Tag: how to

How to Tune an Amplifier


In order to get the absolute best performance & sound quality from your amplifier it is very important to know exactly how to properly tune an amplifier. The most common misconception of tuning an amplifier is that the settings are intended to ‘give you the most power output’, this is not the case. This article will break down exactly what each common setting on an amplifier does and how to properly tune those settings.

For this example we are going to use the DC Audio 7.5k as an example. Onboard, it has the most common settings found throughout the market. The names might be a bit different, but they do the exact same thing, more on that later. Moreover, this article will cover each setting Right to Left – use the picture below to follow along – ending at the Gain, which is easily the most important setting of them all.
DC Audio 7.5k

  • Master/Slave Switch

  • The Master/Slave Switch is ONLY ever used when “Strapping” the amp with another identical-twin amp (i.e. Same Series, Model, etc..). Stay tuned for a future article on how this is done, But for this explanation we are assuming ONE amplifier one, so this switch must stay on MASTER. What does “Slave” do? Stay tuned for the explanation on “Strapping”.

  • Phase

  • Inverted Subwoofer
    The job of the phase setting is to do one thing: change the polarity/direction of the sub(s) being ran off the amp. The most common reason why you would want to use this setting is when you have an ‘inverted’ subwoofer*. You could, however, just as easily swap the polarities of each terminal and accomplish the same thing. Another reason why you would use the setting is if you have two drivers & two amps (one per driver), and one is “Out of Phase”. This means ONE driver is playing OUTWARD (away from the enclosure) and the ‘Out of Phase’ driver is playing INWARD (into the enclosure). What happens in this case is , in theory, the two sound waves coming off the driver cancel/eliminate each other, giving a very undesirable result. So when you hear someone say the driver is “out of phase” THIS is the go-to setting to try to fix that. Beyond that, rarely can an audible change be actually heard, but there are more variables beyond just the setting that will make a change.

    For our example, we assume the driver is wired properly, so this is left at 0

    *Inverted Subwoofers are often done for one of two reasons:

    1. To utilize the absolute most volume of the enclosure. Without a subwoofer displacing the air within the enclosure you have FULL use of that space.
    2. Because it looks cool. Yes, really.
  • LPF

  • Low Pass Filter.The LPF can be thought of as a “Ceiling”. The LPF will not allow the frequencies above where you set it to pass through. Technically speaking, there is a “Roll Off”, the LPF isn’t just a ‘wall’, but we won’t get into that here. The setting is intended to ‘filter out’ frequencies that which the driver – in this case a subwoofer – cannot play and/or will harm the driver if it does so. There isn’t a “right way” to set this, there is only the way the setup is configured and also what the limitations of the driver are.

    Suggestion: The most common (read: ‘dummy proof’) setting is 80Hz-120Hz

    Consider this, however, if the Full Range stage of your setup (i.e. Door Speakers) for some reason are incapable of playing below 120Hz , then you want the subwoofer to pick up at 120Hz; so the LPF will be set at 120Hz! This is because you wouldn’t want your sub Playing 80Hz and Down, then your Full Range Playing 120Hz and Up, because then you will have an inaudible gap between 80Hz-120Hz (i.e. Dead Space). For all intents and purposes we suggest to stick 80Hz; this will make sure all ‘mid-range’ is filtered out, and its often the most easily recognizable crossover point. Unfortunately, Most Amps do not tell you where a specific crossover point is , so you definitely need to ‘Eye Ball’ it. An overlap of frequencies – Sub vs Full Range – isn’t a “bad thing”, but for those who want the “Perfect Setup” you will have to have the right tools to hit the points you want. The only way of doing this is with the use of a Crossover Calibrator; we use the SMD CC-1 in our installation department to hit these points accurately.

