Exploring Purifi Woofer Speaker Builds

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#2,101
jmpsmash said:
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.
Click to expand...
People have mention the bliesma beryllium tweeters in a 8” waveguide
Do these have better distortion below 1.6khz?

Anyone have a view vs the sb 29bnwg?
 
#2,102
jmpsmash said:
Has anyone tried the PTT6.5M midrange? I am building a 3 way and deciding between using the PTT6.5X that I already have as midrange, or should I get a PTT6.5M at extra cost. SPL wise, it is borderline. Depending on the passive crossover design it doesn't have a lot of SPL headroom matching with PTT8 woofer.
Click to expand...
I have 4 x PTT6.5X that I wanted to use as midwoofers. But since I want to have closed boxes to avoid phase issues with my subwoofers, they seem to not like closed boxes. Some say they should only need 5-6 liters to work in a closed box - but then all the distortion advantage also goes out the window becasue of the much higher internal air pressure. So I looked into using them as midrange - maybe as MTM around a 6" waveguide, either with the SB26ADC I already have or maybe upgrade to Bliesma T25B to better match sensitivity and maybe sound quality.
MTM constructions can be tricky though. So that's why I looked at the M-version. But it breaks up severely at 3kHz. And I can't really see the idea of having a passive network between my active system and the driver, to try and dampen the breakup, when other drivers can push the breakup to 5-7kHz - even the alu-version does that easily. And IMD does not seem to be any issue when using it as pure midrange.

I have only two saying anything about the Purifi M-version - that I could find. One said that there was nothing else to say, then that it was clean, low distortion and easy to work with. The other said that it was boring, closed and missing dynamics - he loved the PTT8 though.

So little data to run on - other than raw data. And that's the tricky part, since we as DIY'ers might hope that we can squeeze something better out of it, than others - or at least something better than other drivers.

To really use the claimed strength of the Purifi M-version. I thought that maybe if I used the linear stroke of 3mm to push it to around 150Hz. Then I could imitate the design of the Snell tybe B minor - add a 12-15" woofer on the side to add some true punch. And this woofer would not need a high pass, making it easy to mate with multi-subs. Keeping the speaker narrow, seems to me, as a good way to make it "disappear" acoustically and also make it more elegant.

But I'm in doubt, whether I actually need maybe 2 x 8" minimum, from around 4-500Hz and down, to gain that punch-effect, that makes a speaker sound dynamic and powerful. Only having one 6,5" down to 150Hz seems like it would struggle. Not because it would distort.... but simply because it has too little surface area to make it sound realistic.

Skærmbillede fra 2023-02-04 21-31-41.png
 
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#2,103
I wonder if you’re getting a bit of analysis paralysis.

If you already have the drivers; use them to their strengths.

The M series has higher sensitivity. But your system sensitivity is typically determined by your woofers anyway; at these frequencies they radiate in full space. So if you didn’t already have the PTT6.5X; and had to choose between X, W and M, looking at your woofer system’s sensitivity is a good idea.

If you already have your 6.5X, you don’t need to squeeze it into 5-6L. The biggest cabinet you are practically put up with is better. 10-12 litres is the sweet spot.

eg. Left: woofer sensitivity 92-93dB/2.83V; choose PTT6.5M-04
Right: woofer sensitivity 90dB/2.83V (60Hz to 200Hz); no need to choose M-04; choose something with more excursion eg. 5-6mm x-max.
Allows for a convertible system (ie. may be used without subwoofers, or with subwoofers system; in this case double dual opposed (2 woofers on one side (visible @ lower right), 2 woofers on the other side (not visible))

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#2,104
digitalthor said:
I have 4 x PTT6.5X that I wanted to use as midwoofers. But since I want to have closed boxes to avoid phase issues with my subwoofers, they seem to not like closed boxes. Some say they should only need 5-6 liters to work in a closed box - but then all the distortion advantage also goes out the window becasue of the much higher internal air pressure. So I looked into using them as midrange - maybe as MTM around a 6" waveguide, either with the SB26ADC I already have or maybe upgrade to Bliesma T25B to better match sensitivity and maybe sound quality.
MTM constructions can be tricky though. So that's why I looked at the M-version. But it breaks up severely at 3kHz. And I can't really see the idea of having a passive network between my active system and the driver, to try and dampen the breakup, when other drivers can push the breakup to 5-7kHz - even the alu-version does that easily. And IMD does not seem to be any issue when using it as pure midrange.

I have only two saying anything about the Purifi M-version - that I could find. One said that there was nothing else to say, then that it was clean, low distortion and easy to work with. The other said that it was boring, closed and missing dynamics - he loved the PTT8 though.

So little data to run on - other than raw data. And that's the tricky part, since we as DIY'ers might hope that we can squeeze something better out of it, than others - or at least something better than other drivers.

To really use the claimed strength of the Purifi M-version. I thought that maybe if I used the linear stroke of 3mm to push it to around 150Hz. Then I could imitate the design of the Snell tybe B minor - add a 12-15" woofer on the side to add some true punch. And this woofer would not need a high pass, making it easy to mate with multi-subs. Keeping the speaker narrow, seems to me, as a good way to make it "disappear" acoustically and also make it more elegant.

