
:prost:

[Zvu]

Bitte

It's all about the compromise on axis vs off axis. Here's my quick and dirty take on it.

4423744238

Phase tracking is quite good but keeping the impedance above 3 ohms while maintaining linear frequency response and good phase tracking will be quite challenging.

[bee]

I agree, much better way to sweep the parking lot than those bloody americans with their rental Mustangs.... :D

In case the woofer is too loud, last resort might be to stuff the port and increase Rdc of the inductors in the low-pass until it works o.k. in that CB. May work if the woofer-TSP are so-so.
Yes, I know, nasty.... :o

[Zvu]

You're right on the money there. Factory coil on woofer is 2.2mH but Rdc is quite high. It is ferrite coil so maybe it is smart to change it, regardless if that Rdc suits us. I'm trying to make the crossover with as much components reused -to make it simple and less expensive- but series coil on woofer and midrange definitely should be of higher quality as should series capacitors. Those 10mH are unwinded from factory 22mH that was on woofer notch centered at 90Hz. I've kept that noch to linearize the bass but changed the values to obtain better result, in my opinion. We'll see where this ends. It'll be a journey.

[Zvu]

I forgot to upload pics of impedance and woofer TS.

Woofer impedance in cabinet:
https://s15.postimg.cc/kxq63s27b/image.png (https://postimg.cc/image/kxq63s27b/)


Midrange impedance in cabinet:
https://s15.postimg.cc/5p08q00t3/image.png (https://postimg.cc/image/5p08q00t3/)


Tweeter impedance:
https://s15.postimg.cc/jvfzl83yf/image.png (https://postimg.cc/image/jvfzl83yf/)


TS parameters for woofer:
https://s15.postimg.cc/mt8d1p9iv/image.png (https://postimg.cc/image/mt8d1p9iv/)

[EMP]

Thanks for sharing :prost:

[tschense]

yesterday at about 01:00am some sweeps were heard from the parking lot
You made my day:prost:
regards Jens

[Zvu]

@Jens

Ich freue mich :)

@Bee

Hier ist das original schaltbild für den tieftöner frequenzweiche:

44249

[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:


Midrange in phase:

https://s15.postimg.cc/qs36x005z/Webp.net-gifmaker_1.gif (https://postimg.cc/image/qs36x005z/)
https://s15.postimg.cc/6xh5avkyj/Webp.net-gifmaker_1.gif




Midrange out of phase:

https://s15.postimg.cc/n8h97755z/Webp.net-gifmaker.gif (https://postimg.cc/image/n8h97755z/)
https://s15.postimg.cc/mvpv10mwb/Webp.net-gifmaker.gif




Simplistic crossover:

https://s15.postimg.cc/iml4yn9af/image.png (https://postimg.cc/image/iml4yn9af/)
https://s15.postimg.cc/jovbh6s3v/image.png




"Exploded" view:

https://s15.postimg.cc/ltfoiaolj/image.png (https://postimg.cc/image/ltfoiaolj/)
https://s15.postimg.cc/xvb2cfxu3/image.png


I didn't measure both loudspeaker cabinets but i have just now checked for production consistency with indoor measurements. There is slight difference between the midrange drivers frequency response.


https://s15.postimg.cc/4yml6zmmf/srednjetonci.png (https://postimg.cc/image/4yml6zmmf/)
https://s15.postimg.cc/rake0dlqj/srednjetonci.png


Both loudspeakers now measure the same but it's always a good thing to check. In an interview, with John Atkinson, Jack Oclee-Brown explains - voice coil of their drivers isn't rigidly coupled with the cone. They are interconnected with a damping ring that is incompressible at lower frequencies but acts as a "shock absorber" for frequencies above 5KHz to minimize the breakup. I had my suspicions about damping system of that sort because that fine details are dependent on compressibility of that ring and on amount of glue applied. This lead to a slightly different crossover for midrange - on one loudspeaker series midrange coil is 1mH and on the other it is 0.9mH.

Anyhow, here's how the crossover will look like - few resistors missing but soon to be acquired and all electrolytic caps are going to be bypassed with 0.1uF mkc.


https://s15.postimg.cc/yfv5c6csn/DSC_0070.jpg (https://postimg.cc/image/yfv5c6csn/)
https://s15.postimg.cc/4ny2wzpzf/DSC_0070.jpg

viele grüße :)

[roomcurve]

Thanks for the update, so you have chosen now a tilted on axis frequency response? This is interesting as also this years forum contest winner with a KEF coaxial project (KEFIR https://www.diy-hifi-forum.eu/forum/showthread.php?17657-Projekt-KEFIR ) as well as KEF themselves in their newest models seem also to have chosen a slightly tilted 0° response http://international.kef.com/media/doc/r2018_whitepaper_en.pdf .

