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brunob 21st August 2011 10:20 AM

Stackable ribbon module
 
4 Attachment(s)
I have built a very simple module that can easely be stacked on top of another to build a long line array. The idea is to use the two steel tubes that will fit on two long steel bars.

The ribbon area is 20 cm x 1.2 cm (or 1.0 cm). The steel frame is 22 cm long.

One of the picture shows a ribbon of 0.8 microns thick (no breathing allowed near the ribbon!). Aluminium foils provider: Foils List.

Magnet: 1.4 x 1.5 x 5 cm , N48.
Magnetic field strength: 0.74 and 0.64 T for the 1 cm gap; 0.70 and 0.58 for the 1.2 cm gap. The smaller value is for the middle of the gap, the larger for the magnet surface. Measurement were performed with a Hirst GM05 gaussmeter.

Frerquency response measured at a distance of 52 cm with ARTA.

a.wayne 21st August 2011 10:41 PM

Why not one long run ? disadvantage , advantages with stacking .......

tinitus 21st August 2011 11:50 PM

Quote:

Originally Posted by a.wayne (Post 2680810)
Why not one long run ? disadvantage , advantages with stacking .......

I think the chosen 12mm width is about optimal
magnet field weakens beyond that

and with 12mm a long ribbon becomes hard to handle
mechanical constructing is easier as well

but you get higher Fs with short ribbon
but quite good if it does 1khz

brunob 22nd August 2011 10:25 AM

Quote:

Originally Posted by a.wayne (Post 2680810)
Why not one long run ? disadvantage , advantages with stacking .......

Good question.

Advantages:

- safety: putting together two long rows of magnets is difficult and dangerous because of the strong forces involved
- less weakening of the magnetic field with the increases of the ribbon length
- more choice for the ribbon material (e.g. 2.5 microns, 25 x 25 cm sheet from Lebowfoils)
- I plan to build a straight line and a concave line and compare both

Disadvantages:
- magnetic field in the gap is not as homogenous
- comb filtering could occur if the dead space separating the ribbon radiation areas is too large

brunob 23rd August 2011 11:03 AM

concave line array
 
Has anyone experience with a concave line array of ribbons?

a.wayne 25th August 2011 06:00 PM

I'm going to build a short ribbon and compare .. currently have a 1200MM x42mm mid-range prototype and will compare it's efficiency to say a 350mmx42mm.


we will see....

brunob 3rd October 2011 10:20 AM

Dip at 4 KHz
 
2 Attachment(s)
The frequency response of my ribbon modules shows a dip at about 4 to 5 KHz.

I wonder where this dip is coming from?

If I would increase the width of the left and right sides of the ribbon module, by attaching another 2 x 2 cm rectangular tube on each side (see pictures in the first post of this thread), then the frequency of the dip would go lower. The frequency responses are shown in the first picture atached to this post.

If I cover the back of the driver with felt, then the dip dissapears and the level at 2 KHz is slightly lower (second attached picture).

I first thought this effect was due to the diffraction from the edges. I don't think this is the cause of the dip because when adding felt in the back of the driver, the dip is strongly attenuated.

:confused:

Groove-T 4th October 2011 08:16 AM

Quote:

Originally Posted by brunob (Post 2732878)
The frequency response of my ribbon modules shows a dip at about 4 to 5 KHz.

I wonder where this dip is coming from?

If I would increase the width of the left and right sides of the ribbon module, by attaching another 2 x 2 cm rectangular tube on each side (see pictures in the first post of this thread), then the frequency of the dip would go lower. The frequency responses are shown in the first picture atached to this post.

If I cover the back of the driver with felt, then the dip dissapears and the level at 2 KHz is slightly lower (second attached picture).

I first thought this effect was due to the diffraction from the edges. I don't think this is the cause of the dip because when adding felt in the back of the driver, the dip is strongly attenuated.

:confused:

Cavity resonance.

brunob 11th October 2011 05:10 PM

Quote:

Originally Posted by Groove-T (Post 2734021)
Cavity resonance.

Which cavity do you have in mind? Could you elaborate?
Thanks

tinitus 11th October 2011 05:46 PM

use two, with a crossover around the dip :D


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