Manufacturer: TPO RET, Tallinn.

Purpose and scope: for high-quality reproduction of music and speech programs in stationary living conditions(performance category UHL 4.2 according to GOST 15150-69).

The preferred installation option is outdoor.

The shape of the frequency response of sound pressure, measured along the acoustic axis

Specifications:

Sound pressure frequency response, measured at angles:

• a) in the vertical plane:
  • -----7° up;
  • *****7° down.
• b) in the horizontal plane:
  • -----25° right
  • *****25° left

principled circuit diagram

Design features:

• The AC case is made in the form of a rectangular non-separable box made of chipboard, veneered with fine wood veneer. The front panel, in order to increase its rigidity, is made of 28 mm thick plywood with veneer. The design of the housing provides for elements that increase rigidity and reduce the amplitude of vibrations of the walls, in particular, inside it there is, located along rear wall spacer between the side walls.
• A set of loudspeaker heads was used, specially designed for: manufactured by TPO RET, Tallinn. The heads are mounted on the front panel of the case symmetrically about the vertical axis of the speakers. They are framed decorative overlays made of plastic and painted with metal-like dyes. Overlays have the same shape- rectangular with rounded corners and four mounting holes. On the front panel, in addition, there are: a decorative nameplate with the name of the AC and the brand name of the manufacturer.
• On the front panel there are also two holes with a diameter of 35 mm each, which are the outputs of the AC phase inverter tubes. Tubes 248 mm long are made of plastic. Geometric dimensions phase inverter ensure its tuning to a frequency of 31.5 Hz. In addition, four plastic bushings are installed on the front panel (at the corners of the front panel) for attaching a decorative frame with fabric. To reduce the impact on the frequency response of sound pressure and the sound quality of the AC resonances of the internal volume of the case, sound-absorbing mats are fixed on its walls. Electrical filters are mounted inside the case, providing electrical separation of the AC bands into low, medium and high frequencies.
• Crossover frequencies: between low and medium frequency heads 1000 Hz, between medium and high frequency heads 7000 Hz. In the design of the filters, resistors of the PEV, PEVR-10 type, capacitors MBGb-2-160 V, inductors on plastic frames with "air" cores are used.
• On the rear stack of speakers are special terminals for connecting the connecting cable.

Description

Estonia 35AC-021 - Active 3-way floorstanding speaker system.
Produced by TPO "RET", Tallinn

The speakers are designed for high-quality reproduction of music and speech programs in stationary living conditions. The recommended power of UCU is 20-50 W. Installation option - floor.
Distinctive feature The speakers are reduced dimensions, the use of a flat honeycomb diaphragm in the woofer, a rubberized fabric dome in the midrange head and a polystyrene foam dome in the tweeter. All 3 speaker heads are designed for this speaker.

The AC case is made in the form of a rectangular non-separable box made of chipboard, veneered with fine wood veneer. The front panel, in order to increase its rigidity, is made of 28 mm thick plywood. with veneer. Elements are provided in the housing design that increase rigidity and reduce the amplitudes of wall vibrations, in particular, inside it there is a spacer located along the rear wall between the side walls.

A set of heads was used, especially for 35AC-021:
LF - 35GD-1S
MF - 20GD-1
HF - 10GD-20

The heads are mounted on the front panel of the case symmetrically about the vertical axis of the speakers. They are framed with decorative overlays made of plastic and painted with "metal-like" dyes. The pads have the same shape - rectangular with rounded corners and four mounting holes. On the front panel, in addition, there are: a decorative nameplate with the name of the speaker and the brand name of the manufacturer.
There are also 2 holes with a diameter of 35 mm on the front panel. each, which is the output of the phase inverter tubes. Tubes 248 mm long. made of plastic. the geometric dimensions of the phase inverter ensure its tuning to a frequency of 31.5 Hz. In addition, four plastic bushings are installed on the front panel for attaching decorative fabric.
To reduce the influence of the frequency response of sound pressure and the sound quality of the AC resonances of the internal volume of the case, sound-absorbing mats are fixed on its walls. Electrical filters are mounted inside the case, providing electrical separation of the AC bands into LF, MF, HF.
Frequencies between LF and HF heads 1000 Hz., between MF and HF 7000 Hz.
In the design of the filters, resistors of the type: PEV, PEVR-10 are used. Capacitors: MBGO-2-160 V. Inductors on plastic frames with "air" cores.
On the rear wall of the speaker are special terminals for connecting the connecting cable.

