All microphones convert sound waves into an electrical signal, with the aim of amplifying, recording or transmitting this. Yet one microphone has a different sound signature than the other. Differences in the frequency range make different microphones suitable for different types of use. For example, one microphone ensures fantastic music reproduction, while the other, for example, is very strong in speech intelligibility. Tour Guide systems naturally also use (usually vocal) microphones, but also broadcast the signal over certain frequencies.
Frequency range with microphones
Frequency range, also called frequency response, is the range of low to high sound frequencies that a microphone ‘hears’ and can reproduce. This is one of the most important features that determine which microphone is suitable for a specific application. The frequency response indicates the Hertz range of a microphone. With a frequency range of, for example, 20 Hertz to 20 kilohertz, all frequencies between these two numbers can be reproduced. Frequencies outside this range are reproduced to a lesser extent or sometimes not at all. In general, low frequencies are heard as low tones and high frequencies as high tones. The most used segments within the frequency spectrum are subdivided into bass, low mids, mid range, upper mids, and highs. Some frequencies are exaggerated and others weakened (lowered). The dips and peaks in the different segments of the frequency range of a microphone are graphically represented in a response curve. Each microphone has a different response curve, which means that one microphone, for example, is very good at recording/reproducing music, while the other microphone ensures clear speech intelligibility. The two most common types are flat response and shaped response. In both cases, for the ideal effect, the frequency response curve should be a reasonably smooth line. This means that the microphone will sound natural and will cause less feedback.
Choose the most fitting microphone
Choose a response curve that is best suited to the specific use of the microphone. This way the chance is greater that you get exactly the desired sound, without having to adjust it afterwards through equalisation. In any case, make sure to avoid response curves that emphasize the wrong frequencies. For example, a good vocal microphone is excellent at picking up the somewhat quieter, subtle nuances in a singing voice, and therefore you never use it to record the loud, powerful tones of a bass drum. A microphone that is equally sensitive to all frequencies shows a response curve of an almost completely flat line. This is called a flat frequency response. A microphone with a flat response can be used well for musical instruments or sound effects, but is usually not as suitable as a vocal microphone. This is because such a microphone accurately reproduces the sound source, with little or no deviation from the original audio, because no frequencies are exaggerated or reduced. Condenser microphones generally have flatter frequency responses than dynamic ones. These microphones are therefore very suitable for recording in studios, because of the more authentic and accurate reproduction of the original sound in comparison to other types of microphone. Condenser microphones are also very suitable for choirs, pianos, acoustic string instruments and the cymbals on a drum set. Dynamic microphones are more sensitive to some specific frequencies. Its shaped response curve therefore has more peaks and troughs. A shaped frequency response usually also has a boost in the upper mids, usually between 3,000 and 6,000 Hertz. This boost improves the clarity of voices and instruments. Often these microphones are less sensitive to low frequencies, and therefore pick up less background noise. This makes these microphones for example very suitable for the reproduction of speech in an environment with a lot of background noise. There are more features, such as the polar pattern, that determine which microphone is the right choice for your project. There is a specific microphone for every conceivable application. Tau is happy to help you find the best microphone for your project.
Frequency range with Tour Guides
During touristic city walks or group tours and guided tours in museums or trade fairs, to name but a few, Tour Guides systems are regularly used. These means of communication naturally also use microphones, for which it will generally be the case that they must be suitable for picking up and clearly reproducing speech. In addition, the systems also broadcast over certain frequencies. The Tour Guide system therefore consists of fixed or portable RF transmitters and portable, wireless RF receivers. Tour Guide systems pick up the voice of those who speak in the headset microphone of the transmitter and send it over a specific channel (frequency), in the form of radio waves, to the receivers. These then make the voice audible to the listeners through the earphones/headphones. In addition to these 1-way Tour Guide systems, 2-way systems are also available, which offer the opportunity for listeners to communicate with the speaker. Sending and receiving goes both ways with these communication systems. Most Assistive Listening devices, such as Tour Guides, operate in the frequency range of 72-76 megahertz and 216-217 megahertz.
The correct application of the Tour Guide system
Every listener gets a receiver that is set to the same frequency as the speaker’s transmitter. Many Tour Guide systems offer the possibility to send over multiple channels at the same time. This allows multiple tours to be given simultaneously for different groups with one channel. This also makes it possible to broadcast in different languages, making the system ideal for translations. The signal transmission from Tour Guide systems works within the globally available (Ultra High Frequency) UHF frequency band, although the legally determined free license of this frequency standard varies from country to country. It is possible that the transmission on the standard fixed transmission frequency does not work without problems. If there are other transmitters in the vicinity, they can interfere with each other and cause interference of the signal. This is also called intermodulation. Fortunately, it is usually possible to adjust the transmission frequency of the Tour Guide systems. It is important here that the desired frequency in the country concerned is approved and legal. You may even need to apply for a license to send on other frequencies. When changing the transmission frequency, make sure that the channels are tuned to the same frequency as the receiver. Some systems do this automatically, so the Tour Guide systems from T-audio offer a synchronization kit. This can be used inside the charger and automatically adjusts the frequency of the receivers to that of the transmitter. If several groups are accompanied by one channel, the frequency of one group must differ from that of the other, so that they do not disturb each other when broadcasts are made simultaneously. There are also Tour Guide systems that use radio frequency (RF) or infrared (IR) technologies. These systems offer the most flexible approach with the largest possible, most reliable and highly effective transmission between the sender and receiver(s).
The perfect solution for your project
Looking for the perfect microphone or Tour Guide system for your project. Need advice while purchasing or installing the right audio setup? Or do you, as an end user, want an installation carried out by one of our dealers? Tau has an enthusiastic team of audio specialists, they are happy to help with questions. Contact us via contact form or +31 (0)50 549 90 90.
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