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Old 9th May 2009, 08:23 PM   #5481
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Quote:
Originally posted by xpert


BTW: hasn't been Fincham at K.E.F. been the inventor of the CSD perspective on group delay an amplitude response?

Hmm ... I'm not too sure. Laurie Fincham was one of the first to use FFT's, but he was also closely collaborating with the BBC since KEF made custom-spec drivers for some of the BBC monitors (like the LS3/5A). The BBC and KEF shared a mutual interest in time-decay colorations, and this started with D.E.L. Shorter's publications in Wireless World in the Sixties.

I would put the earliest use of CSD-like measurements in Shorter's Wireless World articles of what he called "buried resonance" and their relation to audibility. Shorter found that resonances that were too small to have much effect on the FR curve (less than 0.5 dB ripple) could still be audible as a coloration - and that the "buried resonance" chopped-sinewave technique would reveal their frequency and Q. Once revealed, the driver could be modified to remove them (dustcap resonances et al).

Ten years later, Laurie Fincham at KEF was using the more direct FFT method - and both the BBC and KEF were interested in minimizing time-storage artifacts. This led directly to the BBC's work on polypropylene cones in the late Seventies.
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Old 9th May 2009, 08:34 PM   #5482
Salas is offline Salas  Greece
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I love Lynn's look in the historical process of audio (and in everywhere else I would suppose). Good order holds keys.
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Old 9th May 2009, 08:40 PM   #5483
mige0 is offline mige0  Austria
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Quote:
Originally posted by gedlee


In that situation, would you bother with anything subjective?

Why are you asking !

Your conflict isn't whatever *I* may answer - but in what you'll may find for yourself over the course.


- you already have gone far...

Best
Michael
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Old 9th May 2009, 08:54 PM   #5484
ScottG is offline ScottG  United States
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Quote:
Originally posted by mige0

Just for the record – its been me who provided “post processing” CSD's – Earl did the IR measurement of his OS wave guide.

What you mean by “less than stellar CSD” if I may ask?
I mean – decay looks great for me – as long as we would not like to go into hairsplitting (sub msec terretory) – no?
Any signs you could identify for reflections at the mouth / throat etc?

Michael

True, it was your effort in processing the data. Thank you.

"hair splitting".

As freq.s increase hair splitting is "where it's at".

..as far as the full bandwidth is concerned, there are significant limitations by not having comparisons to the compression driver without waveguide.. however:

The driver appears to have its fundamental resonance just below 2 kHz (..and frankly looks like the DE 10, not the 250). Of course the waveguide could be "pushing" that resonance farther up in freq.. and in fact I think at the very least it is as you go off-axis. There you can see the ripple prominently near 5 kHz 15 degrees off axis.

It's also interesting that the waveguide appears to be suppressing (in amplitude), and extending (in time) the fundamental resonance of the driver as you go farther off-axis. It also extends (in freq.) the ripple, while again marginally suppressing it (in amplitude).

IMO it rather clearly is intended to be listened to near its 30 degree axis. It not only represents a better low-pass response to be filtered, but it also suppresses the fundamental resonance to a more significant level for its freq. while incurring less objectionable ripple (in comparison to the 15 and 45 degree positions). (..and yes, I realize that "significant level" and "less objectionable" aren't defined.. but that would take a bit more writing.)

The real problem with all of this is:

1. The response shown does not include its CD compensation low-pass filter. When you apply it those upper freq. ripples will become more pronounced.

2. The display is set for 25 db down, not 30 db or 36 db. Again, additional amplitude will display the resonances better.
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Old 10th May 2009, 08:53 AM   #5485
mige0 is offline mige0  Austria
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Quote:
Originally posted by Rick Miller
We have talked about the influence of cabinet material in the past, and I wanted to share a link to some measurement data from Wilson Audio. It shows the different “signatures” of material used to make speaker enclosures. It’s interesting to see how the walls of your speakers react to stimulation. A thanks goes out to Wilson for posting the measurements on the web. http://www.wilsonaudio.com/sasha/science.html

Hi Rick thanks, but its not only Wilson Audio that is interested in getting a handle on that subject.

Below a link to an early reserch done by Friedemann Hausdorf from VISATON published in the ELEKTOR magazine 1988:

http://www.exdreamaudio.de/?Akustik:Geh%E4use

The big advvantage is that Hausdorf also documents his measurement set up. Sadly the scaling of the CSD Y-axix isn't clear.
Scroll down the pix to

"Bild 12b" whis is for marble

or to

"Bild 16b" where you see the benefits of bracing to the opposite wall for simple 19mm / 3/4"chipboard

"Bild 3b" shows the same simple 19mm / 3/4"chipboard *without* bracing for comparison


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Old 10th May 2009, 12:51 PM   #5486
mige0 is offline mige0  Austria
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Quote:
Originally posted by ScottG

True, it was your effort in processing the data. Thank you.

"hair splitting".

......

