Hi-Eff 2 loudspeakers
started on August
st , 2009
After the good experience with the first high
efficiency system using a very low budget I have think to increase the sonic
performances with a little more cost.
The CP380 used in the previous project is a good driver with a very low
distortion if compared to the other compression drivers but it have some
This project born to create a loudspeaker with very high efficiency and a
acceptable cost to be driven by low power single ended amplifier with a 2A3 PSE
or 300B SE.
To keep low the cost has been decided to use only 2 drivers with the lower
crossover frequency possible.
There are very few tweeters with an efficiency
near to 100dB and low distortion, these are based on
is based on the AMT technology
(Air Motion Transformer).
In this type of transducers, invented by the German physicist Oskar Heil, the generation of the sound takes place in a very
different from the habitual one in ribbon tweeters.
In figure one, we can see that in this device, the diaphragm is formed
by longitudinal folds, like in an accordion. In the straight face of
each one of these folds, there is a printed conductive copper thread.
This diaphragm is made in Beyma, on a material able to support extreme
temperatures and of a great flexibility. It is used in military and
aerospace applications to manufacture flexible printed circuits. It is
of a great durability and reliability.
The operation principle is the same one that in a regular tweeter, but
geometry is very different.
As it is
possible to be seen in this figure, the magnetic field
is closed happening by where the diaphragm is located.
When an alternating electrical current circulates along
the copper tracks of the membrane, a movement takes
place in the folds from left to right. The sound wave is
generated when the air between the folds is compressed.
This causes that,
being the displacement of each fold very small, the air
moves at great speed, producing an important sound
The advantages of this type of tweeter can be summarized
surface four times the one of a tweeter or an equivalent
compression driver, thanks to its folded geometry.
- Mobility transformer of air (Air Motion Transformer)
because it causes in the air a speed four times greater
than the one of the folds themselves (relation 4:1).
- This confers an enormous dynamics and an incredible
transient response, vastly superior to that of any
conventional tweeter, including ribbon tweeters and
All these characteristics make of the
TPL-150 an authentic alternative to
the conventional compression drivers,
and contributing an enormous added value
to any sound system that incorporates
TPL150H use a little horn to
increase sensibility and low frequency
range to obtain these following
The cost of
TPL150H + is
about 500 euro each.
click to enlarge
In my previous project I have excluded the SM115N
Beyma that is very interesting for
the price and performances.
incorporates a 3. voice coil made with high quality materials: copper round
wire with high temperature bonding strength and apical former. Moreover, it
features a powerful magnet system with rear air ventilation. All these facts
result in a 15. driver with extended and smooth low-mid frequency response,
If you compare to the
Beyma have a lower resonant frequency and a similar extended frequency
In the same volume the
lower so better bass frequency.
Follows the final Onken box design, 2
bass-reflex holes has be closed to use the
but it will be adjust on the
Follows the measurement of the two
drivers without filter in my room.
Jantzen Audio Z - Superior Caps are high-end components,
delivering a natural, almost holographic soundstage.
I have tested these and compare with my references Solen MKP and
Clarity Cap SA range caps.
In the article of Tony Gee these get a verdict of 10.
I have used stainless
steel and not iron to fix the 3 choke.
The following measurements are valid only
at medium-high frequency and has been created using the box of version 1
with 2 bass reflex hole closed.
Note: not all the measurements are in the same environment conditions.
The sound is good but the
impedance have a min
of 2ohm at 1KHz that is not very good for single ended amplifier
with Rout about 2-3ohm
The TPL150H is a pure resistive load so it
is very easy simulate the filter.
Here the plot of both last versions, 2 in
red and 3 in green.
The Beyma declare 80W above 1KHz with a
12dB/oct filter so with a simple first order filter it will be
reduced but it is compensated by the attenuation of 7dB.
Same frequency response of the previous but a
very good linear impedance
Here the filter has been optimized with Arta software,
EMU 0404 USB and ECM8000 analizing an MLS impulse
for 50msec and after a listen test. All capacitors are Z-Cap,
the cheap Solen has been used only in the impedance correction
A different microphone position
Follows a near field measurement
(15cm in front of each driver)
Follows the impedance measurement with Clio
The two versions are very different, the first is more aggressive but it
give good result with jazz creating a strong feeling of live listening.
The voices in the first version are a little bit compromised by the
compression driver and in some moments these seems to come from a pipe (the
The second version can be used to ear any kind of music like a normal low
efficiency loudspeakers because the sound is very natural without
Also the bass frequency in the second release is more dry but it can be
confused like a less impact.
Using single ended amplifier is very important have a constant impedance
because these amplifiers have a very low damping factor.
The filter version 5 sound much better than the previous when I drive these
loudspeakers with my
amplifier with output impedance near to 1.6ohm.
1 both channels (price in euro)
||version 2 both
channels (price in
I have selected 30 millimeter birch plywood for the
cabinet in order to raise cabinet resonance to a point well above the radiated
For this purpose I have used
www.officinelettroniche.it of Ivan De Cesaris.
For this large
loudspeakers it is impossible use the normal damping articles for loudspeakers
because in this case the cost would exceed the cost of wood.
Following the suggestion of my friend Andrea of
I have used two different damping materials used in the cars:
panels composed of fabric processing residues bottom tar
for the base and the back
bottom in lute
To move this large
loudspekers on my room during the cleaning activity I have used the idea seen on
the TNT website.
I have used a base of MDF 25mm and 3 Glisdome with a diameter of 65mm.