Erin’s Audio Corner web site and YouTube channel are the work of Erin who’s user ID on diyAudio is bikinpunk. On this thread page 62 post #618 Erin links to his YouTube video LIVE! with PURIFI Co-Founder Lars Risbo! As an admitted Purifi fanboy (I’m 65 years old, should that be fan-grandfather?) I believe I was the fourth person to watch Erin’s interview with Lars Risbo once he posted it to ‘Tube. I was 110% geeked out watching Lars show all the previously hidden parts in the Purifi motor assembly. When he revealed for the first time publically the Neo cylinder in the pole piece while explaining how it addresses Force Factor Modulation let’s just say at that point Erin’s video exceeded my expectations by three orders of magnitude. I have now watched the interview twice end to end and reviewed sections within a third time. For reference to the good parts and for those who do not care to spend 2+ hours on the entire interview below is a table of contents with time stamp links direct to major topics. Format is description followed by hyperlink to that start point in the video. Below the TOC I add some personal comments.
LIVE! with PURIFI Co-Founder Lars Risbo! Video Table of Contents
Video interview starts with Lars Risbo introduction, education and professional history.
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
8:51 – Question “How does a transducer work..?”
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
19:36 – Lars discusses why speakers are not ideal.
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
~24 minutes – Discussion of pole piece iron attraction square of current effect, rediscovered from 1949 research, yields understanding of Force Factor Modulation.
27:00 – Reveals publically for the first time Neo magnet in magnetic circuit to address Force Factor Modulation.
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
~29 minutes – “Iron hat” element finishes linearizing the magnetic circuit.
30:40 Erin asks what are the audible effects of the BL linearization elements in the Purifi magnetic circuit?
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
Answer summary reduction of IMD in the midrange. Erin follows up with question about Doppler distortion.
37:00 Discussion turns to the “big surprise” of the hysteresis distortion of iron “the grey dull background”.
https://youtu.be/o90AYyceaMI?t=2220
39:55 Shows the copper shorting rings used in PTT6.5W and discuss their functions.
https://youtu.be/o90AYyceaMI?t=2395
44:25 Begin discussion of cone, surrounds, and other ‘soft parts’ optimizations.
https://youtu.be/o90AYyceaMI?t=2664
46:27 Erin asks question beginning discussion of Purifi’s very unique surround. Lars begins answer with Christmas disappointment anecdote about how after making major improvements in magnetic circuit and motor hoped for distortion reduction ‘barely moved’. This led to investigations into distortion contribution by the surround flying under the radar. Again this led to rediscovery and use of research industry previously ignored.
https://youtu.be/o90AYyceaMI?t=2787
57:08 Venting of the motor assembly discussion.
https://youtu.be/o90AYyceaMI?t=3428
1 hr 1 min - Spider and slightly progressive suspension, priority of IMD reduction vs. THD.
https://youtu.be/o90AYyceaMI?t=3694
1 hr 5 min – Purifi’s custom lab test rig discussion, first demo suffers Murphy’s Law of demos.
https://youtu.be/o90AYyceaMI?t=3931
1 hr 12 mins – Taking question break while tech glitches are sorted. 1 hr 16 min tweeters can be helped, Purifi tweeters are further into the future.
https://youtu.be/o90AYyceaMI?t=4347
1 hr 20 min - Introduction of founding partner Carsten Tinggaard, Co-Owner (PURIFI Transducer Technology) former CTO of Peerless Vifa Scan-Speak when the brands were all part of Tymphany.
https://youtu.be/o90AYyceaMI?t=4798
1 hr 24 min – Demo of Purifi’s in house developed measurement system retry & success (loud test tone at 1h26m38s) after tests run results graphs are discussed.
https://youtu.be/o90AYyceaMI?t=5088
1 hr 39 min – Lars’ son asks an insightful question.
https://youtu.be/o90AYyceaMI?t=5966
1 hr 43 min – Erin asks about drive unit break in.
https://youtu.be/o90AYyceaMI?t=6202
1 hr 51 min – New Purifi amp modules coming? Wrap-up, thanks, and goodbyes.
https://youtu.be/o90AYyceaMI?t=6662
Norman Tracy’s review, comments, and praise.
