Part Four
CONSTRUCTION DRAWINGS AND NOTES
I
Bernard and his Masterpieces (Proud Daddy)
(He will build them for A$500 each as shown)
See Construction
Drawings further below.
The prototype boxes have been made by Bernard (see above) and delivered.
For those not yet in the know, Bernard Chambers from Sutherland Shire here
in Sydney, is part sponsor of the Elsinore Project.
Cutting Sheets
Print both out and take to your supplier. It should not
be difficult to find a suitable business that will supply and cut the MDF
panels. For those in
the Sydney area (Australia) we got ours cut by Bills Board and they very
conveniently got shops on both sides of the harbour:
Kingsgrove:
Bills Board Factory Pty. Ltd
41 Garema Circuit
Kingsgrove 2208
Phone 02-9740 6090
Chatswood:
Bills Board Factory Pty. Ltd
5A Gibbes St (of Victoria Ave)
Chatswood 2067
Phone 02-9417 4656
Last photo before the paint goes on.
(The photos shown on this page is for Mark
1 & Mark 2. For those wishing to upgrade to Mark 3, a 25mm MDF block needs
to be inserted into Tweeter cavity - a page has been prepared with more
detailed instructions.)
Bills Board make very accurate cuts, so assembly work is purely but joins.
You can of course make up your own drawings from scratch, provided the
actual final dimensions are kept. Then other joins can be used, such as
dovetail. But these require professional assembly. You could also take them
to somebody who could build the boxes professionally. But as the design
shown here, this is pure DIY assembly and the cutting sheets reflect that.
Use plenty of white wood glue and also (a must) screws as well. The use of
glue and suitable screws make the assembly not just twice as strong, but
more like four times. The screws should be the type suitable for MDF.
MDF Materials Required
For a single pair, you will need one 2400mm by 1200mm, 25mm thick MDF
board. Then a half sheet of the same, 1200mm by 1200mm. Then some four
panels need to be cut from 18mm MDF, this can either be cut from off-cuts or
a 1200 by 1200mm sheet. Actually, even 1200mm by 6oomm would do the job.
There may also be some small 6mm thick panels needed if the Tweeter offset
requires it. These can always be cut by and a cheap jig saw later. With
Bills Board will be able to work things out nicely, but what you will need
is printed Cutting Sheets.
After the box has been assembled, then use plenty of white wood glue as a
sealant. Use your finger by running glue up and down on all internal joins. This
will ensure that joins are air-tight.
Some may question why a vented box should be air-tight when it has a dirty
big vent there. Surely any pressure would escape there rather than gaps in
the woodwork. This also means that we don’t understand how a
Helmholtz resonator works. At the box frequency, when the cone moves in, so
also in the vent the air is also moving in. Both the cone and the vent is
pressurising the internal volume. In fact, the pressures in a vented box are
potentially larger than those of a sealed box. So, bottom line, make sure
that only air in the vent can get in and out of the box.
Other than that, if you have DIY experience, the rest is doable. Please
note, this is a sizeable box of considerable mass, so if you have a bad back
or not prepared to lift some weight, then beg off or get a friend or other
to help. The finished boxes are likely to be 40-50Kg each. So have fun!
During the next month the boxes will be painted, the terminals will be
fitted as well as the port (this will only be friction fitted, as we will
want to try different lengths and vary the tuning).
The internal of the box will be stuffed with 60/40 Wool/Dacron bats made by
Insulco (although Bradford makes them too). About fourty to fifty percent of
the volume will be covered. The stuffing will be kept away and not to close
to the rear of the drivers, especially the two top ones. Some experimenting
may be needed, but this is excellent material that breathes a great deal and
has low mass. The Dacron (polyester fibres) keeps the 60% wool as a binding
material and becomes a ‘slab’ about 75mm thick. It’s very easy to work with;
gives excellent results and non-critical as well. Can’t ask for more.
Then the drivers will be fitted and then the fun really starts. Expect a
bumper instalment next month when things start coming together. Then we go
back to both electrical (impedance) and acoustical tests and to collect
critical data that we can import into SoundEasy and start to model and build
the crossover within the computer. This will then necessitate what crossover
components to get/buy and then build and start testing the results as a
complete speaker system. This then becomes the Final Tweaking Phase where
you could end up with small or big changes. But hopefully not the latter as
that will only show we messed up in an earlier step. Can happen but if we
are careful and disciplined we should not be so unhappy.
Please Note: The Sub Front Panel are not
entirely visible (except for the Tweeter behind Felt Pieces, see below) but sits exactly behind the
two Front Panels proper. The square Cut-Outs
allows the back of the drivers to have good air-flow into the internal
volume.
Please Note: Cut-Out must be
precisely in the centre and lineup with the Tweeter on Sub Front Panel.
This is how the above are fitted together:
The Main Brace sits 170mm behind the Sub Front
Panels. Later we will show what part of the volume will be treated with
Wool/Dacron Bats.
NOTE: There is a TOP and Bottom - so orientate in
the box as shown.
IMPORTANT: The UPPER round
78mm Cut-Out is for the Tweeter Terminal (two of them). The square Cut-Out
is for MidBass & Bass Terminals (four in all). IF you are using different
types of terminals, then do these Cut-Outs accordingly. Same applies to 91mm
Port Cut-Out. This may need to be changed, so check that the outside
diameter of your port you will be using.
Next: Internal Wiring & Box Damping
The Felt is nominally
6.4mm from our supplier - but uncompressed it is near 8- 9mm thick.
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