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Old 16th July 2010, 03:55 AM   #6701
g3dahl is offline g3dahl  United States
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Originally Posted by chrismercurio View Post
Gary,

I hope the opera was wonderful. It must be quite a rush, even though it's a lot of work' to conduct one of those.
Quite a rush indeed! It was a great experience. I do plan to write more about this, but not until after this weekend's performances.

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Did you spring for the Apollo option for your TD drivers?
I did for the TD15M's, but not for the TD15H's. The latter were purchased secondhand. The price difference between Apollo new and non-Apollo used was substantial!

Gary Dahl
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Old 16th July 2010, 04:08 AM   #6702
BudP is offline BudP  United States
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The usual conflict between me n wood. On the other hand, the DCX2496 is currently undergoing surgery with Jan's control board, the drivers are EnABL'd and Randy, of the wild nude Lowther stand, has shown interest in making fitting nude Lowther fixtures for the boxes. In fact, yet another dithering redesign of the woofer box is underway, just to provide some more dramatic substance for Randy's work to set upon.

So, just as slow as I expected.
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Old 16th July 2010, 11:00 AM   #6703
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Default How does this model...?

Hi Guy's,

Very glad this thread is active again and more interesting ideas to ponder...

When running in big pro bass drivers its common practice to place the left and right speakers face to face, reverse polarity on ONE speaker, turn up the 800 watt power amps , put on some killer bass tracks and leave home for the weekend... Anyone who has tried this knows that even OUTSIDE the building the audible effect of reversing polarity on one channel is huge.
In normal domestic systems try reversing polarity on one of your bass drivers and have a listen. The effect is very easy to hear and feel if you have a true full range system.

Now my suggestion / question...
In recent threads close attention is paid to the nature of sound waves generated by drivers mounted on open baffles, and specifically how the back wave and front wave integrate / effect each other.
All the sims assume that the drivers are true point sources i.e. instruments and voices etc radiating 360 degrees in all directions. But I suspect this is NOT the case, not even with a " naked " driver hanging from a thread.
As all sound waves in the audible ( ignoring sub bass which we feel through our bodies ) 20Hz to 20KHz are only detectable by changes in air preasure- compression and rarefaction- we have an elephant in the room. i.e. When our driver cone pumps forward and COMPRESSES ( INCREASE IN AIR PREASURE ) the air to send us the note / drum strike, transient etc this sound wave rushes out in all FRONT facing directions... meanwhile the same forward pump motion of the cone causes an inverse RAREFACTION ( DROP IN AIR PREASURE) and this sound wave front rushes out in all REAR facing directions.

So when the two opposing forces meet what happens....? How do they mix n match? Do the current sims and models reflect this opposing force reality? If not can they be easily tweaked to compare the results?
So if I am correct, the sims and models should be able to show this fundamental and real world effect clearly. If they can’t does it mean the real world is wrong and the world of “ Matrix simulations “ is correct? In climate modelling they don’t trust any computer simulations to “ forecast” the future weather until the same simulation can accurately reproduce the KNOWN weather of recent years i.e. a few years, up to a few hundred years, of well documented day to day global weather. This is known as PRE-CASTING climate modelling.
Can we as music lovers benefit from this technique? Are we measuring the right things...? As always more questions than answers, over to you guys!

All the best

Derek.
PS I have an interesting FE sim of an 18 inch bass driver in an open baffle, its too big to post, who can shrink it and post it for me? Thanks.
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Old 16th July 2010, 02:29 PM   #6704
Pano is offline Pano  United States
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Derek, have a look at software like "Edge" (or Basta). Simple enough and takes into account all you mention. Drivers are NOT seen as a point source and rear wave and baffle face are calculated.

Many other softwares work this way, too.
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Old 16th July 2010, 05:12 PM   #6705
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Default Software sims

Thanks Pano, glad to hear the software / and simulations recognise the compression / rarefaction effect.

Cheers

Derek.
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Old 17th July 2010, 12:12 AM   #6706
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Originally Posted by Overkill Audio View Post
Hi Guy's,

Very glad this thread is active again and more interesting ideas to ponder...

When running in big pro bass drivers its common practice to place the left and right speakers face to face, reverse polarity on ONE speaker, turn up the 800 watt power amps , put on some killer bass tracks and leave home for the weekend... Anyone who has tried this knows that even OUTSIDE the building the audible effect of reversing polarity on one channel is huge.
In normal domestic systems try reversing polarity on one of your bass drivers and have a listen. The effect is very easy to hear and feel if you have a true full range system.


Derek.
This is basically a room effects, modal excitement phenomena for a widely space dipole.
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Old 18th July 2010, 06:33 PM   #6707
mige0 is offline mige0  Austria
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Here are the measurements to confirm the above simus on the concept of consecutively min phase behavior:

Measurements have been done in door with a NEO3 tweeter in round OB of roughly 43cm diameter.
Hence the 0.7ms do not exactly correspond with the simu where a 1ms delay was shown.

