Studio 41 - Microphones III

Entertainment rlawlsgh275 August 8, 2016 0 0
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After a series of approximately 40 column-like articles on the home studio, now a series in which I pay attention in more detail on certain aspects in and around the home and recording studio. The texts of these articles are based on the previously written by me "The Big Record Book '. Note: I have no financial interest in selling it!

Polar pattern

One of the most striking characteristics of a microphone is the directional characteristic, which prevents from the specific structure of the membrane, house and hairstyle. Each microphone type or design has a certain directional characteristic, which is shown in a typical polar pattern or directional pattern. In a radius of 360 degrees, the response of a microphone for the signals provided does not appear to be everywhere the same. Here is also the sensitivity indicated for certain frequencies. This can be in different shooting situations, both favorable and unfavorable. A pressure microphone has a diaphragm, which, in principle, only the front side is in contact with the incident sound waves and therefore only responds to changes in sound pressure. An example of this is the omnidirectional microphone. A drukgradiëntmicrofoon has a membrane, which both at the front and the back is in contact with the incident sound waves. This type of microphone picks up sound waves only when a pressure differential occurs between the front and back of the membrane.
The eight-shaped cardioid microphone, and are examples of this. The dynamic microphone usually has a directional pattern defined by the manufacturer. Because of the design and the resulting relative insensitivity, as well as the pricing this type has a cardioid directional characteristic. A professional recording studio often provides more polar pattern provides a flexible technician adjustments in various shooting situations. The design of these models is based on the presence of two parallel membranes, which are fixed to a common plate. In fact, it is a mated pair of cardioid microphones with a single coincident point. Through a combination of switchable resistors these membranes according to need in the desired directional characteristic can be put and provided with the necessary polarization voltage. By changing the signal level and the phase of one of the two membranes to rotate is obtained a achtvormig- or omni pattern; a whopping 2-9 combinations are conceivable. The necessary electronics and engineering translate into hefty purchase price. Some manufacturers have a microphone system comprising a microphone housing with detachable elements, in order to adapt the characteristic curve as desired.

Around sensitive microphone

In an omni microphone is, the sound pressure at the membrane is directly dependent on the pressure of the incoming sound wave and not the derivative thereof. This type exhibits only then an omni pattern when the wavelengths of the incident sound waves are large compared to the diameter of the membrane. In order to determine the frequencies from which the microphone will behave with an omni characteristic, the general rule is the frequency that corresponds to the diameter of the membrane. The microphone will then only show good omnidirectional characteristics when the incident frequencies are between two and three octaves below this fixed frequencies. A microphone membrane has e.g. a diameter of 2.25 cm, wherein said corresponding frequency is approximately 15 kHz. An octave is lower than 7.5 kHz, two octaves lower corresponds to 3.75 kHz and 2 kHz with about three octaves. The microphone has an omni frequencies up to this characteristic. Here, the direction sensitivity decreases at higher frequencies according to this reasoning, slightly increasing.
The designers of microphones to keep the construction of the membrane take account of this fact; alongside a number of other factors. For example, the construction of capsule and microphone housing are decisive for which high frequencies are incident at a certain angle on the membrane. In a non-symmetrical shape of the capsule may include intermodulation distortion occurs. Thus, when two different frequencies simultaneously arriving on the capsule, this results in a mixing signal of original frequencies, together with the sum and difference frequencies. This eventually results in a weaker and less defined signal. Some models are specially designed for specific applications, for example, think of bass drum microphones. A good microphone designs is not an easy task, since the microphone the first vital step forward in the registration of sound.
A microphone that can display representative of the frequency of the sound recording source, will pick up less noises. Therefore, many technicians prefer rather a microphone with a neutral response, instead of an appropriate frequency response. The low frequencies are indeed well represented, but the high frequencies are usually a volatile pattern.
A small diaphragm microphone with a diameter of 10-13 mm, at most, typically exhibits a uniform response for all frequencies. Incidentally, some of the older large diaphragm microphones tend to amplify high frequencies, thus sharp peaks fall into the recording signal. A large diaphragm microphone registers the other hand, often low frequencies and thus sounds better warmer, because the self-resonant frequency of the diaphragm is low as compared to small diaphragm microphones.
In recording practice omnidirectional microphones used regularly in performances and recordings of classical performances. This type is less suitable in situations with many disturbing signs around, although they properly can also contribute to an open and spacious atmosphere. Crosstalk occurs in use with this microphone. This means that records microphone signals, which are actually meant for an off microphone. When recording of a single instrument is crosstalk often unfavorable because of the mixing of unwanted interference signals. When recording of a larger whole, such as drums, choir or ensemble, cross-talk contribute to the natural sound.
In live situations works dosed crosstalk often enhance the atmosphere. The technician must then take into account uncontrolled feedback systems to monitor microphones. This allows the microphone signal will loop, which for the musicians on stage and the audience is unpleasant. In the professional recording studio with separate recording and control rooms comes howling rare. Home studio, it is recommended that available when adjusting microphones with only one space - always - to operate at low volumes howling through the speakers and to prevent adverse effects on hearing and boxes.

Directional microphone

The directional shape is suitable for gigs or studio work, for collecting the close and situated right source. The studio work requires a controlled withdrawal of one individual instrument without crosstalk or interference. Examples include the cardioid, the hypercardioid or supercardioid microphone. These forms are stronger directional, but register by construction slightly too the sound that passes directly from behind. By contrast, the contribution of lateral incident sounds is largely negligible. A telephoto or shotgun microphone is provided with a long acoustic extension tube through which the directivity greatly increases. The principle of the interference tube, resulting in phase-quenching of laterally approaching signals. The disadvantage is the reduction of the response of signals having a wavelength which is smaller than the physical length of the interference tube.
The direction of sensitivity is good at relatively high frequencies, but greatly decreases at lower frequencies up to the level of a normal cardioid microphone. This is similar to the response of the microphone without the interference tube. So the microphone shows sensitivity to low frequency interference. A low-pass filter is necessary. The construction has another disadvantage, which is especially in a confined space is reflected; namely indirect sound has reverberations an unpredictable pattern of angles and phase shifts, allowing the principle of interference also functions less well. This type we see regularly in outdoor scenes in the film and video world. For this, a windscreen is required and the sound engineer is required to use the microphone with caution. Due to the high directivity, the unwanted record of unpredictable reflections and low frequencies, the handset is extremely rare in the recording studio.
The human ear is capable of soft sounds in the surrounding our three-dimensional space in the background can be observed, while a directional microphone mainly records the more sure located signal source. A home studio normally has a limited isolation with respect to sounds from the outside to the inside. By opting now for a directional microphone, the background noise can be virtually eliminate. By limiting careful microphone placement and any additional interventions in the field of sound recording is also the level of internal jammers in the recording area to a minimum. The hearing in this respect is so much more critical than a microphone.

Eight-shaped microphone

The 8-shaped microphone is a drukgradiëntmicrofoon with a strong directional characteristic and are performed on both sides of the membrane. One of the side input signal, delivers to both sides of the membrane, a similar motion, so that the resultant of said signal is almost negligible. The microphone is used to record, for example, two background singers, in which their position on both sides is located in the extension of the membrane.
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