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     fast.

   * Solvent to clean up excess adhesive.

Before you start, find a large, clean, flat surface on which to set the
box as you carpet it. Start by unrolling the carpet onto the surface,
smoothing it out so that its flat, and setting the box on top of it
edgewise.  Also, make sure that you remove the speaker, any ports and
terminal cups from the box.

The instructions on how to carpet the box are as follows:

  1. Place the box such that it is centered on the carpet lengthwise,
     and one edge of the box is about one inch from the edge of the
     carpet.

  2. Roll the box back so that the side of the box that was previously
     done faces forward, and the carpet beneath it is exposed. Coat
     both the box and carpet with adhesive, but do NOT apply the carpet
     to the box - the adhesive needs a few minutes to set up (follow
     the instructions from your adhesive to find out how long you
     should wait).

  3. After the adhesive has set up, roll the box back into position.
     Wait a few more minutes for the adhesive to bond.

  4. Now coat the side of the box adjacent to the remaining carpet (the
     side facing backwards) and the carpet next to it with adhesive,
     let the adhesive set up, and roll the side you just coated onto
     the coated carpet.  Repeat this until three sides of the box are
     carpeted.

  5. Before carpeting the next side, the 1 inch of carpet sticking over
     the edge must be removed. To do this, rotate the box so that the
     first side that was carpeted is up. Pull the carpet sticking over
     the edge down towards the uncarpeted edge and cut it off with the
     knife, flush with the uncarpeted side of the box. You will have to
     run the knife nearly parallel to the uncarpeted side to get a
     perfect cut.

  6. This done, spray the remaining side and carpet, and roll the box
     onto it. Shear off the remaining carpet sticking out from all
     edges with the scissors leaving a 1 inch border everywhere.

  7. Clean up the ends of the box so that the carpet is flush with the
     sides of the box as in step 4.

  8. Next cut off the remaining 1 inch flap of carpet (located at the
     point where you began carpeting). This is the tricky part, as you
     don't want to be able to see this seam. Again, pull the flap down
     over the edge of the box, but this time cut it at roughly a 45
     degree angle. If you are successful you shouldn't be able to see
     the wood under the seam, but will probably see the white of the
     adhesive and the back of the carpet.

  9. Soak some of the solvent onto a rag and use this to scrub the edge
     you just cut off. It should dissolve the adhesive and the carpet
     backing somewhat, causing the carpet on the edge to become fuzzy.
     Keep scrubbing the edge until you can no longer see the seam.

 10. Now carpet the ends of the box. Cut two pieces of carpet slightly
     larger than the ends of the box and lay one of them flat on the
     surface. Spray the carpet and one end of the box with adhesive,
     and set the end of the box on the carpet, so the box stands on end.

 11. After the adhesive has dried sufficiently cut off the remaining
     border of the carpet as in 7 and 8.

 12. Repeat step 9 and 10 for the other end of the box.

Congratulations! You've just carpeted your box!


4.12   Are large magnets always better than small magnets? [ST]
===============================================================

Magnet *size* is meaningless!

Every speaker will have an optimal BL ((see Section 4.1),) product,
the field strength in the air gap multiplied by the length of the voice
coil wire in the field.

If the BL product is too low, the speaker is electrically not very well
damped (which will result in a woofer with a high Qts). A bump in
frequency response and a level drop in midband efficiency may be the
result.  If the BL product is too high, the speaker is electrically
overdamped (Low Qts woofer). A very high midband efficiency, but the
driver starts to roll of early.

An high BL product can be achieved in a number of ways: increase field
strength; or increase wire length in magnetic gap.

The increase in field strength is limited; so some manufacturers use
very thin wire for the voice coil, as such they can achieve a high BL
product with a low field strength (cheap magnet). Or they use an 8 layer
voice coil... needless to say that electrical power handling will
decrease enormously.

Long stroke woofers, having only a part of the voice coil in the air
gap, need a very high field strength to achieve a high BL product. Often
this means a big magnet as well...

Use magnet size as an indication, but as nothing more than that.


4.13   I know the box volume required for my subwoofer, but what are
       the best dimensions for my enclosure? [IDB]                 
====================================================================

The specific dimensions of a subwoofer enclosure aren't really
important.  Once you know the appropriate volume of the box, and you
know where in your car you want to install it, you will have some idea
of the restrictions in the dimensions.  For example, if the distance
between the floor of your trunk and the bottom of the rear deck is 16",
then you probably shouldn't make your box any taller than 16".
Likewise, if width of the trunk (between the wheel wells is 38", then
you've got that much space to work with.

