Active loudspeaker, model 2018

Including an audio switch, PCB version 2019-1

By Paul Langemeijer

2020-04-28

Contents What design choices are behind this speaker design? ..................................................................................................... 3

Open cabinet for broadband speakers ......................................................................................................................... 3

Line array....................................................................................................................................................................... 3

Completely closed bass cabinet .................................................................................................................................... 3

Built-in amplifiers .......................................................................................................................................................... 3

Cabinet construction ......................................................................................................................................................... 4

MDF and acrylic panels ................................................................................................................................................. 4

Bill of material ............................................................................................................................................................... 5

Loudspeakers ................................................................................................................................................................ 5

Pictures ......................................................................................................................................................................... 6

Electronics ......................................................................................................................................................................... 9

Schematic crossover, correction filters and power amplifiers ..................................................................................... 9

Schematic audio switch and power supply ................................................................................................................... 9

Print layout .................................................................................................................................................................. 10

Amplifier acrylic panels ............................................................................................................................................... 12

Frequency response ........................................................................................................................................................ 13

At Ars Longa exposition Son en Breugel, October 2018

What design choices are behind this speaker design? The design of the standard loudspeaker sold in stores differs in at least four respects. The standard speaker is usually

a two-way or three-way system with a bass reflex port and no amplifiers are built in. The designed system is a two-

way system in which the mid and high tones are reproduced by nine broadband speakers in an open box and a bass

speaker in a completely closed box. Amplifiers with filters are built into the cabinet. The cabinet has been kept as flat

and narrow as possible to be placed in the living room.

Each of the following four features contribute to quality enhancement:

Open cabinet for broadband speakers When a speaker is enclosed in a cabinet, resonances of the air in the cabinet will occur. Those resonances gradually

disappear through the speaker and cabinet panels. This seriously 'colors' the sound image. The cabinet continuously

stores sound energy that is released in a delayed manner. However, a closed box is not necessary for mid and high

tones. That is why the broadband speakers are mounted in an open cabinet. This results in an uncolored sound.

Voices sound more natural. For this reason, electrostatic speakers also sound so good because they are never

mounted in a closed cabinet.

Line array A line array system consists of a column of identical loudspeakers. This system is used in large spaces (e.g. concert

halls, churches) due to its high efficiency. The efficiency is due to the vertical bundling of the sound. For a living

room, efficiency is not important, but vertical bundling is. This ensures that less sound reaches the listener through

reflection from the floor and ceiling. To the listener, it seems as if he is closer to the speaker. Almost as if he is

listening through headphones.

Completely closed bass cabinet An open cabinet for the bass is impractical because it would require a very large panel. With standard loudspeaker

systems, a bass reflex port is used to get more lower frequencies. However, the bass reflex port is based on

resonance. And at resonance, sound energy is released in a delayed manner. For this reason, a closed cabinet was

chosen. The cabinet is so small that standing waves (resonance) cannot arise. To compensate for the lack of bass,

which a small box entails, correction amplifiers are built in. In this way, the bass sounds quieter than a bass reflex

system.

Built-in amplifiers There are a number of reasons why amps are built in. As mentioned before, correction amplifiers are needed for the

low end. The treble is also slightly corrected. In addition, there is an electronic crossover filter. This is more accurate

than a passive filter as used in standard loudspeaker systems. Separate power amplifiers (LM3886T) are built in for

the low and high frequencies. This means that the speaker is directly connected to the amplifier, without the

intervention of cables, coils, capacitors and resistors. In that way, the speaker is better controlled by the amplifier.

There is a circuit that automatically turns on the power of the amplifiers when the music starts. When the music has

stopped, the power will be turned off after a few minutes.

The "active" speaker can be directly connected to a preamplifier or media player. The loudspeaker can be connected

to an existing power amplifier via a resistance attenuator (1:20).