[Zvu]

Yogi did helluva job there. I really like the name and the looks of this years winner :) - It's obvious that it had to be white :D

Slightly tilted response, yes. Since there are diffraction products on axis (no shadow flare on 2011 R series version - which would be the one thing i'm jealous about what new R series have) i had to observe frequency response off-axis and 6dB smoothing on axis. That way i can see distribution of energy across the spectrum. It looks like this - thank god for VituixCAD and LspCAD:

45431 45432

I listen them with slight toe in - so their 0° axis cross in front of my head more or less. It flattens tweeter response and although it is very good tweeter, that diffraction on axis is perceivable so i had to make it quieter about dB or so. In larger rooms i guess you could get by without tweeter resistor.

The crossover topology in new R series is quite similar to Reference series. If you play with values a bit, you get individual responses quite similar to Kef Ref 1 measured here:

https://www.fidelity-magazin.de/2016/08/23/kef-reference-1-messungen/

Although R300 measured good with that topology, it didn't do it for me soundwise. I think it is because of midrange resonance (around 200Hz) being to high in level - but i cannot be certain. What i do know is that i like my crossover better even though it hits 2.6 ohm impedance at 250Hz.

[roomcurve]

Thank you again very much for your thorough and very interesting response!

[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 about 1.5-2dB hotter but final level is to be determined indoors by listening. So, without further ado...


On axis:

45966

Off axis 10 and 20 degrees

45965

Up to 45 degrees

45964




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 :prost:


viele grüße :)

[Zvu]

es lebt :)

0, 10, 20, 30, 60 und 90 grad


46120

[mtthsmyr]

Eine sehr lebhafte Abstimmung! :joke: ( : quite a lively voicing).

[Zvu]

:p

Es braucht jedoch etwas mehr feinabstimmung. Ich mag es nicht wie es im bereich von 7-12 KHz aussieht.

Sorry for my lousy German. I'm still learning - from GT :D Feel free to send me to the bench when i mess up badly :)

Viele Grüße

[mtthsmyr]

Kann ich verstehen. Wenn ich nach den Bildern in Post #14 gehe, wäre mir das in dem von dir genannten Bereich auch zuviel. Vermute ich.

VG, Matthias

[Zvu]

Es ist jetzt ziemlich kalt draußen (6 grad Celsius). Das wetter wird sich für das wochenende verbessern (20 grad Celsius) also erwarte ich es wieder mit verbesserter frequenzweiche zu messen.

Viele Grüße

[chro]

Servus,

schau mal ich verwende den Mittel/Hochton Zweig mit der grünen Hochton Abstimmung. Bin sehr zufrieden damit :prost:

http://www.audioexcite.com/?page_id=3807


Zum Tieftöner fahre ich aktiv. Und zu deinem deutsch. Das ist wahrscheinlich besser als mein englisch :D

46026

[Zvu]

Es sieht ziemlich idiosynkratisch aus, wie John Atkinson sagen würde. Aber ich denke es muss sein, wenn die Form der Funktion folgt :)

Hast du jeder akustische Messungen ? Wenn Sie wunsch, können Sie hier posten.

Viele Grüße,
Mladen

[Zvu]

Einer noch, mit besserer? frequenzweiche.

46439

Messungen im Haus, so etwas lausig. Es ist noch ein bisschen warm auf 8KHz. Ich möchte Kerbfilter vermeiden auf 8 KHz, wenn ich kann. Wir werden sehen.

Der einzige differenz in der Frequenzweiche ist 2 Ohm Serienwiderstand am Hochtöner, nicht 0,5 Ohm.

[chro]

Ja das ist wohl ziemlich Eigentümlich :D


abgespeicherte Messungen habe ich derzeit nur im Raum, am Hörplatz:built:
46083

[Jesse]

Zum Tieftöner fahre ich aktiv.

46026

Hallo,
sieht sehr edel aus. Diesen Koax find ich sehr spannend. Verätst du uns wo du das Chassis her hast?

[Zvu]

@Chro:

Es sieht super. Es ist überraschend, was heute mit der richtigen Software möglich ist.

Herzliche Glückwünsche zu einem gut ausgeführten Projekt :prost:

Viele Grüße,
Mladen

[Zvu]

Hier sind mehr Fotos von den Innenseiten von lautsprecher.

Das ist sogenannte "constrained layer" dämpfung by Kef. Überhaupt nicht viel.

