EnABL - Technical discussion

[soongsc]

Hi Scott,

I see that Snoogsc has highlighted your words from your Post#193 without explaining why.

In this post you posed a 'think about it' question.;-
>> The impulse response only displays the linear behavior on one axis. The question then is: is a look at one axis sufficient? <<

Surely anything which modifies an amplitude or frequency or phase or group delay response is going to generate a resultant observable as an amplitude response variation in time, and John L's EnABL baffle surface ring tests do have the required second axis - Time ?
Thus all of these aspects must cover the dynamic response too.

There must be a specific time delay related to any possible first change induced by a ring or pattern etc., and therefore any waveform modification must be first apparent after that specific time delay, and a concentric ring wrt a circular driver would have a more recordable effect wrt that driver than to any baffle edge induced effect.

What an impulse test cannot show is any change related to the final development of highly resonant modes, but it would still reveal a time delayed initial change which might induce that same resonance.

I agree that an on-axis response cannot tell the whole story either, but John has shown us that he can accurately resolve to low levels within a waveform, and if *nothing* shows down to say minus 50dB., then that result must be definitive.

An axial microphone which is too close (short time axis) can however cancel out some of the audible beaming effects which are due to driver size and shape and audible at a listening position. We only have to place our own ears closer to a cone driver in order to observe this change.

To retain a short time axis, maybe a close microphone is better positioned where it might detect any change due to edge patterns, as if the edge were the source.

Cheers ........... Graham.

Somehow my typing got inserted into the wrong place, which should say:
As John mentioned the time scale of the graph and the location of the patterns, I do not get the impression that the graph contains the edge diffraction.

 

[Graham Maynard]

Hi soongsc,

Agreed.

The time axis did not appear long enough, nor the excitation regular enough to illustrate possible baffle edge induced wave motion re-combining with (tuning) driver output from within the driver aperture.

So although the thousandths high fixed baffle ring had an expectable neglible effect, no other edge modifications were examined.


Cheers ............. Graham.

 

[john k...]

Hi John,

You wrote;-
>> To the contrary. Everything you are referring to still falls within the realm of linear behavior. <<

Thank you for responding in this regard.

Linear related to amplitude - yes; but all components linear in music time wrt the eventually propagating waveform ?

Not trying to be funny - hope you get my drift - and whether EnABL might modify observed waveform linearity in time.

I'm with Soongsc, and would love to see a pair of edge related measurements with appropriately sized pattern, whether at edge of baffle, driver aperture or port, none of which could affect the cone mass distribution.

Cheers ....... Graham.

I think there is great misunderstanding of what is meant by linear. Just because something is complicated doesn't mean it isn't linear. Acoustic waves and their development are, at the pressures associated with sound and sound generation, governed by linear relationships. We don't get into serious nonlinearity unless pressures and velocities get large. And even then we have to separate out how nonlinearity affects things. For example, when the pressure gets high, which can happen in a compression driver of a PA system the predominant form of nonlinearity is that it causes 2nd order distortion. But even in that case, the resulting distorted wave propagates in accordance with linear relationships. That distorted wave propagates unaltered from the source with only the amplitude being reduced due to expansion into 3-dimensional space. We don't have to consider nonlinear effects in wave propagation until pressures get well beyond those associated with sound generation. (More on that later).

How the wave form radiated from a driver develops can be looked at as being the summation of many point sources on the driver radiating surface. Each of the sources radiates a unique signal, related linearly to the input. At any point in space the final wave form is the sum of the radiation from all those sources.

That loudspeakers are predominantly linear devices is a requirement for any type of sound system with in not going to introduce large distortion. Of course there are limitations to the linear range. Compression, exceeding the excursion limits... introduce distortion. Still, the resulting wave phenomena remains governed by linear physics.

