[Duke]

Hello Jim Croft,

Thank you very much for your in-depth replies here.  I greatly appreciate your insights and observations, and your taking the time to offer your experienced advice about patents.   

I am preparing for an informal showing of several of my conventional-technology bass cabs in Seattle this weekend, so my internet time has been limited for the past several days, but next week I should be able to catch back up on things.

[JICRO]

Jim,
I'd be indebted for your comment on the following.  Maybe 15 years ago Bob Carver (yes, that BC) told me that listening tests support the conclusion that human hearing sensitivity to THD in the bass range is so low that humans perceive little if any difference between 1% and 30% THD. 

I posted the above many times and shockingly, no one ever contradicted it.  (Conversely, I presume there is similar agreement that human sensitivity is extremely high to mid range phase and THD.  John Krutke of Zaph Audio posted that humans have little sensitivity to large FR aberrations in the top most octave, IIRC, windows as large as 6 dB.)

Back to bass THD: What's critical about Carver's point is that any money spent reducing THD below the threshold of audibility is wasted.  IOW, THD spec below the threshold of audibility is, in effect, nothing more than window dressing.  I don't know how true or false is Carver's statement, but my experience indicates a resounding yes.

A friend of mine used to build 400+# floor to ceiling line source subs with four or six active 12s.  Over the years I heard several similar sub systems, including IRS III in dedicated sound room.  Every time I heard them I was impressed.  I became convinced their most attractive quality was exceedingly low THD, you know, woofers barely moving except for canon shots, etc.  Now, with further experience of other sub systems with higher THD but natural mode damping features, I'm convinced the most audible feature of the line source subs was their natural mode damping for one of the most audible modes, being floor to ceiling bounce.       

I think the only spec I've ever seen re. modal effects is FR graph or simple numeric dB.  Considering that modal effects are 100% synthetic bass notes generated by distinct numeric relationships (listener or mic location, boundaries, speaker locations) I have always thought that modes expressed as THD can easily be well over 100%.  Please LOL at my guess and correct at will.

But the most critical defect about modes is their effect on timing.  I think of modal effect as a synthetic note only indirectly related to the original note in the music score, and this unrelated note continues playing over the next note appearing in the score. 

I suspect MVW has natural mode damping quality, and this may be among it's best, most audible, and most desirable features.

Hi James,

Just as a point of disclosure, or disclaimer, Bob hired me as a consultant in the early 1980’s to develop the Carver Amazing Loudspeaker (Planar Magnetic Line Source // Dipole Subwoofer) for him, and then in the early 1990’s, I was the Chief Technology Officer at Carver until 1997.  We did a lot of psycho-acoustic threshold testing over a two-decade period, leading up to, and during, that period.

I will attempt to give the short form answer to your question, and then we may want to take it off-line if you wish to explore it further, as this being Audio Kinesis’ forum, I don’t want to inappropriately high-jack Duke’s forum with a non-AK discussion.

In terms of the high threshold of up to approximately 30% for THD at low frequencies, all thresholds are context dependent, but, I’ll give a conditional answer of “Yes” relative to listening to music in a standard living room as the use-model where this very high threshold tends to be realized.

If you are to listen to sine waves, in an anechoic environment, the majority of listeners will have a much lower JND (Just Noticeable Detection) level threshold, by a factor of 10 or more.

So, what we have in standard living room, use-model conditions, is a situation wherein a number of parameters, such as THD and phase, for instance, are masked by more dominant issues, such as environment boundary reflections (modal and non-modal bands) and source program complexity.

“Linear” room modes at low frequencies will tend to dominate over many other “non-linear” forms of distortion (but not all). 

It is somewhat of an over-simplification, but to a great degree, one can make a Pareto list of variables in order of audible and masking dominance for a given audio system interface environment.  In general, as one minimizes or eliminates a top-level system global variable, the remaining local variables will move up on dominance and JND thresholds.

To restate, THD thresholds are determined to a great degree by our binaural, ear/brain psycho-acoustical hardware scanning an audio delivery system dominantly impacted by a the relationship to the environmental boundaries and the nature of the type of complexity of the particular program source (at a given moment).

Your friend's floor-to-ceiling line-source system delivering impressive sound quality is most likely, strongly influenced by, as you suggested, the vertical room mode (and if he maintained an infinite line source throughout the midrange also, it can make for even more improvement by minimizing vertical, correlated reflections, which can be dominant for voice colorations) and also for the multi voice coil derived minimization of thermal compression, which is a type of audible distortion that is more complex that simple THD.

I would suggest that Duke’s conservative approach to minimizing thermal compression is a significant benefit of his design approach.

The position that money spent reducing THD is wasted, is generally true, at least to the degree that one has not yet spent money reducing modal conditions to a point of equaling an anechoic space.

In terms of your notion that modal effects are 100% synthetic bass notes that could be expressed analogously to equal or greater than 100% THD, is I would say at least partially correct, at least as an analogy.

One has to be careful comparing linear vs. non-linear effects, as they disrupt the signal in very different ways from each other, and are also perceived differently from each other.  Modal effects are, mostly (that’s another story for another time), linear where as THD is by definition, non-linear.

That said, the modal output of a room is like adding an additional set of sound sources (like having more speakers that are not very good!, each with substantial frequency dependent amplitude errors) adding their outputs to the primary “real” LF speaker(s).  From this standpoint, one could say that the ‘positive’ modal output is greater than that of the primary signal, and therefore creates more than 100% “linear” distortion.

In terms of modal impact on timing, I’ll save that for later, as it is a more complex subject, both as a produced reality and a psychoacoustic perception.

In terms of MVW having natural mode damping qualities, I have to say that without your experience of the device, I am skeptical of its ability to effectively damp room modes.  From my initial evaluation of the internal structure, I DO believe, that MVW could be effective at damping the internal resonant modalities that normally are problematic with wave-resonant air-columns. In the past, I have effectively squelched negative modal effects of quarter wave air-columns by way of internal structures similar to that shown in the MVW patent.  But, again, I’m not sure what effect you are experiencing with MVW relative to what you experience as “natural mode damping”, so I’m open to learning more about that effect, if it does exist.

I hope this at least partially addresses some of what you were asking about.  If not, please redirect me to the more specific point you were looking to discuss.

Fun stuff…

All the best,

- Jim Croft

[JICRO]

Hello Jim Croft,

Thank you very much for your in-depth replies here.  I greatly appreciate your insights and observations, and your taking the time to offer your experienced advice about patents.   

I am preparing for an informal showing of several of my conventional-technology bass cabs in Seattle this weekend, so my internet time has been limited for the past several days, but next week I should be able to catch back up on things.

Thanks, Duke.  Glad to come play in your neighborhood.

Good luck with the Seattle showing of your wares.

Cheers,

- Jim C.

[Leland Crooks]

Best MVW thread ever.  I cannot tell you how much I appreciate your interest and intellectual skepticism Jim.  We've gotten pretty used to being called liars and worse, instead of honest discussion.  Also the outside opinion from James, who brings much experience as a designer to the table.

The designers have been building a database as we try various transducers in the cabs.  But no apparent commonality other than FS and QTS really jump out.  That's not to say that there is not something we're not seeing.   

 I will completely confess I am out of my depth in this discussion, all of you have vastly more experience/knowledge than I.   I did know enough that when Steve and Tom first approached me about MVW cabs I pretty much ignored them for 6 months.  Loudspeakers don't do what they were telling me.  I finally made a road trip and heard them, first generation cabs.  Dove in headfirst.  The most convincing demonstration was in a high school gymnasium.  Dead even sound field, virtually no drop off front to back.  Nulls in two corners, about a foot wide and 3 ft long. 

I greatly look forward to providing you some systems to listen to.  I started putting the finishing touches on one of the cabinets yesterday.  Yea or nay, all opinions are welcome. 

Back to what I do best, running a table saw, instead of arguing with industry heavyweights.   

[James Romeyn]

Besides giving a huge thanks to Jim Croft for visiting and commenting, adding his wisdom to this forum, I'd like to say the Carver Amazing Loudspeaker is one of my all time favorite loudspeakers.  A friend of mine owns at least three pairs (industry pro, full time audio engineer) and another friend is a regular guy who owns a pair.  A truly great loudspeaker some times overlooked simply because of controversy related to Bob Carver.  I can't believe how great it is to have Mr. Croft in the house!   