The introduction is nice, Lars Risbo is admirably humble for someone whose story includes an implementation of class-D amplification that after HiFi market success Texas Instruments deemed worthy to buy the company and incorporate into millions of ICs. Interesting career arc how that led to working in cell phone amps, then phone/tablet speakers, and finally back to HiFi speakers again. The 10 to 11 minutes on “How does a transducer work” is for me the slowest of the interview, albeit never a waste to review first principles. Starting at nineteen minutes with Lars lecture on why speaker drivers are not ideal if you are interested in engineering high-end speaker drivers the next hour of material is fantastic. I love how the Force Factor Modulation due to iron attraction via square of current effect was actually documented in 1949 research by Bell Labs PHDs uncovered and used again by Purifi. This tells me the Purifi teams’ previous successes has afforded them the luxury to spend years in simulations, bench work, and digging through a century of research on the subject. I was a very happy HiFi nerd watching Risbo reveal for the first time publically the neo magnet slug in pole piece, pole ends ‘hats’, and the already known copper shorting cylinders solutions for the-problems-with-iron.
Forty six minutes in and Erin starts the discussion of Purifi’s very unique surround. I already knew Purifi considers their surround a key differentiator of the products. Risbo’s explanation starting with the Christmas disappointment anecdote put this innovation into perspective and furthered my understanding of its place in the driver design.
For me one of the most telling moments of the 2 hours is a bit of a subtle point arising during the description of Purifi’s in house designed measurement system here https://youtu.be/o90AYyceaMI?t=5652. The upper right corner test results plot deconstructs from the driver model and measurements the contribution of the individual parts of the driver to its performance, so very impressive. This speaks to a design capability as far away from guess-cut-try-repeat as one can get.
I will finish with a big thanks to Erin who once again proves it never hurts to ask when he approached Lars Risbo asking to interview him. And equally big thanks to Lars Risbo and Carsten Tinggaard for their time and being so open with the details of why each and every time I listen to my PTT6.5Ws and PTT6.5PRs the performance is thrilling.
LIVE! with PURIFI Co-Founder Lars Risbo! Video Table of Contents
Video interview starts with Lars Risbo introduction, education and professional history.
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
8:51 – Question “How does a transducer work..?”
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
19:36 – Lars discusses why speakers are not ideal.
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
~24 minutes – Discussion of pole piece iron attraction square of current effect, rediscovered from 1949 research, yields understanding of Force Factor Modulation.
27:00 – Reveals publically for the first time Neo magnet in magnetic circuit to address Force Factor Modulation.
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
~29 minutes – “Iron hat” element finishes linearizing the magnetic circuit.
30:40 Erin asks what are the audible effects of the BL linearization elements in the Purifi magnetic circuit?
LIVE! with PURIFI Co-Founder Lars Risbo! - YouTube
Answer summary reduction of IMD in the midrange. Erin follows up with question about Doppler distortion.
37:00 Discussion turns to the “big surprise” of the hysteresis distortion of iron “the grey dull background”.
https://youtu.be/o90AYyceaMI?t=2220
39:55 Shows the copper shorting rings used in PTT6.5W and discuss their functions.
https://youtu.be/o90AYyceaMI?t=2395
44:25 Begin discussion of cone, surrounds, and other ‘soft parts’ optimizations.
https://youtu.be/o90AYyceaMI?t=2664
46:27 Erin asks question beginning discussion of Purifi’s very unique surround. Lars begins answer with Christmas disappointment anecdote about how after making major improvements in magnetic circuit and motor hoped for distortion reduction ‘barely moved’. This led to investigations into distortion contribution by the surround flying under the radar. Again this led to rediscovery and use of research industry previously ignored.
