Thoughts after Munich

I'm writing this column on the long flight back to New York City following High End Munich, the big hi-fi show that in regular times takes place each May. Because these are not regular times, this was the first Munich show since 2019. This show was smaller than other recent Munich shows: COVID in the Far East limited involvement by people and companies from East Asia, and German government–mandated attendance caps limited the number of people who could enter at any one time. Even so, it was a big show, with some interesting product introductions and prototypes.

A big hi-fi show is a great place to see and audition new hi-fi equipment. Of at least equal importance to me, it's also a good opportunity to talk about hi-fi with leading people in the field.

Early Thursday afternoon, the first day of the show, I visited an off-site "service apartment" temporarily occupied by folks from Purifi Audio, the company best known for its advanced, low-distortion "Eigentakt" class-D amplification modules. Purifi is also developing loudspeaker drivers, which they were demonstrating in Munich.

Amplifier modules and loudspeaker drivers may seem an odd combination, but both are basic building blocks of a hi-fi system and both are significant sources of distortion. As such, both are obvious foci for people aiming to make hi-fi better.

But haven't people been working to improve speaker drivers and amplifiers for more than 100 years? Surely all the low-hanging fruit has already been harvested—hasn't it? I guess that depends on how tall you are, metaphorically speaking.

Bruno Putzeys, who co-founded Purifi with Peter Lyngdorf and Lars Risbo (the latter also present, as was co-owner/director Claus Neesgaard), told me that when they started Purifi, the main idea was to correct hi-fi problems with DSP—digital signal processing. They soon changed course and started to use science and engineering to attack some of those problems at the source. A result is the Eigentakt module used in some of the best current class-D amplifiers. Another is their loudspeaker drivers, seven of which are already marketed, with others in development. Purifi's drivers are documented by extensive performance data—far more than is provided by most other driver manufacturers.

Many advancements in loudspeaker drivers involve fancy and expensive new materials—anything that makes the cone stiffer and lighter. Purifi's new drivers use old-school cone materials: aluminum and paper. In place of real-world trial and error, Purifi solves many problems in silico before they build the first prototype. Then starts a cycle of measuring, listening, and refining—but less iteration is needed now because their simulation work sets them closer to the optimal solution. Such an approach led to modifications in the shape of the cones used in Purifi's loudspeaker drivers that look subtle but have important sonic consequences.

Less attention has been paid to surrounds, those "floppy pieces of rubber" as one of the Purifi folks—I think it was Putzeys—called them during our meeting. Because they're at the outside edge of the driver's radiating surface, and because area is proportional to the square of the radius, the surround can be close to 20% of a speaker driver's moving surface. You can't ignore that if you want low distortion.

There's nothing special about the material in Purifi's surrounds, either; it's just rubber—but because of the way they're molded, Purifi's surrounds are less floppy than most. I lack the space to detail the technology (footnote 1), and I'd likely get it wrongnif I tried—so I'll merely report that while Purifi's cones look ordinary, their computer-optimized surrounds look kind of, well, funny. Not that you'd care a whit after you heard them.

Purifi's work on drivers isn't limited to the parts you see. Innovations in the motor system reduce hysteresis distortion and solve several other important problems.

But it's not their specific innovations I want to draw attention to. It is, rather, some big ideas that the Purifi approach illustrates:

• Straightforward, clever thinking combined with simulation can still, in 2022, realize major gains in performance even in hi-fi's most basic technologies.

• Easily audible improvement can result from lowering distortion that's already at levels far lower than you (or anyway I) would imagine audible, often lying far below the signal level and deep in the noise. In certain circumstances, lowering distortion from –80dB to –100dB (relative to the signal level) can deliver audible gains. And this ain't some artsy-poetic intuitive tube-amp manufacturer; it's Purifi, home of serious engineering and class-D modules that solve that technology's problems by flooding them with feedback.

• Speaker drivers that sound (and measure) fine with single tones—like, say, a frequency sweep—can run into serious trouble with more complex signals. Like, say, music. Intermodulation, via various mechanisms, is where things get interesting (footnote 2). What happens in the bass can have profound effects on the midrange. But these problems can be solved, and some of them already have been.

Purifi's people are serious engineers, but don't make the mistake of thinking they mindlessly ally themselves with the simple-minded objectivists who populate certain online discussion forums. They understand that science and engineering must be carefully deployed. Members of the Purifi team seemed to me as impatient with measurements-happy reductionists as with the radical antimeasurements crowd. Sure, it's depressing when a forum post asks, "Is it possible for a component that measures well to sound good?" But owning an Audio Precision analyzer doesn't make you an expert, and the unguided application of analytical tools can lead you far astray.

