{"id":5340,"date":"2015-06-29T18:30:45","date_gmt":"2015-06-29T18:30:45","guid":{"rendered":"http:\/\/www.audioexcite.com\/?page_id=5340"},"modified":"2020-11-28T14:32:33","modified_gmt":"2020-11-28T14:32:33","slug":"classic-two-m5","status":"publish","type":"page","link":"https:\/\/www.audioexcite.com\/?page_id=5340","title":{"rendered":"Classic Two – M5"},"content":{"rendered":"

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

 <\/p>\n

\"\"<\/a>\"\"<\/a>\"\"<\/a><\/p>\n

Classic Two \u2013 M5<\/strong><\/span> is a large sized 2-way stand-mount bass-reflex loudspeaker. It\u2019s ideal for medium sized listening room. The tweeter can be fine-tuned to several different levels according to personal preferences and taste.<\/p>\n

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

 <\/p>\n

Classic Two \u2013 M5<\/strong><\/span> uses two low distorting driver units from the ScanSpeak Classic line. The 18W\/8545-01 7″ mid-woofer uses an air dried Paper\/Carbon Fibre cone which is stiff, but without the associated severe cone break-ups of the usual stiff cone drivers.<\/p>\n

The D2905\/950000 1″ textile dome tweeter \u00a0uses a non-resonant chamber and a light ferrofluid in the air gap to ensure optimal linear mechanical behavior and minimal micro-dynamic non-linearity.<\/p>\n

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

18W\/8545-01<\/a>
\nD2905\/950000<\/a><\/p>\n

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

 <\/p>\n

Classic Two \u2013 M5<\/strong> uses a 27 liter enclosure.\u00a0 The enclosure is made of 19mm MDF with internal bracing and 18mm baffle edge round-over. The internal cabinet walls are taped with straps of bitumen pads in order 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 for the mid-woofer.<\/p>\n

\u00a0Baffle drawing and driver unit layout:<\/strong><\/p>\n

\"CT-M5<\/a><\/p>\n

This is a very large stand-mount loudspeaker and that might not fit to everyone\u2019s taste. As long as the baffle width and the driver unit lay-out isn\u2019t changed, it\u2019s up to the builders own choice on how the enclosure is shaped and built. It could be a curved cabinet or a squared box as mine or even be built as a floor-stander.<\/p>\n

If the loudspeaker is built as a floor-stander the listening height should be at the tweeter level or slightly below (20mm). Also, don\u2019t forget to place bracing in the middle of the enclosure and place some damping material at the same place in order to minimize internal standing waves.<\/p>\n

 <\/p>\n

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

\"CT-M5<\/a><\/p>\n

Bass-reflex 27liter Fp=36Hz<\/strong><\/p>\n

-6dB = 32Hz
\n-12dB = 26Hz<\/p>\n

Closed Box 27 liter Qtc=0.65<\/strong><\/p>\n

-6dB = 46Hz
\n-12dB = 29Hz<\/p>\n

Bass-reflex port:<\/strong><\/p>\n

50x110mm<\/p>\n

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

 <\/p>\n

\"CT-M5<\/a>\"CT-M5<\/a><\/p>\n

(click on picture to zoom)<\/p>\n

Left:<\/strong> Bass-reflex option<\/p>\n

Right:<\/strong> Closed box option<\/p>\n

Minimum impedance of 4,2 Ohm @ 430Hz.<\/p>\n

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

\"CT-M5<\/a><\/p>\n

The Classic Two \u2013 M5<\/strong> uses an acoustical fourth-order Linkwitz-Riley (LR4) filter topology.<\/p>\n

The mid-woofer cross-over filter section is an electrical second-order and consists of a coil and a cap (L2+C2<\/strong>) that shapes the cross-over slope to a LR4 roll-off with a targeted 1.9kHz cross-over point. The mid-woofer cross-over filter section also have a frequency response shaping circuit, the (C3+L3+R3<\/strong>).<\/p>\n

C3<\/strong> uses a 22uF and 1.5uF cap in parallell in order to achieve 23.5uF.<\/p>\n

The L3<\/strong> coil and R3<\/strong> should have a total resistance of 6.9 Ohm +\/- 0.2 Ohm.<\/p>\n

The tweeter cross-over filter section consists of two series resistor (R1<\/strong>) and\u00a0(R2<\/strong>), together with a second-order electrical filter (C1 + L1<\/strong>) that shapes the cross-over slope to a LR4 roll-off with a targeted 1.9kHz cross-over point.<\/p>\n

R1<\/strong> can be changed in order to fine tune the tweeter level according to personal preferences. Any value between 1.0-2.2 Ohm is valid.<\/p>\n

 <\/p>\n

Mid-woofer frequency response shaping circuit:<\/strong><\/p>\n

\"CT-M5<\/a><\/p>\n

(click on picture to zoom)<\/p>\n

Green:<\/strong> 15deg off-axis frequency response, no cross-over filter.<\/p>\n

Red:<\/strong> (L2+C2<\/strong>) coil and cap only.<\/p>\n

Blue:<\/strong> (L2+C2<\/strong>) coil and cap plus (C3+L3+R3<\/strong>) response shaping circuit.<\/p>\n

The (C3+L3+R3<\/strong>) response shaping circuit is absolutely essential and cannot be omitted.<\/p>\n

 <\/p>\n

Tweeter level options:<\/strong><\/p>\n

\"CT-M5<\/a><\/p>\n

(click on picture to zoom)<\/p>\n

The (R1<\/strong>) shapes the level and upper frequency response of the tweeter.<\/p>\n

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

 <\/p>\n

\"CT-M5<\/a>
\n\"CT-M5<\/a>\"CT-M5<\/a><\/p>\n

(click on picture to zoom)<\/p>\n

Top:<\/strong> 15deg off-axis frequency response.<\/p>\n

Left:<\/strong> 15deg off-axis frequency response, reverse polarity.<\/p>\n

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

The reverse polarity simulation shows a deep reverse null indicating an excellent phase tracking between the two driver units.<\/p>\n

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

 <\/p>\n

If nothing else is noted in the comments, the following frequency measurements of the finished loudspeaker are made at a 2m distance 20mm below tweeter height.<\/p>\n

All frequency response charts are presented in a 50db scale with 1\/24 octave smoothing and the measurements are valid down to 375Hz.<\/p>\n

\"CT-M5<\/a>\"CT-M5<\/a><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Frequency response on-axis:\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Frequency response 15deg off-axis:<\/strong><\/p>\n

Blue:<\/strong> Left Loudspeaker @ 2m<\/p>\n

Red:<\/strong> Right Loudspeaker @ 2m<\/p>\n

\"CT-M5<\/a>\"CT-M5<\/a><\/p>\n

(click on picture to zoom)<\/p>\n

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

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

 <\/p>\n

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