What does all of this mean in terms of what my ears detect?

I have noticed that with a sub in my car, I can definitely tell that the
bass is coming from the rear of the car. If I cross over at a lower
frequency, then the remaining frequencies get transferred to my 6.5"
woofers, which causes them to sound obviously overworked at high
volumes. It seems impossible to get a decent balance.

Comments?

says...
"daxe" wrote:




I must insert that I came in here about a year ago with a question about why
my sub sounded like crap in my new car unless the trunk was open. Eddie
Runner took the time to answer my question and also refer me to his
excellent site and it solved my problem completely. My sub box now sits
facing the rear of the car, backed up against the back of the rear seats
with a little extra space for amp breathing room. If I move it even about 6
inches towards the rear of the car, the standing waves kill the bass.

Plus I'm a fellow 4 wheeler, so he gets points for that, too. )

~daxe

Actually the standing wave region in a car occurs above the 'bass' range. In a
living room the standing wave region encompasses roughly the 25-30 to 300 Hz
range. Below the frequency of the longest room dimension (26 Hz for a 22 ft
long room, for example) the speaker displacement directly pressurizes the space
and above approx 300 Hz the wavelengths are short enough that they become
statistically dense.

In a smaller space, such as a car, every thing is shifted up an octave or so.
Fort example in a Corvette, CRX, Integra and cars of similar interior volume
the lowest axial mode occurs at 60 Hz and the standing wave region is 60 to 600
Hz, give or take.

Below 60 Hz then, SPL is reinforced by 12 dB per octave as frequency falls.
Because this is a pressure phenomenon speaker location is irrrelevant below 60
Hz. Moving the woofer back and forth makes no difference; nor does cone
direction.

With large cars the effect may start as low as 40 Hz but 50 Hz is a good rule
of thumb.

It is true that sound above the lowest axial mode will change with location but
we should be careful to attribute effects to the proper cause. It is also true
that opening a window or trunk will have cavity-tuning effects but this has
nothing to do with standing waves at bass frequencies.