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Howto: Seal your ported cab - for $15.72

Discussion in 'Amps and Cabs [BG]' started by barthanatos, Apr 12, 2006.


  1. barthanatos

    barthanatos Insert witty comment here

    Feb 8, 2006
    South Carolina
    Get yourself some of these from Lowe's/Home Depot/wherever:

    pipe_plugs.

    $3.93 each. They should be in the plumbing section. These particular ones fit in an Aguilar S810 cabinet, which has 4" ports. I also saw plugs that were 3" in size. They are perfect for the application. You stick 'em in the port, and then tighten the wingnut. This compresses the rubber part which doinks out (okay, it extrudes) and makes a nice tight fit. Easy in, easy out.

    I tried these in my cabinet the other day, but haven't done extensive comparisons. I'm not really gonna discuss the pros/cons of sealed vs. ported right now - I just wanted to throw this out there for someone who might wanna try it. For sixteen bucks you can't really go wrong.

    My Aguilar cab has a divider between the top four speakers and the bottom four. You might try just sealing of one section, or sealing off one port per section. It may be that you have different speakers in one section of your cab than another - you might just seal the section that the smaller or more upper-frequency-oriented speakers are. Or vice versa. Some cabinets, I understand, have the same size speakers throughout, but with different specs (i.e. they are somehow biased to support mid-range rather than low). Experiment.

    Sorry, no sound clips right now. Kinda busy.

    When installed, looks like so:
    plugs_installed.
     
  2. Quadzilla

    Quadzilla Supporting Member

    I could be wrong about this, but aren't there differences between a sealed cabs volume vs a ported cabs (cubit square feet) and also aren't speakers designed assuming that they will be used for sealed OR ported cabs? In other words, I don't theoretically this is going to work for you, but I'll let the experts chime in...
     
  3. I blew an eminence speaker rated at 500 watts thanks to blocking the ports on an avatar 15" cab. I was running the 15 with 150 tube watts, and blew the speaker after a gigging for about 3 hours. I liked the sealed sound better, but it can change the frequency/power handling of the speaker dramatically. Before I ported it, I ran the cab at full volume with the tube amp and with a 1500 watt solid state amp with no problems.
     
  4. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    You must be mistaken, he clearly said

     
  5. barthanatos

    barthanatos Insert witty comment here

    Feb 8, 2006
    South Carolina
    Ha! Well, I'll be sure to be careful, then. From something I was reading earlier, it is bad to port a sealed cabinet, because it allows greater excursion of the speaker, which could be bad. Sealing a ported cab should have the opposite effect?
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Sealing a ported cab will kill its bass response, which one would tend to compensate for by using excessive EQ/power. Cabs are built either sealed or ported for a reason, if you don't know what you're doing you'd be best off to let them work as they were designed to.
     
  7. Greg Clinkingbeard

    Greg Clinkingbeard

    Apr 4, 2005
    Kansas City area
    KC Strings
    A ported cabinet will have an emphasis slightly above the lowest frequencies of a few db. Sealing the ports should smooth this 'hump' in the response and may yield a lower minimum frequency.
    i.e. a ported cab may have a 3db down point of 30hz, but a bump at 40 hz. Sealing the cabinet may lower the 3db point to 28 hz with a smoother response. Sealed cabinets are more accurate because any air coming out of the port is out of phase with the driver, so at high volumes a sealed cabinet may sound better.
    It's been too long since I studied this stuff (thiel-small parameters).
    Some HIFI designs have straws, like drinking straws stuffed in the port as a compromise.
    Best to use the cabinet as intended IMO.:rollno:
     
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The port source is only out of phase below fb, otherwise vented systems would have less average sensitivity than sealed, not more, and would serve no purpose.
    Not necessarily. It can be that way if so designed.
    If anything sealing a box will raise the f3, by as much as an octave depending on the driver and cabinet.
     
  9. guy n. cognito

    guy n. cognito Secret Agent Member Gold Supporting Member

    Dec 28, 2005
    Nashville, TN
    Sounds like good advice to me. If you don't like the sound of your cab, sell it and buy a different one. Or, build one yourself......right Bill? :bassist: :)
     
  10. Thor

    Thor Moderator Staff Member Gold Supporting Member In Memoriam

    My cabs don't leak water so I haven't considered rubber
    wingnut stoppers in them.
     
