Sub 100 hz 15" box design help please.

Discussion in 'Amps and Cabs [BG]' started by fatNfunky, Apr 3, 2018.

  1. fatNfunky


    Jan 31, 2012
    I have a vented 250 watt2 x 10 cab that I like a lot, for normal volumes rehearsals and almost everything its enough for me, but I have always been a "low end junkie" I want to build a ported/vented/horn? 15" that can be used with my 2x10 in the event i need or want the extra 'low lows' Reggae / outdoor / extra fun -gig...

    I have a separate 250 bass amp to dedicate to this second cab and will split the signal before the amps. The driver I have chosen is the Eminence Delta LF 15" because its designed to play lows only and i can afford it.

    what i need help with is box design, i don't understand any of the box design programs.If someone could 'model up' a simple box for me, that might make the driver mentioned deliver a very specific bandwidth I would be grateful.

    I only need this 15" to start to play where the 2x10 starts to roll off, so if my 2x10 start to roll off at about 100hz and produces 12 or more db less, the closer we get to 41 hz (4 strings only)

    I understand 'boom' and 'nodes' and 'phase' etc, I have loved bass a looooong time.

    I know my idea is flawed in many ways, but i want to try it anyway.

    so this 15 in a big ported (very well braced I have built many boxes over the years)

    flat (or close to) from 100- 41 hz only.

    (my *guess (after reading eminence suggested boxes)would be a 4.1 cubic feet box with 2 x 6" ports at 9" long each)

    I know i can only have 2 of the 3 (loud/cheap/good sound) I understand it wont get loud ;) or is it 4 ? and size comes into play, i don't care how big it is up to 6 cubes :D or so...

    anyone bored and want to run it through a program for me please ?

    simple build (ported) preferred over complicated (rear loaded horn) *unless results are DEFINITELY worth the extra effort building a horn..

    and i will need box dimensions not just the volume, i have tried working out box volumes via measurements for decades !!!! no luck,

    i have to mess around with various port lengths typically to get anything sounding 'right' Id like to get close with the math and design first this time with the help of someone 'smarter' then me :D
    Last edited: Apr 3, 2018
  2. Stumbo

    Stumbo Guest

    Feb 11, 2008
    Last edited: Apr 3, 2018
  3. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    Sensitivity of the delta15 LFA
    Is horrible at 96 dB

    Probably have better luck or basic same performance with a CB158 but sensitivity
    Would be much much higher around 98 dB

    CB158 likes a big box too the same 3.8 to 4 cubic feet.

    BB4 alighment just basically uses fs of the driver so 39hz for delta or 34hz for the cb158.

    Since most Butterworth alignments start going 5hz to 7hz above fs of driver

    Basically you can build 3 cubic box or 4 cubic box tuned to 40hz and be done with life and models.

    Expect the same old F3 responces of around
    57 to 63 hz in 3 cubic feet
    48 to 59 hz in 4 cubic feet

    Increased cabinet volume for few hertz of non audible f3 effects power handling dramatically.

    Dont waste time with a 96dB woofer
    With basic 2.5 voicecoil and 4.8 mm xmax.

    The legend isnt far from it same 2.5 coil and 4.8 xmax

    Paying a few dollars more for the 80 ounce magnet to the 50 ounce magnet gets you more sensitivity.

    And in a power eating big box you need every bit of sensitivity you can buy.

    3.8 to 4.3 cubic feet at 40 hz pretty much end of the road.
  4. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    I think you made a good woofer choice. The real-world efficiency difference between the Delta 15LFA and CB158 is negligible south of 100 Hz. The CD158 IS a little bit flatter south of 100 Hz, but if you're going to put the woofer into a big box, then we have to start looking at xlim, or damage-limited excursion. The xlim is much greater on the Delta 15LFA, and imo that detail tips the scales in its favor.

    If you are okay with 6 cubic feet, and you want a big low end, then do a well-braced ballpark 6 cubic foot box. I suggest these internal dimensions: 36" tall by 22.25" wide by 13.75" deep. These dimensions are in a golden ratio, which is optimal from the standpoint of staggering the internal reflections. You may be able to get away with no damping material, which is imo desirable for this application, because damping material reduces the low end "thump" a little bit.

    For the ports, I suggest three 6" diameter round ports, each 9.0" long. These will tune the cab to about 49 Hz. I realize this is higher than what you had in mind with 41 Hz as your target, but you might like it better than a 41 Hz tuning in some situations. If possible, mount one of the ports higher than the woofer magnet, and one lower, so that you get a bit of chimney effect cooling even with the middle port plugged (hot magnets are weak magnets).

    Assuming you buy the port tubing at the hardware store, at the same time, buy three 6" diameter expandable test plugs, from the plumbing department. Make sure they will fit into your port tubing. These will be your secret weapon.

    You see, you can plug one of the ports and now the box is tuned to 41 Hz. Or plug two ports and now it is tuned 30 Hz. Plug all three and, you guessed it, it's a sealed box. So you can choose between four different low-end voicings, and while one port plugged will probably be your favorite, in a boomy venue you may want more ports plugged, and for an outdoor venue you may want all ports open.

