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

It's also usually called a phase plug.

Having said that, Purifi is recessing the dome inside a surround wall that seems to diminish the apparent diameter of the dome? Maybe adding this part is why they are calling it a coherer rather than a phase plug?
 
Lars Risbo said:
the old infinity’s have only radial spokes and they are acoustically innocuous. it’s the rings that have a huge impact and it requires intense computer optimisation to get a useful result. This was not available back in the days of Infinity
Click to expand...
So radial spokes are only in place for protection?
 
Lars Risbo said:
the 104mm is launching now and the the 147WG version follows in Q2 (being tooled now)
Click to expand...
I guess that the 104 mm directivity is to be mated with 4" and 5.25" mid(woofer)s and the 147 mm with the 6.5"? Eventually the 8"?

In the SPK16 tech note, you explained that the wave-guide was optimized for both the tweeter and the box.
Will you provide an optimal box shape to be mated with the integrated wave-guide from both versions?
 
Looking at the recessed dome inside a surround wall - diminishing the diameter of the dome - together with the coherer, I am reminded of a Helmholtz resonator.

You have air loading and a ring acting as a nozzle to control the diffusion/direction of air.
 
boXem said:
I guess that the 104 mm directivity is to be mated with 4" and 5.25" mid(woofer)s and the 147 mm with the 6.5"? Eventually the 8"?

In the SPK16 tech note, you explained that the wave-guide was optimized for both the tweeter and the box.
Will you provide an optimal box shape to be mated with the integrated wave-guide from both versions?
Click to expand...
the coming 147mm WG is optimised for the Spk16 box. we may do a larger (eg 176mm) that matches the 8” in a slightly bigger box. the current 104mm version is optimised for infinite baffle, not for a particular box shape.
 
tomchris said:
Looking at the recessed dome inside a surround wall - diminishing the diameter of the dome - together with the coherer, I am reminded of a Helmholtz resonator.

You have air loading and a ring acting as a nozzle to control the diffusion/direction of air.
Click to expand...
it might be hard to see on the pictures but the ‘wall’ is just the outer coherer ring and there is air around it, ie not fused with the waveguide. It is very important not have a Helmholtz resonator. the surround is tiny and inverted so hard to see
 
Lars Risbo said:
it might be hard to see on the pictures but the ‘wall’ is just the outer coherer ring and there is air around it, ie not fused with the waveguide. It is very important not have a Helmholtz resonator. the surround is tiny and inverted so hard to see
Click to expand...
Then it seems that the first ring acts as a nozzle/wing and the second ring as a diffuser.
 
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The Purifi I'd expect will be more optimised. That said :

MB Quart
Screenshot_2025-02-01-09-02-21-79_e4424258c8b8649f6e67d283a50a2cbc.jpg


Vifa
Screenshot_2025-02-01-09-02-48-08_e4424258c8b8649f6e67d283a50a2cbc.jpg
 
The superficial me searches way to hide the screws in my mind,it's difficult the way they are.
Driven ones will find ways of course.

Integration with waveguides will be tricky as well if the coherer is part of the face plate.I mean seemingly integration,invisible.
 
Philips, e.g., has been doing it since approximately the dawn of time -- well, the early 1970s, at least. :)
1738370821305.jpeg


1738370844459.jpeg

1738370885210.jpeg

(various and sundry internet images)
 
On the one hand phase plugs are nothing very mysterious, on the other hand, implementation is king.

I've seen enough speakers with waveguides and yet pretty subpar directivity to know that just seeing the same general shape means nothing. The same applies here.
 
thewas said:
the non-linearity of the air becomes a big issue for typical small hifi domes at high SPLs, which is the reason for example Genelec uses compression drivers with horns on their 12xx main monitors.
Click to expand...
HF compression drivers are typically worse than domes with respect to air nonlinearity. The problem is twofold:
  1. Compression ratios are usually around 10:1, meaning the total area of the phase plug openings is 1/10th the effective diaphragm area. For a typical 1" exit driver with a 1.75" (44mm) voice coil, this means that the sound is "squeezed" through an area similar to that of a 0.55" (14mm) dome. SPL is thus extremely high near the phase plug entry.
  2. The area expansion is usually much slower, which further increases distortion (2nd harmonic dominant) at high frequencies. In this case, the mechanism is a mismatch in propagation speed between the high and low pressure regions of the sound wave. The pressure peaks "pile-up" against the troughs, gradually distorting the wave toward a sawtooth shape. Higher frequencies are distorted more than lower frequencies and the effect is cumulative with propagation distance—long, slow-expansion horns have higher distortion at HF than short horns for the same throat SPL.
Look at harmonic distortion measurements of some good loudspeakers with HF compression drivers (examples: Genelec S360, JBL 4367 and M2) and you'll notice rather high 2nd harmonic compared to good dome tweeters at the same SPL. Also note that the 2nd harmonic increases with increasing frequency due to #2.

Personally, I'm not so sure the above effects are of much audible consequence at normal domestic listening levels. My own speakers have compression drivers and the sound is top notch (in my opinion, of course).
 
bmc0 said:
HF compression drivers are typically worse than domes with respect to air nonlinearity. The problem is twofold:
  1. Compression ratios are usually around 10:1, meaning the total area of the phase plug openings is 1/10th the effective diaphragm area. For a typical 1" exit driver with a 1.75" (44mm) voice coil, this means that the sound is "squeezed" through an area similar to that of a 0.55" (14mm) dome. SPL is thus extremely high near the phase plug entry.
  2. The area expansion is usually much slower, which further increases distortion (2nd harmonic dominant) at high frequencies. In this case, the mechanism is a mismatch in propagation speed between the high and low pressure regions of the sound wave. The pressure peaks "pile-up" against the troughs, gradually distorting the wave toward a sawtooth shape. Higher frequencies are distorted more than lower frequencies and the effect is cumulative with propagation distance—long, slow-expansion horns have higher distortion at HF than short horns for the same throat SPL.
Look at harmonic distortion measurements of some good loudspeakers with HF compression drivers (examples: Genelec S360, JBL 4367 and M2) and you'll notice rather high 2nd harmonic compared to good dome tweeters at the same SPL. Also note that the 2nd harmonic increases with increasing frequency due to #2.

Personally, I'm not so sure the above effects are of much audible consequence at normal domestic listening levels. My own speakers have compression drivers and the sound is top notch (in my opinion, of course).
Click to expand...

Intermodulation distortion is also increased due to the same thermodynamic phenomena, I might add.
 
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