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DIY 1x12 sealed cab: Some advice needed please

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  • DIY 1x12 sealed cab: Some advice needed please

    HI guys, I use a Marshall Haze 40 (40 watt tube) at the moment, and while I'm happy overall with the sound of it, I know it can sound a lot better.

    Basically the low end is a bit loose and flubby, which makes it bad for power chords (I'm in a punk band btw).
    I got a chance to plug into a 1960a recently and it was amazing the difference it made.

    My idea (cuz I'm on a budget) was to build a sealed 1x12 cab (the haze is heavily ported/open back) and put the stock speaker in it, then maybe later get a G12T-75 inside it, if I feel the need.

    Does this sound like a good idea? I'm hoping that being sealed will tighten the low end and add more punch overall?

    The Haze is 56cm wide, would this be an OK width for a 1x12? What about height and depth? Would I need to vent it? Should I add insulation inside?

    Material would be 18mm MDF BTW (again, I'm on a budget).

    Thank you for reading, cheers
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  • #2
    Start by covering the ports with something, maybe put a piece of plywood across the back of the amp. Play through it and see if it sounds better. If it does, you'll know you're headed in the right direction. Don't leave the ports covered because a tube amp needs ventilation. That's why you don't see many tube combos with completely sealed backs. The Haze 40 is supposed to have a Celestion G12T-66 speaker. Normally you'd use a Thiele/Small calculator to figure the ideal enclosure volume and the effect of a port (if any) but Celestion doesn't publish detailed specs for that model (at least none I can find) so you're kinda left guessing. Go ahead and start with a sealed cabinet. 56cm is fine for width. The idea is to make sure no two internal dimensions are multiples of each other so you don't get resonances. Something like 2X*3X*5X would work. If 5X = 56cm then X would = about 11cm. Take your other dimensions from there, about 22.4cm and 33.6cm. Hope this helps.
    Last edited by DeepEnd; 09-16-2018, 04:04 PM.
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    • #3
      Putting the speaker in a sealed can isn't going to do jack squat for the sound. The problem isn't with the speaker, its the head.

      That amps drive channel gets highly congested when cranked, and practically unusable above 1/2 up even when lower gain classic pickups are used. Below half way it produces a fairly decent 70's style AC/DC guitar tone you'd expect from a Marshall. Above it produces a decent ZZ Top tone. Not exactly what I'd call punk rock tones but there again, Punk rock was never about good sound, it was about playing loud.

      Bands like the Ramones used small combos when first starting out until they could afford better and then went to using Three Marshall Super Lead and Ampeg amps. Sealing the back of a Marshall combo isn't going to make it sound like a 1960 cab and given the head is 40W you'll only need to crank it more to be heard.

      That Marshall cab is ported, not a full open back. All you'll wind up doing is screwing up the bass response. The ports tune the speaker to the cab and the heads EQ is designed to make the can sound bigger then it actually is.
      When you seal the cab, you'll restrict the cone movement and increase midrange. It's also likely to produce a frequency bump the heads EQ may have a hard time adjusting away.

      If you combined a factory built sealed can with the existing combo speaker you'd be much better off because you'd only be adding half the sound of a sealed cab.

      My advice would be to work with the clean channel and find pedals that suit your music type. Marshall cleans channels take pedals well and you can find the right drive tones from a pedal instead of the drive channel which tend to be a one trick pony. I did that with my Marshall years ago. I used the drive channel when I first bought it but the sound became boring very quickly. Using several different drive pedals gave much more variety as did additional guitars.

      Like I said, punk has little to do with sound quality, at least in the beginning. Bands literally cranked amps to maximum which went beyond their ability to sound good and from there it was the hyped style of music that was unique.
      Last edited by WRGKMC; 09-17-2018, 07:54 AM.

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      • #4
        Sealed vs. open cab mainly affects the low end of the speaker, which is where you're having problems. Covering the ports temporarily is cheap and easy. That said, the G12T-66 in your Marshall is supposedly similar to the G12T-75, which is supposed to have a "tightly controlled low-end": https://celestion.com/product/15/g12t75/. You may not get much improvement no matter what you do.
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        • #5
          The Haze was an ok amp. The speaker I believe was designed for that amp.



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          • #6
            Originally posted by Mikeo View Post
            The Haze was an ok amp. The speaker I believe was designed for that amp.
            Pretty sure you're right but it may have also been made to fit a specific price point. We're not talking about a boutique amp so overall cost was certainly a consideration.
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            • #7
              The G12T-75 and G12T-66 are Celestion budget line of speakers. They are similar to what Jensen did when they made the Mod series which had a generic sound. The budget Celestion are OK for most situations but you shouldn't expect it to sound as good as their top end speakers.

              If you heard a difference between the T66 and T75 it was the cab.
              The 1960 cab not only has 4X12's but its got a large baffle and allot of air volume. The sound was big because the cab is big. Period
              The slant 1960 produce a tight bass end which is part of the Marshall Sound.

              The 1960 cab I bought cost me $450 used at a Guitar Center. It had the stock Creamback G12H 75W speakers that sell for $169 each so I made out pretty good on that cab. I had to change the Grill cloth but that was a simple task of unscrewing the baffle and stapling a new cloth on.

              The cab does produce a broad, tight neutral sound with those speakers. I've owned another Marshall cab that had Green Back 30W speakers which I really disliked. Besides having a lower SPL, they were designed to roll off the top end and produced allot of mids. Sounded OK with a Marshall head because its got excess highs to compensate and the tube heads could make the mids overdrive nicely. Sounded terrible with a Fender head however, unlike the Creambacks which sound good with any head you use.


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              • #8
                If the G12T-75 is a "budget" speaker, what does it say that Marshall puts them in the 1960A and B cabs? (https://marshall.com/marshall-amps/p...960a-and-1960b.) Note that's G12T-75, not G12H-75.

                As for a big cab "sounding big," that's an oversimplification. Let's look at how a speaker cab works: It's not just there to keep the speaker from falling on the floor. A speaker creates pressure waves--sound waves--as it moves. At lower frequencies the wave from the back of the speaker can come around and cancel the wave from the front because the two waves are "out of phase." One side of the speaker goes out when the other goes in. There are ways to eliminate this. If the "baffle"--the board the speaker is attached to--is big enough the waves will never meet. This is called an "infinite baffle." The drawback is that a true "infinite" baffle isn't practical and it wastes the sound coming from the back of the speaker. A second possibility is a sealed cab. it also prevents the back wave from interfering with the front wave and again it wastes the energy from the back wave. If the cab is small enough it also creates resistance to the movement of the speaker, which can tighten the bass. A smaller cab can also make the overall sound "boxy." since there's less bass because the speaker doesn't have "room to move." This could be an issue with a sealed cab the size you're considering. A properly designed ported cab can use the back wave to reinforce the front wave and increase the SPL at lower frequencies but you need to get everything just right.

                The 1960 cabs are 75.5cm * 77.0cm * 36.5cm (H * W * D). Let's assume 2cm of that is the thickness of the sides all around and you get 169633.75 cubic cm or 169.63375 liters. Whether you'd need a cab of similar size to get the same sonic effect is debatable but the bigger you can afford to make it the better.
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