Excellence Two – M1 DXT

Concept:

 

Excellence Two – M1 DXT is a small sized 2-way stand-mount bass-reflex loudspeaker. It’s ideal for small to medium sized listening room. The tweeter can be fine-tuned to several different levels according to personal preferences and taste.

Loudspeaker driver units:

 

Excellence Two – M1 DXT uses two low distorting driver units from SEAS. The SEAS W12CY001 is one of the best 4.5” 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.

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.

For further details see:

W12CY001 (E0021)

SEAS 27TBCD/GB-DXT (H1499)

Cabinet:

 

Excellence Two – M1 DXT uses a 4,7 liter enclosure.  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 “breathe” properly, don’t forget to chamfer the baffle for the mid-woofer.

Remove the magnet rubber boot as it only hinders the air-flow and is of no use other than cosmetic.

 Baffle drawing and driver unit layout:                                               Chamfered baffle:

ET-M1-DXT -- Baffle drawingW12 chamfer

 

Box simulation:

ET-M1-DXT -- Box tuning

Bass-reflex 4,7liter Fp=54Hz (anechoic response)

-6dB = 46Hz
-12dB = 38Hz

Closed Box 4,7 liter Qtc=0.64 (anechoic response)

-6dB = 69Hz
-12dB = 44Hz

Bass-reflex port:

29x120mm

 

Impedance measurements:

 

ET-MM DXT -- Imp 1L vs 2R BR WT3ET-MM DXT -- Imp 1L vs 2R CB WT3

(click on picture to zoom)

Left: Bass-reflex option

Right: Closed box option

Minimum impedance of 6,2 Ohm @ 250Hz.

Cross-over design:

ET-M1-DXT -- x-over

The Excellence Two – M1 DXT uses an acoustical second-order Linkwitz-Riley (LR2) filter topology.

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’s not feasible.

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.

Thanks to the depth of the DXT lens, the acoustical center off-set is perfectly aligned without the need for such techniques.

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

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

Note! The tweeter should be connected with reversed polarity as shown in the cross-over schematics.

 

Mid-woofer frequency response shaping circuits:

ET-M1-DXT -- Sim 15deg notches

(click on picture to zoom)

Black: On-axis frequency response, no cross-over filter.

Blue: (L1) coil only.

Red: (L1) coil and (C4+L3) circuit only.

Green: (L1) coil, (C4+L3) and (C3+L2+R3) frequency response shaping circuits.

The (C4+L3) notches out the cone break-up at 10kHz and the (C3+L2+R3) 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.

Tweeter level options:

ET-M1-DXT -- Sim 15deg tw level

(click on picture to zoom)

The (C2+R2) shapes the level and upper frequency response of the tweeter. The value of (R2) can be changed to tailor the tweeter’s level to personal preferences.

R2 = 12 Ohm Reference Level

R2 = 15 Ohm +0,5dB

R2 = 20 Ohm +1dB

Cross-over simulation:

 

ET-M1-DXT -- Sim 15deg
ET-M1-DXT -- Sim 15deg RPxET-M1-DXT -- Sim 15deg phasex

(click on picture to zoom)

Top: 15deg off-axis frequency response.

Left: 15deg off-axis frequency response, reverse polarity.

Right: Individual driver unit phase tracking.

The reverse polarity simulation shows a deep reverse null indicating an excellent phase tracking between the two driver units.

Frequency measurements:

 

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.

All frequency response charts are presented in a 50db scale with 1/24 octave smoothing and the measurements are valid down to 400Hz.

ET-M1-DXT -- Freq 0deg 1L vs 2RET-M1-DXT -- Freq 15deg 1L vs 2R

                 Frequency response on-axis:                                                      Frequency response 15deg off-axis:

Blue: Left Loudspeaker @ 2m

Red: Right Loudspeaker @ 2m

ET-M1-DXT -- Freq 0-15-22.5deg 2RET-M1-DXT -- Freq 30-45-60deg 2R

(click on picture to zoom)

Left: On-axis, 15 and 22.5deg off-axis @ 2m
Right: 30, 45 and 60deg off-axis @ 2m

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.

 

Distortion measurements:

 

Measurement setup:

  • 42mm below tweeter-axis near-field measurement at 15cm
  • Frequency Range: 200-10000Hz
  • Baffle size WxH: 15×31cm

The distortion measurements are done in near-field and the amplifier output level was adjusted so that the fundamental is 90dB and 95dB at 1m. This setting simulates medium-high and high listening levels.

System-1L -- 90dB 15cmSystem-1L -- 95dB 15cm

(click on picture to zoom)

Left: 90dB @ 1m

Right: 95dB @ 1m

The large cone-break at 10kHz and its corresponding 3.3kHz third-order distortion profile is very well suppressed by the notch filters. Even at higher listening levels, this small loudspeaker has a remarkable low distortion profile throughout its usable frequency response.

Component list:

 

Component list ET-M1 DXT

The suggested components would cost about 700 US$, but the cost can be reduced by choosing less expensive cross-over components.

 

Summary:

 

This small mid-woofer driver can produce more bass than its size suggests. I haven’t yet heard a mid-woofer in this small size that can fill a room with such well defined and effortless bass.

However, the law of physics still applies and the small size has its limitations, but with a powerful amplifier you can play respectably strong before it loses control.

The midrange is clean, neutral and has a touch of warmth in its character.

The tweeter is well extended and neutral in its character.The tweeter works in harmony with the neutral clean character of the mid-woofer and they work well together.

The loudspeaker has a generous sound stage with a nice width and height. Thanks to the tweeters DXT lens the sweet spot exceptionally large.

With a sensitivity of 82dB 2.83v/1m, this loudspeaker does need some power to come alive  and I recommend an amplifier of at least 50W or more.

Recommended loudspeaker placement:

  •         No or little toe-in, slightly below tweeter height.
  •         >0.5 meters from back wall.
  •         2.5-3 meters apart.
  •         2.5-3 meters listening distance

 

The loudspeaker is optimized for a listening distance of >2.5m, but everything between 2-3.5m works fine. As always it pays off to test different loudspeaker placements and see what fits the room and personal preferences the best.

Technical specification:

 

Excellence Two – M1 DXT
Type: Two-way small sized stand-mount loudspeaker
Enclosure type: Bass-reflex
Woofer driver unit: 4,5” Magnesium cone. SEAS W12CY001 (E0021)
Tweeter driver unit: 1” Magnesium/alu dome with DXT lens SEAS 27TBCD/GB-DXT (1499)
Cross-over frequency: 2100Hz.
Cross-over function: LR second-order acoustically, first-order electrically with frequency response shaping circuits.
Frequency response: 45-20000Hz
Sensitivity: 82db 1m/2.83v
Nominal impedance: 8 Ohms
Minimum impedance: 6.2 Ohms
Enclosure volume: 4,7 liter
Weight: 6,8kg
Enclosure dimensions: (height x width x depth): 31,0×15,0x20,8cm

 

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Thank you!

/Göran

Author of the “AudioExcite Loudspeaker Design” website