[JICRO]

Besides giving a huge thanks to Jim Croft for visiting and commenting, adding his wisdom to this forum, I'd like to say the Carver Amazing Loudspeaker is one of my all time favorite loudspeakers.  A friend of mine owns at least three pairs (industry pro, full time audio engineer) and another friend is a regular guy who owns a pair.  A truly great loudspeaker some times overlooked simply because of controversy related to Bob Carver.  I can't believe how great it is to have Mr. Croft in the house!   

Thank you for the generous accolades, James.

Good to hear from a fan of the Carver Amazing Loudspeakers.  One of my favorite development projects.  It was a rare opportunity, in that we truly had a clean slate as a starting point.  The goal was to create new local variable elements to fall below known psychoacoustic thresholds, and to interface and couple with the Global environment as effectively as possible, regarding both modal effects and wide band room interaction, while achieving bandwidth extension (19Hz to 30kHz) and dynamic capability that had no precedent in prior art gradient devices. 

Almost every component had to be created from scratch.  There was nothing in the transducer and loudspeaker supplier catalogs that could meet our requirements.  So, we developed a new large area full range line source planar magnetic transducer from components and processes adapted from unusual, non-audio sources, such as weather-stripping component manufacturers and automobile pin-stripers. 

David Graebener (formerly of Speakerlab, Bohlender-Graebener, and now Executive VP of technology at Wisdom Audio) and I developed the planar magnetic line source transducer together.

The open-dipole woofer transducers had such unusual parameters we were rejected by over a dozen transducer manufacturers with the same reply; “It can’t be done”.  So we had to design them ourselves and have them built in Japan by the one manufacturer that was willing to be adventurous. 
(To optimize the novel gradient alignment, the four 12” woofers each had a 12 gram moving mass, an X-max of 20 mm, 26 Hz fs, and a Qts of 2.7; unusual to say the least).

Okay, enough self-serving reminiscence.  But, for those interested, I will be repeating the story daily, at the Old Folks Home for Loudspeaker Engineers, starting in about 15 years.

All the best,

- Jim C.

[James Romeyn]

My professional studio experience ended circa Herbie Hancock's Headhunters and soon after Roy Buchanan's last album In The Beginning.  (Dr. Patrick Gleeson was likely at least equal to then-Walter-now Wendy Carlos in analog synthesizer proficiency...Gleeson tutored me in synthesizer programming, introduced Hancock to the synth, co-owned Different Fur Trading Co. studio at which Headhunters was recorded, and I'm pretty sure co-engineered the album with John Viera...I was apprentice engineer and programmed synth for In The Beginning at Sausalito Record Plant).

Suppose some particular studio or pro sound person "X" found every single performance quality of MVW simply irresistible...except for one quality being dynamic range increasing with SPL.  What is the least costly method whereby such person X could modify the signal inversely relative to the unwanted dynamic range expansion, and being otherwise completely transparent to performance quality?     

[JICRO]

My professional studio experience ended circa Herbie Hancock's Headhunters and soon after Roy Buchanan's last album In The Beginning.  (Dr. Patrick Gleeson was likely at least equal to then-Walter-now Wendy Carlos in analog synthesizer proficiency...Gleeson tutored me in synthesizer programming, introduced Hancock to the synth, co-owned Different Fur Trading Co. studio at which Headhunters was recorded, and I'm pretty sure co-engineered the album with John Viera...I was apprentice engineer and programmed synth for In The Beginning at Sausalito Record Plant).

Suppose some particular studio or pro sound person "X" found every single performance quality of MVW simply irresistible...except for one quality being dynamic range increasing with SPL.  What is the least costly method whereby such person X could modify the signal inversely relative to the unwanted dynamic range expansion, and being otherwise completely transparent to performance quality?     

Hey James,

Great to learn more about your background.  Very interesting.

In terms of the dynamic range issue, assuming that it is real, then the first thing we would need to do is to capture the transfer function of the effect.  Then we can decide if there is a direct inverse process that is practical. 

