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Cabinet for single "Eminence Delta 15": help please.

Discussion in 'Amps and Cabs [BG]' started by Rockin John, Jun 26, 2001.


  1. Bizzaro's thread inspired me to make this post. Clearly there are a few speaker / cabinet wizards on this board so I wonder if I might seek some guidance?

    I've got a drive unit above and I'd like to make a cabinet for it to use with the bass: it's not so much that I WANT to make one, but that's how it's got to be.

    Anyway I followed the links on Bizzaro's thread and the cab design dimensions I end up with is different in each case and is radically different to the design suggested to me by Jom James @ Eminence.

    So I'm confused. So could someone please help me sort this out? I'm up for any sort of sensible design. Please ask whatever questions you need.

    Suggestions gratefully received. Thanks.

    John
     
  2. First, what did Eminence suggest for a design?

    If you run the numbers for the Delta 15 model, you get a cabinet of 21 cubic feet, tuned at 31 Hz, and dead flat (1 dB) to 33 Hz.

    This also gives you a cabinet 55 x 35 x 22 inches, approximately. I estimate this as 54 square feet of material to build the cabinet. MDF weighs 49 pounds per cubic foot, and a 4x8x 3/4" sheet is two cubic feet. 3.375 cubic feet of MDF weighs 165 pounds. Add the weight of the speaker, grille, covering, casters, handles, etc...

    This is the "optimum" alignment for this cabinet. The designer can deviate substantially from optimum as part of the compromises needed to reduce size, weight, etc. The smaller you make this cabinet, the more it will roll off in the bass octaves. Cut it back to 10 cubic feet, and it is down nearly -7dB at 31 Hz. Cut it back again to 5 cubic feet and it is down nearly -12dB at 31 Hz. The Delta 15 does not like living in cramped cabinets.
     
  3. Good morning bgavin, and thanks for coming back on this.

    Tom James @ Eminence (not Jom James as I said @ first) said, and I quote:

    "....knowing you already have the driver; build a larger box 107.8L and asuming a wall thickness of 3/4" (19mm) you'll need a port of 116.8mm. No tube required_just a wall thickness of 19mm."

    Now, I also tried WinISD. For a closed box the volume obtained was 270.9 Ltrs: and 556.8 Ltrs for a vented box with 1 x 102mm port @ length = -35mm (minus 35mm). The results gave the vented box tuning @33.01 Hz.

    Does that make any sense to you. It doesn't really make much to me!!

    John
     
  4. MikeyD

    MikeyD

    Sep 9, 2000
    This was very informative, bgavin. It gives people a much better idea as to the size/LF tradeoffs for a particular driver. I find this much more useful than giving just one option for "flat" alignment. Thanks for posting the alternatives.
    - Mike
     
  5. 107.8 litre is 3.81 cubic feet. Far too small a box for this driver. The WinISD program is very close to my own in the 556.8 litres as the recommended size. If your program lets you play with the box size, plug in the 107 litre value and plot the response curve. The results will be obvious. If you have a text plot of the SPL values by frequency, this will be even more revealing. The bass will droop to zilch. It will be down nearly -14 dB at low B from middle E. It will be real loud above middle E.
     
  6. Hi.

    Well, I might be OK on some tech-y stuff but this speaker cabints design business baffles me....:D

    On the face of, bgavin from what you've said, the optimum is either a vented box @ 557 Ltr or a closed box @ 270. I've seen the plots of both cabs and the vented looks much better. But a 556 Litre box is clearly too big so I need to reduce that size to something more, well...sensible.

    Is there any way, perhaps, to come up with a design that's not too big but that gives some sort of reasonable bass response?

    In short, because this is well out of my field, I really need someone (you, please?) to tell me what dimensions to build my box and I'll go away and do it. I'm happy with a vented or infinite baffle box.

    Help please; ask whatever else you need to know.

    Thanks V much.

    John
     
  7. No

    :D

    This driver is even worse in a sealed box. It is designed to be installed in a big ported cab.

    To answer your question, a 3.81 cubic foot box tuned to 31 Hz is 30.6" x 18.75" x 11.6" using (2) 3" diameter by 8.25" long ports. It will be safe for a 5-string bass.
     
  8. No. Sorry. Perhaps I wasn't making myself too clear. I didn't mean that I wanted to stick with the 3.81 cubic foot box. I meant that perhaps there was some compromise to be had somewhere between the 20 cu ft and the 10 cu ft boxes. I dunno, say a 10 cu ft ported box or even a 5 cu ft ported box that will give me some reasonable low end response. Down to B is questionable cos I play a 4 and have grave doubts whether I'll ever have a 5.

    I'll have another bash with these downloaded programs I've got and see what I come up with: see if I can get some numbers out.

    :D:DI'll be back later:D:D

    John
     
  9. OK. Back with some numbers. They're attached as a Notepad file.

    I did this with the software running on www.kbapps.com

    Does any of this seem sensible to you?

    Thanks.

    John
     
  10. This makes the design a whole lot easier.

    Choose a tuning frequency of 41 Hz, and bump up the cabinet volume while watching the response curve. With this driver, bass response improves as the cabinet size gets closer to 21 cubic feet. The compromise comes with how much cabinet size you are willing to carry around.