https://youtu.be/o90AYyceaMI?t=2787
57:08 Venting of the motor assembly discussion.
https://youtu.be/o90AYyceaMI?t=3428
1 hr 1 min - Spider and slightly progressive suspension, priority of IMD reduction vs. THD.
https://youtu.be/o90AYyceaMI?t=3694
1 hr 5 min – Purifi’s custom lab test rig discussion, first demo suffers Murphy’s Law of demos.
https://youtu.be/o90AYyceaMI?t=3931
1 hr 12 mins – Taking question break while tech glitches are sorted. 1 hr 16 min tweeters can be helped, Purifi tweeters are further into the future.
https://youtu.be/o90AYyceaMI?t=4347
1 hr 20 min - Introduction of founding partner Carsten Tinggaard, Co-Owner (PURIFI Transducer Technology) former CTO of Peerless Vifa Scan-Speak when the brands were all part of Tymphany.
https://youtu.be/o90AYyceaMI?t=4798
1 hr 24 min – Demo of Purifi’s in house developed measurement system retry & success (loud test tone at 1h26m38s) after tests run results graphs are discussed.
https://youtu.be/o90AYyceaMI?t=5088
1 hr 39 min – Lars’ son asks an insightful question.
https://youtu.be/o90AYyceaMI?t=5966
1 hr 43 min – Erin asks about drive unit break in.
https://youtu.be/o90AYyceaMI?t=6202
1 hr 51 min – New Purifi amp modules coming? Wrap-up, thanks, and goodbyes.
https://youtu.be/o90AYyceaMI?t=6662
Norman Tracy’s review, comments, and praise.
The introduction is nice, Lars Risbo is admirably humble for someone whose story includes an implementation of class-D amplification that after HiFi market success Texas Instruments deemed worthy to buy the company and incorporate into millions of ICs. Interesting career arc how that led to working in cell phone amps, then phone/tablet speakers, and finally back to HiFi speakers again. The 10 to 11 minutes on “How does a transducer work” is for me the slowest of the interview, albeit never a waste to review first principles. Starting at nineteen minutes with Lars lecture on why speaker drivers are not ideal if you are interested in engineering high-end speaker drivers the next hour of material is fantastic. I love how the Force Factor Modulation due to iron attraction via square of current effect was actually documented in 1949 research by Bell Labs PHDs uncovered and used again by Purifi. This tells me the Purifi teams’ previous successes has afforded them the luxury to spend years in simulations, bench work, and digging through a century of research on the subject. I was a very happy HiFi nerd watching Risbo reveal for the first time publically the neo magnet slug in pole piece, pole ends ‘hats’, and the already known copper shorting cylinders solutions for the-problems-with-iron.
Forty six minutes in and Erin starts the discussion of Purifi’s very unique surround. I already knew Purifi considers their surround a key differentiator of the products. Risbo’s explanation starting with the Christmas disappointment anecdote put this innovation into perspective and furthered my understanding of its place in the driver design.
For me one of the most telling moments of the 2 hours is a bit of a subtle point arising during the description of Purifi’s in house designed measurement system here https://youtu.be/o90AYyceaMI?t=5652. The upper right corner test results plot deconstructs from the driver model and measurements the contribution of the individual parts of the driver to its performance, so very impressive. This speaks to a design capability as far away from guess-cut-try-repeat as one can get.
I will finish with a big thanks to Erin who once again proves it never hurts to ask when he approached Lars Risbo asking to interview him. And equally big thanks to Lars Risbo and Carsten Tinggaard for their time and being so open with the details of why each and every time I listen to my PTT6.5Ws and PTT6.5PRs the performance is thrilling.
^ Thank you for taking the time to create the chapter marks. I wanted to do that but just don't have the time with everything else going on. I added those to the video and gave you credit. 
My understanding of the itty bitty details is miniscule at best. But, those details are where (as you see) the big revelations are made. I have listened to this interview a couple times. Just impressive the amount of knowledge and engineering coming from the PURIFI team, as a whole. I cannot thank Lars enough for coming on and explaining and then giving us even more detail than I had hoped to have. The audio community needs more people like him: brilliant, humble and happy to teach (and being able to do so).
