Exploring Purifi Woofer Speaker Builds

Jonone

Member
2013-02-02 10:22 am
It would be nice to see a power and DI plot for this speaker. One hopes that he took into account these parameters. I like some of his earlier designs... well balanced, smooth.

If I was going to offer a public domain open-source design, I would make available both the simulations and the final measured results.



You are on the right track, this is a concept that has some potential. I recently made some measurements of my TW29BNWG, and I estimate it could be used down to ~ 1.5k. I think to get the most out of the Purifi 8" driver, you should be looking at a 1.2 k crossover. I think the Satori waveguide is a bit on the small side to match up with a high end 8" driver. I would look into an 8" waveguide using either the Satori TW29BN or the Bliesma T34B. Or wait for @augerpro to finalize the waveguide designs for the TW29TXN-B tweeter. Overall, I think the Purifi 8" driver is just perfect for mating up with a larger 8" waveguide.

j.
Is there any preference between Bliesma T25B-sb tw29bn or the tw29txn-8?
 
Another one of Paul Carmody's designs without a single off axis measurement. Maybe good enough for 1990, but obsolete approach in 2023.

Not disagreeing, in fact, very much agree.

But then, with any non-waveguided tweeter and a 6.5" crossing at 2-3kHz, we can pretty much guess what the off axis looks like, no?
 
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But then, with any non-waveguided tweeter and a 6.5" crossing at 2-3kHz, we can pretty much guess what the off axis looks like, no?
More or less, yes. The vertical spacing will have an impact, and the slope of the filters (2nd, 3rd, or 4th order) will have an impact. But you are correct.

Many fine speakers were designed and built before the concept of calculating and using Directivity Index, Predicted In-Room Response, Power Response, and Early Reflections became widely known. A set of good Power & DI curves will make a speaker easier to position in a room, more flexible in where it is located. But if a person is willing to place the speakers optimally, and do some room treatment if needed, the Power & DI performance becomes less relevant.

Nonetheless, with the tools we have today, speaker designers who offer their designs to the public should make the effort to manage the Power & DI performance of the design.

j.
 
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Directivity Index has been my issue with the Purifi drivers from the start. All of this excellent power response, impedance and distortion are great. Why are they advertising an 8" should be used up to 5khz? It makes no sense to me. I don't care if a circuit can correct the breakup modes, there won't be any reflections that high!
 
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Hi I’m new to diy and looking into some ideas
I currently have a pair of active 2 ways using a sb acoustics 6” mid and tw29 tweeter

Was thinking of diying something active for myself and the Purifi amps and drivers look great

Has anyone got a design or idea for a Purifi 8” 2way with something like the sb tw29bnwg tweeter ?

It is a very very promising combination. There are a few areas of concerns and compromises to be aware of.

You will need to cross the 2 at 1.2-1.5kHz. It is a compromise as the TW29BNWG distortion starts to rise pretty quickly below 1.6kHz or so. And on the other end, the PTT8 gets directional after 1kHz. Even then, you will find the PTT8 beats the TW29BNWG in distortion at the crossover point. The PTT8 is that good.

Your bass alignment will need some thoughts. Ported PTT8 works. A small-ish box around 30L will get down to 33Hz or so. You will have a very long port for that though, more than 1 foot in length even with 3". Purifi demo box has some trickery to minimize the issue that arises with such long ports.

As for passive radiator, which is the popular solution for the PTT6.5, I don't recall seeing anyone tried it with the PTT8 yet.

As the 3rd option, if you choose to do closed box, it will cut off around 50-55Hz. Perfect to transition to sub-woofer in a non-directional crossover frequency.

I have personally tried very close to that combination. TW29BNWG + Dual PTT8 ported. Dual coz I wanted to make sure it will have enough omph plus it cuts the port length in half. There are other issues to deal wish such a center-to-center distance between the TW29BNWG and the 2 PTT8. But honestly it sounds pretty good but obviously not technically perfect.

Both TW29BNWG and PTT8 have fairly flat response, so there won't be much correction needed so designing the crossover passive or active will be a breeze.
 
Note that the usual 2pi/IB directivity/off axis plots are great if you do inwall but can be misleading if the driver is in a box and measured in 4pi.

The box is causing a transition from omni 4pi in the bass to more directional approaching the 2pi data sheet response at HF. This transition is benefiting the tweeter a lot so that its DI is kept up lower down in frequency than what we would think from looking at the 2pi data sheet curves. The baffle dimensions can be used to optimise this. It has been very interesting to explore comsol simulations of drivers in a box in 4pi space.

For me it looks like there is a current trend to drive the xover lower than it needs to be. This causes more distortion from the tweeter and more diffraction ripple (tweeter being a smaller source with less spatial averaging).

cheers

Lars
 
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Directivity Index has been my issue with the Purifi drivers from the start. All of this excellent power response, impedance and distortion are great. Why are they advertising an 8" should be used up to 5khz? It makes no sense to me. I don't care if a circuit can correct the breakup modes, there won't be any reflections that high!
it is desirable to have clean response an octave or even two octaves above the XO frequency - depending on how sharp filters are used. The PTT8 can be crossed at say 1.5k and it has extremely low distortion and IMD well above.
 
The midrange is 91db sensitive. It matches a pair of their woofers pretty well, and can be crossed up to 2khz for a decent on-axis. I still wish it was in their 5" frame, but there's a lot of good justification for it.
I meant how does the PTT8 sound in the 300 to 1300Hz range (approx) vs the PTT6.5 in the same range? My tweeter reaches to 1200Hz with low distortion and approx 80° dispersion so wondering if I would loose midrange quality if I crossed to a PTT8 instead of a 6.5.
 
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I take it you’ve seen @Yevgeniy’s review ?

https://www.diyaudio.com/community/threads/some-speaker-driver-measurements.317632/post-7237652


You can compare and contrast using the comparison feature at his website (registered user only) or open 2 tabs to compare and contrast.

Useful graph here-
91E64903-568E-4B12-9656-33DBDAB45722.png


Depending on your cabinet design, in-cabinet dispersion and tweeter’s in-cabinet dispersion a crossover from 1000-1800Hz looks like a reasonable start to play with; and depending on phase alignment at crossover region or other factors it might move up or down.
 
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