LIVE! with PURIFI Co-Founder Lars Risbo!

This episode I am joined by PURIFI Audio co-founder Lars Risbo. Join us for an open Q&A regarding the tech behind PURIFI's unique transducers plus a quick view of their in-house analyser, built as part of their R&D.



Some background on Lars:
Pioneered direct switching PCM-PWM audio amplifiers as founder of Toccata Technology, later acquired by Texas Instruments. Elected TI Fellow (2012) and Audio CTO (2013). Research interests include digital signal processing, system-level and signal chain optimization, oversampled data converters, transducers and mixed-signal architectures. Ph.D. from DTU (1994). Holds more than 30 US granted patent families.


Chapters and Notes graciously provided by DIYaudio member Norman Tracy:
8:51 – Question “How does a transducer work..?”
19:36 – Lars discusses why speakers are not ideal.
24:00 – 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.
29:00 – “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?
37:00 - Discussion turns to the “big surprise” of the hysteresis distortion of iron “the grey dull background”.
39:55 - Shows the copper shorting rings used in PTT6.5W and discuss their functions.
44:25 - Begin discussion of cone, surrounds, and other ‘soft parts’ optimizations.
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.
57:08 - Venting of the motor assembly discussion.
1:01:00 - Spider and slightly progressive suspension, priority of IMD reduction vs. THD.
1:05:00 – Purifi’s custom lab test rig discussion, first demo suffers Murphy’s Law of demos.
1:12:00 – Taking question break while tech glitches are sorted.
1:16:00 - Tweeters can be helped, Purifi tweeters are further into the future.
1:20:00 - Introduction of founding partner Carsten Tinggaard, Co-Owner (PURIFI Transducer Technology) former CTO of Peerless, Vifa, and Scan-Speak when the brands were all part of Tymphany.
1:24:00 – Demo of Purifi’s in house developed measurement system retry & success (loud test tone at 1h26m38s) after tests run results graphs are discussed.
1:39:00 – Lars’ son asks an insightful question.
1:43:00 – Erin asks about drive unit break in.
1:51:00 – New Purifi amp modules coming? Wrap-up, thanks, and goodbyes.