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


Hier sind Anschlüsse und Bassport.

https://i.postimg.cc/dh3DsW1g/DSC-0036.jpg (https://postimg.cc/dh3DsW1g)
https://i.postimg.cc/rwC493Ly/DSC-0036.jpg

https://i.postimg.cc/SY4Jmk2G/DSC-0034.jpg (https://postimg.cc/SY4Jmk2G)
https://i.postimg.cc/mkzMNrTK/DSC-0034.jpg

https://i.postimg.cc/3kf4msVK/DSC-0035.jpg (https://postimg.cc/3kf4msVK)
https://i.postimg.cc/43s6kZ1h/DSC-0035.jpg


Hier ist das Highlight des Lautsprechers, ein kleiner konzentrischer Treiber. Vielleicht nicht die besten Bilder, aber man kann leicht einige der Designmerkmale erkennen.

https://i.postimg.cc/VdRbLrF0/DSC-0033.jpg (https://postimg.cc/VdRbLrF0)
https://i.postimg.cc/t40dkFZk/DSC-0033.jpg

https://i.postimg.cc/dhVZ7sWH/DSC-0030.jpg (https://postimg.cc/dhVZ7sWH)
https://i.postimg.cc/VkjqV5X8/DSC-0030.jpg

https://i.postimg.cc/FdLL9TPh/DSC-0032.jpg (https://postimg.cc/FdLL9TPh)
https://i.postimg.cc/76BMnc0J/DSC-0032.jpg

Oh, und der Grill sieht auch ganz nett. Es ist gemacht aus MDF mit kleinen Nd-Magneten an den Ecken. Cool :)

https://i.postimg.cc/7JqYp9ds/DSC-0037.jpg (https://postimg.cc/7JqYp9ds)
https://i.postimg.cc/C5qBn6Ng/DSC-0037.jpg

https://i.postimg.cc/ftcR2p2S/DSC-0038.jpg (https://postimg.cc/ftcR2p2S)
https://i.postimg.cc/RF8JFzwd/DSC-0038.jpg

Ich mag glänzendes Kef-Zeichen auf der Rückseite. Normalerweise ist es nur schwarz, also ist es schön dass jemand daran gedacht hat. Ich werde etwas bituminöse Beschichtung auf die Außenseite der Mitteltöner kammer auftragen und die gehäuse zum lackieren schicken.

Viele Grüße

[chro]

Hallo,
sieht sehr edel aus. Diesen Koax find ich sehr spannend. Verätst du uns wo du das Chassis her hast?

Servus Jesse,

ich hatte ja eigentlich meine Manger mit den PHL B4021, und war auch super zufrieden. Als ich bei Ebay mal etwas gestöbert habe, hatte jemand die Koaxe für 140€ inklusive Versand (Paarpreis) drin :D Da konnte ich nicht nein sagen. Und als ich die Koaxe getestet habe, gefielen sie mir auch noch besser (Sind halt nicht so Laserbeams, wie die Manger) :prost:

BG Timo

[Jesse]

Hallo Timo,
na Top, da muss man ja zuschlagen. :ok:

Dann noch viel Spaß damit.

[Zvu]

Es tut mir leid, aber ich muss diesmal auf Englisch schreiben. Es ist jetzt auf Deutsch zu kompliziert für mich.

It's been a while since i've addressed the sound of modified Kef R300.

When the initial impressions of sound settle, then comes that long lasting feeling you get when you get to know your loudspeakers very well. Kef did an amazing job with these drivers, well almost. Almost everything sounded the best ever but i will not write about qualities of this loudspeaker but more on the weak spots. R300 when modified has two of them. Low bass - it's there but not really. In my room it worked perfectly but when put in larger rooms 40sqm or more, it needs help - and i'm talking about hard walls, not wood or drywall - i'm guessing it would behave worse in that situation. Other one being low mids. Concentric at the top does such a good job that i wonder what could sound better than that. When Kef says -obsessed with high resolution- they really mean it. It's one of the finest midranges and tweeters i have ever heard, and i've heard quite a few loudspeakers. Woofer is crossed at about 450Hz to midrange, and there problems begin. I'll post a picture оf its construction first:


