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Chaudhary 1
Shiva Chaudhary
Andy
Live Sound I- T Th. 2:30-5
8 May 2014
Impedance
Audio electronics has many concept and ideas that are misunderstood and can be
confusing. One such concept is impedance and its involvement in electronics and audio. If
ignored, impedance can cause many complications and negative consequences. In a nut shell
impedance is what it sounds like the electrical flow that is impeded through a circuit. With ideas
such as impedance matching and math formulas to help estimate impedance, several of these
pitfalls can be avoided and a better audio signal can be created.
As said before impedance is the electrical flow that is inhibited through an electrical
circuit. A step above that, impedance is the combination of reactance and resistance, which can
be expressed in a mathematical formula. Reactance is the obstruction of electron flow in
alternating current, and resistance is the same but in direct current. As shown by Tutorial the
formula used to express impedance is = √𝑅 2 + 𝑋 2 , where Z is impedance, R is resistance, and
X is reactance.
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Similarly the formula is the same as Pythagorean Theorem used to find the hypotenuse of a
triangle. This will be discussed later as to why. Another thing to take note is the impedance of a
resistor and a capacitor with this formula. A perfect resistor has no reactance because it only
resists current in a direct current flow (Tutorial). This makes its impedance 𝑍 = √𝑅 2 + 02 = 𝑅.
With a perfect capacitor there is no resistance and only reactance with alternating current. This
makes its impedance 𝑍 = √02 + 𝑋 2 = 𝑋. This all shows how the combinations of resistors and
capacitors have an effect on the overall impedance of a device, and how individually each one
affects the formula. If graphed on a piece of paper impedance has two dimensions to it (Gibilisco
267). If it was on a graph the reactance would be the Y-axis and the resistance would be the Xaxis. If a point was placed on the graph for a device with a certain reactance and resistance of (X,
Y) the impedance would be the distance from (0, 0) to (X, Y). Coming full circle, this is solved
with Pythagorean Theorem because if noticed a triangle is formed if the lines are connected from
point (0, 0) to (X, 0) and (X, Y) with the legs of the triangle being X for resistance and Y being
reactance. This is how the formula was made to discover impedance, which is the same as
Pythagorean Theorem.
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The angle at which the vector, or the hypotenuse of the triangle, is pointing also helps in
deciding how the impedance of the circuit acts within the circuit (Tutorial). These formulas all
help one understand how impedance is figured out and if necessary, one can find out the
impedance of an electrical circuit given the tools to figure out voltage and current. With a
general understanding of impedance now, the topic of impedance matching can begin.
The biggest concept to understand with impedance would be impedance matching.
Impedance matching is the way that one can have the least amount of power lost between two
devices. If not done properly, one can damage one’s equipment or not have the power wanted to
fully run one’s speakers, for example, at optimum levels. Many devices, such as microphones
amps, and speakers have their impedance written on them or in their guide. With amps the
possibility of choosing the impedance is possible with two or three options to pick from.
When it comes to impedance matching the best policy is to go 1 to 1 (Biederman 290). This
meaning that if the resistance of a speaker is 4 ohms, the impedance to pick on the amp is also 4
ohms. This makes it very simple to remember. Now the confusion occurs when one wants to not
have one hundred percent of the power sent possibly due to not overheated or conserving power.
Biederman states “…it is never advisable to use an amp to power a speaker that has lower
impedance than the amplifier, but it is perfectly safe to power speakers that have higher
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impedance” (290). This means that if an amp had the options of 4 ohms, 8ohms, and 16 ohms to
pick from and one was using an 8 ohm speaker, a person who picked 4 ohms would be perfectly
safe. In this example a 4 ohm amp to an 8 ohm speaker only draws in fifty percent of the power
into the speaker. This could be done purposefully if one wanted to not overheat the device or if a
limited amount of energy was available. If 8 ohms were used on an 8 ohm speaker one hundred
percent of the power would transfer, which is usually optimal. The last example would be using
16 ohms on an 8 ohm speaker. This would cause two hundred percent of the power to be pushed
into the speaker, most likely overheating it and possibly frying the amp and speaker. Another
thing to consider is if one was using more than one speaker and if the speakers were connected in
series or parallel. Biederman says “When two or more speakers are placed in series, the
impedances add together to produce higher impedance. R=resistance (the ohm rating of your
loudspeaker): R=R1+R2+R3+R4” (291). This means that if two speakers were connected in
series and each had 4 ohms then the amp would need to be 8 ohm for it to be 1 for 1 or balanced
and having matched impedance.
Biederman also states “When two or more speakers are placed in parallel, the impedances
combine in a different way to produce lower impedance. Multiply the resistance of all speakers
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and then divide the product by the sum of the resistance of all speakers. For two resistors, this
simplifies to: R= (R1 X R2)/ (R1 + R2), or if the resistors (speakers) have exactly the same
value: R= R1/2” (291). This means that if two 8 ohm speakers were connected parallel, that the
resulting impedance to match the amp with would be 4 ohms.
One last thing to notice is that speakers connected in series increase the impedance while
speakers connected in parallel lower the impedance. This can come in handy if an amp has only
one setting for impedance and several speakers are wanted to be used. One can create a
combination of speakers in series and in parallel to make a balanced impedance match.
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Another thing to consider is the impedance of cable lines if a large distance is between devices.
After a certain distant, usually around twenty five feet plus, interference can occur in ones cables
and distort the signal. The same rule in matching impedances is with a cable which is one for one
(Robjohns). So an 8 ohm amp should use 8 ohm impedance cables to have the best signal pass
through it. This still occurs under twenty five feet but is negligible with distances that low. All of
these concepts are important to understand when it comes to impedance and impedance matching
so that one can have the best signal with the least amount of power loss in one’s sound system.
In conclusion impedance is basically the combination of resistance and reactance that can
be expressed in a mathematical formula. It is also a necessary concept to understand so as to
match impedances with devices so as not to damage them. With the information given the cloud
of unsureness has been lifted from impedance and can finally be understood for what it is, an
electrical circuit concept that has many facets to it depending on its implementation, but to
simplify it for the average audio guy, just match the numbers together as the same.
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Works Cited
Biederman, Raven, and Penny Pattison. Basic Live Sound Reinforcement: A Practical Guide for
Starting Live Audio. Burlington: Focal, 2014. Print.
Gibilisco, Stan. "Impedance and Admittance." Teach Yourself Electricity and Electronics. 3rd
ed. New York: McGraw-Hill, 2002. 264-83. Print.
Robjohns, Hugh. "Understanding Impedance." Understanding Impedance. Sound on Sound, Jan.
2003. Web. 07 May 2014.<http://www.soundonsound.com/sos/jan03/articles/impedance
workshop.asp>.
Tutorial: Electrical Impedance Made Easy - Part 1& Part 2. Dir. Ben Krasnow. Perf. Ben
Krasnow. You Tube, 8 June 2011. Web. 2 May 2014. <http://www.youtube.com/watch?v
=xyMH8wKKAg>.