3-way DIY cabinet (building crossover)

Discussion in 'Amps [BG]' started by Mixi, Oct 30, 2008.


  1. Mixi

    Mixi

    Joined:
    Apr 9, 2007
    Hi guys!

    I'm building a 3-way bass speaker. I actually posted a thread a month ago but my plans have changed so much since because (from 2 way 2x10 to 3-way with custom crossover etc) your good advices that I thought that it might be good to start a new thread.

    Here is link to the last one:
    http://www.talkbass.com/forum/showthread.php?t=472134

    So now I my new plan is to build my own crossover and use these speakers:

    -Eminence kappa pro 15lf-2 sensitivity 97.8db
    -Eminence LA6-CBMR 6.5" sensitivity 97.8db
    -Eminence APT 80 tweeter sensitivity 105db (going to use L-pad)

    Im building crossover with this websites help http://www.diyaudioandvideo.com/FAQ/XOver/ and calculators.

    I'm thinking to use 3rd order crossover (high/mid) @3.5khz and 1st order @ 600hz (Bass/mid) good idea? and using L-pad for the tweeter.

    And I was going to check what the impedance values are on the datasheet plot at those frequencies. The other choice would be to build a zobel network to get about equal impedances if the datasheets aren't enough accurate. What do you think? I don't have equipments to test impedances...

    One other problem is that APT 80 doesn't have impedances on it's data sheet and doesn't have enought information to build a zobel for it so can I just say that it's 8 Ohms? Does it matter?

    There is also one thing on that website that really confuses me: [B"]For this example, a 3rd order crossovers at 3000Hz and a 1st order crossover at 800Hz will be used. The Crossover Calculator was used to determine the crossover components. These are the results of the 2 crossover calculations"[/B]

    And after this the showed calculations are made like this: 3rd order butterworth for 800hz and 1st order for 3000hz. Have this article's writer made a mistake or is this the right way to calculate this?

    Lots of questions... Would really appreciate if you could help me. This is my first DIY project so it doesn't need to be perfect...

    Thanks

    Mikko
     
  2. alexclaber

    alexclaber

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    Brighton, UK
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    Director - Barefaced Ltd
    A first order 600Hz highpass on the mid will not protect it sufficiently from low frequencies - use a steeper slope and move the frequency higher. Also be wary of crossing over too close the the drivers' resonant frequency as the huge impedance peak there really messes up the filter response.

    Alex
     
  3. billfitzmaurice

    billfitzmaurice

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    Owner, Bill Fitzmaurice Loudspeaker Design
    Build a tested design, or use a commercial crossover. The level of expertise required to design a dedicated 3-way crossover takes years of study and experience, along with measuring tools to test the result.
     
  4. MuzikMan

    MuzikMan

    Joined:
    Feb 21, 2004
    Location:
    Bristol, Connecticut, USA
    I have a 2-way cab with the Kappalite 15LF and the 6 CBMR. I would like to point out that this setup isn't lacking in highs one bit and is much easier to design the crossover. A good 3-way design is hard to pull off.

    With that said I use an off the shelf Eminence pbx2 1.6 crossover (1.6kHz 2nd order low pass and 3rd order high pass). It blends seamlessly to my ears and the off axis response sounds good too. I wouldn't go any lower than 800 hz with these two drivers. They sound disconnected at 500hz somehow. I know it doesn't make a lot of sense on paper but that's what I heard when I swept an active crossover on them. Maybe it has something to do with a nearfield phenomenon.
     
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  6. Mixi

    Mixi

    Joined:
    Apr 9, 2007
    So do you think that something like Eminence PXB3:3K5 3-Way Crossover would end up sounding better, even if I tested the right impedances and used the same calculator.

    Actually the only part I'm missing is audio millivoltmeter. Or could I just use normal millivoltmeter? Is there any difference?

    Maybe using 2nd (or even third) order lp crossover @ 800hz and 3rd order @ 4khz?

    I could also use a bit more expensive parts like Polypropylene capacitors and copper foil inductors if they would give me better results?
     
  7. billfitzmaurice

    billfitzmaurice

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    Your asking these questions makes my point. Results using a calculator will be no better, if as good, as buying off the shelf. The ability to test impedance and RTA the cab while swapping different size components is a necessity, so a shelf full of components is another requisite. Even for an experienced designer coming up with an optimized 3 way crossover is a long process, on average at least ten hours work.
     
  8. Mixi

    Mixi

    Joined:
    Apr 9, 2007
    Ok thanks I got your point... Maybe then Im just going to use a stock crossover. Would I get any better results if i build a zobel network for the speakers with it?
     
  9. greenboy

    greenboy

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    remote mountain cabin Montana
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    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Use a stocker just as it is. Carvin and Peavey also have crossovers that are suitable. In fact, while you are at it, if you want a cheap 6.5" driver that sounds better, check out Carvin's. I've used both, and though you have to build a subenclosure for the Carvin/Em OEM version, that's part of the reason it sounds better when properly filled with absorptives (damping).

    If you want a driver is flatter, has a smoother impedance curve, and about half the weight and twice as capable, look at 18 Sound's 6ND410. And use a 3015LF for the woofer, which shaves a lot more weight too and is further along the R&D evolution chain.
     
