No, I am interested. Does the one you have use analog circuitry to convert the velocity feedback to positional, or a DSP, or something else? the link you gave was promoting a subwoofer driven by a servo motor!!! Now that is different, the feedback is directly related to position, unlike a feedback coil on the woofer.

Servo there is used as short for servomechanism, to mean a technique for controlling the voice-coil using motion feedback, not necessarily using a servo motor.

Here's another article from Rythmik Audio, that discusses their approach.
They describe the feedback as from a specialized microphone, so it's not clear exactly what that means.
My initial understanding was that it was a small added coil.
That's as much as I know about the one I have (and that it works well).

Interesting, when I bought mine (just the bare speaker and feedback-amp as he didn't sell cabinets), I went directly to the company owner/designer, who was working out of his garage at that time in southern California (seems like he's expanded a little since then).
I then had a custom cabinet built to house it.
It's a really heavy speaker, so I need to use a hand-truck to move it any significant distance.

 

So a passive filter (integrator?) operating with no delay. That explanation makes me even more skeptical.

Or, perhaps everyone who uses a PID controller to accurately control position is just over engineering it. What do I know?

 

So a passive filter (integrator?) operating with no delay. That explanation makes me even more skeptical.

Or, perhaps everyone who uses a PID controller to accurately control position is just over engineering it. What do I know?

Delay?
Why would you want a delay?
Seems any delay would have an adverse affect, as this is for real-time control of a moving voice-coil.
I would imagine he's not real clear about the feedback circuit, so as to not give potential competitors any useful information.

But you obviously remain a serious skeptic of the approach, so have no more info to help with that.

 

Why would you want a delay?

Where did I say I would want a delay? My physics knowledge tells me that no delay is impossible. How much force does it take to move a 50 gm mass 1cm in 0 seconds?

What they said is clearly a lie, so why should I trust anything they say? Had they said minimal delay, I would have been less skeptical, and if they said a 15 microsecond delay per mm of excursion, I would take it seriously.

Edited: Changed 10g to 50g, which is the typical moving mass of a 10 inch subwoofer.

 

Okay, I misunderstood.
You are referring to the article saying that it operates with "no delay".
I would assume that means no discernible or practical delay in controlling the cone movement (note that we are talking about movements of no more than about 100Hz maximum), since he was writing for the general public, not engineers.

But if you want to get your shorts in a snit about that, I can't help.
I recommend you read no more about it and keep your naysayer status clean.

 

Probably that "delay" is like the "feedback transient delay" that some brand of amplifier company was touting that they had beaten. The claim had been that the "delay" in an amplifier's feedback loop was the source of some exotic form of distortion, which was claimed to exist "until the feedback system stabilized itself". Their system evidently sensed the distortion prior to it existing, thus solving the problem. I never got to see the negative time circuit, unfortunately.

As for the speakers with the feedback servo system being so very heavy, consider that if the section with the magnetic field is made a bit longer than the voice coil motion, there will not be much variation in the force for the servo to correct. So the servo is solving a problem that has been removed already. That sort of solution is easily demonstrated to work very well.

 

So the servo is solving a problem that has been removed already.
That sort of solution is easily demonstrated to work very well.

Really?
Who has demonstrated this?

There are non-linearities in the spider return force causing harmonic distortion, frequency response peaking due to speaker resonance, low-frequency rolloff, and transient response issues, all unrelated to the uniformity of the magnetic field, that are also addressed by using motion feedback.

Don't quite understand all the negativity to using this form of motion feedback in a subwoofer.
The improvement in performance requires only a small increase in complexity and cost.
Nobody but a few with the "golden ear" argues about not using feedback in an audio amp, why should it be different for the sub?

 

Nobody "Demonstrated this." What I see is that if a package already includes additions that will tend to remove the cause of problems, then the addition of mechanisms intended to solve those problems may be redundant.

I also question the ability of folks to perceive the difference from removing that last 0.02% of distortion.
I also question the benefit and value of removing that very last shred of distortion. Is it the emotional satisfaction of believing one has achieved what others have not achieved??? Certainly any actual benefit is transient, existing only for the moment that claimed distortion is present. So my question is how much is that momentary thrill actually worth???

 

 

Nobody "Demonstrated this."

Well, you implied that someone had.

What I see is that if a package already includes additions that will tend to remove the cause of problems, then the addition of mechanisms intended to solve those problems may be redundant.

As I noted, not all the deficiencies of a subwoofer are solved by just having a uniform magnetic field, so I don't see negative feedback as redundant.
So what other "additions" are you referring to?
Or is that another rhetorical comment?

I also question the ability of folks to perceive the difference from removing that last 0.02% of distortion.

