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Old 28th July 2007, 12:05 PM   #1611
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Default Heartaches by the number ...

Graham ... You did realize by clusters I meant in a 4 x 4 or grouped circular fashion? Put on a large dish (satellite) should eliminate most notch problems. Big cone area, too.
Zene
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Old 28th July 2007, 12:25 PM   #1612
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Yes.
I was thinking of outer drivers not having same hf to prevent beam ripples.

Clearest PA I had was 8x Elac 5x9s with 2x Fane soft-domes in centre (3x3 patterned spacing), but lacked bass, which needs to be integral to maintain transient timing.

If you are thinking of a shield shape - intesting !

Cheers ........ Graham.
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Old 29th July 2007, 09:04 AM   #1613
mige0 is offline mige0  Austria
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Default VVLOB / Virtual Very Large Open Baffle

Hi


When I came up with my first OB in post 797 (http://www.diyaudio.com/forums/showt...t=#post1214299 )
to me it was a successful proof of concept.
By then I didn't recognise the excellent work of Ferekidis
( http://www.randteam.de/papers_lf/daga_2001-lf.pdf ).
The baffle shape and size was found through simulation reflecting the desire to provide a somehow correctable frequency response that is rather predictable over radiating angle.

Auditioning the OB was much fun and it turned out that FR can be corrected almost completely and fairly simple –with limited SPL capability at low frequencies of course - like assumed / predicted and also outlined by some measurements in later posts.

What I didn't mention then was that this OB's behaviour is quite a mixed bag sound wise.
It has a really astonishing presentation of classic music with an excellent and realistic reproduction of big stages.
I found myself listening to operas for hours though not being a fan of that kind of music at all. Also spoken words from single speakers and dialogs or discussions of a group of people especially within reverberant rooms are really great to listen to.
The most smashing experience was to hear a certain jingle that announces the news on radio here.
This gong hasn't changed since my childhood - a roughly 40-50 years back - and with that OB's I "could swear" it is EXACTLY the same gong recorded in EXACTLY the same room that I have heard so many decades ago through my fathers vintage tube radio.

The biggest disappointment was listening to pop music. I very much like the "special effects" that are so common now, producing virtual rooms with astonishing clarity and lightness.
In this manner the OB's failed almost completely degrading many records to almost unlistenable crap.

On a first glance this two experiences look completely contradictory as both are about room perception. On a second look the explanation may be that classic music is rather embedded into strong reverberation whereas pop music is almost certainly close mic recorded or completely from synthetic sources.



My guess here is that the different in room behaviour of OB's compared to closed boxes described above is largely due to the different phantom sources established by room wall mirroring – much rather than from different edge diffraction effects.

To overcome that was my main goal that lead to the VVLOB concept ( even more so than
improving the low frequency reproduction – which is always a good thing to have and in fact was a nice surprise to discover to that large extent ).










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



The pic's above show the position of a single speaker and its phantom sources in a relative typical small room arrangement.
For simplicity there are NO ceiling, floor and rear wall reflections included and also NO multiple wall mirroring.

What can be seen is that the most prominent and disturbing phantom source is the one from mirroring through the front wall. It is the one with almost the same SPL, inverted polarity (in case of OB), very low delay and also towards almost the same direction than the loudspeaker itself.
The phantom source from mirroring through the left side wall in contrary is the most attenuated and most delayed one.
The phantom source from mirroring through the right side wall is well attenuated IF the speaker is OB AND within its dipole frequency range AND aimed to the listening position like shown.

Clearly the biggest improvement one can predict for VVLOB over OB here is concerning the phantom source behind the front wall. Basically this one will become the same as created from closed boxes ( at close proximity to the front wall ) whereas all other phantom sources will roughly stay the same as with OB.

The phantom source behind the front wall in case of OB is almost at full SPL as the attenuation of the rear wave at this radiation angle is almost negligible at pure dipole operation AND there is only slightly attenuation due to sparse additional distance.

Converting this most prominent phantom source to something less objectionable should improve spatial impression and room perception reasonably.
This sounds like good forecast – I am quite in excitement how it turns out with measurements and when auditioning.


Greetings
Michael


PS
**** = C-R-A-P
this kind of censorship is hard to understand for european peope BTW
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Old 29th July 2007, 10:25 AM   #1614
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Patterned wall furnishings or wall curtains, or, carpet back to OB ?

Reflected OB and bipole rear waves are so different here, though with same directionalities.

