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Sound/Projection characteristics of 18s, 15s

Discussion in 'Amps and Cabs [BG]' started by Brendan, Feb 7, 2003.


  1. Brendan

    Brendan

    Jun 18, 2000
    Austin, TX
    I've been thinking about the whole rig...and I've never really gotten the sound I want out of the Eden XLT I have. They get plenty loud, and low enough (I suppose), but they never create the effect I want when I'm out and playing.

    What I always hear in my head is just a wall of air moving at the audience, oppressive and thick. The one time I felt that was when I heard an Ampeg SVT-4PRO powering an SWR Goliath Sr. and a Big Ben. For those of you playing along at home, that's a 6x10 and an 18". I've played through 8x10s (2 410XLTs) so I'm reasonably sure it wasn't just the 10s that made it feel like there was a lead weight on my chest, which is the effect I'm going for.

    Now, I know of 18s that the sound doesn't really congeal until about 15+ feet back, but do they move air with in a few feet? I mean, even if you couldn't hear it, could you feel it to a degree that would resemble it's optimum distance/projection?

    Same goes for 15s, or, rather, 2x15s.

    Really, I'm not one for highs. I've been thinking about getting a couple 18s, and either a 2x10 or a 2x12 to pretend like I care about highs and mids.

    That, and what do you think about SWR, Eden, Yamaha (PA type) and Bag End 18s?

    Just wondering...
     
  2. cb56

    cb56

    Jul 2, 2000
    Central Illinois
    Just as a side note. I discovered by accident that an Ampeg SVT18e sounds pretty good by itself. They don't make them anymore but you can still find them used. I've wondered how two of those would sould with my ampeg 610 cab powered by my B4r or a SVT 4pro.
     
  3. No surprise, but I'm partial to big drivers for big bottom. My needs require the free air resonant frequency of the driver (Fs) be at or lower than the lowest note I want to play. This is the domain of the large driver, or (multiple) small subwoofer.

    An Adire Maelstrom 18" sub displaces 1534 milli liters at maximum Xmax. The Delta 10 used in the Avatar boxes displaces 55 mL. These are extreme examples on both ends, but they make the point. The 18" driver has 3.45x the piston area of the 10".

    I cannot accurately judge the impact of my subs from the stage, so I must rely on somebody in the audience for a hand signal. A wireless would be good here, but low bass and wireless don't seem to get along. At least not the Shure models.

    Outside, or 40 feet from the stage, my subs are very massive and well defined. Closer in, the sound is more of an indistinct roar. Many players object to large drivers as being "muddy" compared to 10" drivers. I ask if this not a failing of the large driver, but the result of a listening position less than 1x wave length from the cabinet.

    Assume a typical 10" cabinet doesn't produce solid fundamentals below 60 Hz. A low B at 31 Hz is essentially produced as the 2nd harmonic at 62 Hz and the true fundamental is poorly produced, or entirely lost. The 62 Hz note has an 18 foot wave length, meaning it would be fully developed (1x) at a listening distance of 18 feet from the cabinet.

    A 10" subwoofer producing a true 31 Hz note would not develop one full wave length until 36 feet away from the cab. Closer in, this could be heard as mud. This is pure speculation on my part, based on observations made with my subs

    The concept of bass bloom is known to us all, but I don't yet have a valid engineering paper that accurately describes it. My guess is, bloom is directly related to the wave length of the note being accurately reproduced. If the listener is 1x wave length or farther from the stage, he hears it fully developed. On stage, or less than 1x wave length, it is heard differently.
     
  4. Brendan

    Brendan

    Jun 18, 2000
    Austin, TX
    Bruce to the rescue!

    So you use 18s in closed in areas? Would that indistinct roar you mentioned, would it still be felt? As in, even if an audience member was withing, say, 5 or so feet of the 18", they would feel that big mess of air moving at the, but the note would be lost to them (which isn't that particularly important).

    I'm wanting to hit them in the chest, hit them hard, and even if they can't make out the note that well, I want them to FEEL like they have a force pushing on their sternum. So, would the SPL (sound pressue level...right?) be the same at 3 or 5 feet at it would at 36?
     
