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Old 11th January 2013, 09:51 AM   #111
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Join Date: Jul 2002
Location: N-W Balkans
Quote:
Originally Posted by båndsei View Post
Yesterday i was a happy man,mesurements where stunning.
Today...

Red is ESS, blue diy.
Yesteday I mesured at 10cm. distance.
Today at 40cm distance as i usual do,and with a 40cmvide baffel.
Any comments?
I could make a longer AMT,but have to make new tools.

Bernt
I think there is a reason for measurement standards such as 1m x 1m baffle, 1m mic distance, asymmetric driver placement in baffle, etc

Since you have all the needed equipment and experience that should not be a problem for you.

Longer AMT- absolutely. I'm thinking to start with 28-30 cm.
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Old 11th January 2013, 12:17 PM   #112
WrineX is offline WrineX  Netherlands
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its still not bad, just indeed make measurements at 1 m so you wont be disapointed with real results. but also be ware of the room interacting much more so just use it to see really how low it can go, and not so much for the upper frequency response or humps and bumps. also when you see a nsty bump try moving the mic a little to left right front back. to see what happens because it could well be a reflection of some sort. wich has nothing to do with ur driver. outside measurement would be even better. fire it upwards if posible, in a big garden ?
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Old 11th January 2013, 03:23 PM   #113
Paul W is offline Paul W  United States
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Here is "baffle" I use to take measurements more representative of driver only. Driver is smoothed to carpet floor with sheets of 1/2" wool felt, mic above.

Click the image to open in full size.
__________________
Paul
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Old 12th January 2013, 01:44 PM   #114
solhaga is offline solhaga  Sweden
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Quote:
Originally Posted by båndsei View Post
Here is a drawing in femm.shoving magnet polarity:[IMG]Click the image to open in full size.[/IMG]

Bernt
I´m experimenting with another magnetic setup for AMTs based on what I´m been working about making bass panels.

So I´d like to correlate your simulation with the one I´ve done on your setup.

I get this field intensity:

Click the image to open in full size.

Is it more or less what you get?
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Old 12th January 2013, 03:03 PM   #115
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Exactly the same.I have made some adjustments to get stronger and more liniar field.
[IMG]Click the image to open in full size.[/IMG]
I have used 12x12mm iron.Active diaphragm is 28mm.
[IMG]Click the image to open in full size.[/IMG]
[IMG]Click the image to open in full size.[/IMG]
Using 12x12 it is posibly to place the frame between the magnets.Frame, 5x4mm wood, is not on drawing.

Sorry square showing diaphragm is named steel , it has to be air.It affekts mesurements

Bernt,

Last edited by båndsei; 12th January 2013 at 03:12 PM. Reason: Wrong drawing
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Old 12th January 2013, 03:21 PM   #116
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Here the right pictures.
[IMG]Click the image to open in full size.[/IMG]
[IMG]Click the image to open in full size.[/IMG]
[IMG]Click the image to open in full size.[/IMG]
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Old 12th January 2013, 03:40 PM   #117
solhaga is offline solhaga  Sweden
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Thanks Bernt! Especially for the last update, it makes more sense with air in the gap and a B.n plot

I understand now that yours is the engine to use.

My idea of using a flat setup for sure has a more linear field, but there is still the back wave to consider.

Click the image to open in full size.

Click the image to open in full size.

b.n plot 3 mm in front of magnets:

Click the image to open in full size.

b.n plot 6 mm in front of magnets:

Click the image to open in full size.

Of course has the b.t field has to be considered as well:

Click the image to open in full size.

So I guess that configuration goes down the drain.

Last edited by solhaga; 12th January 2013 at 04:04 PM.
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Old 12th January 2013, 04:31 PM   #118
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What happens if you remove the iron.Air or alu (non magnetic)

Bernt
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Old 12th January 2013, 05:22 PM   #119
solhaga is offline solhaga  Sweden
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Not much really.
I have to shorten the membrane to only cover half the width of the magnets in order to get in the vicinety of a b.n/b.t ratio of 10/1.
I don´t think that´s good enough. The membrane will have too much movement "in and out".

Last edited by solhaga; 12th January 2013 at 05:30 PM.
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Old 12th January 2013, 11:31 PM   #120
solhaga is offline solhaga  Sweden
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Looking at your configuration a little bit, I did this simulation:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

The question is if it´s okay with such a large variation over the gap.
That the both sides in a V that produces the soundwave are influonced by slightly different forces doesn´t matter.
Worse is that the soundwaves that are produced in the middle of the gap will have much less amplitude.

b.t field looks well though:

Click the image to open in full size.
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