WIRELESS MICROPHONE FAQ
1. Differences between VHF and UHF
VHF wireless microphones are utilized mainly in the 170-200 MHz band range. The UHF is mainly used at the 600-900 MHz band. Presently, the VHF range is saturated due to a large number of users. It is worsened with excessive self-interference signals and other types of electrical RF interference. Consequently, the professionals tend to move to the UHF ranges. Additionally, the PLL Synthesized feature allows multi-channel agility. It avoids interference caused by other RF signals and electrical appliances to assure better performance.
2. True Diversity vs. Non-Diversity Design System
Signal drop-out is enemy #1 of all wireless microphone users. Unless an uninterrupted signal can be guaranteed, users will always favor a wired microphone.
This is where diversity reception comes in to its own. Diversity reception is basically the use of two antennas, which simultaneously poll the incoming transmitter signal and combine to provide an uninterrupted signal to the receiver. The chances of experiencing signal drop-out are 5 times less using diversity reception than they are with single antenna systems. Further, by increasing the signal strength by 10dB, the improvement is a factor of 45 times. Therefore, with a diversity system, neither signal drop-out or noise will be problems over normal transmission distances. Based on this principle, a diversity system is a must for applications that require guaranteed professional audio performance.
Similarly, where longer distance transmission is required, diversity reception offers a much greater chance of the receiver providing a clean output. Wireless microphones are not two-way radios or walkie-talkies
Many users do not realize that single antenna systems can be subject to dead spots in their pick-up pattern. This is because the transmitter signal arriving at the receiver antenna is actually a combination of several signals, some direct (from the transmitter) and some reflected (off walls for example). If these signals arrive at the receiver antenna in an out-of-phase condition, then they can combine to cancel each other, causing a signal drop-out as a result. Of course, the closer the transmitter is to the receiver, the less frequent dead spots or dropouts will be. So, many manufacturers offer single antenna, non-diversity systems for entry level, non professional use ¨C applications where transmission distances are short and some signal drop-out can be tolerated. The MR-823 is designed for the entry-level market where a non-diversity receiving mode is acceptable. The MR823 is ideal for short-distance Karaoke shops, but NOT applications on the professional stage, difficult environments or for long-distance transmissions. Users should choose a receiver with dual-antenna "diversity" receiving operation (e.g. MR-801 or similar) for these professional and critical applications.
3. How many multiple systems can be operated simultaneously without interference?
The most difficult challenge facing wireless microphone systems is to use multiple systems simultaneously without interference. The more frequencies used, the worse the interfering problems. In order to avoid interference one must first choose non-interference frequencies, reject the surrounding external interference, have an excellent selectivity feature and filter out cleanly at the radiating spurious emissions. The average VHF range receivers can be operated with 12 non-interference systems. That is considered a good result. However, every MIPRO series can be installed up to 24 non-interference systems. In testing, MIPRO has achieved over 50 VHF and 64 UHF non-interference frequencies.
4. Does Your Wireless Microphone Receiver Need A Volume Control?
A volume control on a wireless receiver can cause problems:
For many years, manufacturers of wireless microphone systems have included a volume control (VR) feature on their receivers, usually on the front panel. This was to allow the user to adjust the wireless microphone (receiver) output level going to the mixer or amplifier. However, experience has shown that even with the benefit of a detailed explanation in the operation manual, many users set the VR incorrectly and do not fully understand the VR's place in the overall signal chain. If the VR is set incorrectly, it can cause either a poor S/N ratio due to insufficient sensitivity, or overload distortion due to too much level at the mixer/amplifier input. Either problem results in perceived poor performance from the sound system. When this occurs, users commonly complain or think ill of the wireless system, citing poor sound quality or insufficient dynamic range instead of the identifying the true cause of the problem: an incorrect VR setting.
Understanding the input characteristics of mixers and amplifiers:
A mixer or amplifier usually includes both "LINE IN" and "MIC IN" inputs. These inputs may use the same input connection with selectable settings or be separate. "Line In" inputs are used for inputs from "line level" sources, such as a radio tuner, cassette recorder, CD player, etc. "Mic In" inputs are used for microphones and are at lower signal levels than line level signals. In both cases, the inputs of the mixer/amplifier are roughly matched to the expected input signal level in terms of sensitivity and dynamic range. The mixer/amplifier usually includes a sensitivity trim adjustment for each input, allowing the user to exactly match any input signal to the performance specification of the mixer/amplifier. Therefore, as the output signal from a wireless receiver is optimized for that particular wireless system (and the output can be at microphone level or line level depending on the specification of the system), level adjustment and matching should take place at the mixer/amplifier, not at the wireless receiver output. The mixer/amplifier should process an optimized input signal, not a signal that has possibly been degraded by an incorrectly set VR on the wireless receiver.
