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Making ported cabs sealed

Discussion in 'Amps and Cabs [BG]' started by i_got_a_mohawk, Jul 28, 2005.

  1. Is you stuff/block the ports on a ported cab will it give the sound of a sealed cab? or will it throw off and screw up the tuning of the cab/speaker?

    Im sure i saw someone who had 2x10's with removable "plugs"
  2. vintageampeg

    vintageampeg Supporting Member

    Feb 2, 2005
    Was just speaking last night with a really good local tech about my '67 Ampeg B18-x cab. One option recommended we try was to block the port - there were no concerns about throwing off the tuning of the cab, other than it will be quieter, but get a different sound as the drivers are forced "pump" more w/o the relief of the port.

    Of course, I'm talking about a cavernous plywood relic of a box with a hole in it, compared to the more sophisticated and efficient cab designs available today.

    Anyway, you should try it. You won't break nuthin.

  3. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    Fremont, Ohio
    Editor-in-Chief, Bass Gear Magazine
    You may be thinking of my Azola custom Super Wizzy's!

  4. cheezewiz

    cheezewiz Supporting Member

    Mar 27, 2002
    I've had several Trace Elliot cabs that come with "port plugs"
  5. There is no guarantee you will like the results but you won't hurt anything and you should try it if you're curious. Generally the cab will be quieter on the low end but it will sound tighter. The results will change from cab to cab.
  6. Thats it :)

    Thanks guys, ill give it a shot when i have some spare time, i just want to see the difference having the cab sealed is like for the good ol valve amp
  7. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    Fremont, Ohio
    Editor-in-Chief, Bass Gear Magazine
    I thought that I would prefer the cabs with the port plugs in for use with the V8 (and with many cabs, I think I would), but the Wizzy drivers seem pretty resistant to overexcursion, and Steve builds a nice box, so as it turns out, I prefer them with the ports "open."
  8. KJung

    KJung Supporting Member

    Super Wizzy... Super Wizzy... Super Wizzy.... I just like saying it :hyper:
  9. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    Fremont, Ohio
    Editor-in-Chief, Bass Gear Magazine
    Try "Swizzy" for short! ;)
  10. Phil Smith

    Phil Smith Mr Sumisu 2 U

    May 30, 2000
    Peoples Republic of Brooklyn
    Creator of: iGigBook for Android/iOS
    Trace Elliot info on port tuning of their loud speakers and combo's. Note that these are for the earlier models as the new models have the port on the bottom and are tuned to 40Hz.

  11. Petebass


    Dec 22, 2002
    QLD Australia
    That's a good article. I'd like to add to it if I may:-

    The speaker cone movement between a sealed and a vented cab is very different. In a sealed cab, the lower you go, the more the speaker cone moves. This is pretty simple and falls within most peoples expectations of what a speaker should do.

    Vented cabs on the other hand behave very differently. Speaker movement initially increases as frequency decreases, but as the port starts to take over, speaker cone movement actually starts to decrease. At the cab's tuning frequency, the speaker won't move at all if fed a sine wave free of harmonics, and should only move very slightly when fed a harmonically rich signal such as a bass guitar note. If you go lower again, you'll find that speaker cone movement increases very rapidly, making a vented cab almost useless at frequencies below the cabs tuning frequency.

    Has anyone seen the "Myth Busters" episode where they were trying to find "the brown note? They used a wall of Meyer subs driven by 25,000W of power to produce frequencies as low as 5Hz. John Meyer himself was overseeing the test. At those low frequencies, lower than Fb (the cab's tuning frequency), they sealed the ports with compacted foam. Why? Because if they didn't, the speakers would move so far, they would have jumper out of the cab. The didn't free up the ports until the frequencies being produced got above Fb.

    My point is that I don't like to use any old speaker in any old cab. For mine, a sealed bass guitar enclosure needs a speaker with a hefty length of suspension travel. Why? Because at 40Hz, a vented speaker is barely moving but a sealed speaker will be moving quite a bit. We need decent a x-max for both types of enclosures, but IMO the sealed cab's x-max needs to be longer.

    So if the cab is offering plugs for the ports, you can be your bottom dollar that the speakers would have been engineered to work that way, and by that I mean a compromise was made. Loudspeaker design is full of compromises. So don't rush out and block the ports of any old cab. If you must do so, make the mod reversible.
  12. My friend built a pair of speaker enclosures and put a 12" jbl speaker in each and forgot to port the cabs. It sounded like crap he said so he took out the jbls and threw in some very cheap radio shack speakers....said it sounded awesome. I found it very strange bacause the radio shack speakers had far less travel space than the jbls. Any comments? I have always been puzzled by this.
  13. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    If the JBLs were E120s or any of the variants therof they have a very low Qts figure, which means very little bass unless mounted in a horn loaded or very large vented cabinet. Cheaper speakers have smaller magnets/higher Qts/more bass, although with less average sensitivity throughout the full bandwidth. In other words you can't just throw a driver into a box and expect it to work properly. Even if he'd ported them they probably wouldn't have worked right, as this tale points to his probably not having had the technical knowledge to know how to port them properly.
  14. A driver that is designed to go into a sealed box aslo requires a greater motor strength (BL) in the Theille-Small parametrs. Generally and driver with an EBP of over 100 should go into a venetd box one with less is probably better in an Infinite Baffle (sealed) enclosure. Eminence suggest there are always exceptions to this rule though, the their Kilomax driver being an example...
  15. Sorry to drag up an old thread but I was just thinking about this yesterday as I have recently bought a tube amp.

    The cabs I have are both made by Gallien Krueger. One is a sealed 4x10 and the other is a ported 2x12.
    As I've read several times that tube amps sound best through sealed boxes and I need to use both 8 ohm cabs with my tube amp which will work at 4 or 2 ohms but not 8, would I be okay to block the two ports on my 2x12?
    I'd have to find something like a cap that I could fit into the ports - removable caps in case I don't like the result though!

    Would blocking the ports on my 2x12 work?
  16. It's not true.
  17. Ah well I have to say, my current setup sounds pretty darn fine as it is although I'm mixing a sealed cab and a ported cab I don't seem to be getting any phase cancellation. Well..not that I can detect anyway.

    So I may as well just leave it the hell alone?
  18. Yep. The whole "sealed" bit comes out of the fallacy that tube amps have too low damping to "properly" control a speaker, which is again, a fallacy.
  19. Yeah I was thinking that eight 6550 tubes may be able to hold on to a few speakers. :smug:
  20. staindbass


    Jun 9, 2008
    nail a board over the ports with weather stripping to seal it. the cab will be less loud, but more articulate. speakers for ported enclusures have different specs than sealed bow speakers, the compliance (stiffness) of the surround is looser on sealed cab speakers. that said, i think a ported speaker sealed will sound better than a sealed speaker with a port installed. use drywall screws, that way if it doesnt please you, it can be removed. johnny a