Revelation Two – Monitor WG

Concept:

 

Revelation Two – Monitor 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 smooth power response.

Loudspeaker driver units:

 

The Revelation Two – Monitor 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 Dayton Audio RS28F-4 soft dome tweeter paired with a WG148R waveguide from Visaton.

For further details see:
ScanSpeak 15W/4531G00
Dayton Audio RS28F-4
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 waveguide tweeter setup down to about 2.3-2.5kHz.

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 Dayton Audio RS28F-4. 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 RS28F-4 + WG148R:

 

RT-M-WG_WG -- Freq 0-15-22.5degRT-M-WG_WG -- Freq 30-45-60deg
RT-M-WG_WG -- Freq 0-15-22.5deg 10kRT-M-WG_WG -- Freq 30-45-60deg 10k
(click on picture to zoom)

Raw frequency response without cross-over:

Left: On-axis, 15 and 22.5deg off-axis

Right: 30, 45 and 60deg off-axis

The RS28F-4 + WG148R combo has a usable output down to about 2kHz. It has a very smooth frequency response up to 10kHz. In addition to the RS28F-4 tweeter’s natural rising response an elevated frequency response can be seen above at 15kHz.

Cabinet:

 

Revelation Two – Monitor 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.

Baffle drawing and driver unit layout:                                Chamfered baffle:  

RT-M-WG Baffle drawingchamfer

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

 

If the loudspeaker is placed close to the back wall, the closed box version can be an alternative. It has a surprisingly good bass performance when room gain is included.

Both bass-reflex options are good. Use the bass-reflex tuning that fits the room best and your personal preference and taste.

Bass-reflex ports:

Option 2: 50x150mm

Option 3: 50x200mm

Cross-over design:

 

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

When using a shallow sloped cross-over like the LR2 filter topology, one of the most important design factors for a successful implementation is to time align the loudspeaker drivers. The mid-woofer and the tweeter need to have their “relative acoustic center off-set” adjusted. In this case a waveguide is used for the purpose of time align the drivers as well as to improve the dispersion and the power response.

Three different cross-over versions are available as follows:

The Simplistic cross-over (SIM):

RT-M-WG_SIM -- x-over v2

This is really an unusual sight for a true LR2 cross-over topology. With only 4 components, where only two components are in series with the drivers signal path and with no resistor in series with the tweeter. This is truly a super simple cross-over design, hence the name Simplistic.

The mid-woofer cross-over filter section consists of a coil (L1) and an impedance equalization circuit (C2+R1) which shapes the cross-over slopes to a LR2 (acoustical) roll-off with a targeted 2.5kHz cross-over point.

The Tweeter cross-over filter section consists of a single cap (C1). That’s it!

Note! The tweeter should be connected with reverse polarity.

Cross-over simulation (SIM):

RT-M-WG_SIM -- Sim 15deg

RT-M-WG_SIM -- Sim 15deg RPRT-M-WG_SIM -- Sim 15deg phase

(click on picture to zoom)

Top: Tweeter-axis, 15deg off-axis response.

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

Right: Individual driver unit phase tracking.

The reverse polarity simulation shows a very deep reverse null at the 2.5kHz cross-over frequency, indicating a good phase tracking between the two driver units at the cross-over point. The mids region (0.5-1 kHz) have some 1.5dB extra energy and gives a bit more “presence” to the sound character.

The mid-woofer have a perfect smooth low-pass frequency roll-off. The tweeter have a small knee around the tweeters resonance frequency which a single cap can’t deal with, but overall the tweeters high-pass frequency roll-off work as intended.

The Intermediate cross-over (INT):

RT-M-WG_INT -- x-over

The Intermediate cross-over uses a response shaping circuit (C2+L1+R1) to linearise the impedance peak at the tweeters resonance frequency. This circuit produces a smoother high-pass frequency roll-off compared to the Simplistic cross-over. If using a different coil (L1) than shown in the schematics, the sum of the resistance for the coil (L1) and the resistor (R1) should be about 5,4 Ohm.

The mid-woofer cross-over filter section is the same as the Simplistic cross-over and consists of a coil (L2) and an impedance equalization circuit (C3+R2) which shapes the cross-over slopes to a LR2 (acoustical) roll-off with a targeted 2.5kHz cross-over point.

Note! The tweeter should be connected with reverse polarity.

Cross-over simulation (INT):

RT-M-WG_INT -- Sim 15degRT-M-WG -- INT and PER vs SIM tweeter

RT-M-WG_INT -- Sim 15deg RPRT-M-WG_INT -- Sim 15deg phase

(click on picture to zoom)

Top left: Tweeter-axis, 15deg off-axis response.

Top right: The effect of the response shaping circuit (C2+L1+R1).

Lower left: Tweeter-axis, 15deg off-axis response, reverse polarity.

Lower right: Individual driver unit phase tracking.

The reverse polarity simulation shows the same deep reverse null at the 2.5kHz cross-over frequency as the Simplistic cross-over, indicating a good phase tracking between the two driver units at the cross-over point. The Intermediate cross-over also have the same 1.5dB extra energy in the mids region (0.5-1 kHz) as the Simplistic cross-over.

With the response shaping circuit (C2+L1+R1) the tweeter have a perfect smooth high-pass frequency roll-off.