  11. Greg Clinkingbeard

    Greg Clinkingbeard

    Apr 4, 2005
    Kansas City area
    KC Strings
    Thank you for the corrections. As I said, it has been a long time (15 years) since I did much in this area and I just can't remember it all anymore.:(
     
  12. Puru

    Puru

    Mar 13, 2006
    Alachua, Florida
    Hey Thor, is that the old Blodwin Pig cover from the 60's?
     
  13. joelb79

    joelb79

    Mar 22, 2006
    Lansing, Michigan

    not always the case. Ported boxes are more efficient, but most 'Hi-Fi' bass cabinets are designed for extended frequency response, rather than the 'humped' efficient ported box that your talking about.

    a ported box can be tuned, which allows for more air that would be trapped inside the box to be released at a certain frequency. however, the frequency rolls of sharply below the tuning frequency of the port, somewhere around 18-24dB/octave. This means, for an Ampeg BSE410HLF, which is tuned for 55hz, the response of that cabinet would be -24dB at 27hz, which is unaudible on stage.

    where as a sealed box, traps all the air inside the cabinet. this creates a 12 db/octave rolloff below 55-60hz, depending on the 'Q' of the box, which is basicaly a measurement of the rolloff, and the transient response around 60hz. Using the example of the Ampeg BSE410HLF (although, this is not a true example), a roll-off of 12db/octave from 55hz would create a response of -12dB at 27hz. this is MUCH louder than the ported box for the given frequency.

    For a VISUAL example, i will use a Emenince Kappa Pro 15LF, a wonderful speaker, which can be used in small boxes.

    [​IMG]

    The ported box recomended for low frequency response, is 3.775 Cubic Feet internal volume tuned to 50hz. This works WONDERFUL for Rock Bass, as it provides flat response to 50hz, with an 18db / Octave rolloff. however, at 42hz, which is the low E note, the cabinet is -8db, meaning a low boost will be needed to create a flat response. 8db difference between G and E is HUGE.

    Sealing the same box, will provide an audiophile response curve, however the rolloff starts at around 91hz, but only rolls off at 8db per octave. this means, the difference between E and G is only 2dB. Less bass boost would be needed to realize a Flat response.

    Plus, its hard to mess up a sealed box. Port tuning can be easily messed up. Sealed boxes are less complicated and easier to work with, abet not as loud as a ported, which is only a focused volume.

    Personaly, my 2x10 is sealed, and it works FINE thank you. The man who blew his cabinet after sealing it must have done something wrong, or have been using the sealed box in the wrong enviroment. A corner loaded (meaning a sealed box in the corner of a room) would sound no different than a ported box in the middle of a room as far as volume goes.
     
  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Are we looking at the same chart? The VB is higher in sensitivity than the IB from 34Hz or so up to 200Hz. The sealed box is only superior below 33Hz, where there's nothing to reproduce.
     
  15. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Even if overall system response goes down when the port is blocked, the excursion of the driver is almost guaranteed to increase at low frequencies. That's what kills drivers.

    You could always measure it. You can do a nearfield measurement of just the driver without needing an anechoic chamber. Follow the link in my signature to find out how. Take curves at a safe power level, both with and without the port plugs.

    If you want to get fancy, there is a document at my site showing how to compute the system response from the near-field driver response curve.

    When you are done, share the results here, and it will be a learning experience for all of us.
     
  16. MikeBass

    MikeBass Supporting Member

    Nov 4, 2003
    Royal, Oak, MI.
    Didn't Trace Elliott offer this design like 10-15 years ago??
    I seem to remember their 210 coming with "plugs" to plug the two front ports.
    Had instructions and all, "Block one for this... Block both for this....."
     
  17. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    There are drivers that can, if designed into the right box, tolerate this.
     
  18. barthanatos

    barthanatos Insert witty comment here

    Feb 8, 2006
    South Carolina
    I'll look into your link fdeck, thanks.
     
  19. yamaha

    yamaha

    Apr 7, 2006
    Montreal
    Possibly, this is something that could be done to older, modified, or custom cabs, but I would really like to see the response from the guys at AE , Berg, and Epi, etc... when it is mentioned to them how we are able to make their cabs sound much better, simply by plugging to holes they made in their design.
     
  20. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    My hypothesis is simply that attenuated lows sound better to your ears, and you were not playing at high enough volume for the drivers to fart out.
     

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