spk5 - app note 1.23 · 2021. 2. 11. · sound pure building a straight wire to the soul of music...
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SOUND PURE
Building a Straight Wire
to the Soul of Music
SPK5
DEMO SPEAKER
KEY SPECIFICATIONS
Type Passive, 2-way, ported
Woofer PTT6.5X04-NFA-01
Tweeter AMT21CM2.1
Crossover ~3.2kHz
Port tuning ~30Hz
Volume ~15L
Size 230x340x315mm
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1 Description
SPK5 is intended as demonstration platform for the PTT6.5X04-NFA-01 (earlier known as PTT6.5W04)
transducer.
The design is deliberately kept very simple: a small ported wooden box, traditionally shaped with a simple
12.5mm chamfer for management of edge diffraction, and a passive cross over at ~3.2kHz. Although extremely
simple, with numerous possibilities for enhancement by the skilled speaker designer, the SPK5 design very
successfully demonstrates the tremendous improvements in sound quality which is possible to achieve when
using the long-stroke ultra-low-distortion PTT6.5X04 woofer from PURIFI Transducer Technology.
Figure 1 SPK5 Demonstration Speaker
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2 Crossover
Figure 2 SPK5 Crossover Schematic
Figure 3 SPK5 Demonstration Speaker crossover
C3 R3 L2
L3
R1 C1 C2P
TT
6.5
X0
4-N
FA
-01
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Important note:
Due to the extremely low distortion of PTT6.5X04-NFA-01 it is VERY important to choose good crossover filter
components. Inductors must by airInductors must by airInductors must by airInductors must by air----core type.core type.core type.core type.
Jantzen Type Jantzen part number
InductorsInductorsInductorsInductors
L1 0.267mH Air Coil 0.267mH,
0.3mmØ
1.9Ω1)
000-1000
L2 1mH
Air Coil 1mH, 0.3mmØ
3.98Ω2)
000-0826
L3 1.5mH
Wax Coil 1.5mH
14AWG
340mΩ3)
000-8390
CapacitorsCapacitorsCapacitorsCapacitors
C1 10µF Cross Cap 10µF 001-0264
C2 4.7µF Cross Cap 4.7µF 001-0250
C3 22µF Cross Cap 22µF 001-0272
C4 22µF Cross Cap 22µF 001-0272
ResistorsResistorsResistorsResistors
R1 10Ω Superes, 10W 10Ω 002-0223
R3 12Ω Superes, 10W 12Ω 002-0226
R4 1Ω Superes, 5W 1Ω 002-0034 1) The DC resistance of inductor L1 is 1.9Ω. In case of other inductor is used, add a series resistor (R2) to keep
combined DC series resistance as close as possible.
2) The combined DC resistance of inductor L2 and resistor R3 is 16.98Ω. Combined value should be kept as close as
possible in case another inductor type/brand is used.
3) Higher DCR can influence bass performance
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3 Cabinet, Port and Damping
The cabinet is constructed of 21mm birch plywood with a 25mm front baffle made of black MDF.
To minimize resonances the cabinet is supported by a diagonally placed 15mm birch plywood brace. See
drawing.
The 63mm OD rear-facing port has two 90 deg bends in order to fit the cabinet and have the required length.
Two 3D printed flares help minimize wind noise.
The cabinet is stuffed with cotton/fibre damping material: 85% Cotton, 15% Polyester. 370g/m^2.
Approximately 120g of the material is placed behind the driver and another ~180g around the tube almost filling
the entire volume above the internal brace.
The crossover is placed externally and connected to SPK5 via a 4-wire Speakon NL4MPR connector.
Refer to drawings section for all dimensions.
Table 1 Cabinet, cut-away view to visualize port and brace
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4 Measurements
Measurement equipment and setup:
Clio 12, 1m microphone distance, gated measurement (valid down to 330Hz)
Figure 4 SPL, On-axis SPL @ 1m (with gating). Normal response, inverted phase to check alignment between woofer and tweeter
, woofer response, and tweeter response
10k5k2k1k50020010050201055 20kHz
95
dBSPL
85
75
65
55
45
Microsoft LogChirp - Frequency Response 13-05-2020 14.17.04
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Figure 5 SPL, 30-deg Off-axis SPL @ 1m, normal response, and inverted phase to check alignment between woofer and tweeter
Figure 6 SPL, -30-deg Off-axis SPL @ 1m, normal response, and inverted phase to check alignment between woofer and tweeter
10k5k2k1k50020010050201055 20kHz
95
dBSPL
85
75
65
55
45
Microsoft LogChirp - Frequency Response 13-05-2020 15.26.21
10k5k2k1k50020010050201055 20kHz
95
dBSPL
85
75
65
55
45
Microsoft LogChirp - Frequency Response 13-05-2020 14.31.02
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Figure 7 Impedance, no port damping
5 Revision History
RevRevRevRev DateDateDateDate DescriptionDescriptionDescriptionDescription IDIDIDID 1.00 2019-12-19 Document replaces SPK4 – App Note KNM
1.10 2020-01-31 Jantzen part numbers added for cross over components SPO
1.20 2020-05-18 Updated crossover tuning and measurements. Off axis measurements added SPO
1.22 2020-07-02 Updated to include SPK5 crossove kit information SPO/CNN
1.23 2021-02-10 Woofer has a new name: PTT6.5X04-NFA-01 (the woofer is identical to what was earlier known as PTT6.5W04-01 – only a name change)
CNN
10k5k2k1k50020010050201010 20kHz
50
Ohm
40
30
20
10
0
Microsoft Sinusoidal 13-05-2020 15.27.52
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