Cabinet
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Cabinet made from
22 mm MDF, except for front panel (30
mm), should make 2.56*2.98*5.56 = 42.4 liter net
volume. Adding bitumen pads, port, braces,
drivers, etc., will further reduce volume a liter
or two. Do not be too keen on this, anything from
38-42 liters will work perfectly as long as front
panel dimensions and driver placement is
maintained. For my cabs I used 21 mm Baltic birch
and 30 mm for the front panel laminated from 21 +
9 mm sheets. Front panel fillets are made from 30
x 50 mm solid maple wood.
I often have the question
whether Baltic birch is better than MDF and I
honestly can't tell. I never made two pairs of
speakers from both materials to compare sonic
impact. From a well-braced cabinet added bitumen
pads, I don't think there will be much
difference.
I use Baltic birch as it gives me the final
finish without having the trouble of applying
veneer - and I just happen to like the appearance
of lacquered Baltic birch although it's not an
easy material to use. Read below.
The QUATTRO need stands.
To my ears - and sofa - 45 cm height. I listen to
the QUATTROs slightly toed in and as usual in my
living room, 1 meter from the front wall and ~1.8
meters from side walls. My speakers are placed on
the long side of the room, thus very little
roomgain.
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constructions pics
BOX SIMULATION
Click
image to view large.
To reduce system sensitivity some 4-5 dB compared to TQWT
and DTQWT, a 3.9 mH coil bypassed by ~3.3 ohm is used.
Eventually during fine-tuning, R1011 was set to 5 ohms
consisting of two 10 ohms (10 watt) resistors in
parallel.
We do burn some energy here and we want R1011 (R2011 in
schematics below) to stay cool.
The port:
Fb = 36 Hz, port
dimensions: 68 mm Ø x 112 mm length
(don't change the supplied port of 120 mm length)
Fb = 38 Hz, port dimensions: 68 mm Ø x 110
mm length.
Fb = 40 Hz, port dimensions: 68 mm Ø x 84
mm length.
Don't expect any significant changes to the sound from
the suggested port tunings. Going from Fb = 36 Hz to as
high as 45 Hz only makes + 1 dB @ 63 Hz.
Crossover
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The tweeter's
simplistic crossover is basically an LR2
at 3 kHz. Fine-tuning tweeter crossover was done
extensively with the help of a sampled and
multiplied sequence of "Siri's
Killer Note". This proved extremely
useful and eventually gave a crossover that would
never have emerged from modelling alone.
Tweeter attenuation may be fine-tuned to personal
taste, your front gear and room acoustics. I
think 4R7 is absolute minimum. Try 5R6 if you
find the treble too forward. My default is 5R6
but I'll most likely end up with 6R0 or 6R2
giving e.g. piano and vocals the most natural
blend of overtones. 5R6 actually means treble
range above 5 kHz 1-1½ dB below average midrange
level. I've almost always found this voicing to
produce the most natural timbre.
6R0 or 6R2 are not common values. 8R2 in parallel
with 22R will make 5.97 ohms and 8R2 in parallel
with 27 ohm will make 6.29 ohm, so this may be
useful.
3R9, 4R7 and 5R6 are included in the crossover
kit, so order extra if you like to experiment.
3R9 is way too high treble level for my taste but
some like it hot!
The crossover for the
midwoofer is more complex as we need to
lower system sensitivity by L2011 bypassed by
R2011. Next we have the usual series coil, here
1.2 mH bypassed by an RC circuit of 0.47 uF and
22 ohm in series. Together with R2031+C2031 this
helps shaping the 8008 roll-off, which
acoustically is close to 3rd order, thus we can
maintain positive polarity of both drivers thanks
to the added acoustic distance to the tweeter
caused by the waveguide. A lot of things were
tried to omit the midrange notch filter
(R2041+C2041+L2141) but this minor 1.5 dB bump at
600 Hz just proved too much in the long run. Not
having the notch filter on certain recordings
just made the 8008 driver say: Hey - look at me!
Some midrange, huh... Drivers should draw as
little attention as possible. Check measurement
page to see what it means. Link below.
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Crossover Layout
Click
image to view large.
 
 
 
Wiring. Click image to view large.
  
Left: Soldering wires to terminal tags. Middle: C-Coil at
bottom of cabinet, fastened with screws through felt
layer. Right: Both sections in place.
  
Left: Damping material covering C-coil at bottom. Middle:
Main board on rear panel fastened with screws. Right:
Damping material covering main board and side panels next
to 8008 driver.
Measurements
on finished speaker
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Left:
SPL at 1 meter, 2 8 volt. Overall system sensitivity = 90
dB/2.8V/1 m.
Right: Final system impedance. Minimum where is matters
is 8.3 ohms at 36 Hz and 160 Hz. 7 ohms minimum above 7
kHz.
My 20 watts Audio Mirror SET amps just love these
speakers!
For those addicted to measurements, click here to view it all.
Cabinet
construction pics
Generally:
Never route for ports and drivers before at hand! Nor
drill holes for terminals before at hand.
Do
your own measurements and make test routings before doing
the actual cabinets. With Baltic birch there's no room
for errors.
Last but not least: Below is an attempt to
make a nice Baltic birch solution. Baltic birch is not a
particularly easy material for cabinet construction and
the
front panels take solid maple and mahogany fillets, not
something that can be made without access to a decent
table saw. Obviously the same cabs can
be made from 8 sheets/cabinet of MDF - and the sonic
results will most likely be the same. Choice is yours.
Happy building!
 
