Bass with glass up vs down

[DJ Q]

Can someone explain what characteristics of the sub prevents you from getting bass when the glass is up?

When I put my little 8" sub in the car, I get nice musical bass that flows really nice whether the glass is up or down, but when I put the two 10"s in the car and turn the glass up... practically NOTHING. Glass down sets off alarms easily and bass drops right down to some near subsonic notes.

What causes this?

It's really bothering me because I want to do a permanent fiberglass install soon and I don't want this to be a problem!

Please help.

[nervewrecker]

I dont even know how to start to explain this....or attempt to.

a sub moves air, with the glass down the air moves in & out freely, with the glasses up the 2 10" subs simply compress more air & it kinda restricts their excursion. the 8" sub has less cone area & will compress less air & actually function better in a way. it depends on the ability of the medium through which the energy passes to be compressed too.
its kinda like a single 12" sub in a 20 x 20 closed room as opposed to 10 18".

[DJ Q]

So basically in an A/C environment... less cone area is better?

Looking at getting one 10" in any case...

But would tuning the sub a specific way (lower/higher) help to compensate for this issue?

[nervewrecker]

it may have soimething to do with the size of the vehicle cabin too.

I will like to believe it affects mainly the lower notes.

I get something similar with my car, the lower notes dont come out like they do if I wind down the glasses a few inches.

[Brian Steele]

a sub moves air, with the glass down the air moves in & out freely, with the glasses up the 2 10" subs simply compress more air & it kinda restricts their excursion.

Nope. Unless you're a member of the BAB Crew, excursion behaviour is dominated by the characteristics of the driver and the box it's mounted in, not the cabin (which tends to be many times greater in volume than the subwoofer box).

When you roll down your car's windows, you're basically converting the cabin from a sealed environment to a (badly-tuned) bandpass/horn environment, with your head located near one of the vents, so it's no wonder the bass seems to sound louder when that happens .

[nervewrecker]

I think that explains it better

[jack hammer]

the reason why you not are getting a good bass response with the 10 is because while having your windows up, it creates parallel surfaces which induces Standing Waves due the the geometry of your vehicle's cabin that suppresses some frequencies "mainly low one" while exciting others under 300hz. if u have access to a RTA,play pink noise an place the mic at the listening position and u will see large peaks and deep null in the response, putting down the window should lessen these peaks and nulls therefore increase the low extension in your response, when the standing wave is no longer present. try repositioning the enclosure in the vehicle or rebuilding the enclosure to better help counteract the peaks and null in your response, also using an eq to may assist with your problem.