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Multi-Way Conventional loudspeakers with crossovers

May my problem be diffraction?
May my problem be diffraction?
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Old 8th March 2020, 07:03 PM   #1
andreaemme is offline andreaemme  Italy
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Default May my problem be diffraction?

Hello, I come from this thread and I've thought that it may be better to start another thread because original topic was quite different than this one.

It's time to publish my night-time measurements as suggested by you, putting microphone at various distance from driver.

Let's begin with the most important driver for me because driver which gave me more hard time, mr. Scanspeak D2905-9500 (follows as 'SS'), baffle-mounted as visible in previous photos (7.1 cm from left, 5.7 cm from top, 9.4 cm from right, 17.5 cm from bottom and 5.5 cm from Vifa edge), unfilterd (of course with just a 10 uF cap to protect from bass frequancies), flush mounted:

@5cm:
01_D2905_baffle_5cm.png
here we can see that driver is rather in perfect working conditions, just 6-7 khz slight peak that can be its tipical trademark

@50cm:
02_D2905_baffle_50cm.png
response begins to crinkle..

@100cm:
03_D2905_baffle_100cm.png
here response's crinkleness become paroxysmal!

Conclusion: SS in that baffle sounds very poorly
_________________________________________________

Now let's see SS's behaviour in baffle-less configuration, mounted on the front of a cilinder with its same diameter:

@5cm:
04_D2905_baffleless_5cm.png
in grey overlayed baffle response at the same distance: baffle-less is more irregular evidently

@50cm:
05_D2905_baffleless_50cm.png
in grey overlayed baffle response at the same distance: baffle-less is as irregular as baffled, just in different region

@100cm:
06_D2905_baffleless_100cm.png
n grey overlayed baffle response at the same distance: baffle-less is less irregular as baffled
07_D2905_baffleless_100cm vs 5cm.png
in grey overlayed baffle-less at 5 cm

Conclusion: we can see that baffle-less is less sensitive to distance from driver than baffled and maintains its timber at various distance.
_________________________________________________

For comparison, Sipe tweeter's measurement mounted on the same baffle (not flushed):

@100cm:
08_Sipe_baffle_100cm vs 5cm.png
in grey overlayed response at 5 cm: there's still much crinkleness but maybe less than SS's one
_________________________________________________

For comparison, Vifa fullrange's measurement mounted on the same baffle under tweeter as visible in previous photos:

@100cm:
09_Vifa_baffle_100cm vs 5cm.png
in grey overlayed response at 5 cm: there's crinkleness but less than previous situations
_________________________________________________

Here's final measurement of Vifa+SS as midrange+tweeter, took nearer than standard to verify flatness of crossover design without more possible crinkle's effects on distance:

@25cm:
10+11_Vifa non comp +SS_B_25 cm_filtrati.png

Conclusion: seeing this chart response seems quite good... but.... listening is really horrible!! Full of harshness and sybilance!
Foolishly I didn't take the same measurement at 100cm but from what seen before we can deduce that summed response may be still a seismogram.
_________________________________________________

Now the questions:
- is my problem definitively a diffractions problem?
- if yes, why this diffraction shooted in this damned manner my project while there's at least a thousand project using a similar baffle, rather narrow, not well rounded on the edge of course, but however asymmetrical?
- may this problem be amplified by the wide dispersion feature of SS?
- if yes, may be a good choice to use in a narrow baffle as mine a waveguide to shrink dispersion and reduce baffle's interactions or it's time to migrate definetively to a baffle-less configurations remaining content of its however imperfect timber?

I also made some measurements with some felt around tweeter but without significant effects, probably due to my felt's non adapt features.
To see by the way this beatiful thread and a related very well made article Diffraction Doesn't Have to be a Problem about these issues.

Thank you very much!
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Old 8th March 2020, 07:12 PM   #2
andreaemme is offline andreaemme  Italy
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Of course, some image of my project:

SS on baffle:
IMG_20200206_082731.jpg

SS in baffle-less configuration:
IMG_20200228_001520.jpg

Sipe tweeter in brutal place of SS:
IMG_20200223_115047.jpg
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Old 8th March 2020, 08:02 PM   #3
norman bates is offline norman bates  United States
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I wrap tweets and horns in open cell foam or f10 felt.

I have no measurements.
But it sounds "sharper", or a bit more detail.
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Old 8th March 2020, 08:27 PM   #4
silverprout is offline silverprout  France
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How old are your D2905-9500 ? the ferrofluid is perhaps dry.
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Old 8th March 2020, 09:30 PM   #5
system7 is online now system7  United Kingdom
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I enjoy a chat with some of diyaudio's brighter lights.

IMO, Michael Chua is one of them:

Dome Tweeters – are manufacturers’ Response plots realistic? – AmpsLab

He likes the Morel CAT378 which I want to try:

Click the image to open in full size.

He also likes the Morel MDT29, aka the Morel CAT298 which I happen to have:

Click the image to open in full size.

TBH, I think the CAT298 is a stinker! Harsh, spitty and sibilant even on my best 4th. order crossover. Maybe I need a good foam-filled grille?
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Old 8th March 2020, 10:20 PM   #6
Lojzek is offline Lojzek  Croatia
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No, you need to stop thinking the way you fancy so much and admit it to yourself. Not once in my life have I come across a tweeter that was not managable to perform decently, and I never guess a crossover, nor do I rely on manufacturer's plots. I do my own each time.

Last edited by Lojzek; 8th March 2020 at 10:22 PM.
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Old 8th March 2020, 11:19 PM   #7
system7 is online now system7  United Kingdom
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IMO, the greatest speaker genius was Steen Duelund.

TBH, it seems like only me and John Kreskovsky understood him. John is an algebra man, me, I like geometry.

Nobody here ever got this Steen Duelund idea:

Click the image to open in full size.

What he is telling us is the speaker cabinet is no different from the room. Pure genius, IMO. You might line the inside of your cabinet with damping. Steen says you might as well line your room or the outside of the cabinet!

How good is that?

TBH, speakers are small beer IMO. A mere 2-dimensional Clifford algebra. The serious Physics people have moved into much higher dimensions. But sufficiently simple to be accessible. Sufficiently complex to be interesting.

It's all about that fascinating Transcendental number "Pi" in the end:
Quanta Magazine

Not many people know this, but for every algebraic number you know, there are infinitely many more transcendentals. Yet we really only know "Pi" and "e".

Quote:
Originally Posted by E.T. Bell
"The algebraic numbers are spotted over the plane like stars against a black sky; the dense blackness is the firmament of the transcendentals."
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Old 9th March 2020, 01:20 AM   #8
norman bates is offline norman bates  United States
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I found the cat378 too limited for 7' off axis listening.

The cat308 in the solstice is amazing
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Old 9th March 2020, 09:36 AM   #9
celef is offline celef
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Quote:
Originally Posted by system7 View Post
What he is telling us is the speaker cabinet is no different from the room. Pure genius, IMO. You might line the inside of your cabinet with damping. Steen says you might as well line your room or the outside of the cabinet!

How good is that?
there is a huge difference in size between the smaller box and the larger room, that makes them behave very differently, just look at the high pressure inside a speaker box for one parameter, another parameter is that you for most part sit in the room and not in the loudspeaker enclosure, unless you are using open baffle designs
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Old 9th March 2020, 09:40 AM   #10
celef is offline celef
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Quote:
Originally Posted by silverprout View Post
How old are your D2905-9500 ? the ferrofluid is perhaps dry.
that could be an issue, but in my experience with dried ferrofluids makes the tweeter sensitivity drop like a stone (in a pond)
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