Understanding Impedence/Ohm Load

In car audio community, you will often hear the terms impedence, ohm load or sometimes you will even get asked what are you wired down to.  To put it simply, the electrical signal sent from amplifier to the speakers has electrical resistance. 

That resistance is measured by Ohms.  You can increase and decrease your resistance by wiring your speaker in parallel or series.

***PLEASE NOTE*** All information on this site is for educational and informational processes.  Any guidelines, tips or recommendations are considered general knowledge and we strongly encourage you to consult with a professional before installing, adjusting, or altering a car audio system.

Speakers can be purchased in a variety of types and in car audio they are usually in the range of 4-16 Ohms.  Depending on how many speakers you are wiring to an amplifier as well as how you wire them (series or parallel) will determine you Impedence or “Ohm Load.”  When purchasing an amplifier you will notice it has a variety of output ratings.  These rating variations are referring to the output depending on ohm load put to the amplifier.

For more on wiring in parallel versus series, check out this article by Geoff the grey geek: https://geoffthegreygeek.com/calculator-speakers-in-parallel/ or watch his video below:

 

Watch the original video on YouTube:
https://www.youtube.com/watch?v=gvaojICThzg

 

***PLEASE NOTE*** All information on this site is for educational and informational processes.  Any guidelines, tips or recommendations are considered general knowledge and we strongly encourage you to consult with a professional before installing, adjusting, or altering a car audio system

Impedence Matching

Loudspeaker amplifiers

Schematic diagram of amplifier and speaker, with two tubes and an impedance-matching transformer.

Typical push–pull audio tube power amplifier, matched to loudspeaker with an impedance-matching transformer

Audio amplifiers typically do not match impedances, but provide an output impedance that is lower than the load impedance (such as < 0.1 ohm in typical semiconductor amplifiers), for improved speaker damping. For vacuum tube amplifiers, impedance-changing transformers are often used to get a low output impedance, and to better match the amplifier’s performance to the load impedance. Some tube amplifiers have output transformer taps to adapt the amplifier output to typical loudspeaker impedances.

The output transformer in vacuum-tube-based amplifiers has two basic functions:

Separation of the AC component (which contains the audio signals) from the DC component (supplied by the power supply) in the anode circuit of a vacuum-tube-based power stage. A loudspeaker should not be subjected to DC current.  Reducing the output impedance of power pentodes (such as the EL34) in a common-cathode configuration.

The impedance of the loudspeaker on the secondary coil of the transformer will be transformed to a higher impedance on the primary coil in the circuit of the power pentodes by the square of the turns ratio, which forms the impedance scaling factor.

The output stage in common-drain or common-collector semiconductor-based end stages with MOSFETs or power transistors has a very low output impedance. If they are properly balanced, there is no need for a transformer or a large electrolytic capacitor to separate AC from DC current.



Similar to electrical transmission lines, an impedance matching problem exists when transferring sound energy from one medium to another. If the acoustic impedance of the two media are very different most sound energy will be reflected (or absorbed), rather than transferred across the border. The gel used in medical ultrasonography helps transfer acoustic energy from the transducer to the body and back again. Without the gel, the impedance mismatch in the transducer-to-air and the air-to-body discontinuity reflects almost all the energy, leaving very little to go into the body. The bones in the middle ear provide impedance matching between the eardrum (which is acted upon by vibrations in air) and the fluid-filled inner ear.

Horns are used like transformers, matching the impedance of the transducer to the impedance of the air. This principle is used in both horn loudspeakers and musical instruments. Most loudspeaker systems contain impedance matching mechanisms, especially for low frequencies. Because most driver impedances which are poorly matched to the impedance of free air at low frequencies (and because of out-of-phase cancellations between output from the front and rear of a speaker cone), loudspeaker enclosures both match impedances and prevent interference. Sound, coupling with air, from a loudspeaker is related to the ratio of the diameter of the speaker to the wavelength of the sound being reproduced. That is, larger speakers can produce lower frequencies at a higher level than smaller speakers for this reason. Elliptical speakers are a complex case, acting like large speakers lengthwise and small speakers crosswise. Acoustic impedance matching (or the lack of it) affects the operation of a megaphone, an echo and soundproofing.


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