A Symmetrical Transducer Topology

[smowry]

Patents help protect exploitation of someones life work. Those with resources learn from your work innovate and lock you out of your own expertise your by enhancing prior art patenting it. If one receive a patent nothing stops one from licensing it a modest fee or royalty. Such is the way of universities to receive operational funds and collaborations with outside organizations which in turn hire more people. It is not black and white and what one does with one's ideas is okay and their choice.

Hi Timcognito,

The irony is that in general I agree with almost everything you stated; however, I strongly disagree as the USPTO relates to Audio Transducer Patents. I presented an example above and below I will present another.

A Tale of 2 Transducer Motor Patents

A technical discussion of the Borresen ironless mid/bass moving coil audio transducer

www.linkedin.com

Now Mark and Jack claim that the industry is mature but what does that mean? Actually Dick Small said the same in 2006, ...pretty "mature". (https://audioxpress.com/article/voice-coil-interviews-dr-richard-h-small). To me that means that most of the new stuff after Harry Olson's work is innovation and not invention.

"Innovation is a process by which a domain, a product, or a service is renewed and brought up to date by applying new processes, introducing new techniques, or establishing successful ideas to create new value. The creation of value is a defining characteristic of innovation."

"Invention is something that has never been made before, or the process of creating something that has never been made before."

Note that Design Patents are granted for 14 years and protect from copying a product; whereas, a Utility Patent is granted for 20 years to protect an invention.

Can you or anyone else give me two (2) examples of your claim, "Patents help protect exploitation of someones life work" within the development of Audio Transducers only after Harry Olson, please?

 

[Lars Risbo]

The difference in testing is what makes the Purifi numbers appear better.

hey Mark, perhaps you would like to elaborate here?

Cheers

Lars

 

[olieb]

So this is 90db at a one metre equivalent, that is 2 metres groundplane measurement. Almost all the extant distortion measurements are taken in the nearfield and extrapolated to 1 metre. In other words they are not exactly real. They look good, but they are not real 1 metre measurements. The difference being the excursion needed to get the SPL greatly favours a nearfield impressively low distortion measurement. This is the real deal. It is at 2 metres.

I understand that 90dBspl ground plane in 2m distance is equivalent to 90dBspl in 1m. But why is a measurement in, say, 0.31m (like hificompass.com is doing) at 96dBspl not equivalent to 86dBspl in 1m? Or if spl is measured at 8Vrms and adjusted for 1m distance and harmonic distortion is measured at 8Vrms, too?

 

[mwmkravchenko]

hey Mark, perhaps you would like to elaborate here?

Cheers

Lars

Yeah. I'd be happy to Lars. Post distortion measurements made at 90db one metre. That's what I posted.

The difference in excursion between a nearfield measurement that is normalized to 90db and a true 90db measurement at one metre. I did mine a few ways. As shown 5 metres up in the air. SPL verified via a Class 2 metre. And I have done it as well as a groundplane measurement, mic at 2metres of course to get the equivalent.

The most accurate independent distortion tests I can find are:

Purifi PTT6.5X04-NAA-08A | HiFiCompass

The HD measurements at distance 315 mm and voltage levels of 2.83 - 11.2 Volt were carried out with High Pass Filter "on" (2nd order Butterworth type, 50 Hz cutoff, HPF2-50) The HD measurements at distance 315 mm and voltage level of 16 Volt were carried out with High Pass Filter "on" (2nd order...

hificompass.com

They are great results. And I can look at the higher voltage results and extrapolate.

What I never see is a simple apples to apples measurement. 1 metre 90db or 94db as a baseline.

This is my underhung groundplane

 

[mwmkravchenko]

I understand that 90dBspl ground plane in 2m distance is equivalent to 90dBspl in 1m. But why is a measurement in, say, 0.31m (like hificompass.com is doing) at 96dBspl not equivalent to 86dBspl in 1m? Or if spl is measured at 8Vrms and adjusted for 1m distance and harmonic distortion is measured at 8Vrms, too?

Point accepted. And in agreement as I posted.

I'll make an overlay chart later today I don't think that I have ever done that.

Off to the races now! Windows to fix. Glass ones.....

 

[Lars Risbo]

Yeah. I'd be happy to Lars. Post distortion measurements made at 90db one metre. That's what I posted.

The difference in excursion between a nearfield measurement that is normalized to 90db and a true 90db measurement at one metre. I did mine a few ways. As shown 5 metres up in the air. SPL verified via a Class 2 metre. And I have done it as well as a groundplane measurement, mic at 2metres of course to get the equivalent.

