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Old 24th July 2008, 04:35 PM   #1
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Default Cone weight vs Cone stiffness

Hi Guys,
I am one of those people with too many ideas and too little time. I have two projects on the boards with glue drying, but an idea I want to try. This idea might be completely insane, but I wanted some input from the much more educated on this if I might ask.

The reason many people like certain full range drivers seems to be super light weight cones and heavy driver motor for superior control. Assuming I am looking at something like a fostex driver with banana pulp cone, what happens if the cone becomes heavier in the real world? Truncated high frequency response? Loss of "airy" sound?

Here is the reason I ask and the idea that I have. I like the sound of omni directional speakers. I have heard several omni designs and the ability to be forgiving of room acoustics makes them very appealing to me. I am thinking of using a good driver like a fostex or other with close tolerance to voice coil and gap etc and building a cone for it. The idea would be two (or more) motors in the center of the speaker with the cone shaped like a half-tube. I have several 3" full range drivers at home to experiment with first so I will probably destroy these to test the idea. Basically I would extend the voice coil out to the center of the cone with a pole and attach it to the cone. Using two motors facing opposite directions I would have a tube split down the middle and use a half surround at the tops and bottoms with a straight tube of surround material in between the two halves. I will try to make a drawing that might help, but my question is about the performance of the cones themselves. If they are too heavy, will the frequency response be muddy or limited? if they are too light, will I sacrifice their ability to produce lower frequencies due to flexing? Too big might be too flexible I think so I am certain it would be limited by size and attachment.

If I can't do it as full range, I at least would like to do it as a mid+ frequency unit augmented by a sub. I think I can make that more seemless (due to room interaction) than needing help on the high end.

Drawing in progress. let me know what opinions you guys have.

Thanks!
Robert
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Old 24th July 2008, 05:13 PM   #2
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OK So I can't post the pic in the thread from work. I will attach it for now:
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File Type: jpg omni design.jpg (37.0 KB, 227 views)
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Old 24th July 2008, 05:18 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
read the T/S params of some of the 6inch to 8inch fullrangers.
What is the weight of the cone+voice coil (Mms)?
What is the weight of your moving assembly?
Now go and read the Mms of some low efficiency bass drivers.
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Old 24th July 2008, 05:26 PM   #4
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That's kind of what I was thinking. Considering the size of the cone if I do it this way, it might explain why Electrostats and the like were designed the way they are.

I wish I was good enough to design an electrostat with a curved surface. Pure omni-directional tube with advanced design criteria seems like a great idea, but the science behind even a simple panel is way past my budget or limited education. lol

I will do some comparisons of drivers Mms to see what seems to work with conventional design and then try to come up with real world weights of the assemblies I am after.

Still, does this make the difference in frequency range? I have a pair of tubes I built last year where I wrapped a cylindrical assembly with mylar and sealed it to an enclosure with the driver firing up into the tube. It actually sounds really good for what it is. It won't produce anything below about 80hz without real distortion and it isn't very efficient, but it does a great job of imaging etc.

I will get back with more specs on what I am working with. Trying to think of a material for the cones.

Take care,
Robert
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Old 24th July 2008, 06:20 PM   #5
GM is online now GM  United States
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Quote:
Originally posted by AndrewT
Hi,
read the T/S params of some of the 6inch to 8inch fullrangers.
What is the weight of the cone+voice coil (Mms)?
What is the weight of your moving assembly?
Now go and read the Mms of some low efficiency bass drivers.
Greets!

Sorry, but Mms is totally irrelevant to a driver's HF response. Ignoring the effects of the VC's diameter (smaller = greater HF potential), dustcap or whizzer, what matters is its relative motor strength and inductance: http://www.adireaudio.com/Files/WooferSpeed.pdf

GM
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Old 24th July 2008, 07:21 PM   #6
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Thanks for the link GM!

that is exactly the information I was looking for. I may never do anything at all with this concept, but I like to research and I might play around with it. This makes the ideal a little more plausible so I will continue to read and research while my other projects are coming together.

One can never learn too much ya know! lol

Take care,
Robert
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Old 24th July 2008, 10:53 PM   #7
AndrewT is offline AndrewT  Scotland
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has the woofer speed PDF anything to do with a full ranger?
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Old 24th July 2008, 11:12 PM   #8
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The info contained applies to all point source drivers.

GM
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Old 25th July 2008, 05:10 PM   #9
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Wow,
After reading that article and looking at some "famous" full range drivers I can see that the weight really isn't a factor. It makes me wonder though. I found speakers with Mms ranging from 2.9 grams all the way up to 18g!

So if the inductance of the VC is what determines the speakers ability to do transient movement and power handling capability determines the SPL ability of the speaker, does that more or less define the crux of speaker builders? I mean, full rangers inherently have rather small voice coils and rather large magnets. So they only handle so much current, but do so under much more control right?

If that is the case, does the cone material matter so long as it doesn't flex too much? I say too much because I can't see how a paper cone doesn't flex at all.

It certainly gives me some things to start researching. It also brings up the ideas of building unconventional drivers. Does anyone have more papers describing this sort of thing? That was a great read, but there really wasn't any more at the site about the subject. I would like to read more on that.

Thanks again GM
Robert
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Old 25th July 2008, 08:16 PM   #10
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I read the first part of the Adire paper and it certainly tries to proove something by confusing labels. Using their terminologi we have a = BL/m*i. Now the quota BL/m is certainly not the same constant for every loudspeaker. The higer the quota the better the acceleration. Assuming Bl and m as constants is OK, but denoting both these values with the same C is plain wrong, and probably intentionally done one would think. People would be lead to think that the BL/m quota doesn't matter, it does. The relationship should read: a = f(BL/m,i).

Experiment with one driver does not prove very much as it does not handle the possible trade-offs between BL/m quota and the possibility of handling current. One would have liked to see comparable units compared (!) just as they are.

/Erling
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