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Building my own 215

Discussion in 'Amps and Cabs [BG]' started by dirk, Dec 27, 2003.


  1. dirk

    dirk

    Apr 6, 2000
    Memphis, TN
    I'm considering building my own 215 cab. I think I'm going to use Eminence Delta 15. I've been playing around with it on WinISD and I'm confused about ports. I was thinking of 2 round ports, but no matter what diameter I put in it says the vent length would be short. Plus I'm not quite sure what vent mach is. I'm completely a newbie at cab building. I'm also not that smart in Physics and stuff, but I would love to understand the principles of cabinet building. So any help would be appreciated, especially from the pros who have some experience.

    Thanks,
    Dirk
     
  2. first of all build your self a 2x18 and u will have the coolest cabinet in town most likely the heaviest but you will also have the lowest of lows goin on it will make people barf anyway do a search. i have got to sorta understand the baiscs just by reading so do a search and then ask.
     
  3. dirk

    dirk

    Apr 6, 2000
    Memphis, TN
    Thanks for the advice and I have searched, just didn't up anything on ports and vents specifically. And if I wanted to build a 218, I would have asked about a 218.

    Dirk
     
  4. yah i supposed u would have but it was just a idea thats my dream cabinet.
     
  5. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    You start with a tuning frequency and cabinet volume, and then figure out what kind of ports work best; it may not work out to be 2 round ports.

    One rule of thumb I have heard is that you want to have your ports at least 1/3 the area of your speakers.

    "Mach" refers to the speed of the air moving thru the ports. If your ports are too small, the air moves too fast and makes noise because it is being squeezed thru the ports (normally described as "chuffing" I believe).
     
  6. dirk

    dirk

    Apr 6, 2000
    Memphis, TN
    ESP-LTD,
    I want the frequency to be around the 42-43 Hz neighborhood, and the cabinet volume to be around 55.316 ft^3. The actual cab dimensions will be 24x36x16. So the ports should add up to 10 in? b/c I had two round ports 4 in. in diameter and it still says the vent length is too short with the vent mach at .1
    Thanks for the reply.

    Dirk
     
  7. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I think you slipped a decimal place. 5.5 cu ft is about what you are describing, not 55 cu ft.

    Rough numbers, using the construction techniques I use, I end up with about 6.5' without counting the drivers and ports; call it 6 cu ft.

    Tuning that at 42 makes for a pair of 5" ports about 6.4" long or a pair of 4" ports 3.5" long.

    The thing you need to search on and study, is excursion vs frequency vs power. Your speaker will exceed Xmax at some frequency below Fs without a whole lot of power- this will probably be the limiting factor in how low the cab goes.
     
  8. dirk

    dirk

    Apr 6, 2000
    Memphis, TN
    I'm not understanding the whole Xmax thing. I do see the graph sloping, so how does that relate to the Xmax thing? I crunched more numbers and came up with 5.837 cu ft. at 42.83 Hz with a pair of tube ports 4" in diameter and 3.32" long. This also allows for the cab to be a bit shorter too. I'm concrete on the 24" W and 16" D b/c this will go under my Ampeg 210.

    Thanks for your help ESP, I'm hoping Bgavin will show up pretty soon. Also what are some ideas on bracing and internal padding? Is the padding even necessary?

    Thanks again to all those who have replied with some useful help.

    Dirk
     
  9. Selta

    Selta

    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
    Do you HAVE to have ports? I just caught this thread, and am interested. I know for like car audio you can get sealed cabs, so why not for bass amps? What are pros and cons of it? :) I'm building a 2x15+3x12 right now (in an old 4x12 cab by the way) and kinda need stuff to help myself on ports....

    Ray
     
  10. dirk

    dirk

    Apr 6, 2000
    Memphis, TN
    from my limited knowledge it seems to me having a ported box will give you more volume at lower frequencies. There is more than likely someone one the board that can answer that question a little better than me.

