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Speaker "Dispersion"

Discussion in 'Amps and Cabs [BG]' started by Chris Fitzgerald, Mar 5, 2003.


  1. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    A couple of weeks ago I was talking to Larry @ Euphonic Audio about their line of equipment (I currently own a CXL112, a VL208, and an iamp800). I made a remark to the effect that the CXL112 sounds really harsh and ragged when I'm sitting next to it, but when I get 6-10 feet away (or further), the sound smooths out and is smooth as silk. He called this phenomenon "dispersion" (sp?), and said it was a necessary evil of that particular speaker design. My VL208 doesn't seem to exhibit much of this same tendency. My Bergantino HT112 does have some of this, but not as much as the CXL112. I've noticed that most speakers sound better when you give them room to "open up" before listening, but never had a name for it until now.

    Can any of the resident acoustic/techie folks explain in the simplest language possible what dispersion is, and if possible why some speakers exhibit this tendency more than others? Thanks in advance.
     
  2. Whappo Grande

    Whappo Grande

    Feb 9, 2002
    Santa Clara, CA.
    Manager: AccuGroove Speakers
    There maybe multiple reasons for the "harsh and ragged" sound you are hearing.

    Notice that the VL208 does not use a "compression horn" (as those used in PA systems) like the CXL112 & HT112. Instead they chose a "cone" tweeter that does not get "harsh & ragged."

    I you need to play up close where it bothers you, simply adjust the L-Pad for the compression horn down. When you are playing farther away, turn it back up.
     
  3. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Thanks for the reply. I tried that, but it didn't entirely solve the problem, and I lost much of my highs as well. I'm not really looking to solve the problem, just to understand what's actually happening better. Whenever possible, I try to get as much space between the speaker and my ears as I can. Unfortunately, I don't get to do this nearly as often as I'd like.
     
  4. The design of the cabinet acts as a focusing "lens" for the sound coming out of it. Dispersion is the distance that the sound remains focused the farther away from it you get, but conversely, if you get too CLOSE to the speaker then you hear each of its components as separate entities and not the "whole" sound of the cab. The horn sounds harsh up close beacuse you're hearing it predominate the sound. As the sound gets farther away from the speaker, it "comes into focus" and has less peaks and valleys in its sound.

    Different cab designs have different dispersion patterns usually expressed as polar diagrams at whatever frequency is being shown, just like a microphone polar pattern. PA speakers are designed to have the greastest dispersion possible while studio monitors deliberately sacrifice this projection for having a small, highly accurate, 'sweet spot.' A side effect of a a long- throw or wide dispersion cabinet is that certain areas will have very strong peaks and valleys due to phase cancellation.
     
  5. I understand long-throw vs short-throw characteristics in high frequency horns are controlled by the taper rate. Since there is no taper for bass direct radiators, a good explanation of dispersion eludes me. I don't see anything in a typical bass cab that acts as a wave guide or other focusing device, other than driver arrays. Stacking multiple horn arrays reduces the amount of vertical coverage angle. It should work the same for bass frequencies.

    Multiple bass drivers within 1/2 wavelength benefit from mutual coupling, which is essentially increasing the effective area of the (combined) cone, but without increasing the mass. What I'm wondering is, does mutual coupling also increase the "beaming" effect due to the apparent increase in the cone area.

    A 10" driver with an 8.25 piston diameter (53.45 square inches) is fully beaming by 1641 Hz. Four mutually coupled 10" drivers in the D410XLT have 213.8 square inches total area, or a single piston diameter of 16.5 inches. A single piston of this diameter is fully beaming by 820 Hz.

    I'm speculating that multiple drivers in mutual coupling have a tendency to beam at a lower frequency. It would be interesting to see if the 8x10 cabs have a very narrow vertical response, and if they also tend to beam.
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I wouldnt expect much coupling at 1.6k. I would have thought that a 4x10 would produce 4 seperate "beams" at 1.6k each, but I'm also only speculating.
     
  7. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Interesting stuff, everybody. This may just be a coincidence, but the most efficient speaker is the most ragged up close, and the least efficient is the smoothest, even at the same volume. Of course, it may have more to do with the speaker/cabinet design than the efficiency. Still....
     
  8. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    If I'm not mistaken all HF units that use compression drivers and horns exhibit much more distortion at lower volumes than dome tweeters. However horn-based HF units can put out much more volume before they start to really break up. I suspect that with your CXL112 you're hearing that distortion as raggedness when you're close enough that the tweeter and woofer sound like separate sources but once you're far enough away that they act like a single point source the woofer is masking the imperfections in the HF sound.

    Alex