Revelation Two – M4 WG

Concept:

Revelation Two – M4 WG is a medium sized 2-way stand-mount loudspeaker for small to medium sized listening rooms. The main feature of this loudspeaker is the use of a tweeter waveguide for improved dispersion and a smooth power response.

Loudspeaker driver units:

 

The Revelation Two – M4 WG uses the ScanSpeak 15W/4531G00 Revelator mid-woofer. The 15W/4531G00 is one of the best mid-woofers available to the DIY market. It has a nice low extension and a very nice mid-range reproduction.

The tweeter section consists of the ScanSpeak Classic D2905/9500 soft dome tweeter paired with a WG148R waveguide from Visaton. This tweeter has a very smooth frequency response and works perfectly with the Visaton waveguide.

For further details see:
ScanSpeak 15W/4531G00
ScanSpeak D2905/950000
Visaton WG148R

Waveguide:

 

 

The Revelation Two – Monitor WG design uses the Visaton WG148R waveguide. This is a good quality waveguide which is easily modified to fit just about any 25-30mm dome tweeter with a flat face-plate. With a size of 148mm it’s usable in a  tweeter waveguide setup down to about 2.2-2.5kHz.

This waveguide is also available in square formed waveguide, the Visaton WG220x150. If the round version isn’t available, the squared version can be used, but needs some additional modifications since it’s wider and doesn’t fit the baffle without modification.

Waveguide mounting:

 

The original screw attachment is made for Visaton tweeters and doesn’t fit the ScanSpeak D2905/9500. This is easily fixed by attaching a couple of strips of double sided tape to the tweeters front-plate and then attach it to the waveguide while carefully checking that it’s exactly centered on it.

Now it’s possible to drill new holes for a M4 screw and nut. In the picture a 4x16mm screw and M4 nut was used.

In order to make a 14cm center to center distance between the mid-woofer and tweeter it’s necessary to route off some material from the waveguide. The easiest way to do this is to first route and cut the hole for the waveguide. Then fasten it with screws to the baffle and then route the mid-woofer cut out while the waveguide is attached to the baffle.

Frequency response D2905/9500 + WG148R:

 

(click on picture to zoom)

Upper Left: 0-60deg off-axis frequency response @ 1m 200Hz-30kHz.

Upper Right: 0-60deg off-axis frequency response @ 1m 2kHz-30kHz.

Lower Left: On-axis D2905/9500+WG148R vs D2905/9500 frequency response @ 1m.

Lower Right: On-axis D2905/9500+WG148R vs D2905/9500 + cross-over frequency response @ 1m.

The Scanspeak D2905/9500 tweeter has a very smooth frequency response, but it also works very well together with the Visaton waveguide and it doesn’t have any deep suck outs around 11-13kHz, which is very common in these type of waveguide and tweeter combinations. The waveguide gain is about 7dB @ 2.2kHz.

Cabinet:

 

Revelation Two – M4 WG uses a 14 liter “Dayton Audio” enclosure. This is a very nicely built curved cabinet with a 25mm (1″) 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 – drivers, filter and port).

Cabinet drawing: Dayton 14 liters Curved Cabinet #302-721

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 “breathe” properly, don’t forget to chamfer the baffle.

Note! The waveguide should be flush mounted 4.2mm and the mid-woofer should be flush-mounted 5.5mm.

Baffle drawing and driver unit layout:                                Chamfered baffle:  

RT-M-WG Baffle drawingchamfer

Note! In order to optimize driver integration and the phase response of the loudspeaker the Dayton Audio enclosure should be tilted 2 degrees backwards. As an alternative, the Dayton Audio enclosure can be turned upside down and the mid-woofer should then be placed at ear height. If a custom made enclosure is used, I recommend to build it with a 2 degrees sloping baffle.

Box simulation:

RT-M-WG -- Box tuning

There are three different box tuning options in order to satisfy different bass preferences and room tuning options.