My understanding of the itty bitty details is miniscule at best. But, those details are where (as you see) the big revelations are made. I have listened to this interview a couple times. Just impressive the amount of knowledge and engineering coming from the PURIFI team, as a whole. I cannot thank Lars enough for coming on and explaining and then giving us even more detail than I had hoped to have. The audio community needs more people like him: brilliant, humble and happy to teach (and being able to do so).
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Hehe Oh dear so you will not approve of mine which is 4 way, similar to m99 but with a pair of old school Peerless xl 10 inch perside crossing over at 50.
View attachment 917671
I recently started using VituixCAD to extract the FRD and ZMA data from jpg/png files made from the FR/Imp plots, as posted by the manufacturers (using the Tools/SPL Trace menu item).
Attached are Purifi data, as you requested, for the 8 ohm driver, along with data for the Bliesna T34B tweeter from these jpg/png extracts.
[Unless I missed it, it would be nice to have a central repository, a specific sticky, only containing FRD/ZMA driver data on the forum.]
I also added an XSim file for a crossover between these two drivers if anyone wants to play around with it. (Keep in mind, you'll have to reload the attached FRD/ZMA data files, based on your file/folder set-up.) The T34B can cross over fairly low (~1.5K) before the Purifi starts to get beamy.
The XSim FR plot looks good (shown below), but I don't have all the parts to see how accurate it is.
Nice work Mainframe! Great choice for the midrange. The best! These drivers are all well behaved. I bet a passive is not hard to do. If you care to post the FRD’s and ZMA’s maybe we can all have a good time fiddling with Xsim.
I recently started using VituixCAD to extract the FRD and ZMA data from jpg/png files made from the FR/Imp plots, as posted by the manufacturers (using the Tools/SPL Trace menu item).
Attached are Purifi data, as you requested, for the 8 ohm driver, along with data for the Bliesna T34B tweeter from these jpg/png extracts.
[Unless I missed it, it would be nice to have a central repository, a specific sticky, only containing FRD/ZMA driver data on the forum.]
I also added an XSim file for a crossover between these two drivers if anyone wants to play around with it. (Keep in mind, you'll have to reload the attached FRD/ZMA data files, based on your file/folder set-up.) The T34B can cross over fairly low (~1.5K) before the Purifi starts to get beamy.
The XSim FR plot looks good (shown below), but I don't have all the parts to see how accurate it is.
Attachments
I'd call that a 3.2 system!
I'm actually waiting for someone to try the purifi with a volt VM752 for max WTH.
Normally I'm the one on this thread to question non-Purifi midranges but a few years ago I was commissioned to do a large monitor using 10" Volt woofer + RAAL foil ribbon tweeter. Volt is not as well known in N. America as "the usual suspects" but my client had been steered to Volt by the owner of Solen (solen.ca) and that was such a fine driver. Very very impressive.
Seeing the referenced Volt VM752 is a 3" dome I think perfect for a Purif grounded 3-way using a Duelund crossover. Challenge with that pipe dream is resurrecting enough of my vector calculus to navigate Steen Duelund's equations.
I'd call that a 3.2 system!
I'm actually waiting for someone to try the purifi with a volt VM752 for max WTH.
Yes that is the very flame I find myself drawn to - perhaps an A527? - but so far I have been strong.
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Yes that is the very flame I find myself drawn to - perhaps an A527? - but so far I have been strong.
Same here. After the mention of the VM752, I checked out the VM527. It seems to me that either can keep up with the PTT6.5 with respect to distortion from, say, 800 to 3k. So, I can no longer say that such a driver does not exist regardless of cost. But... that cost!
Higher breakup frequency. The 4" has a 5 kHz peak, which is about the same as the 8" W22EX. Shows up in the waterfall as early as ~1.5 kHz.