Cheers ......... Graham.
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Old 29th July 2007, 10:49 AM   #1615
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My favourite walls here in the wilds of Canada are transparent.
Direct to reflected errors are virtually eliminated, however the overall dB level is diminished substantially. Working on treatment to correct this. Next week I am going to try some sheets of plywood held up with 5cm x 10cm lumber to contain the music better.
BTW, soft dirt floors are only semi-reflective.
Sorry, could not help my self. Last semi off topic post. tee hee
Zene
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Old 29th July 2007, 11:33 AM   #1616
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Default Back to Normality

Here is a quick look at 9 x 8" OB speaker baffle. Note, it is +1 dB flat from 80hz to 3700hz give or take a little. Panel can be stood up as well, not sure of floor influence. Maybe someone could comment on that.
Zene
P.S. Quit putting speaker(s) in middle of panel, that's not what edge diffraction is all about.

Click the image to open in full size.
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Old 29th July 2007, 11:53 AM   #1617
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Hi Zene,

These were aspects I have tried in *real life*, and there are indeed different aspects relating to classical/pop reproduction, so yours is not the only tee-hee.
At least I am not scared to throw in comments which some might find useful.

Your last Edge is similar to the good baffle I mentioned in Post#1608. It was clean and could produce high SPLs from just 100W.
Now with a decent tweeter in the centre .......
Bass still weak, so additional contribution still to be arranged.

Cheers ......... Graham.
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Old 29th July 2007, 02:59 PM   #1618
Paul W is offline Paul W  United States
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Mige,
For a speaker within a couple of meters of the front wall, the front wall reflection you spotlighted, for me, produces a bloated image with oversized insturments. This front wall reflection is one of the reasons I have used a wool felt filter to attenuate the rearwave. Felt has worked well in several speakers, the most recent shown in this post . The 12mm felt is not shown in those photos, but you can easily imagine it installed.

Zene,
In addition to Edge, you may want to examine the radiation pattern of the driver array to make sure it performs the way you want. I don't know what software you have, but tools available at the FRD consortium will work.
Paul
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Old 29th July 2007, 07:06 PM   #1619
mige0 is offline mige0  Austria
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Default VVLOB / Virtual Very Large Open Baffle

Hi

PaulW, I have followed your thread completely and was impressed though had nothing special to contribute.

Do you apply the ( wool- ? ) felt over the complete rear of the speaker? This would convert the radiation pattern from dipole to omni in the extreme I guess
( post #1553 http://www.diyaudio.com/forums/showt...12#post1259712 ).
Applied on the front wall between the loudspeakers like a wall carpet, 12mm wouldn't be enough to cover a considerable frequency spectrum to attenuate IMO.

I find it interesting that you still was able to associate instruments even when oversized and bloated – this was no more possible with my setup ( around 0,75 m off the front wall ), an almost complete mess within the soundstage especially towards the depth and no congruence / redundancy over frequency ( with pop music only ).

One other distinction between classic and pop in this respect came into mind in the meanwhile. I always have sort of feeling that room perception in classic is more defined over the lower octaves whereas in pop the higher octaves seem to be more used to create all that 3D effects ( maybe adding a rear tweeter would have changed everything ...).
This might point towards a different perception du to phase and intensity discriminating – OB versus closed box, in-room. Just a guess though.

I also have had simulated around with arrays of speakers like yours and it seems no bad idea from the standpoint that the overall covered area of the 4 speaker array with respect to the baffle size allows for n-times larger baffles with almost congruent FR shifted down an octave and 4 times the SPL capability before pushing them into high harmonics and compression ( Zene is showing something likewise two posts ago ).

Greetings
Michael
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Old 29th July 2007, 11:48 PM   #1620
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Nothing very profound here, just following ScottG's and PaulW's thread and the comments about various densities of felt behind the OB - a method going right back to the original Quad ESL57. My instincts are that felt (on the rear of the driver) combined with an appropriately adjusted rear tweeter would give just the right degree of front-wall reflection energy - one of those "trim to taste" things, mostly adjusting for the speaker-to-wall distance for the listening room.

I think what matters is the frequency spectrum of the front-wall reflection - a conventional monopole has lots of bass energy (the monopole is omnidrectional at LF), with rapidly falling response as the frequency gets higher, and a sharp ripple at the mid-to-tweeter crossover. By contrast, a true wideband radial speaker (such as the MBL) has the same spectrum on the front-wall reflection as the direct-arrival sound. I do think a happy medium is possible - not quite as much energy as a radial speaker, and smoother response than a conventional monopole 2 or 3-way speaker.

Why leave the FR of the front-wall reflection to chance? The frequency response is easy to measure at this particular emission angle, and with MLS methods, the in-room response of the front-wall reflection can be directly measured (just window out the direct sound).

The BMS 18N850 does look interesting, another good candidate for the close-to-floor mounted drivers. Thanks for the tip and posting your experiences with the driver!
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