    The port calculation formulas should be taken as guidelines, not absolutes. The final port tuning should always be done with a digital volt meter and signal generator. This compensates for variations in volume from bracing, driver displacement, the port itself, math errors, etc.

    To keep the same loudness, the cone has to move 4x farther for each octave down. Cone movement is the smallest at the tuning frequency because most of the sound radiates from the port. Tuning to 41 Hz will give you maximum loading and minimum cone movement at the lowest frequency you plan to use. This makes it safer to turn up the bass tone control.

    The best of all combinations happens when the optimum driver alignment is also tuned at your lowest note. For example, the Eminence Kilomax Pro 15" driver is perfect in 5.2 cubic feet at 41 Hz. This alignment is the optimum, and coincides perfectly with a 4-string bass. The Kappa 15LF is another driver that is a natural in 5.4 cubic feet for a 4-string bass. Both are loud as well.
     
  11. Hmmm. Perhaps the Delta 15 isn't the best unit for portable bass guitar cabs.

    But I didn't buy the driver, I was given it. I'm trying to do put it to use by building a box that's most suitable all ways round.

    Being realistic, the 270 Ltr cab is about the biggest I can accomodate. And something smaller would be better still.

    What you seem to be saying - if I understand correctly - is that above the -3db point, the flatness of the curve gets worse the smaller the box even though the speaker+cabinet will run down to the low end.

    John
     
  12. I know you already have the Delta...but that's not a really good speaker for a bass. The Delta LF comes closer. Kappa Pro LF is the bomb-diggity. Best guideline I can give you is a cab w/ KP lf at about 4 cuft and a front slot (no ports, slots louder..no lie) at or below 8:1 ratio w/h. Start small, then open up the slot till you're happy. I would recommend 18" Wide by 2.75" Tall. And glue it together when you're done. And brace it. And use T-nuts to hold your speaker in...etc.

    And I'd take eminence's suggestions. The numbers might not work out guys, but drivers don't always react exactly as numbers point to. They've done way more R&D on their speakers than anyone here has.

    And this tuning a box to 31 Hz is not 100% necessary (I am gonna get flamed on this one). I don't know about the other 5'ers out there, But I rarely use a low B. Another reason for this is Perceived sound levels to the human ears. Look up a sound characteristic called Phons. This reweighs sound levels to the sensitivity of the human ear. Our (human) ears are most sensitive to a frequency of 1000Hz. It then drops off until about 50-100 Hz. Then It goes back up again briefly until 35-40 then drops off rapidly after that. So what this would mean that at 100dB, 1000Hz would "feel" like 100 dB, Whereas @ ~60Hz would "feel" like ~80dB. This is part of the study acoustics. There is lots of other reweighing scales out there (Sones, dBA, dBC, etc..) But Phons applies to humans...so, makes sense to stick with that level.

    So I prefer a box resonance at around 50-70 Hz. Make this stand out, and the response of the box will help to even out the levels that our ears are most sensitive to.

    But this is just my research, and it's been fairly successful so far for guitar and bass cabs. And all the technobabble comes from taking Mech Eng. classes and a few independant studies (Some for Credit!! Get a grade to have fun!) I've worked on. I'm not trying to lay down the law, I'm just stating what I've learned from what I've done.

    Okay, guess I should go back to work.
     
  13. Man oh man. Am I really confused now.....

    John
     
  14. Heh, Sorry about that man. You can keep it fairly conservative and simple by just using the formulas you get from whatever program you are using. Just remember you're prolly gonna wind up w/ a box that's 4 foot high, 2 foot wide, and 1.5 foot deep. For that Delta that is.

    I'd just make a cab w/ about 4.5 cuft of interior volume, 16x2 slot in the front. Simple design. Will work okay with a lot of different manufacturer's speakers. Real Middle of the Road design.

    And if you wanted more confusion (everyone) I've found some articles/calculators for sound levels..etc.


    http://www.ryde.demon.co.uk/page2.htm

    http://www.measure.demon.co.uk/Acoustics_Software/stevens.html

    http://www.britannica.com/seo/p/phon/


    And just another little hint. It's called R&D, But it should be called R&D,&RD&R,&FD, Research and Design, And Redesign and Research, And Final Design. Just keep on studying, and whatever sounds like the solution to you, then do it. You can't make a box that is completely mute:) And it'll sound like you want it cause you made it:) And no one can ever tell you different
     
  15. Hello tufnuts.

    Thanks for the trouble. I was going too apologise to you anyway. Didn't want you to think I'd not appreciated your input. I do.

    I was confused because I know nothing about speaker bins and how to design them. What I know is what I've learned from this thread.

    'Fact is, I'll only get one shot at making this bin. If it's wrong now it'll always be wrong. So I MUST be certain that the box I build will do the job, and do it properly first time.

    You see, don't really know how to interpret (what is on the face of it) quite different advice on the same speaker.

    Unless anyone's anything else to add I guess I'll just have to take the plunge.....

    Thanks.

    John