{"id":5200,"date":"2015-05-23T15:59:28","date_gmt":"2015-05-23T15:59:28","guid":{"rendered":"http:\/\/www.audioexcite.com\/?page_id=5200"},"modified":"2020-11-28T14:37:53","modified_gmt":"2020-11-28T14:37:53","slug":"excellence-two-m1-dxt","status":"publish","type":"page","link":"https:\/\/www.audioexcite.com\/?page_id=5200","title":{"rendered":"Excellence Two – M1 DXT"},"content":{"rendered":"

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

 <\/p>\n

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

Excellence Two \u2013 M1 DXT<\/strong><\/span> is a small sized 2-way stand-mount bass-reflex loudspeaker. It\u2019s ideal for small to 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

Excellence Two \u2013 M1 DXT<\/strong><\/span> uses two low distorting driver units from SEAS. The SEAS W12CY001 is one of the best 4.5\u201d mid-woofers available to the DIY market. It has a nice low-frequency extension and the magnesium cone act as a piston within its usable frequency range, a class of its own.<\/p>\n

The SEAS 27TBCD\/GB-DXT is an aluminium\/magnesium alloy dome tweeter with a DXT lens. The DXT technology solves several well-known issues regarding; directivity control, off-axis response, integration with midrange units and baffle diffraction.<\/p>\n

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

W12CY001 (E0021)<\/a><\/p>\n

SEAS 27TBCD\/GB-DXT (H1499)<\/a><\/p>\n

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

 <\/p>\n

Excellence Two \u2013 M1 DXT<\/strong> uses a 4,7 liter enclosure.\u00a0 The enclosure is made of 19mm MDF and the internal cabinet walls are taped with 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

Remove the magnet rubber boot as it only hinders the air-flow and is of no use other than cosmetic.<\/p>\n

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

\"ET-M1-DXT<\/a>\"W12<\/a><\/p>\n

 <\/p>\n

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

\"ET-M1-DXT<\/a><\/p>\n

Bass-reflex 4,7liter Fp=54Hz (anechoic response)
\n<\/strong><\/p>\n

-6dB = 46Hz
\n-12dB = 38Hz<\/p>\n

Closed Box 4,7 liter Qtc=0.64 (anechoic response)
\n<\/strong><\/p>\n

-6dB = 69Hz
\n-12dB = 44Hz<\/p>\n

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

29x120mm<\/p>\n

 <\/p>\n

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

 <\/p>\n

\"ET-MM<\/a>\"ET-MM<\/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 6,2 Ohm @ 250Hz.<\/p>\n

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

\"ET-M1-DXT<\/a><\/p>\n

The Excellence Two \u2013 M1 DXT<\/strong> uses an acoustical 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 as in this design when using LR2 filter topologies it\u2019s not feasible.<\/p>\n

Other choices for dealing with the driver units relative acoustic center off-set is to use a slanted or stepped baffle as well as the use of an electrical circuit to time delay the tweeter in order to adjust the acoustical center off-set.<\/p>\n

Thanks to the depth of the DXT lens, the acoustical center off-set is perfectly aligned without the need for such techniques.<\/p>\n

The mid-woofer cross-over filter section is an electrical first-order and is very simple and consists only of a large coil (L1<\/strong>) that shapes the cross-over slope to a LR2 roll-off with a targeted 2.1kHz cross-over point. The inductor (L1<\/strong>) also tunes the \u201cBaffle Step Compensation\u201d (BSC). The mid-woofer cross-over filter section also have two frequency response shaping circuits, the (C4+L3<\/strong>) and (C3+L2+R3<\/strong>).<\/p>\n

The tweeter cross-over filter section consists of a single tweeter series resistor (R1<\/strong>) and\u00a0(C2+R2<\/strong>) together with a first-order electrical filter (C1<\/strong>) that shapes the cross-over slope to a LR2 roll-off with a targeted 2.1kHz cross-over point.<\/p>\n

Note!<\/strong> The tweeter should be connected with reversed polarity as shown in the cross-over schematics.<\/p>\n

 <\/p>\n

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

\"ET-M1-DXT<\/a><\/p>\n

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

Black:<\/strong> On-axis frequency response, no cross-over filter.<\/p>\n

Blue:<\/strong> (L1<\/strong>) coil only.<\/p>\n

Red:<\/strong> (L1<\/strong>) coil and (C4+L3<\/strong>) circuit only.<\/p>\n

Green:<\/strong> (L1<\/strong>) coil, (C4+L3<\/strong>) and (C3+L2+R3<\/strong>) frequency response shaping circuits.<\/p>\n

The (C4+L3<\/strong>) notches out the cone break-up at 10kHz and the (C3+L2+R3<\/strong>) notches out the remaining frequency peak between 5-7,5kHz. These two frequency response circuits are very important and cannot be omitted. If they are not implemented correctly, the mid-woofer will sound very bad. The cross-over and the response shaping circuits dampens the cone break-up at 10kHz by more than 55dB and shapes the mid-woofer roll-off to a LR2 cross-over slope.<\/p>\n

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

\"ET-M1-DXT<\/a><\/p>\n

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

The (C2+R2<\/strong>) shapes the level and upper frequency response of the tweeter. The value of (R2<\/strong>) can be changed to tailor the tweeter’s level to personal preferences.<\/p>\n

R2<\/strong> = 12 Ohm Reference Level<\/p>\n

R2<\/strong> = 15 Ohm +0,5dB<\/p>\n

R2<\/strong> = 20 Ohm +1dB<\/p>\n

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

 <\/p>\n

\"ET-M1-DXT<\/a>
\n\"ET-M1-DXT<\/a>\"ET-M1-DXT<\/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 42mm 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 400Hz.<\/p>\n

\"ET-M1-DXT<\/a>\"ET-M1-DXT<\/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

\"ET-M1-DXT<\/a>\"ET-M1-DXT<\/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

My tweeter samples have slightly different frequency responses above 15kHz. On-axis, the frequency response is a bit “hot” between 6-9kHz, but is smooth around the 15deg off-axis response and beond.<\/p>\n

 <\/p>\n

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

 <\/p>\n

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