I've just purchased a MTX 12' Sub.
Qts 0.8
Fs 36.8
Vas 40.4 l
Xmax 9.4mm
Diam. 26.04 cm

I wanted to find out what the advantages and disadvantages are of
having a Qts of 0.8.

Is it true that for best bass(not the boomy type) Qts of 0.5 or lower
is best in a ported box?

My research has showed that I should go for a sealed enclosure.
Wanted to confirm that this is the right choice?

What would be the best enclosure volume for this sub?

Thanks in advance.

It's a little late to ask some of these questions once you've bought the
woofer, but such is life.

Car subs are designed with a high qts so they can be used with small
enclosures. Also, cabin gain in the car causes an increase in low
frequency response that you don't get in free space or inside a home
environment, so auto woofers are designed with higher qts, higher fs than
those intended for home use. Once the driver qts is high, such as .8 it
can't be made lower by enclosing the driver in a cabinet.

For home use, at QTC (that is the Q as installed in the cabinet) around
..7 or so used for tight bass and .8 or higher for boomy bass.

You will find lots of stuff to study on Brian's website at:

http://www.diysubwoofers.org/caraudio.htm

You didn't give the part number and Qes is missing in your specs. BTW,
brian has an excel template for designing various enclousures on his
website.

You can also search the MTX web site for your particular unit. They give
box designs for many of their products.

http://www.mtxaudio.com/caraudio/products/subwoofers/

I would recommend a sealed unit if you want tight bass. You won't need
the extended bass response of a ported box inside the car because of
cabin gain. Construct your enclosure with MDF and use plenty of internal
bracing so the box doesn't buzz. Use lots of dowels and glue to hold it
together while the glue dries. Quarter inch dowels work nicely in 3/4"
MDF board. Just clamp it together and drill the 1/4" dowel holes through
from the outside. You can veneer or cover the box once finished if you
want a completed appearance. Don't make any removable doors on a sealed
enclosure because you won't be able to stop them from leaking air or
buzzing. Install the woofer from the front using T-nuts. MDF will not
hold wood screws for long.

Good luck with your project.



Shawn wrote:

I've just purchased a MTX 12' Sub.
Qts 0.8
Fs 36.8
Vas 40.4 l
Xmax 9.4mm
Diam. 26.04 cm

I wanted to find out what the advantages and disadvantages are of
having a Qts of 0.8.

Is it true that for best bass(not the boomy type) Qts of 0.5 or lower
is best in a ported box?

My research has showed that I should go for a sealed enclosure.
Wanted to confirm that this is the right choice?

What would be the best enclosure volume for this sub?

Thanks in advance.

"soundman" wrote in =

I would recommend a sealed unit if you want tight bass. You won't need
the extended bass response of a ported box inside the car because of
cabin gain.

A sealed box is not inheretely tighter than a ported. A ported box is every
bit as tight as a sealed, until you get below the tuning frequency.

Construct your enclosure with MDF and use plenty of internal
bracing so the box doesn't buzz. Use lots of dowels and glue to hold it
together while the glue dries. Quarter inch dowels work nicely in 3/4"
MDF board. Just clamp it together and drill the 1/4" dowel holes through
from the outside.

Although sound construction, which would work, it is overkill and highly
unnecessary. A sub box in your car does not require that much bracing. Some
yes, but there is not need to get into complicated techniques. It is only a
single 12" sub.

You can veneer or cover the box once finished if you
want a completed appearance. Don't make any removable doors on a sealed
enclosure because you won't be able to stop them from leaking air or
buzzing. Install the woofer from the front using T-nuts. MDF will not
hold wood screws for long.

Why would wood screws not hold? Unless you plan on taking the driver out of
the box repeatedly then T-nuts are overkill. If you want to spend the time
then go ahead, just know that once it is in there the wood screws will hold.
I have several boxes with speakers held in with wood screws that have held
for years.


Les

Les wrote:

"soundman" wrote in =

I would recommend a sealed unit if you want tight bass. You won't need
the extended bass response of a ported box inside the car because of
cabin gain.

A sealed box is not inheretely tighter than a ported. A ported box is every
bit as tight as a sealed, until you get below the tuning frequency.

We were discussing Shawns driver configured in his car. That suggests a small
box size so that it fits his car. A ported design in a small box will
inherently be a bandpass design which will not sound "tight". If we were
discussing home audio and unlimited cabinet volume, yes a ported box can be
designed that has tight bass. One would not select this particular driver for
that application though.

