{"id":2386,"date":"2012-06-22T14:36:44","date_gmt":"2012-06-22T14:36:44","guid":{"rendered":"http:\/\/www.audioexcite.com\/?page_id=2386"},"modified":"2020-11-28T14:41:33","modified_gmt":"2020-11-28T14:41:33","slug":"prestigious-two-monitor-dxt","status":"publish","type":"page","link":"https:\/\/www.audioexcite.com\/?page_id=2386","title":{"rendered":"Prestigious Two – Monitor DXT"},"content":{"rendered":"

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

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

The loudspeaker uses \u201cDiffracton Expansion Technology\u201d (DXT) for optimum power response, reduced baffle diffraction influence, off-axis dispersion and directivity control.<\/p>\n

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

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The Prestigious Two \u2013 Monitor DXT<\/strong><\/span> loudspeaker uses affordable driver units from the SEAS Prestige series.<\/p>\n

The SEAS U16RCY\/P is a mid-woofer with a woven polypropylene cone. It has an extended frequency response with a smooth frequency roll-off above 5kHz.<\/p>\n

Considering its size the mid-woofer has an astonishingly fast, powerful and accurate bass reproduction.<\/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 diffractions.<\/p>\n

For further details see:
\nSEAS U16RCY\/P (H1520)<\/a>
\nSEAS 27TBCD\/GB-DXT (H1499)<\/a><\/p>\n

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

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\"\"<\/a>The Prestigious Two \u2013 Monitor DXT<\/strong><\/span> uses 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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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

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

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The\u00a0 bass-reflex port tuning frequency can be fine-tuned to fit personal preferences. I think the Fp=44Hz gives the best balance between fast bass articulation and bass depth.<\/p>\n

The closed box version isn\u2019t really an option, unless it\u2019s paired and crossed-over with a sub-woofer.<\/p>\n

~13 liter bass-reflex box with port tuned to 44Hz (anechoic response)<\/p>\n

-3db = 51Hz<\/p>\n

-6db = 42Hz<\/p>\n

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

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

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The Prestigious Two \u2013 Monitor DXT<\/strong><\/span> uses a true symmetrical second-order Linkwitz-Riley (LR2) filter topology and has a minimalistic design approach with only one cross-over component + tweeter padding resistor in series with the driver units.<\/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

However, 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 slopes to a LR2 roll-off with a targeted 3kHz cross-over point. The inductor (L1<\/strong>) also tunes the \u201cBaffle Step Compensation\u201d (BSC).<\/p>\n

The tweeter cross-over filter section consists of a single tweeter padding resistor (R1<\/strong>) and a first-order electrical filter (C1<\/strong>) that shapes the cross-over slope to a LR2 roll-off with a targeted 3kHz cross-over point. The value of (R1<\/strong>) can be changed to tailor the tweeter level to personal preferences.<\/p>\n

R1<\/strong> = 1.8Ohm -> +1dB
\nR1<\/strong> = 2.2Ohm -> 0dB (Reference Tweeter Level).
\nR1<\/strong> = 2.7Ohm -> -1dB<\/p>\n

The tweeter is connected with reverse polarity and (C2+R2+R3<\/strong>) shape the tweeters frequency response and flatten the response at higher frequencies.<\/p>\n

(L2+C3+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 6 Ohms, within 200-10000Hz.<\/p>\n

Update! (20120710)<\/span><\/strong><\/p>\n

I recommend everyone who is interesting in this loudspeaker design to look at the additional tweeter level options that\u2019s available here:<\/p>\n

Additional tweeter level options<\/a><\/p>\n

I highly recommend buying a couple of more resistors in order to fine tune the tweeter level to your personal liking.<\/p>\n

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

The reverse polarity simulation shows a deep reverse null indicating an excellent phase tracking between the two driver units. The reverse polarity response is a little ragged , but as can be seen further down in the frequency measurements section it\u2019s only visible in the cross-over simulation.<\/p>\n

I personally prefer the 0dB or the +1dB tweeter level depending on which HiFi equipment I\u2019m currently using or for that matter, which recording I\u2019m listening to. As usual, tweeter level padding must be fine-tuned to personal taste and preferences, hence I always give some level options to try out.<\/p>\n

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

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

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

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

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

It doesn\u2019t get better than this, a perfect impedance match between left and right loudspeaker. With the “System Impedance Correction” circuit the average impedance is 6 Ohms, which makes the loudspeaker an easy amplifier load that is tube-amp friendly.<\/p>\n

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Frequency measurements:<\/strong><\/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 400Hz.<\/p>\n

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

Top:<\/strong> Blue = Left Loudspeaker Red = Right Loudspeaker \u2013 15deg off-axis @ 2m<\/p>\n

Lower left:<\/strong> System and individual driver unit frequency response<\/p>\n

Lower right:<\/strong> Reverse null response<\/p>\n

Nothing to complain about here, a nice frequency response match between the two loudspeakers. Above 17kHz some variation in the top-end response.<\/p>\n

A very deep reverse null indicating excellent phase behavior in the cross-over region.<\/p>\n

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

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

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\u201cPower response”, showing the average frequency response for the 0, 15, 22.5, 30, 45 and 60deg frequency measurements.<\/p>\n

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

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