# Xmax

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#### dallaire

Hello again, I was wondering if someone had a link that would help me find out the amount of cone extention I will be placing on my four inch mids at a cross frequency of 300hz. I am using the Peerless four inch mid/woofer HDS PPB. Is there a simple formula for fig. for this? I am using two and wiring in parallel so my rotel anp will see about a four ohm load. The driver I am using says it has a linear excursion of +or- three mm, thats about all the info I can find on this driver on this parameter. I'm sure this is dependant on volume level, I do listen to movies at reference levels, and like my music pretty much the same. Crossover is 24db per and electronic.
Thanks,
dallaire

#### Svante

Yes, the RMS cone amplitude for a given sound pressure p in free space is

x=p*4*pi*r/(Sd*w²*rho0)

r is the distance at which p is measured, w=2*pi*f, rho0=1.2 kg/m³

p can be derived from sound pressure level as p=pref*10^(Lp/20)

where pref=20 µPa, Lp is the sound pressure level in dB.

So, for example, if the Lp=94 dB, r=1 m, f=300 Hz and Sd=100 cm², then

p=2e-5*10^(94/20)=1 Pa

x=1*4*pi*1/(0.01*(2*pi*300)²*1.2)=0.294 mm

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