The real problem with all of this is:

1. The response shown does not include its CD compensation low-pass filter. When you apply it those upper freq. ripples will become more pronounced.

2. The display is set for 25 db down, not 30 db or 36 db. Again, additional amplitude will display the resonances better.

Yes, but I wouldn't go too deep into the very details as we don't have data of other horns to compare with done under same measurement circumstances and – even more important – the ripples are small - not really worth to complain IMO as long as there are no pronounced decay tails that can be seen..

But - I did some more processing on Earls IR files - as said - Acourate software is pretty powerful stuff:

What I did, is to explore what we would see on axis with a XO optimised for 30deg response.

Click the image to open in full size.

Well, as the 30deg response gets close to perfect (as should be)

Click the image to open in full size.

the on axis response gets more rugged also showing some decay tails in CSD.

I don't wanna show this pix' as they might be a little bit "overcooked" and also – not knowing the exact circumstances of measurement - there might be (over) compensation for diffraction effects not related to the OS wave guide .

But all in all I feel save to say from the IR files got, that even OS isn't constant directivity (be this good or bad) when it comes to a veeeery close look.

Compared to my OB measurements – they both are pretty close regarding decay time range and smoothness - not that much better in this regard one or the other.

Though OS does *not* show the clear shift in directivity as does OB.

Maybe we could put it that way:
in the macro view OS is CD
in the micro view OS isn't CD (I doubt any horn is anyway)



Michael
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Old 10th May 2009, 03:09 PM   #5487
Sheldon is offline Sheldon  United States
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The measurements Michael shows feel like they have a realistic level of detail. I could be off base, but I'm skeptical of trying to dig fine detail our of these type of measurements. I'm no mathematician, but I have spent a lot of time doing analytical work in biochemistry. And it strikes me that the measurement errors for the typical set up, have to obscure much of what can be read into some of these detailed CSD profiles. Most of what I see here are single measurements of two or more different conditions. Looking at the comparison that BudP cited, for instance: how much different are they really? Would you see as much difference by moving the mic a few cm? Can you duplicate the measurement on a different day to that level of detail? How much is measurement/calculation artifact, how much represents real differences?

Sheldon
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Old 10th May 2009, 03:47 PM   #5488
gedlee is offline gedlee  United States
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Sheldon

I have done a lot of work in the past on the repeatability of acoustic measurements and I agree that one cannot reasonably look at the fine detail as its not stable.
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Old 10th May 2009, 03:58 PM   #5489
mige0 is offline mige0  Austria
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Quote:
Originally posted by Sheldon
The measurements Michael shows feel like they have a realistic level of detail. ...

Looking at the comparison that BudP cited, for instance: how much different are they really? Would you see as much difference by moving the mic a few cm? Can you duplicate the measurement on a different day to that level of detail? How much is measurement/calculation artifact, how much represents real differences?

Sheldon
As for my own measuremets - I feel pretty confident - within the limits outlined.


Quote:
Originally posted by gedlee
Sheldon

I have done a lot of work in the past on the repeatability of acoustic measurements and I agree that one cannot reasonably look at the fine detail as its not stable.

Agree - as said several times..

Maybe we should say results are almost stable *if* we would repeat at the exact coordinates for the speaker and the mic.

even one or two cm / 1" is quite a difference if we look into "micro directivity" of a speaker plus whatever diffraction "artefacts".
From that - smoothing isn't necessarily a bad thing when used to get an overview - rather than to hide small but irritating errors by intention.

As said it does not make sense to do equalisation down to the last dB of every ripple by measurement.
To tune to sub dB values is more a matter of good taste to get the tonal balance right..


Michael
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Old 10th May 2009, 04:12 PM   #5490
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by mige0



Yes, but I wouldn't go too deep into the very details as we don't have data of other horns to compare with done under same measurement circumstances and ?even more important ?the ripples are small - not really worth to complain IMO as long as there are no pronounced decay tails that can be seen..

But - I did some more processing on Earls IR files - as said - Acourate software is pretty powerful stuff:

What I did, is to explore what we would see on axis with a XO optimised for 30deg response.

Click the image to open in full size.

Well, as the 30deg response gets close to perfect (as should be)

Click the image to open in full size.

the on axis response gets more rugged also showing some decay tails in CSD.

I don't wanna show this pix' as they might be a little bit "overcooked" and also ?not knowing the exact circumstances of measurement - there might be (over) compensation for diffraction effects not related to the OS wave guide .

But all in all I feel save to say from the IR files got, that even OS isn't constant directivity (be this good or bad) when it comes to a veeeery close look.

Compared to my OB measurements ?they both are pretty close regarding decay time range and smoothness - not that much better in this regard one or the other.

Though OS does *not* show the clear shift in directivity as does OB.

Maybe we could put it that way:
in the macro view OS is CD
in the micro view OS isn't CD (I doubt any horn is anyway)



Michael
Aren't Earl's files 44.1KHz? It seemed that sample rate based on the text file you posted a while back. If so, what's with the 48KHz sample rate setting here?

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