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Mister.Lull - 29 Mar 2005 18:58 GMT

If I've done all the algebra and stuff to tune a ported box, by
dertimining the length of the port. Does the port necessarily need to
be within the sub enclosure?

My idea is to have a subwoofer enclosed in a ported box, in the trunk,
and to have the port actually come up into the car...

Any thoughts? Has this been done before? Does it work?

Mister.Lull

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Scott Gardner - 29 Mar 2005 19:37 GMT

>If I've done all the algebra and stuff to tune a ported box, by
>dertimining the length of the port. Does the port necessarily need to
[quoted text clipped - 6 lines]
>
>Mister.Lull

I dont believe the port has to be inside the box, but keep in mind
that the internal box volume will change depending on whether you put
the port inside or outside the box. Any part of the port that is
*inside* the box is counted as a solid object and must be subtracted
from the internal volume.

For instance, if you have a box with an internal volume of two cubic
feet (3456 cubic inches), and you have 12 inches of 4-inch diameter
port inside the box, you have to subtract about 150 cubic inches from
the internal volume.

With ported boxes, it's important to be as exact as you can with the
internal volume and the port size, since they're not as forgiving of
inaccuracies as sealed boxes are. Also, don't forget to subtract out
the volume of the sub's magnet/basket structure when you calculate box
volume.

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Scott Gardner

"Marge, dont discourage the boy. Weaseling out of things is important to learn. Its what separates us from the animals...except the weasel." (Homer Simpson)

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Mister.Lull - 29 Mar 2005 19:58 GMT

Thank You!!! If I can put the ports outside the box without hurting
the sound, that'll help two ways: First, I can be more accurate on
tuning the port since I won't have to calculate the length over and
over again due to the changing volume of it (I hope that makes sense).
Second, I can port directly into the car therefore enhancing the sound
in there...

Best news I've had all day!
Mister.Lull

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Daniel Snooks - 30 Mar 2005 04:06 GMT

> Thank You!!! If I can put the ports outside the box without hurting
> the sound, that'll help two ways: First, I can be more accurate on
[quoted text clipped - 5 lines]
> Best news I've had all day!
> Mister.Lull

I did exactly what you are describing ... I am very happy with the results.
HOWEVER, I now realize that I am only happy because of blind luck. When you
port the box into the cabin of the car (I assume through the rear deck like
I did) you are in essence creating a VERY huge bandpass enclosure, as
opposed to a vented/bass reflex enclosure. The sub is still inside the
confines of the trunk, but the backwave (through the port) is not in the
trunk ... it is in the cabin. Hence the trunk becomes the "front" enclosure
of the bandpass, and the box itself becomes the "rear" enclosure that is
vented.

Does that make sense? The reason this is important is that depending on the
vehicle and just about every other variable you can think of, the end result
may sound like complete a.s. I believe (and this is complete conjecture)
that I was lucky because I planned to tune the box ridiculously low when I
fist built it (27Hz). This made for a very large box with a very large port
(2.6 cuft with an 11" long / 3" diameter port for one 10" sub). This matched
the "rear" enclosure of the bandpass well with the trunk space. Believe me
... the deep bass is astounding, although overexcursion is an issue with
this setup so I keep the gains down and bass boost off.

Hope any of that helps. Any thoughts or ideas about my thinking from you
all?

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Dan Snooks

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Scott Gardner - 30 Mar 2005 04:35 GMT

<trim>

> The reason this is important is that depending on the
>vehicle and just about every other variable you can think of, the end result
>may sound like complete a.s.

<trim>

That one sentence pretty much sums up all of car audio. You plan your
system, do the research, pick your parts and do the math. Then, you
have to install all of it into a car, which is one of the least
predictable, least uniform environments you can imagine, and hope for
the best.

You can improve your chances by making good design decisions and
picking the right parts, but there's always that nagging possibility
that you're going to get everything installed, and it's going to sound
like hammered dogshit.

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Scott Gardner

I'm all out of altitude, airspeed, and ideas..."

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Mister.Lull - 30 Mar 2005 07:16 GMT

Thanks you two,

I agree completely with that last statement especially, Scott! I think
I'm going to give this a try on my friend's system... I was doing some
beginning math with a sub that I happened to have the manual sitting
around for, and found out that if he has a comparable 12" (the 10"
shouldn't be so bad), then he'll have a 4" port that'll be around 21"
long (I think that this was to tune it to 31hz or somewhere around
there)!! It will be a lot more fun (and kind of neat looking) to have
that huge length of port hanging around outside the box. Also, I do
understand what you were saying about the box becoming a giant bandpass
box, Dan. That's what I was worried about. I've been screwing around
with subs and enclosures for a couple of years now, and out of all of
the pictures I've seen (thank you google image search) I still have yet
to see a ported enclosure with an external port... This was leading me
to beleive that there was something faulty with the idea. Now that I
have a better idea what to look out for, I can try and avoid a pitfall
that I hadn't seen before.

Again, thanks to you all!
Mister.Lull

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Daniel Snooks - 30 Mar 2005 22:35 GMT

> Thanks you two,
>
[quoted text clipped - 18 lines]
> Again, thanks to you all!
> Mister.Lull

Remember ... there is no fault with designing a box that has the port
sticking out of it. That box will act the same as any other ported enclosure
if the port is working in the same airspace as the driver (eg. the trunk).
The difference (read "bandpass instead of ported") occurs when venting into
a seperate airspace (eg. the cabin)

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Dan Snooks

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