But I'm in doubt, whether I actually need maybe 2 x 8" minimum, from around 4-500Hz and down, to gain that punch-effect, that makes a speaker sound dynamic and powerful. Only having one 6,5" down to 150Hz seems like it would struggle. Not because it would distort.... but simply because it has too little surface area to make it sound realistic.
Click to expand...

Very interesting info!!

I played around with some of the ideas. I have PTT6.5X in a 7.5L closed box. The distortion is not bad. Relatively, looking at dBr It hugs around -60dB until starting to rise below 200Hz. Purely looking at SPL it follows the official distortion profile fairly closely, maybe 5dB higher sub-100Hz. Originally I tried something similar, which is to cross to a 4 sub arrays tuned with MSO. I tried 80Hz which is the lowest it will go but, despite all theoretical claims, I still find there is still directionality at 80Hz. Low frequency sounds more like home theater sub rather than stereo music. I believe it will need to go down to 50-60Hz which PTT6.5X in a sealed box won't go.

I also tried MTM with different tweeters (including TW29BNWG) and PTT6.5X in individual 7.5L boxes. I haven't been able to tuned it to sound as good as a single PTT6.5X. Lack of skills probably and it won't gain much other than SPL at lower frequencies, so I gave up on that idea.

Now PTT8 came along and the bass extension problem solved. Dual PTT8 goes low enough that I don't have any urgency to add a sub. I will still do it in the future to balance out some room modes but at the moment, I am content. I am crossing at ~350Hz which matches baffle step. And yes, there is comparison with PTT6.5. I have bottomed out a single PTT6.5 sealed box, but not even close with Dual PTT8 ported.

And that's why I am asking about PTT6.5M. I have a relative large room and Dual PTT8 (4R in series, so around 90dB@1m) energizes it well. But it calls for a 3 way with a mid. I tried Dual PTT8 + TW29BNWG, it was actually not bad. But adding a PTT6.5X in the middle makes it sounds better. But matching with a pair of 90dB woofer PTT6.5X is struggling a bit in terms of SPL. It works but I have no series resistance on the passive mid-crossover. So I am wondering if PTT6.5M will give more leverage on the crossover design.

I still need to do some more accurate measurement for the PTT8 to really say if it works. Unfortunately it has been raining crazy in California (and esp on days when I have free time) and I haven't been able to go outside to get some accurate measurement.
 
#2,108
That happened to me once... a steel tool (screw driver) got too close to the cone without a firm grip... the magnet pulled the tool through the diaphragm. Fortunately for me it was a $45 driver, not a highend driver like purifi.

I'm curious as to what happened to mainframe...

j.
 
#2,109
Always turn amps off after measurements, always turn amps off after measurements, always turn amps off after measurements

Damn you purifi extreme excursion! /s

So I was taking a nearfield measurement and had the mic about 10mm from the cone. The measurement went smoooothly. Heres where I shouldve A. turned the amps off, or B. removed the mic. Right after the measurement I went to open VCAD to do the baffle step response to load onto the measurement, but no!, the VCAD logo is right next to the Firefox (web browser) logo in the stupid windows 11 Dock. I accidentally click firefox, it fires open so fast, goes straight to the last webpage I was on which happened to be youtube and proceeds to immediately play the music video I was watching the previous day. As windows volume was at full and I was using volume control in REW for the measurements, the kick drum immediately proceeds to send the purifi into the mic with such force the mic stand fell over. If you look close, you can see the mics imprint in the dust cap 😢

RIP purifi cone. I have some paper cone versions to fit in place, to listen to while I sob.

EDIT - and I'm not a mug, I always switch my amps on, measure, switch them off. I've been doing it for years. Today was a brain fart of expensive proportion. Also excuse the sanding dust on the cone. Rags were thrown.
 
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#2,111
That sucks! RIP. It's still usable. Maybe you can use it do some experiments.

I was doing measurements and both tweeters with 22uF protection on were connected. I had my laptop on my lap and stood up, the USB connector got nudged and that resulted in a spike in the DAC output. Blew BOTH Bliesma T25B6. 😢 I was depressed for days.
 
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#2,116
tktran303 I'll buy you a beer. I feel slightly better now with this collective sorrow. Perhaps a trade, 2x (good) paper woofers for 1x aluminium, anyone? one can dream. I shoulve stopped DIYing at dayton audio.

All good "not what to do" content for the exploring purifi woofer build thread.

Keep up the good work everyone 👍
 
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#2,119
Is the dust cap just dented or is that a hole in it?

Removing metal dust caps is relatively straightforward. Just an application of gentle heat eg. Hairdryer (or butane powered heat blower) and gentle pry with a spudger (or scalpel) All hail @5th element

6739045B-5C96-43A0-8279-999695563B64.jpeg

9D0E1B9B-4D70-41E3-925B-026361F78D05.jpeg


http://5een.co.uk/SB17Coax.htm

…Then when you go to do your next order from Purifi, ask for a replacement dustcap to travel in the post, then reattach…
 
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