The quality and volume of the sound of the speakerphone system (SSU) is not just a matter of comfort, but a critical parameter of the safety and efficiency of operational services, security structures and organizers of mass events. In conditions of urban noise, dense traffic and complex acoustic environment, the signal must be not only audible, but also legible. Wrongly tuned soundtrack It can turn an important warning into a slurred buzz, which will negate all the efforts of the crew.
Many owners of special vehicles face a problem when a powerful amplifier gives a hoarse sound, and the radio creates background noise in the speakers of the SSU. This indicates errors in installation, poor-quality switching or incorrect equalization. Understanding the physical processes of sound propagation and electrical characteristics of the equipment avoids typical installation errors.
In this article we will discuss in detail the technical aspects of the operation of sound systems of SSU, consider methods of eliminating interference and bring order to the frequency ranges. Competent approach acoustical cabin and proper calibration of equipment will ensure maximum range and clarity of the operator's voice.
Principles of operation and types of sound systems of SSU
Modern warning-system is a complex complex consisting of a microphone unit, a control controller, a power amplifier and a set of emitters. The basic element here is a microphone that converts acoustic vibrations of the voice into an electrical signal. The quality of this primary transformation depends on 80% of the final intelligibility of speech. Cheap microphones often cut high frequencies, making the voice deaf.
The power amplifier in the SSU system must have a sufficient current reserve so as not to cause distortion at peak volume values. If you hear that when the volume increases, the sound begins to “choke” or wheezing appears, then range The amplifier is exhausted. Professional systems such as Whelen or Federal SignalClass D circuitry is used, which provides high efficiency and minimal heating.
It is important to distinguish between the modes of operation of the sound signal. In addition to voice communication, SGU is often combined with siren. Switching between modes should occur instantly and without clicks or voltage lapses. Some models have a “mic priority” function that automatically reduces the siren volume when the tanget is activated.
⚠️ Warning: Never connect the SSU microphone to phantom powered inputs unless instructed. The supply of voltage 12-48V to the dynamic microphone is guaranteed to disable it, into the coil.
To understand the differences in technology, consider comparing the main types of emitters used in automotive systems:
| Type of emitter | Frequency range | Efficiency | Application |
|---|---|---|---|
| Horn (Horn) | 300 Hz - 3 kHz | Tall. | Sirens, long-range alerts |
| Dynamic (Cone) | 100 Hz - 5 kHz | Medium | Inside, voice. |
| Piezoelectric | 2 kHz - 10 kHz | Low (for voice) | Alerts. |
| broadband | 150 Hz - 15 kHz | Medium | Universal systems of the SMSS |
Frequency Characterization and Equalizer Configuration
The human voice requires a certain frequency range, often called the “intelligibility band,” for maximum legibility. The main energy of speech is carried by frequencies from 300 Hz to 3400 Hz. However, in order for the sound of the SSU to be heard through the noise of the engine and aerodynamic chassis, it is necessary to adjust the sound correctly. timbral. The amplification of low frequencies (bass) in the alert system often results in a mush-like sound that hums but carries no information.
When setting the equalizer or timbre regulators on the head device of the SSU, you should adhere to the principle of “cutting off excess”. Low frequencies below 200-250 Hz in the vocal tract are better attenuate. This will remove the hum and free up the dynamic range of the amplifier for useful mid-range frequencies. High frequencies (above 4-5 kHz) is also worth a little clean up, as they fade quickly from a distance and can create an unpleasant whistle when feedback is given.
There's a concept acoustic feedbackWhen the sound from the speaker hits the microphone, it is amplified and radiated again, causing a characteristic piercing whistle. To avoid this, the SSU microphone must be directed strictly away from the speakers. If the vehicle does not allow this, it is necessary to use filter or programmatically cut out the problem frequency.
Dynamic microphones, often used in SSU, have a decline at high frequencies, which sometimes requires a slight rise in the 2-3 kHz region to improve articulation.
Elimination of interference and tips in the sound tract
One of the most common problems when installing SSU is the appearance of extraneous noise: a hum, a crackle or a whistle synchronized with the operation of the engine. This phenomenon is known as the “ground loop” or ground-loop. It occurs when the equipment has different potentials of the earth. For example, the head unit is grounded through the body at one point, and the amplifier at another, and between these points, current flows through the body.
To eliminate low-frequency hum (usually 50-100 Hz and harmonics), you need to check all the points of connection of the mass. The contact must be cleaned to metal, treated with conductive lubricant and tightened reliably. Use of the free-former A ground loop isolator in an audio line is often the only way to completely get rid of the hum if reworking the wiring is impossible.
High-frequency interference, beeping sounds, changing the tone when dialing engine speeds, often indicate tips from a generator or ignition system. In this case, the shielding of the wires helps. The cables transmitting the audio signal must be shieldedThe screen must be grounded on only one side (usually the side of the signal source) to avoid creating a new loop.
⚠️ Attention: It is strictly forbidden to lay audio cables of the SSU parallel to power wires of the amplifier power supply or harnesses of the car wiring. The minimum crossing distance is 90 degrees, and the parallel gasket must be excluded.
Another source of interference can be radio channels. If a powerful radio station is installed in the car, its harmonic can penetrate into the SSU tract. Here will help install ferrite filters-rings on the microphone cable and the use of high-quality connectors with a metal body that acts as a screen.
