To explain what a resistor is for audio equipment, let us compare it to sports.
If you’ve never watched basketball, then you should know that there are 5 people on each team.
Each person on the team has a role, but some players have a bigger responsibility than others.
Let’s take a closer look at what we mean.
Lebron James; a superstar, future hall of famer, and current holder of the title as “best player” in the National Basketball Association has the job of generating points. But with Lebron, he can do that either by passing, or scoring the ball himself.
The other 4 players such as Kyle Korver (who is also a great player) has 1 responsibility on offense…
SHOOT THE BALL.
This is similar to a resistor in the sense a resistor only has 1 job. Everything from the power to output is handled by the bigger components, similar to Lebron.
All a resistor has to do is reduce voltage.
To simplify, a resistor’s main job is to resist current, which is why it’s called a “resistor”.
A resistor is a passive device meaning it doesn’t talk about problems but avoids direct confrontation and acts like nothing is wrong when their actions state otherwise….hahaha.
In all seriousness though, a resistor is a passive device because it helps you with a design of a circuit. It doesn’t actively bring electricity in like an amplifier, but it does play a big part for audio equipment.
Too much electricity at one time causes distortion and interrupts signal.
Think of a resistor like a storage for electricity. It doesn’t need energy to be considered functional unlike a television.
If you’re worried about how you can connect a resistor, remember, this device is bi-directional, making it accessible from all sides on a circuit.
Even though resistors may seem like they aren’t important, remember, if you don’t pick the right one, you will have to deal with bad sound quality.
How To Choose A Resistor
The most important factor when choosing a resistor is power.
The best practice for finding the right resistor for your audio equipment is to find a resistor which doubles in power.
To find power in a resistor use this formula:
P=V squared/R
The P in the equation is power, while the V is for voltage, and the R stands for resistance.
Technically, the P which stands for power represents watts. This is easy to remember, and we’ve gone over watts before so there isn’t anything advanced with this concept.
As for the V, it doesn’t just mean voltage, but it represents voltage drop.
Do you remember when we discussed impedance? Seems like every article now, but the point is, voltage drop is the amount of voltage loss that happens on a circuit because of impedance.
Voltage drop is most associated with passive devices like a resistor. Conductors and connectors fit this description and would cause voltage drop in an electrical circuit.
One roadblock audio enthusiasts might encounter when doing this equation is finding the voltage drop.
Find out how to calculate voltage drop by clicking the link. Once you click the link, go under “choosing a resistor” and they discuss how to find voltage drop.
This finally takes us to the last piece of the equation, resistance.
The Resistance in the equation should be seen in ohms. This information can be found on specifications of the product so you shouldn’t have difficulty.
Once all your numbers are configured, pop them in and watch the magic happen!
When you finally find your power rating, times it by 2 and wallah, you’re one step closer to finding your resistor.
Most of the work is done…but learning more about the different resistor types will help you narrow down the perfect resistor for your situation.
Resistor Types
Just like computer chips before, resistors are getting better and better. Not only are they smaller, but their performance is better overall.
The trick is to find the right resistor for your specific audio equipment. We do this first by understanding the 2 resistor groups.
Fixed Resistor: The first type of resistor is a fixed resistor which sets how the electrical circuit will work from the beginning. Similar to fixed cost in accounting; fixed resistors don’t change electrical values once it’s built.
Their purpose is to keep the circuit in line and to never change value. It is what it is once installed.
Variable Resistor: A variable resistor has 3 components, 2 of which are fixed, and the 3rd is a slider which is meant for adjusting. The slider is like a devil’s advocate in the sense it champions the alternating current.
Although a variable resistor isn’t common in electrical circuits, it sets the limits so it doesn’t go overboard. Similar to having great parents, they provide emotional and financial support, but will often reign you in if you get out of control.
The 4 Fixed Resistors
Foil Resistor: For low-level noise application a foil resistor will do the job. Made up of metal/metal alloy, one result of its composition is its resistivity and great signal to noise ratio.
By signal to noise ratio we mean how much desired signal do we get in comparison to background noise we don’t want. Metaphorically, we think of signal to noise ratio as how much useful/relevant information we are getting in comparison to useless information.
So the better the signal to noise ratio, the better the resistor is in unison with audio equipment.
Film/Cerment Resistor: Film resistors have a thin metal layer surrounding it. They usually have low wattage values which translates to low power, so if you have a large outdoor speaker you’re trying to install, this wouldn’t be the right choice.
A typical use for a resistor of this type is something which uses low noise. So something like a cellphone or other handheld device would work.
Other disadvantages included with film resistors are low temperatures and tight tolerance.
Tight tolerance means the components need to be exact so it can fit the design. Any mishaps or deviation from manufacturing on size cause the whole device to fail.
