Results 1 to 4 of 4

Thread: porting

  1. #1
    Senior Player Registered Member dizzle's Avatar
    Join Date
    Jul 2004
    Location
    YaeArea
    Posts
    43

    porting

    got another question,
    why/how exactly does porting/bandpass work as opposed to a sealed box?
    i kno the difference's performance-wise but im just curious how the changes in sound are achived....
    really not even sure so i thot i'd thro it out there...

  2. #2
    DIY Audio Registered Member ron.eddy's Avatar
    Join Date
    Sep 2004
    Location
    Grand Forks, ND
    Posts
    70

    Porting Basics

    Porting works by taking advantage the wavelengths of bass frequency. I won't go into detail since there are many great websites on the science behind it, so here is the deal:

    When a subwoofer moves in and out while you are playing audio with it, acoustic waves are obviously emitted off the front of the speaker (which is why you here it), but there are also waves emitted from the rear of the woofer. Now, these rear firing waves are inverted from the front firing waves (obviously) and so the purpose for a sealed box is to dampen these rear waves as much as possible. The reason you don't want these rear waves to escape the box is because they will end up combining with the forward firing waves. When they combine it is like adding a negative number to a positive number (-5 + 5 = 0). This gives you less bass (ever tried a sub with no box whatsoever? its pathetic). By trapping the rear waves in they can't cancel the front waves and so your bass is maximum (with a properly designed sealed box). Again, I could go on just about sealed boxes for hours, but i will spare you the details.

    Now, what if we could harness those rear waves and turn them into useful bass which we can hear... This is what the port is for. A port, basically, is designed to only let out a certain frequency of the bass, and it is usually "tuned" to a specific value, for example: 22hz. There is a lot of math behind it, but once you calculate the proper length and size of your port, you can tune it to any frequency you want. When properly built, a ported box will block mostly all the waves coming from the back of the sub, but it will allow it's resonant frequency (the frequency you tuned it to with its length and size) to come out in a non-inverted form. When you add the bass coming out of the port to the bass coming out of the speaker, they will combine and you will get a boost on and around the tuning frequency, while the inverted waves stay in the box (basically).

    A sealed box is typically punchier because it allows the woofer to be controlled much better (air tight seal). A port is typically "bassier" but unfortunately in car applications it is usually overkill and results in either poor quality bass or boomy bass, which may be to some people's likings, which is fine.

    Hope that answers your question.

  3. #3
    I'm in your head Registered Member CVStroker's Avatar
    Join Date
    Oct 2002
    Location
    Madison WI
    Posts
    2,280
    Good explanation, but I think I can make it a bit shorter and simpler.

    With a sealed box, you're only hearing the bass wave comeing off the front of the cone, the rear wave is being "absorbed" by the box.

    With a ported box, the port acts to switch the rear wave 180 degrees "out of phase". This acts to essentially turn the port into a second woofer. With a ported box, you've effectively turned one sub into two, as you're using the front of the cone as well as the back of the cone. A ported box will gain you 3 dB net just like adding a second woofer will gain you 3 dB net.

    In both boxes, the air inside the box acts as a suspension to control the movement of the cone. A sealed suspension is stiffer resulting in the punchier sound, a ported suspension is softer, resulting in a boomier sound. It's pretty much the same idea as soft shock absorbers vs. tight shock absorbers.

    As for ported being overkill in a car, I disagree. Some times the vehicle is such a bass trap a ported box is needed to get any form of decent output. I have never used a sealed box for anything, and I doubt I ever will. I always use ported boxes that I have built myself and that are designed for each specific sub.
    Life: It's the ultimate sin; a game with no rules that you're expected to win

  4. #4
    DIY Audio Registered Member ron.eddy's Avatar
    Join Date
    Sep 2004
    Location
    Grand Forks, ND
    Posts
    70

    Porting Being Overkill

    As I said in my post, it is all up to one's personal tastes. There are many woofers that recomend NOT using ported, and there are others that recommend against sealed. In those cases it is usually best to follow those guidelines, but today most woofers for Car Audio are designed with flexibility in mind. So ported, or sealed, will work just fine... totally a personal taste.

    I myself used ported for the longest time, since the types of music I liked seemed to work best with ported. My tastes in music have changed over the years and now I use sealed. The advantages/disadvantages of both could be discussed for hours. But thats the beauty of putting a sound system together, YOU get to decide.

    Anyway, CV, your explanation was almost identical to mine (shorter, like you said), but i am not sure why you even took the time to repeat it. I am sure the original poster was fully capable of understanding my explanation. But in any case it does sound like you know what you are talking about, which is a welcome addition to any post.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •