Chris, What is your take on the new line of Purifi drivers? They tout very low distortion and exceptional transient response but I was wondering what you thought of them after reading their spec sheets? Thanks, Paul
I think the Purifi drivers are very cool. Whatās unique isnāt really any single feature, itās the business model. Hiring several heavyweight engineers and letting them do pure research for five years before shipping product is not something most speaker companies can or will do. Lars, Bruno, Carsten, and Morten are all serious people, and my understanding Lars and Carsten are responsible for the bulk of the transducer work. Iāve chatted with Bruno at the Ascot High End show and it was very interesting and am on some facebook groups in forums with Lars and he always contributes and lot of interesting comments.
Where those drivers shine is intermodulation distortion. Theyāre excellent as a midrange or bass/midrange, because thatās where the mechanisms they attacked - force factor modulation, inductance modulation, surround-induced area modulation - do the most audible damage. Itās worth saying that larger multi-way systems have always been a way to minimize the same problems, by limiting excursion and bandwidth per driver rather than by linearizing the driver itself. But that doesnāt diminish what they did; they went after the mechanisms directly and quantified them properly, which is arguably the bigger contribution. Their force factor modulation paper has some genuinely novel conclusions:
https://purifi-audio.com/documents/content/WT1Pkt9-SxijAvNyifNN4Ao2a2
Their work is a big part of what motivated me to build a much more capable in-house simulation tool for our drive units. Iād been working in FEMM, which is fine for static magnetostatics but doesnāt get you to the coupled behavior and advanced anaylsis. Iāve since developed a much more comprehensive FEA package so I can simulate BL(x), Le(x,i), and reluctance force behavior directly ā including modeling several of the design features Purifi uses ā and iterate on motor topology before cutting steel.
For context on where weāre coming from: weāve been using split-gap āXBLā style motors that give very linear BL and compliance. What they donāt do as well as the Purifi units or the best woofers on the market is control inductance versus excursion and frequency, though Iāve recently made some improvements there partly inspired by some of the work KEF is doing on their latest uni-q (which also uses a split gap topology). And our planar drivers sidestep the issue entirely with essentially no inductance and no steel in the magnetic circuit means no hysteresis distortion and no force factor modulation, so they simply donāt distort in the midrange in the same ways cone drivers do.
But weāre building more 2-ways now and using cone mids in some applications, and Iām just interested in new woofer technology regardless. So Iāve been looking closely at a few things: variable-pitch voice coil winding (TC Sounds did this years ago) to linearize BL over the stroke; hybrid neodymium motor structures that eliminate pole steel to linearize inductance and remove hysteresis distortion; and deliberately balancing the remaining steel in the circuit to minimize the DC reluctance force that drives force factor modulation.
Iāve also started doing 2D/3D simulation in CalculiX with a genetic optimizer to explore novel surround geometries that minimize radiating area modulation versus displacement ā the problem Purifiās neutral surround addresses, and one the industry largely ignored for decades. Iām sequencing my efforts toward motor research and changes first and looking at surround profiles later. Accurate material definitions can be a hard part and I want my models validated against measured Kms(x) and impedance data before I trust an optimizer to hand me a surround shape.
Purifi optimized hard for one point in the design space, and they pay for it in cost and sensitivity. So the goal for us isnāt to clone a Purifi motor ā itās to understand which of those mechanisms actually matter in our applications and solve them our own way.
Iām planning to do a short YouTube video walking through some of this once I have results worth showing. We want to keep our own technology story and keep pushing on our own innovations, but itās great to take inspiration from people doing work at this level and use it to make our products better.
Purifi is also responsible for the next gen Class D amp technology in the Marantz Model 10, which has gotten great reviews. Obviously, an impressive audio company.
Purifi amps are in the latest generation of Kii speakers. Each individual driver has its own Purifi amp and its own DAC. All of this was designed by the same guy who brings us Mola Mola products.
I have been following one super genius named Edgar. Now I wish to follow another great genius named Bruno. I am amused that those two are buddies and they work together on projects. Fun!
It seems to me itās a cycle: golden ageāstagnationāgolden ageāetc.
I think weāre in a golden age in the audio world.
I really wonder what will come once they turn ai loose on Audio design. My friend Serguei who designs Stealth cables told me he is spending as much time as he can studying ai tools. He wants to understand them so he can use them to design bigger, fatter, and much more expensive cables. Waitā¦
Those cables have no use for you now. Lol.
I am too old to dream about bigger and fatter thing now.