  10. billfitzmaurice

    billfitzmaurice

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    A Zobel is what you use when you don't have the ability to measure impedance. Most professional crossover designers, including the acknowledged best in the field Joe D'Appolito, don't use them, and in fact consider them a waste of parts.
     
  11. alexclaber

    alexclaber

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    But sometimes that kind of circuit gets you the response you want when nothing else will. A huge number of the top quality crossovers I've looked at have remarkably non-standard topology, nothing like you'd end up with if you followed a standard 'cookbook' approach.

    Alex
     
  12. billfitzmaurice

    billfitzmaurice

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    My point exactly. The best crossovers are designed for a particular set of drivers and cabinet, and the components take into consideration the acoustic response of the system to arrive at the final desired result. The results are far and away better than anything you can get using either a cookbook or a pre-made. But if you don't have the skills and tools to go that route a pre-made will probably work at least as well as a cookbook design, and you are sure with something like an Eminence PXB that the right grade of components are in there.
     
  13. spode master

    spode master

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    Jan 21, 2007
    What part of the world are you in MIXI?
     
  14. spode master

    spode master

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    Jan 21, 2007
    I don't know that you would call it a zobel, but I do find I normally have to use a series resistor and a capacitor shunt to ground to help mitigate, the resonance caused be the drivers inductance and the xover interacting with eachother. The biggest problem seems to happen with the mid drivers in a three way, but I also find that sometimes I have to use them on the Woofer too.

    That said I really do think that impedance flattening (Zobels ?) networks are a waste of parts, and the values are often rediculously large.
     
  15. Mixi

    Mixi

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    Apr 9, 2007
    Right now I'm in australia as exhange student untill next may. I'm building the cabinet here and I was planning to buy the speakers when Im going back to Finland to save in shipping costs.
     
  16. Mixi

    Mixi

    Joined:
    Apr 9, 2007
    Hi I saw your 3 way speaker plan, looks really interesting. Probably if I hadn't already started to do he cab (have to get it done before christmas) and had noticed your plan earlier thats the plan I would have used.

    The biggest difference is that my cabinet is going to be a bit smaller (because I have to send it to finland.) and I designed it for kappa pro 15-2 because I got better low end response.

    If I used kappalite 3015Lf I would use 5kg in weight and low end response would be -5db@ 44hz. With kappa pro -3db @ 44hz. What do you think? Can I even hear 2db difference. I thought that if I ever needed more low end I could make a subwoofer. Now I can't really make it any bigger if I wan't to send it to Finland without paying hunderts of bucks

    18 sound mid looks really good. Just needs a bit padding. Is apt 80 still a good small horn or should I use something better. Is its power rating 45w crossover (3.5khz) enought?
     
  17. billfitzmaurice

    billfitzmaurice

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    Run a Maximum SPL plot for both drivers. Frequency response alone doesn't tell the story.
    You'll find the shipping costs of a cab to Finland higher than your airfare. You'll also puke when you see what you have to settle for in Oz for plywood compared to what's available at home at a third the price.
     
  18. Mixi

    Mixi

    Joined:
    Apr 9, 2007
    This is a school project so I got the wood for free and shipping is 130dollars which is right now only about 60e for me. +can send 5kg other stuff with it. Good Bass strings in finland cost about the same.
     
  19. fdeck

    fdeck Supporting Member

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    Madison WI
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    HPF Technology: Protecting the Pocket since 2007
    While toying with the idea of making some home studio monitors for the computer room, I arrived at a possible technique of combining the crossover circuit with equivalent circuits for the drivers, using the free LTSpice program. I simply used voltage as an analogue for acoustical output, because I had sensitivity curves for the drivers that I was considering. I also used current (at constant voltage) as an analogue for impedance.

    Indeed I also arrived at some nonstandard topologies. Reinforcing what Bill mentioned about Zobels, their purpose is only to make your drivers look like resistors. If you are in total control of the design, it seems quite likely that the desired response curve can be achieved with fewer parts. In addition, being able to add resistors at will eliminated the need for the L-Pad.

    For the amateur hacking that I was doing, and without bins of parts, I would have had to make a fair number of assumptions about the behavior of components such as inductors. Still, I got myself into what I thought was the ballpark.

    Then I decided that if it was going to be a DIY project, there was no reason not to dispense with the crossover, and simply bi-amp the whole thing.

    Then I decided to procrastinate long enough to reach this point where I can safely talk about it without actually having built anything. :D
     
  20. Mixi

    Mixi

    Joined:
    Apr 9, 2007
    \Kappa pro 15-2 is about 3db worse @ 50-100hz. Still about 119.6db.

    Still 5kg less weight would be nice with better max SPL so I'll probably use 3015LF
     
  21. Mixi

    Mixi

    Joined:
    Apr 9, 2007
    With apt-80, should I use Eminence PXB3:5K0 3-Way Crossover Board 500/5,000 Hz or Eminence PXB3:3K5 3-Way Crossover Board 500/3,500 Hz.

    Crossing as high as 5khz would give apt 80 better power raiting (from 45wats rms to 85w) but would probably sound worse. What do you think guys?

    Thanks

    Oh and is crossing 500hz too low 18 sound mid?
     

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