Audio Engineering

P.A. Systems

Amps are designed to produce it's maximum power (W) to a given amount of impedance (Ohms). This impedance is most often 4 Ohms, and is usually marked close to the speaker outputs. This value indicate that the amp will produce it's most power (W) when the speakers connected to it apply totally 4 Ohms. Due to the formula P = (U^2) \ R, every value above this will give less power (W) to the speakers, and if the connected value is less than this the amp might overheat since it gives more power (W) than it is designed for. To connect more speakers to the same amplifier will commonly increase the connected impedance, and decrease the power (W) out, and therefore not increase the sound level. Modern amps have a "sikring" which turn the amp off, or automatically decrease the volume if it pulls to much current from the "nettspenning", or if the temperature gets to high.

Impedance of two speakers is calculated by the formula for two shunt-resistances. Rt=(R1*R2)\(R1+R2)

Impedance of more speakers is calculated by the general formula for shunt-resistances (1\Rt) = (1\R1) + (1\R2) +...+ (1\Rn)

A mixer will often have two different impedance values, one for the microphone amps, and another value for the speakers out. Mixers without microphone amps will usually have two input-impedances, "Low impedance" and "High impedance". XLR-connectors are low-impedance, and jack-connectors are high-impedance. If connecting the wrong signal to the wrong input will not brake anything, but just lower the input volume and cut away some of the incoming frequencies.

There are two types of equalizers, graphic and parametric. Graphic EQ's has a set of predefined frequencies where the volume can be adjusted. Parametric EQ's have variable frequency-controllers, and will affect a chosen area around the selected frequency as well.

"Delefilter" is used in all speaker-systems with more than one element, and divides the incoming signal into two or more separated signals containing different frequencies. This will stop the low frequencies from reaching the high-pitch element. If a "delefilter" is inside a speaker, it is usually passive, but if it is connected to a voltage source by itself, it is active. That means that they contain own amplifiers for each separate signal. A "delefilter" will usually therefore increase the sound quality.

Dictionary:

"2-Way" A speaker with two elements

Microphones:

"Polar patterns"? :

Omni directional - Pick up sounds from all directions. Commonly rarely used in music-recording.

Uni Directional

1) Shotgun - Picks up sound only from straight in front of the microphone.

2) Cardioid - Picks up sound in a "heart-shaped" pattern, with most from the front of the microphone.

Drums:

A drum is a cylinder-shaped "shell", made out of wood, "kompositt"?, plastic, steel or steel"legeringer".

Tree"sorter":

Maple (Lønn) Hard wood. Good resonance nice "finish"? Warm and rich sound with an even frequency-spectrum.

Birch (Bjørk) Kompact wood. Gives 10% less bass-tone, and 20% more high pitch sounds, compared to maple.

Mahogany (Mahogni. From USA or Honduras) gives 20% more bass-tone then maple. Warm sound because of this.

Beech (Bøk) Somewhere between maple and birch.

Oak (Eik) Bright, "gjennomtrengende" tone with high attack.

Less common wood types:

Basswood (Lind), Poplar (Poppel), Philippine Mahogany (Filipinsk mahogny) or combinations of wood types.

Shells (Trommeskjell)

The smoother shells are on the inside, the more resonance the drum gives. Using thick shells means that it is mostly the skin which gives the tone. Thin shells gives more resonance, and has a lower pitch than thick ones. Drums with reinforcement rings (forsterkingsringer) has a shorter decay (etterklang) and more powerful attack in the middle-pitch area.

Skin

Clear (Transparent) Bright sound with "overtoner". Nice attack which cut through the soundscape.

Coated (White) More powerful attack, warmer sound and lower high-pitch than the Clear. This type is nessicary for using "visper"

"2-Layers" (2-lags) Reduce "overtoner", deep and heavy sound which can handle harder playing, but less "feel".

Underskin is usually clear for tom-toms, example Remo Ambassador, Genera G1. For snare is it custom-made for "seider"

Hoops\Rims (Ringer)

Flanged\Triple flanged hoops (valsede) gives a deep and fat sound, mostly used for tom-toms. trickier to tune than Die Cast Hoops. Steel rims give a deeper pitch than aluminium.

Die Cast Hoops (Støpte) Thicker and stronger than Flanged rims. Gives more smooth tuning, and better response and less "overtoner". A bit drier sound and more powerful attack than Flanged rims.

Wood Hoops (treringer) Can sound as both above dependent on it's thickness. The higher pitches are more reduced than the above.