In the diagram, the large peak corresponds to a point at which both mass (the cone, cone suspension, spider and the voice coil) of the assembly and spring resonate most freely. If the frequency values decrease, then so too does the reactance and impedance of the coil. The diagram below provides a visual representation of how a speaker impedance changes with changes in frequency:Ĭhanges in impedance occur due to 1) resonant frequencies 2) increase and decreases in impedance i.e voice coil of the speaker acts like an inductor.īecause frequency and inductive reactance are directly proportional, a 4Ω voice coil only measures 4Ω at a specific resonant frequency. Reactance: An important factor in the circuit is the speaker and how it reacts to changes in the signal frequencies with regards to impedance. For the most part, the tone will not be impacted by increasing attenuation using T or Π topology. T or Π topologies will allow for both input and output impedances to match those impedances prior to adding the attenuator e.g. Any impedance presented to a speaker which is lower than the optimal impedance will result in a 4Ω amp out/4Ω speaker in after attenuation results in the following: 4Ω amp out/2.2Ω speaker in). For example, an L section attenuator is not fit for purposeĭue to the fact that the input impedance remains the same and the output impedance does not (e.g. Impedance Matching: It is important that the load the attenuator presents to both amplifier and speaker remain the same (or as close to) as they were before the attenuator was added into the circuit. There are two important factors to consider when designing or buying a attenuator: It is important that when using an attenuator to attenuate a guitar amplifier signal that the tone is not impacted in any way. The T pad attenuator, the Π pad topology keeps both input and output impedences the same.Īpplication of Passive Attenuators in Amplifiers The topology has a single resistor in the signal line and input and output resistors to ground. Π pad are balanced passive attenuators (although can be made unbalanced). This inĮffect means the tone of the amp should remain the same during attenuation. impedance presented to the amplifier and to the speaker, for the most part (see notes on reactance), remain the same as before therefore no impact on amplifier output section or speaker input. Input and output impedances remain the same i.e. The use of this type of topology for guitar amp attenuators is more effective because both The topology has a single resistor to ground and a series of resistors on the input and output. T pad are balanced passive attenuators (although can be made unbalanced). The drawback being that the speaker no longer sees the same impedance from the amplifier therefore impacts the strength of the signal and tone. Many guitar amplifiers and pedals use this simple design because it is cheapĪnd effective for attenuation. L pad is basically a potential divider circuit which is designed to match Zi (input impedance) but not Zo (output impedance). L pad are the most basic form of passive attenuators. There are common forms of passive attenuators which use simple resistor networks: The circuit is made up of a signal source, input impedance (Zi), attenuator and output impedance (Zo).įor the purposes of this article only passive constant impedance attenuators ( both Zi and Zo remain the same) and their application within amplifiers will be covered. The diagram above provides a simplified visual representation of an attenuator circuit. While an amplifier provides gain, an attenuator provides loss, or gain less than 1. An attenuator is effectively the opposite of an amplifier, though the two work by different methods. An attenuator is an electronic device that reduces the power of a signal without appreciably distorting its waveform.
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