Why Mipro prefer not to provide a user adjustable receiver volume control:
MIPRO wireless receivers have an optimized output level that is factory QA aligned to exactly match the microphone capsules sensitivity. This means that the receiver can be connected directly to a mixer/amplifier with guaranteed optimum sensitivity and dynamic range levels. Therefore, users can operate MIPRO wireless microphone systems exactly as if they were working with a wired microphone, that is, without the need for any receiver adjustment.
The absence of any user accessible VR means that premium results are guaranteed every time, without the fear that some well intentioned assistant may have changed any of the settings.
Volume controls are traditionally a source of induced system noise, particularly as the system ages. Eliminating the VR simply means that premium results are guaranteed for longer.
The absence of a volume control allows the designer to provide a cleaner and less cluttered front panel layout.
5. What is a SQ? Functions and How to use it?
SQ means squelch control. The receiver needs to receive a certain degree of RF signals in order to maintain clarity of sound quality. When signal strength falls below the signal/noise ratio, the SQ will activate, muting the receiver and preventing noise output. Due to certain noise strengths, SQ must be adjusted to eliminate interference signals. If SQ activates at 12dBuV and when SQ is adjusted clockwise, it strongly eliminates external noise, however, it shortens the operating distance.
When stand-by receiver is being interfered, SQ can be adjusted this way to eliminate the problem. When noise persists at this adjusted maximum level, it means the external interference signal is too strong. In this situation, substituting a new system with a different frequency is advised.
6. How to Hold a Wireless Hand-held Microphone in order to Achieve the Best Sound Performance
It is with regret that I often see many users holding their wireless hand-held microphones in various major stage, TV and concert performances using incorrect techniques. Inappropriate usage of a premium microphone can not only diminish its original superb performance characteristics and sound quality, but can even make it seem no better than an inferior quality microphone.
Many audio engineers have their own microphone sound preferences and feel that they can obtain the sound they want by simply using a leading brand name of microphone coupled with their own sound adjustments. The importance of mentoring the users in the art of correctly using a microphone is often sadly overlooked. A microphone is simply a part of the complete audio system. A satisfactory sound cannot be achieved, even when using the most expensive microphones, without a thorough understanding of the proper usage and adjustment of the microphone as well as the other related audio components. The same principle applies in driving an expensive sports car. If drivers are not fully aware of a car's unique characteristics and operation, they will be unable to get the maximum performance out of the car.
Below are a few recommendations to enhance the sound of a microphone:
Do Not Grab and Cover the Microphone Grille
Many performers tend to hold the microphone by the grille. Unfortunately, this position seriously degrades both the sound quality and directionality of a microphone. Even the most expensive microphone will have its original sound quality compromised by this method. Grabbing a microphone by the grille will isolate the capsule's acoustic resonance circuit and/or change the capsule resonator's frequency. This results in an inferior performance in both frequency response and the separation of directionality. In addition, a palm's sound-focusing effect will tend to strengthen resonances in certain frequencies and can cause unwanted feedback.
Although a wireless microphone is convenient and safe to use without those tangling cables, users often negate their inherent superior characteristics by the use of improper techniques in holding the microphone. Therefore, to achieve the best sound possible, a microphone user must learn the proper techniques, which fortunately are rather simple. The single most important principal to remember is to always hold the microphone by its housing or body instead of covering the microphone grill.
Do Not Hold Over the Antenna
Traditional design has protruding antenna . Modern design has built-in antenna or external design. If users hold the microphone over or near these areas the transmission range will deteriorate. The transmission range will deteriorate severely if holding it with both hands.
Do Not Hold Two Microphones in One Hand
Holding two different frequency transmitters in close proximity can cause intermodulation interference. This is especially risky in multi-channel system operations where issues such as interference and unstable reception can easily cause the audio quality to deteriorate.
Close proximity causes interference in a microphone's audio frequency phase and directionality, and can destroy a microphone's default characteristics, apart from just RF interference. When both microphones' audio signals are in phase, it adds up to two microphones' audio output and a subsequent sudden increase of the amplifier volume, thus causing feedback. Conversely, if the signals are out of phase, they will offset each other's output and result in insufficient volume.
When two microphones get close to each other, their directionality will interfere with each other and destroy their default directionality. Performance tends to get worse as the distance between two microphones diminishes. Therefore, users should avoid the practice of holding two or more microphones simultaneously in one hand to prevent an undesirable loss in output volume, frequency response, and directionality. If more microphones need to be used simultaneously, then keep one microphone at least 30 cm away from the others to reduce the likelihood of detrimental changes in performance.