The most accurate independent distortion tests I can find are:

Purifi PTT6.5X04-NAA-08A | HiFiCompass

The HD measurements at distance 315 mm and voltage levels of 2.83 - 11.2 Volt were carried out with High Pass Filter "on" (2nd order Butterworth type, 50 Hz cutoff, HPF2-50) The HD measurements at distance 315 mm and voltage level of 16 Volt were carried out with High Pass Filter "on" (2nd order...

hificompass.com

They are great results. And I can look at the higher voltage results and extrapolate.

What I never see is a simple apples to apples measurement. 1 metre 90db or 94db as a baseline.

This is my underhung groundplane
View attachment 476205

are you saying that the distance law does not apply (extrapolate SPL at eg 40cm to. eg 1m)? there is of course an acoustic center that is not necessarily flush with the baffle but i think the deviation is rather small (i checked with Comsol at some point). the acoustic center can be much outside the baffle for a speaker in 4pi but usually close to the baffle level in infinite baffle.

For a very distortion driver, we also easier have harmonics falling into the noise floor when measure at 1m or 2m compared to closer. Ground plane is of course nice since it adds 6dB signal.

your nice plot shows the fundamental dropping from 100Hz to 1kHz. is this due to the blocked impedance (inductance )?

 

[mwmkravchenko]

are you saying that the distance law does not apply (extrapolate SPL at eg 40cm to. eg 1m)? there is of course an acoustic center that is not necessarily flush with the baffle but i think the deviation is rather small (i checked with Comsol at some point). the acoustic center can be much outside the baffle for a speaker in 4pi but usually close to the baffle level in infinite baffle.

No! I get it Lars. I am not the greatest mathematician admittedly, but I can do the math. My complaint is simply a personal opinion. I have the same issue with 2.83 volts. I understand that the SPL for a 4 ohm driver at 2.83 volts is not 1 watt 1 metre. But, when I was young learning all these things those were the reference points. 1 watt one metre, distortion at 90db 1 metre or 94 db 1 metre. Old dog complaining about having to learn new tricks. As a consultant working for many different types of clients I end up having to explain the differences in the measurements regularly, and walking people through the math with tools that they can work with themselves.

your nice plot shows the fundamental dropping from 100Hz to 1kHz. is this due to the blocked impedance (inductance )?

Thanks. This driver had no inductance compensation sleeve at all. It was a prototype. The cone and surround were mature, the motor was a new idea. The latest version using a slightly variant motor and the same cone and surround has even lower distortion, but that driver is proprietary and I have an NDA on that one.

You and your team produce great drivers. In fact they are one of the few drivers that I pay attention to in terms of performance.

 

[mwmkravchenko]

From HiFi Compass:

The HD measurements at distance 315 mm and voltage levels of 2.83 - 11.2 Volt were carried out with High Pass Filter "on" (2nd order Butterworth type, 50 Hz cutoff, HPF2-50)

I did not use any filtering.

 

[Timcognito]

Hi Timcognito,

The irony is that in general I agree with almost everything you stated; however, I strongly disagree as the USPTO relates to Audio Transducer Patents. I presented an example above and below I will present another.

A Tale of 2 Transducer Motor Patents

A technical discussion of the Borresen ironless mid/bass moving coil audio transducer

www.linkedin.com

Now Mark and Jack claim that the industry is mature but what does that mean? Actually Dick Small said the same in 2006, ...pretty "mature". (https://audioxpress.com/article/voice-coil-interviews-dr-richard-h-small). To me that means that most of the new stuff after Harry Olson's work is innovation and not invention.

"Innovation is a process by which a domain, a product, or a service is renewed and brought up to date by applying new processes, introducing new techniques, or establishing successful ideas to create new value. The creation of value is a defining characteristic of innovation."

"Invention is something that has never been made before, or the process of creating something that has never been made before."

Note that Design Patents are granted for 14 years and protect from copying a product; whereas, a Utility Patent is granted for 20 years to protect an invention.

Can you or anyone else give me two (2) examples of your claim, "Patents help protect exploitation of someones life work" within the development of Audio Transducers only after Harry Olson, please?

I am very familiar with patents, spending virtually all of my career in R&D in medical device startups. I am listed as an inventor over one hundred patents and participating in two successful infringement lawsuits. I am not an expert in speaker design or their patents and as you state the tech as had only minor improvements. However magnets and materials have had many performance gains and changes in the last twenty years and their use in combination with existing speaker tech would seem to have some innovation. As far the value of patents in medical, 100's of billions of dollars have made due the exclusive use of devices and pharmaceuticals, keeping copycats away. I do not doubt what you believe when it comes to speakers and further, do not want to hijack this interesting technical discussion in this thread debating or discussing patents. Unpatented tech opens the door to business failures by competition and countries like China have thousands of companies that operate on those strategies. Ironically magnets are a confounding example where much of the tech is home grown there with much innovation.

