{"id":1988,"date":"2012-05-19T06:33:41","date_gmt":"2012-05-19T06:33:41","guid":{"rendered":"http:\/\/www.audioexcite.com\/?page_id=1988"},"modified":"2020-11-28T14:46:14","modified_gmt":"2020-11-28T14:46:14","slug":"sequence-two-monitor-be","status":"publish","type":"page","link":"https:\/\/www.audioexcite.com\/?page_id=1988","title":{"rendered":"Sequence Two \u2013 Monitor BE"},"content":{"rendered":"

Concept:<\/span><\/h3>\n

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Sequence Two \u2013 Monitor BE<\/span><\/strong> is a medium sized 2-way stand-mount loudspeaker for small to medium sized listening rooms.<\/p>\n

This is basically the same loudspeaker as the Sequence Two \u2013 Monitor<\/a>, but uses a ScanSpeak \u201ctop of line\u201d Beryllium<\/strong> tweeter instead of the ScanSpeak D3004\/660000 textile soft dome tweeter.<\/p>\n

\u00a0Loudspeaker driver units:<\/span><\/h3>\n

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Sequence Two \u2013 Monitor BE<\/strong><\/span> uses a mid-woofer driver unit from AudioTechnology. The 15H520613SDK mid-woofer uses a Kapton voice-coil in order to reproduce a more detailed midrange with higher dynamic and less coloration and distortion. This mid-woofer is one of the very best mid-woofers available to the DIY market. It has not the lowest bass extension, but has a wonderful \u201csnap\u201d and bass articulation together with a remarkable natural mid-range presentation, a class of its own.<\/p>\n

The tweeter section consists of the ScanSpeak Illuminator D3004\/664000 \u201cBeryllium\u201d tweeter. This is a very low distorting tweeter and it has an extended frequency response in both ends. There is no sign of the odd-order distortion remnants from the cone break-up, which is common for metal domes.<\/p>\n

This tweeter is perfect for designs requiring a low cross-over point or as in this design a low-order cross-over with shallow cross-over slopes.<\/p>\n

Sonically it matches the AudioTechnology mid-woofer beautifully and it has a neutral effortless sound characteristic and with great high frequency extension, but without ever sounding exaggerated or harsh or for that matter \u201cmetallic\u201d.<\/p>\n

For further details see:<\/p>\n

15H520613SDK<\/a><\/p>\n

D3004\/664000<\/a><\/p>\n

Cabinet:<\/span><\/h3>\n

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\"\"<\/a>In this design I\u2019ve used a 14 liter \u201cDayton Audio\u201d enclosure. This is a very nicely built curved cabinet with a 25mm (1\u2033) MDF front-baffle. The enclosure walls are made of 18mm MDF as well as a 15mm brace from the bottom to the top. The enclosure net volume is around 13 liters (enclosure volume \u2013 drivers, filter and port).<\/p>\n

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Cabinet drawing: Dayton 14 liters Curved Cabinet #302-721<\/a><\/p>\n

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\"\"<\/a>The internal cabinet walls are taped with strings of bitumen pads to reduce resonances. The enclosure is lightly filled with sheep wool. All drivers are flush mount and in order to let the mid-woofer \u201cbreathe\u201d properly, don\u2019t forget to chamfer<\/strong> the baffle.<\/p>\n

The internal cabinet walls are taped with strings of bitumen pads to reduce resonances. The enclosure is lightly filled with sheep wool. All drivers are flush mount and in order to let the mid-woofer \u201cbreathe\u201d properly, don\u2019t forget to chamfer the baffle.<\/p>\n

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Box simulation:<\/span><\/h3>\n

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~13 liter bass-reflex box with port tuned to 45Hz (anechoic response)<\/p>\n

-3db = 46Hz<\/p>\n

-6db = 40Hz<\/p>\n

-12db = 33Hz<\/p>\n

A classic QB3\u00a0 bass-reflex alignment.<\/p>\n

Cross-over design:<\/span><\/h3>\n

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The Sequence Two \u2013 Monitor BE<\/strong><\/span> uses a true symmetrical second-order Linkwitz-Riley (LR2) filter topology.<\/p>\n

The most common way to address the driver units relative acoustic center off-set is to use asymmetrical cross-over slopes, but in this design I use an electrical way to time delay the tweeter to adjust the acoustical center off-set. This is done by using a \u201cLadder Delay Network\u201d filter circuit, also often called an \u201cAll-pass Network\u201d, \u201cLattice Network\u201d or \u201cPhase Control Circuit\u201d.<\/p>\n

