Canary
Silver
Flute W17RC38-08 with Waveguide
13 Liters Bass Reflex Satellite
by
Michael Chua
This design is free for DIY. Not for Commercial
Use.
This article may not be published in part or full without
the express permission of AmpsLab.
|
 |
|
Pellegrene 6.5"x4.5" Elliptical Waveguide
Why use a Waveguide?
Put
very simply, a waveguide is an acoustic amplifier. Fig
1 below illustrates the point succinctly. The Black trace
is of the XT25TG30 with the original faceplate. The Red
trace is with the faceplate replaced by a Pellegrene 6.5"x4.5"
Ellipitical Waveguide. For the same power input, the SPL
for the waveguide is higher, approximately 8dB on average.
Another
property is the shape of the response. It's much smoother
and flat from 2kHz-8kHz before tapering off linearly to
20kHz. The roll-off is steeper (almost 12dB/oct) and more
linear. These are very favorable conditions where crossovers
are concerned.
But
the idea behind using a horn or waveguide is not for the
higher SPL only. That can easily be achieved with a higher
powered tweeter. By focusing the soundwaves toward the
listener instead of allowing them to scatter across the
room, a waveguide improves on the speaker's imaging and
clarity.
|
Fig
1 - Vifa XT25TG30 with Waveguide Frequency Response
(mic 1 meter Tweeter Axis | 5ms Impulse Window | 1/12 oct smoothing)
(Short Sine Sweep - Bass Removed | Raw - No XO)
Waveguide
Dispersion
The raw horizontal dispersion properties of the waveguide
are in Fig 2.
Every
curve is from a 15° rotation. Even at the extreme
(75°), the frequencies are well maintained. There
are no ugly notches or peaks all the way up to 20kHz.
By all accounts, this Pellegrene Elliptical Waveguide
is quite impressive.
|
Fig
2 - Horizontal Polar Plots of Vifa XT25TG30 with Pellegrene Waveguide
(mic 1 meter Tweeter Axis | 5ms Impulse Window | 1/12 oct smoothing)
(Short Sine Sweep - Bass Removed | Raw - No XO)
Distortion
XT25TG30 + Waveguide
Fig 3 is the distortion of the raw XT25TG30. For this
measurement, a 170uF capacitor was inserted for protection.
The capacitor serves to reduce the bass frequency entering
the tweeter.
High
levels of distortion, from 2nd to 5th harmonics, were
observed from 250Hz to 350Hz. We should be mindful of
this inherent distortion when using this tweeter.
|

Fig
3 - XT25TG30 THD
170uF in line for protection
(mic 20 ins On Axis with XT25TG30 | 5ms Impulse Window | 1/12
oct smoothing)
Distortion
XT25TG30 + Waveguide + XO
Fig 4 is the XT25TG30 with a 2.5kHz, 12dB/oct filter.
The XT25TG30 distortion at 250Hz to 350Hz has completely
vanished. THD (Blue trace) registered a low 0.18% (-55dB
attenuation).
For
this plot, no LCR was installed. It goes to show that
at a high enough fc, even a moderate roll-off from a 12dB/oct
filter is sufficient to arrest the built-in distortion.
As
the fc is lowered, it would be prudent to make further
measurements to ensure that the distortion of the XT25TG30
is well suppressed.
|

Fig
4 - XT25TG30 + Waveguide
2.5kHz 12dB/oct passive XO (NO LCR)
(mic 20 ins On Axis with XT25TG30 | 5ms Impulse Window | 1/12
oct smoothing)
Silver
Flute W17RC38-08 (shielded version)
We now turn our attention to the 6.5" Silver Flute
W17RC. This Silver Flute is the Shielded version, so the
T/S parameters may not be exactly the same as the non-shielded
version.
Fig
5 is the W17RC with a 18dB/oct filter with fc at 2.5kHz.
Two distortion peaks (THD=0.56%) were recorded, one from
2nd harmonics at 1kHz while the other from 3rd harmonics
at 1.75kHz.
Fortunately,
these distortions are inaudible, at least to me. I can
live with some imperfections considering this is a relatively
cheap mid-woofer. The postive attributes of the W17RC
far outweigh the negatives.
|

Fig
5 - Silver Flute W17RC08 (shielded version)
2.5kHz 12dB/oct passive XO
(mic 20 ins On Axis with W17RC | 5ms Impulse Window | 1/12 oct
smoothing)
Canary
Frequency Response
Fig 6 is the Frequency Response of the Canary. The W17RC
is with an 18dB/oct filter. The XT25 with the Waveguide
is filtered at 12dB/oct.
Notice
how closely the acoustic slopes resemble the theoretical
roll-off.
|

Fig
6 - Canary Frequency Response
(mic 1 meter Tweeter Axis | 5ms Impulse Window | 1/12 oct smoothing)
(Low Pass 18dB/oct | High Pass 12dB/oct)
Canary
Distortion
Crossing the Waveguide at 2.5kHz does not cause any distortion
in the tweeter. The two distortion peaks of the Silver
Flutes do not interfere with music playback. Overall,
the Canary distortion is acceptable.
|

Fig
7 - Canary Distortion
(mic 20 ins On Axis with Tweeter | 5ms Impulse Window | 1/12 oct
smoothing)
Canary
Impedance & Phase
The Canary presents an easy load for power amplifiers.
Though the Impedance (Fig 8) is not as linear as I would
like it to be, it doesn't dipped below 9 ohms. The electrical
Phase is within a 20° window.
Power
amplifiers like the LM3886TF are ideal for the Canary.
The LM3886 can be designed to cater for 8 ohm loads instead
of 4 ohms. This will maximize the voltage swing, resulting
in higher power output.
|

Fig
8 - Canary Impedance & Phase Response
Canary
Crossover Network
Fig
9 - Crossover Network of CANARY
the sound of Canary
The
Canary is an ideal 2-way speaker. Unlike 5.25" midwoofers,
the larger 6.5" in the Canary delivers substantially
more bass. As such, the Canary can be used without subwoofer
support.
Vocals
are forward as in the Ultima. Treble is clear. Thanks to
the waveguide, there's no spitting, sibilance or harshness.
All in, a very likeable speaker.
next
> Canary | Canary-II
Sep
14, 2013
|
|
|
|
|