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Old 10th January 2020, 12:09 AM   #2841
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by scottjoplin View Post
I understand the discussion is about open baffle and not necessarily dipoles exactly, but I'm wondering if using felt effects the radiation reaching the baffle edge such that the cancellation is compromised?
Felt is a great baffle material. I documented some experiments with it in a thread a while ago.

The best thing about them is that the felt doesn't even need to be thick (I used 3 layers in that thread but a single layer is enough, even down to 100 hz). The sound wants to take the path of least resistance and even a single layer of felt present more resistance than free air and a bit more distance. In fact I got worse results when I used too much felt. Too much in this example was a monstrosity with where I glued 20 cm of felt glued together and carved it into a donut shape. Sadly I never photographed that monstrosity, it was vanquished shortly after I measured and saw how horrible it was.
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Old 11th January 2020, 09:22 AM   #2842
MITsound is offline MITsound  Canada
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Quote:
Originally Posted by Kjeldsen View Post
The tiltet approach. I used felt, but on the full surface

OB “omni" experiment
Gotcha. Thanks.
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Old 11th January 2020, 09:25 PM   #2843
warrjon is offline warrjon  Australia
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Quote:
Originally Posted by scottjoplin View Post
I understand the discussion is about open baffle and not necessarily dipoles exactly, but I'm wondering if using felt effects the radiation reaching the baffle edge such that the cancellation is compromised?
I made a lot of measurements when I added the felt to the baffle. I also tried a few different adaptations of the felt and found full cover on my speakers made the biggest difference.

From the measurements I made I came to the conclusion the felt dealt with 2 sources of colouration.

The first - baffle is quite large compared to the cone and using an accelerometer to measure the vibration on the baffle the felt reduces these vibrations significantly.

Second is the wave emanating from the baffle edge. I placed the mic at different angles around the baffle edge, there was a reduction in amplitude around the edge.
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Old 15th January 2020, 06:45 PM   #2844
MITsound is offline MITsound  Canada
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Quote:
Originally Posted by warrjon View Post
I made a lot of measurements when I added the felt to the baffle. I also tried a few different adaptations of the felt and found full cover on my speakers made the biggest difference.

From the measurements I made I came to the conclusion the felt dealt with 2 sources of colouration.

The first - baffle is quite large compared to the cone and using an accelerometer to measure the vibration on the baffle the felt reduces these vibrations significantly.

Second is the wave emanating from the baffle edge. I placed the mic at different angles around the baffle edge, there was a reduction in amplitude around the edge.
I have ordered some large 4mm felt sheets for an unboxed cabinet experiment.

The plan is to make a simple u shaped frame, with the front acting as a baffle, and the other parts as the top and bottom of the unbox.
The sides and rear of the unbox will be the felt.
I'm guessing it will damp the rear wave, without reflecting anything to the back of the driver, in this case, my Alpair 12P pair.
I'm hoping it'll act as an aperiodic vent system, while still allowing plenty of ambience all around.
I also think it's worth cutting nearly full length slots around all four sides of the front, parallel with the baffle. It's my thinking this will be the easiest path for the out of phase backwave to escape.
Maybe this will provide enough edge cancellation to provide mini monitor like imaging: it will effectively isolate the front baffle from its surroundings. Hopefully.
Got the idea from another poster's idea of putting a reflecting panel behind his open baffle main driver, to limit front wall reflections.
Plus the recent benefits of felt discussed here.
Images to follow sawdust.
This seems less fussy than my original idea: same frame, but wrapped in grill cloth, then experiments with the degree of stuffing for damping.
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Old 15th January 2020, 07:16 PM   #2845
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by OllBoll View Post
Felt is a great baffle material. I documented some experiments with it in a thread a while ago.

The best thing about them is that the felt doesn't even need to be thick (I used 3 layers in that thread but a single layer is enough, even down to 100 hz). The sound wants to take the path of least resistance and even a single layer of felt present more resistance than free air and a bit more distance. In fact I got worse results when I used too much felt. Too much in this example was a monstrosity with where I glued 20 cm of felt glued together and carved it into a donut shape. Sadly I never photographed that monstrosity, it was vanquished shortly after I measured and saw how horrible it was.
Thank you for the link to that thread. I saw it some time ago but forgot what it was called. I shall enjoy reading it
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Old 15th January 2020, 07:46 PM   #2846
Peter Campbell is offline Peter Campbell  Canada
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I got a big clarity improvement by taking warrjon’s felt baffle idea to heart.

I mounted the driver through the first layer of felt tight to the baffle, and then secured a second layer separated 1/4” from the first that wraps around to the rear of the baffle, such that the baffle edges are rounded felt.

That, and a 10 degree backward tilt on the fullrange make it almost ok without equalization. The tilt also makes the freq response as you move side to side vary much less than it used to. Image isn’t just clearer, it’s more stable vs listening position.

Most but not all of the harshness I perceived has gone with these changes, very happy with it.
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Old 16th January 2020, 04:07 AM   #2847
MITsound is offline MITsound  Canada
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Default Finally set for surround

Open baffle full range + horns as helpers for L/R, MarkAudio dual 12PW as centre U Frame.
There's enough resonance there to knock the bass down 6db to maintain normal balance in sound, so that's a little extra free headroom for my little amp, on the left. The other little amp on the right powers the horn hybrids.

The centre channel's twin does the rear surrounds, with each driver separately amplified.
My first open baffle/ open back surround sound system, and I think it rocks!
My first all class A amplified surround sound system ,too.
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Old 16th January 2020, 06:27 AM   #2848
warrjon is offline warrjon  Australia
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Quote:
Originally Posted by MITsound View Post
I have ordered some large 4mm felt sheets for an unboxed cabinet experiment.

Maybe this will provide enough edge cancellation to provide mini monitor like imaging: it will effectively isolate the front baffle from its surroundings.
Let us know how it goes.

My speakers with the 12P's magnet mounted with a 400mm wide MDF plywood sandwich even without the felt image superbly. In fact with closed eyes it is impossible to locate the speakers. I found the felt improved detail.
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Old 16th January 2020, 10:17 AM   #2849
TNT is offline TNT  Sweden
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For inspiration :-D

First some prototyping with light and soft material - some re-thinking, then going for gold, but, eventually fail.

Midrange (400Hz ->) is/was a Göbeln inspired carbon bending wave transducer.

Why didnt I do an "open back" mold? Stupid!! (I think I wanted smooth surface on both sides really)

No retry - yet

//
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Last edited by TNT; 16th January 2020 at 10:24 AM.
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Old 22nd January 2020, 08:40 AM   #2850
Leonidas is offline Leonidas  Netherlands
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For those who are interested :

Audio Dandy - How to enjoy High Resolution Audio

have fun

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