What? A wave is a wave, regardless the size of the driver producing it.
Qyota is correct, a wave is a wave. No matter what size driver is producing it, the speed of sound is constant. Therefore at any altitude, the sound wave produced by an 8" driver will reach your ear at the exact same time as the wave produced by a 15" driver. The only variant between the two drivers will be amplitude, which is more a function of power than driver size.
I think what you are trying to explain is time alignment. In a vehicle the subwoofer is usually located in the rear. Therefore the front speakers, which produce the majority of the music, are much closer to your ears. This can cause the sound from the subwoofer to reach your ears a fraction of a second later than the sound coming from the front speakers. In extreme cases it can produce a "muddy" sound to the music. 99% of listeners will never notice it.
A light is also a light. No matter what the source, light travels at the same speed. The only difference there is intensity.
To the OP: in any vehicle, the optimum location for a subwoofer is in a rear corner. However, you can place one anywhere and get decent sound. I have never heard a sub faced forward sound good. The bass frequency waves are very long and usually need to be bounced off the rear of the vehicle to give them enough length to develop a full cycle.
Good luck with your project.
Light.
Visible light has a wavelength in the range of about 380 nanometres to about 740 nm – between the invisible infrared, with longer wavelengths and the invisible ultraviolet, with shorter wavelengths.
The Quantum Atom
Light - Wikipedia, the free encyclopedia
HowStuffWorks "Light Frequencies"
Bass waves
RealTraps - Bass Waves in the Control Room
Frequency - Wavelength - Period Chart
http://www.dynacord.com/downloads/dsp244_info_bass_en.pdf
The Soundry: The Physics of Sound
Sound waves
Bass wavelength is dictated by Hz, and not all driver/subbs sizes produces same exact wavelenght(Hz). Long wave length (low frequency), short wave lengths (high frequencies).
Example:
15" 24Hz - 150Hz
10" 39Hz - 150Hz
MTX Audio Thunder 9500 Subwoofers
12" 22Hz - 100Hz
10" 30Hz - 104Hz
MTX Audio TS85 Subwoofers
Here you can compare Freq differences between different drivers/subs and its sizes.
18Hz to 500Hz
6-1/2" to 15".
KICKER | Livin' Loud
http://www.mediacollege.com/audio/01/sound-waves.html
Sound waves exist as variations of pressure in a medium such as air. They are created by the vibration of an object, which causes the air surrounding it to vibrate. The vibrating air then causes the human eardrum to vibrate, which the brain interprets as sound.
And as we all know, there is no sound in space.
What im trying to say, is that your ear-buds arent going to be as loud from 5 feet away as is they would in your ear, or a 15" sub would at same Frequency and distance.
The closer(to some degree) you are to a sub/driver, the louder it will sound. Its not just amplitude that matters. A 15" sub wont sound the same from 5 feet away as it would 500 feet away. Because air also acts as a barrier for waves to travel through. Just as Prius will have less air resistance compared to a School Bus as they both travel at same exact speed.
There is also thing called real state. More subs of same size of same amplitude, move(vibrate) more air and increase dB, creating a larger bass wave. Think of Ocean/water waves; a 15 foot tall wave moving at 20mph or a 10inch foot tall wave moving at 20mph.
So if we place 20 ear-buds side by side, they will sound much louder at same distance vs 1 ear-bud, simply because 20 ear-buds vibrate more air. Other way to think of it, is 1 fan at 10cfm vs 20 fans at 10cfm(more air volume).
Speed of sound.
Altitude also makes a difference since air density, temp and pressure varies.
Speed of sound - Wikipedia, the free encyclopedia
Speed of sound, loooong read. Covers Temp, solid and liquids through which sound travels, etc etc etc, and everything there is on speed of sound.
Speed of sound - Wikipedia, the free encyclopedia
Here is a good read on Subwoofers: 4, 2, or 1?
http://www.soundandvisionmag.com/article/subwoofers-4-2-or-1-0?page=0,0
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Edited to add links and information.