Again, I don't yet know if it is a significant issue or not, but, if so, I think it would probably be best dealing with it acoustically.  It will be interesting to see how much the effect actually manifests itself, and then also determine how entrenched the effect is in the MVW "acoustic process".  Is it possible to isolate, and control, without altering other favorable attributes.

But, I think we are getting ahead of ourselves.

I am certainly curious to learn more about how a dynamic range expansion effect within a passive acoustic loading system can even come into existence in the first place.

Currently, if you were to list all of the individual positive attributes of the MVW, what would be on that list?

Also, is the system supposed to have inherent bandwidth/enclosure volume/efficiency advantages over the prior art, such that it surpasses Hoffman's Iron Law?

All the best,

- Jim C.

[steve f]

From someone who finds some of this "over my pay grade" I am fascinated with the MVW concept. Also way cool to read the related anecdotal  stories. Thanks guys.

Steve

[genjamon]

While the technical issues are also absolutely beyond my pay grade, I have to say this dynamic expansion business sounds suspiciously like a violation of either Newton's first or second laws, or both.

[James Romeyn]

While the technical issues are also absolutely beyond my pay grade, I have to say this dynamic expansion business sounds suspiciously like a violation of either Newton's first or second laws, or both.

Yes, it certainly does seem to turn certain laws of physics upside down.   

[Leland Crooks]

I'll give some of these a go. 

I am certainly curious to learn more about how a dynamic range expansion effect within a passive acoustic loading system can even come into existence in the first place.

Electrically there's no change in sensitivity in the cabs.  Acoustically there appears to be.  At least to the ear.  What we do know for sure is the system creates a soundfield unlike anything else.  The closest comparison is a line array.  Most of our testing and real world applications have been in the pro sound field.  The MVW system creates a defined sound field that changes in size with the amount of power applied.  There's boundary that's very apparent when running a system outside, or in a large venue.  For example, running 4 2x8 prototype cabs per side at an outside show last year the engineer and I were walking the venue prior to the show with low power running.  About 30ft from the stage you would take a couple of steps and the sound would just drop, at least 6db.   During the show while the cabs were running up to power, that boundary effect had moved out approximately 300ft from the stage. My admittedly inaccurate phone was showing 3db dropoff per doubling of distance until I got to the boundary, when it converted to farfield dropoff.   A 4ft tall stack is certainly not enough to create line array effects via traditional cabs.  I will be providing the system for all the concerts in the park in my town this year, and this time I'm bringing real test gear. 

All I know for certain is the louder you play them, the better it gets.  One of the gremlins we've been chasing for a year is getting that at lower power levels.  The originals required about 30% to really create the soundfield.  We've got that down to about 10-15% for the full effect, and it's there even at low power, just not as apparent. 

Currently, if you were to list all of the individual positive attributes of the MVW, what would be on that list?

It feels like wearing a fine pair of headphones.  Very in your head sound.  Imaging that rivals practically anything I've heard. Not just width, but depth also.  Imaging that has almost no sweet spot.  You can be on axis with a cab and still have imaging, not as wide, but it's still there.  Very little regard for placement.  It's just not critical.  They just work about anywhere.  That's not to say there's no optimums, but for the vast majority just set them up and play. 

Also, is the system supposed to have inherent bandwidth/enclosure volume/efficiency advantages over the prior art, such that it surpasses Hoffman's Iron Law?

Nope, Hoffman still rules, but he gets bent pretty hard.  Because we get reinforcement through the side waveguides up to almost 5k, there's nearly as much output from them as there is off the face of the driver.  A typical MVW alignment with 2 drivers will have spl in the range of a normal ported cabinet with 4 drivers.  Complete integration occurs about 1-2 ft in front of the cabinet.

[steve f]

Is there any chance that a pair might make the rounds of shows like Axpona or similar?

[Duke]

Just as a point of disclosure, or disclaimer, Bob hired me as a consultant in the early 1980’s to develop the Carver Amazing Loudspeaker (Planar Magnetic Line Source // Dipole Subwoofer) for him, and then in the early 1990’s, I was the Chief Technology Officer at Carver until 1997.  We did a lot of psycho-acoustic threshold testing over a two-decade period, leading up to, and during, that period.