  • Bass Boost

  • The Bass Boost is fairly self explanatory. It literally boosts the frequencies that you send it. We DO NOT recommend using this setting, if at all possible, because drivers go here to die. Assuming the amp is tuned right, there is seldom a reason to come to this setting. The reason it exists is because:

      1. Manufacture’s need to compete with another, so if multiple amps have this setting, then theirs does too
      2. It can actually have a practical use

    The latter only ever happens when the Full Range completely over powers – or “Drowns Out” – the subwoofers’ outputs. In order to “balance” the setup, you go to the Bass Boost to give the output a bit more output. THIS ISN’T A VOLUME KNOB!! You are toying with introducing a distorted signal if this setting isn’t used responsibly. Use at your own risk.

    Suggestion: Leave at 0

  • Subsonic

  • For all intents and purposes think of the Subsonic as a HPF (High Pass Filter), the ‘opposite’ of the LPF, or as a “Floor”. The Subsonic will not allow the frequencies below where you set it to pass through. Like the LPF, this setting is intended to ‘filter out’ frequencies that which the driver – in this case a subwoofer – cannot play and/or will harm the driver if it does so. This setting is often established by the limitations of the driver. For example, the NVX VCW104 has a frequency response of 20Hz-220 Hz, which means it is physically incapable of playing below 20Hz. This tells us that if we want to protect the driver, we should set the subsonic to 20Hz. Many in the industry will say that the ideal setting, for this example, would be ~25Hz because “just because its capable of doing 20Hz doesn’t mean it Should”. The often cited analogy is “your car Redlines at ~7,000 RPMs, that doesn’t necessarily mean you SHOULD ride the engine at 7k just because it can”. Nevertheless, in a properly tuned setup, and with an able/responsible user, there is very little concern for setting this point to the limitation presented by the driver.

    Suggestion: Set to 20Hz , for most subwoofers

  • Gain

  • This is NOT a volume control!! Whatever you want to call this setting, it is intended to do One thing and that is to match the sensitivity of the source/headunit. So, in theory, if your headunit provides a solid 5v out of the preouts, then the Gain (Sensitivity, Level, Input Level, Sensitivity Input, (V)) will match that when set properly. Due to several variables it is more likely that it is not going to match EXACTLY (i.e. at 5v) but it will come fairly close. Unfortunately, without special tools or an oscilloscope it is very hard to get this “Right”. It isn’t impossible to set this without special tools however. In fact, most installer set up their customers’ amps by ear! This will be the most common method you – the reader – will use. In addition, there is also a creative way of using a common DMM (Digital Multimeter) & Ohm’s Law to establish an AC Voltage Figure to aim for when adjusting the Gain; a quick search for this method will generate a lot of useful information. However, it is important to know that using the DMM method ASSUMES that the figures/variables you use are SPOT ON , which – to be fair – is not likely. This is because the rated figures on an amp are often rounded up/down, and – worse – a lot of manufactures will give overrated figures. So, using this method can be precarious if you the figures aren’t True To Spec.

    Suggestion: Too many variables to provide a “right answer”

    To Recap:
    Master/Slave – Master (Assuming ONE Amp)
    Phase – 0
    LPF – 80Hz
    Bass Boost – 0
    Subsonic – 20Hz
    Gain – ____
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    How to Discharge a Capacitor

    Capacitors add stability to any audio system

    Car audio capacitors add stability to any audio system by keeping a small reserve of power available for the amplifiers when they need it for quick musical peaks. If you need to remove your capacitor or move it into another vehicle, it is always a good idea to discharge it. Capacitors store energy and can take a long time to dissipate that energy, sometimes a year or more, leaving a disconnected capacitor a disaster waiting to happen. Larger capacitors can store more energy than smaller ones so it takes longer to discharge and they are more dangerous to handle as a result. Always use caution when working with these devices. There are many different ways to discharge a capacitor and it is important that it discharges slowly. Here are a few methods you can use to discharge your capacitor:

    Method 1: Remove the capacitor from your vehicle and make sure to handle with care. Take a 12V test light or resistor and touch the positive and negative terminals on the capacitor bridging them together. Make sure to wear safety goggles and heavy duty gloves or hold the light/resistor with insulated pliers. The resistor or light will get very hot and could pop. Once the light goes out the capacitor is discharged. When the resistor becomes cool the capacitor is discharged.