Wire-Wound Resistor: A wire-round resistor in comparison to a film resistor contains high wattage. It’s made from three different elements which are plastic, ceramic, and glass. These materials give wire-wound resistors a high resistivity.
A high wattage and high resistivity resistor hasn’t prevented wire-wound resistors from becoming one of, if not the most manufactured resistor to this day.
Another benefit to their composition is their ability to handle higher electrical currents. Thanks to their aluminum heat sink body, both cooling and heat loss are activated.
Carbon Composition Resistor: A carbon composition resistor is a low-wattage resistor made up of carbon dust or graphite paste.
The melding to get a resistor of carbon composition is pretty cool. Using carbon particles, it is then mixed together with clay to turn it solid which gives you the carbon composition resistor.
Due to its composition, carbon resistors can withstand a lot of energy at one time and its thermal mass (ability of material to absorb and store heat) allows it to do that.
A common use for a carbon resistor is to protect electrical circuits. If you’re amplifier generates a lot of power, this is a suitable component to your audio equipment.
One perfect example of this is party speakers. Loud speakers are obviously used for parties; to generate the type of volume you need, you’re going to need power. Naturally, high voltage audio equipment comes with that so a carbon resistor is perfect.
Clear disadvantages of a carbon resistor are temperature coefficient and voltage dependency load.
Temperature coefficient is simply a change in a physical product because of a change in temperature. This happens if you place your party speakers under the sun, or better, use them often.
Technically, you can say temperature coefficient happens to all electronics, but carbon resistors are more prone because of the material it’s composed of.
As for voltage dependency load, we’re talking about how much power a resistor can handle. Not all resistors are created equal when it comes to handling voltage and wattage.
Besides the disadvantages of a carbon composition resistor, do you know what the 2 most important factors are when it comes to resistors?
The 2 Most Important Factors Of Resistors
Resistor composition plus design are the 2 most important factors when you consider advantages and disadvantages of each resistor.
But there is another quality consumers need to consider when buying a resistor.
What’s With All The Noise?
There is a concept called “noise” when it comes to resistors. From the design perspective of your audio system and loud speakers, considering what type of noise you’re willing to deal with is like asking yourself what type of problem am I willing to have.
For resistors, there are 3 different type of noises:
Thermal: Thermal noise depends on 3 factors; Temperature, resistance, and bandwidth. To find bandwidth, look at the specifications of the amplifier you’re using.
The more resistance there is, the more thermal noise thrives.
A deeper explanation on why thermal noise happens starts with temperature. As heat rises, more electrons start moving, and when they start moving, the random movement of electrons causes an unwanted AC signal.
Once the thermal dynamics take place inside a resistor it sets a limit on the smallest voltage which can be amplified.
This causes the temperature to start rising causing thermal noise to come in.
Current: Current noise depends on the type of resistor. Most current noise comes from material made up of carbon film, metal oxide, or carbon composition.
Besides the materials there is another factor which current noise comes from, and that factor is current. The direction of the current (DC/AC) doesn’t matter, what matters is if there’s current or not.
If there’s no current, current noise and thermal noise are the same.
Shot: Both current noise and shot noise are the same in the sense both are triggered by currents.
The main difference is shot noise comes from DC currents instead of AC currents. The problem is DC currents correlate with sound quality, and the more DC current the better the sound. The key is to find the right balance between shot noise and sound quality.
Although we condensed everything that will help you with resistors, here are some practical tips to help you:
- Find the right balance between DC current and sound quality
- Resistance is proportional to thermal noise
- Bigger wattage resistors help with current noise because current noise is proportional to area of electrical circuit
- Here is a video on how to reduce current noise:
Final Thoughts
Resistors are probably as exciting as looking at a wall, but trust us, they’re important.
Their passivity is not proportional to the impact they make. As we were introducing resistors in the beginning of this article, we talked about Kyle Korver and Lebron James.
One player does everything on the offensive end while the other has a specialized role in the offense. Think of resistors in the same likeness as Kyle Korver.
Although they’re not as hyper-specialized, their main job is to resist and configure the electrical circuit when need be. They’re not the biggest component of an electrical circuit, but they do have a role, and sometimes that role is different.
Foil resistors and carbon composition resistors have the same responsibilities, but they don’t have the same materials. Foil resistors on one hand is better for low audio equipment application while carbon composition is better at storing higher wattage because of its thermal dynamics.
So if you were wanting to find a resistor for a small radio, you would go with a foil resistor. But there are other specifications which will help you with your decision.
Other qualities to look out for is how much output does your amplifier give out. You want to make sure your resistor is compatible with your amplifier or else the whole circuit can collapse. An easy start to this would be to look for the amplifier’s power and take it from there.
You’re probably reading this and thinking they didn’t even answer the question of which resistor is best for audio equipment.
The truth is, there is no one size fits all. It’s all about finding the right fit.
Hopefully reading this article will help you take the steps necessary to find the right fit.
