closed back vs open back vs front ports

Discussion in 'Shock Brother's DIY Amps' started by AndyPanda, Dec 5, 2019.

  1. AndyPanda

    AndyPanda Tele-Meister

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    I have quite a few interesting and vintage 12" speakers that need a home (a cabinet to live in). I recently picked up a used 2x12 slant cabinet for cheap money on CL. It is closed back but has two round ports on the front - no length to the port (no tubing - just holes in the baffle board). Right now I have two EVM12L in there. I have various old Jenson, Rolla, Celestion 12" I've salvaged over the years.

    I think it sounds pretty good but I'm new to the whole guitar thing (long time musician - just new to guitar) so I don't really play well enough, yet, to know what a good sounding guitar cabinet sounds like.

    I occasionally see inexpensive closed back (no ports) 2x12 cabs on CL or an Open back (fender type) 2x12 cab on CL and I'm sort of tempted to buy one of each just so I can see what the difference is (and to give a home to some of these raw speakers I have lying about).

    Anyway ... hoping some of you might be able to tell me what the pros/cons are between the different types of cabinet. Also curious if you guys would leave these ports alone or experiment with making port covers to plug them and compare?
    Ports.jpg
     
  2. tubelectron

    tubelectron Tele-Holic

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    Supposing the same speaker in a same volume enclosure :

    Port cabinets will give you more bass (correctly tuned = i.e. EVM12L in Thiele Cab).

    Closed cabinet will give you tighter bass.

    Open cabinet will give you a widespreaded sound (I mean : largely open back, OK ?).

    With port and closed cabinets, you may front adverse noise problems (typically unwanted air leaks) that won't exist with open back cab.

    But port and closed cabinets (if well built) allow a higher power handling to the speaker (due to the damping they provide) than the open cab.

    A largely open cab usually sounds less "boxy" than a closed or port cab.

    I made comparative tests with an EVM12L, ALTEC 417-8H and Eminence Legend 1218 speakers to write this.

    I personally much prefer the tone of the open cab, but it's a matter of taste and, of course, there's exceptions to the rules... ;)

    -tbln
     
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  3. bftfender

    bftfender Friend of Leo's

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    Closed- marshall
    open- fender in my usage
     
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  4. Phrygian77

    Phrygian77 Tele-Afflicted

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    Add me to that camp also. I do like the sound of my closed back 1936 with Weber 1225s, but my bandmates complain that they can't hear me as well as when I'm playing my open back combo amps. Nothing except the vocals through PA in the small venue we play in.
     
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  5. Preacher

    Preacher Friend of Leo's

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    to my ear I prefer open backs.

    But I have an old Peavey 2x10 cabinet that it ported in the front with a closed back that sounds pretty good.
     
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  6. scottser

    scottser Tele-Afflicted

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    My combo and both my cabs are open backed, which I prefer ss closed cabs tend to be too directional. I would use an open cab in a jam or gig and a closed for recording.
     
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  7. schmee

    schmee Poster Extraordinaire Silver Supporter

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    Closed seem to "compress" more to my ears. Maybe why a Marshall cab, when cranked has that sweet sustained tone.
    I used to have a blonde Tremolux and cab. I loved it in the music room but it seemed to lose definition in a band mix with that warm compressed tone.
    I experimented with opening up the cab back. With the back just 1" open full width it's like the sound came alive. More sparkle, more definition. This continued on a lesser basis until it was open 3-4 ". After that I heard little difference.
    Cab depth, regardless of open or closed makes a big difference if it gets too deep.
    I prefer open backs myself.
     
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  8. teletimetx

    teletimetx Doctor of Teleocity

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    From what I've seen, bass players and lower frequencies tend more towards closed or ported cabs. Guitarists seem to like both or one or the other, but for specific reasons. Certainly with closed back or ported enclosures, there's a deep dive into the acoustics and physics involved, if you like. Here's a sample of that kind of thinking, from your local car audio electronics folks:
    http://www.bcae1.com/spboxnew2.htm
    The serious audiophile folks just can't get enough of this stuff.

    I mostly prefer open back cabs. But I have a '69 Bassman with a 2 X 15 cab and that combination can be thunderous, in a good way. (Well, that's the intent anyway).

