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The Monitor 4 - full range loudspeakers with ceramic drivers
March 2013 - June 2014

INTRODUCTION

This project born to exceed the performance of all my previous loudspeakers using ceramic drivers and an active integrated subwoofer.

Update 4 July 2014

Yesterday evening there was the first serious listening session of this loudspeakers and this meeting was attended by a couple of my friends with a great experience in audio recording and playback.
For the test has been used my KT88 push pull, the second version of the ES9018 DAC with solid state output stage and the Synchestra SIGNATURE Speaker Cables.
After a few seconds of listening is immediately evident the complete lack of distortion even at high listening levels.
The details of each musical instrument are easily identifiable and the transparency of the sound message is total.
Tube amps may be better suited to soften the crystal clear medium-high frequency, mainly with poor recordings.
Low frequencies are handled very well by the built-in amplifier and the woofer with aluminum cone and there are no queues and resonances.
The low-Q sealed box ensures a perfect coupling in domestic environments even in small environments.
During the test many time has been verified the improvement obtained by converting PCM to DSD tracks while listening with the new functionality made ​​available by JRiver Media Center 19.0.145.

 

TWEETER

 Transducerlab N26C-T
  • High purity molded Al2O3 Alumina ceramic dome
  • High flux double magnet design
  • Decompression chambers
  • High dynamic range/ Acoustic dampening; no ferro-fluid
  • Frequency matched to +/- 0.75db
  • Under-hung voice coil (1mm linear excursion)
  • Frequency bandwidth = Response: 950hz - 40khz/ Recommended range: 1800hz - 24khz
     
  • parameters
  • frequency response
  • frequency response off axis
  • impedance
  • size

WOOFER-MIDRANGE

 Accuton C158-8-085
  • 6.25 inch bass-midrange for small bookshelf monitors or slim floorstanders
  • small and light voice coil with 25mm titanium voice coil former for high midrange resolution
  • long excursion design for high SPL capabilities

    Closed Box design parameters:

    Vb: 8.5L, -11dB @ 40Hz, F-3dB: 70Hz, Q: 0.71 (typical)
    Vb: 22L, -8.5dB @ 40Hz, F-3dB: 70Hz, Q: 0.50 (extended bass)

     

  • datasheet

SUBWOOFER

 Wavecor SW263WA03

SW263WA03 is a 4 ohm woofer designed for dedicated subwoofer applications.
It works equally well for high-end hi-fi, high quality home theater systems, and top multimedia setups.
The extremely stiff aluminium cone, the long linear throw, exaggerated ventilation, and the special dynamic linearization short circuiting rings together makes up for an unusually linear and low-distortion woofer.
Even at very high signal levels, the unit behaves controlled and without distortion.
Due to low mechanical losses SW263WA03 masters equally well low level details and extreme dynamic requirements.

SUBWOOFER AMPLIFIER - part 1

These loudspeakers inside the back of the box will integrate an active subwoofer with a class AB amplifier module.

see the part 2 for more details.

PASSIVE FILTER

This filter should be inserted on the input of the main amplifier to exclude the very low frequency range on the Accuton mid-woofer.
If your amplifier have an input impedance near to 10Kohm you need to use R=1Kohm and 10 times the capacitor value otherwise if you are sure of input impedance you can use only the capacitor.

 

BOX

To get the best transient response the my choice is a sealed enclosure in a large box with a Qtc near to 0.6 for both woofer drivers.

1. Baffle design and size

After reading these articles and some simple tests I have decided to test different front panels before start to design  these loudspeakers.

The N26C has a very wide dispersion pattern due to the fact that it is not horn loaded at all.
Most tweeters have a small semi-horn around the dome, which helps to direct the wave form but this decrease the dispersion.
The N26C dome is completely exposed and forward flush with the face plate so for this reason, the tweeter is even more sensitive to baffle placement and shape.

Follows the design of the different baffles in testing phase.

Conclusions: both drivers are more linear with the larger baffle, the baffle type 4 is  the best.

 

2. acoustic damping materials and distortion analysis

Now follows a sinusoidal analysis about acoustic damping materials Polyurethane Foam with and without Dacron.

Now follows a sinusoidal analysis about tweeter distortion.

Conclusions: Both the drivers have a very low distortion, near to 0.2%, in all the main frequency range.
                   The acoustic damping materials does not change the frequency response and distortion.

                  

3. baffle degrees

I decided to tilt the front panel of the speaker system to eliminate the offset between the 2 acoustic centers.

Conclusions: also with an inclination of 10 degrees there is not loss at high frequencies.

 

4. design

Follows an idea of the design for this loudspeakers.

CROSSOVER

The mid-woofer and tweeter using a passive crossover of the highest quality centered at a frequency higher than the human voice.

Will be implemented a network for impedance compensation to facilitate the work of vacuum tube amplifiers.

This crossover is the result of a long series of measurements of the frequency response and several listening sessions with a my friend who makes live recordings.

The ceramic drivers need a notch cell in parallel to the driver to eliminate all the effects of the natural peak of this material.

 

 

 

 

 

 

 

 

 

 

SUBWOOFER AMPLIFIER - part 2

The LME49810 assembled board buy on Ebay shop should ensure high performance, I will test soon.

The LME49810 is a high fidelity audio power amplifier driver designed for demanding consumer and pro-audio applications. Amplifier output power may be scaled by changing the supply voltage and number of power transistors. The LME49810’s minimum output current is 50mA. When using a discrete output stage the LME49810 is capable of delivering in excess of 300 watts into a single-ended 8Ω load.

Unique to the LME49810 is an internal Baker Clamp. This clamp insures that the amplifier output does not saturate when over driven. The resultant “soft clipping” of high level audio signals suppresses undesirable audio artifacts generated when conventional solid state amplifiers are driven hard into clipping.

The LME49810 includes thermal shutdown circuitry that activates when the die temperature exceeds 150C. The LME49810’s mute function, when activated, mutes the input drive signal and forces the amplifier output to a quiescent state.

I have got on Ebay also an active crossover module to create a low-pass (NE5532 Subwoofer processing circuit).

The original schematic have a big problem, the output voltage change with the frequency setting.

so I have changed some components and the schematic to obtain a good low-pass and a sub-sonic high-pass.

The power supply has been create with:

Subwoofer - MidWoofer Crossover detail

 

PROTECTION GRILL

To protect my woofer from the claws of the cat I have used the SGF-250 protection grill.

TEST SYSTEM

    

PHOTOS

 

COSTS

description item unit cost total
carpenter R.D. Arredamenti 1   500
Transducerlab N26C-T 2 149 298
Accuton C158-8-085 2 260 520
Wavecor SW263WA03 2 260 520
SGF-250 protection grill 2 15 30
Toroidal transformer 2 80 160
Slit Foil capacitor 22000uF 63V 4 20 80
Subwoofer amplifier kit 2 50 100
Subwoofer filter + modification 2 20 40
Jantzen Audio Superior Z-cap 6   170
Air coils and resistors 8   100
Connectors and other coils 8   50
total cost     2568