• Basic electricity formulas

    Although it not specific to sound, we include this document with some basic electricity formulas. They can be found in any electricity textbook, but we have added them to the DoPA Library for reference.

    Ohm's law

    The most basic formulas derive from Ohm's law, which specifies that the electric current between two points is proportional to the potential difference (voltage) between them and inversely proportional to the resistance between them. The formula is:
    V
    I = ———
    Z


    where I is the current (intensity) in amps and V is the voltage in volts. Since we use alternating current in audio, we have replaced resistance with impedance (Z, and this could also be resistance R), measured in ohms. Clearing Z and V we have these other two formulas:

    V
    Z = ———
    I

    and
    V = I*Z

    Joule's law

    Electrical power is the rate at which an electrical circuit transfers electrical energy. It is measured in watts, after the engineer James Watt famous for his advances in steam engines.

    This formula is erroneously assigned to Ohm's law even though the original law did not include it. Joule's law determines that electrical power is given by the product of voltage and current:
     
    P = V*I
     

    Combinations of both laws

    When we combine both laws (Ohm's law which determines the current and Joule's law which determines the power) we obtain numerous derived formulas which are added to the original ones. A usual way of bringing them all together is by means of this circle of formulas:






  • Ad

  • News

    Proel launches WX series stage monitors

    Italian manufacturer Proel has introduced the WX series of compact self-powered stage monitors. According to the brand they have "perfect sound intelligibility, uniform directivity, high SPL and an ultra-compact form factor,... Read more

    Celestion debuts CDX1-1412 compact HF compression driver

    Celestion, suppliers of professional loudspeakers and compression drivers for sound reinforcement applications is pleased to introduce the new CDX1-1412 1” exit, neodymium magnet high frequency... Read more

    New single magnet coaxial speakers from lavoce

    Lavoce Italiana are introducing the first products from their new Common Magnet Coaxials category, starting with a ferrite magnet 8”, and neodymium magnet 12” and 13.5” models, available with or without aluminium... Read more

    EAW launches NTX Series articulated line array

    Eastern Acoustic Works (EAW) has announced its NTX Series line array and SBX Series subwoofer complement.

    EAW’s NTX201L is a powered articulated line array (unlike Anya and Anna's flat hang concept) with an on-board 1600W (peak)... Read more
  • Recent articles

    Intelligibility and its measurement

    1. What is intelligibility?

    The state or quality of being understood. It can apply to an idea or a writing, but in our context it relates to the spoken word and, less commonly, to music.... Read more

    Choosing loudspeaker cable

    The importance of cables for the connection between the amplifier and the speaker is often controversial. Hi-fi aficionados spend fortunes on cables that promise spectacular results, and our short auditory memory and subjectivity lead many to confirm these improvements in their systems.... Read more

    Constant voltage systems (70V, 100V lines)

    Constant voltage, high impedance or line transformer systems are often a somewhat confusing concept for professionals used to rock and roll. They are actually very simple to design, among other things because they are intended to be installed by electricians and the like, with little experience in sound systems. In this article we will try to clarify the simple concepts needed to understand this type of system.... Read more
  • PAcalculate app