Cabinet construction

MDF and acrylic panels

drawn with Microsoft 3D Builder

118x11x1.8

55.4x8.2x1.8

22.4x11x1.8

26

118

22.4x45.4x1.8

Top views

Monacor SPH-5M 4 Ohm

Contents: ~6 liter

11

11

26 8 10 8

26x11x1.8

55.4x9x1.8

59x26x0.3 acrylic

59x8x0.3 acrylic

59x10x0.3 acrylic

Visaton FR58 4 Ohm

48

11

Amplifier cabinet

amplifier

59

59

45.4x5.5x1.8

Edges only, see picture

1.8

10x11x1.8

10x11x1.2

10x17.6

55.4x6

Bill of material

# MDF black (cm), ordered at: www.Opmaatzagen.nl

4 118 x 11 x 1.8 (1 short side miter)

6 22.4 x 11 x 1.8

2 26 x 11 x 1.8 (2 short sides miter)

4 55.4 x 9 x 1.8 (2 long sides miter)

4 55.4 x 8.2 x 1.8 (1 long side miter)

6 45.4 x 22.4 x 1.8

2 45.4 x 5.5 x 1.8 (shorten by hand)

4 11 x 10 x 1.8

2 11 x 10 x 1.2 (note the different thickness!)

Glue acrylic on wood with: OTTOSEAL S72. You can remove excess glue with benzene.

Woofer cabinet can be opened from the back (screwed shut).

Woofer mounted on the inside. Kick-back nuts (milled 1 mm) on the front.

Woofer mounted 8 mm flush (remains 1 cm thickness of the MDF).

FR58 are mounted with 2 component adhesive (Bison Combi Plastic).

Woofer acrylic diameter: 123 mm, position depends on hole in MDF.

FR 58 acrylic diameter: 55.2 mm.

Glass base 26x20 cm, 1 cm thick, PP cut (www.glaskoning.nl), glue with “Tec7 Trans” (www.tec7.com)

Drawings for acrylic panels:

- BlackAcrylicPanels.dxf (check and correct position of woofer cut out)

- RedAcrylicPanels.dxf

Loudspeakers Woofer: Monacor SPH-5M 4 Ohm

Wideband speaker: Visaton FR58 4 Ohm

Note that a small cabinet needs a small woofer.

# Acrylaat laser cut by www.Laserbeest.nl

2 26 x 59 black, frosted, 3 mm + woofer hole

2 10 x 59 black, frosted , 3 mm + 9 holes

4 8 x 59 red, opaque, 3 mm

Pictures

Electronics

Schematic crossover, correction filters and power amplifiers

The nine Visaton FR58-4 are wired as follows: 3 sets in series where each set consists of 3 speakers in paralel.

Schematic audio switch and power supply

7

V-

C4220n

-

+

U3A

NE5532A

3

21

84

LOW -

/

4

R8 5k6

Place inductor or resistorin case of capacitive loudspeaker (ESL)

-

+

U2B

NE5532A

5

67

84

C5220n

R=1/(2.pi.f.C)

R26 82k

R29

47k

590 Hz

V-R14 1k

ON

BK1

3

V-

Of f

4

R9 120k

C2 22n

ON

R4 10k

low pass filter 268 Hz, 18 db/octave

R16 5k6

9

-

+

U2B

NE5532A

5

67

84

-

+

U3A

NE5532A

3

21

84

R20 12k

2 R

R18

47k

Cinch

10

R25 12

R27 82k

/

J3

1,5

to Audio switch

R12 2k7

R10 2k7

V+

V+

V-

3

-26V

C14220n

R28 15k

LOW +

C7220n

R15

100k

high frequencycorrection 19.4 kHz

Of f

V+

R=1/(2.pi.f.C)

C3220n

.

R21 3k3

Bruel & Kjaer frequency response

R3 10k

(XLR 1) GND

Low boost @ 129 Hz

2 * PI * C * R

1,5L1

INDUCTOR

R13

6k8

/

16 Hz

7

* Adjust R27 for flat frequency response

while P1 is in the center.

