sub bottoming out

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DYohn

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Joined: April 22, 2003

Location: Arizona, United States

Posted: May 02, 2004 at 6:58 PM / IP Logged

The theory is that more exrursion capability = better downfiring performance, since the effect of gravity on the cone will not use up too much of the Xmax (excursion) capability. Longer throw woofers with extended 'bump plates" work best in downfiring installations.

Woofer with the specs you list = sag percentage of about 5.32%. WAY too much for downfiring, it could easily be "bottomed out" and the voice coil will eventually fry.

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dudek38

Copper - Posts: 250

Joined: March 28, 2004

Location: United States

Posted: May 02, 2004 at 7:19 PM / IP Logged

can u tell me the formula for sag using my numbers. i looked up the other post but cant get it.

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stevdart

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Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: May 02, 2004 at 7:49 PM / IP Logged

"The following is the same formula, including the relationship of acceleration and Pi in this case:

Percentage of Sag = 981,000 / (Xmax * (2 * Pi * Fs)²)

where

- 981,000 is acceleration due to gravity (mm/S²) * 100 (for the percentage).

- Xmax is the maximum linear excursion of a loudspeaker voice coil while remaining within the magnetic flux field (mm). - Fs is the free-air resonant frequency of the woofer (Hz)

- Pi is the ratio of a circle's circumference and diameter, usually rounded to 3.14.

As a general rule of thumb, any time the sag exceeds 5% of the driver's Xmax, it's not recommended for a down-firing subwoofer application."

I wanted to see if I understood this too. Above is from the post DYohn made about downfiring. Now when I use your numbers, 14.15 mm XMAX and 23.32 Fs, I come up with 3.23% sag. But I'm no mathmatician.

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Beerman354

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Joined: April 11, 2004

Location: United States

Posted: May 02, 2004 at 8:31 PM / IP Logged

What if the sub has 25 xmax and 0 fs? Does it have 0 % sag?

stevdart

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Posted: May 02, 2004 at 8:34 PM / IP Logged

Try some real numbers. 0 Hz Fs, sheeeesh.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Beerman354

Member - Posts: 19

Joined: April 11, 2004

Location: United States

Posted: May 02, 2004 at 8:37 PM / IP Logged

Maybe its just a typo but here ya go http://www.crutchfield.com/S-HzjgElmizSO/cgi-bin/ProdView.asp?a=0&s=0&cc=01&g=67600&id=features_and_specs&i=107MM104

stevdart

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Joined: January 24, 2004

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Posted: May 02, 2004 at 8:51 PM / IP Logged

Dude, I thought you were pulling some legs here. But it is a typo anyway. It should be 32 Hz.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Beerman354

Member - Posts: 19

Joined: April 11, 2004

Location: United States

Posted: May 02, 2004 at 8:56 PM / IP Logged

If my calc's are correct thats .97% of sag. So this sub should work great downfiring correct?

dudek38

Copper - Posts: 250

Joined: March 28, 2004

Location: United States

Posted: May 02, 2004 at 8:58 PM / IP Logged

i got 3.23 too.

owner of

Motion Marine & Car Audio

the florida keys

stevdart

Platinum - Posts: 5,816

Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: May 02, 2004 at 8:59 PM / IP Logged

Yeah, can't go wrong with an inch of XMAX.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

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