If you look at this figure from Art Ludwig's web site

it shows the near field pressure from a cone driver at a frequency with wave length equalt to the cone radius. It appears to be very complex but it is calculated using linear theory. Here is the far field radiation pattern

An externally hosted image should be here but it was not working when we last tested it.

It is clear in the near field plot that the pressure develops into this pattern as the waves move off the cone. It is a linear result though.

From my point of view, the most difficult part of this threat is that the audience is composed of many people with different level of understanding of the physics involved. Can you imaging Newton posting on the internet that by dropping objects of different mass from a tower he was able to determine that all objects fall at the same rate and the acceleration due to gravity is constant? Sure Isaac, but what if you drop them from a different height? What if you throw them up in the air and watch then drop? What about the turbulent boundary layer? And how about that feather? Some of his audience just wouldn't get it. It's the same way here. If you don't get it, that is fine. I am just going to present my data and/or analysis and for those who understand it, fine. For those who care to accept it, fine. For those who reject it, fine. I will only say that anything I do should be easily repeatable by anyone who have the capability for perform similar measurements/analysis and that most if not all of any analysis I post can be verified by examining relevant reference material. No black magic, not mystery, no hyperbole. In that sprit please don't expect me to address each and evey question or objection to what I post.

 

[john k...]

I might be missing somthing as well, but it seems much more easier to measure at a location that captures both original impulse and diffraction impulse by using an existing speaker, why go through all the effort to measure from a baffle and flush mount the mic? If the diffraction impulse cannot be measured, then that means the pattern effects cannot be measured either. However, if we can look at the main impulse and the diffraction impulse, things are brought into perspective.

One thing to also consider is look at the SPL of the impulses before and after the rings. What seemingly is very small in the impulse might show more differences when looking at the frequency composition.

1) Soongc, you really don't get it. This is NOT about edge diffraction. It is about, and only about, how an enable patch effects an acoustic wave passing over it, void of other influences. PERIOD.

2) the frequency for all three conditions in my last impulse response data post is identical. You can not see any differences at all.

 

[dlr]

Re: Re: Re: Re: Anyone, please offer your analysis of John's posted data

Since i've only started to be able to capture FR data, my comment was based on impedance (T/S parameters) which show significant chandes depending on weather.

dave

Be wary of basing too much on T/S parameters. They vary from measurement to measurement and aren't as repeatable as an FR measurement is. The T/S params vary with break-in of the driver as well, of course. You'll find far less variation in the FR, other than around the driver Fs with break-in. The other consideration is voice coil heating. That can change the T/S params very quickly. Make two T/S measurements back-to-back and you're likely to see differences. Do that with an FR and you'll see much less change.

Dave

 

[Graham Maynard]

Hi John,

I agree with your comment;-
>> I think there is great misunderstanding of what is meant by linear.<<

Without doubt wave motion /propagation through a constant medium like room air is linear, but between a cone and the eventual effective launch plane for any wave (which arises wrt the aperture and not at the cone), molecular motion must be complex.

Thanks for the near-field pressure illustration from Art Ludwig's Website. Very interesting.

I cannot help but note that where Bud has empirically found the best position for his raised EnABL pattern to be applied is where the pressure gradations are green.
I have not seen a visualisation like this before and thus I cannot know the significance of any coincidence at this stage.

Going back to my earlier posting, I would love to see the pressure gradients when the radiating wavelength equals an odd number of half wavelengths wrt aperture/cone diameter.

Cheers ............ Graham.

 

[auplater]

more unsupported speculation

Hi John,

I agree with your comment;-
>> I think there is great misunderstanding of what is meant by linear.<<

Without doubt wave motion /propagation through a constant medium like room air is linear, but between a cone and the eventual effective launch plane for any wave (which arises wrt the aperture and not at the cone), molecular motion must be complex.

and you know this how? Any tests you've run to show this would be of value. or perhaps you can point to the definitive study on the web?

Thanks for the near-field pressure illustration from Art Ludwig's Website. Very interesting.