Left:
All parts for one speaker. Right: Test assembly with
painter's tape. Mahogany fillets for front panel.
 
Left:
Checking rear panel fit before gluing.
 
Routing
the brace panels. Quite some holes, but with a 6 mm
router bit Baltic birch is easy. I rounded the edges
because it looks nice.
 
Left:
Gluing the first cabinet. Only painter's tape and two
straps are used. Measure front diagonal to make sure it's
truly rectangular!
Right: Placement of port and terminals.
 
Routing for the port. Diameter = 96.5 mm. Make a hole
having a diameter approx. 0.2 mm less than measured
diameter of port base so that
you have to squeeze in the port and it stays firm - and
can be removed again for preferred port tuning.
 
Left: Drilling holes for terminals (7 mm). Right: Gluing
front panel vertical fillets. Only tape is used.
 
Left: Checking top and bottom front panel fillets before
gluing. Right: Gluing the same.
 
Left: Gluing front panel side fillets. Right: Routing for
the waveguide. When routing for the 8008 driver, the
waveguide must be in place.
Routing finished. Final thing I do is cutting length of
front panel on a table saw.
Front panel side fillets have been trimmed by routing,
keeping the front in place by two clamps.
This I do before routing for drivers to have a place
surface for the router. Sliding over holes is not a good
idea.
Trimmer router bit.
Do not forget to chamfer JA8008
driver hole on rear side. 45 deg. at ~15 mm depth.
Router bit used for chamfering.
Before gluing the front panel:
Gluing a front panel to the cabinet will never be 100%
perfect, thus before gluing the front panel to the
cabinet I always make a small groove, 1.5 x 1.5 mm, on
cabinet front edges.
This is also a way of handling the real drawback of
Baltic birch: Ripped edges. The outer veneer of Baltic
birch is rather soft and either sawing or routing will
often lead to a ripped edge.
 
Left: Router with guide. Right: Smooth the groove with
some grade ~400 sandpaper and start sanding the opposite
way of routing not to rip edges.
Bitumen damping pads
First of all: Bitumen pads damp panel
resonances. It does not absorb sound at all. (I have this
question regularly).
Adding the first 4 mm bitumen layers. Although the
bitumen pads I use are self-adhesive,
I use an adhesive meant for floor vinyl, having flexible
properties - and presumably adds to damping properties.
Self-adhesive pads like these heavy 4 mm sheets tend to
fall off over time if not glued.
Bitumen pads used for damping panel vibration.
In total 1 m^2 bitumen pads is needed.
Cabinet damping
Two materials are used for cabinet
damping: 10-12 mm (green) felt and Monacor MDM3.
In replacement of MDM3, use any kind of 4-5 cm
dacron/polyester/whatever damping material and if felt is
not available, 10 mm polyester foam.
GREEN FELT
 
Green
felt on all internal panels except front panel, that is:
On front panel in front of the vent I added green felt
too plus a layer of MDM3.
For keeping the felt in place I used Pattex
"no-more-nails" glue. Three strips of glue/felt
sheet.
MDM3:
In total (2 cabs) 3 rolls of MDM3 is used. One roll
contains two sheets of 63 x 33 x 3.5 cm damping material.
One sheet at top, one sheet at bottom and one sheet on
top of crossover and on sides behind 8008 driver.
In total approx. 1.25 m^2 of damping material is
needed if thickness is close to 35 mm as for MDM3.
FINALLY -
 
Finally! Sanded, lacquered, ready for mounting of
drivers, ports, terminals, etc.
 
Left: Cheap trick: If your routings are tight, you may
have trouble removing drivers for changing damping
materials, crossover tweaking, etc.
Chassis holes are Ø 5 mm, make 6 mm threads in two
opposite holes! Makes life a lot easier when removing the
driver :-)
 
Secure leads from drivers like seen on photos. Ripped
terminals are a real pain! Wires used are silver plated
copper in teflon.
Read here how you fasten
the waveguide to the tweeter.
Parts
list
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schematics
Example
of level-2 parts list.
Complete kit only
available from Jantzen Audio: contact@jantzen-audio.com
Contact Jantzen Audio for shipping
details - please state which country.
All technical questions at troels.gravesen@hotmail.com
Download level 1 here:
Superior-Z-Caps - STANDARD Z-Cap - all baked wire
coils (845 EUR incl. VAT)
Download level 2 here: Silver
Z-Caps - Superior-Z-Caps - C-Coils/WAX/baked wire
coils (1,065 EUR incl. VAT)
Download level 3 here:
Silver/Gold-Caps - Superior-Z-Caps -
C-Coils/WAX/baked wire coils (1,155 EUR incl.
VAT)
Download luxury version level 4 here:
Silver/Gold Caps - Superior-Z - WAX/baked wire
coils. (1,308 EUR incl. VAT)
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Damping material
available:
Order 1 sqm "bitumen pad with felt
layer" - and
2 sqm polyester "damping cloth material" (20 mm
thickness). I suggest 3 layers of this material for 2
layers of MDM3.
Download crossover layout for low-cost
version here.
Also check out TQWT, DTQWT, OB9 and
OBL-11 for
other constructions featuring the JA8008/TW034wg duo.
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