{"id":5710,"date":"2016-03-16T17:10:06","date_gmt":"2016-03-16T17:10:06","guid":{"rendered":"http:\/\/www.audioexcite.com\/?page_id=5710"},"modified":"2020-11-28T14:38:58","modified_gmt":"2020-11-28T14:38:58","slug":"kensho-two-m2","status":"publish","type":"page","link":"https:\/\/www.audioexcite.com\/?page_id=5710","title":{"rendered":"Kensho Two – M2"},"content":{"rendered":"

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

 <\/p>\n

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

Kensho Two \u2013 M2<\/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 level can be fine-tuned according to personal preferences and taste.<\/p>\n

“Kensho” is Japanese for “seeing nature.” It means seeing one’s true nature; perceiving the self, but can also in Zen Buddhism mean “a brief experience of enlightenment”. <\/em><\/span><\/strong><\/p>\n

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

 <\/p>\n

Kensho Two \u2013 M2<\/strong><\/span> uses a 5″ mid-woofer from SB Acoustics and a ribbon tweeter from Fountek.<\/p>\n

The SB15MFC30-4 is a low distorting 4\u2126 mid-woofer with a mineral filled polypropylene cone.<\/p>\n

The Fountek NeoCD3.5H is a horn-loaded true ribbon tweeter that uses a reinforced sandwiched-aluminum ribbon diaphragm together with a strong neodymium magnet and it has a wide horizontal dispersion.<\/p>\n

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

Fountek NeoCD3.5H<\/a>
\nSB Acoustics SB15MFC30-4<\/a><\/p>\n

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

 <\/p>\n

The Kensho Two \u2013 M2<\/strong><\/span> uses an 8 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 7 liters (enclosure volume \u2013 drivers, filter and port).<\/p>\n

Cabinet drawing: Dayton 8 liters Curved Cabinet #302-701<\/a><\/p>\n

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

\"KT-M2<\/a><\/p>\n

It\u2019s a part of the design that the ribbon tweeter shouldn’t be flush mount, which in turn simplifies the loudspeaker build a lot.\u00a0 On the other hand,\u00a0the mid-woofer is flush mount and in order to let it \u201cbreathe\u201d properly, don\u2019t forget to chamfer the baffle.<\/p>\n

If you are building the 11 liter version you must keep the baffle width and driver unit lay-out, but you can make the loudspeaker taller by adding a couple of cm below the mid-woofer and make the enclosure deeper.<\/p>\n

I recommend using a separate compartment for the Fountek ribbon tweeter if you are building your own enclosure and not using the Dayton enclosure option.<\/p>\n

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

\"KT-M2<\/a><\/p>\n

Bass-reflex 8 liter Fp=46Hz<\/strong><\/p>\n

-6dB = 44Hz
\n-12dB = 35Hz<\/p>\n

Bass-reflex port:<\/strong> 30x90mm<\/p>\n

(Optional) Bass-reflex 11 liter Fp=43Hz
\n<\/strong><\/p>\n

-6dB = 38Hz
\n-12dB = 32Hz<\/p>\n

Bass-reflex port:<\/strong> 45x155mm<\/p>\n

Make the bass-reflex port about 25% longer than the above example. Measure, cut, measure, cut and so on until you get the desired port tuning frequency.<\/p>\n

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

 <\/p>\n

\"KT-M2<\/a><\/p>\n

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

Blue:<\/strong> Left loudspeaker<\/p>\n

Green:<\/strong> Right loudspeaker<\/p>\n

Minimum impedance of 3,55 Ohm @ 200Hz.<\/p>\n

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

\"KT-M2<\/a><\/p>\n

The Kensho Two \u2013 M2<\/strong><\/span> uses an acoustical fourth-order Linkwitz-Riley (LR4) filter topology.<\/p>\n

The mid-woofer cross-over filter section is an electrical fourth-order and consists of two coils and two caps (L2+L3<\/strong> and C3+C4<\/strong>) that shapes the cross-over slope to a LR4 roll-off with a targeted 3kHz cross-over point.<\/p>\n

The L2<\/strong> coil and L3<\/strong> should have a total series resistance of 0.4 Ohm +\/- 0.1 Ohm.<\/p>\n

The tweeter cross-over filter section consists of two resistor (R1<\/strong>) and\u00a0(R2<\/strong>), together with a third-order electrical filter (C1 + L1+C2<\/strong>) that shapes the cross-over slope to a LR4 roll-off with a targeted 3kHz cross-over point.<\/p>\n

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

R2<\/strong> can be changed in order to fine tune the tweeter level according to personal preferences. Any value between 4,7-8,2 Ohm is valid.<\/p>\n

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

R2= 8.2 Ohm +0,5dB<\/p>\n

R2= 6.8 Ohm Reference level<\/p>\n

R2= 5.6 Ohm -1dB<\/p>\n

R2= 4,7 Ohm -2dB<\/p>\n

Warning!<\/strong> Never connect your ribbon tweeter without a protection cap or the tweeter cross-over attached. You will most likely destroy your ribbon tweeter when measured or played without any cross-over.<\/p>\n

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

 <\/p>\n

\"KT-M2<\/a>
\n\"KT-M2<\/a>\"KT-M2<\/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. The mid-woofer response is bit elevated in the mids between 0.6-1.3kHz. It rolls off steep above 6.5kHz.<\/p>\n

The rising response of the ribbon tweeter between 12-20kHz can be corrected for, but it’s a design choice not to do so. Correcting it doesn\u2019t improve the sonic performance and the rising response only adds more airiness to the sound character.<\/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.<\/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

\"KT-M2<\/a>\"KT-M2<\/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

\"KT-M2<\/a>\"KT-M2<\/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

\"KT-M2<\/a>\"KT-M2<\/a><\/p>\n

Left:<\/strong> 15 deg off-axis @ 2m
\nRight:<\/strong> 15 deg off-axis @ 2m, reverse tweeter polarity<\/p>\n

The tweeter is a bit \u201chot\u201d in the on-axis frequency response, but at 15deg off-axis it’s very linear between 1.5-10kHz. The 15deg off-axis response is the angle the design has been optimized for. The ribbon tweeter has an extended frequency response up to 35kHz with a rising response between 12-20kHz, but this evens out off-axis.<\/p>\n

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

 <\/p>\n

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