    Method 2: Remove the main fuse located on the power wire near the battery of the car that connects to the amplifier and capacitor. This will then make the capacitor act as the battery for your audio system. Turn on your audio system and wait for the amplifier(s) to turn off completely signaling that the capacitor is completely discharged.

    Method 3: Remove the capacitor from your vehicle and hook it up to any device that uses 12V DC for power. Connect the positive and negative wires of the device to the positive and negative terminals of the capacitor. The capacitor is essentially the battery and once the device shuts off your capacitor is discharged.

    Method 4: Disconnect the negative terminal on your vehicles battery and activate the dome light. Once the light goes out, your capacitor is discharged. Be mindful of other batteries in your electrical system. If the light does not go out within a few minutes your vehicle could be receiving power from add-on batteries.

    Once the capacitor has been discharged, check the voltage across the terminals of the capacitor using a multi-meter or voltmeter. If the meter reads zero volts or very close to it, the capacitor has been successfully discharged. Make sure to properly recharge the capacitor before connecting it again, please view our article titled “How to Charge a Capacitor” for assistance.

    WARNING: Do NOT connect the positive and negative terminals of the capacitor together with standard wire, screwdrivers or wrenches as this will damage the capacitor and could cause bodily harm to the user.

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    How To Charge A Capacitor


    A stiffening or power capacitor is a great addition to any stereo system. Sometimes however the installation instructions for these devices tend to be lacking in description and can cause a bit of confusion. Let’s straighten things out and make “pre-charging” your capacitor as painless as possible. There are often two terminals on a capacitor, one positive and one negative. Unless otherwise specified, the power terminal of the capacitor will be placed in line with the amplifiers power cable. The negative or ground terminal on the capacitor will go to chassis ground, not the amplifiers ground. Try to get the capacitor as close to the amplifier as possible, a few feet is acceptable, this minimizes any performance loss due to the cable distance. To charge your capacitor, simply follow the steps listed below:

    Step 1) Remove the fuse for your audio system that connects it to your battery. This fuse is often in-line with the power wire of the amplifier that your capacitor is going to be connected too.

    Step 2) Wire up your capacitor by following all the instructions in the installation manual or refer to our “How to Install Car Audio Capacitors” knowledge base. Make sure the power, ground and if applicable the remote turn on wire of the capacitor is connected.

    Step 3) To begin charging the capacitor you need either a test light or a resistor. Often times these are included with the purchase of a capacitor but can be purchased separately if necessary.

    A) Using a Test Light: A test light is the simplest way to charge a capacitor. All you need to do is take the power and ground of the test light and stick them in-line where your fuse used to be. You can use alligator clips to simplify this process. Hold the test light in place of the fuse until the light bulb turns off meaning the voltage went from 12V to 0V and the capacitor is charged.
    B) Using a Resistor: You will need a 1 watt, 30 – 1,000 Ohm (1kohm) resistor for charging your capacitor unless otherwise specified (you capacitor may have a resistor included). Try to use a higher impedance resistor so that the capacitor is charged slowly. This will prevent the capacitor from charging too fast and sustaining damage.  Also, a lower wattage resistor will heat up very quickly and could crack or explode so make sure NEVER to hold a resistor with your bare hands. Put the resistor in line with your fuse holder, as though it were the fuse. Place the voltmeter positive node on the positive terminals of the capacitor and the negative node on the ground terminal of the capacitor and set the meter to Volts DC. Once the volt meter reads 11 or 12 volts you can remove the voltmeter and replace the resistor with the power fuse. The fuse may spark when you reinstall it, this is normal and should end quickly.

    Regardless of which charging method you use, the results will end up being the same. Some capacitors come with a charging card that is attached to the posts of the capacitor and acts like a resistor or test light. Follow the instructions provided when using a charging card. Remember when installing any electrical equipment that you need to remove the negative terminal of the battery or the fuse in-line with the power wire connecting to the battery. In this situation, the fuse in-line with your power wire will need to be removed. For information on how to discharge a capacitor, view our article titled “How to Discharge a Capacitor“.

