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tweeter horn flare - best shape? best size?

Discussion in 'Amps and Cabs [BG]' started by globert, Mar 20, 2017.


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  1. globert

    globert

    Mar 15, 2017
    New Zealand
    The bass cabs I see use a high frequency horn flare with the same horizontal and vertical dispersion - but which shape is the best - or what are the pros and cons - and why? PA cabinets often use horns or wave guides that lack rotational symmetry.

    And how to choose what size horn opening?

    If you have tried different types of tweeter horn shapes and sizes, I'd be interested in your experiance.

    My context:
    I have a reasonably high quality rcf n281 1 3/8" compresion driver. I have an approx 10" x 4" plastic horn. It sits it on top of my DIY 1x10 cab that sports a 10" markbass (b&c) driver. I will be building another 1x10 cab so I can stack them or whatever. Markbass uses a 3.5kHz crossover point, so I use approx the same.
    I'm happy to buy the best shaped horn for it. If it is 6" x 6" or less I can mount it in the cabinet, but I'm happy with it on top.

    My initial thinking is that a horn with rotational symmetry is good when you move around a lot when you play or other musciains rely on your cab as a monitor, and you want a consistant sound.
    I guess a rectangular horn is useful if you need to beam your HF.

    Is it for size and because it means less area is cut out in the front baffle?

    Thanks :)
     
  2. fast slapper

    fast slapper

    Dec 11, 2001
    Fresno, CA
    Typically for bass cabs it's about space and costs. For PA you generally want a wider controlled horizontal dispersion pattern and a narrower vertical. Bigger horns are better for this.

    For bass cab use I prefer to spread sound as wide as possible. A small symmetrical 6x6 should work well with a 10". Eminence APT200 looks like your best bet.
     
    Last edited: Mar 20, 2017
  3. 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)
    Here are some of the things I look for in a horn for a bass cab, in no particular order:

    1. Constant directivity, but without relying on diffraction to get there. You can spot a diffraction horn by the sharp-edged slot or kink(s) inside the horn.

    2. Sharp-edged lips are also undesirable, but okay if you have some round-over leading into them.

    3. Fairly wide radiation pattern both horizontally and vertically... the latter so that the bass player can hear his overtones.

    4. Ideally we'd want the radiation patterns of woofer and horn to match up in the crossover region, at least in the horizontal plane. This has implications for the design of the woofer section and the crossover.

    5. Can't be too big, and can't be too expensive.

    The disadvantage of this approach is, constant-directivity horns require the crossover to equalize for their generally falling response. So they may not be ideal for the DIYer who is limited to off-the-shelf and/or textbook crossovers. If you DIY it, never use a first-order highpass filter on a compression driver - it's got to be at least second order to deal with the driver's resonant impedance peaks.

    The Dayton Audio 6" elliptical horn is probably the best small and affordable constant-directivity horn from a coloration standpoint. Unfortunately its pattern is only 80 degrees horizontal by 50 degrees vertical. Still, not a bad choice.

    My current first choice is the Eminence APT200S "baby butt cheeks" horn. It's a gentle diffraction horn, so it doesn't sound edgy (assuming the crossover does its job), and its radiation pattern is about 90 by 90 degrees. It's not perfect, but imo has the best combination of characteristics currently available.
     
    globert likes this.
  4. globert

    globert

    Mar 15, 2017
    New Zealand
    Two votes for the Eminence, a preference for spreding the sound around, and an excellent list of points to consider - thanks.
    I'll try the eminence.

    I'm concerend about the noise artifacts and the crossover - is it important to put a 2nd or 3rd order crossover on the woofer too? Or does just the tweeter suffice?
     
  5. 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'm not sure what you mean my "noise artifacts". Could you explain?

    As for whether the woofer should also have a lowpass filter, at what slope and what frequency, all of that depends on the characteristics of that specific woofer, and also on what your goals are. For the sake of simplicity and minimizing the chances of making things worse instead of better, I'd suggest that you use the woofer the way MarkBass used it, as I'm sure they knew what they were doing.
     
  6. globert

    globert

    Mar 15, 2017
    New Zealand
    Thanks DukeLJ. By noise artifacts I was meaning reasonant impedance peaks, falling response, and radiation pattens of woofer and tweeter not matching at the crossover point.

    Markbass crosses over their 10" cabs at 3.5kHz. I don't know what order filters they use, or if they apply them to both woofer and tweeter. I aquired to 10" drivers but have no theile small paramaters, so all by trial and error. All good fun.
     
  7. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    You can measure the T-S parameters yourself, which is not particularly difficult.
     
  8. globert

    globert

    Mar 15, 2017
    New Zealand
    Thanks - I'll look into how to measure them. Since I have built the cab I guess what I would need most is impedance around the crossover point ... and the both drivers frequency response.

    I imagine I'll end up using a 2nd order high pass at 3.5khz and the eminence flare and use an adjustable l-pad network. Or I risk trying to design to parameters when i dont understand how they interact with the system as a whole ... unless their are obvious and fairly fail safe parameters to use for the woofer/tweeter/flare design that will make a significant improvement.
     
  9. 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)
    Three suggestions (in addition to the one about not using a first-order highpass) if you're planning to design your own crossover:

    First, you might try calculating crossover component values that would theoretically spread the low-pass and high-pass frequencies apart somewhat, like maybe a half-octave or so. In other words, on paper, it would look like you'd have a hole in the crossover region. Real-world, this often works better than using "textbook" values.

    Second, try the compression driver in BOTH polarities and see which one works best. The textbook will tell you one thing, but there are so many things going on affecting the relative phase of the woofer and tweeter that you might as well try it both ways.

    Third, run an impedance curve just to make sure you haven't done something that could cause a problem for your amp.

    Best of luck to you!
     
    globert likes this.
  10. globert

    globert

    Mar 15, 2017
    New Zealand
    Thanks heaps. I've ordered the horn. It should be here in about 2wks. I'll report back how it goes.