12s vs 15s

Seriously? Read http://www.bcae1.com/ Read it again. Then read Stevdart's excellent WinISD tutorial, and my addendum. Learn how to evaluate bass drivers yourself. That said, here are the -very rough- and -stupidly overly general- differences: 15' will be: More efficient More expensive Require much larger enclosures Able to provide slightly deeper response A 15 is not "better" for many installations. That's about it, generally. Like I said, you should learn how to evaluate specific subwoofers. Assumptions and generalizations, well, you know what they say... New Project: 2003 Pathfinder

First, review your math. Area of a circle is pi*r^2. The ratio of displacement is actually higher than 30:24. Not that this matters much, see my second point. Second, the biggest mistake I see new car audio people make is to get hung up on displacement. Displacement is NOT a critical parameter of a driver. Again, displacement is not a critical parameter of a driver. Displacement is a relatively useless stat speaker manufacturers use to sell bass-heads on speakers. Instead, look at efficiency and an xmax limited frequency response curve. Radiating area (a component of displacement) is reflected in the efficiency statistic. The efficiency number will tell you how loud a speaker will get with X number of watts. This is limited by the thermal power handling ability of the subwoofer and the driver's excursion limits. Excursion limits vary by frequency. A driver may be able to handle 500 watts at 60hz, but only 200 watts at 25hz. If this isn't complicated enough, the xmax limited frequency response curve also significantly depends on the enclosure. In my opinion, any sophisticated driver comparison requires either first hand evaluation/testing or computer aided modeling using reliable T/S parameters. See the WinISD sticky by Stevdart and the addendum by me for more information on how to get started with computer aided driver evaluation. "Driver X has more displacement than Driver Y" means absolutely nothing. This observation has zero value. New Project: 2003 Pathfinder

kfr01 is right on! 3.141592*(7.5^2)=176.7 square inches. 1 15 inch woofer, actually it's quite a bit less than that, as the 15" dimension includes the frame, but we'll do it this way for simplicity's sake. 3.141592*(6^2)=113.1 square inches. 1 12 inch woofer, same as above. Using the numbers above, a 12 inch woofer has 64% of the area of a 15. This number will NEVER change, no matter HOW many woofers you use... (as long as you use the same number of 15s as 12's) I have an Eclipse Ti 12 in my car. Now it's Sd is not as high as a regular 12 inch woofer, because of it's surround. I think the Sd is around 90 square inches, but it's 3-1/2 inch throw FAR exceeds the displacement of ANY standard 15 out there. 315 cubic inches. When is the last time you saw a 15 move almost 2 inches? I am overemphasizing displacement, but since that was the specific parameter you seemed to be fixated on, I thought I'd just give an example. Clicky here for a thread regarding these very points... Good read!It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

yep a lot of people confuse about the diameter of the sub with the surface area, some people think that 2 10" will be louder than 1 15" sub because the 2 10" have 20 inches and the 1 15" have 15" of diameter 20" against 15". Here i post a picture that i've found on another webiste so you can see it better that 1 15" will have more surface area than 2 10" and that if everything is fine the 1 15" will be louder, but it depend on the installation. same goes with 2 15" versus 2 12" subs. Shaking The Neighborhood

12" or 15" ?? A Node is no motion at the circle edge of the speaker. An Anti-Node is motion at the speaker center. The dominant sinewave is between nodes. So the speaker diameter is it's dominant halfwave. 15 inch dia. speaker = half wavelength. 15 x 2 = 30 inch wavelength. Speed of sound = 1130 ft/s. Frequency = 1130 ft/sec (sound speed) x 1/30 inch x 12 inch/ft. = cyc/sec = 452 Hz. 12inch = 565 Hz. Human ear range 20hz to 20khz. 15" diameter = 452 Hz = musical note A4 12" diameter = 565 Hz = musical note C#5 4 notes difference. 15" over 12" gives 4 music tones better which is hardly a minor scale difference. Minimal. You want at least an octave increase which is a doubling of the speaker diameter. 12" to 24" dia speaker is great. 12" to 15" dia speaker is minimal benefit. ... in music fidelity terms. :-)

b_sharp, what in the world does that all mean.  If the others are anything like me that meant pretty much nothing.  I think it can be summed up that they both have their advantages and disadvantages and it all depends on what your goals are.

Damn! Thanks for clearing that all up, b_sharp...

you gotta take some advanced music and physics classes to understand it, I half understand it, lol wish i could figure it out tho as well.99 Blazer LT.   Yellow Top. Big 3. Infinity Kappa Speakers All Around. Jensen CD/DVD flip out. 2 Infinity Kappa Perfect 12DVQs powered by a Alpine PDX600.1 (in one custom box, building a FG box)