Option 1:
Closed box (anechoic response)

-6db = 52Hz

-12db = 35Hz

Option 2 (reference):
Bass-reflex box with Fb = 44Hz (anechoic response)

-6db = 37Hz

-12db = 30Hz

Option 3:
Bass-reflex box with Fb = 40Hz (anechoic response)

-6db = 35Hz

-12db = 28Hz

The closed box version can be an alternative if the loudspeaker is going to be placed close to the back wall. This loudspeaker design has a surprisingly good bass performance when room gain is included.

Use the bass-reflex tuning that fits the room best as well as your personal preference and taste.

Bass-reflex ports:

Option 2: 50x150mm

Option 3: 50x200mm

Cross-over design:

(click on picture to zoom)

Revelation Two – M4 WG uses a second-order (acoustical) Linkwitz-Riley (LR2) filter topology.

When using a shallow sloped cross-over like in this case a LR2 filter topology, the mid-woofer and the tweeter need to have their “relative acoustic center off-set” adjusted. In this case a waveguide and a slight baffle slope is used for the purpose of time aligning the drivers as well as to improve the loudspeakers dispersion and power response.

The mid-woofer cross-over filter section is an electrical second-order and consists of one coil, a cap and a resistor (L1+C2+R3) that shapes the cross-over slope to an acoustical LR2 roll-off with a targeted 2.2kHz cross-over point. The L1 coil should have a series resistance of 0.3Ω +/- 0.1Ω.

The mid-woofer cross-over filter section also have a frequency response shaping circuit (C3+L2+R4). The summed resistance of the L2 coil and R4 resistor should have a summed total resistance of 12Ω +/- 1Ω.

The System Impedance Correction circuit (L3+C4+R5) is optional and is only needed when using tube amplifiers. The summed resistance of the L3 coil and R5 resistor should have a summed total resistance of 5.8Ω +/- 0.5Ω.

The tweeter cross-over filter section consists of two resistor (R1) and (R2), together with a first-order electrical filter (C1) that shapes the cross-over slope to an acoustical LR2 roll-off with a targeted 2.2kHz cross-over point.

Note! The tweeter is connected in reverse polarity. The tweeter level can be adjusted by changing the (R1 and R2) resistors according to the cross-over scheme.

Mid-woofer frequency response shaping circuit:

(click on picture to zoom)

Left: The effect of C3+L2+R4.

Right: The effect of C2+R3.

The response shaping circuit (C3+L2+R4) together with the large L1 coil makes a full Baffle Step Compensation (BSC) for this loudspeaker. Without the response shaping circuit the mid-range can sound a bit raw and rugged, but the circuit helps to smooth out the mid-range and makes the 0.5kHz-1.5kHz frequency response more linear. The C2+R3 ensures that the low-pass frequency roll-off is kept at a LR2 topology above 3kHz.

Alternative cross-over design:

(click on picture to zoom)

This cross-over achieves exactly the same LR2 toplogy, frequency, phase and impedance response as the other conventional cross-over. The difference is that this is a Symmetrically Balanced Cross-over design (SBC). This cross-over version is a bit more complex since it requires additional cross-over components.

Why use a SBC type of cross-over? The claims made is that this type of cross-over has sonic advantages and that the cross-over is an easier load for the amplifier when the components are evenly distributed between the + and – poles.

Since this is DIY and it’s fun to experiment, test and judge by yourself if it gives any sonic improvements!

Details:

The 4.4uF value of C1 and C2 is achieved by using two 2.2uF caps in parallel. This requires four 2.2uF caps per speaker. A 4.7uF cap can be used instead of 4.4uF and results in a slightly lower cross-over point of 2.1kHz instead of 2.2kHz.

The 0.75Ω value of R1 and R2 is achieved by using two 1.5Ω resistors in parallel. This requires four 1.5Ω resistors per speaker. A 0.82Ω resistor can be used instead of two 1.5Ω resistors in parallel, but dampens the tweeter lever slightly more.

Note! The tweeter is connected in reverse polarity. The tweeter level can be adjusted by changing the (R1, R2 and R3) resistors according to the cross-over scheme.

In this version two 0.56mH foil coils are used, but two 0.55mH air-core coils can be used as well. The difference between 0.55mH and 0.56mH coils is negligible, but foil coils have sonic improvements compared to air-core coils.

Cross-over simulation:

 

(click on picture to zoom)

Top: On-axis frequency response.

