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Cabinets : Front Ported vs. Sealed vs. Rear Ported

Discussion in 'Amps and Cabs [BG]' started by LowDown Hal, Apr 5, 2009.


  1. I'm sure it has been discussed before but I can't find it....

    So can anyone explain the science behind the three types of speaker cabinets?

    How they are expected to sound different and how the cabinet accomplishes that?

    Or else point me to any previous threads?

    THANKS,
     
  2. KJung

    KJung Supporting Member

    I'll leave the sealed versus ported to those with more technical knowledge.

    Front versus rear ported (if done correctly) makes no difference (i.e., any frequencies coming out of the port are omni directional), and is typically just a 'box size' decision by the designer (i.e., rear ported boxes can be smaller, since you don't need room for the port in the front baffle).

    There are some 'bad executions' of rear ports, like the little Bag End 115 cubes that just have a big hole cut right behind the driver, which results IME in direction upper bass coming out of that port. However, that's a rare situation. With an otherwise identical cab (tuning, internal volume), you would not be able to tell the difference between a front and rear ported cab if executed correctly.

    I was always under the impression that rear ports caused problems, since the only rear ported cab I was familiar with was that small Bag End cube for a long time. However, the EE's on this site set me straight, and since I've now experienced many other 'correctly designed' rear ported cabs (Aguilar DB, BergantinoAE, Acme, etc.), I now realize it doesn't matter where the port is if done correctly.
     
  3. Jim Carr

    Jim Carr Dr. Jim Gold Supporting Member

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    The old SWR goliath II, built by Eden, is a classic rear-ported 4x10. I use one from time to time. I find it sounds great, but the back needs to be kept away from the wall--I'd say a couple of feet--but am uncertain if there is a rule of thumb.

    I suppose it makes sense because part of the speakers' output is poppin' out the back.

    I too, am no engineer, but I assume there is probably an optimal placement for rear-ported cabinets. Can anyone knowledgeable guide us?
     
  4. KJung

    KJung Supporting Member

    Nope, any sound coming out of the back will be ominidirectional (i.e., frequencies so low as to be completely non-directional). You do need to keep the cab at least 6" from the back wall so you don't block the port, but that's the only rule.

    The idea of directional sound coming out of the back of a properly designed rear ported cab is a 'myth' that I too believed, based on, again as posted above, my early experience with a particularly poorly designed (but still good sounding for the most part) rear ported execution that actually did seem to have some higher frequency direction sound coming out of the port (not a good thing!).

    For your Goliath, or the Acme, or Berg or Aguilar, they will behave no different that a front ported cab regarding placement, etc.
     
  5. Jim Carr

    Jim Carr Dr. Jim Gold Supporting Member

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    OK! That leaves me one less danged thing to worry about. Thanks, Ken.

    Uh...why are ports ever in front?
     
  6. KJung

    KJung Supporting Member

    My guess is it's purely based on the size of cab and where the port or ports best fit. I know Don at Low Down Sound bases his porting on where it 'fits the best' in each given cab design. I assume if there is room for a cutout on the front baffle, this is the easiest to do from a production standpoint. If not, it goes in the back.

    However, I'll defer to the experts on that. There is a very nice write-up on the port placement issue on the Acme site.

    K
     
  7. pgk

    pgk

    Aug 19, 2007
    which results IME in direction upper bass coming out of that port

    i could be wrong but i think that's intentional. this is purely speculation on my part, but i think it's a big reason that when i walk into a club, don't look at the bass rig and think "wow, nnnnice tone" just how often it's been a bag end cab or two (around these parts usually one or two 15" cubes). amps ranging from a gk 400 to a blueface ashdown magnifier (WOW) to a bf bassman/showman, so the amp choice is really kinda irrelevant. yeah, it's those cabs that have been the constant. i dunno, but i think those rear exiting mids combine with the lows coming out back, bounce off the back wall and make for a wonderful blend you can hear all over the room. now mind you, i could be talking completely outta my ass here, so i don't know if that's true or not from a technical standpoint. but what i described has happened to me a lot, and it's the reason i bought my S15L-D. man oh man, to have a stacked pair of those puppies, whoa.....
     
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It's easier/less expensive to build the cab that way.
    Rear exiting mids will reflect off walls and combine with the cone output at various angles of phase, and when that happens there are huge peaks and valleys in the response. That's never a good thing, so if mids exit through a port it's a major design flaw.
     
  9. pgk

    pgk

    Aug 19, 2007
    oh i see, thanks bill. like i said i dunno if bag end cabs actually do that, or not, but i sure do like the sound of them.
     
  10. Mulebagger

    Mulebagger

    Dec 12, 2007
    poppin in the corn belt
    Endorsing Artist: Zon Guitars, Tsunami Cables, DR Strings, GK
    I have loved all my BagEnd cabinets and I feel they have the truest voices. My rear ported 2x10 is a powerful and very nice sounding cab. I had two Mesa cabs, one being rear ported and the other a 6x10 that has the tri-port design. I much prefer the projection the tri-port design offers. Plus I can place The Mesa 6x10 pretty close to a wall without creating a bass trap as easily as with rear ported cabs.

