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This DIY loudspeaker system follows my last year tentative with full-range drivers. Many thanks to Frédéric Ayer (atelier ligne bois, Fribourg) for the well finished cabinet work, and to Ward Maas (Pilgham Audio, Almere NL) for doing the electronic mods with so much care.
I used LinearTeam WinISD freeware speaker designing software. Measures were taken with a Phonic PAA3 31-band real time spectrum analyzer.
The front speakers are based on a E.J.Jordan Linear Array of four JXR6 HD in a closed 13 liters box (Qtc= 0.69, Fc= 116 Hz) fully filled with polyurethane foam (Tyrotex) and a puffy polyester fleece (i.T. Sonofil). The panels are damped by self-adhesive bitumen mats (Bitumex). The baffles are mirror oriented at 30 degrees facing the auditor, while rounded and obtuse angles reduce baffle discontinuities. There are two pairs of speakers, the upper one intended to reinforce the low frequencies.
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The bass extension is provided by Tymphany Linear Array Transducers (with a tubular form factor) LAT 500-4 in 80 liters vented enclosures filled in the bottom third with a polyester fleece. Bitumen boards damp the inner surfaces. The baffles are mirror oriented at 30 degrees. The length of the external 7 cm diameter vent can be adjusted for room response, actually ~10 cm (Fb ~30 Hz).
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Surround speakers are E.J.Jordan JX92S single drivers in 12 liters vented enclosures (tubular vent: 4.3 x 14 cm, Fb= 45 Hz) filled with a polyester fleece, without foam. Inner surfaces are damped by bitumen mats. The baffles are mirror oriented at 60 degrees.
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The speakers are powered by two
Rotel
RMB-1565
5 channels Class D amplifiers.
Loudspeaker filtering, equalization and time adjustment are done by a
Behringer
UltraDrive Pro DCX2496
digital system prepared by Ward Maas at
Pilgham Audio,
following Jan Didden
Linear Audio
modifications: a
linear power supply
replaces the smps and a
6-channel volume control
gives the DCX pre-amp capability.
The 24-bit/96 kHz digital signal is provided by a Behringer
UltraMatch Pro SRC2496
A/D D/A & sample rate converter. Up to three digital and one analog sources can be connected.
A
Denon
AVR-4306
surround receiver in a 4.0 configuration is used for decoding multichannel formats.
The table below shows the applied filters with the compensations for room effects, phase and loudspeakers linear distortion.
| Section | Bass at the bottom | Upper bass at the top | Wide range in the middle |
|---|---|---|---|
| Level & delay | +3 dB +4.08 ms | 0 dB | -6 dB +4.37 ms |
| 25 Hz | high-pass 48 dB Butterworth | ||
| 50 Hz | +3 dB LS: 12 db/Oct | ||
| 100 Hz | low-pass 48 dB Butterworth | ||
| 115 Hz | high-pass 48 dB Butterworth | high-pass 48 dB Butterworth | |
| 250 Hz | low-pass 48 dB Linkwitz-Riley | ||
| 2.56 kHz | 
| -3 dB Q: 7.1 | |
| 3.77 kHz | -2.5 dB Q: 2.5 | ||
| 7.80 kHz | -1 dB Q: 7.9 | ||
The yellow grid in the graph shows the ten octaves and a ±12 dB range.
The red, green and blue lines display the resulting action of the filters on each section.
The black line represents the
frequency response for JXR6 HD
measured by E.J.Jordan Designs.
The base of the alignment is wide range with stereo subs (or two-way with sub-bass) but there is an additional set of identical wide range speakers to reinforce the third octave.
This could cause severe anomalies due to phase displacements.
The combination of high order filters and well chosen delays makes it work here.
The delay applied to the wide range speakers has been obtained by searching the maximum volume difference between normal and inverted polarity.
A shorter delay and a slight shift of the low-pass filter frequency produce the flattest response through the crossover region.
The dip around 3 kHz attenuates a peak of the JXR6 arrays in order to eliminate fatiguing stridencies.
| Frequency | Surround left | Surround right | |
|---|---|---|---|
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| 63 Hz | -1.5 dB | ||
| 125 Hz | -2.0 dB | ||
| 250 Hz | -1.0 dB | +1.0 dB | |
| 500 Hz | -0.5 dB | -1.0 dB | |
| 1 kHz | -2.5 dB | -2.0 dB | |
| 2 kHz | -2.0 dB | -2.5 dB | |
| 4 kHz | -0.5 dB | -1.0 dB | |
| 8 kHz | -0.5 dB | -0.5 dB | |
| 16 kHz | +1.0 dB | +1.0 dB |
The surround speakers are maybe too 'hot', so we attenuate the medium a little more than would be otherwise necessary. Above it, there is a compensation for the off-axis response and a recessed 4 kHz.
The Jordan Linear Arrays are very sensitive, reacting to tiny modifications of the setting.
These light aluminium full-range drivers make natural timbres, a clear and detailed sound that engage the attention.
The line arrays act as sound projectors, partly because of their increased vertical directivity, so that
imaging or spatial localization is very precise, without the exclusive "sweet point".
The bass drivers are really vibration free, produce articulated notes for an excellent integration and go down low enough to rattle the windows.
Given enough Watts, realistic loudness can be achieved in my medium sized living room.
Carefully optimized, this system becomes like a strong smooth single malt
for better enjoying the music
May 2008 - August 2009
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