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MultiWay Conventional loudspeakers with crossovers 

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7th October 2008, 12:21 AM  #1 
diyAudio Member
Join Date: Jan 2004
Location: Toronto, ON, Canada

The ideal spring type, or minimizing the effect of Cms on distortion
Is the ideal restoring force applied by the spring on the moving assembly:
1) constant => F(restoring) = c for all x, c is a constant 2) linear => F(restoring) = kx for all x 3) parabolic => F(restoring) = kx^2 for all x (might be another coefficient in there) I think Klippel covered this in one of his papers but either I can't find it or it disappeared off the Internet. 
7th October 2008, 10:12 AM  #2 
diyAudio Member
Join Date: Sep 2002
Location: NL

ideally, the mechanical compliance of the moving system or (1/stiffness) is constant for each position of the cone. So answer (1). This is also the assumption in the most simple electromechanical models.
Unfortunately, this is not the case for real world drivers as can be seen in Klippel measurments of Cms kindly borrowd from npdang on diyma. The measured Cms values can be reasonably approximated by an quadratic fit, so (3). 
7th October 2008, 12:57 PM  #3 
diyAudio Member RIP
Join Date: Nov 2003
Location: Brighton UK

Hi,
I'm sorry but 1) is a nonstarter and not the definition of a spring. 2) Is of course a classic ideal spring, theoretically zero distortion. 3) you can reword to as nonlinear, not necessarily parabobic. Practically all suspensions are 3). The air in box is very nearly 2 except at very high compression. /sreten. 
7th October 2008, 01:02 PM  #4 
diyAudio Member
Join Date: May 2002
Location: Switzerland

Which 4) leads to the conclusion that the combination of 3) and the linear behaviour of the air spring is also quite linear IF the effect of the air spring is dominating.
Regards Charles 
7th October 2008, 05:09 PM  #5  
diyAudio Member
Join Date: Jan 2004
Location: Toronto, ON, Canada

Quote:
2)  is F=kx really the ideal for zero distortion? This conflicts with what LaMa said. 

7th October 2008, 05:44 PM  #6 
diyAudio Member RIP
Join Date: Nov 2003
Location: Brighton UK

Hi,
A constant force is exactly that  a constant force, no springyness. LaMa did not read your list slowly enough, constant compliance = 2). /sreten. 
7th October 2008, 11:28 PM  #7 
diyAudio Member
Join Date: Jan 2004
Location: Toronto, ON, Canada

So a negator spring is not a spring? I think you are reading too literally into the relationship between linear springs and Hooke's Law.

8th October 2008, 07:22 AM  #8 
diyAudio Member

A linear spring is one that obeys Hooke's law!
spring = force is a function of displacement linear = force is a linear function of displacement (f = kx) 
8th October 2008, 11:02 AM  #9  
diyAudio Member
Join Date: Jan 2004
Location: Toronto, ON, Canada

Quote:


8th October 2008, 01:34 PM  #10 
diyAudio Member
Join Date: May 2002
Location: Switzerland

Just one question: If a linear restoring force were the way to go, how would you want it to behave within a loudspeaker driver (which should be able to move in two directions) ? How about the situation at zero displacement ? Equal restoring force in two directions at once ?
A spring following Hooke's law as closely as possible is still the way to go. There are possibilities to implement progressive restoring force at high excursions in order to achieve mechanical protection at high excursions though. Regards Charles 
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