spk5 - app note 1.23 · 2021. 2. 11. · sound pure building a straight wire to the soul of music...

[email protected] PURIFI Information

00

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

SPK5 - Design Document

[email protected] PURIFI Information Feb 2021 1

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



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



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



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



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



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



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


10k5k2k1k50020010050201055 20kHz

95

dBSPL

85

75

65

55

45




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

spk5 - app note 1.23 · 2021. 2. 11. · sound pure building a straight wire to the soul of music...

Documents