    The above is just a suggestion, feel free to modify as you see fit.
    Last edited: Apr 3, 2018
    Al Kraft, Stumbo, Guitalia and 3 others like this.
  5. BadExample


    Jan 21, 2016
    ^^^Very good advice!

    Do you plan to crossover the signals before the two amps (biamp), rather than send everything to all the cabs? Highly recommended for both efficiency (as in not using power for the undesirable frequencies... both in the cabs and the amps) and sound quality.
  6. fatNfunky


    Jan 31, 2012
    Thank you, The math and logic makes sense to me, altho Id still need box dimensions and port length / width ...

    Brilliant !! a 'tune-able' sub bass fun box for my bass guitar This will be hard to resist.

    lets see what other folk have to say before i get my skill saw out....
    Last edited: Apr 4, 2018
  7. fatNfunky


    Jan 31, 2012
    "You see, you can plug one of the ports and now the box is tuned to 41 Hz. Or plug two ports and now it is tuned 30 Hz. Plug all three and, you guessed it, it's a sealed box."

    I was hanging on REALLY HARD to read what plugging all 3 ports would tune the box to :D

    that was funny .... thank you... every time i play my bass ill think of it ....
  8. fatNfunky


    Jan 31, 2012
    "internal dimensions: 36" tall by 22.25" wide by 13.75" deep. These dimensions are in a golden ratio, which is optimal from the standpoint of staggering the internal reflections"

    unbelievably helpful thanks again
  9. fatNfunky


    Jan 31, 2012
    30 Hz ! ? .... yes please...
  10. fatNfunky


    Jan 31, 2012
    I KNOW your math and logic makes sense, leaves me wondering if there might be any difference in 'tone and volume' between a hifi driver and a pro audio driver, if they were both in the correct box for this desired bandwidth.....100-41... ish

    my guess would be a pro audio approach would sound better for music on a stage, sound projecting forward towards the crowd

    the 'hifi' approach would make everybody in a large basement feel nauseous with 'just' an open E @ 41hz.
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    The HiFi approach would likely trade sensitivity for low frequency extension... now you are looking at drivers in the low 90's or high 80's and lower (mechanical) power handling.

    With a box this big, and weight not being a big deal, there are some 18" drivers that might be more suitable to achieving what you are trying to do.

    Another option, one that I would recommend, is looking at a used pro audio subwoofer that has the specs that suit your needs. That would likely be less expensive and you can try before you buy.

    When using 2 amps and signal paths, you will need to verify acoustic polarity of the system... ie. both cabinets share the same system acoustic polarity. Different signal paths can have a different polarity due to the circuitry involved.
    Gabbs, FugaziBomb, rogypop and 3 others like this.
  12. beans-on-toast


    Aug 7, 2008

    Attached Files:

  13. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    At 6 cubic feet yes agreed might as well be in 18" territory.

    And put you back up to 98 dB

    Or any basic 2x15 would be in that much airspace lol. And have plenty more overhead and clarity than a 4mm driver in wayyyy to much airspace.

    2x15 fullrange still works its wonders.

    Keep in mind most audible range is in second harmonic. Managable deep bass and punch is in 80 to 150hz.

    Your 40hz dreams are a octave higher at 80hz
    Last edited: Apr 3, 2018
    rogypop and Downunderwonder like this.
  14. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    Hi Fi approach is using speakers with very poor efficiency as mentioned. In large room or band situation would not be very audible with a single driver. And reach distortion at low levels

    Likewise but yes as in my previous post 41hz at loud levels is incredible boomy and sub bass with bass guitar.

    Players are thinking they need a system for 41hz would find that most players woulnt know what to do with 41hz or plain hate it. Your whole playing style and note attack/ sustain has to change and adapt and use that deep deep ringing boomy bass to work.

    Its pretty much a octave below what most players are use to hearing or feel. And doesnt work for most genres.
    Downunderwonder and Stumbo like this.
  15. Stumbo

    Stumbo Guest

    Feb 11, 2008
    You gotta adjust to the venue, it doesn't adjust to your "tone" or frequency.
  16. Be very careful what you wish for.

    Trading off extension for power handling and loudness, do you know what that means?

    Also, the fundamental of those low notes plays hell indoors.

    Low frequencies are very hard to hear, even harder with other loud sounds going on.

    The popularity of the HPF is due to these factors. Lots of guys with 60hz capable cabs high passing even higher for better overall sound.

    You can get a hell of a lot louder by making 60hz rather than 30hz, without breaking your woofer.

    By all means, build the giant box though! I love Frankenrigs as much as anyone. Indeed a 215 would be a much more sensible thing.
    oldNewbie and Stumbo like this.
  17. Lows do not project, they go every direction with equal volume. Then they bounce back with high efficiency from solid walls and floors and create large standing waves on some notes.
    Stumbo likes this.
  18. Coolhandjjl


    Oct 13, 2010
    If you’re a low end junkie, and want a sub 125Hz box, I suggest looking at Bill Fitzmairice plans. He has many such horn loaded box designs
    dheafey likes this.
  19. DavC


    May 17, 2005
    Tallmadge , Ohio
    i'd just buy a cheaper power sub ... instead of making more firewood .. !?
  20. fatNfunky


    Jan 31, 2012
    how about a 4mm driver in the correct amount of space (for desired bandwidth) ?
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