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speakerbuilders-->help!

Discussion in 'Amps and Cabs [BG]' started by SRSiegel, Feb 12, 2002.


  1. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    hey all you speaker gods out there (yall know who im talkin to)

    im going back home for spring break in two weeks, and well... i need something to do besides work and party. i really want to rebuild my 18 cab, but ive been messing around with winISD, and am having trouble coming up with some good numbers. i know you guys have helped me before, and did a great job of explaining things, so i was wondering if you could point me in a good direction.

    heres youre assignment:
    ive got a 4 ohm eminence omega pro 18" woofer. here are the T-S parameters:

    Resonant Frequency 28Hz
    Impedance (RE) 5.1 ohm
    Coil Inductance (Le) 1.67mH
    Electromagnetic Q (Qes) 0.25
    Mechanical Q (Qms) 5.53
    Total Q (Qts) 0.24
    Compliance Equivalent Volume (Vas)
    354 liters
    12.49 cu. ft.
    Peak Diaphragm Displacement
    Volume (Vd) 635cc
    Mechanical Compliance
    of suspension (Cms) .19mm/N
    BL Product (BL) 25 T-M
    Diaphragm Mass inc. Airload (Mms) 171 grams
    Equiv. Resistance of mechanical suspension loss (Rms) 5.46N*sec/M
    Efficiency Bandwidth Product (EBP) 114
    Voice Coil Overhang (Xmax) 5.5mm
    Surface Area of Cone (Sd) 1159cm2
    Impedance at Resonance (Zmax) 97 ohm

    im just trying to come up with the best overall cabinet using this driver with a 5 string bass. any input? be creative! it should make for an interesting spring break, and if i go through with it i will use my digital camera, and post pics as i go through the process.

    of course i left a ton of room for yall to play with, im looking for opinionated answers!

    thanks,
    ~Scott
     
  2. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    It looks like it will need a fairly large cab. I came up with about 6ft tuned to around 32hz, if you throw in some extra stuffing you should be able to tune a little lower. 23.6w x 29.5 high x 18.25d. This is with 3/4 inch material. Hope it helps a little. FWIW I have yet to build a cab using winisd.
     
  3. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    thanks man. yeah im currently running 7.7 cubic feet, so big isnt a problem. smaller would defenity be a plus compared to the box its currently in.

    any porting tricks/advice? reccomended materials, etc? im trying to get a fair amount of research done before i start this.

    does anyone know how to determine the ideal size of the box for the driver, as well as the volume taken up by the "guts" of the driver inside the box? one of my goals here is to be as precise as possible.
     
  4. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    If size is of no matter I would go with 11 cubic feet. As far as tricks I just started getting into this stuff about a year ago so I got no tricks (yet). I would go with 3/4 mdf as thats what books and the pro's here on tb recomend. The "ideal" size of the cab depends on what you want out of it. Do you want portable, or to heck with size and go for low and loud, or portable and low but not very loud. You cant have it all (low,loud,small) somrthing has to give. The dimensions I gave you earlier where outside dimensions using 3/4 inch material for a 6 cf box. There are different sizes for different uses. Do you allready have your driver?
     
  5. bizzaro

    bizzaro

    Aug 21, 2000
    Vermont
    Hey Thunder are you a Daddy yet?? I would disagree with the use of mdf. It would work great for smaller cabs. The mdf is nice and stiff, but really isn't all that rugged when the weight starts moving up in your cab. Great for home fidelity speakers. It is the most economical though. If you can afford it, I would go with the 3/4 inch birch with no voids. Very expensive, but worth it in the long run. MDF is a good second choice. I just know if I dropped mine off the back of a pickup truck it would probably crack.

    Anyway, this should give you enough to chew on for awhile. Do a search for this, I tried to link it but I don'tknow how..........." Cabinet Building 101"
     
  6. geshel

    geshel

    Oct 2, 2001
    Seattle
    I'm not terribly happy with the TS params for that driver, it's a difficult one to get a good bass cab out of.

    Do you need it full range, or just as a subwoofer?

    Full-range, yeah a big (7+) vented cab is pretty much the way to go.

    If it's just a subwoofer, the same size cab but 6th order bandpass might be the stuff: front chamber 60l, 70Hz, rear chamber 150L, 30Hz. Response from about 33Hz to 100Hz, 3dB more efficient than the vented box at these frequencies. But that's still not really very good performance from a 7+ cu. ft. box.

    Then again, I can't seem to get anything better out of the other 18s in the WinISD database.

    [edit] My brain lapsed, 7 cu. ft. isn't as big as I was thinking. Thought the box behind me was 4, but it's really 6 (2x2x1.5).
     