Knowing what to measure is critical, and getting to that point is hard work. As is written in a Purifi blog post—it's unsigned, but the voice and some biographical details sound like Putzeys's—"We don't so much hear distortion levels as distortion mechanisms. You need to understand the mechanism before you can design a test that will quantify it sensibly."


Footnote 1: If you're interested, check out patents.google.com/patent/WO2020208070A1.

Footnote 2: See, for example, this Purifi blog entry. If you're a tech-minded audiophile, I encourage you to monitor the Purifi blog, at purifi-audio.com/blog/. New posts aren't frequent, but they're meaty.

COMMENTS
remlab's picture

or a small(4"or less)) pure mid. Absolutely fascinating what they've created so far.

Jim Austin's picture

I didn't see a tweeter, and in their demo boxes, they were using an off-the-rack tweeter that they weren't happy with. No doubt they'll get to it eventually though.

Jim Austin, Editor
Stereophile

The Tinkerer's picture

... is that I should go out and buy an AP analyzer (and maybe a Klippel NFS?) and then proceed to measure a bunch of stuff, make a forum, provide 1/4 screen grabs of the AP's screen for "THUH DATA", criticize the inventors and makers of any products that "fail my standards", harass/mock/ban anyone who disagrees, Monday-morning-quarterback established product engineers and designers in the industry as often as possible (ESPECIALLY when they cost more than ChiFi), and then devise some type of iconography with which I could associate my rating system. Mayhaps a Panther???.....

I joke, I kid.

Another great article, Jim. Excited to see what Bruno and the gang create next.

rt66indierock's picture

Get an EE degree, start using an AP Analyzer when Sony gets one in the eighties, Work on two projects that win Technical Emmy’s, work on various projects at Microsoft and win another Technical Emmy, retire start a VAR Madrona Digital. Agonize over the cost of the Klippel but buy it anyway. Believe that audio equipment should be transparent and make a forum to report testing results and discuss measuring audio equipment.

And of course, criticize products that aren’t transparent and the people who make it. Nothing wrong with harassing, mocking and banning those who disagree with you. That seems to be how audio sites work.

If a golfing panther is the top rating, and a headless panther is the bottom rating I’m fine with it.

According to Similarweb in March of this year ASR had more visits than all the AV Tech sites combined so his plan seems to be working. Except for the black mark of supporting MQA. That has backfired on him and every other audio writer. He has the resources to buy the Klippel I wonder if AV Tech has the resources to buy one? I doubt it, I’ve looked at the financial statements.

JHL's picture

...necessarily - or even commonly and reliably - relates to sound or, e.g. SPhile's case, excellence in journalism.

The Tinkerer's picture

.... doesn't feel like a cult. At all. Really.

Amir agonized but did it anyway. 1st Audio Chronicles 1:16

No culti-ness here.

None.

MrMumbly's picture

Having actual electronic design experience adds significant "bona fide" to rendering opinions about measurements. A few hours of training all that is necessary to turn knobs and flip test equipment switches. Ensuring test conditions are correct and then understanding what measurements actually reveal is a horse of a different color. Performing "industry standard" tests does not make one an expert authority. Audio "industry standard" testing is aimed at revealing only gross problems and significant differences. Fine for separating out bad actors. Not sufficient for identifying the characteristics between good, better, best. It is naive to believe an FR Curve, SINAD, or THD is the end all - be all. Listening is the final test to perform. As Dr. Toole said, "Two ears and a brain respond very differently to a complex sound field — and are much more analytical — than an omni-directional mic and analyzer".

Fidji from Firenze's picture

Honestly, if I am looking how to spend my money - I go to ASR, rather than to ANY site, that lives off "magical cables" advertisements and where there has been no negative review since 20 years.

I like Stereophile for new music, that it discovers for me [I read reviews just for the music that is mentioned there] . Equipment reviews per se - not so much.

Stereophile used to my go-to site/magazine for good 20 years, but not anymore. And I strongly believe, that if our hobby is to survive - it needs more sites like ASR, rather than one more subjectivist blog/site.

And as one member on ASR [discussion about TRINNOV] nicely summed it up: "Discussions about audio equipment are vicious and bitter, because the stakes are so low"

Glotz's picture

Constant misinformation disguised as news.

Sounds like MQA scars deeply or something... Try some ointment.

The Tinkerer's picture

...a steroidal cream as well? Might also cure the smugness of ostensibly "discovering" everyone else's errors.

Update: I'm referring to ASR

Glotz's picture

That smugness you speak of has an extra strong smell, based soley on your responses.