 

[Lars Risbo]

From HiFi Compass:

The HD measurements at distance 315 mm and voltage levels of 2.83 - 11.2 Volt were carried out with High Pass Filter "on" (2nd order Butterworth type, 50 Hz cutoff, HPF2-50)

I did not use any filtering.

probably to limit excursion. we don’t use high pass for woofers. only for mids and tweets

 

[Lars Risbo]

Note about patents: you need to read the claims to see what the patent protecting. The drawings include s lot more and typically many prior art elements. So please do not judge on drawings alone. Read the claims thoroughly. The claims have to state an intended effect/benefit which can be surprising compared to what the reader may think from just seeing some of the drawings.

Only thing with industrial relevance can be patented.

Needs to have absolute novelty

And inventive step. This means that is surprising to a’man skilled in the art’. that man is not one you want to hire. he is looking for know methods or solution and he is not creative (yes think lawyer).

The patent examiners at generally very thorough and nit picking. They challenge clarity, novelty and inventive step. The claims have to be adjusted and narrowed. It’s a painful process and extremely expensive.

Of course, some times one get surprised about patent claims being granted when prior art is obvious. It’s not a perfect system. People can file oppositions to stop grant of patents. some time it’s strategic not to file etc The real battle happens i the court rooms which is insanely expensive.

 

[Timcognito]

Note about patents: you need to read the claims to see what the patent protecting. The drawings include s lot more and typically many prior art elements. So please do not judge on drawings alone. Read the claims thoroughly. The claims have to state an intended effect/benefit which can be surprising compared to what the reader may think from just seeing some of the drawings.

Only thing with industrial relevance can be patented.

Needs to have absolute novelty

And inventive step. This means that is surprising to a’man skilled in the art’. that man is not one you want to hire. he is looking for know methods or solution and he is not creative (yes think lawyer).

The patent examiners at generally very thorough and nit picking. They challenge clarity, novelty and inventive step. The claims have to be adjusted and narrowed. It’s a painful process and extremely expensive.

Of course, some times one get surprised about patent claims being granted when prior art is obvious. It’s not a perfect system. People can file oppositions to stop grant of patents. some time it’s strategic not to file etc The real battle happens i the court rooms which is insanely expensive.

Agree with most here but technically the specification allows one to get additional claims. So if the figure shows something novel and the spec discusses it can be claimed at a later date but length of coverage always comes from the filing date in the US. The spec is as important as the claims when it comes to novelty. one must get the claim to enforce it and if the filing predates a competitors implementation they are infringing.

 

[Lars Risbo]

that’s true and the game is that the inventor can change the claims far into the process as long as there is basis in the spec. this makes it a bit like poker playing. The inventor can also do a divisional application based on the same spec and priority date.

 

[mwmkravchenko]

probably to limit excursion. we don’t use high pass for woofers. only for mids and tweets

We both know that will also limit distortion. As I posted earlier. Knowing the measurements conditions is important.

I stand corrected on a statement about not posting 1 metre 94db testing results. I have not looked at the Purifi data sheet for a few years. I must have missed it from the beginning, because you do indeed post that information. My apologies Lars.

 

[smowry]

What some folks consider to be an Industry Landmark Patent Infringement Case is Sunfire Corporation (Bob Carver) vs. Audio Products International in 2003. During a two-and-a-half-week trial, a jury considered Carver's allegations that API had infringed certain claims of two of his US patents relating to small-box subwoofer technology.

https://patentimages.storage.googleapis.com/92/cb/7c/884d8841e4dd7f/US5748753.pdf (frivolous commutated voice coil invention*)

https://patentimages.storage.googleapis.com/d0/69/9e/b2a028a1f93591/US5937074.pdf

"Since the patents claimed rights in driver design and the operating conditions within the speaker box, if API's designs infringed any of the claims in the Carver patents, those claims were considered invalid by the jury because they were either covered by designs that already existed or were a natural and straightforward progression of existing engineering design methods."

Having been employed at TC Sounds as Chief Engineer (only engineer) in 1998, I am intimately familiar with Bob Carver's subwoofer transducer and system. At that time, TC Sounds was the sole manufacturer of the Sunfire Subwoofer Transducer. I claim that 30% Bob's objective was to prevent subwoofer R&D for 20 years. Fortunately for the loudspeaker industry, the jury agreed.

The critical statement from the jury is consistent with the claims of "mature". The claimed inventions were covered by designs that already existed or were a natural and straightforward progression of existing engineering design methods. How many existing audio transducer related patents can that jury's statement be applied to since Harry Olson? https://en.wikipedia.org/wiki/Harry_F._Olson

*To this day and although three (3) patents were granted, transducer engineers have failed to realize the commutated voice coil in dynamic audio transducers.

