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Old 24th February 2013, 02:43 PM   #171
Zen Mod is offline Zen Mod  Serbia
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temp related rising of FC resistance is easily addressed if you use CCS as FC PSU
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Old 24th February 2013, 03:31 PM   #172
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Quote:
Originally Posted by Hentai View Post
Hello audiofilofine,

Temperature of the whole system depends on a few factors. Fieldcoil power disipation being perhaps the most important one. The amount of steel and geometry plays a role also.

The drop in current with increased field coil resistance due to rising temp i found to be around 0.1-0.3A depending on the driving current with the same number of turns on each layer.







About formulas, there is no general formula for what you are asking. Giving inside and outside dimensions all you need to calculate is a coil that will a specific DC resistance in order to meet your power requirements.


this is formula
Click the image to open in full size.

In my design proccess i started from the voice coil actually, chose diameter, underhung topology, voice coil height, plate thickness and then moving down to fieldcoil. Core diameter is in close relationship to voicecoil diameter about 150-200% so that you dont saturate plates too soon.
So designing the field coil i did knowing what i want to get in the gap and the structure around the gap.

use hbc ? [COLOR="Blue"]

Since you brought up the temperature subject, i am developing a tool for this kind of analysis. It is almost done and will allow monitoring of fieldcoil resisntace increase and voice coil resistance increase in time. A temp probe can be placed on the center pole piece near the voice coil to calculate a temp coef. This can help in determining large signal parameters and create a more precise model.
The tool is based on PIC18F4550 and connects to the PC via USB for data logging and visualization. It can export data for archiving.
Will show you what it can do once it is completly done but here are some teasers with a test unit, i heated up the temp senzor with a lighter thats why it goes up. Im designing a PCB now hope by next weekend to be done.

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

PS. Not sure what you refer to as dual core electromagnet naked
example for professional work

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Click the image to open in full size.

Last edited by audiofilofine; 24th February 2013 at 03:38 PM.
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Old 24th February 2013, 03:55 PM   #173
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Quote:
Originally Posted by Zen Mod View Post
temp related rising of FC resistance is easily addressed if you use CCS as FC PSU
are you sure?
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Old 24th February 2013, 03:58 PM   #174
Zen Mod is offline Zen Mod  Serbia
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if constant current through FC is the goal , yes , I'm sure
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Old 24th February 2013, 06:42 PM   #175
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what kind of power supply and how many volt-ampere?
electric train toy ps? battery charge ps ( tungar) ?rectifiers tube ps?
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Old 24th February 2013, 07:50 PM   #176
Hentai is offline Hentai  Romania
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Quote:
Originally Posted by audiofilofine View Post
example for professional work

Click the image to open in full size.

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Click the image to open in full size.
Whats your point exactly? I assume we all know Ohm's law. Also if you post material in other languages please provide a translation.
Quote:
Originally Posted by Zen Mod View Post
temp related rising of FC resistance is easily addressed if you use CCS as FC PSU
Yes that is true, flux density in gap wont be influenced by change in FC Rdc with temp. Even so, with a normal PSU the differences will be very low. Once you reach saturation region 200mA wont make a difference.

Also i liked the idea of people having the ability to use even a laptop adapter PSU with the proper current rating. For the purist however a CCS would be the best.
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Old 25th February 2013, 06:10 PM   #177
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just a little personal observation related to the topic discussed some posts earlier : ideal stiffening solution.

when i wanted to stiffen the centre-part of a paper cone, i got inspired in violin-making territory. There's a lot alchemy going on in bowed instruments' finishes, but there are known hardness attributes of various resins, from wich the hardest is gum sandarac, (harder than shellac for example). So i chose it since i wanted the best stiffness-to-lightweight ratio (=high dilution in pure alc=not much material added, but stiffening effect to the desired level achieved)

maybe helps. take care

misok
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Old 1st March 2013, 06:34 PM   #178
Frank40 is offline Frank40  Denmark
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Hi there

misok, thanks for the info sound like a good material.

I am working on my new cone, this time I will make it with a positive and a negative from. I bought some two component silicone to make the positive from, this will make it easy to experiment with other cone materials. The new form has a build in surrounding, It is my goal to make cone and surroundings in one part.... But I have to see how it works out.

A note of observation.

I was in a hurry to listen to the driver so I used a standard spider that I had, it has a very high suspension. I have always believed that a spider should be soft, so I was surprised how good it's sound. Any comments regarding the spider, pro or cons on soft spider will be appreciated.

Take care
Frank
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Old 2nd March 2013, 05:06 PM   #179
Hentai is offline Hentai  Romania
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Hi Frank,

Good work there.
Regarding spider and Cms value. You need to reach a balance somewhere. I too like softer suspesions because it will enable the loudspeaker to perform well at low volumes and seems to be more revealing in details.
However it must be carefully chosen as there is the danger to have a long impulse response because the recovering force that brings the cone back to its resting position is smaller.
In your case and mine with a low moving mass the inertia will be lower and allows for a softer suspension system. Also a powerful motor will help in controlling its movement.
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Old 4th March 2013, 12:55 PM   #180
Frank40 is offline Frank40  Denmark
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Thanks for your replay hentai.

I have made a positive and negative mould made today, needs a bit rework... but no to bad.
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