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Fat Man joins Little Boy

Discussion in 'Amps and Cabs [BG]' started by kartiste, May 7, 2017.


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  1. kartiste

    kartiste

    May 5, 2008
    At long last, I’ve finished building a couple of boxes to house my old JBL K140’s – sort of an old-wine-in-new-bottles story. I wanted to put these drivers back into useful work again, providing an old-school sound and look for the mostly classic blues-rock-R&B of the two bands I’m in. (And by “old-school look”, I mean there should be a visible correspondence between the wavelength of the notes and their source on stage. In other words, you ought to be able to spot at a distance where that great bass line is coming from by looking for the guy standing in front of the biggest amp with the largest diameter speakers, preferably ones with 4” dull aluminum dust caps that look like they came out of the Lockheed skunkworks in the ebullient decades after WWII. As someone once said, people hear what they see. This fetish for tiny bass rigs deprives the audience and further commoditizes live music. No wonder they stare at their phones while you’re playing. But I digress...)

    Later on, I’m planning to add a box on top with two K110’s, biamped (see “Where is the Equal Power Frequency?” thread), but for now it’ll be full-range. With my rack on top of both boxes, I dub this rig “Fat Man”. Its stable mate is my obligatory Mini-Rig of Doom, a Fearless F210 driven by a Peavey MiniMega, which I dub “Little Boy”.

    As with the rigs’ namesakes, there is a performance difference between them, but not much. The K140 sensitivity is 98 dB, 1W/1m, with the pair nominally able to dissipate 300w. The F210’s 3010LFs’ sensitivity is 92.7 dB, with a rating of 900w together. Therefore, Fat Boy’s nominal maximum SPL should be 0.53 dB greater than Little Boy’s (Just for fun: the Fat Man bomb had a yield of 21kT, and the Little Boy 15kT, a 1.46 dB advantage to Fat Man).

    I started out thinking of building a 2x15 box, possibly with a JBL 2305 horn (I have two), but eventually came to my senses. Even though each of these boxes weighs 55lbs, they are somewhat easier to load than the F210 (34lbs), due to the ergonomic configuration of the handles – I can lift with a nearly straight back and clutch the box to my chest. The angle of the handles allows a higher lift without straining my wrists. In the design phase, I located them by summing moments, and it came out exactly balanced.

    For economic reasons, I built these from Fearful 15sub flat-pack kits from Leland Crook at Speakerhardware.com. However, for the K140’s I didn’t need as much internal volume as for a 3015LF, and also needed them to be a bit slimmer to fit better in my hauler. Leland cooperated with me in reducing the depth by 0.75” compared to the plans you can find online. He does great work, by the way, very accurate. I already had the handles, but got the rest from Speakerhardware, except for the grilles. Expanded metal may be passe’, but it fit the 15sub standoffs and was much cheaper than custom-cut ones from one of those online sources. It also fits the industrial aesthetic I’m going for. Used lath screws to mount them, by the way.

    At first I had some grille buzzes, even with the screws tight. I determined that the grille membrane, with no flanged edge like you can get if you want to pay for it, was vibrating in between nodes at the mounting screws. I cured this with strips of black waffle drawer-liner from Walmart (in the tool aisle), mounted with half-inch double-sided 3M tape (office supplies aisle) – easy, cheap and effective. Also, I substituted oval-head stainless machine screws (from Lowes) and rack washers (on hand) for the SHCS’s and flat washers that came with the clamps from Leland, due to a grille clearance issue (perhaps the intended 3015LF’s frame isn’t as thick as the K140’s).

    Due to the different driver intrusion and box dimensions, I expected built Fb to be higher than what’s advertised for the 15sub (“45 to 46.5 Hz”, as best I could find), and anticipated having to retune for the K140’s. In my initial measurements, they came in at 49.06 and 47.98 Hz, for Box A and B, respectively, using the “Salt Method” (but in my case sugar, since I didn’t want any chlorides on those aluminum domes). This was with the shelves and port dividers not fastened in, and in fact with a partial debond on one side of the baffle on one box. It’s a tribute to Leland’s accuracy that the divider and shelf fit tight enough to enable this first test.

    I never know quite how to calculate internal volume with a shelf-type port, especially where the edge of the shelf begins to approach the back of the box – where does the air column end and the free volume begin? What I knew for sure were the actual measured Fb’s, and from that I backed out “effective” Vb from the models – about 119.66 liters (average). I then used this as my baseline volume to figure out what I wanted to retune to. After doing some experimental partial blocking of the port, I finally decided to simply block one side of the divided port, recessing the block deep enough so that it’s not visually apparent, but still reclaiming a bit of Vb to offset the additional bracing I added at the edges of the baffle boards and shelves. Air velocity in the duct should not be a problem with these drivers

    After blocking the ports and adding the extra bracing, but before adding damping, Fb came in at 36.00 for Box A and 35.77 Hz for Box B, implying an “effective” Vb of 120.44 liters or thereabouts. After adding minimal damping, Box B went to 35.65 Hz while Box A, with a little more damping, went to 35.09. I think I can remove some damping and get Box A up to exactly the same as Box B.

    Questions for the acoustico-boffins: If I run these as a stack, where the open ducts are adjacent, will that 0.68 Hz difference lead to any comb filtering or anything? And why does damping lower Fb? Since Fb is proportional to the square root of the inverse of volume, any reduction in internal volume should make Fb go up, not down. What am I missing? Incidentally, my measurements method is probably precise to a half-digit at that second decimal place. I made two trials per box, observing the upper and lower bounds of the dead zone at Fb, then averaged the averages for the stated numbers.