  5. Brooks

    Brooks

    Apr 4, 2000
    Middle East
    Back in late 70s, my rig was a 200W all-valve head, JBL 4x15 cab and a JBL 18" folded horn. That horn was never heard on stage, but it would flap legs on my jeans like crazy. People 40-100ft further away would BEG me to lower the volume. It was producing exactly what you are describing, huge, powerful wall of sound that would hit you in the chest and turn your guts into a mush...awesome!

    Never had any trouble being heard over two Marshall full stacks, amplified drums and a Hammod B3 through a double Leslie setup, even when we played outdoor gigs for 2000+ people.
     
  6. Captain Awesome

    Captain Awesome

    Apr 2, 2001
    PDX
    So the distance required to hear the "full" sound from a speaker cab is related to the frequencies produced, not the size of the speaker cone?

    My observations with my gear is that my Avatar 2x10 cab usually sounds more or less the same regardless of where you are standing, but with more bass response near the cab. My Hartke 12" combo on the other hand, can create a wall of mid-bass mud for someone far enough away yet sound fine right in front of the amp.
     
  7. Brooks

    Brooks

    Apr 4, 2000
    Middle East
    Yeah, I believe so.
     
  8. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Bass Bloom! I like that description. I've just returned to using a 15 in amongst 10's. For years I was using 10's only. I EQ them so they sound similar to me but to my surprise, people have started commenting that they can FEEL the bass better now. I'm talking about fellow band members, the audience, and even sound engineers. My initial response was "What R U talking about, sounds the same to me?" but they all assure me it sounds meatier. Why? BASS BLOOM!!!!!!!!

    I retrospect I've probably made a mistake. One of my home made wedges is a 15. Given that I'm never too far away from these wedges I'm probably not hearing the bottoms, they're probably blooming just as they hit the ceiling.......what a waste...
     
  9. In an earlier post, I was specific that bass bloom is pure speculation on my part, based on personal observations. I have yet to find a valid, published work on the subject to confirm my speculation.

    My cabs produce a true 41 Hz fundamental and apparently require a wave length's distance or more for clear definition.
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    hmm.... speculation maybe. But I believe you're onto something. My recent expreience certainly backs it up. There's gotta be a way for us to prove it scientifically? I'm game. Any suggestions?
     
  11. geshel

    geshel

    Oct 2, 2001
    Seattle
    It does not take time/distance for a sound wave to "develop". It simply radiates. If that were true, the tight, well-defined low bass that a good pair of headphones can give would be impossible.

    Experience such as Bruce's seems to indicate that something changes from the stage to the audience when using large drivers. I don't know what that is, but it's not because the sound wave isn't "developed" at the place where it originates.
     
  12. geshel

    geshel

    Oct 2, 2001
    Seattle
    Ah, thanks for MikeyD for pointing this thread out to me:

    http://www.talkbass.com/forum/showthread.php?s=&threadid=9774

    It's not a simple issue, that's for sure. Though I'll say again to make certain, just because a sound has a 30' wavelength doesn't mean it takes 30' to "form". It might take some good distance for room effects and the like to come into play however.
     
  13. A sound wave "travels" much like a wave on a beach. Like geshel says, you don't have to be 30 feet out in the water to have a wave go past you if the wave has a wavelength of 30 feet. The wavelength is just the distance from one point (crest, trough, whatever) to the same point on the next portion of the wave. As you stand in the water, the wave will rise and fall....regardless of whether you're 5 feet in or fifty.

    I think it's room acoustics, stage acoustics, the way the speaker radiates the wave, all combined. There's nothing magical about a given wavelength.
     
  14. What is being overlooked here is the *source* of the acoustic waves. The beach analogy is accurate, but those waves *originated* farther than 1 wave length from the surfer, so they are fully developed when he encounters them.

    It's my understanding the driver is a high impedance pressure device that couples its energy to the low impedance atmosphere. This conversion of alternating pressure to waves is the point of origin.

    A high frequency horn is essentially an impedance matching device (transformer) that results in a high efficiency coupling of the diaphragm to the atmosphere. I also understand that high frequency horn "throw" is directly related to the taper rate of the horn. Long, slow taper horns have a long throw, and short fast taper horns have a wide, short throw.

    I dunno, but would sure like to see if anybody has published a paper on this.
     
  15. Captain Awesome

    Captain Awesome

    Apr 2, 2001
    PDX
    Low frequencies are omnidirectional, that's not a problem.