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Question for Cab Design Wizards

Discussion in 'Amps and Cabs [BG]' started by ESP-LTD, Jan 19, 2003.


  1. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I have been trying to come up with a cabinet plan for a few months, and have learned a lot from the posts here (thanx to Bgavin, Joris, Geshel, and others). My wife has convinced me not to build a box for resale value, so I will be redesigning one and I'd like some input from anyone with an opinion. My design goals are primarily ease of carry, and second low end response. I'll be making 8 ohm boxen, and can push about 250w into several of them and will biamp (Yamaha PB-1 / QSC RMX-1450). I play mostly classic rock and blues or country with a neck-thru 5 string.

    I will buy an Avatar B112 (Eminence Kappa 12 and a tweeter) in a 2' box; (2) 4"d x1"l rear ports tune it at 92hz as I calculate. This box will be driven either full range or biamped for the highs (so I don't kill it). I will probably block one of the ports and replace the other with one 5.5" long to retune at 45hz (Fs for the driver) although that's optional if I biamp; might be nice for very quiet gigs with lots of EQ.

    I will then buy a B112 empty cabinet and fill it with a Kappa Pro 12; block up the tweeter hole and one of the port holes, and fill the other port hole with a 4"d x 11" l tube, tuning the 2' box at 35hz for the fundamental of my 5 string. I will make as many of these boxes as I require to make volume, and could biamp and still push 2-4 of them off one channel of the QSC.

    I chose the Kappa Pro 12 because it has the best Fs of the bunch, and it's $100. The Delta 12LF was close, but has a smaller magnet and higher Qts. The Omega Pro is nice enough but I couldn't see a reason to spend $150 when $100 would do (until you tell me otherwise).

    I believe that a single 4" port should be adequate, but perhaps I'd be interested in other opinions on that as well.
     
  2. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    From looking at Winisd you would get better bottom out of the Delta 12 lf.
     
  3. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    There was a great thread about that a week or so back (Delta 12LF discussion)

    in which Bgavin ran the numbers and the Delta 12LF could only handle about 25w at 32hz without going into distortion. He liked the Omega Pro 12 a lot better.
     
  4. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    Any other suggestions before I start writing checks?
     
  5. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    But your not going with the Omega 12. I was talking about the Kappa.
     
  6. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I'm assuming the Kappa Pro will respond as well or better than the 12LF but I have no proof of it.

    BGavin's spreadsheet lists the 12LF as a midrange driver and the Kappa Pro for 4 string. I'm just trying to interpolate from his statement that the more upscale Eminence drivers are going to be better for this application than the Delta series. I'm afraid I don't have any software which will show me the excursion vs power at frequency; I was surprised to hear the Delta LF would run out of steam at 26w/32Hz; that's the sort of thing I don't want to discover when I'm $200 into a project.

    I appreciate your following this thread; I'm looking for more input like yours.
     
  7. You can find it here:

    Link to Eminence Spread Sheets

    I wouldn't be particularly concerned about the low power handling at low frequencies. An honest plot of the Edens, Avatars, etc, will show the same results.

    I don't quite understand why everybody is so insistent about bottom-end performance, yet also insistent on getting it from small drivers. Dinky drivers don't have the air moving capacity of the 15" and larger drivers.

    When you read the spread sheets and check out the EXCURSION tab, note the over-excursion point is for Xmax and *not* Xmech. There is a difference. Xmax is the limit of *linear* operation, not the point of damage. The Xmech of the various Eminence drivers is also in my spread sheet, and it is MUCH larger than Xmax.

    Operating beyond Xmax rapidly increases distortion, but I can't see this as a point of much concern. The SVT guys drive hell out of their amps, so distortion obviously isn't a concern for them.

    The spread sheet cannot calculate power limitations beyond Xmax, because the non-linear response of the cone cannot be predicted. The thermal limits (rated power) of the driver cannot be exceeded in any case, so use that as a guide. If the driver is farting and beating itself against the stops, that is another indication to turn down.

    :D
     
  8. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I am willing to accept a lower SPL in trade for an easier box to pack around in this case. I had hoped (2)1x12 subs and a single 1x12 for mids/highs would get me enough volume in a size I can transport easily.

    Thank you for the spreadsheets. They are VERY complete and I admit I only grasp the sigificance of fractions of the information. They don't paint a very pretty picture for low end response and excursion control for any of the drivers I have been considering.
     
  9. Driver quality is directly proportional to price.

    12" is too large for high frequencies. Check out the REFERENCE tab of my spread sheet and look for the BEAMING formulas. You can plug in various pistion diamters (inches) and see where the driver begins to beam.

    A 10" driver with an 8.25" piston diameter is fully beaming at 1,700 Hz and higher. Look into the Eminence B102 10" driver for your highs. It goes way up for a cone driver and requires a very small cabinet volume. This is my choice to match with the Magnum 18LF for the low end.

