| Proposed Project Plans
The speaker must fit this specific design
criteria:
- 2-way full range tower speakers which
can be used as the left and right main speakers in a stereo system or
home theater.
- Flush mounted drivers for a very smooth
and accurate frequency response with bass into the 40's.
- Soft dome tweeter preferred with very
low fs adapt for low crossover point.
- Woofer must be at least 6-1/2" to 8"
but no bigger or smaller or multiple drivers.
- Woofer and tweeter SPL @ 1W/1M must be
within 1 dB of each other.
- 8 ohm nominal impedance.
- Aesthetics - slim design, tall, thin
and deep enclosure.
- Must be floor standing - no
bookshelves.
- Both left and right speakers must be
able to be constructed from a single 4' x 8' sheet of wood.
- Ported enclosure preferred with rear
firing port to avoid pipe resonances being heard by listeners.
- Port diameter must be half the diameter
of the driver to allow minimum compression and reduced
distortion.
- Maximum amount of internal bracing for
structural integrity while maintaining the proper enclosure
volume.
- Built from 3/4" MDF to ensure the
smallest footprint possible while still maintaining the proper enclosure
volume.
- MDF will be covered in 1/4" oak
plywood.
- The oak will be stained the color of
choice, varnished with a high gloss polyurethane, and then buffed with
bees wax.
- The crossover will be no more than a 12
dB/octave L-R type near 2,000 Hz.
- Gold plated binding posts.
- Cabinet must also be spiked.
- Rectangular grill cover which just
covers drivers is optional.
- Total system cost must not exceed
$300.
The actual design version 1.1 which will
suit the above criteria:
- The bass unit will be the Vifa
P21WO-20-08, 8" cast frame woofer.
- The treble unit will be the Vifa
D27TG-35-06, 1" silk dome tweeter.
- Enclosure size: 40-7/8"H x
9-1/2"W x 11-3/4"D (before veneer).
- Enclosure volume: 1.6285 cubic
feet.
- Footprint: 10"W x 12-1/4"D
(after veneer).
- Rear firing 4" round port made from
standard PVC which elbows inside the enclosure and is just over 12"
long.
- There will be 5 internal shelf braces
that will reside approximately every 6" along the inside walls of the
enclosure.
- 3/4" MDF will be used and 1/4" oak
plywood will be used as veneer.
- Custom 12 dB/octave L-R type crossover
at 1,950 KHz.
- Black Toe Spikes will be
installed.
Specifications on Vifa
components:
- Vifa D27TG-35-06, 1" silk dome
tweeter.
- Ferrofluid cooling
- Linear response
faceplate
- Braided tinsel leads
- Double chamber for lower
resonance
- 100 watts RMS/140 watts
peak
- Impedance (Z) = 6.0 ohms
- DC resistance (Re) = 4.6
ohms
- Frequency response:
1,500-30,000 Hz
- Magnet weight: 8.5 oz.
- Fs = 650 Hz
- SPL = 90 dB @ 1W/1M
- Dimensions: 4-1/16" across with
2-7/8" cutout
|
Vifa
D27TG-35-06
|
- Vifa P21WO-20-08, 8" cast frame
woofer.
- Cast magnesium basket
- Mineral filled polypropylene
cone
- Rubber surround
- 80 watts RMS/115 watts
peak
- Voice coil diameter:
1-1/2"
- Inductance (L) = 0.90 mH
- Impedance (Z) = 8.0 ohms
- DC resistance (Re) = 5.7
ohms
- Frequency response: 28 -
4,000 Hz
- Magnet weight: 24.6 oz.
- Fs = 28 Hz
- SPL = 91 dB @ 1W/1M
- Vas = 3.99 cubic feet or
113.1L
- Qms = 1.60
- Qes = 0.41
- Qts = 0.33
- Xmax = 4.0 mm
- Dimensions: 8-1/2" across with
7-3/8" cutout
|
Vifa
P21WO-20-08
|
Enclosure specifications and plans:
- Net internal volume: 1.6285 cubic
feet
- Tuning frequency: 36 Hz
- Port: 4.00" round x 12-3/4" deep
(via elbow)
- Calculated f3: 40.5
Hz
- Predicted frequency
response
Freq
Gain
SPL
20.00 -20.38
89.65
25.00 -14.13
95.90
30.00 -9.37
100.66
35.00 -5.79
104.24
40.00 -3.25
106.78
45.00 -1.62
108.41
50.00 -0.66
109.37
55.00 -0.13
109.90
60.00 0.14
110.17
65.00 0.27
110.30
70.00 0.33
110.36
75.00 0.35
110.38
80.00 0.34
110.37
85.00 0.33
110.36
90.00 0.31
110.34
95.00 0.30
110.33
100.00 0.28 110.31
- CAD picture of speaker and MDF
cut layout.
The crossover network
- 12 dB/octave all-pass or Linkwitz-Riley design
- Tweeter is wired with reverse polarity
- Crossover Frequency: 1,950 KHz
- Required component values:
- L1: 1.30 mH (266-830)
- C1: 5.10 uF (027-554)
- L2: 0.98 mH (266-826)
- C2: 6.8 uF
(027-560)
- All capacitors and inductors are standard values available
through Parts Express.
- Use Solen Metallized Polypropylene 5% Capacitors and 18 gauge
perfect layer wound air core inductors.
|
The Design
v1.1
Crossover
Schematic
|
To date this is all that has been planned. The drivers
will be purchased through Parts Express or Madisound. I may even
have Madisound design the crossover for this speaker as well. I
would like the keep the crossover as simple as possible but still have it
be around 2,000 Hz. If any kind of notch filters or zobel networks
are required, then they will surely need to be included also. I have
never worked with either of these Vifa components, so I am basically going
into this thing blind, hoping that their reputation will uphold the
performance of their drivers. The port will be a single 4" round PVC
elbow which will connect directly to the rear baffle. This will in
effect have a small flare to it, since the mouth of the PVC is actually
4-1/2" to accept a straight piece of PVC. Any additional length that
is required will be added onto the other end of the elbow and point
upwards as shown in the diagram. This will make it fairly easy to
tune the enclosure to the calculated 36 Hz. |
