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[John Roberts {JR}]

I would be interesting in knowing what powered speakers might be doing this.   In my experience people really give powered speakers a lot of credit for doing things they really don't.

I vaguely recall finding a patent back in the 70s from Phillips covering a feedback sensor on the LF driver. At the time this was probably used in modest bookshelf sized speakers.

JR

PS: Powered speakers are rich in potential for smart features (mostly protection in early days). Modern low cost DSP offer even more options. Cheap powered boxes are just like cheap non-powered, and at a minimum they probably use active EQ to win side by side comparisons at POS.   

[David Sturzenbecher]

I vaguely recall finding a patent back in the 70s from Phillips covering a feedback sensor on the LF driver. At the time this was probably used in modest bookshelf sized speakers.

JR

PS: Powered speakers are rich in potential for smart features (mostly protection in early days). Modern low cost DSP offer even more options. Cheap powered boxes are just like cheap non-powered, and at a minimum they probably use active EQ to win side by side comparisons at POS.   

In my early audio days (late 90's) I know Kenwood was pitching something similar in their car audio subwoofer line up.   I found this link, which is surprisingly technical for the car audio market. Kenwood Sigma Drive
{EDIT}  After rereading the above article that I posted, it looks like Kenwood borrowed this from their other markets, and not directly originating it from Car Audio{/EDIT}

It does appear that powersoft has the discussed feature set in its IPAL module.   The marketing line states  "One of the greatest limits on achieving outstanding acoustical performance is the lack of a global amplifier-loudspeaker feedback system, linking the electrical and the acoustical signal directly. The Differential Pressure Control" (DPC®) does exactly this: it allows a differential pressure signal, mechanically obtained from the two sides of the moving loudspeaker membrane, to be fed to the amplifier just as any other electrical feedback signal. This grants a complete real-time characterization of the transducer and its acoustical load conditions, allowing for an input signal-to-SPL closed loop design."

https://www.powersoft-audio.com/en/oem-solutions/ipalmod

Is anyone aware of commercial products with this module?

[Frank Koenig]

I would be interesting in knowing what powered speakers might be doing this.

I would, too. But I'm pretty sure no one is going to tell me. I can't help but to speculate.

[Frank Koenig]

I vaguely recall finding a patent back in the 70s from Phillips covering a feedback sensor on the LF driver. At the time this was probably used in modest bookshelf sized speakers.

It was Phillips. The Center for Computer Research in Music and Acoustics (CCRMA) at Stanford had a set of four around 1978. They thought they were the cat's meow back then. Some years later I asked someone about them and they said the speakers always sounded like they were underwater. People's perceptions...

There have been a number of attempts at position-feedback speakers over the years. Meyer had (has?) one that was sold as a large studio monitor. And then Powersoft has the integrated amplifier/actuator for large subwoofers that David mentioned. Has anyone seen one in the wild? No doubt there are others.

--Frank

[Art Welter]

I've been looking at input impedance as a way of getting to excursion but the model is not so simple, requiring values of parameters that we'd rather not have to know a priori. This might be what the better powered speaker manufacturers do for their excursion limiters. I think what folks here would like is a fairly direct way to measure excursion that can be used as a post-design check and for DIY side chain filter equipped peak limiter settings.

All for now. Guess I better stew awhile and save up for that interferometer 

--Frank

Frank,

Although measurement of excursion could be done with an interferometer, and you might find other uses for it, it's easy enough to simply see excursion, and can be easily recorded with video if you want to avoid proximity to the noise.

That said, since you seem to be on to the excursion measurement pursuit as it is related to distortion, since distortion is not specifically tied to excursion, excursion measurement in itself is of limited value.

The "better powered speaker manufacturers" do not employ "excursion limiters" per se, but a combination of high and low pass filters with frequency selective voltage limiting, and drivers designed to withstand the excursion within the voltage delivered. Drivers that can deliver high SPL output with low distortion require very high excursion, very high BL (motor strength) and very robust cones and suspensions, all of which are expensive.

A differential pressure sensing device feedback control loop based system like the Powersoft/B&C Ipal (Integrated Powered Adaptive Loudspeaker) can improve output linearity even more, although few will pay for the improvements that most can not detect in normal concert situations.

Art

[Frank Koenig]

Frank,

Although measurement of excursion could be done with an interferometer, and you might find other uses for it, it's easy enough to simply see excursion, and can be easily recorded with video if you want to avoid proximity to the noise.

That said, since you seem to be on to the excursion measurement pursuit as it is related to distortion, since distortion is not specifically tied to excursion, excursion measurement in itself is of limited value.

The "better powered speaker manufacturers" do not employ "excursion limiters" per se, but a combination of high and low pass filters with frequency selective voltage limiting, and drivers designed to withstand the excursion within the voltage delivered. Drivers that can deliver high SPL output with low distortion require very high excursion, very high BL (motor strength) and very robust cones and suspensions, all of which are expensive.

A differential pressure sensing device feedback control loop based system like the Powersoft/B&C Ipal (Integrated Powered Adaptive Loudspeaker) can improve output linearity even more, although few will pay for the improvements that most can not detect in normal concert situations.

Art

Art, I was pretty much kidding about the interferometer, although if I saw a deal on a nice used one I might be tempted 

My interest in measuring excursion is part just curiosity, but to the extent that there's a practical goal it's more to come up with good limiters for "all conditions" damage protection than controlling distortion in and of itself. In my personal use I rarely push things that hard anyway, but there's always the dropped mic or phantom power pop.

When it comes to what's inside powered speakers, I can only speculate based on what I might try were I the designer. Going in I didn't know how effective a peak voltage limiter using a simple side-chain equalizer is, but, based on what you, David S. and JR are saying, it sounds like it's good enough. On the other hand, amps such as Powersoft do have instantaneous output current measurement built-in, so an approach utilizing that might be a "simple matter of programming", as they say. But it may also fail to confer any advantage.

Thank you all for this discussion.

--Frank

[Lee Buckalew]

In my early audio days (late 90's) I know Kenwood was pitching something similar in their car audio subwoofer line up.   I found this link, which is surprisingly technical for the car audio market. Kenwood Sigma Drive
{EDIT}  After rereading the above article that I posted, it looks like Kenwood borrowed this from their other markets, and not directly originating it from Car Audio{/EDIT}

It does appear that powersoft has the discussed feature set in its IPAL module.   The marketing line states  "One of the greatest limits on achieving outstanding acoustical performance is the lack of a global amplifier-loudspeaker feedback system, linking the electrical and the acoustical signal directly. The Differential Pressure Control" (DPC®) does exactly this: it allows a differential pressure signal, mechanically obtained from the two sides of the moving loudspeaker membrane, to be fed to the amplifier just as any other electrical feedback signal. This grants a complete real-time characterization of the transducer and its acoustical load conditions, allowing for an input signal-to-SPL closed loop design."

https://www.powersoft-audio.com/en/oem-solutions/ipalmod

Is anyone aware of commercial products with this module?

David,
The Martin Audio MLX subwoofer uses the ipalMod and associated B&C 18" drivers. 
They used to have a 21" for clubs called the ASX but it is now discontinued. 

I am not sure who else has an ipalMod system out in commercial production.

Lee

[Caleb Dueck]

David,
The Martin Audio MLX subwoofer uses the ipalMod and associated B&C 18" drivers. 
They used to have a 21" for clubs called the ASX but it is now discontinued. 

I am not sure who else has an ipalMod system out in commercial production.

Lee

Power Sound Audio has a few subs for home theater.  Not for small apartment use!

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