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Simple Questions?

post #1 of 4
6/23/09 at 6:32am
Thread Starter 
I know someone who is fond of saying "no replacement for displacement".

What is the strict technical definition of displacement?

Is it limited to enclosure volume?

Does it include driver excursion, and amp power?

In a ported design is the port part of the equation?

Or, again, is it simply the size of the enclosure?

Thanks in Advance
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post #2 of 4
6/23/09 at 8:35am

Re: Simple Questions?

It's how much air your sub driver(s) can move.

As an example, I use a pair of 15" TC-3000 drivers in my home theater. First you have to find the Sd parameter. It's not given for my driver but the cone diameter of 325mm is.

Sd = 829cm^2

Multiple that times the xmax*2 = 30mm*2 = 6cm.

829*6 = 4974cm^3 or 4.974L of displacement per driver or 10L of total displacement.

I'm upgrading to quad 18's with an Sd of 1210cm^2 and an xmax of 27mm. That gives me about 6.5L of displacment per driver or 26L of total air displacement.

Ported, sealed or PR subs are not factored into this equation but it should be based on your goals and buying decision. Because that is like saying a car that has a 5.0L motor will always be faster than a with a 4.5L motor. The displacement equation doesn't factor in driver sensitivity or the extra extension gained by ported/PR subs.

-Robert
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post #3 of 4
6/23/09 at 10:30am
Thread Starter 

Re: Simple Questions?

Quote:
Originally Posted by Robert_J
It's how much air your sub driver(s) can move.

As an example, I use a pair of 15" TC-3000 drivers in my home theater. First you have to find the Sd parameter. It's not given for my driver but the cone diameter of 325mm is.

Sd = 829cm^2

Multiple that times the xmax*2 = 30mm*2 = 6cm.

829*6 = 4974cm^3 or 4.974L of displacement per driver or 10L of total displacement.

I'm upgrading to quad 18's with an Sd of 1210cm^2 and an xmax of 27mm. That gives me about 6.5L of displacment per driver or 26L of total air displacement.

Ported, sealed or PR subs are not factored into this equation but it should be based on your goals and buying decision. Because that is like saying a car that has a 5.0L motor will always be faster than a with a 4.5L motor. The displacement equation doesn't factor in driver sensitivity or the extra extension gained by ported/PR subs.

-Robert

Thanks Robert

That led me to this page:

Car Audio Advice | Understanding Theile/Small Parameters

So Sd is the area of the cone.

I find it a bit confusing between Vas and Fs. Not sure if Fs takes all of the Vas factors into consideration.

Still, like you said, cone area multiplied by excursion seems to be the (basic) bottom line.
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post #4 of 4
6/23/09 at 2:10pm

Re: Simple Questions?

Eminence has the best description of the different parameters. But none are independent. Change 1 and others will change.

-Robert
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