'What ever happened to the digital audio transducer and the commutated voice coil ?'

Mar 21, 2025

The moving coil audio transducer as we know it was invented by Rice-Kellogg in 1924. Notice that in more than 100 years, the asymmetric topology appears remarkedly similar to audio transducers of today.

Is that the GENELEC coaxial's patented flat surround et al?

Note that the digital audio transducer still seems father away than Mars, even though IBM and Bell Labs tried and failed to develop one in the 1960's.

I found three (3) expired US Patents that claim the Commutated Voice Coil as an invention.
1. US8284982 Positionally sequenced loudspeaker system by Adam...

• smowry
• Replies: 17
• Forum: Speaker Reviews, Measurements and Discussion

 

[smowry]

Who controls the Loudspeaker Industry?

Competition related to the 901 vs. L100 and thus BOSE vs. JBL in competition for sales volume has set the stage for BOSE vs. Samsung. However, Samsung is a larger and more diversified company. Note BOSE sued Consumer Reports over CR's review. Having worked in the BOSE Transducer Research Group from 1995-1998, I observed that we had one scientist and three or four transducer engineers within TRES but BOSE had approximately an order of magnitude more of Attorneys on staff. Smaller companies tend to fear BOSE.

So now Samsung leads the world in Patents. "Samsung Electronics holds a vast patent portfolio, though exact numbers vary by source and date, with recent data from early 2025 indicating they received 6,377 U.S. patents in 2024 and possessed around 99,000 U.S. patents by early 2025. Globally, Samsung holds a massive number of patents, with some reports listing over 200,000 worldwide patents and others citing approximately 48,798 active patent families as of late 2023." Samsung owns and controls the following companies: JBL, Harman Kardon, AKG, Infinity, Mark Levinson, Revel, Arcam, Bowers & Wilkins, Denon, Marantz, and Polk Audio.

BOSE has over 2,600 registered patents, with the majority falling into the "Electric Communication Technique".

My guess for third place in Loudspeaker Patents would be GP Acoustics (KEF and Celestion) with just shy of 200 Patents with Celestion Patents dating back to 1924 but Celestion only has a handful of Patents in 100 years

There have been many thousands of loudspeaker patents granted worldwide by national patent offices, and while a precise global number is unavailable, the United States' Patent and Trademark Office (USPTO) alone has issued thousands since the 1950s.

Having said all that, I claim that in effect the USPTO controls the Loudspeaker Industry! This is a significant reason that the Loudspeaker Industry is several decades behind the other A/V industry segments. Just compare a 1950's TV to today's video monitors or compare a 1950's telephone to today's telephones. Then compare a 1950's audio transducer to today's. Something happened to retard loudspeaker development. Then I make the claim that the USPTO has in effect discouraged loudspeaker R&D by imposing 20 year barriers as innovation steps. How can there be thousands of inventions while the transducer topology has hardly changed at all since the 1950's? Then can anyone claim that the USPTO has encouraged and/or supported loudspeaker R&D and keep a straight face?

 

[mwmkravchenko]

What some folks consider to be an Industry Landmark Patent Infringement Case is Sunfire Corporation (Bob Carver) vs. Audio Products International in 2003.

I remember this well. An example of a patent examiner that did not understand the implications of the patent claim, and a patentee that was looking to either game the system. Or get a windfall in royalties. Mr. Carver was no fool.

The claimed inventions were covered by designs that already existed or were a natural and straightforward progression of existing engineering design methods. How many existing audio transducer related patents can that jury's statement be applied to since Harry Olson?

That would be a blanket statement for a great majority of loudspeaker patent claims. I would think is a very fair statement.

 

[smowry]

A natural and straightforward progression of existing engineering design methods on designs that already existed = innovation but not invention. Products can be protected from copy with 14 year Design Patents without claiming invention.

What would happen to the Loudspeaker Industry if we had a 20 moratorium on All Utility Loudspeaker Patents? This would give the industry a break from USPTO's control and hopefully have a chance to heal itself.

 

[mwmkravchenko]

Steve how goes the battle with the new software toys?

 

[smowry]

Hi @mwmkravchenko,


I have the toys installed on my notebook but have not done any simulation yet. The inputs are .dxf files.

Can you send me a surround that you have simulated, so that we can compare results? I will use FINEsuspension which I have never used before. I previously used FINEcone and FINEmotor but the updated programs now have optimizers which are new to me. I was interested in your pro surround that you posted here. Can your send me a .dxf file of that one?