Overview:
The RAAL 140-15D is a ribbon tweeter made by the RAAL Company in eastern Serbia.
The RAAL 140-15D ribbon is made of a 21 sq. cm (14×1,5cm) pure aluminium flat foil which weighs 22mg. It has a sturdy build quality with a 2mm metal faceplate and uses a very powerful neodymium motor system. The ribbon provides a linear frequency response up to +40kHz with an outstanding horizontal off-axis dispersion and for a ribbon tweeter, low distortion and great vertical dispersion.
With special “foam deflection pads” it’s possible to adjust, control and improve the vertical dispersion and the so called vertical “beaming” of high frequencies, which is commonly seen among large ribbons.
The “foam deflection pads” are working as an acoustic lens, by slowing down the velocity of sound and thus shaping the sound wave front from cylindrical to spherical.
By using the “deflection pads” the high frequency response level can be adjusted to personal preferences without the need of additional padding resistors as well as adjusting and controlling both the vertical and horizontal dispersion.
Even though this ribbon tweeter is expensive, it’s one of the best measuring ribbon tweeters on the market and with innovative design features such as “foam deflections pads” and specially designed face plates etc.
To ensure a nice distortion safety margin I recommend using the RAAL 140-15D from 3kHz or higher. However by using steep cross-over filters it can be used from 2-2.5kHz with some elevated distortion and limited max output.
RAAL Spec sheet: RAAL Ribbon Tweeter 140-15D
T/S Parameters:
Nice consistency between the two tweeter samples.
Impedance:
(click on picture to zoom)
Free air impedance measurement:
Left: No protection cap
Right: 44uF protection cap
Sample 1 = Green
Sample 2 = Blue
A perfect match between the two samples.
Frequency:
Frequency measurement conditions:
The ribbon tweeter is measured mounted on a baffle with the following conditions:
Baffle size: (WxH): 33×20cm (baffle edge round-over r=19mm)
Driver position: Mounted on center-line with driver unit centered on the baffle. Flush-mount using felt carpet.
Mic position: 1m distance, on tweeter-axis (horizontal measurements). 0.75m distance, on tweeter-axis (vertical measurements).
Smoothing: 1/24 octave smoothing applied.
Tweeter configuration:
DPN = No “deflection pads”.
DP1 = With “deflection pads” and 7cm visible ribbon.
DP2 = With “deflection pads” and 5cm visible ribbon.
DP3 = With “deflection pads” and 3cm visible ribbon.
All frequency measurements are made with a 44uF protection cap.
Horizontal frequency measurements comparing sample 1 and 2:
(click on picture to zoom)
Blue = Sample 1 on-axis
Red = Sample 2 on-axis
Upper Left: DPN
Upper Right: DP1
Lower Left: DP2
Lower Right: DP3
Virtually the same frequency response between sample 1 and 2. Note the extended frequency response and the possibilty to shape the response with the “foam deflection pads”
Horizontal frequency measurements:
(click on picture to zoom)
Blue = on-axis
Red = 15deg off-axis
Green 22.5deg off-axis
Upper Left: DPN
Upper Right: DP1
Lower Left: DP2
Lower Right: DP3
(click on picture to zoom)
Blue = 30deg off-axis
Red = 45deg off-axis
Green = 60deg off-axis
Upper Left: DPN
Upper Right: DP1
Lower Left: DP2
Lower Right: DP3
Horizontal frequency measurements: (comparing different “deflection pad” settings”
(click on picture to zoom)
Blue = DP1
Red = DP2
Green = DP3
Upper Left: On-axis
Upper Right: 15deg off-axis
Middle Left: 22.5deg off-axis
Middle Right: 30deg off-axis
Lower Left: 45deg off-axis
Lower Right: 60deg off-axis
Vertical frequency measurements:
(click on picture to zoom)
Blue = on-axis
Red = 5deg off-axis
Green = 10deg off-axis
Upper Left: DPN
Upper Right: DP1
Lower Left: DP2
Lower Right: DP3
(click on picture to zoom)
Blue = 15deg off-axis
Red = 20deg off-axis
Green = 25deg off-axis
Upper Left: DPN
Upper Right: DP1
Lower Left: DP2
Lower Right: DP3
Vertical frequency measurements: (comparing different “deflection pad” settings”
(click on picture to zoom)
Blue = DP1
Red = DP2
Green = DP3
Upper Left: On-axis
Upper Right: 5deg off-axis
Middle Left: 10deg off-axis
Middle Right: 15deg off-axis
Lower Left: 20deg off-axis
Lower Right: 25deg off-axis
Frequency measurement summary:
The dip and peaks between 1.5-2.5kHz is the effect of the baffle size and the diffraction associated with it. The dip gets less pronounced when moving off-axis
By using the supplied “foam deflection pads” the frequency measurement performance are truly amazing, both horizontally and vertically. By removing the “deflection pads” (DPN) setting, the measurements shows the common vertical “beaming” effect of a large ribbon as well as a rising high frequency response.
The best overall balance and linearity between the horizontal and vertical frequency response is to use the “deflection pads” in the DP1 or DP2 setting e.g. 7cm or 5cm visible ribbon.
Distortion:
Measurement setup:
- Tweeter near-field measurement at 15cm
- Frequency Range Tweeter: 500-10000Hz @ 85dB and 1000-10000Hz @ 90-95dB
- Baffle size: (WxH): 33×20cm (baffle edge round-over r=19mm)
Tweeter configuration:
DPN = No “deflection pads”.
DP1 = With “deflection pads” and 7cm visible ribbon.
DP2 = With “deflection pads” and 5cm visible ribbon.
The distortion measurements are done in near-field and the amplifier output level was adjusted for each driver so that the fundamental is 85dB, 90dB and 95dB at 1m. This setting simulates normal, medium and high listening levels.
85dB @ 1m (click on picture to zoom)
Left: = Sample 1
Right: = Sample 2
Upper: DPN
Middle: DP1
Lower: DP2
90dB @ 1m (click on picture to zoom)
Left: = Sample 1
Right: = Sample 2
Upper: DPN
Middle: DP1
Lower: DP2
95dB @ 1m (click on picture to zoom)
Left: = Sample 1
Right: = Sample 2
Upper: DPN
Middle: DP1
Lower: DP2
Distortion measurement summary:
Low second order harmonics, but third order harmonics increases with higher SPL. Still for a ribbon, the RAAL 140-15D tweeter performs very well.
To have some distortion safe margin even at higher SPL:s a cross-over of 3kHz or higher is recommended. If the need for SPL is more modest, a cross-over at 2-2.5kHz could work depending on how steep the filter is.
It’s interesting to see is that the distortion is even lower when the “foam deflection pads” are used.