Printer Friendly Forum Posts - Facts about Sealed vs. Vented

Ok.. correct me, definetly if i am wrong.. but this is what I have found about sealed vs. vented.. True or not true.. Help if out if i screwed it up somewhere..

Selecting an Enclosure

Sealed vs. Vented

Sealed Enclosure

Sealed enclosure are simple to build and install, they provide good transient response,

Low frequency extension, (12 dB/octave) and high power handling in a small box.

As with all enclosures they should be sealed airtight.

A foam gasket is recommended between the woofer and the box.

Box performance is measured by the Q factor (ripple) and F3 (Hz /-3dB)

Smaller sealed boxes, have better power handling, due to less cone excursion, and they have a higher frequency roll off and more output gain, (Qtc1.0 to Qtc1.25 or higher).

Which in most applications is better for SPL.

The trade off with smaller Sealed box is that you loose deep bass extension.

The larger sealed box, is better for deep bass, with better transient response, due less ripple,

(Qtc .707 to Qtc .850) which is ideal for Sound Quality systems, but you loose power handling and SPL.

Do Not exceed the Larger recommended box size and the rated RMS power.

For sound quality we recommend to cover, at least one wall with one or two inch of Polly fill material.

For SPL competition no Polly Fill is necessary.

Woofer displacement should be added to the internal Box volume.

Vented Enclosure

Vented enclosures are more difficult to build; usually they are bigger then sealed boxes.

They provide better power handling down to the port tuning, and less acoustic distortion.

They are more efficient, (+3 dB or more for the same size sealed box system) play louder, and tune

lower in frequency, (F3) than sealed box, but rolls of at faster rate, 24 dB/octave which relates into

a loss of deep bass extension below the port tuning.

The type of alignment, Fb (Hz) and Gain (+dB) determine box performance.

Power handling below the port tuning is poor to the point of damaging the woofer if excessive power

is applied, due to driver unloading (as if it is working in free air).

The type of music played is critical in choosing box size and tuning frequency.

For Rock, Disco and Country 42 to 45 Hz

Wide range, Rap, and Boom type bass 36 to 40 Hz.

Jazz, Classical, Bass CD’s 32 to 38 Hz.

Do Not boost equalizer frequencies that are lower frequency then the port tuning.

Care should be taken wen building vented enclosures, to add to the box internal volume the port

Displacement, as well as the woofer displacement.

For SPL competition the port tuning it’s not necessarily the best frequency to achieve a high SPL score.

Vented Enclosure Design and Construction

When calculating enclosure volumes remember to add woofer and port displacement.

Avoid perfect cubic box shapes for better sound quality.

The use of square section port is a better choice for high excursion woofers to reduce port noise and more SPL output.

Simple Math For Enclosure Volume

Enclosure volume Width x Height x Depth divided by 1728 = Cub ft.

To calculate port displacement use the same formula

Port displacement Width x Height x Length divided by 1728 (depth of port) = Cub ft. (volume)

Port area Width x Height = Square inch

If port length is to long to fit in the box you can turn it

Around the back wall forming an L shape.

To find the area of a round port,

Measure the port diameter and divide by 2 = radius (1/2 of diameter)

Then multiply

(radius x radius x 3.14) = Square inch

Port Conversion

Keep distance from end of Port to back of box the same or greater then the Port width or diameter (A = B)

Round Area sq.in

3 in. = 7.10 ( 7.10 x 1= 7.10)

4 in. = 12.57

6 in. = 28.27

5 in. = 19.64

8 in. = 50.26

-------------
Girls can do anything guys can do!!
2~12" Kove Armageddon Z's
US Amps 2000x
US Amps 4300x (mids & highs)
US Amps X2R Crossover
Clarion DXZ745MP
2~Kove 5 1/4" KC Components
CompuStar Alarm :o)