True, they likely can't, but subs have a couple orders of magnitude distortion greater than that.
A typical good subwoofer distortion is in the several percent region, and second-harmonic distortion adds tones that audibly clouds the sound of very low frequency effects, so a reduction of that distortion is quite perceivable.

Below from Audio Science Review shows how low frequency distortion is more audible than higher frequency distortion, which is because the ear is much more sensitive to the low-frequency harmonics as compared to the fundamental:

Very low frequency distortion is perceived “inflated,” based on Fletcher-Munson as updated in ISO226:2003. For example in the chart (transposed as Equal-SPL contours), at 30Hz a typical mid-quality SW measuring 3% THD sounds like 25%; like 10% at 60Hz. The harmonic artifacts generated, mostly by the SW driver, are post crossover, so are not filtered by it, causing auditory confusion with the main speakers’ “soundstage.”

 

Here’s what good transient response would get you:

I’ve seen them live a couple of times, a really fun show.

 

Really, Now I am wondering as to what sort of music with the very low frequency elements is being reproduced. Not symphonies and not violins and certainly not operas or most other vocals.
What I HAVE HEARD with the very deep bass would SOUND MUCH BETTER with at least 50% harmonic distortion. And if the only comparison is to a live performance, most of the live performances I have seen utilized quite a bit of electronic equipment. Many concerts in most venues use some sound system assistance. And if the mixing panel is set for anything other than perfectly flat, that is distortion.

 

Your take on sound reproduction gets more and more interesting.
Okay, down the rabbit hole--

Now I am wondering as to what sort of music with the very low frequency elements is being reproduced.

How about a pipe organ with with the largest going down to 8Hz.
A Grand Piano has the lowest note of 27.5Hz, a double bass is around 41 Hz, and the contrabassoon gets down to around 32 Hz .

From Google AI:
In an orchestra, low frequencies, also known as bass or the low-end, are produced by instruments like the double bass, contrabassoon, and the lower sections of the cello, viola, and violin. These frequencies typically range from 16 to 250 Hz and are crucial for establishing the rhythmic foundation and harmonic depth of the music.

What I HAVE HEARD with the very deep bass would SOUND MUCH BETTER with at least 50% harmonic distortion.

Well, we've all heard of those with a "golden ear".
Yours apparently is tin.

Hard to imagine why you think low bass notes sound better with 50% distortion(?).
Obviously you should buy the cheapest subwoofer you can find.

Many concerts in most venues use some sound system assistance. And if the mixing panel is set for anything other than perfectly flat, that is distortion.

No.
Distortion is harmonics added to the music due to non-linearities in the reproduction system.
Variations from flat in the room frequency response are just that--variations, and not necessarily due to anything non-linear.
The mixing panel may be adjusted to compensate for the room acoustics, which is generally far from flat with numerous resonant frequencies, to make a flat response in the room, and that's not adding distortion.

 

OK, the only reproduced "music" that I have heard with that extended bass, in the past few years, is that garbage called "rap", mostly with lyrics intended to offend, and always delivered at a level louder than heavy traffic noise.
The pipe organ music I have heard was always LIVE, and the live symphony music in performances that I would not expect any recordings to possibly duplicate in any form. While somehow reproducing the "presence" of a concert-hall performance is certainly interesting, in reality I don't see it being practical. Reproducing a copy includes understanding that it is only a copy, not the original. A lot like an excellent photograph of a wonderful meal setting versus the actual "wonderful meal setting." The copy is not the original nor can the copy ever be the original. That is just how reality works.

 

I would not expect any recordings to possibly duplicate in any form.

A really good stereo system will come close.
Look up Linkwitz audio.

The copy is not the original nor can the copy ever be the original. That is just how reality works.

And how does that pertain to this discussion about subwoofers?

 

A Grand Piano has the lowest note of 27.5Hz, a double bass is around 41 Hz, and the contrabassoon gets down to around 32 Hz .

And it would be extremely rare to use those notes in any music performance. My piano teacher plays a wide variety of music for me at the end of my lesson, and I don’t think any of it has included any of the bottom half octave or so.

 

And it would be extremely rare to use those notes in any music performance. My piano teacher plays a wide variety of music for me at the end of my lesson, and I don’t think any of it has included any of the bottom half octave or so.

So I guess you don't need a subwoofer for any system you have.

 

My crappy 10" Yamaha sub has "Advanced Yamaha Active Servo Technology II"

So, it can't really be anything special or unusual.

 

My crappy 10" Yamaha sub has "Advanced Yamaha Active Servo Technology II"

So, it can't really be anything special or unusual.

Depends upon how they implemented it.
Could be just mostly an advertising gimmick phrase (gasp).

 

So I guess you don't need a subwoofer for any system you have.

FWIW, some home theater receivers have a "pure direct" mode meant for music listening, without any special processing. This setting disables any signal to the subwoofer.