Whatcha Think

Discussion in 'General Car Audio Discussions' started by MoK, Feb 6, 2004.

  1. MoK

    MoK New Member

    Alright i dont know to much bout speakers, so i got some questions? I got a 12JLw7, Whats louder, ported or sealed? What about a whole box made of '3/4 plexiglass? $300 to much ??? thanks
     
  2. BlkX

    BlkX Full Member

    Ported will be louder 99.9% of the time. That's a good price, but i'd use thicker plexi unless you have real small panels...
     
  3. Steven Kephart

    Steven Kephart Full Member

    I just want to be the devils advocate here.

    Couldn't you say that sealed is louder throughout the whole bandwidth? In other words ported is louder in a narrow bandwidth, but drops off a lot sooner. So sealed can be louder at more frequencies. Of course the design will effect this idea as well. The added efficiency of the larger ported enclosure being an example.

    I heard this a long time ago and thought it was somewhat intriguing. I'm curious to hear some of your opinions on this.
     
  4. BlkX

    BlkX Full Member

    Yep, i agree fully, but most people would be concerned about what their score was if they were to be metered. The ported box will 99.9% of the time yield the higher score.

    I have never liked the sound of a ported box mainly because of the reasons you mentioned. They sound very monotone to me, with no musical quality.
     
  5. geolemon

    geolemon Full Member

    No, that's actually not true...
    Ported will be louder across the whole bandwidth, with the exception of some small percentage of the lowest of frequencies... and that's simply due to the fact that the sealed box is rolling off slower than the ported box.

    But wherever those rolloff-lines cross.. anywhere above that, the ported enclosure will be louder, by as much as 3dB. B)
     
  6. Steven Kephart

    Steven Kephart Full Member

    I could have been remembering this wrong and it was bandpass compared to sealed, or something like that.

    I have a question though. Is that 3dB gain only because of the added efficiency? In other words, what if the sealed enclosure and ported enclosure were the same size? To cover everything, how about two scenarios for the ported enclosure; one including port area in the enclosure size, the other not.
     
  7. deyton

    deyton Full Member

    I don't know where the 3dB number comes from exactly, but in my modelling if you have a ported box and a sealed box that are the same size, it is possible to get a +3dB boost throughout the entire frequency range, usually by tuning pretty low. (Ex. Shiva in 2 cubes sealed and 2 cubes @ 22Hz). Group delay (compared to large ported) and excursion (compared to sealed) are really kept in check as well, so this seems like an intriguing option to me.

    Generally I don't think i believe the whole Port = 3dB thing, you don't really get 3dB louder, it's just whatever the graph says.

    Someone correct me if I'm way off base.
     
  8. geolemon

    geolemon Full Member

    The 3dB is a maximum value... as in "you aren't going to be able to get any more than 3dB by porting, compared to sealed".
    It is that number, because the port and subwoofer are never more than 90 degrees in-phase with each other... and over most of the frequency band are more than 90 degrees out of phase.

    If you had one speaker in a sealed box, and then you added a second speaker in a sealed box, you'd gain 6dB, by doubling your displacement.
    But then, let's say you had a phase shift knob on your amp...
    And you turned it so that the one sub was 90 degrees out of phase relative to the other one...
    Now, you'd only be seeing 3dB more than you saw with the single subwoofer.
    That's where the 3dB comes from. It's because the port isn't really ever able to delay the signal coming out the port by more than 90 degrees, so that's the closest you get to being "in phase" with the cone.

    There are quite a few things that you can do to get a gain less than 3dB from porting...but there's nothing you can really do to get more than a 3dB gain. ;)

    But fundamentally speaking, the 3dB gain comes because the port is essentially 'recycling' the rear-of-cone sound energy, rather than just constraining it, never allowing it to escape the inside of a sealed enclosure. So you end up with an enclosure that has two sound sources... like adding an extra half a sub, if you will. :D
     
  9. delvryboy

    delvryboy Full Member

    i would think this to be more of a general statement

    take my compVR's for instance

    1.25 p/c sealed, 1000w - 137.2

    3 cubes @ 32hz - 138.7

    4 cubes @ 30hz - 140.1

    5 cubes @ 35hz - 143.2

    1 sub, 2.5 @ 30hz - 142.1

    all used the same amp, subs, vehicle, mic...except the last score...which is after i cut the trunk sheet metal out

    i would say it really depends on the box size and design

    so all in all i saw a 6db gain with the final enclosure, yet only a 1.5db gain with my first ported enclosure
     
  10. geolemon

    geolemon Full Member

    But that's not all gain simply due to porting...

    You also manipulated your enclosure size, and therefore efficiency...

    Two techniques together to increase dB. B)