Blog Posts | PURIFI

A Symphony in 4 Movements

PURIFI ApS, Lars Risbo

A Symphony in 4 Movements

Prolog I recently gave an invited keynote at the AES convention, "Unreasonable Audio Innovation." We posted it on our web for you to enjoy. The writing process made me reflect on the state of our indu...

Sep 17, 2026

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Tech Notes

Building Purifi: From a Cold Office in "Siberia" to Powering the World's Best Audio

PURIFI ApS, Claus Neesgaard

Building Purifi: From a Cold Office in "Siberia" to Powering the World's Best Audio

Purifi builds the amplifier and transducer technology inside some of the best-sounding products in high-end audio — NAD, T+A, Lyngdorf, and Kii Audio all run on our engineering. Last week, we hosted D...

Sep 11, 2026

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Tech Notes

Unreasonable Audio Innovation

PURIFI ApS, Lars Risbo

Unreasonable Audio Innovation

1. OPENING Good afternoon. I am told this room has some acoustic challenges. Consider that a live demonstration of one of my central arguments. A few years ago we received a review of one of our produ...

Jun 1, 2026

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Tech Notes

What is the Baffle Step?

PURIFI ApS, Lars Risbo

What is the Baffle Step?

Introduction You are perhaps familiar with the terms baffle step and box diffraction. But what is this exactly? The short story is that a driver mounted on a box will radiate sound uniformly in all di...

Mar 25, 2026

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Tech Notes

Discrete Op Amps: When and Why It Actually Matters

PURIFI ApS, Bruno Putzeys

Discrete Op Amps: When and Why It Actually Matters

“Discrete is an old audiophile hobby horse,” said Lars. “It proves nothing. Consider writing a few words.” Yes, precisely. Doing things discretely has no inherent value. The normal procedure is that y...

Eigentakt

Jun 24, 2025

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Tech Notes

The PURIFI Tweeter Project - Part 2

PURIFI ApS, Lars Risbo

The PURIFI Tweeter Project - Part 2

Introduction In Part 1 we learned why we chose touse a hard dome as the radiator: the dome simply yields the best dispersion for a given size. A further advantage of a dome is that has high geometric ...

Jan 31, 2025

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Tech Notes

Side effects of Passive Crossover Filters

PURIFI ApS, Lars Risbo

Side effects of Passive Crossover Filters

Introduction We use crossover filters to partition the frequency bands between drivers in a multiway speaker. In addition, the crossover filter may provide EQ such as baffle-step compensation. A passi...

Ushindi

Oct 8, 2024

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App Notes

The PURIFI Tweeter Project - Part 1

PURIFI ApS, Lars Risbo

The PURIFI Tweeter Project - Part 1

Introduction The tweeter project has been an intensive R&D effort for the last 3 years. Yes, we know, the long waiting time until it is released is painful for all of us. Since we are getting closer, ...

Ushindi

May 24, 2024

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Tech Notes

Time/Phase Alignment, Acoustic Center, Lobing etc.

PURIFI ApS, Lars Risbo

Time/Phase Alignment, Acoustic Center, Lobing etc.

Introduction There is widespread confusion regarding the terms phase and time-alignment of loudspeakers. Moreover, the fundamental concepts of latency, delay, phase-delay and group delay are often con...

Ushindi

Sep 22, 2023

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Tech Notes

SPK16 Reference Design

PURIFI ApS, Lars Risbo

SPK16 Reference Design

Note: SPK16 is now released as a kit with build description SPK16 is a passive 2 way speaker system with a 6.5X-NAA alu cone woofer assisted by two passive radiators on the sides of the box combined w...

Ushindi

May 9, 2023

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Tech Notes

Low Distortion Filter for PTT6.5X04-NAA

Low Distortion Filter for PTT6.5X04-NAA

In the following, we show that not all methods of equalization are created equal. In particular, using a series notch reduces distortion, which does not happen with alternative methods. The proposed circuit results in an extremely clean low-pass response combined with low distortion...

Ushindi

Nov 16, 2022

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App Notes

Some Speaker Problems That Needed Solving

Some Speaker Problems That Needed Solving

Some time ago we posted on our website a pair of sound demos that we thought were quite instructive. One showed that Doppler distortion was much less audible than an equivalent amount of amplitude modulation, thereby sinking a lot of “masking theory” based audio discourse...

Ushindi

Oct 14, 2021

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Tech Notes

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