This may help.
But note I am challenging that respected source.
Hmm, there's a suspended mass (Cms, Mms) and the gravitational force applying a constant force on it, so what's missing to make it more complex?
I'm not sure which aspect you are challenging, but it all looks OK to me (not going to the source, just what you wrote):
"Mms =1 / [(2*Pi*Fs)^2*Cms]"
The spring constant can be written k=1/Cms. Then writing the angular frequency ws = 2*Pi*Fs makes the equation match the standard form of the result for the resonant frequency of a "simple harmonic oscillator" - aka a mass on a spring - that looks like "w^2 = k/m".
"sag=Cms*Mms*g = g / [2*Pi*Fs]^2"
Again the spring constant is 1/Cms and the force stretching the spring is indeed the weight Mms*g so multiplying them gives the sag is as written.
"so sag depends of Fs squared, as I said it sounds too simple."
The result follows and - in case anyone is interested - is normal for systems of a mass on a spring under gravity (because the same "mass" is involved in calculating the gravitational and inertial effect - a deep, but mysterious, principle of physics). At which point I'd better stop or this is too much like the day job
Hope I did not misunderstand your challenge.
ps. posted here because here is where we are
pps. (edit) I'm always posting too slowly - already answered...
good point, I've not noticed before.4fun said:Long time creep due to plastic properties of the suspension materials may eventually come into play as time goes by,
Does the air load depend on cone velocity or cone displacement?
What proportion of the total dynamic mass comes solely from the actual mass of the moving components?
How high would Fs' rise above Fs?
Regarding sag, why not just write:
And include a reservation for Cms nonlinearities.
Why should xbl^2 be more sensitive than a standard motor for VC offset? If that would be the case xbl^2 would not have such good BL linearity as it obviously have.
I was thinking the same thing when I looked over the equation yesterday. Using Mmd instead of Mms would produce a more accurate result.
What actually spawned this request was a "chat" I had with someone regarding what alignment tolerances were available when using a motor equipped with XBL2. It was explained to me that alignment of the voice coil in the gap was very critical and that the tolerances were very tight in order to be fully effective.
That made me think of the potential sag issue when mounting an XBL2 sub horizontally. Would the technology be less "effective" due to suspension sag? Even less after suspension break-in?
The length of the coil relative to the top plate widths and spacing *is* critical, if this is even slightly wrong there'll be a dip or a hump in the middle of the BL curve which will give bad distortion even with displacements much smaller than Xmax.
This is what I was thinking about.
I doubt this would actually translate into anything audible anyway. I have yet to come across someone who can actually pick an XBL2 driver out of a blind A/B listening test, let alone identifying the changes in tolerances...