difference between sealed cabs and ported cabs

Discussion in 'Amps and Cabs [BG]' started by sidhk817, Jan 6, 2005.

  1. whatz the difference in structure between the two kinds of cabs?and the sound produced?
    the manufacturers seem not to put it in the specs,how do i know which is sealed and which is ported? :help: :help:
  2. Not totally certain, but I think ports are added to tune a cab to a higher frequency.
  3. unrealrocks


    Jan 8, 2004
    Ported cabs generally give more sound for your money, but sealed tends to be more controled and tighter - although if you wanna player loud and get real deep sounds a ported cab would be better.

    I don't think many people bother taking much notice as at this stage ones not really better than the other, its just the style and sound you want.
  4. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    Porting extends low frequency response allowing a smaller cabinet size than a sealed design.

    The tradeoff is that below the port resonance frequency the speaker cone excursion gets very uncontrolled, which makes it easy to blow the speaker if you push it hard below that frequency. In a sealed cabinet, the air trapped in the box stiffens the cone preventing overexcursion, though it tends to be much less efficient. There are two main types of sealed cab designs, infinite baffle and acoustic suspension. Acoustic suspension cabs are smaller but the woofers have to be designed to have less stiff cones; these used to be commonly used for home stereo speakers. Another type of cab design is horn loaded, which can be either front or rear loaded; these are commonly used for large PA cabinets.

    I hate to get back to the old freq. response questions, but ported cabs have a steep rolloff below the resonance (12 or 24 dB per octave is typical), while sealed cabs may have only a 6dB or so rolloff. So when you look at a sealed cab's specs it may seem to have a rather high -3 dB point but with extra wattage and EQ boost it may be possible to get flat response well below where a ported cab with a lower -3 dB point can go.

    Very few bass guitar cabs are sealed. Ported and horn loaded cabinets dominate the market. The classic SVT 8-10 design is one of the few sealed cabs out there.

    I'd suggest you do a web search on speaker cabinet design for the nitty gritty.
  5. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    Whoah - good explanation, Brainroast. I read the intital post and thought "Oh, I can explain this!", but I couldn't have explained it that well or completely.

    I didn't know the rolloffs got that steep with ported cabs - 24dB/octave?! -a +/-12dB graphic's going to do nothing for you with that kind of knee, huh? Considering that along with the uncontrolled excursion below cutoff, and it makes me see how one shouldn't be trying to cheat any thunder out of a ported cab. It makes me think about that 'LOW' control that's right now positioned at 2:00 on the head that's wired to my PORTED Hartke 4X10! I can just picture this fairly flat cab response with the sudden 24dB drop - then some goof like me goes and lumps-up the lows with a four-band tone bank; I'll end-up with a big peaky-peak just above the knee, but at the same time my low-Q boost-band is no match for the 24dB/oct rolloff of the cab. Yup: Nuthin' but trouble...

    Thanks for the insight -

  6. Ported cabs extend low frequency response by producing nearly all the output from the port at the tuning frequency (Fb). Cone movement is almost nothing. Without the port, the driver is very inefficient at this frequency and is subject to large cone excursion. Moving up from the tuning frequency, port output drops rapidly while driver output and cone movement increases. The additive port benefit extends roughly 1/2 octave above and below the tuning frequency. A system resonance point occurs both above and below Fb.

    Cone movement is lowest at Fb and highest at the upper resonance point. Below Fb, the cone behaves as if it were in open air, with no loading. This is where they get destroyed from over excursion. Operating below Fb is not recommended. The driver is prone to over-excursion at the upper resonance.

    The size of the port is a direct function of how much air the driver moves. A small port with a large displacement driver will result in very audible port noise. As the cabinet gets smaller, using a large port becomes more difficult. At the extreme small end, a passive radiator is a much better solution.

