PURIFI finally did a fully purified passive speaker design! The SPK 16 prototype is here - with a PTT tweeter

[mocenigo]

Is phase plug /coherer really necessary? ・・・・

Yes it is. It is what guarantees the unbelievable dispersion up to 20khz. It is not only regular, but also extraordinarily wide. Wider than the examples you cited. Do not look at the colours but at what they mean. You get the -6db at 90° from the normal with the Purifi tweeter.

 

[boXem]

Acoustic Horn Design – The Easy Way (Ath4)

I tried it in the same WG as the T25A above. This kind of tweeter would need a different approach... Agreed, top octave very similar behaviour to what I've seen in my various simulations and actual measurements in one of augerpro's waveguides. I've been working on a theoretical mitigation...

www.diyaudio.com

Exploring Purifi Woofer Speaker Builds

I was fortunate to hear the SPK16 at the Time House gathering and hear Bruno briefly explain the research Purifi conducted. Stunning small speakers but even more amazing were the SPK16. Amazing like there was no speaker at all but an orchestra in the room even though I was not in the sweet...

www.diyaudio.com

Is phase plug /coherer really necessary? ・・・・

Did you read the paper?

 

[JohnnyNG]

I was at their Open House in Munich. Words cannot describe how spectacular the sound was.

Not even “spectacular”?

 

[Savi]

Do not look at the colours but at what they mean. You get the -6db at 90° from the normal with the Purifi tweeter.

Between 70° and 75° but not 90°. That is still very impressive. Mabat and fluid simulation in DIYaudio are also promising (around 60° to 65°) but need to be confirmed empirically (which have already been done with other simulations from mabat so I am confident)

 

[mocenigo]

Not even “spectacular”?

Yes, but how spectacular!

 

[mocenigo]

Between 70° and 75° but not 90°.

At exactly 20Khz it is about 80° if not slightly more, but we are splitting hair here!

That is still very impressive. Mabat and fluid simulation in DIYaudio are also promising (around 60° to 65°) but need to be confirmed empirically (which have already been done with other simulations from mabat so I am confident)

In fact I suggested to Claus and Bruno to try also with a more “elliptic” waveguide, to increase a bit more the horizontal dispersion and reduce the vertical one - this would make it fit better in normal rooms. They found the suggestion interesting.

 

[fluid]

Is phase plug /coherer really necessary? ・・・・

Depends if this wide and even enough

Normalised to 10 degrees off axis so not quite the same as Purifi’s conditions. Black line is the -6dB beam width. Coloured polar maps are not that easy to read values off directly.

It is a simulation not a measurement but I see no reason to think reality would be much different.

I haven’t tried to make this elliptic yet to see the result, but the conditions that make for wide even high frequency directivity run counter to the steeper vertical wall angle an elliptic profile will create.

 

[changer]

In fact I suggested to Claus and Bruno to try also with a more “elliptic” waveguide, to increase a bit more the horizontal dispersion and reduce the vertical one - this would make it fit better in normal rooms. They found the suggestion interesting.

Lars mentioned that he had for now opted for an axisymmetric device due to its simplicity, for the demonstrator, but would be looking into elliptical geometries in the future.

Those offer more freedom with baffle placement and hence sound power optimization, and can be used to tweak the tilt of the combined DI, when a horizontal constant and a vertical pseudo-exponential profile are combined.

Re VHF dispersion, the simulation results without a phase plug look very encouraging. The 130 degree horizontal pattern (65 degree) of the Jbl M2 is commonly describe to present a big image. This is reached already in the simulation results. Also, the phase plug that Purifi relies on for an even wider top octave creates a very strong loading of the top octave. This might lead to rising frequency response of the LW angles.

 

[fluid]

I tested a simple elliptic version of the above, the horizontal was made slightly worse and the vertical was a bit of a mess. Perhaps with more time and effort something better could be found, the goal seeking ability of COMSOL would certainly help speed that up.

 

[changer]

The other downside of the elliptical device is that in comparison with a rectangular, approximately 2-profile device, only a few of the horizontal angles actually establish the target dispersion. We still need to learn more, if the constant change of the profile in an elliptical device is as important as i. e. having more angles provide a desired horizontal dispersion, and if a constant change is at all required. Obviously, JBL went down the rectangular way, while Genelec and Neumann, just to name the most prominent producers, the elliptical.