I cannot help but note that where Bud has empirically found the best position for his raised EnABL pattern to be applied is where the pressure gradations are green.
I have not seen a visualisation like this before and thus I cannot know the significance of any coincidence at this stage.

Cheers ............ Graham.

Actually, they don't.... if you look carefully. And this is for one frequency only. I believe any perceived coincidence is just that.

John L.

 

[soongsc]

1) Soongc, you really don't get it. This is NOT about edge diffraction. It is about, and only about, how an enable patch effects an acoustic wave passing over it, void of other influences. PERIOD.

2) the frequency for all three conditions in my last impulse response data post is identical. You can not see any differences at all.

I know I must be missing something because if our goal is not to determine whether it helps reduce baffle diffraction impulse. Why do we want to make the study at all? I'm not looking into it just for the fun of it even though it is a small part of the reason.

 

[sreten]

From my point of view, the most difficult part of this thread is
that the audience is composed of many people with different
level of understanding of the physics involved.

Hi,

From my point of view, it what you are saying, and only what you
are saying, that is not being understood, seems sometimes willfully.

The point of enquiring deconstruction of a particular case to the
more general case for a phenomena seems to be lost on some.

It seems to me that the postulate is :

if A is measurable then so must B be measurable.
On investigating B it is not measurable.
It follows that A will not be measurable.
That B is not A is irrelevant (and all the "details" of A).

So you are back to the postulate, which seems to me to be however
complex A may be, the simpler B must be shown to have an affect
for an interference with other known effects to be viable in A, this
seems a valid position to me.

/sreten.

a reference for dlr :
http://www.klippel.de/pubs/Klippel papers/Measurement_and_Visualization_Cone_vibration_06.pdf
this ones been mentioned by dlr :
www.klangkultur.net/site/media/pdf/FaitalPRO/Laser_Doppler_Vibrometry_Ancona_2002.pdf

 

[auplater]

Hi,

From my point of view, it what you are saying, and only what you
are saying, that is not being understood, seems sometimes willfully.

The point of enquiring deconstruction of a particular case to the
more general case for a phenomena seems to be lost on some.

It seems to me that the postulate is :

if A is measurable then so must B be measurable.
On investigating B it is not measurable.
It follows that A will not be measurable.
That B is not A is irrelevant (and all the "details" of A).

So you are back to the postulate, which seems to me to be however
complex A may be, the simpler B must be shown to have an affect
for an interference with other known effects to be viable in A, this
seems a valid position to me.

/sreten.

a reference for dlr :
http://www.klippel.de/pubs/Klippel papers/Measurement_and_Visualization_Cone_vibration_06.pdf
this ones been mentioned by dlr :
www.klangkultur.net/site/media/pdf/FaitalPRO/Laser_Doppler_Vibrometry_Ancona_2002.pdf

I think your syllogism will be lost on those it was intended for...

John L.

 

[dlr]

a reference for dlr :
http://www.klippel.de/pubs/Klippel papers/Measurement_and_Visualization_Cone_vibration_06.pdf
this ones been mentioned by dlr :
www.klangkultur.net/site/media/pdf/FaitalPRO/Laser_Doppler_Vibrometry_Ancona_2002.pdf

Thanks for the document links. The graphs from the second one were first referenced and posted by john k, however.

Dave

 

[john k...]

Hi John,



Without doubt wave motion /propagation through a constant medium like room air is linear, but between a cone and the eventual effective launch plane for any wave (which arises wrt the aperture and not at the cone), molecular motion must be complex.

Thanks.

Cheers ............ Graham.

We are dealing in the realm of continuum mechanics here. Not free molecular flows etc. We do not need to look at things on a intermolucular level until the length scales are on the order of the mean free path. In air at normal conditions that is about 6.5 x10^-8 meters (2.55 x 10^-6 inches). If you consider that as a relative length scale we need to be looking at frequencies of the order of 5 x 10^9 /sec, ( 5 Gigahertz) well above the audible upper range at 2x 10^4/sec (20 K Hz.