YOU DESIGNED THE CARVER AMAZINGS?  Wow, that is one of the most intelligent loudspeaker designs of all time!  You are invited to talk all you want about the Carver Amazings or any other subject here, anytime!   I take off my virtual hat and bow deeply in your digital presence.   Bob Carver is indeed as smart as we thought, but for a different reason - he was smart enough to hire you! You are more than welcome to talk about anything you want here - in fact, you are actively invited to - I don't care if it's about designs that I compete against, your work is legendary and I don't want you to feel like you have to censor your speech.   

Also, is the system supposed to have inherent bandwidth/enclosure volume/efficiency advantages over the prior art, such that it surpasses Hoffman's Iron Law?

That's not a claim that I would make at this stage; I've seen woofers in MVW enclosures go a bit lower than I would have expected, but the box size ends up being large enough (in the MVW speakers I've had hands-on experience with) that, in my opinion, Hoffman doesn't seem to be overthrown.   

While the technical issues are also absolutely beyond my pay grade, I have to say this dynamic expansion business sounds suspiciously like a violation of either Newton's first or second laws, or both.

This is just speculation on my part:  Maybe as the SPL goes up, the acoustic radiation resistance of the MVW enclosure increases, resulting in improved impedance matching with the air, and the net result is a bump in efficiency compared with the low SPL condition.   

Is there any chance that a pair might make the rounds of shows like Axpona or similar?

We will be showing a MVW speaker at Rocky Mountain Audio Fest in early October, room 1100.  Current plan is to show a stand-mount design that is still under development at this point, but that hasn't been carved in stone yet.

[PMAT]

Duke, you hooked me and others with the openness of that invitation to speak of the Carver designs. Can't we all learn from other great deigns? Yes we can.

[Duke]

Duke, you hooked me and others with the openness of that invitation to speak of the Carver designs. Can't we all learn from other great deigns? Yes we can.

Thank you!

JIRCO, if you want to start a new thread here with Carver Amazing in the title, or if you would rather I start the thread (as long as you'd be willing to post in it), let me know.   I think that would be of interest to a lot of people, and would do better with its own thread title.   If you don't have time and/or don't feel free to do so because of confidentiality agreements or considerations, like need to keep trade secrets secret, I certainly understand.

[JICRO]

YOU DESIGNED THE CARVER AMAZINGS?  Wow, that is one of the most intelligent loudspeaker designs of all time!  You are invited to talk all you want about the Carver Amazings or any other subject here, anytime!   I take off my virtual hat and bow deeply in your digital presence.   Bob Carver is indeed as smart as we thought, but for a different reason - he was smart enough to hire you! You are more than welcome to talk about anything you want here - in fact, you are actively invited to - I don't care if it's about designs that I compete against, your work is legendary and I don't want you to feel like you have to censor your speech.   

Very kind words; Thanks, Duke.

Of the many loudspeakers I have developed over the years, the Amazings for Carver, and more recently, ( the clue ) for Sjofn HiFi, are two that were most enjoyable, primarily, because they were developed from a clean slate of no preconceived notions, other than attempting to raise the bar.  Both systems took about two years each to develop, which is a longer time frame than what is normally allowed.

I have a hard deadline to finish a new LF signal-processing patent I'm filing in the next couple days, but once that is complete I'm glad to answer questions or discuss any topic with you and your gang here any time or in any format that is works for all involved. 

I'll watch for any questions that pop up here, and just let me know if the conversation moves elsewhere.

Thanks again for your generous comments.

All the best,
 - Jim C.

[JICRO]

For those that are interested, the Spring 2014 issue of the online magazine Bass Gear has a review of an MVW product, with a background story,  a measurements section, and a little bit of technical disclosure by the inventors of the MVW systems.

Three different sections, from page 60 to page 73.

I was surprised that it hadn't been posted here, so I thought I would do so.

http://btpub.boyd-printing.com/publication/?i=204655&p=60

Enjoy,

- Jim C.

[Rubbbq]

These were Just delivered. To soon to know if it will be a love affair  , need to run them in for a bit. Didn't have proper stands, so I whip up some made of copper pipe I had sitting around....

[Russell Dawkins]

Very curious about your impressions. I like the copper pipe stands!