 

[IamJF]

Don't forget "augerpro" - he provides fantastic designs, also elliptical: https://www.somasonus.net/waveguides

Open source Waveguides for CNC & 3D printing!

I've been working on a waveguide project where I would develop high performance waveguides for some popular tweeters, and than share the files for anyone to print or CNC as they are able. The discussion started here: 3D printed waveguides - Techtalk Speaker Building, Audio, Video Discussion...

www.diyaudio.com

 

[mocenigo]

Lars mentioned that he had for now opted for an axisymmetric device due to its simplicity, for the demonstrator, but would be looking into elliptical geometries in the future.

Those offer more freedom with baffle placement and hence sound power optimization, and can be used to tweak the tilt of the combined DI, when a horizontal constant and a vertical pseudo-exponential profile are combined.

Re VHF dispersion, the simulation results without a phase plug look very encouraging. The 130 degree horizontal pattern (65 degree) of the Jbl M2 is commonly describe to present a big image. This is reached already in the simulation results. Also, the phase plug that Purifi relies on for an even wider top octave creates a very strong loading of the top octave. This might lead to rising frequency response of the LW angles.

Well, you notice that I put the word elliptical in quotation marks. I meant both elliptical and 2 profile, actually, as alternatives, and mentioned both to them. In my hand-wavy report on my conversation I just used out to describe anything flatter than a disc, and a flattened disc is an ellipse. Of course I cannot expect people to read my mind if I do not write what exactly I am thinking, so my bad.

 

[Waxx]

Lars Risbo (One of the owners of Purifi) said on FB (diy loudspeaker pad group) that this is a prototype, and any release would be at least after Q4 of this year. He did not say if the speaker itself would be released, but the tweeter should be arround at the end of the year.

 

[Da cynics]

He commented

Exploring Purifi Woofer Speaker Builds

Here is an appetizer of the new tweeter with ultra wide controlled dispersion. in-box measurement at 1m (gated). Will demo next week at the High End Show in Munich. See our FB/LinkedIn for more details. Our web is also updated to a brand new version in the coming days. There will be a white...

www.diyaudio.com

 

[fluid]

The shape and dimensions of the dome and surround are critical to whether a particular dome tweeter will work well in different types of waveguides. This will also determine if any kind of wavefront modification is needed to reach a certain type of directivity. The height of the Bliesma T34A is part of what allows it to have super wide high frequency directivity in the right waveguide without any 'coherer' or similar device to spread the high frequencies. It is this same feature that causes it to perform worse in an elliptical or any other waveguide with a narrower wall angle.

Some tweeters like the SB26 for example work well in a wide range of waveguide profiles but if you want that top octave wide it will need some help.

Purifi have been quite open with information so when they release the tweeter there is a good chance other waveguides can be simulated to see the effect.

 

[Leif]

@IamJF @DanielT

Got me thinking about Ole Lund Christensen's cast iron JERN speakers:

Has anyone measured these? Any user impressions here? I auditioned a pair of Jern 11s in a shop’s listening room and they seemed to lack bass. They were gorgeous, the surface texture is lovely, and very heavy. I do wonder if my sound impressions were mistaken, my hearing can be thrown by my mood and state of mind, not to mention the room acoustics.

 

[alex-z]

The concept of inverting a dome tweeter to measure interior cabinet pressure is such an obvious thing in hindsight, I will certainly be using that little trick in future DIY work. Thanks Purifi.

 

[boXem]

The concept of inverting a dome tweeter to measure interior cabinet pressure is such an obvious thing in hindsight, I will certainly be using that little trick in future DIY work. Thanks Purifi.

I thanked them too and they told me to thank Thiele & Small

 

[Matias]

The concept of inverting a dome tweeter to measure interior cabinet pressure is such an obvious thing in hindsight, I will certainly be using that little trick in future DIY work. Thanks Purifi.

Sorry, I missed that, can you link where it was explained? Thanks.

 

[alex-z]

Sorry, I missed that, can you link where it was explained? Thanks.

SPK16 Reference Design

White Paper

purifi-audio.com

Under the section "Co-optimized Box Tuning and Crossover" they say "To measure the very high acoustic pressure inside the box we mount a low-cost dome tweeter with the dome facing inwards."