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Old 6th April 2012, 10:09 AM   #1
solhaga is offline solhaga  Sweden
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Default Baffle surface for a long ribbon

I have 125 cm (49 inches) long ribbons in a open baffle arrangement with 20 cm (8 inches) wide baffles. The baffle is however extended by the side wall at one side and by a h-frame bass column at the other.

I'm in the remaking of the setup, the h-frames will be exchanged with an OB and the ribbons will be more integrated into one baffle.
So I'm currently doing some research on mounting, baffle geometry and such and stumbled across the issue of the actual baffle surface via the EnAbl and felt threads.
I got edge diffraction already covered; the baffle edges will be sloped.
But I cannot get the baffle surface influence on the sound out of my mind...

I've started with using a kitchen drawer mat from IKEA:
Click the image to open in full size.

resulting in:
Click the image to open in full size.
I think I hear some improvement, some instruments is more detailed and so on.
But that could of course be placebo or my listening to the music more intense.

Other ideas is to use highly textured wall paper.

So, what's your verdict? Is this a dead end and will in fact my new setup with edge diffraction taken into consideration prove the baffle surface to be a minor issue?
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Old 7th April 2012, 10:49 PM   #2
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Quote:
Originally Posted by solhaga View Post
I'm in the remaking of the setup, the h-frames will be exchanged with an OB and the ribbons will be more integrated into one baffle.
Hej!
Do you mean that the baffle (OB) for the woofers will be the same baffle for the ribbon? (As I could imagine this will reduce the overall width.) If so, I would worry most about keeping woofer vibrations out of the ribbon, and thus make it as stiff and massive as possible....

PS. Is that a pair of AKG K340?
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Old 8th April 2012, 06:20 AM   #3
solhaga is offline solhaga  Sweden
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"keeping woofer vibrations out of the ribbon":
The woofers will be magnet mounted and thus isolated from the baffle.

"Is that a pair of AKG K340?":
Yes, bought some 30 years ago.
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Old 8th April 2012, 05:20 PM   #4
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Can you post a sketch of your intended layout?
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Old 8th April 2012, 05:51 PM   #5
solhaga is offline solhaga  Sweden
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Basically it will be a rude and enlarged clone of the soul sonic design:
Click the image to open in full size.

Click the image to open in full size.

I will have a baffle on the ribbon side in order to reach the wall.
On the woofer side, the baffle will be broader and possibly foldable.
Same kind of slope though, using Edge to get the minimal diffraction.

I quad-amp the speakers with one Trimodal driving the ribbons and one GainClone for each woofer. The Gain Clones are fed with the same signal. A modified EMU 0204 (removed attenuator and headphone output stage and replace the OPs with LM4562) is the DAC for a four channel output from Frequency Allocator. Cutoff somewhere between 180 Hz and 400 Hz and otherwise PEQ according to measurements. A PC with J.River Media Center is the source
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Old 8th April 2012, 08:20 PM   #6
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I cant help thinking that the baffles are very wide, much too wide? With the B&G RD-75 ribbons I have, I have no baffle other than rounded edges, so its probably just 12-13 cm wide. And I XO as low as 200 Hz. Smaller baffle will get you better directivity.
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Old 8th April 2012, 10:44 PM   #7
solhaga is offline solhaga  Sweden
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Isn't 13 cm too narrow @ 200 Hz due to the dipole cancellation?
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Old 9th April 2012, 03:41 AM   #8
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Quote:
Originally Posted by solhaga View Post
"Is that a pair of AKG K340?":
Yes, bought some 30 years ago.
I think your instincts were better 30 years ago. What do you not like about the K340? Why not a nice little ESL panel next to your OB woofers? 300-400 xo, perfect. Don't fight the laws of physics; make them work FOR you....

(Because I think you are going in the wrong direction with a wide baffle and also having it against the wall.....)
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Old 9th April 2012, 04:51 AM   #9
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Hi solhaga,

I get the best soundstage with my dipole linesource ribbon speakers when the ribbons are on the inside of the soundstage and the woofers are on the outside. Having separate bass and tweeter cabinets allows additional soundstage tuning by toe-out of the woofers to use wall bounce to increase the bass delay and reduce room modes, plus toe-in of the ribbons so their vector crosses just in front of the listener position.

A separate shallow H-frame woofer line array can produced good results since it: 1) provides a very sturdy I-beam type construction; 2) the H-frame wings increase bass extension without wasting floor space; 3) the wings block a large portion of the woofer air from rattling the delicate ribbon; 4) it is easy to sew a thin lycra material sock for a grill cloth; 5) it is important to isolate the woofer vibrations from shaking the ribbon.

To reduce lobing, it is necessary to keep the bass-ribbon separation distance less than the crossover quarter wavelength. A 200Hz crossover requires <17" seperation.

Have you ever experimented with:
1) putting the ribbons on the inside of the soundstage
2) cutting the ribbon wings down to say 2" . This will provide strength plus a decent edge round-over.
3) adding some ribbon cavity edge diffraction control by using a small quarter-round or angular bezel .
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Old 9th April 2012, 07:56 AM   #10
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Quote:
Originally Posted by solhaga View Post
Isn't 13 cm too narrow @ 200 Hz due to the dipole cancellation?
With a single cone-driver with circular chassis yes it would be, as the dipole peak is placed around 1500 Hz. But the long ribbon line-source dont behave that way beacause of the lenght and line-source behaviour. My RD-75's measure flat to 200 Hz without any baffle.
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