    I'm not up on all the technical aspects of it, but to my ears, I like the projection of front ported cabs, but prefer the overall sound of the rearported BagEnds.

    I really dislike cabs that are ported with slots or transmission line ports. These seem to give the cabinet a deeper response, but I feel they loose clarity. I prefer to have speakers and a simple box that can produce low frequencies without the mechanical function of a long slot port.

    Just my 2 cents from 20 yrs of playing. If anyone has the technical info it would be great to know the actual differences in the different cabinet designs.
     
  11. KJung

    KJung Supporting Member


    This is how the 'myth' of front port versus rear port tone gets propigated IMO.

    You are comparing cabs with many, many, many differences (internal volume, driver type and size, type of wood, tuning, etc., etc.) and attributing the very different sound of all these cabs to whether the port is in the front or in the rear:smug:

    Same thing with, for example, the Markbass 410's, which are described as the 'front ported' and 'rear ported' models. They sound very different, but due to a lot of things other than the simple placement of the port.
     
  12. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The difference in sound is the result of the cabinet size; the smaller ones are rear vented because there's no room for vents on the front. The larger cabs are front vented because there is room for them and it's less expensive to put them there. As to the rest, there are some two dozen parameters that determine how a particular speaker will sound. Vent location and shape, other than flawed locations and/or radical shapes, are not among them.
     
  13. Kenny Allyn

    Kenny Allyn

    Mar 25, 2006
    Memphis
    I personally have no problem with either front or rear ports

    It comes down to what works on that box and clarity is not an issue in a correct design given any port shape.

    ;) ... Currently testing a new 410 sealed cab too ...
     
  14. I have a Goliath II, and a Goliath III.
    The II, with rear tuned port, has a smoother frequency response in the low mid/bass range.
    The III, with front shelf port, has a lumpier response in the low mid/bass range, but is louder and seems more efficient in that range.
    These differences may be due to things not related to the porting, I don't know. The III cabinet is of course larger.
     
  15. KJung

    KJung Supporting Member

    :D I think different drivers also:smug:
     
  16. KJung

    KJung Supporting Member

    +1 The problem is that everyone describes them as the 'rear ported' versus the 'front ported' models, and that simplified discriptor starts to be perceived as the causal driver of the difference in tone between those two cab lines. As you point out, they are VERY different cab designs in general.

    I'm again posting in this thread since I also misunderstood the impact of port placement (none!) until you guys all took me to school and I didn't base my opinion on experience with just one rear ported cab! I no longer use port placement as even a small factor in determining which cab to purchase. Thank you BillF., Alex, Greenboy, etc.!
     
  17. James Hart

    James Hart

    Feb 1, 2002
    toms_river.nj.us
    Endorsing Artist: see profile
    one of my favorite cabs 'tone wise' with the band. When I gigged with an S15 (the cube in question) I NEVER had an issue indoor or out... with or without PA support for YEARS.

    I got regular compliments on my tone... and moved a few 'badly executed' cubes for Bag End due to bassists hearing what my little cubes could do. Sometimes sharing the stage with Hartke 4x10 + 1x15 stacks and Ampeg fridges (early 90s) only to put out better tone, move more air and produce less boom.

    That said, I do like the S12 better... slightly smaller cab with a port 1/4 the size of the S15's port.
     
  18. KJung

    KJung Supporting Member

    I always get in trouble when I use that little Bag End cube as an example of a 'questionable rear port design'. I too used the stack (the 'x' version with tweeter on top of the regular version). I also think they sound very good, but I did find that there was actual 'sound' coming out of that rear port that seems directional and not behaving like any other port I'd ever experienced. That resulted in those cabs IMO and IME being more variable in regards to placement than any other cab I've ever played. They could sound just GREAT and then sound quite thin or overly boomy, again more than any other cab. Again, this is not a general Bag End issue as far as I know, just those little cubes with the big hole cut literally right behind the driver. You can literally hear mids coming out of that hole if you stand behind the cab.

    Anyway, given that as the exception to the rule (and maybe not even that... I might just be nuts!), the point is in 99% of the cases, port placement has no impact on sound, all other things being equal.
     
  19. James Hart

    James Hart

    Feb 1, 2002
    toms_river.nj.us
    Endorsing Artist: see profile
    I was just coming back to edit...

    I do know exactly what you mean... just needed to defend the little S15. Like any piece of gear "you need to know how to use it". Poorly executed or not... they are a great little cab if you know how to use it (as I know you know how to)... but yes, some rooms / stages make it hard to place them right.

    Perhaps the tiny rear port(s) on the S12 (and my current D12) are the reason I prefer the 12" version so much better?
     
  20. Mulebagger

    Mulebagger

    Dec 12, 2007
    poppin in the corn belt
    Endorsing Artist: Zon Guitars, Tsunami Cables, DR Strings, GK
    The two cabs I was comparing were both Mesa 6x10s one being rear ported and the other having the tri port front design. Good call on making note that there are many variables involved besides the porting that contribute to a difference in sound. I'm not trying to add to the myth, just giving my impression from experience.

     

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