Selection and placement of speakers for maximum impact
The effectiveness of the SSU system directly depends on where and how the dynamics are directed. For external broadcasting (working with the crowd, negotiations through glass) horn emitters are used. And their key feature is that radiation. The mouthpiece focuses sound energy into a narrow beam, which allows sound to be transmitted over long distances, but narrows the coverage area. If you set the horn too high, you will stun people under the car, but you will not be heard in front.
For internal communication (communication between machines in the column or inside the cabin) broadband speakers are used. When installing them in the cabin, it is important to consider room-acoustics. The interior of the car is a closed space with many reflective surfaces (glass, plastic, metal). This creates reverb that “smears” the sound. Placing an SMS speaker in the door niche or under the seat often results in the loss of high frequencies.
The optimal place to place the speaker of voice alert in the cabin is the upper part of the center console or the space under the ceiling (for minibuses). This ensures the sound spread throughout the volume and minimizes absorption of the seats by soft materials. For external work, it is important to protect the speakers from moisture and dust, using models with a protection class not lower than IP54.
When installing several speakers, phasing must be observed. If you connect one speaker in antiphase (mix plus and minus), the low frequencies will be mutually destroyed, and the sound will become thin and weak. Phasing checks can be done by feeding a low-frequency signal and observing the movement of the diffuser.
Integration of the SSU with the car audio system
Often there is a need to integrate a speakerphone system with regular multimedia. This allows you to use the existing car speakers to broadcast messages. However, standard head units (HDs) are not designed to prioritize interruption of sound. To implement the function Audio Mute (Mutning music when switching on SSU) a special control wire is used.
The connection circuit usually looks like this: the control output of the SSU unit (usually marked as "Mute" or "Audio Interrupt") is connected to the corresponding input on the tape recorder or external relay. When the SSU microphone is activated, this wire is closed to mass (or delivers 12V, depending on logic), and the tape recorder is lowered or switched to external input (AUX). Without this integration, the operator will have to manually remove the volume of the music, which distracts from the control.
Using an external mixer allows you to more flexibly manage sound streams. Through the mixer, you can miss the signal from the radio, navigator (voice prompts) and SSU. This creates a single audio environment where priorities are set by software or hardware. For example, the voice cues of the navigator can be quieter than the SSU signal, but louder than the background music.
It is important to consider impedance (resistance) of regular acoustics. Connecting the SSU amplifier to the inputs of the standard tape recorder, not intended for this, can lead to overloading of the output cascades of the head device and the appearance of distortion. Always use matching devices or connect at Line Out level if available.
Maintenance and diagnostics of malfunctions
Regular maintenance of the SSU system is necessary to maintain its combat readiness. Vibrations, temperature changes and humidity are the main enemies of electrical contacts. Periodically, at least once every six months, it is necessary to conduct a visual inspection of the places of anchorages of speakers and microphone connectors. The weakened fastener of the horn can lead to its resonant vibration and the appearance of rattling.
Diagnostics of faults begin with checking the integrity of the chains. If the sound is lost, the first thing to check the presence of a signal at the input of the amplifier. To do this, you can use a test signal or simply touch the entrance with your finger (a characteristic hum of 50 Hz should appear). The lack of reaction will indicate a cliff in the cable or a malfunction of the microphone. The presence of a hum when touching the input indicates that the amplifier is serviceable, and the problem is in the source of the signal.
Particular attention should be paid to the state of the membranes of the speakers. In horn emitters, moisture often accumulates, which can cause coil corrosion or short circuit. If the speaker is “hrizzing” at low volume, it is often a sign that the coil has burned or deformed, and its turns affect the magnetic circuit. In this case, the radiator is replaced.
⚠️ Note: When cleaning the mouths of the SSU, do not use aggressive solvents and do not direct a jet of water under high pressure directly into the speaker's socket. Water trapped inside can cause corrosion and change in acoustic properties.
The system operation must be checked in conditions close to real. Testing in a quiet garage may not reveal problems that will become apparent in a noisy street. Regular calibration of volume and checking the clarity of voice transmission is the key to effective work.
Why does the SCU wheez at maximum volume?
Wheezing at maximum volume is most often caused by clipping (overloading) the amplifier when it lacks the supply voltage to reproduce the signal peaks. The second reason is mechanical restriction of the diffuser speaker or its damage. It is also possible to drop the voltage in the onboard network when you turn on a powerful load.
Can you use conventional car speakers for SMSU?
It can be used, but not recommended for external work. Staff "pop" or Hi-Fi speakers have paper or composite suspensions that are afraid of moisture and temperature changes. For SSU it is better to use specialized speakers with a rubber suspension and a protected coil, designed to work in harsh conditions.
How to increase the range of the horn?
The range depends on the power of the amplifier and the sensitivity (CEP) of the horn itself. You can increase the range by choosing a horn with a narrower directional diagram (a large angle of the socket solution) and making sure that the amplifier gives the declared power to the load of this resistance. It is also important to have no obstacles before the scaling.
What to do if the microphone of the SSU flashes?
The background of the microphone can be caused by poor contact in the connector, a break in the cable screen or tips from nearby radiation sources (radio stations, generator). It is necessary to check the integrity of the cable, the quality of the soldering contacts and, if necessary, install a ferrite filter or decoupling transformer.