    I've seen cabs that can go either way; three panels on the back, remove one or two as you please. If you've got the time to experiment, that might be just the thing to do.

    If you're playing with ports, you might want to look at aperture size and tube length as well. Uh, here's where some one tends to say something lame like, it's not the length, it's the girth...:cool::D:).
     
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  9. johnDH

    johnDH Tele-Meister

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    For guitar cabs, it seems only the smaller ones are sometimes ported. Among Marshall ones, the 1912 1x12 cab has a port, and also the 1933 had one (JCM800 era).

    Ports cause a resonance, which may be for good or evil. If you do one, it has to be carefully designed to suit the cab, to lift the response where needed but without resulting in a boomy peak.

    I built a large 1x12 with one, which I adjusted to give a boost just below guitar frequencies, so that the upper tail of the resulting peak lifted up my bass response how I wanted it - which then allowed me to sell a 4x12
     
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  10. rolandson

    rolandson Tele-Holic Silver Supporter

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    I find that I prefer open. Currently, aside from two fender combos, I've three that can be open or closed...

    A 2-10 cab and two 1-12 cabs. Everything sounds nicest to me with the back open.
     
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  11. jvin248

    jvin248 Poster Extraordinaire

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    .

    It always seems that very little cabinet sizing is done to maximize speaker performance, especially because the guitar world is full of open back designs.

    Here is what the stereo audiophiles will do when building a speaker cabinet: https://www.diyaudioandvideo.com/Calculator/SpeakerBoxEnclosure/

    Guitar amps are more marketing:
    -is it big enough for us to price it at the top of the market? (like the Back To The Future scene where Marty plugs into that ten foot tall cabinet).
    -is it heavy enough to make a buyer feel like they got their money's worth? Too light, must be a toy.
    -is it just like the styling from the 50s?
    -is it the same box we used last year, will these other drivers fit in there?

    A correctly sized box will give a speaker the optimal amount of air 'spring' behind it to get the most efficient output.

    .
     
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  12. Bill Moore

    Bill Moore Tele-Afflicted Silver Supporter

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    I have built several with an oval opening in the rear, generally the width of the speaker, and about 1/4 the width high. (No science to back that up!) But I do get a little more bass response.

    PB7.jpg.JPG Lead 12-3.jpg VL Cab 2.JPG
     
    Last edited: Dec 6, 2019
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  13. RodeoTex

    RodeoTex Poster Extraordinaire

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    Great thread.
    I have nothing to contribute, but I noticed there was very little discussion on this subject back when I was building a few cabinets.
     
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  14. eddiewagner

    eddiewagner Poster Extraordinaire

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    Open front is for Bassgitarre, right?
     
  15. rolandson

    rolandson Tele-Holic Silver Supporter

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    You know, almost every bass player I've played with uses a closed back cabinet. So...I don't know, but...?
     
  16. LightningPhil

    LightningPhil Tele-Meister

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    Go for it, get a couple of cabinets and give the drivers a home.

    Room size and placement (both where the cabinet is and where you are in relation to it) will have a huge effect on perceived tone.

    Away from the bass region, open back can be up to 3 dB louder than closed due to a goodly amount of sound from the rear joining in. It’ll be less than 3 dB as speakers are better throwing sound forward. At the back, the magnet, spider, chassis and bits of cabinet get in the way. And since it can be projected at a reflective wall, the sound from the rear will seem wider and a little delayed. Most of us like a little reverb or delay so this is great. However, slam it against the wall and this all vanishes.

    In the bass region, the speaker if under damped, will have a resonance hump and sound boomy/boxy. For a sealed back, the smaller the enclosure, the tighter the air spring and the higher the driver resonance. Since the electrical and mechanical dampening remain the same, this raises the Q factor. Above the threshold of 0.707, you end up with a hump in the bass response. Since guitar speakers are light and have a huge surface area, a rather large cabinet (read, much larger than standard) is often required to get a flat response. And if adding ports to have an extended, flat bass response, then the starting point requires an over damped sealed enclosure. Which tends to be huge. Then adding a port an tweaking it can give a good fraction of an octave of extended response if everything went right. It will be huge though. Ball park future of 60l per 12 inch driver or more.