You can also infer some other information about your box, from the
speaker specifications (for a PPI PC10):

          Mounting Depth:         4.5625"
          Speaker Displacement:   .032 ft^3

Here is an ASCII drawing of a subwoofer enclosure to help illustrate a
few things:


           |--- L ---|
           __________     ___
          /         /|     |
         /     +   / |     |         + = Center of speaker
        / x       /  |     D         x = center of port
       /_________/   |     |
       |         |   |    _|_        W = Width of box
       |         |  /     /          L = Length of box
       |         | /     W           D = Depth of box
       |_________|/    _/_

Because of the speaker's mounting depth, you know that the box MUST be
at 5.5" deep (it's always good to leave at least 1" of space behind the
speaker, but leave more if you can).  If you use a straight port (3"
diameter PVC) then the box will need to be at least 13" deep (leaving 2
inches between the end of the port and the back of other side of the
enclosure), assuming that your port will reside completely within the
enclosure.  If you use Flex-Port or choose to have a portion of the
port extending outside of the enclosure, you can make the box less deep.

We also know that with a 10" woofer, the length and width should both
be a minimum of 12" (leave 1" on either side of the woofer). Obviously
both dimensions can't be 12" otherwise we can't put the port on the
same face as the speaker.

With volume, remember a couple of things.  Recommended volume is the Net
Internal volume.  Both the speaker and the port will displace volume
from the box - this means that you MUST account for these (i.e., make
the interior volume of the box larger than the recommended value).  In
this case, you know the following:

          Required Volume:       1.25 ft^3
          Speaker Displacement:  0.032 ft^3
          Port Displacement:     ??

3" (interior diameter) PVC will usually have an exterior diameter of
3.5" (0.25" wall thickness).  Volume of a cylinder = pi*r^2*h, where r
= 1.75" and h=12.25" (13" port length - 0.75" for the thickness of the
MDF).  Therefore the port displacement is: 117.9 in^3 or 0.068 ft^3
(1728 in^3 = 1 ft^3).

          Required Volume:       1.25 ft^3
          Speaker Displacement:  0.032 ft^3
          Port Displacement:     0.068 ft^3
     
          TOTAL INTERIOR VOLUME: 1.35 ft^3 or 2332.8 in^3

Now, to calculate the dimensions of the box:  For a rectangular box, L
x W x D = Volume.

If we know that the minimum interior depth is 15" (because the port is
13" and you should leave 2" between the port and the wall of the
enclosure), we can say,

          L x W x 15"  = 2332.8 in^3   or
          L x W        = 155.52 in^2

Since we know that L must be at least 12" (since the speaker is 10" in
diameter), we can continue:

          12" x W      = 155.52 in^2
          W            = 12.96"

So, we have determined that the interior dimensions of the box must be
12" x 12.96" x 15".  Obviously this can't work, since there is nowhere
to put the port!  You will either have to have the port extend outside
of the enclosure, or use flex-port.  Keep in mind that if you have part
of the port "sticking out" of the enclosure, the Port Displacement will
also change!!.

For simplicity, (in this example) let's use flex-port.  This will let
you decrease the thickness of your box to about 6".  So,

          L x W x 6"  = 2332.8 in^3
          L x W       = 388.8 in^2
          12" x W     = 388.8 in^2
          W           = 32.4"

This is a little more reasonable.  This will be a flat, wide box.
Again, keep in mind that these are internal dimensions.  If you use
3/4" MDF (and you should) to build the enclosure, this will add 1.5" to
each of these figures for the external dimensions.  e.g.:

         13.5" x 33.9" x 7.5"

Remember, the 6" depth and 12" length are just the minimum values, you
can alter them if, for example, you don't have enough space between your
wheel wells for a 34" box.  If you only have, say, 28", then:

          maximum external width = 28"
          maximum internal width = 26.5"
     
          L x W x D        = 2332.8 in^3
          L x 26.5" x 6"   = 2332.8 in^3
          L                = 14.7"  (internal)

Got it?  It can be a pain, but that's part of the fun in building a
speaker enclosure.




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