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Hi-Eff 2 loudspeakers system
 started on August 13 st , 2009 

INTRODUCTION

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 limits.

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.

HIGH FREQUENCY

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 pressure.
The advantages of this type of tweeter can be summarized in:
- Radiation 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 compression drivers.


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 it.

The new TPL150H use a little horn to increase sensibility and low frequency range to obtain these following specifications.

The cost of TPL150H +  is about 500 euro each.

click to enlarge
 

 

LOW FREQUENCY

In my previous project I have excluded the SM115N Beyma that is very interesting for the price and performances.

 The SM115N 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, reduced harmonic.

If you compare to the Celestion FTR15-3070C the SM115N Beyma have a lower resonant frequency and a similar extended frequency range.
 

In the same volume the SM115N have 6Hz lower so better bass frequency.

Follows the final Onken box design, 2 bass-reflex holes has be closed to use the SM115N but it will be adjust on the final environment.

Follows the measurement of the two drivers without filter in my room.

CROSSOVER

Jantzen Audio Superior Z-cap

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.
www.humblehomemadehifi.com
 

 
Jantzen Air Coils

To get the lower distortion it is necessary use only air coils inductance with a good wire section

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

Same

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 cell.

A different microphone position

Follows a near field measurement (15cm in front of each driver)

Follows the impedance measurement with Clio system

SOUND

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 horn). 
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 colorations.
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 813 amplifier with output impedance near to 1.6ohm.

 

COST

version 1 both channels (price in euro) version 2 both channels (price in euro)
CP380 320 TPL150H 1000
1" HORN 160 HORN -
FTR15-3070C 300 SM115N 280
Crossover 150 Crossover 300
Wood 300 Wood 300
Cut 250 Cut 300
damping materials 70 damping materials 70
total 1550 total 2250

WOOD

I have selected 30 millimeter birch plywood for the cabinet in order to raise cabinet resonance to a point well above the radiated frequencies.

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 PuntoMusica I have used two different damping materials used in the cars: 

1) panels composed of fabric processing residues bottom tar for the base and the back
2) moquette with longhaired and 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.