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Anyway – the measurements where done in relation to simus (0.7 / 1) – meaning at the nulls and peaks and also well below first OB peak to give a good visual grip on the subject ( just time scaling is different ).


First the IR – with a particularly clear displayed second part of the doublet:

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and the well known OB FR – not any different for this particular one except the pronounced nulls and peaks due to the circular baffle (in need to keep issues seperated):

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Now switching back into time domain and showing measurement sine burst – comparing simu and measurement (In the simu compare to the BROWN trace):

Second null :

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second peak :

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first null

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first peak :

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below first peak :

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Though measurements are only „as good as it gets“ - the concept I guess is clearly shown to apply in audio reality – no?
We can see that correlation between simu and measurements is actually excellent (taking into account the band pass character of a real world speaker like the NEO 3)

Also clearly seen is that the two parts of consecutively min phase behaviour are separated pretty sharp one from the other – even better measurable than I've hoped for.

The last important point to be aware of is that this goes all the way down in frequency – there is no limit here where this concept applies.

So we now can possibly proceed to the „fun part“ of discussing how to EQ out (or not) any „consecutively min phase behaviour“...




Michael

Last edited by mige0; 18th July 2010 at 06:41 PM.
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Old 19th July 2010, 05:35 AM   #6708
mige0 is offline mige0  Austria
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A good „starter“ to the paramount implications of the concept of „conscecutilely min phase behaviour“ may present a question to ask for at first when we dive into EQing of that form of distortion.


The question arises :
“how actually do we check if any EQing was applied sufficiently?”

Lets take a look at the simu / measurements at the first null – at a frequency of 1360Hz where the marker is set :

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.


The ususal answer would be :
Easy !
We take a measurement !
Exactly like shown in the frequency response above !
– no ?

BUT :
comparing the FR plot and the time domain plot for this particular 1380Hz (at the first null) - where destructive interference happens – we see that after the first min phase period there is considerable less signal than the roughly -10dB indicated by ARTA in-room measurement.

The measurement was gated at the usual 4ms to avoid any room reflections creeping in. This means that ARTA has actually calculated only data within that time period. This also means that this value of -10dB does neither reflect correctly for the the first period of min phase behaviour nor for the following.

So we come to the simple but pretty scary conclusion :
Our usual tools in measurement – eg FR plot - are flawed and totally useless when it comes to „consecutively min phase behaviour“ .

Perfectly EQing this FR first notch, with a standard equalizer like the DCX2496 for example, would be possible without any question (at least as it seems at a first glace) – but the measurement we would rely on to verify would only show us a fake !

So we have to be aware that such EQing must be ex amend more closely - and also in the time domain - to tell if we *really* got any perfect EQing or not.

Is there agreement so far?



Michael

Last edited by mige0; 19th July 2010 at 06:02 AM.
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Old 19th July 2010, 11:05 AM   #6709
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The problem with your entire argument is that you are addressing a problem of what happens above the dipole peak, well above what would be considered the useful frequency range of a dipole. The response should be LP filtered and well attenuated by then. Above the dipole peak the response is just that of two uncorrelated sources interacting with each other.
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Old 19th July 2010, 06:05 PM   #6710
mige0 is offline mige0  Austria
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Originally Posted by john k... View Post
The problem with your entire argument is that you are addressing a problem of what happens above the dipole peak, well above what would be considered the useful frequency range of a dipole. The response should be LP filtered and well attenuated by then. Above the dipole peak the response is just that of two uncorrelated sources interacting with each other.
Actually I don't get your point.

CMP behaviour is part and parcel to OB – be in the „true dipole range“ well below first peak or be it in the „correlated inverse monopole range“ elsewhere above.

I guess I have shown OB to be a CMP system all the way by theory (my „concept“), by simu and by measurement too - I mean - two point sources separated by some distance simply *must* be CMP - there is *no* frequency dependency in CMP behaviour at first hand.
Have a close look at the sine bursts well below the first peak - they show "exactly" whats predicted by CMP concept and simu : two different min phase areas sharply separated at the point of time delay.

This probably is a good point to renew that not only OB is a CMP system, but also many other speakers – as already outlined.
OB is only a pretty good example because many people think about its specialties (obviously me included ), whereas other forms of speakers – affected by CMP behaviour just as well - have dumbly been accepted „as is“.
I also use OB for demonstration – simply because I love it and see „some possible room for improvement“
And I also use OB for demonstration as OB is way easier to build and measure than a back loaded horn for example

Though I will continue to demonstrate effects „well above dipole peak“ - at the point of full destructive and constructive interference especially - this is more due to the most clearly plots to obtain than really related to OB.
We could switch into a mere and theoretical discussion about CMP systems if you like – but I guess we would loose the interest of many in this discussion.

The area below first peak (true dipole behavior if you will) – also a department of destructive interference – I will of course also come back to.

But possibly I have not understood where you are pointing at?

Michael

Last edited by mige0; 19th July 2010 at 06:18 PM.
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