    The trick to portability is splitting the drivers into multiple cabs. It requires an extra wiring connection between the two cabs, but so what? You can put an Eminence crossover into either cabinet, and use a double jack plate on that cabinet to provide the cross connect.
     
  10. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I am coming to that realization. I thought for awhile that I might find some wonderful combination that had been ignored by everyone else but I've been kidding myself- it's a mature market and you do get what you pay for (at least in raw drivers).

    Other unpleasant truths:

    1. I probably need to make at least 120db to be heard with a band.

    2. Given the way outlets are wired, I have no more than about 1500w to work with and half of that should be headroom.

    Regardless of what kind of what I may desire in size/weight, to meet the above on a budget I'm almost certainly looking at 1-2 Omega Pro SBB4 boxen with a pair of B-102's in the smallest box I can make.

    Much like what you posted several informative threads back.
     
  11. I think the wattage thing is causing more worry than necessary.

    My standard stage rig consists of a PLX 3002, several Rane boxes, IOD, Hammond XK-2 keyboard, pair of subs, pair of JBL E110. I power all this from a sh*tty (but safety tested) wall outlet in the bar.

    My left channel is constantly tickling the clipping LED, so I figure I must be putting 900 watts into the 4 ohm sub load.

    One guitarist plugs his Fender Blues Deluxe into my power strip and adds even more drain to the wall plug. In two years, we have never blown a circuit breaker.

    As for 120 dB to be heard.. this is relative. 120 dB on stage, at 25 feet away... where? My dB meter shows my band produces 105 dB(A) at 20 feet from the stage. This is excruciatingly too loud and a constant source of irritation to me. It also drives customers away. Customers come to bars to hear music, dance, and get laid. They aren't looking for bleeding ear drums.

    If you build your rig like a box of Legos, you can take as many parts with you as required for the venue. A single 12" is nice for coffee shops and quiet venues, but won't do squat in a gymnasium. Add more cabs.

    An Omega Pro 12 and B102 crossed over at 500 Hz will work nicely.

    [ edit ]

    One driver each, will work nicely. Two B102 will be too hot and overpower the single 12". Worse, two B102 will be a big impedance problem for a passive crossover such as the PXB2:500 Eminence model.

    You have to put the B102 into a sub chamber anyway, so why not put each into a separate cab? Two smaller cabs are easier to move around than a big one with an internal sub-chamber. Use a double-jack dish in one cab and put the crossover in that cab. Run a short interconnect cable between the two and you're done.
     
  12. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    You are of course correct on how much volume I need to make. I was using a less than scientific reference point from when I was in a band that WAS bleeding-ear loud.

    I have starting writing checks and will be spending much as you have described above, with a small but interesting addition.

    I have read about your subs with interest (love the search feature here). I also recently acquired a stereo by JBL which they claim is flat to 40hz- it makes an AMAZING difference; not loud, just very clean and clear; I'm hooked.

    In any event, I have ordered a pair of JBL GT-120 - Fs 25, 4 ohm, 12mm XMax (Qts is a little sloppy however). They seem like a nice sub from 30-200hz in 2.25' tuned at 30hz.

    I will indeed construct 1-2 Omega/B102 boxen for volume, and add a pair of these in 1x12 configuration underneath. I know the subs won't make much volume, but when the rest of the system is running quietly (like a single Omega at 1/2 power), they should add a lot to the tone, I hope; enough for coffee house gigs.

    Thanx muchly for your excellent advice and spreadsheets. What software are you using to produce those?
     
  13. ESP-LTD: Your mail system fails DNS lookup, so I will post the answer here.

    Thanks for the info. I have added it to my sheet.

    I figure the net internal volume is about 1.6 cubic feet after subtracting
    for the driver, tweeter and bracing. Using your measurements, the box
    appears tuned at 99 Hz.

    Enclosed is a plot of what it does: the classic Eden hump. The yellow plot
    without the hump is the SBB4 alignment of 1.25 cubic feet tuned at Fs.
    There is very little difference in the plot between 1.25 and 1.6 cubic feet.

    The SBB4 will give you MUCH better transients and no hump.

    If this cab never goes below 200 Hz, it won't matter any.
     
  14. Bruce said......

    "Customers come to bars to hear music, dance, and get laid. They aren't looking for bleeding ear drums."

    IMHO this is one of THE most important and overlooked philosophies in modern music. How many times have we seen bands blast their audience into oblivion and believe they've done a top job?

    Nothing to do with the thread, as such, but I wanted to make that input.

    :D

    John
     
  15. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I e-mailed sysadmin so I can get that e-mail address updated; that domain went away last year.

    Overall I must say I am pleased with the nice construction of the cabinet; I'd say Avatar's good reputation is well deserved, and I would encourage anyone to consider them.

    The "Eden hump" is an interesting concept; I never would have considered non-flat response to be a feature but it must be considered desireable today judging by how common it is.

    Next stop- JBL GT-120 subs.