    Dirk
     
  11. Selta

    Selta

    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
    Thanks for that answer....it's just with the box I'm using, along with the speaker combination, it'll be hard to get useful ports, so I was thinkin' why even bother...Thanks man

    Ray
     
  12. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I'm not sure what sloping line you are seeing, but-

    XMax is a measure of how far the cone can move before it starts leaving the magnetic effect of the voice coil. When it gets beyond XMax the sound becomes non-linear and somewhat "unpredictable" (by non-linear you can consider this territory "distortion").

    XMech is the measurement beyond which mechanical parts start smacking into each other; mechanical damage.

    If a speaker has a lot of excursion it will go very low (but not get very loud). An example are car audio subs (mine have XMax=12mm) which do not exceed XMax at 250w at 30hz.

    If a speaker has little excursion, it will get loud, but exceed XMax at a pretty high frequency with much power at all (like most bass guitar speakers) and start distorting.

    You need to examine it with software which will compare cone excursion, frequency, and power, at the same time. I'm told WinSD Pro has that funcionality but I haven't tried it. I did a search on "Xmax Delta" in Amplifiers and found a lot of good discussion.
     
  13. Each Delta 15 requires 11 to 20 cubic feet for proper tuning. A 2x15 requires 2x the internal volume, or 22 to 40 cubic feet total volume.

    Wrong choice.
     
  14. dirk

    dirk

    Apr 6, 2000
    Memphis, TN
    Bgavin,
    Is this just a poor choice of drivers for a 215 cab. I just chose those kind of randomly because they are available in 16 ohm and I want this to be an 8Ohm cab. What are some recomendations of a good 16 Ohm 15" drivers? Thanks for any help.

    Dirk
     
  15. JBL made many 16 ohm drivers, almost all are obsolete. All are expensive.

    There is a much wider variety in a pair of 4-ohm and going in series. Peavey, Carvin, JBL M151-4,

    Your biggest problem is going to be the huge cabinet.
     
  16. bizzaro

    bizzaro

    Aug 21, 2000
    Vermont
    Bruce you are such a gentleman:)


    DIRK,
    Grab yourself a large cup of coffee and smokes if you need them, Then chew on this for a while:
    "Cabinet Building 101" search in Amps ;)
     
  17. dirk

    dirk

    Apr 6, 2000
    Memphis, TN
    bgavin,
    First I'd like to say I'm not one of those guys who asks a question and then disregards the advice or attacks those who advise against what the poster is trying to accomplish. I'd like to know specifically what makes these drivers inadequate for a 215 cab. I've worked and reworked the specs and as of right now I have this: 22.051 cu ft. at 41.9 Hz in a 24x38x16 box with 6 2.25 tube ports.

    the reason I've raised the question on why it will not work is because I read a post earlier today where bgavin discouraged someone from building a 212 cab with Eminence Delta 12s. Obviously since Avatar makes one that wasn't such a farfetched idea.

    I'm going to test out some other speakers and see if I can come up with something better than the Delta 15s. Thanks for everyone's help, it's great to have a place like this to learn new things, share opinions, and bouce ideas off of other bass players.

    Dirk
     
  18. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I am confused.

    You have designed a cab that requires 22 cubic feet of internal volume (a huge box to carry) that matches the parameters of the speakers.

    What does that have to do with a box 24x38x16 ?

    The box you want to build is still 6-7 cubic feet. The box you need to build is about 3x that size. One of these two sizes is not important since you are building one box with a fixed internal volume. If you want to build the box 36x24x16 then you need to pick speakers that are happy in about 3 cubic feet (look at BGavin's spreadsheet).
     
  19. Not to split hairs, but 24"x38"x16" = 9.51 ft(3). I've got a Mesa 2x15 cabinet with roughly those same dimensions and it's got a couple front loaded ports (4" x 6.5" I think) and I'm pretty sure there's no internal baffling. There is padding stapled to the entire inside of the cabinet.
     
  20. dirk

    dirk

    Apr 6, 2000
    Memphis, TN
    ESP-LTD

    You're not the only one that's confused, but your post has made the most sense to me. Now I suppose the search for drivers is on. I'm guessing I'll end up with two 4 ohm drivers in series to get my desired 8 ohm load. Thanks again for all the help.

    Dirk