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    How to Use A Multimeter


    You may have seen a multimeter being used by your local electrician or even a stereo installation shop. This universal tool is a must-have in all homes for many reasons. You do not need to have a degree in Electrical Engineering to find a use for a multimeter, also known as a volt/ohm meter (VOM). A VOM is an electronic measuring device that combines several different measurement functions into one handheld, easy to use device. No worries, I understand if you fear that you won’t be able to understand any of the weird symbols and numbers! Hopefully I can quell your fear here and now with helpful information and instructions on how to use a multimeter. Enough talk, let’s get to it!

    There are two types of meters, auto ranging meters and manual meters. Auto ranging meters have a few selections on the dial; the meter will guess what your using it for based on the information it receives from the probes. Then there are manual ranging meters that make you select the input range it is going to use. The auto ranging meters still have the same functions as the manual meters; except auto ranging meters guesses the input range for you. This is similar to how automatic and manual cars essentially do the same thing, except one requires more user input.

    The first thing you will normally see on all multimeters is the circular mode dial. The mode dial allows you to choose from many different measurements. The most common are AC/DC voltage, resistance and current. Occasionally multimeters test continuity, and they may also have diode testing functions.

    The next thing you will notice are the input jacks. The black jack is called the common. It never moves from its slot. Then you have two red jacks, you choose the jack based on what you’re going to do. Measuring voltage and ohms tend to be on one jack, while measuring amperes tends to be on another jack. The reason amp measurement requires a different jack is because it lets the electrical signal flow through the meter to test it, whereas voltage/ohm measuring sends the signal out from the meter. A red and black probe connects to these jacks on the multimeter. These probes will be used to collect these different measurements. Higher end meters will have more measuring options and jacks.

    Lastly, at the top of most multimeters is the display. The most important function of the display is to show as much information as possible. Some show just digits and decimal points, some show the unit of measurements as well, such as volts (V) or milivolts (mV). Higher quality units display much more information.

    Now that you have the basic idea of the various components of the multimeter, lets dig a bit deeper into the mode dial and explain what all of the numbers and symbols mean. The picture displayed is a basic multimeter which I will reference throughout this article. Multimeters come in many different configurations, but all serve the same function and have similar symbols. The standard user should be able to pick up any standard multimeter and use it without a headache.

    Multi Meter

    DC Voltage (V with a straight line and a dashed line under it): In the meter pictured, DC Volt is written, not expressed as a symbol. The range of this meter is 200 milivolts to 1000 volts. The 1000 is highlighted in red to remind you that working with voltage is extremely dangerous. The Car DC Volts setting is commonly used to monitor a circuit to see how it’s working. If you reverse the probes you will get a negative measurement. You can measure DC voltage while the circuit is working. The most common use of this setting is to test remaining battery voltage, alternator output, power to a car radio, amplifier, etc.

    AC Voltage (V~ with a wavy line): In the meter pictured, AC Volts is written, not expressed as a symbol. This meter has a 200V setting and a 750V setting. The 750 is highlighted in red to remind you that working with that voltage is extremely dangerous.  The Home AC Volts setting is used to measure wall voltage, unregulated power supplies, etc. AC voltage has no polarity; if you reverse the probes you will still get the same reading.

    DC Amperage (A with a straight line and a dashed line under it): In the meter pictured, DC Amps is written, not expressed as a symbol. To test amps, the red plug needs to be removed from POWER and plugged into the slot above it. Other multimeters might have this slot labeled or in a different location. This meter measures from 2000 microamps(µ) to 200 miliamps(m).

    Resistance(Ω): In the meter pictured, resistance in ohms is expressed as a symbol Ω. This setting is used to measure the resistance of a circuit in ohms (Ω). Ohm measuring is typically used to determine the resistance that a subwoofer is wired at. Make sure the device is turned off before taking a resistance measurement to avoid damage to your multi-meter.

    Continuity(>+): In the meter pictured, continuity is displayed with a symbol. Continuity is used to measure the resistance of a closed circuit; a beep will sound to indicate solid continuity. Think of it as a way to test if a wire or circuit is continuous, meaning electricity flows from one end to the other. If there is no continuity, the circuit is broken or you are not on the correct circuit.