The Perfectionist cross-over (PER):

RT-M-WG_PER -- x-over v2

Compared to the Intermediate cross-over the Perfectionist cross-over uses a response shaping circuit (C3+L3+R2) to smooth out the mids frequency response bump between 0.5-1kHz. If using a different coil (L3) than shown in the schematics, the sum of the resistance for the coil (L3) and the resistor (R2) should be about 8,4 Ohm.

Note! The tweeter should be connected with reverse polarity.

Cross-over simulation (PER):

RT-M-WG_PER -- Sim 15deg v2RT-M-WG -- SIM and INT vs PER mid-woofer
RT-M-WG_PER -- Sim 15deg RP v2RT-M-WG_PER -- Sim 15deg phase v2

(click on picture to zoom)

Top left: Tweeter-axis, 15deg off-axis response.

Top right: The effect of the response shaping circuit (C3+L3+R2).

Lower left: Tweeter-axis, 15deg off-axis response, reverse polarity.

Lower right: Individual driver unit phase tracking.

The reverse polarity simulation shows the same deep reverse null at the 2.5kHz cross-over frequency as the Simplistic and the Intermediate cross-over, indicating a good phase tracking between the two driver units at the cross-over point.

The Perfectionist cross-over have an almost perfect flat and linear frequency response where the 1.5dB extra energy in the mids region (0.5-1 kHz) is completely flattened out.

Impedance measurements:

 

RT-M-WG_INT -- Imp 1L vs 2RRT-M-WG_INT -- Imp INT vs PER

(click on picture to zoom)

Left: Blue=Left loudspeaker, Green=Right loudspeaker
Right: Blue=Perfectionist cross-over, Green=Intermediate cross-over

4 Ohm impedance minimum @ 400Hz and 3.8 Ohm @ 20kHz for the Intermediate cross-over version.

Frequency measurements:

 

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.

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

RT-M-WG_INT -- Freq 0-60deg PR

Average frequency response from the on-axis, 15, 22.5, 30, 45 and 60deg off-axis measurements:

RT-M-WG_INT -- Freq 0deg 1L vs 2RRT-M-WG_INT -- Freq 15deg 1L vs 2R

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

Blue: Left Loudspeaker

Red: Right Loudspeaker

RT-M-WG_INT -- Freq 0-15-22.5degRT-M-WG_INT -- Freq 30-45-60deg

(click on picture to zoom)

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

The Intermediate cross-over have overall a very smooth frequency response. The tweeter response gradually rises from about 15kHz.

Distortion measurement:

 

Measurement setup:

  • Tweeter-axis near-field measurement at 20cm
  • Frequency Range: 200-10000Hz
  • Baffle size WxH: 21,56×35,56cm

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

System-1L_SIM--20cm 95dbSystem-2R_SIM--20cm 95db

System-1L_INT--20cm 95dbSystem-2R_INT--20cm 95db

System-1L_PER--20cm 95dbSystem-2R_PER--20cm 95db

(click on picture to zoom)

Top left: Left loudspeaker, 95dB @ 1m  (Simplistic cross-over)

Top right: Right loudspeaker, 95dB @ 1m (Simplistic cross-over)

Middle left: Left loudspeaker, 95dB @ 1m (Intermediate cross-over)

Middle right: Right loudspeaker, 95dB @ 1m (Intermediate cross-over)

Lower left Left loudspeaker, 95dB @ 1m (Perfectionist cross-over)

Lower right: Right loudspeaker, 95dB @ 1m (Perfectionist cross-over)

The Revelation Two – Monitor WG is a very low distorting loudspeaker with a remarkable low odd order harmonics above 1kHz. The third order harmonics is well below 0.1%, even at higher listening levels. The more harmless second order harmonics is somewhat elevated compared to the odd-order at lower frequencies, but is reduced in the Perfectionist cross-over.

There isn’t much difference between the “Intermediate” and “Simplistic” cross-over versions and from a distortion standpoint, either one can be chosen.

Component list:

 

RT-M-WG -- Component list

(click on picture to zoom)

With an approximate cost of 1150 US$ a pair it’s not a super cheap stand-mount loudspeaker, but it can be built cheaper if not using premium cross-over parts, binding posts and prefabricated enclosures. However I can strongly recommend Mundorf cross-over parts which sounds very good with these drivers.

Summary:

 

The ScanSpeak Revelator mid-woofer is a very nice sounding driver and it has a mid-range with good resolution and the bass is deep and well defined for its size.

Even though the waveguide mounted tweeter has a slightly rising frequency response above 15kHz, it doesn’t sound too bright or exagerated.

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, especially on vocals. They have a pure, yet a soft, effortless, refined and open sound without sounding cold or analytic.

 

Recommended loudspeaker placement:

  • Toed-in 0-15deg towards the listener.
  • >0.5 meters from back wall.
  • 2-3,5 meters apart.
  • 2.5-3 meters listening distance with tweeter slightly above ear height.

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:

 

Revelation Two – Monitor WG
Type: Two-way medium sized stand-mount loudspeaker with waveguide.
Enclosure type: Bass-reflex
Woofer driver unit: 5,5” Sliced paper cone. ScanSpeak 15W/4531G00
Tweeter driver unit: 1-1/8” Soft dome. Dayton RS28F-4 and 5,5″ waveguide
Cross-over frequency: 2.5kHz
Cross-over function: LR second-order acoustically, first-order electrically
Frequency response:  35-25000Hz -6/+0 db (on-axis)
Sensitivity: 87db 1m/2.83v
Impedance: 4 Ohm
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