I have consulted for some of the leading chip vendors over the years (TI, NXP, Maxim, Fairchild, and more) in amplifier and audio signal processing applications for speaker optimization, and we consistently ended up "rediscovering" Dr. Wolfgang Klippel’s patents for smart speaker protection with feedforward distortion nulling. While Dr. Klippel is famed for his transducer analyzer test instruments, back in 1991 a younger Dr. Klippel at JBL Pro was issued a patent (US5438625A) for "Arrangement to correct the linear and nonlinear transfer behavior or electro-acoustical transducers." About 30 years ago, DSP processing had too much latency and cost and there was still much to be learned on speaker failure modes. Dr. Klippel went on to found Klippel GmbH in 1997 with the focus on audio test instrumentation.

This fall, Klippel GmbH will celebrate its 25th anniversary and that will provide a good reason to revisit interesting and less known stories from the company, including its path toward the Klippel Control System (KCS) that is now starting to get recognition. The extensive published research and the implications on the speaker industry for much of Klippel's work deserve to be revisited. But there's also a lot more history on amplifier protection circuits and why they became important in transistor designs.

Direct coupled amps that were transformer-less without coupling caps could lead to burning out the speakers if the amplifier had a meltdown – especially in the earlier generations of high-power and switching-mode amplifiers. Most protection circuits were really about protecting the amplifier, not the speakers. Some protection schemes even ended up chattering ultrasonically, frying the tweeters/compression drivers as they attempted to protect the amplifier's output stage from problematic speaker loads.

Conversely, smart speaker protection from being overdriven by the program signal is more about excursion limiting for the bass combined with voice coil thermal limiting in mid and high frequencies. Pioneers in these techniques were Meyer Sound and Apogee Sound in the early 1980s with their processor-controlled touring sound systems. These were closely matched controllers and speakers that not only stayed out of trouble in the field, but never distorted no matter how hard they were over driven. Standalone speaker management systems from dbx and others followed, but ideally the speaker and amplifier designers would work together for defining the boundaries in integrated solutions. The cost of these rackmount processors were in the range of $500 and up (affordable for pro audio applications...), depending on how many amplifier channels they could handle.

Smart amp integrated circuit chips with just about everything the professional speaker protection processors accomplished were introduced more than a decade ago, essentially designed for mobile phones, laptops, Bluetooth speakers, and TVs. Astonishing at the time, all this was combined in a chip along with a few watt amplifier – for less than a buck! Those chips have been trickling up the product development chain into more expensive "smart" home audio products - first with smart speakers intended to promote the ecosystem for voice assistants, and now with a large focus on soundbars and speakerphones.

Advanced speaker protection processing can be a two-sided sword. We want to increase the maximum clean acoustic output without creating new failure modes by inadvertently crossing the line. Specifically, the concern is transducer fatigue issues by dancing at the edge with a high duty cycle (especially on ring tones), creating new fatigue failures that could cause smartphones to be returned by unhappy users (which Apple, Samsung, and Huawei, might find annoying).

NXP, Maxim, Texas Instruments, Cirrus Logic, Infineon, and Qualcomm have succeeded with their Smart Amps (sometimes also called "speaker amps"), all of which are a couple of watts - more than enough for smartphones, considering battery drain and what the speaker can handle. At this point smartphone speakers can play as loud as possible without rattling, buzzing, or most importantly without damage — allowing everyone in the business to sleep soundly.

I have always pressed the product managers at the Smart Amp companies to consider a version of this dynamic protection processing in a form that could be used from soundbars to subwoofers to concert sound to military hailing and civil defense voice warning systems. To further enable the expansion of Smart Amps is the prevailing trend of integration of the signal processing, amplifier, speakers and enclosures into finished products – not just smartphones, soundbars, subwoofers, but also self-powered pro sound speakers and automotive sound OEM. Closed systems enable close-coupled protection to do its job effectively.

But what more could speaker system designers want? How about where this article started: not just to protect the speaker from overload, but enable the speaker to play louder with reduced bass distortion. For functionality, aside from saving the speakers from damage, how about we drop distortion? And for applications where there are full-duplex signal paths with acoustic echo cancelers, add graceful barge-in, providing significantly wider gain margins before echoes?

Here we are, over a quarter of a century after Dr. Klippel’s patent, and feed-forward distortion nulling protection circuits are practical and in mass production. In 2020, Nuvoton Technology Corp., a Taiwan-based semiconductor maker unveiled a collaboration with Klippel and announced the world’s first smart amplifier with integrated Klippel Control Sound (KCS) technology and nonlinear speaker control algorithm. The Nuvoton NAU83G10 device can deliver up to 8W output power into a 4 ohm load and 6.5W for 8 ohms using a highly efficient boost converter. The NAU83G20 device can deliver up to 20W for 4 ohms and 11W for 8 ohms around 12.6V external battery supply levels.

The Nuvoton KCS audio amplifier chips have now entered mass production and are a versatile solution to improve speaker performance and sound quality by compensating for speaker nonlinearities. Correction is dynamic, and the higher the excursion the distortion nulling dramatically keeps the sound clean.

As I found with some recent projects, KCS actually delivers. I cannot talk about ongoing product developments that so impressed me (some won’t be shipping until long after this is published) but let’s just say I am a believer. KCS increases what a system designer can demand from smart speakers, Bluetooth speakers, OEM autosound, soundbars, conferencing, or huddle room voice lift, and eventually concert sound speakers.

What we can talk about here is about Nuvoton’s Smart Amps, which are already in Dell’s latest collaboration products. These are their mini-conferencing soundbars, SB522A and SP3022, which are in mass production, available online and in stores, and have been generating enthusiasm and impressed the first YouTube reviewers who got to try them out. I don't make my conversations available on YouTube, but I've been playing with my samples and I'm also impressed.

The last few years have been ones of frustrated innovation for much of the pro audio industry. Many product designers and manufacturers in the audio industry the world over have been making huge leaps forward in hardware, software, and interoperability that they have been largely unable to show off thanks to a disruption to live events of all kinds. Following the return of trade shows in 2022, the lid has been lifted on a whole host of innovations in the pro audio space, and among them Holoplot has emerged as a standout with its X1 Matrix Array sound system. This article is an inside account about how the Holoplot team has been pushing the boundaries of what is possible in the pro audio space. This article was originally published in audioXpress, September 2022. Read the Full Article Now Available Here

This is an interesting Test Bench explication of a 3"" dome midrange from Tang Band Speaker (aka TB Speaker), model 75-1558SH, intended for high-end and home audio applications. Tang Band is increasingly recognized as one of the most innovative and prolific OEM speaker manufacturers from Asia, and the company once again submitted a unique and creative transducer design. The unit sent to Voice Coil was a new 75mm diameter soft dome midrange, using a coated cloth diaphragm and surround, a 75.5mm diameter voice coil wound with round copper wire on a black anodized vented aluminum voice coil former with magnetic fluid in the gap area. The motor system on this model 75-1558SH consists of large neodymium slug magnet with a low carbon content steel return cup with a black emissive coating that also incorporates a distortion reducing shorting ring. The steel cup has a foam damped vent that loads into a shaped and 100% polyester-filled injection-molded back enclosure. The driver is rated for 25W power handling (200W on program material) with nominal 8 ohm impedance, with 90dB 1W/1m sensitivity. This article was originally published in Voice Coil, June 2022.  Read the Full Article Now Available Here