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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 = โ๐ 2 + ๐ 2 , where Z is impedance, R is resistance, and X is reactance. Chaudhary 2 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 ๐ = โ๐ 2 + 02 = ๐ . With a perfect capacitor there is no resistance and only reactance with alternating current. This makes its impedance ๐ = โ02 + ๐ 2 = ๐. 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. Chaudhary 3 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 oneโs equipment or not have the power wanted to fully run oneโs 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 โโฆit 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 Chaudhary 4 impedanceโ (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 โWhen 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+R4โ (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 โWhen 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 Chaudhary 5 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= R1/2โ (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. Chaudhary 6 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 oneโs 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. Chaudhary 7 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>.