    As for the response curve, I’m interested in any opinions. I like the shape of the curve. Characteristically for a K140, it has that flat shelf in the bottom octave. In my living room, they sound very satisfying – warm and fat, with a creamy bottom underneath. First gig will be Friday. I’ll probably just run one at that venue.

    I should add, I built these so that I can remove the port blocks later and put in modern speakers, maybe a 15PR400 or 3015.

    All comments welcome.
     

    Attached Files:

    12BitSlab and Bugeyed Earl like this.
  2. DigitalMan

    DigitalMan Wikipedia often mistakes my opinions for fact Supporting Member

    Nov 30, 2011
    They seem like awesome and yet somehow culturally insensitive cabinets.
     
  3. kartiste

    kartiste

    May 5, 2008
    Evidently smaller pix are required to attract interest. rsz_600_1503. rsz_600_1510. rsz_600_1517.
     
  4. I agree with you 100% but I use SVT's nowadays rather than JBL's but years ago I had 2 Sunn 2000S cabs with 2 JBL D-140's in each, powered it with a 200 watt Marshall Major tube head, now that rig moved some serious air. Nothing more disappointing than looking for the bass rig and not being able to find it until you spot what you thought was a small vocal monitor and then realize it's the bass rig.:roflmao:
     
    Count Bassie and kartiste like this.
  5. Interceptor

    Interceptor Supporting Member

    Mar 29, 2005
    Madison, WI
    I would not worry a bit about those differences.

    I recently built a TL606 using current materials approach. The authoritative look and feel of a classic 15 are forces all their own.

    I'm happy as can be with a 50 Watt tube amp and the TL606.
     
    Count Bassie, TAZ and kartiste like this.
  6. kartiste

    kartiste

    May 5, 2008
    Played a gig tonight with one box (I guess I could call this Fat Boy). Had a fDeck Series 3 on at 35hz, kept the XLS1500 out of the red (mostly, but near). No fart out, no overheat, just suh-WEET tone, and plenty loud. I think this is the beginning of a beautiful friendship!
     
    jnewmark likes this.
  7. fast slapper

    fast slapper

    Dec 11, 2001
    Fresno, CA
    Very nice rigs!

    Have you compared the max output differences between the "Fat Man" and "Little Boy"?

    Maybe switch between the stacks with the XLS1500 rack and hear which one sounds more effortless when cranked. Not enough to threaten vintage JBL's of course.

    I suspect the big stack will sound quite a bit bigger than the half a decibel difference found on paper. Curious to your findings. Thanks.
     
    kartiste likes this.
  8. kartiste

    kartiste

    May 5, 2008
    I haven't compared them in a controlled way, though I want to. Room effects come into it too much in my house. I suppose I could set them up side by side at a gig and do it in sound check with my old Rane RTA and its mic strategically located, and then alternate sets, but the logistics are difficult. May take a while to hear from me on that, but it's now in the hopper. And thanks for your comment.
     
    fast slapper likes this.
  9. DigitalMan

    DigitalMan Wikipedia often mistakes my opinions for fact Supporting Member

    Nov 30, 2011
    Actually it's just inline pictures that are needed. No one clicks pic links anymore.
     
  10. kartiste

    kartiste

    May 5, 2008
    Actually that's what I was trying to say, since if the pic is too big the TB site won't upload it except as a link.
     
  11. How are you liking these k140 cabs? Did you retune them like you mentioned?
     
  12. kartiste

    kartiste

    May 5, 2008
    I just now posted about that very thing in the other thread, the one you started.
     
  13. bklee

    bklee Supporting Member

    Nice work on the Tolex application.
     
  14. kartiste

    kartiste

    May 5, 2008
    Thanks, but it's just black satin paint from Lowe's.
     
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  15. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    I only.made it through chapter 2, but the cabs look great! :D
     
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  16. kartiste

    kartiste

    May 5, 2008
    ADD, huh?
     
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  17. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA

    Yeah, I've been told....SQUIRREL!!!!
     
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  18. bklee

    bklee Supporting Member

    I guess they haven't invented spray Tolex yet. Although you might get away with spray bedliner for pickups (the truck kind).
     
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  19. kartiste

    kartiste

    May 5, 2008
    19144074_400510970343492_1747839859586596245_o. First gig last night with Fat Man, boxes re-tuned upward to 45.5 Hz (give or take whatever uncertainty you wish to attach to that). Gig was outdoors in a beer garden. Sansamp RBI with a tick of bass boost, fDeck HPF in the EFX loop set at 35Hz, then each box on its own channel of my XLS1500 (300w, 8 ohms). Our guest drummer, a full-time pro, practically gushed over the tone, clarity and note definition. He plays a lot of notes, and it was a joy to lock in with him on One Way Out and Skin it Back, for instance, on really fast sixteenth patterns. I'm still not satisfied with the tone, but it's gonna take several gigs to dial it in. Volume-wise, it was plenty, with no hint of hitting limits or overheating. The channel LED's were toward the top of the green every time I glanced at them. The angled handles are working out great - I'm really surprised commercial manufacturers don't do this, because the ergonomics are much better.
     
    Last edited: Jun 17, 2017
    Count Bassie likes this.
  20. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Banned

    Feb 23, 2011
    Denmark
    If ever you get big in Japan, you better rename them Batman and Little John.
     
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