Low boost @ 129 Hz2 * PI * C * R

C1 220n

C8 470n

C18

3n3

HIGH +

R5 10k

J2

J1

(XLR 2) IN+

R110k

9

V-C10

10u MKS

1/2 R

High pass6 db/oct 225 Hz

2 * PI * C17 * R22

R7 6k8

HIGH -

high pass filter 106 Hz 18 db/octave

-

+

U1A

NE5532A

3

21

84

C17

10n

R23 820

+

-

U5B

LM3886TF

13128

911

610

C13220n

R19 6k8

R11 2k7

V-

ON

R2 10k

R17 120k

+26V

P1

2k

R

Of f

V+

C11

220n

+

-

U4BLM3886TF

13128

911

610

+

C12

100u

C6220n

-26V

J4

32 Hz

+

C20

100u

10

880 Hz

C16 470n

R6 2k2

C15220n

R22 12k

BK2 C19

2n2

(XLR 3) IN-

8

8

+26V

R24 1k5

-

+

U1B

NE5532A

5

67

84

C9 100n

V+

V+

-

+

C205

470u

X4

C211

100n

Blue

Q1BC547B

+

1600 Hz

F1 500mAT

+R107 4k7

Black

R101 4k7

338 Hz

100x Capacitor amplifier

X5

.

v iolet

enable audio switch

R120 180

VCC

R11010k

R202 12

R1136k8

U8

78L05

COM1

IN2

OUT3

R105 4k7

+ C20110000u

.

C101 470n

J5TEST

C210

100n230V~

R114390

R11610k

Normal timeout when no music: about 5 minutes

C102 10n

twist black and red

twist white and violet

230V~

.R111

100

R10622k

-

R121

47

L2

LED RED

traf o-blue

TLC2274

+

C206470u

Do not use an elco, but e.g. MKS R119 270Q3

BC547B

+9V

R109 1M

X3

VCC

+26V

C203

100n

-

R118 470

15nA

-

C207

100n

AudioSwitch

R203 12

twist blue and brown

-26V

.

X4

traf o-brown

J6

T1

2 x 7.5V 1.8 VA

2 6

97

104

L2 L1

LED GREEN

72 Hz

R1122k2

230V~

230V~

R108 82

R201

33k

C10622n/400V

VCC

Jumper: select common cathode or common anode LEDs

.

-9V

(white) 0V

VCC

+

X6

TS912 connected to VCC and ground

C104

4n7

L3LED

chassis

.

TLC2274

L5

LED GREEN

R10322k

TLC2274

(red) ~18V

(black) 0V

SSR - S202T02

C107100n

In TEST mode, the switch off time is short (15 sec).

- +D2

B80/70

1

3

2

4

R115 100k

C204

100n

Audi switch

D3

1N4148

+

C208

470u

P101

100

- +D1

B80/70

1

3

2

4

C1053u3

+

J7

+ C20210000u

R104

100

R102 47k

RedTraf o

2 x 18V 30VA

2 6

97

104 White

(pink) ~18V

sensitivity

8nA

switch

X3

+

C209470u

R1224k7

TLC2274

+

C103 10uX9

L4

LED RED

R1174k7

1

2 4

5

Brown

L1

Q2

BC547B

Print layout PCB 2019 version 1 needs some small correction: add R122 and change R121 wiring according to schematic.

Amplifier acrylic panels

AmplifierPanels.dxf

Thickness: 4 mm

Panel size: 20 x 30 cm (for four amplifier units)

Frequency response Measured at 3 m in listening room (speaker placed in center position, see picture),

with electronic corrections, 1/6 smoothing.

A flat response, especially at the lower frequencies, is not possible due to all reflections in the listening room.

Room correction will help here.

Jumper J3 placed. No jumper on J4.

Note that a flat response is not necessarily the best response!

The Brüel & Kjaer curve shows a slow rolloff at the higher frequencies.