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Purpose of a box

 

New member
Username: Rds11

Louisville, Kentucky

Post Number: 4
Registered: Nov-04
I am looking at getting 1 subwoofer to go in my car, SPL oriented but retaining SQ. anyways that really has nothing to do w/ my question. I was wondering why the size of the box affects how much power a subwoofer needs to reach maximum excursion and performance. I just want to understand the "physics" behind that
 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5452
Registered: Dec-03
the enclosure size is based on the thiele-small specs of the driver, but in short, the box supplies suspension for the driver. the size of the box determines the amount of suspension supplied, and thus how easily the sub can excurse with a given amount of power.
 

Bronze Member
Username: Skema

Manch, NH US

Post Number: 74
Registered: Aug-04
Hey just curious, what would be the result of putting a smaller component speaker in a box scaled to its size. I know smaller speakers arent designed for such, but what would be the result anyways?
 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5465
Registered: Dec-03
you mean like putting a 6" driver in a sealed enclosure, instead of infinite baffle like a door panel?
it entirely depends on the TS specs of the driver.. most smaller speakers are made to be mounted 'free air' and have a fairly high EBP (Fs/Qes) so putting them in a sealed enclosure makes them perform very poorly.
mind you, a few speakers are meant for small enclosures, but they generally specify this, too.
 

Bronze Member
Username: Blownriv

OH USA

Post Number: 14
Registered: Nov-04
the size of the enclosure also affects the shape of the response curve for a given woofer, measured as Qtc (total system Q). the woofer and the airspace act together to define the type of bass response (and overall quality) you will get.

IMO, tuning for total system Q is FAR more important than picking a sub that is supposed to be a "SQ" sub or an "SPL" sub. you have much more control over how a woofer will sound by experimenting with its enclosure size vs. picking a sub that is supposed to just give you SQ or SPL right out of the box.

in sealed enclosures, Qtc values vary from 0.5 (very large boxes) to 2.0 (very small boxes). low Qtc values have very quick response and deep base. higher Qtc values have a boomy response good for SPL. somewhere in the middle is an ideal value that will sound good to you in your car.

if you want accurate bass (flat response w/ deeper roll-off and quicker response), go with a bigger enclosure (low Qtc). if you want more boom and higher power handling (peaky response good for SPL w/less deep bass), use a smaller box (high Qtc).

Qtc can be calculated based on the size of your box and the T/S parameters of the woofer.
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