# Essentials

## Formulas and tables

### Load-to-Power Relation in 100 V Systems

 10 Ω = 1000 W 20 Ω = 500 W 25 Ω = 400 W 40 Ω = 250 W 50 Ω = 200 W 100 Ω = 100 W

### Crest Factor

The Crest Factor of an amp represents the relation between the peak voltage and the RMS value. It can be taken as a measurement of the quality of the response of an amp.

 Crest Factor = Peak = 1 x Peak RMS √2

### Resistance – Power

 Ohm’s Law: U = I x R ;   I = U ;  R = U R I
 Power: P = I2 x R ;   P = U2 ;  P = U x I R

Resistors in series:  Rtotal = R1 + R2 + … + Rn

Resistors parallel:  Rtotal =   1
 1 + 1 + … + 1 R1 R2 Rn

### Voltages in dBV und dBu

 10 V = 20 dBV = 22.2 dBu 1.55 V = 4.2 dBV = 6 dBu 1 V = 0 dBV = 2.2 dBu 775 mV = -2.2 dBV = 0 dBu 316 mV = -10 dBV = -7.8 dBu

### “dB”-Relations

 Voltage: dB = 20 log10 U1 U2
 Power: dB = 10 log10 P1 P2

### Conversion of THD to dB below signal level

 THD % dB belowsignal THD % dB belowsignal 10010510.50.25 0-20-26-40-46-52 0.10.050.010.0050.00250.001 -60-66-80-86-92-100

### Voltage to Power

 Volt Watt4 Ω Watt8 Ω Volt Watt4 Ω Watt8 Ω 63.244.831.628.222.4 1000500250200125 50025012510062.5 2014.1106.32 1005025101 502512.550.5

### Pinouts

 XLR : Pin 2 (+), Pin 3 (-), Pin 1 (Ground) XLR unbal. : Pin 2 (+), Pin 1 and 3 (Ground) 6.3 mm TSR : Tip (+), Ring (-), Sleeve (Ground)
• Infobox
• Markus Ackermann
September 2011