Given the specifications that Shawn provided for his 12" woofer, what ported box
size and what port frequency would you propose to give tight bass? Have you
considered the cabin gain inside the car? What is the optimum box size and port
tuning considering his driver specs? With the driver specifications Shawn
provided, a reasonably sized box, say 2 cubic foot (which is already large for
some trunks) a ported box will tune up with an in car peak of 12 db or so...
Some folks prefer this design because it provides higher efficiancy. MTX
provides ported box dimentions for this "bandpass" alignment. I would define
that as boomy bass. Shawn said he does not want boomy bass. That suggests
designing the enclosure for a flat in-car frequency response. You could mistune
your ported two cubic box with a a low Fb, but the port becomes large and you're
really simulating a sealed box by setting the port that far mistuned. This
speaker, when ported for the greatest bandwidth, is optimum in a 13 cubic foot
enclosure.

As discussed on Brian's web site, cabin gain in the car causes an increase in
response at 6dB per octave. A sealed cabinet will produce a corresponding
opposite 6db/octave roll off that will yield a composite in-car response that
is flat. For car use this driver mounted in a sealed box of 1-1/2 to 2 cubic
foot volume will provide reasonably flat in-car response and tight bass.


Construct your enclosure with MDF and use plenty of internal
bracing so the box doesn't buzz. Use lots of dowels and glue to hold it
together while the glue dries. Quarter inch dowels work nicely in 3/4"
MDF board. Just clamp it together and drill the 1/4" dowel holes through
from the outside.

Although sound construction, which would work, it is overkill and highly
unnecessary. A sub box in your car does not require that much bracing. Some
yes, but there is not need to get into complicated techniques. It is only a
single 12" sub.

Jason's speaker has an Xmax of 9.4 mm. That gives it a displacement of +/-
4/10 liter. Presumably Jason picked this sub because he wants loud bass and may
play it close to it's capabilities on occasion. A box that is not solidly
constructed will eventually deteriorate and buzz with each bass note. That is
no pleasure to listen to. I'm not suggesting exotic construction, just 3/4" MDF
board, properly dowled, internally braced and glued. I suppose that
construction method may add two hours to the build time compared with using 1/2"
cdx plywood and roofing nails. Last time I priced 3/4" MDF, it was around $18
for a 4 x 8 sheet. That leaves plenty of material for internal bracing and some
corner blocking to construct a solid enclosure. I've not even said he needed to
dado cut the panels. I've not proposed anything difficult, exotic or expensive.

A friend brought by his commercially fabricated sub box last week to try out.
It was a popular push/pull configuration with two 700 watt 10" Pyramid drivers
that he installed with wood screws, four ports and a plexiglass viewing window.
We tried it out and this box sounded badly distorted at louder settings from
loose box construction with less than 60 watts peak as measured on an
oscillosope. It distorted before amplifier clipping and well below the driver
X-max. The wood screws stripped out the MDF in a few places so he couldn't get
all the fasteners in.



You can veneer or cover the box once finished if you
want a completed appearance. Don't make any removable doors on a sealed
enclosure because you won't be able to stop them from leaking air or
buzzing. Install the woofer from the front using T-nuts. MDF will not
hold wood screws for long.

Why would wood screws not hold? Unless you plan on taking the driver out of
the box repeatedly then T-nuts are overkill. If you want to spend the time
then go ahead, just know that once it is in there the wood screws will hold.
I have several boxes with speakers held in with wood screws that have held
for years.

Les

I guess you used plywood instead of MDF board. MDF does not retain wood screws
very well, especially if the driver is removed once. Plywood is about the same
price and is less suited for speaker enclosure construction. Plywood will cost
more than MDF if it is void free and sanded on one side. Eight #10-32 t-nuts
will cost around $2.00 to install one driver and they will not vibrate loose or
deteriorate with age or use. It is really not overkill to select the
appropriate hardware for the project.

Dowels don't cost more than wood screws. It's not exotic or difficult
contruction. It avoids having to cut dados. You simply match drill through
from the outside of the box into the panel you're joining to. It's the same
hole you would have pilot drilled in order to install your wood screws. The
difference is that you drill the hole 1/4" diameter and tap in a 1/4" dowel.
The dowels hold the box together while the glue dries.