Kef R series dual concentric

[Draki]

Zvu: Yes, four (2+2)

q3: You are right, but this is one of the possible concepts. Could suit a particular room/setup, it is not a panacea. Nothing is. IMO, the bass region (read: room) has many possible scenarios and one can't know what is right...

 

[Zvu]

Sloooowly... Free time is sparse these days. MDF for first pair of test cabinets is here.



Few quick sims:



Since i intend to put crossover point between 200-400Hz and do it actively with at least 24dB/O slope, i'm not too worried about predicted port resonance at 750Hz. I will experiment with position of the ports on the back side and choose the cleanest outcome.

Steel mounting rings (2mm thick, 150mm diameter, 115mm hole diameter) are ordered. They should be here on tuesday. Front baffle will be double 19mm mdf so that it can acommodate any depth of routing needed for midrange mounting. I have some constant radius ports (a la JBL M2) printed, so i'll be testing these as well.

 

[bo_knows]

Sloooowly... Free time is sparse these days. MDF for first pair of test cabinets is here.

View attachment 129998

Few quick sims:

View attachment 129999View attachment 130000

Since i intend to put crossover point between 200-400Hz and do it actively with at least 24dB/O slope, i'm not too worried about predicted port resonance at 750Hz. I will experiment with position of the ports on the back side and choose the cleanest outcome.

Steel mounting rings (2mm thick, 150mm diameter, 115mm hole diameter) are ordered. It should be here tuesday. Front baffle will be double 19mm mdf so that it can acommodate any depth of routing needed for midrange mounting. I have some constant radius ports (a la JBL M2) printed, so i'll be testing these as well.

View attachment 130003

KEF reference 1 killer? Keep going, you are on the right track.

 

[Zvu]

Just a small detail of woofer cone.

 

[Nusse]

I wasn't aware of this thread until now
I did measure the midrange cone and the surround with an optical measurement equipment and had my brother print a flare. I think the flare is quite similar to the original that I have in my R3.

Will follow this thread closely as I also have an extra pair of the new R Uni-Q drivers.

 

[Zvu]

It started like this:



2mm steel, laser cut ring. Diameter is 150mm, hole diameter is 115mm. Suspension rubber is about 2.3mm thick so it makes flare near suspension sit on the hard rubber part glued to the midrange frame. Since it is not stainless but regular steel, it needed some coating to prevent rust and since i'm confident in my sexuality



Driver opening in speaker baffle will be as large as the diameter of midrange is. Ring is the medium between the front baffle and the driver chassis. You'll notice that the screw holes aren't lined up. That is not by mistake. If anyone noticed on previous pictures, screw holes on chassis do not line up with the spokes on the basket. Trying to get minimum diffraction, i intend to chamfer the back of the midrange baffle between spokes to allow midrange to breathe, but i will keep extra thickness where mounting screws go in to the MDF. Similar to THIS.



If you are asking yourself am i exaggerating i'd usually say -probably-. But i noticed that the aluminium frame in midrange has its own chamfer and if at KEF they cared enough to make it, it is probably wise to invest some thinking in to minimum shading of midrange cone. I intend to make the baffle chamfer continue from chamfer molded in frame. I don't know how visible frame chamfer is but here it is:



Screw heads would get in the way but Magnus (aka Nusse) predicted it in printed version so they align perfectly with small holes on the back of the flare.

 

[Zvu]

It still looks macho enough with flares.



There is still one "little" problem - how to mount the flare to the cabinet. It has to be removable, to not suffer from flare popping out and preferably without any visible screws.

I've been thinking to attach bolt heads on the back of the flare (by melting them into the flare or drill shallow holes and epoxying), then drill through the front baffle and use nuts from behind to attach them. As if that doesn't sound complicated enough, it would require that cabinet rear baffle and rear baffle from midrange chamber remain removable. I did plan to leave rear speaker baffle removable, but didn't plan that for midrange chamber, though i can do it.

If anyone has any fresh idea, do share.

 

[BrokenEnglishGuy]

It still looks macho enough with flares.

View attachment 132573View attachment 132574

There is still one "little" problem - how to mount the flare to the cabinet. It has to be removable, to not suffer from flare popping out and preferably without any visible screws.

I've been thinking to attach bolt heads on the back of the flare (by melting them into the flare or drill shallow holes and epoxying), then drill through the front baffle and use nuts from behind to attach them. As if that doesn't sound complicated enough, it would require that cabinet rear baffle and rear baffle from midrange chamber remain removable. I did plan to leave rear speaker baffle removable, but didn't plan that for midrange chamber, though i can do it.

If anyone has any fresh idea, do share.

looks nice the idea xD a metal shadow flare in orange gonna looks awesome in the r series black

 

[Zvu]

The biggest problem, imo, is to color match flare witgh copper cone.

I really like the looks of Reference 1 in black with copper flare.

 

[Zvu]

Internal struts are done. Cabinet has been coated with 3 layers of boat varnish inside and out to seal the mdf and prevent it from absorbing any air moisture. Then it was sanded with 120 grit paper and sprayed with some spray putty. If it sounds right, it will get thorough finish it deserves.

Flare will be attached by 4-6 pieces of nd magnets. I'll insert the magnets into the cabinet and into the flare (opposite poles of course) to make the connection stronger.



At this point it is not worth waiting for magnets to arrive. On the pics flare is just there to see how it will look. Some duct tape to temporarily attach the flare and prototype is ready for measurements and deriving simulation files.

 

[Ata]

Congrats, this is coming up nicely! A mighty contender for Reference 1s.

 

[Godataloss]

Very interesting build. following

 

[Zvu]

Thanks guys

@Ata If it doesn't sound at least a little bit better than Reference 1's, i'll consider that a failure

 

[Nusse]

Really nice!

I've been lazy, but had my brother milling an aluminium mold to try out the Prepreg carbon fibre stuff I bought almost a year ago...
First attempt.

 

[Zvu]

@Nusse This looks incredibly good

 

[Nusse]

Do "we" know if the current flare is as good as it gets, or could it be modified/improved? I guess it depends what the goal is...
But making it wider/deeper, baffle needs to be wider.

 

[Zvu]

We will know that as soon as i make 0-90 degrees horizontal measurements. That is probably going to happen this weekend.

I can measure coax with a larger flare/waveguide on a larger test baffle. It would eventually need a larger woofer - for looks if for no other reason.

 

[Nusse]

I'm sure I can have my brother mill whatever shape of flare or baffle, if you would like and if you think it's worth it.

 

[Zvu]

Let us wait and see what will measurements tell us. If it behaves well, maybe there is no need for a larger flare.

That being said, if it doesn't measure well (which i really doubt) i'd be willing to go up to 12" diameter flare so we can use FaitalPro 12PR320-8 and cross it around 500Hz to Kef. This would have to be DSP active because of difference in sensitivity, of course. It is always good having hi-eff bass for lower power needed and lower distortion.

 

[Zvu]

Here are some measurements.

Midrange 0-90 degrees in 10 deg increments


Tweeter 0-90 degrees in 10 deg incerements


On axis some diffraction products are visible. My guess is that it origins from tangerine phase plug. It is very mild though and tangerine waveguide enables it to have such a great off axis response above 10kHz. Here are the same tweeter measurements but without on axis measurement:


I must say that it behaves beautifully. No aberations and quite consistent response that should make designing a passive crossover between midrange and tweeter easy. Midrange also behaves like a dream from 200Hz up to 3.5kHz.

Impulse responses for midrange and tweeter


And waterfall of course. It is as revealing as home conditions allow.


Next step - basketball hall to lift the speakers 3 meters from the ground and make some high resolution measurements for crossover design