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The mid-woofer cross-over filter section is very simple and consists of a large coil (L1<\/strong>) and a response shaping filter circuit (C1+L2+R1<\/strong>) that shapes the cross-over slopes to a LR2 roll-off with a targeted 2.7kHz cross-over point. The large inductor (L1<\/strong>) tunes the design with a full \u201cBaffle Step Compensation\u201d (BSC).<\/p>\n

The tweeter cross-over filter section consists of a single tweeter padding resistor (R2<\/strong>) and a second-order electrical filter (C2+L3<\/strong>) that shapes the cross-over slope to a LR2 roll-off with a targeted 2.7kHz cross-over point. The value of (R2<\/strong>) can be changed to tailor the tweeter level to personal preferences.<\/p>\n

R2<\/strong> = 3.3Ohm -> +1dB
\nR2<\/strong> = 3.9Ohm -> 0dB (Reference Tweeter Level).
\nR2<\/strong> = 4.7Ohm -> -1dB<\/p>\n

(C5+L6+R3<\/strong>) flattens out the tweeters impedance peak at the resonance frequency and it\u2019s necessary to shape the filter to a LR2 filter slope, as well as to avoid \u201cringing\u201d at the resonance frequency that could cause audible distortion. It\u2019s ok to use a 68uF value for (C5<\/strong>) when using a high quality component or as in this design combine a cheaper electrolyte cap (68uF) together with a high quality 1.0uF cap.<\/p>\n

(C3+L4<\/strong> and C4+L5<\/strong>) contains the \u201cLadder Delay Network\u201d circuit that time delays the tweeter so its acoustic center off-set matches the mid-woofer and makes a perfect phase behavior around the cross-over frequency with minimal phase distortion.<\/p>\n

The tweeter is connected with reverse polarity and as can been seen in the schematics, the tweeter isn\u2019t connected directly to ground. It\u2019s of the outmost importance that the tweeter is connected exactly as shown, otherwise the delay network will fail.<\/p>\n

(L7+C6+R4<\/strong>) is a \u201cSystem Impedance Correction Circuit\u201d used to flatten out the impedance when using the loudspeaker with tube amplifiers. It\u2019s optional to use this filter section and it can be omitted when using conventional amplifiers. By using this circuit the impedance is 7 Ohms +\/- 1 Ohm within 200-20000Hz.<\/p>\n

Cross-over simulation:<\/span><\/h3>\n

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Top:<\/strong> Tweeter-axis, 15deg off-axis response (0dB Reference level).<\/p>\n

Upper left:<\/strong> Tweeter-axis, 15deg off-axis response (0dB Reference level) reverse polarity.<\/p>\n

Upper right:<\/strong> Individual driver unit phase tracking.<\/p>\n

Lower left:<\/strong> Tweeter-axis, 15deg off-axis response (+1dB).<\/p>\n

Lower right:<\/strong> Tweeter-axis, 15deg off-axis response (-1dB).<\/p>\n

Impedance measurements:<\/span><\/h3>\n

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Left:<\/strong> Blue=Left loudspeaker, Green=Right loudspeaker.<\/p>\n

Right:<\/strong> Blue=Left loudspeaker, Green=Right loudspeaker + \u201cSystem Impedance Correction\u201d.<\/p>\n

Overall an easy load for the amplifier. Nice consistency between left and right loudspeaker. With the System Impedance Correction circuit the average impedance is 7 Ohms and makes the loudspeaker tube-amp friendly.<\/p>\n

Frequency measurements:<\/span><\/h3>\n

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If nothing else is noted in the comments, the following frequency measurements of the finished loudspeaker are made at a 2m distance at tweeter height and for the 0db tweeter reference level.<\/p>\n

All frequency response charts are presented in a 50db scale with 1\/24 octave smoothing and the measurements are valid down to 350Hz.<\/p>\n

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Frequency response 15deg off-axis, reference tweeter level:<\/strong><\/p>\n

Blue:<\/strong> Left Loudspeaker
\nRed:<\/strong> Right Loudspeaker<\/p>\n

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Left:<\/strong> Tweeter-axis @ 2m, 0, 15 and 22.5deg off-axis.
\nRight:<\/strong> Tweeter-axis @ 2m, 30, 45 and 60deg off-axis.<\/p>\n

Distortion measurement:<\/span><\/h3>\n

Measurement setup:<\/strong><\/p>\n