    Ported cabs roll off at 24dB/octave. Sealed cabs roll off at 12dB/octave. Band pass cabs have different steep roll off rates, depending on the particular order of band pass design. Ported cabs roll off at a lower frequency than do the sealed cabs, hence extended low frequency response.

    The optimal size of the cab is entirely dependent on the driver parameters. Efficient drivers usually require large ported cabs, where inefficient drivers require small cabs. The driver parameters determine the use of a ported or sealed cab. An EBP < 50 indicates a sealed cab, where EBP > 100 indicates ported. The middle area can swing either way.

    It is possible to tune a too-small cabinet to the correct tuning, but quality degrades. The too-small cabinet reduces port output at Fb and increases output at the upper resonance. This causes a booming, one-note bass effect. The more the cabinet size is reduced from optimal, the more pronounced this effect.

    Very few ported cabs are optimally sized for their drivers. Most cabs are too small, and result in a mid-bass response hump in the 80 ~ 120 Hz range. This gives the appearance of fat bass, and is called "saleable" or “cut through” by the marketers. The SBB4 ported alignment comes very close to the tight bass qualities of a sealed cab. The SBB4 response (higher F3) is very similar to sealed cabs but with much better power handling and less excursion at Fb.
  7. What is the typical roll-off of a transmission line vented cab design. Does the frequency response extend below the tuning point on a TL design?

    The cab I have in mind is the EA Whizzy 112. I think the stated spec is a low end limit of 45hz. I do not know if that is the tuning frequency or a measured result from a frequency sweep. Further, I do not know if it is down at 3db, 10db or what.
  8. I've never built one, nor have I tested one. For that amount of design and construction effort, I much prefer horn loaded cabs.
  9. Mike Dimin

    Mike Dimin Inactive

    Dec 11, 1999
    How would you know if you never built or tested one?
  10. so what kind,sealed or ported,has a tighter-sounding low B?
  11. luknfur


    Jan 14, 2004

    Kudo's on the bgavin/brianrost posts. Concise, informative, and cover a lot of ground.
  12. What's a good example of the SBB4, or describe it please.?
  13. The same way I know having gay sex or sleeping on railroad tracks is not for me.


    I've done a large amount of reading on TL designs. They are quirky at best, and design consists of many iterations of trial by build, test, refine, repeat.

    Unlike a horn, the TL is a resonant device and operates like a vented box at a very small range of frequencies. Considering the complexity of building a TL, and iterations of refinement, I'd rather put that energy into a bass horn. If TL designs could compete with horns, the brilliant minds such as Tom Danley, Dr. Bruce Edgar, et al, would be working in TL. They work in horns instead.
  14. SBB4 is an alignment attributed to Robert Bullock. The performance characteristic is nearly identical to a D2 sealed box. SBB4 always tunes at the free air resonance of the driver. This usually results in a larger cabinet than the QB3 or Optimal (WinISD) alignments, and with a lower tuning.

    The D2 sealed alignment is the optimum-flat group delay model. This translates to the tightest and "fastest" bass reponse. The roll off occurs higher up, and at a slightly faster rate than the B2 sealed alignment. Both B2 and D2 have superior group delay (tight) than a vented box.

    For tight bass, the vented SBB4 does come pretty close, plus offers maximum cone loading and power handling at the bottom end of the players' range. The downside is the higher F3 which means less bottom. This is an optimal tuning for a driver, and does not result in a mid-bass hump (Eden honk).
  15. Mike Dimin

    Mike Dimin Inactive

    Dec 11, 1999
    I can tell by your posts that you have done quite a bit of reading.
    What is quirky about TL. Having played through TL cabinets for the better part of 3 years now, I can assure you that there is nothing quirky about it. I will admit that the design is difficult and that is why many in MI don't bother. They don't have the time, money, energy or expertise. They are unable to see the sonic advantages, as I do.

    That is pure speculation. For someone who seems to be as specific as you, you make a huge generalization here. That is not like you. There are many brilliant minds that do see the advantages of TL and have worked a long time perfecting the idea.