Again, ASR is not a review site. It's a place for thousands of hate-filled mutes who demand to insult, draw false correlations and misinform out of context findings. Oh yes, while acting smugly about it all...

Anton's picture

Take a look at the diagram in the title of this thread. Obviously a superior product, and that will translate to better sound.

Anton's picture

“ Purifi's people are serious engineers, but don't make the mistake of thinking they mindlessly ally themselves with the simple-minded objectivists who populate certain online discussion forums. They understand that science and engineering must be carefully deployed. Members of the Purifi team seemed to me as impatient with measurements-happy reductionists as with the radical antimeasurements crowd.”

Just out of curiosity, which driver makers are the simple minded reductionists who are not serious engineers?

JHL's picture

...the discipline of managing multiple speaker drivers in one box, I doubt driver engineers are automatically synonymous with the speaker designers making genuinely musical sounds.

Professional engine builders are not professional drivers. Science and engineering must be carefully deployed.

Jack L's picture

Hi

Not neccessary so.

My audition experience tells me what decidedly makes a loudspeaker system sound superb is the box, not the drivers !!

As I already posted in other Stereophile forums before, the best sounding (i.e. natural & livelike performance) loudspeaker I ever auditioned so far was a pair of 2-way miniatures of the size of Rogers LS3/5a, & the box was PURPOSELY built in special curved profile, so flimsy & light to vibrate with the soundwaves coming out from the drivers. Built by a leading brandname guitar manufacturer in Japan using drivers built in Japan as well.

Musical instrument makers to build excellent sounding loudspeakers ? Yes, no kidding ! They built the loudspeaker box like an musical instrument !!!

When I first auditioned it in the regional rep's studio, I dropped my jaw big bigtime, wondering how come such miniatures could deliver studio filling overwhelming soundstaging like live performance with well balanced tonal spectrum, no bass shy at all !!

Beating the conventional wisdom, apparently.

Listening is believing

Jack L

Jonti's picture

Jack, that sounds intriguing. Which manufacturer was behind the speakers? Perhaps the concept is wildly different in many respects, but what you describe puts me in mind of Teragaki Labo's SP-300, which has a box roughly the size of a KLH Model 6 but weighs only 7kg and is all about the vibration of natural wood. Check it out: http://www.teragaki-labo.co.jp/products/products.html

Jonti's picture

Jack, that sounds intriguing. Which manufacturer was behind the speakers? Perhaps the concept is wildly different in many respects, but what you describe puts me in mind of Teragaki Labo's SP-300, which has a box roughly the size of a KLH Model 6 but weighs only 7kg and is all about the vibration of natural wood. Check it out: http://www.teragaki-labo.co.jp/products/products.html

Jack L's picture

Hi

Nope. As I said above, it was small like Rogers LS3/5A if not smaller but lighter. Apparently it was built to work like a musical instrument with its internally braced thin natural wood box enclosure vibrating with the sound.

It was many years back then & somehow I lost loudspeaker catalogues to tell you who makes what.

Jack L

KlausDenmark's picture

The Company is valle Kiso Avoustic and the model must be the HB1 or HB-X

https://www.kisoacoustic.co.jp/

http://www.kisoacoustic.com/

I have newer heard them but must admit that I find them highly interesting.

Greatings from Denmark.

Klaus

KlausDenmark's picture

The Company is valle Kiso Avoustic and the model must be the HB1 or HB-X

https://www.kisoacoustic.co.jp/

I have newer heard them but must admit that I find them highly interesting.

Greatings from Denmark.

Klaus

Jonti's picture

...

JHL's picture

are *not* synonymous, Jack.

eriks's picture

So, the answer is to DIY 2-way speakers with Purify mid-woofers, right?

Seriously though while the Purifi drivers are interesting this is unnecessarily focused on one brand. Lots of speaker drivers out there are making innovations in motors, cones and surrounds.

I would be very interested to see a comparison of 2-way speakers using similar drivers from say Satori or ScanSpeak vs. Purify to see if any of these improvements actually play out.

Jarno's picture

...lies somewhere between What Hi-Fi and Audio Science Review. The truth about those sites is both are about as relevant as a tory politician's spouting of disingenuous statistics in relation to his/her party's achievements in government.

What I will say is at least What Hi-Fi encourages auditioning equipment rather than just panning it or giving it the thumbs-up based on reductive data followed by strawman conjecture by a load of internet randoms who've never even been in the same room as the equipment they're gleefully slating/gushing about.

The truth about misinformation is it's equally worthless at both ends of the argument.

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