Beyond the Ariel

[Jmmlc]

Hello Michael,

Arrival time of an impulsion doesn't show the whole picture.

The rise of such an impulsion is mostly made of the highest frequency content.

To have a view on how the lowest frequencies are delayed from those high frequencies you must use the group delay curve (as you use Arta, this should not be difficult).

What we can see on you pulse responses from the one at the top to the one at the bottom is a kind of rounding on the negative arch following the main pulse. This is partly due to the change in frequency response curve but this also surely due to a modification of the group delay curves when increasing the angle from the axis.

Best regards from Paris, France

Jean-Michel Le Cléac'h

Originally Posted by mige0

directivity control *is* the same as controlling impulse response (coherence in time of arrival) over radiation angle
So - you have to decide

[mige0]

Originally Posted by soongsc

I was wondering when CSD data was going to be posted on that design. Didn't they promise to post some data?

Yeah, I was under the same impression..

Originally Posted by soongsc

Oops, the vertical scale of your impulses are different... Non-minimum phase.

Isn't vertical scale the equivalent in SPL ? So - I don't see the problem ?

Remember its linear scale in IR plots !
Frequency response certainly looks good enough to be called "min phase" - no?

Originally Posted by Jmmlc

Arrival time of an impulsion doesn't show the whole picture.

Thanks for pointing there Jean-Michel

I seldom look at GD as I haven't found the "key" to interpret any usefully nor do I have expertise in how it *should* perform in context of other designs.
....except maybe one or two basics I picked up here:
Horn vs. Waveguide







Can you tell me what actually could be said from above plots?
(same 0 10 20 30 deg measurements as before and same gating at ~4ms, lower plot zoomed in and with "no" smoothing)

Michael

[Pano]

Originally Posted by Jmmlc

To have a view on how the lowest frequencies are delayed from those high frequencies you must use the group delay curve

Does the phase plot show the same thing? For example in software like HOLMImpulse or ARTA. I'll have to compare phase vs GD to see.

[Jmmlc]

Hello Michael,

What I can say looking at you last screencopy is that there is 2 different phenomenons mixed.

One is the normal rise of the group delay when the frequency decreases toward the "cut-off" frequency (whatever it means regarding waveguides).

The other one is shwon through large positive or negative anomalous values of the group delay (normally negative values of the delay should not exist). This is the result of a width of the signal window embedding peaks of reflected energy or delayed energy (HOMs?). You should look at magnification of the pulse graph in order to locate the corresponding delayed peaks (of small amplitude). When there is interference between the direct and the delayed signal then such group delay anomalies appear.

You can also send me the .pir files so I can study them.

Best regards from Paris, France

Jean-Michel Le Cléac'h

Originally Posted by mige0

I seldom look at GD as I haven't found the "key" to interpret any usefully nor do I have expertise in how it *should* perform in context of other designs.
....except maybe one or two basics I picked up here:
Horn vs. Waveguide

Can you tell me what actually could be said from above plots?
(same 0 10 20 30 deg measurements as before and same gating at ~4ms, lower plot zoomed in and with "no" smoothing)

Michael

[mige0]

Originally Posted by panomaniac

Does the phase plot show the same thing? For example in software like HOLMImpulse or ARTA. I'll have to compare phase vs GD to see.

Yes – the referenced plots for
- frequency response
- group delay and
- impulse response

are all one and the same measurement

Originally Posted by Jmmlc

Hello Michael,

You can also send me the .pir files so I can study them.

Thanks for you kind offer – you got mail...


Michael

[Jmmlc]

Hello Michael,

Here are the group delay curves after correct windowing.

You'll notice the evolution of the GD in the interval of frequency between 900 and 1500Hz (GD decreasing with angle from the axis) and then between 2200 and 3000Hz (GD increasing with angle from the axis).

This surely means something...

Best regards from Paris, France

Jean-Michel Le Cléac'h

Originally Posted by mige0

Yes – the referenced plots for
- frequency response
- group delay and
- impulse response

are all one and the same measurement



Thanks for you kind offer – you got mail...


Michael

[mige0]

Again, thanks a million Jean-Michel !
The region around 2500 Hz you point at clearly is the frequency where polar wiggles are.

You better see them in a normalized FR plot:






If we let this polar wiggles aside for a moment - the overall directivity tracking of that horn is pretty good - some 1-2 dB from 1kHz up to 10kHz.

Even the top end from 10kHz until 20kHz is easily within the (nonsense) 10dB limit of CD horns – sure – its a smoothed FR – but even so – I'm pretty happy...

Interestingly this polar wiggle does not show up in the simulation of the min phase horn.
When I saw it slightly smoothing out with the different NEO3-W version I first thought that its been a mis-match of the wave front injected into the horn.

Have tried to close some of the holes the membrane of NEO3 is "breathing" through today – but it does not make that much of a difference – so seems there is more research needed on that effect.
Might be its simply the parallel top and bottom boundary, dunno, will see


Michael


Michael

[mige0]

One more question regarding group delay of horns :
What can be considered to be sort of practical limit - meaning for example in the case given - where would be the lowest XO point to be recommended - seen from a pure GD point of view?



Michael

[Pano]

Good question.
Your GD at 1KHz would = about 80mm, right?

[mige0]

For standard *passive* XO I possibly have to add...