Technical details:

- Frequency response - 25 (-16 dB) - 31500 Hz;
- Average sound pressure at rated power in the range of 100 - 8000 Hz - 16 dB;
- Uneven frequency response in the range of 100 - 8000 Hz - ± 4 dB;
- Sensitivity - 85 dB;
- Harmonic distortion speakers in the frequency range:
250 – 1000: 1,6 %
1000 – 2000: 1,5 %
2000 – 6300: 0,8 %
- Nominal electrical resistance of the passive input - 8 ohms;
- The minimum value of the total electrical resistance - 6.8 Ohm;
- Maximum noise (passport) power of the passive input - 50 W;
- Limiting short-term passive input power - 250 W;

Dimensions: 320x540x320 mm;
Weight: 19.5 kg

Design features

The AC case is made in the form of a rectangular non-separable box made of chipboard, veneered with 28mm thick veneer of precious wood. The front panel, in order to increase its rigidity, is made of 57mm thick plywood with veneer. Elements are provided in the housing design that increase rigidity and reduce the amplitudes of wall vibrations, in particular, inside it there is a spacer located along the rear wall between the side walls.

The heads are mounted on the front panel of the case symmetrically about the vertical axis of the speakers.
On the front panel there are also holes with a diameter of 35 mm each, which are the outputs of the AC phase inverter tubes. Tubes 248 mm long are made of plastic. The geometric dimensions of the phase inverter provide tuning to a frequency of 31.5 Hz. In addition, four plastic bushings are installed on the front panel for attaching a decorative frame with fabric.
To reduce the impact on the frequency response of sound pressure and the sound quality of the AC resonances of the internal volume of the case, sound-absorbing mats are fixed on its walls.

The filter crossover frequency is 1000 and 7000 Hz, the filter inductors are made on plastic frames with "air" cores

In 35AC-021, all heads are framed with decorative overlays made of plastic and painted with metal-like dyes. The pads have the same shape - rectangular with rounded corners and four mounting holes. On the front panel, in addition, there are: a decorative nameplate with the name of the AC and the brand name of the manufacturer.
In modifications 35AC-021-1 and 35AC-021-2, there was no nameplate in front, there were also no overlays on the midrange and tweeters; to protect them, two curved metal rods were located in front of them.

History of creation

By the end of the 70s, Technics and a number of other Japanese manufacturers began producing radiators with flat honeycomb diaphragms. In theory, flat honeycomb radiators are as close as possible to an ideal sound source. In the Soviet Union, this concept was embodied in its own way. First of all, the weight of the rather small 20 cm diaphragm proved to be too heavy. Secondly, the design of the magnetic system is made with an emphasis on high maximum power. Because of this, the speaker has a very low sensitivity, about 85 dB / W / m. This decision of the engineers came from GOSTs, under which the parameters of the speaker were made. For example, high-end acoustics, according to GOST 15150-69, should have a lower cutoff frequency of 25Hz (-12dB) and a rated power of 35W. The sensitivity parameter was not regulated by GOST. It is clear that in order to reach 25Hz, from such a modest speaker size, the engineers had to reduce the sensitivity.

Further, the set of dynamic heads was quite different from those of the Japanese prototypes. MF/HF dome drivers, made of impregnated textiles, were more typical of European manufacturers of that time. The use of such different speaker designs caused problems with phase and timing characteristics.
But for the Soviet consumer, these speakers were the height of perfection and technology. In spite of small size, they outperformed the popular S-90 the quality of the transmission of musical material.
Estonia 35AC-021 had a design flaw - the lead wires to the woofer coil were bent. The designers did not calculate the flexibility and length of the wire for such a long-throw speaker. You can determine this by ear - when listening at high volume, it may click in the woofer or the sound is interrupted. Suspensions and other nodes in this acoustics are quite durable and do not noticeably age.