    You can promote any idea you like, but what it comes down to is real world application. How does it sound when you get out there and your livelyhood depends on it. Everyday I depend on TL cabinets, not because of the design or the genius who can design a TL for MI applications but because of the SOUND!

  16. Hawkeye

    Hawkeye Canuck Amateur

    Aug 8, 2002
    North of GTA, ON, Canada
    Long&McQuade Employee
    This is a very good question to which I looked for answers on some speaker manufacturer's websites who make TL enclosures (Meadowlark, PMC). I didn't find anything specific other than the commonly held knowledge that the roll-off below resonant frequency is milder (less steep) than sealed designs. The market-speak indicates that you can get a half octave lower response "for free". I THINK it might be 6db per octave but I'm not sure. Someone with more technical expertise in this area might care to comment.

    Besides the theoretical advantages, there are practical disadvantages of transmission lines that are of particular interest to bass players. Because you must construct the "pipe" in back of the woofer/s that is tuned to a specific length (this is typically a "folded horn and is usually accomplished by a series of MDF or plywood braces and channels within the cabinet) they:

    A. Add complexity and therefore cost.

    B. Add weight because there is more internal structure and bracing within the confines of the actual cabinet compared to ported / sealed to make the folded horn. AFAIK each driver theoretically requires its own "pipe" or "horn" which may make multiple driver cabinets quite complex to design / build.

    C. Some audiophile types are of the opinion that TL speakers have bass that "sounds weird" because the back wave off the speaker driver (which ends up being in phase by the time it comes out of the port) is not time-aligned with the direct wave from the front of the bass driver.

    FWIW, I've auditioned PMC FB1's and GB1's in my home stereo system and haven't really noticed that characteristic. These speakers had good slam and extension given their internal cabinet volume and driver size.
  17. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    Very interesting thread. I was looking at sealed cabs a while ago. The ones I found (to answer the question above) include:

    Bergie NV 610 and 215
    GK SBX 410 and 115
    Ampeg 810E and 410HE
    Fender 410H

    I ended up getting ported cabs, not because I preferred the sound but because they were available used locally (cheap). I auditioned the Fender 410H compared to the similar ported version which is slightly bigger but identical power ratings. The 410H was snappier, faster and cleaner which I liked in the store. The ported fender that I ended up getting is a bit muddier in the mids and lows but is more efficient, particularly in the lows which is in agreement with the posts above. I actually cut the lows a bit now so I might have been better off with the sealed cabs. I like that tight sound and power is getting cheaper all the time. However you really don't want to haul 2 4x10s to a gig and then not have enough lows.
  18. bmc


    Nov 15, 2003
    I would really appreciate some comments on this one.

    What are the differences in sound between a front ported and a rear ported cab? I realize that's a wide open question, but can there be general conclusions. Bag end 15's are rear ported. Is there a big difference in sound between that and any other front ported cab.

  19. IvanMike

    IvanMike TTRPG enthusiast, Happy, Joyous, & Free. Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    IME, rear ported cabinets sound "tighter" than front vented cabinets. I've found this to be true in general, but not across the board. All of my bag ends are rear ported, and so was my swr goliath 1. My eden 210xlt was front vented, and while it had more apparent lows/low mids, it just didnt sound as controlled. I've heard the same from a lot of other front ported cabs. But, there are a ton of front ported cabs that are super tight as well. It depends upon the manufacturer.

  20. Thanks.

    I wonder if the internal piping, shelving or bracing is actually load bearing or structural. The Bose wave radios are just cheap molded plastic and the labyrnth extends through the unit, only using a single 3" driver.

    Why can't we bass players have a high-tech molded TL cab? My Yorkville PA NX series are a high tech material said to be a hardened foram and not a plastic. Who knows?

    A horn is impractical for me, as I like sporty cars. But I would like to see people build small affordable ones that take advantage of current technology.

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