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Woofer Size and Speed

Discussion in 'Amps and Cabs [BG]' started by S. Byrnes, Jan 27, 2005.


  1. I always see people on this board referring to 10's as being punchier, faster, or tighter than 12's or 15's. This always drives me a little nuts because the mass and size of the woofer cone has nothing to do with woofer speed. A lot of what makes a driver sound “punchy” or “tight” has to do with group delay and midbass and upper bass performance.
    I also see people saying that 15's and 12's will go deeper than a 10, but that’s not right either, because it has more to do with the resonant frequency (Fs) of the driver. A lot of 10" drivers used in bass cabs (Eminence Delta 10's) have Fs of around 60 Hz, and they don't provide good lows because the woofer will not perform well below that frequency. As a comparison, the Eminence Delta 15a has a lower Fs of 40 Hz, and it produces lows better. I don't mean to insult anyone's intelligence on here, but I always see these misconceptions and decided to write something about it. These two articles explain the role of mass and group delay (transient response) on the sound of drivers.

    http://www.adireaudio.com/Files/TechPapers/WooferSpeed.pdf

    http://www.adireaudio.com/Files/TechPapers/GroupDelay.pdf

    I'm not going to take credit for any of this knowledge. Although short, this thread contained some useful information also. http://forum.sounddomain.com/ubb/ultimatebb.php?ubb=get_topic;f=11;t=075126#000000
     
  2. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    While it's true that there are 10's that go just as deep as 12's and 15's, you have to include efficiency as a very large factor when you're looking at speakers for bass guitar. 10's that go really low are going to be less efficient than a 15 that goes equally low. Efficiency isn't a big deal in hi-fi and car audio because you're generally dealing with relatively small spaces. But efficiency is a very big deal in live sound reproduction. You've got to have enough efficiency to reach very high SPL's in a relatively large space without using a truckload of speakers and amps. Aside from the listening area being larger, the main factor setting the rather high baseline levels of live sound is the loudness of an acoustic drum kit. If you can get one of those rare drummers with a light touch, or one who plays an electronic kit, you can bring the whole sound level of the band way down, allowing you to use less efficient, smaller speakers and still get really good low end.

    So the generalization that 15's are deeper than 10's is correct, when you're talking about speakers that are efficient enough for bass guitar use in the typical fashion - the typical fashion being situations that require high efficiency.

    Efficiency can be boosted by using more complex cabinet designs (folded horns), allowing you to use less efficient speakers. But unless you're a DIY'er, the expense of a well built folded horn for bass frequencies is going to be pretty discouraging. So most bass players use the typical front loaded vented cabinet, where driver efficiency is very important. The overall equation of desired tone/required loudness/lowest cost still mostly leads to basic vented cabinets, especially when you're buying and not building.
     
  3. Kindness

    Kindness

    Oct 1, 2003
    Chicago
    Thanks for the post S. Byrnes, those same misconceptions drive me nuts. While BruceWane makes some good points, I wanted to add that with the increased use of high powered amps for bass reproduction, it is no longer quite as difficult to set up a relatively inexpensive, off-the-shelf bass rig utilizing 10's that go as low or lower than the average 15. There are plenty of 4x10's and certainly a fair number of 2x10's that get down below 40 Hz and are loud enough to keep up with even the heaviest hitting drummers when fed proper power.

    If the challenge is to fill a stadium, that's an entirely different matter.
     
  4. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    It is nice that the cost of wattage, both in dollars and in weight, keeps getting lower and lower. But you've still gotta have speakers that will handle all those watts. And the thing you'll find is that speakers that handle lots of watts are less efficient than a speaker that is equal in size and frequency response that have a smaller wattage handling ability. That's just physics. When you build a voice coil, the additional material neccessary to handle the heat of higher wattage add weight to the moving structure of the speaker; since the speaker takes more energy to move, it is now less efficient. So you could build a 10" speaker that goes down to 30Hz and handles 1000 watts - but due to the heavy duty voice coil this kind of wattage capacity would require, it would be horribly innefficient, which means that even though you're hitting it with 1000 watts, you're only going to get maybe 110db max out of it. You'll probably get more volume out of a speaker that handles less wattage but is more efficient due to it's lighter voice coil. It's a balancing act, and it is getting better, but we're still a long way from being able to play a 5 string through a single 2x10 at a typical rock gig with anything close to decent tone. Put a nice 18" cab under that 2x10, limit the lows hitting the 10's either through passive or active filtering, and you've got a rig that'll do the job.
     
  5. Kindness

    Kindness

    Oct 1, 2003
    Chicago
    I agree with everything you said from a pure physics point of view, but reach a different conclusion when it comes to how that translates into equipment desired for a gig. I have been very happy with the volume and tone I get playing a 5 string through a single AMCE 2x10 at a typical rock gig. In fact, I have stopped using additional cabinets (either 1x15 or another 2x10) because of the volume and tone I can get from a single 2x10. Obviously, your experience may differ. We may simply have different tone and volume expectations.
     
  6. The SBB4 vented alignment comes the closest to a sealed box. It is very similar to the D2 sealed alignment, which is the one to use for tighest group delay.

    Note that nobody is making the SBB4 that I've seen in commercial cabs. They are all too busy building small cabs with acoustically large drivers, to get the mid-bass hump that makes them sell.

    Some folks might consider the SBB4 to be anemic in the bottom, compared to one of the commercial humpers. But the increased tightness (punch) makes up for it.

    A snappy 12", such as the Omega Pro 12, has a reasonaly low inductance voice coil, an excellent magnetic motor, and does SBB4 in 1.23 cubic feet tuned at 39 Hz. The Magnum 12HO runs in an even smaller box, and a much lower voice coil inductance (more punch), but rolls off higher up.