“Headphone for stereo? This is too much, can mind reader. — How can provide high quality playback of regular head phones? After all, this requires a wide range of frequencies, a slight harmonic distortion and a relatively high volume level”.
Indeed, the usual (TONE-2, TA-56M, etc.) are not suitable for high-quality sound reproduction due to the limited electro-acoustic parameters. Electromagnetic system of these headphones don’t reproduce frequencies above 3000 — 5000 Hz, harmonic distortion is significant, and the unevenness of the frequency characteristics of sound pressure is great.
The efforts of acoustics, and thanks to the latest advances in technology created a phone that meets all the requirements of high-quality audio as mono and stereo. In a normal monaural phone headset both connected, usually in parallel. In stereo phone each headphone (left and right) is connected to the appropriate amplifier channels via a three-wire flexible cord. Converters the electrical signal into sound — the basic elements of a phone — in high quality stereo headphones exclusively electrodynamic or electrostatic system. These phones provide a wide frequency range (20-20 000 Hz) minor harmonic distortion (1-2% for electrodynamic and 0.2—0.5% for. electrostatic system), the small unevenness of the frequency characteristics of sound pressure (5-12 dB for the first and no more than 5 dB for the second).
Fig. 1. Comparative frequency characteristic of sound pressure:
a) speaker b) headphone.
Fig. 2. The appearance of the phones with the headband from the TONE-2:
1 — phone; 2 — headband; 3 — cord.
A natural question arises: why do we need to go to the phones, when present, produced a variety of high-quality speakers? A living room usually has poor acoustics. And improve it is a difficult task. And hardly it is expedient in the living room to create a special environment for listening to music. Disturbing noises frequently occur in the home environment, or, on the contrary, increased the volume of sound required for high-fidelity playback, not always pleasant to others. Here’s the essential set of stereo head phones. In General terms we can say: the sound quality on head phones, the speakers are of high class. And here’s why.
First, the range of frequencies of stereorelease wider than the high-quality loudspeaker. Most of stereotelevision reproduces low frequencies from 18-20 Hz, which from the speakers to achieve is extremely difficult. For comparison, figure 1 shows a typical frequency response phone system and an electrodynamic loudspeaker of high class.
Second, the nonlinear distortion of the phones is insignificant. This creates a special purity and transparency of sound.
Third, phones can easily develop a sound pressure level corresponding to the natural sound (up to 100 -110 dB) with little of the electrical power input (10 mW). At the same time, the most common speakers develop at a distance of 1 m sound pressure level of about 80 dB at a power of 0.1 watts. For the 90 dB required power of 1 W, 100 dB — 10 W, 110 dB for 100 watts. These speakers and amplifier are technically difficult to perform.
Fourth, converters headphones are small and having a small mass, almost instantaneous. Stereorelease much easier to demirovici, so they provide a good transient response (the ability to accurately reproduce the sound of a pulse character). Quality control records using phones allows you to identify any defects in the track and fix them quickly.
Head stereociliary to create a strong stereo effect that does not depend on room acoustics and the location of the listener. They can be used not only in stereo, but mono.
In a makeshift stereo headphone as a transducer using a small-sized head for handheld receivers and earpieces microphones. A simple design can be performed, for example, based on a compact electrodynamic head 0,05 GD-1 (Fig. 3). The phone consists of a head, is placed in the body of the cover, strip of foam located on the lid, inner padding and headband (not shown).
The casing and cover can be made of any plastic. The gasket is cut from foam and glued to the outside of the lid with glue 88Н. Hole cover pre-glued silk fabric: when equipped phone foam padding will not SAG and touch the inside of the diffuser head. Then the cover is glued head 0,05 GD-1. Among its conclusions fluster wire and passed through the hole in the side of the case. On the bottom of it, put a foam thickness of 8-10 mm and the lid head is inserted into the housing. The joints connections in several places and smeared with glue.
Lead wires and pre-mark phase. With flexible three-wire cord phone is connected to the connector SSH-5. The cord is fixed to the body of the phone and one of the wires connected to the same two conclusions of the heads, and the other two to the rest. Connecting wires stretch out the headband.
Fig. 3. The design of phone-based head of 0.05 GD-1:
1 — head 0,05 GD-1; 2 — housing; 3 — cover; 4 —foam seal; 5 — inner padding.
Fig. 4. The design of phone-based MIC capsule:
1 — body; 2 — fuse; 3 — cover; 4 — gasket; 5— place bonding; 6 — (hollow rivet); 7 — inner padding.
Fig. 5. Wiring diagram for phones.
Headband can be homemade or from industrial phones. In the latter case it is only necessary to change the dimensions of the forks of the headband in accordance with the diameter of the casing of the telephone.
In each case drill grooves into which the fork is located on the headband pins.
Figure 2 shows the headphones with the headband phones TONE-2.
Relatively simple, but high stereorelease can be made in Amateur conditions, on the basis of the capsule of the microphone МД47 or МД64 (Fig. 4). The design consists of a hull, primer, caps, spacers and findings.
The body and cap are made of plastic, organic glass. From the microphone, carefully remove the cap being careful not to touch the diaphragm. It is inserted into the shell of the phone and glue where indicated in the figure. The insights of the voice coil pass through the hole.
After the installation of the percussion cap glued to the hull with glue 88Н silk cloth covering the hole, and on top — the foam padding.
Both are headband. Electrical installation is the same as in the previous design. The correct phasing check by connecting the phone to the sound generator in parallel. Setting the scale of the instrument frequency 100-400 Hz, reversing the polarity of the inclusion of one of the phones. In the position of greater signal loudness stereo speakers are phased correctly (at constant voltage generator).
But the phones are ready and they can be tested. Headphones connected to a special stereo amplifier. Such devices are designed for connecting stereotelevision resistance 8 — 10 Ω. Self-made phones, which we are told have a resistance of about 60 Ohms (I variant) and 250 Ohm (option II). If they connect to an amplifier, the sound volume compared to standard vasiliani phones will be less. However, it is easy to compensate with the volume knob.
Phones can connect to the jacks “supplementary loudspeaker” or through the damping resistor the resistance of 200-1000 Ohms, instead of the main speakers.
To the vacuum tube amplifier phone plug according to the diagram of figure 5. Resistor R1 is the equivalent of the loudspeaker. The damping resistor R2 reduces the voltage on the phones. The resistance R2 is chosen from the condition that the subjective feeling of volume when listening through speakers and phones was about the same (the position of the volume control remains unchanged).
Stereo headphones can be connected to mono equipment, including, left, and right phones in parallel. The sound in this case, must appear to be radiating out from the center front of the listener and shifted slightly upward. This shows about the same sensitivity phones. Otherwise, the overall sound is stereo recording will be broken.
V. SKLYAROV, engineer