    The pressures in a closed back cabinet act on the cabinet and excentuate any panel resonances, adding to boxyness if not stiff and heavy. Ports can be complex beasts and have resonances and otherwise be troublesome if not designed really well too (such as phase errors if too far from driver and different coupling to the room if close to the floor or on the back).

    So it’s easy to go in a circle and end up returning to an open back system, especially if not playing bass notes too often or being ok that they’re a little attenuated, and enjoy a smooth open sounding response. I did, and am now going through a VOX AC30 phase with blues in it and light mods for a bit more top boost. Even the bass guitar goes through it. But to detox from that, there’s a custom, over damped, sealed 1x12 with a very cool Volt speaker and an attenuator.

    If you are keen on making a ported system, perhaps start with a closed back 4x12 enclosure, then blank off 2 holes with some ply. Install 2 speakers with large magnets and low resonance, the experiment with ports by installing them in the blanking plates. Totally reversible. Giving each driver twice the air volume, resonance should remain low.
     
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  17. Paul G.

    Paul G. Friend of Leo's

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    I love the bass response and compression of closed back cabs. In a large venue, where amp is mic'd and put into monitors, whoo hoo!

    Unfortunately, closed back cabs tend to be very beamy, with a narrow field and sharp falloff. This is why your band can't hear you. This is why, if you go off axis, you can't hear you. This is why they don't really work in small venues where you need the sound to spread.

    I use only open, or semi-open backs live. They don't sound as tough or tight, but they provide the best sound over the widest area, helping balance the band, and offering built-in monitoring.

    Note: there are ways to fix the narrow beam, but these are not normally used on guitar cabs.
     
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  18. archetype

    archetype Fiend of Leo's

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    I prefer open back cabs for the “open” more room-filling tone and less bass punch.

    My J.D. Newell reproduction Tremolux 2 x 10 cab had a pair of 3 1/2” ports between the speakers. No tubes, just holes. The cab came loaded with a Weber Blue Pup and a 10A125. The low end was loose and flabby until I blocked off the ports.

    I suspect the entire system of cab dimensions, port dimensions, and speaker characteristics needs to be calculated, like with a stereo speaker, to yield good results. We don’t typically bother with “system design” in guitar cabs.
     
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  19. GoldDeluxe5E3

    GoldDeluxe5E3 Tele-Afflicted Silver Supporter

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    Since you're asking, I'll post this video of a 5e3 I built a few years back. The cabinet is designed to be either open or closed. The second video gives sound samples:



     
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  20. mexicanyella

    mexicanyella Tele-Afflicted

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    Two semi-related observations to add to the pile:

    Several years ago I had a Fender Acoustasonic Jr. amp (stereo 40 x 40 watts, 2 8” speakers and a piezo tweeter in a closed cabinet) that wasn’t selling and I started messing around playing electric through it. I tried disconnecting the tweeter and it quit sounding like playing direct through a PA and started sounding kind of like a solid state Princeton Chorus. Then I tried removing the tweeter, leaving the empty hole as a port, and the lows got looser and bloomier and it actually sounded pretty good when you cranked it up to “just barely clean,” especially with a compressor pedal. Eventually it sold but it was a fun experiment that worked surprisingly well.

    I have a Peavey TKO 115 bass combo that sounds pretty good but is underpowered for my needs, while being quite unpleasant to carry around due to weight/height/handle placement. I discovered that while underpowered for bass with my band situation, it sounds really good for gnarly, twangy almost clean guitar. And it seems loud enough to gig with at guitar frequencies. The closed-back front-ported cabinet and 15” Scorpion speaker sound really good when pushed hard with guitar frequencies once you wrap your head around the active graphic/shelving EQ and apply settings that slope off some lows and push the upper mids. It still retains some “heft” in the lower mids without sounding muddy, and I don’t think anyone blindfolded would guess that it’s just a largish solid-state bass practice amp from the early 90s.

    I guess my point is, try everything you can get your hands on. Learn how different frequencies sound and how that correlates with what you personally want to hear. Takes patience, but eventually you might find a sound you really like in an inexpensive, surprising place.

    Apparently I like heavy duty speakers pushed hard by mostly clean sounds in front-ported, closed-back cabinets (after a period of thinking I wanted midrangy Marshall distortion and speakers that broke up musically and tubes and open-backed combos). I might not have discovered that had I not goofed around with those two way-uncool amp choices for electric guitar.
     
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