    Here are a few examples where a multimeter proves handy and how exactly to use the meter. Once you understand the basic concepts, you can easily start working on more than what is listed here.

    Testing Batteries: Testing batteries is a great way to practice with a multimeter and it is useful in this day and age considering all of our electronics have a thirst for energy that is quenched with battery power. The most common battery types are AAA, AA, C and D, all of which will have different voltage ratings usually listed on the battery.  Some meters have a 2 Volt DC setting for the lower voltage batteries. If your meter does not, start high and work your way down. So if you’re testing a 9V Alkaline battery, put your multi-meter on 20V DC and place the red(+) probe on the positive side of the battery (usually marked) and the black(-) probe on the negative side of the battery. If it’s a new battery and your reading higher than 9V, let’s say 9.53V, that is not a mistake. The voltage listed on batteries is the average voltage you can expect from it, as it dies it will slowly drift down past 9V. When it reaches its lower operating range it is safe to assume the battery is almost used up and that it’s time to replace it.

    Testing a Wall Socket: This is originally what a multimeter was designed to do and is the easiest test. Make sure you have a house rated multi-meter that can withstand 120V. House current is 120V AC, so switch your multi-meter to 200V AC. Usually the narrow prong in the wall is the positive (hot) and the wide prong is the negative (neutral). With AC voltage it does not matter which probe is plugged into which slot. Plug one probe into the hot and one into the neutral, the meter should read between 110-120V AC. If your wall socket also has a circular prong, that is the ground. If you test the hot and the ground with the same 200V AC setting, it should read 110-120V. If you test the neutral and the ground, it should read 0V.  Readings that deviate slightly from the average are ok.

    Testing Speaker Wires: You have your dash open and the radio pulled out with the door panels off. You removed your speakers, but as you get ready to put in new ones, it doesn’t say which is positive and which is negative. Multimeter to the rescue! Simply turn your radio on to low volume and pull the speaker out, and you are ready to test for voltage. Turn your volt meter to 20V DC and put the negative probe on a chassis ground and put the positive probe on one of the speaker terminals. The one that has a voltage is going to be positive. Most vehicles have a black or white stripe on the positive wire, but there’s always the chance that they are incorrectly marked.

    Determining Subwoofer Ohms: You bridged your subwoofers together, then sit back and pray, hoping that they equal the ohm rating the amplifier needs. If you connect the positive and negative speaker wires from the sub to the amp, it could end in disaster if you did not wire them correctly. A multimeter can tell you exactly the ohm level those subwoofers are at. Connect the two ends of the multimeter to the speaker terminals of the amplifier. Set your multimeter to 200 ohms (Ω) and connect the red probe to the positive and the black probe to the negative speaker wire.

    Testing a Car Battery: If you have a sneaking suspicion that your car battery is running low on juice, a quick test with a multimeter can put your suspicions to rest! Wear safety glasses and gloves to protect you from any harmful chemicals on the battery. Locate your battery under the hood and follow the manufacturer’s directions to properly disconnect the cables from the battery. Set your multimeter to 20 Volts DC to give an accurate reading. Connect the red probe from the multimeter to the positive battery terminal. Attach the black probe from the multimeter to the negative battery terminal. After a few seconds read the meter, it should read at least 9.6 volts for the battery to accept a charge if you have a 12 volt battery. Even then it may not be worth keeping. A fully charged 12V battery should test at 12.4 – 12.7 volts when it is not attached to the car.

    Testing a Car Alternator: You tested your battery and it’s functioning properly, but your car’s electrical components are having problems. It’s time to test the alternator. Wear safety glasses and gloves, and keep away from moving components. Set your multimeter to DC 20 Volts. Leave your battery connected to the car, and with the car off, connect the red probe of the multimeter to the positive lead on the battery. Then connect the black probe to the negative lead on the battery. With the car off, it should read 12.5-12.8V if your battery is good. Now start the engine with the multimeter still hooked up. It should now read 13.8-14.8V if the alternator is working properly. Finally, have someone turn on the headlights and heater blower on high. The volts will drop slightly at first but then return to 13.8-14.8V if the alternator is working properly.

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