Left: On-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. Also, the tweeter and mid-woofer’s individual phase track each other closely above and below the cross-over point.  The tweeter rolls off slightly steeper than a secon-order slope below 1.5kHz and the mid-woofer rapidly rolls off above 10kHz.

Impedance measurements:

 

(click on picture to zoom)

Left: Measured system impedance vs system impedance with impedance correction.

Right: Measured electrical phase vs electrical phase with impedance correction.

Impedance minimum of 3.8Ω @ 180Hz. Bassreflex port tuning @ 44Hz. The system impedance corrected cross-over has an impedance of 5.5Ω between 0.6kHz-20kHz +/- 0.2Ω.

Frequency measurements:

 

The following frequency measurements of the finished loudspeaker are made at a 2m distance. All frequency response charts are presented in a 80db scale with no smoothing and the measurements are valid down to 375Hz.

(click on picture to zoom)

Top: 0-60deg frequency response and 0-60deg average horizontal frequency response @2m.

Left: On-axis frequency response @ 2m.

Right: 15deg off-axis frequency response @ 2m.

The actual measured system frequency response match the simulations very well and the frequency response is smooth, but there is small bump at 2kHz. This is mainly caused by a small bump in the mid-woofer’s response in the same frequency area. The bump is so minor so it doesn’t affect the overall sound quality.

Distortion measurement:

 

Measurement setup:

  • Tweeter-axis near-field measurement at 20cm
  • Frequency Range: 200-10000Hz
  • Baffle size WxH: 21,6×35,6cm

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.

 

(click on picture to zoom)

Left: SBC x-over version, 90dB @ 1m
Right: SBC x-over version, 95dB @ 1m

Below 1kHz the distortion profile is dominated by a harmless elevated 2nd order distortion. Odd order distortion is low throughout the measured frequency range. Overall, this is a very low distorting loudspeaker!

Component list:

 

(click on picture to zoom)

Left: Component list.

Right: Component list, SBC cross-over version.

This loudspeaker isn’t exactly cheap when premium drivers like ScanSpeak is used, but it can be built less expensive if the enclosures are custom built instead of the prefabricated from Dayton Audio. Cheaper cross-over components can also be used, but at least a high quality capacitor for the tweeter circuit is recommended.

Summary:

 

The ScanSpeak Revelator mid-woofer is an amazing driver that sounds several sizes larger than it is. In this fully “baffle step” compensated design, the bass is very powerful and authoritative with a lush mid-range.  The waveguide supported tweeter has clarity, detail and is well balanced and delicate.

The loudspeaker have a pinpoint imaging and a large soundstage with a good sense of depth and three dimensionality.

The crossing between the mid-woofer and tweeter is seamless and together they deliver a nice presence and a effortless, refined and open sound.

Recommended loudspeaker placement:

  • Toed-in towards the listener.
  • >0.6 meters from back wall.
  • >2.5 meters listening distance with tweeter at ear height.

The loudspeaker is optimized for a listening distance of >2.5m. As always it pays off to test different loudspeaker placements and see what fits the room and personal preferences the best, but since this lodspeaker is very bass capable, it shouldn’t be placed too close to back walls or corners. If the speaker must be placed close to the backwall, a closed box or front ported enclosure is recommended.

Technical Specification:

 

Revelation Two – M4 WG
Type: Two-way medium sized stand-mount loudspeaker with waveguide supported tweeter.
Enclosure type: Bass-reflex
Woofer driver unit: 5,5” Sliced paper cone. ScanSpeak 15W/4531G00
Tweeter driver unit: 1” Soft dome. ScanSpeak D2905/9500 and 5,5″ waveguide
Cross-over frequency: 2.2kHz
Cross-over function: Second-order Linkwitz-Riley (acoustically)
Frequency response:  37-25000Hz -6/+0 db (on-axis)
Sensitivity: 85db 2.83v/1m
Impedance:
Enclosure volume: 14 liter
Weight: 11kg
Enclosure dimensions: (height x width x depth): 356x216x317mm (14″x8.5″x12.5″)

 

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Thank you!

/Göran

Author of the “AudioExcite Loudspeaker Design” website