  7. Eminence doesn't make a 4 ohm 18" driver in the omega range....it's going to take quite a bit of juice to push a 600w 8 ohm 18". You'd want something that could push about 1000w into 8ohms. They make a 4ohm 1000w kilomax 18". Is that what you have?
     
  8. Download my spreadsheet from my signature. Each entry in the DRIVERS tab has the corresponding DBK VOLUME for the optimum volume, tuning frequency, and F3 lowest frequency.

    Note there is color coding here for drivers best suited for 4 and 5 string use.
     
  9. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    Man I have been THE DADDY (jk). But im not a father yet. The due date is march the 5th . My wife is HUGE, I had to put one of those back-up beepers on her after she took out a couple of children and furry mammals. Really she is doing fine and im skeered but exited. Im ready to do this deal, tired of 9months of hype. Thank you very much for asking , I will let all of you guys know when he is here. Thanks


    On subject: SR - if you dont have your driver yet there are better drivers for the task.
     
  10. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    thanks guys. unfortunatly, i already have my driver. and yes, it is a 4 ohm omega pro 18.

    heres the story. i paid a guy at a speaker repair shop to build it for me. its an omega pro 18, but he modified it (new voice coil) so that it would run at 4 ohms. because it was essentially being built form spare parts, i got a deal on it and only paid 120 bucks. (it was brand new).

    ive also posted at the live audio boards, asking if i could convert it into a subwoofer. its not that im not happy with it, i just need something to do, and i enjoyed building the first one... so...

    hope to hear more from yall!
     
  11. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    A true "sub" will be finished by 200-500hz. You cant (AFAIK) "convert" a driver to a sub. Your 18 is a loudspeaker not a sub. Subs are a special breed designed to go low but have no highs (or mids really), normally a sub is really ineffecient and have a higher power handling. If you want to go flat to 31hz it will take about an 11 cubic foot box tuned around 30 hz. To me thats a very large cab and to dang heavy to tote around. 3 ports 4 inches in diameter about 7 inches long will get ballpark but just ballpark. The port dimensions are only for an 11cuft box.
     
  12. geshel

    geshel

    Oct 2, 2001
    Seattle
    What worries me is that, changing the voice coil from 8 to 4 ohms, probably changed the T-S parameters anyway. That, combined with inconsistencies in production (you'd be suprised), means they could be different enough not to sound horrible but to have a noticeable effect. I'd have the TS params measured for your driver if you can find somebody with the equipment and know-how.

    ThunderStik, I generally agree but I think your comments can be misleading. A subwoofer, plainly, is designed only to cover the lowest frequencies. Depending on home/car/PA use, this can mean different things, but you're right 200Hz is about the upper limit of a subwoofer. 500Hz is pretty square in the "midbass" region, so not really sub territory. Home audio subs usually cover 20-80Hz or os. This can describe a driver specifically designed for that task, or a more general-purpose driver installed in a system (box, crossover) that fulfills that goal.

    For a sub, bandpass is a pretty decent way to go, and if I recall from when I was messing around this morning, the 6th order I described earlier will get down to 31Hz (+1, -5dB) in a total box of about 7 cubic feet. Still not small, but not 11 feet either.

    Thing is, since it drops out at 100Hz, you'd probably still need a 2x10 or something to cover the midbass and up.
     
  13. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    thanks guys. the bandpass idea is sounding interesting. i do have a 210 cab that can handle the mids/highs. would it be possible for me to mount the driver in a front loaded, ported enclosure so that it could be run as a subwoofer with an additional crossover and poweramp, and then as a fullrange cab should i decide to? i know its an odd request... but just an idea.
     
  14. geshel

    geshel

    Oct 2, 2001
    Seattle
    I can't tell if those two things go together - yes, you could use it as a front-loaded ported cab as either full-range or sub (with a crossover). But you couldn't do that with a bandpass design.
     
  15. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    thanks geshel.

    i like that idea of flexibility. im thinkin thats what i will do. (front mounted, front ported, used as sub or full range depending on situation)

    is there such a thing as a poweramp with a sub crossover built in? that would be ideal.
     
  16. geshel

    geshel

    Oct 2, 2001
    Seattle
    Indeed there are, I think the Mackies do (80Hz?). They're not usually listed as anything special, it's just an added feature on some amps.
     
  17. Ty McNeely

    Ty McNeely

    Mar 27, 2000
    TX

    Just an observation from a completely inexperiences cab builder, but offering insight none the less.....

    If you decide to use a 2x10 with it also, are you willing to run your amp at 2 ohms, or does it even run at 2 ohms? I know MANY big players won't run their amps at 2 ohms due to the fact that they usually run so hot.

    Like I said, just something I thought about....
     
  18. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    thanks for the concern man, but my head will run 2x300watts at 2 ohms, or 2x250 at 4. bridges to 600watts mono at 4 as well. im glad youre watchin out for me tho. ;)