A sealed box can give more noise outside the vehicle?

The ported box is much louder than the same sized sealed box. In fact, it has a 3dB higher efficiency.

The ported box also increases the acoustic load at the rear of the speaker. This is good for two reasons. One: Lower cone excursion near box resonance frequency. Two: Higher power handling and lower modulation distortion.

The port adds to the output of the woofer, the reason its louder

What???? We don't want air to move through the port, we want sound waves. If air velocity gets too high it disturbs the sound that we want to come out of the port. So if you feel a lot of air being pushed in and out of the port, increase its size. Small ports hurt performance because the vent velocity is too high

And I have no Idea of what your talking about, please clarify

 

Well reading all this including Ranger's reply just gave me a headache and something to think about. I certainly wish i knew more about boxes and how they effect your final product in sound. All i really know is that ported is louder then sealed and its simply because your getting sound from the front and rear of the woofer. Ive had my 3 12's in a sealed box and the tightness of the bass really grew onto me. Altho im sure if i had a perfectly built ported box for my subs, my thought's would change.

 

From my understanding a box that is ported can go no lower than whayever the port is tuned to. If its 35 hz then thats the lowest frequency it will do. Sealed has no pre tuned frequency to cut off at. I may be way off though.

 

100% correct

And the sealed box has a "tighter" more controlled sound than a ported box. Thats why most SQ people use sealed boxes. Also a sealed box typically has better transient responce than a ported box. In other words, the sound from a sealed box blends better with the rest of your speakers than a ported box would.

Thats not correct, I've tuned boxes to 45Hz that had NO Problem playing 35 hertz tones. But we do need to be careful. We can lose control of the woofer at frequencies substantially below tuning frequency. So the next question would be define substantially. I can't. Different woofers, box size, and tuning all effect how much below tuning we can safely go.

This is one of the downsides of the ported box. But it can be fixed with a sub sonic filter. Thats why many upper end amps have sub sonic filters on them.

 

Interesting side note on this, several high end home audio speakers use vented designs, or even passive radiaters (essentially the same thing)...I remmber B&W 801 matrix's, several Polk audio's, Klipsch, etc....

 

Did you know that the first patent describing driver and vent interaction was granted to A.C. Thuras in 1932. It wasnt until 1954 that things began to change. Edgar Villchur began a series of articles in Audio Magazine that established the Air Suspension (Sealed Box) as the ultimate speaker design.

The Polk audio RTi home speaker does use a ported design. Why, they need to fill a living room with bass and the woofers are dual 7-inch. Yet the bass output is incredible. A lot of research goes into home speakers.

But again we cannot compare home audio with car audio, two completely different environments.

:lol:I won't charge you anything for the history lesson^_^

 

A ported box merely makes use of the sound waves from the back of the woofer and the port controls the timing of the sound wave so it exits in unison with the sound wave from the front of the woofer. The reason you don't get bass with a woofer mounted outside an enclosure is because the two waves counteract one another. In a sealed enclosure, you get only the front wave. That's why a ported enclosure is twice as efficient.

The problem with ports is, that at a certain frequency, the driver is effectively operating in free-air, as if it wasn't in an enclosure at all. Woofers in sealed boxes handle more power than in ported ones. Press a cone in with your hand in a ported box, then try the same thing in a similar sized sealed box. It is much harder to push because it is dampened by a cushion of air. "Air Suspension" was developed by Acoustic Research way back. Before then, most home speakers were ported and very large. AR proved that good sound could be obtained from smaller sealed enclosures.

Take a look at a lot of home subwoofers at the low and high end. I'll bet you that the majority of low-end subwoofers use ported enclosures and the high end ones are sealed. Think there's a reason for that? It's cheaper to make ported systems because they don't need as powerful an amplifier to make a lot of boom, which sounds okay for movies. When you play music, however, most of the ported designs fail.

 

Only I wouldn't consider Polk Audio or Klipsch as high end, more like mid-fi.