Further, after the collapse of the USSR, columns 35AC-021-1 and 35AC-021-2 Estonia were produced in Russia under the name 130AC-002 and 130AC-003 Soyuz, and in Estonia - 30AC-002, 130AC-002 and 30AC-003, 130AC-003 Audes. Here, they did not adhere to GOST, they tuned the phase inverter to a higher frequency, which increased the bass response, upgraded the filter, bass and tweeters. But the build quality was very low, the body was thin, the bass driver suspensions were made of short-lived polyurethane foam.

Description

It was very interesting to listen to the domestic version of acoustics with flat honeycomb diaphragms. As you know, the company Technics and a number of other Japanese manufacturers (see our other tests) began producing similar emitters by the end of the 70s. In theory, flat honeycomb radiators are as close as possible to an ideal sound source (see article - tab " Acoustic systems"). In the Soviet Union, this concept was embodied in its own way. First of all, the weight of the rather small 20 cm diaphragm proved to be too heavy. Secondly, the design of the magnetic system is made with an emphasis on high maximum power. Because of this, the speaker has a very low sensitivity, about 85 dB / W / m. This decision of the engineers came from GOSTs, under which the parameters of the speaker were made.

For example, high-end acoustics, according to GOST 15150-69, should have a lower cutoff frequency of 25Hz (-12dB) and a rated power of 35W. The sensitivity parameter was not regulated by GOST. It is clear that in order to reach 25Hz, from such a modest speaker size, the engineers had to reduce the sensitivity.

Further, the set of dynamic heads was quite different from those of the Japanese prototypes. MF/HF dome drivers, made of impregnated textiles, were more typical of European manufacturers of that time. The use of such different speaker designs caused problems with phase and timing characteristics.

But for the Soviet consumer, these speakers were the height of perfection and technology. Despite their small size, they easily outplayed the entire line of popular 35AC (S-90). Time has shown that the design is not hopeless and has great potential for an upgrade, there is a lot of information about this on the net.

An amplifier for acoustics needs a uniquely transistorized one, and as powerful as possible, a good drive in sound is achieved only in the region of 100W (on a music signal).

Estonia 35AC has a small illness - the lead wires to the woofer coil are bent. The designers did not calculate the flexibility and length of the wire for such a long-throw speaker. You can determine this by ear - when listening at high volume, it may click in the woofer or the sound is interrupted. Even if you come across such a speaker, then owning a soldering iron, you can easily replace the faulty wiring. Suspensions and other nodes in this acoustics are quite durable and do not noticeably age.

Further, after the collapse of the USSR, Soyuz 130AC 002 speakers were already released in Russia. Here they did not adhere to GOST, they tuned the phase inverter to a higher frequency, which increased the bass response, upgraded the filter, bass and tweeters. But the build quality was very low, the body was thin, the bass driver suspensions were made of short-lived polyurethane foam.

Sound. We got, the usual non-modernized acoustics Estonia 35AC 021. The first thing that cuts the ear is, of course, low sensitivity. But when compared with other speakers not at the same volume, the sound is quite interesting. There is a slight coloration at mid-high frequencies, which gives excessive refinement and lightness to the sound. The bass is a bit tight, but correct placement, you can achieve very good results. In any case, the bass is very low for such small speakers, soft, and not humming. Bass lacks energy in the upper range.

In general, according to the sound of modern speakers, we didn’t find anything better up to 20,000 rubles. And after the rework, perhaps Estonia will be able to compete with even more expensive speakers.

Summary. Acoustics can be recommended not only to nostalgic lovers of products of the Soviet industry. But also for novice audiophiles with a very limited budget. Acoustics has its own pronounced "voice", which is very rare for inexpensive modern speakers.

Estonia 35AC 021

Design 4

Sound 4

Price range 0