48381

It's made by attaching large aluminium plate to a paper cone that is connected to voice coil former. In the paper cone there are elliptical openings to let the pressure out. Something similar can be seen in typical car subwoofer units. When it comes to bass frequencies boy does it deliver. It is one of the most punchy bass drivers i've laid my eyes (ears???) on. It would be almost no compromise loudspeaker if midrange could be crossed to it at say 120-150Hz but pushing it to 400-500Hz has taken its toll. Since i made quasi-anechoic measurements with almost 11ms gate time, i get very good resolution from about 90-100Hz. I've made the flattest measuring loudspeaker (on and off axis) up to about 2KHz i've seen. But something was missing. i first thought that midrange was a bit quieter than it should be so i reduced the attenuation in 0.2dB increments to set its level by ear. That's wasn't it. Then, after some time i started to look at the crossover frequency between midrange and woofer. With few slight adjustments i moved it to 380Hz - it was better. Then i moved it to 310Hz, even better still. All the time i kept linearity and good phase tracking. The more i let the midrange work, the better the rendering of that thing missing was. Then i just played some music i know well and got really close to loudspeaker listening to midrange and woofer up and down. Every tone that wasn't pure bass frequency (say 80Hz and up) it played virtually the same. Every note sounded the same. They've made it work well and deep enough at low frequencies but they've damaged the transients of lower midrange on the way. I guess the price had to be payed somewhere and it was right there where it hurts the most. That couple hundreds hertz it should be playing it doesn't do well.

Knowing that, there were couple of options. To buy used Q300 and use its 6.5" woofer. I'd remove the tweeter and make a phase plug. But that's an investment of more or less 300-400 euros and leaves me with having to measure new trim rings dimensions and have them made out of plastic or aluminium, new crossover etc. Color of Q300 woofer looks really ugly when combined to concentric midrange in R300 so i gave up. Next thing would be trying to find a 4 ohm woofer that will work as well as factory one in about 15 liters of volume. That was cheaper option but i haven't found it.

Anyhow, i'd strongly recommend concentric driver from R series as it really sings but to use it with another woofer that will not absorb transients on the way. If you're listening electronic music, you'll never want for another loudspeaker. Couple of my friends does so i sold my R300's to one of them.

This was a very good experience. I've learned a lot and it showed me that Kef is a force to be reckoned with when concerning their concentric drivers.

Viele Grüße :)

[roomcurve]

Very interesting reading, thank you, also interesting that KEF kept the high crossover frequency of 400 Hz for their successor series:
http://nl.kef.com/media/doc/r2018_whitepaper_en.pdf

[mtthsmyr]

Hi Zvu,

Do you have off-axis measurements of your flat-to-2kHz-Voicing? I have found this measurement of the R300:

https://www.soundandvision.com/content/kef-r300-speaker-system-ht-labs-measures

I would expect the original KEF voicing to yield a straight declining power response and a similar behavior at 20..30° hor off axis. Which appears sensible to me. Also, the LS50 speakers that I have seen and heard demoed at audio shows were always placed parallel (not toed in) which seems to validate this point.
If my suspicion about the off-axis behavior is correct, that would also explain why you felt the midrange to be recessed because that hump is actually needed for a balanced response. Also the limited baffle-step-compensation.


... damaged the transients of lower midrange...
I had a similar experience in the flight speakers, but in that case it was not the woofers deficiancy but could be traced back to room interaction (floor bounce). Changing the crossover point had a significant impact on power response and room interaction. In my case, the effect was maximized around 380 Hz. Crossing over at 300 Hz made it disappear, as did crossing beyond 500 Hz. It still could be a property of the woofer, as you say, but I wouldn't rule out other influences. I find this frequency range very challending to deal with.

Viele Grüße, Matthias

P.S.: did you get the PM over on htguide?

[Zvu]

@Roomcurve:

They've seem to keep the woofer construction as well so the stuff i'm talking about could and should be test listened before purchase.

@Mtthsmyr:

I have simulated response but it matches measurements i made outside (disregarding tweeter response which for some reason turned out to be 2dB hotter on axis which may have been influence of temperature outside on the tweeter itself).

Here's my sim - high resolution on axis and 45 deg off axis:

4838348382

My opinion is that they've tailored the response to make impression on first listening session. There are measurements of R3 (equivalent of R300) that are pretty flat and are very similar with what i have done with my R300. The topology of the crossover given in their R series whitepaper is virtually the same as in R300 but with the right values they've made it measure flat. The hump in R300 comes from woofer, not midrange. Mid is pretty flat. Recessed midrange was felt in nearfield also - listening at 0.5m makes off axis behavior much less important. Nearfield revealed to me that the woofer is the problem.

Since i enjoyed R300 sound so much, if we disregard woofer, i've bought LS50 and it is soon to get the same treatment as R300 did. But it'll get one or two woofers covering frequencies <120Hz.

I did get the PM and i'm still pondering on where i am right now and where i want to be. Thanks for providing peronal perspective :)