Let's try to keep it real.

 

[Graham Maynard]

Hi John L.

Of course that illustration was for only one frequency !?

Hi John K.

>> "Keep it real" <<
So where did I write "molecular flow" ?

Until 'experts' with equipment do the tests already requested and reveal the truth either way, I cannot see any point in anyone making any further communications within this thread.

Only fools make assumptions; whether those be technically related or about what they imagine other people 'get or don't get'.

Manners maketh man ....... Graham.

 

[john k...]

Hi John L.

Of course that illustration was for only one frequency !?

Hi John K.

>> "Keep it real" <<
So where did I write "molecular flow" ?

Until 'experts' with equipment do the tests already requested and reveal the truth either way, I cannot see any point in anyone making any further communications within this thread.

Only fools make assumptions; whether those be technically related or about what they imagine other people 'get or don't get'.

Manners maketh man ....... Graham.

Sorry I've upset you so, Graham. Bye.

 

[sreten]

I cannot see any point in anyone making any further communications within this thread.

Hmmm.....

To be frank I've got no interest in your pompous pontifications,
incoherent pseudotechobabble and your hypocritical habit of
ending each post with a snide at someone / some people.

Your full of the proverbial it seems me.

/sreten.

 

[BudP]

John K,

Thanks for your diligence. This is getting very educational.

For what it is worth, the added red spots here are where the rows would be placed on the cone, from Art Ludwig's site. The set in the middle area of the cone, from empirical applications, appears to need to be placed at about the 2/5's distance from dome joint to cone edge. These are soongsc's pattern set additions, arising from his testing.

It is quite interesting to me to see what is going on at that point.

Bud

 

[auplater]

wrong thread

John K,

Thanks for your diligence. This is getting very educational.

For what it is worth, the added red spots here are where the rows would be placed on the cone, from Art Ludwig's site. The set in the middle area of the cone, from empirical applications, appears to need to be placed at about the 2/5's distance from dome joint to cone edge. These are soongsc's pattern set additions, arising from his testing.

It is quite interesting to me to see what is going on at that point.

Bud

I think we all know where the dots go.... this is misrepresentation, as the dot scale - to driver is much smaller than what you've drawn in. Besides, as I said to Graham, they don't really correlate to anything shown in Art's plot, and even if they did (which they don't) so what? John K's already shown that waves passing over micro-dots don't do anything special.

I think this should go to the other thread, since it's psuedo-technical grasping at straws.

John L.

 

[dlr]

John K,

Thanks for your diligence. This is getting very educational.

For what it is worth, the added red spots here are where the rows would be placed on the cone, from Art Ludwig's site. The set in the middle area of the cone, from empirical applications, appears to need to be placed at about the 2/5's distance from dome joint to cone edge. These are soongsc's pattern set additions, arising from his testing.

It is quite interesting to me to see what is going on at that point.

Bud

What's the relevance? The graph is for a single frequency, useful for analyzing the radiation pattern at that frequency for that driver. The pattern placement, any pattern placement, doesn't show anything useful in that context.

Dave

 

[Graham Maynard]

Hi Sreten,

I do not appreciate you taking my words out of context to make it appear I said something different to those written.

You might not appreciate my sincerity in wishing to progress towards a solution, but your Post#215 is a deliberate misrepresentation which turns personally qualified opinion into an unmade statement.

Proof of no effect on a flat baffle, is not proof of no effect at points where EnABL is applied beside cone surface discontinuities !

We could have already had definitive answers by now, and we will have them some day, but when ?


Graham.

 

[Carlp]

To be frank I've got no interest in your pompous pontifications,
incoherent pseudotechobabble and your hypocritical habit of
ending each post with a snide at someone / some people.

Your full of the proverbial it seems me.

As if he's the only one... This is really quite humorous.

Carl