sub sound getting through the seat

[puttster]

I have a large sedan that has a great shelf for a sub behind the rear seat.
About 12" high, 20" deep and as wide as the rear seat. I worry though that
the sound from the sub I want to put there will be muffled by the rear seat.
But probably I just do not understand he principles involved.

Should I just aim the sub at the seat and the sound blasts on through?
Should I set up a free air sub baffle instead of a box? I don't need a
whole lotta noise anyway - was thinking of making a, 8" sub and pointing it
up through the 6x9 hole in the package shelf. Should I forget that shelf
location and go with somewhere else altogether?

Thanks in advance

[MOSFET]

OK, let me start by saying that it might be helpful for you to review this
group's FAQ because you are touching on several issues in your question and
I believe a review of some subwoofer basics would be REALLY beneficial for
you. Our FAQ can be found at:

http://www.mobileaudio.com/rac-faq/

I'm a little confused by what you mean by a "shelf behind the rear seat" for
mounting the sub.

Here are, it seems to me, the most important things you need to keep in
mind. First, it is MOST important that sound waves from the front of the
woofer cannot make contact with waves from the back of the woofer (which are
180 degrees out of phase and will cause an explosion, just kidding, will
cancel each other out). This is why enclosures are so necessary, to keep
the front waves from interacting with the rear waves (and to provide a an
air-spring for the cone). An infinite baffle type of enclosure is really
hard to do right because if you decide to use your trunk as an enclosure, it
can be VERY difficult to completely isolate the trunk acoustically from the
passenger cabin. This is because bass can travel through seats with ease,
or through any non-airtight opening, no matter how small (which in an old
car, will be plentiful).

My experience has been that going the enclosure route will yield better
results.

OK, if you do go the enclosure route, it is ALMOST ALWAYS best if the subs
face the rear of the car (NOT the sets) or face the rear corner of the car.
This is another reason why this "shelf behind the rear seats" idea is
probably not the best way to go. This has to do with the way bass loads and
cancellation and if I try to explain it Matt Ion will pick my explanation
apart so just trust me on this one (it is probably explained in the FAQ).
Suffice to say, if you have ever worked with a home subwoofer, you have
noticed it works best when against a wall or in a corner. For the same
reasons, this is also true in a car. It is best if the subwoofer faces a
"wall" (like the rear of the trunk) or corner.

Now, will the bass travel through the rear seats? Yes, if there is no hard
obstruction like metal or thick plastic sheets between the trunk and
passenger cabin. But the rear seats WILL reduce the bass some. If there is
some way you can help port the bass from the trunk to the passenger cabin,
that will certainly help. Often, people will remove the speakers on their
rear shelf and use those empty holes as ports for the bass to come through.
This technique usually works pretty well.

Again, take a look at the FAQ as I've probably not answered all your
questions. Hope this helps.

MOSFET

"puttster" > wrote in message
...
> I have a large sedan that has a great shelf for a sub behind the rear
seat.
> About 12" high, 20" deep and as wide as the rear seat. I worry though
that
> the sound from the sub I want to put there will be muffled by the rear
seat.
> But probably I just do not understand he principles involved.
>
> Should I just aim the sub at the seat and the sound blasts on through?
> Should I set up a free air sub baffle instead of a box? I don't need a
> whole lotta noise anyway - was thinking of making a, 8" sub and pointing
it
> up through the 6x9 hole in the package shelf. Should I forget that shelf
> location and go with somewhere else altogether?
>
> Thanks in advance
>
>

[MOSFET]

"puttster" > wrote in message
...
> I have a large sedan that has a great shelf for a sub behind the rear
seat.

I just realized that the "great shelf" you are talking about is just the
rear-shelf. Yes, this WOULD be a good place to mount your subs in an
infinite baffle (using the trunk as an enclosure) arrangement. But for the
reasons I stated in the previous post, I believe a regular enclosure in the
trunk (and then remove the speakers in the rear-shelf and those holes will
act as ports) in the trunk will yield better results.

Again, infinite baffle type enclosures are VERY difficult to do right (with
a minimum of cancellation). However, it CAN be done and CAN be very
effective. But it usually means having to apply dynamat, fiberglass and/or
MDF around the entire trunk to be sure no sound waves get into the passenger
cabin. For this reason, it is generally easier just to build a regular sub
enclosure.

MOSFET

[puttster]

"MOSFET" > wrote in message
m...
>
> "puttster" > wrote in message
> ...
> > I have a large sedan that has a great shelf for a sub behind the rear
> seat.
>
> I just realized that the "great shelf" you are talking about is just the
> rear-shelf. Yes, this WOULD be a good place to mount your subs in an
> infinite baffle (using the trunk as an enclosure) arrangement. But for
the
> reasons I stated in the previous post, I believe a regular enclosure in
the
> trunk (and then remove the speakers in the rear-shelf and those holes will
> act as ports) in the trunk will yield better results.
>
> Again, infinite baffle type enclosures are VERY difficult to do right
(with
> a minimum of cancellation). However, it CAN be done and CAN be very
> effective. But it usually means having to apply dynamat, fiberglass
and/or
> MDF around the entire trunk to be sure no sound waves get into the
passenger
> cabin. For this reason, it is generally easier just to build a regular
sub
> enclosure.
>
> MOSFET
>
I could not find info about the rear seat in the FAQ, maybe a reference?
The seats are backed with some kind of tarpaper. If I set the sub box on
the trunk shelf (where the rear tire is now) how would I aim it up throught
he package shelf cut-outs? Just aim it upwards? make a ported box and
stick the port tube through?

[mfreak]

> I have a large sedan that has a great shelf for a sub behind the rear seat.
> About 12" high, 20" deep and as wide as the rear seat. I worry though that
> the sound from the sub I want to put there will be muffled by the rear seat.
> But probably I just do not understand he principles involved.

I used to worry about that, and it does muffle to a small extent, but
for the most part those low frequencies go right through the padding
and upholstry.. A seat is good at filtering out highs, not lows.
Ideally, you could mount your subs in a box that fires up through
cutouts in the rear deck. I wouldn't go with free-air or inf. baffle,
especially since I know nothing about it..

[keith]

Hi Puttster,

It's easy to be confused on this topic, and many before have asked
similar questions... Really though, what it comes down to is that sonic
frequencies below 100hz or so are omni-directional. there are particular
things you can do to increase bass response using a trunk mounted sub
set-up, but in a practical sense, the best thing to do is try our
different configurations, and see what sounds best.

Here is a good article, written by an RAC old timer that addresses box
positioning. It doesn't exactly address your particular question, but it
does bring the discussion of sub-bass frequencies into a more complete
light. I hope you find it useful. Note that there are no ports running
into the cabin, and the rear deck speakers are still in place. Again,
when discussing sub-bass frequencies, it's not so much a matter of the
woofers firing directly into the cabin, it's a matter of wave propogation.

http://installer.com/tech/aiming.html

KeithS



puttster wrote:

> I have a large sedan that has a great shelf for a sub behind the rear seat.
> About 12" high, 20" deep and as wide as the rear seat. I worry though that
> the sound from the sub I want to put there will be muffled by the rear seat.
> But probably I just do not understand he principles involved.
>
> Should I just aim the sub at the seat and the sound blasts on through?
> Should I set up a free air sub baffle instead of a box? I don't need a
> whole lotta noise anyway - was thinking of making a, 8" sub and pointing it
> up through the 6x9 hole in the package shelf. Should I forget that shelf
> location and go with somewhere else altogether?
>
> Thanks in advance
>
>