In our ongoing series of articles about car audio electrical theory, we are going to introduce the concept of alternating current power sources and signals. Understanding the basics of AC is crucial to understanding how a mobile audio system works. This article uses a lot of references to the electricity delivery systems used in our homes and offices to help establish a basic understanding of AC circuits. We’ll build on this foundation in this and subsequent articles to help form an understanding of the complexities of AC systems.

The Difference Between AC and DC

The voltage produced by the electrical system in our vehicles is called direct current. The electrons flow in one direction from one terminal of the battery to the other (except when we are recharging the battery). While there are changes in the voltage level as we add loads to the circuit, or when the alternator starts recharging the battery, the direction of current flow to the electric and electronic devices in the vehicle never changes.

Conversely, the power supplied by your local electric company to drive the lights and appliances our homes and at work is called alternating current. It has this name because the flow of electrons changes direction 60 times a second. Yes, this sounds weird. Who would want their power to go back and forth? Don’t fret; we’ll explain it all shortly. Just keep reading.

Power Loss in Transmission Wires

Researchers believe that the first electrical power source was a clay pot that contained tin plates and an iron rod. If filled with an acidic solution like vinegar, a voltage would be produced on the metal terminals. The belief is that this first battery was created more than 2,000 years ago. All batteries are direct current power sources.

Using electricity to do work started to become popular in the late 1800s, and as such, the need to deliver electricity to homes and offices became necessary. The problem with delivering power over long distances is voltage loss in the wires because of their resistance.

As we know from Ohm’s law and the power calculations we have recently discussed, the power in a circuit is directly proportional to the current and voltage (P = I x V) in the circuit. Power is also proportional to the square of current in the circuit relative to the resistance (P = I^2 x R). If we can transmit power with more voltage and less current, less power is wasted in the transmission wires.

Adoption of Alternating Current

A significant benefit of alternating current power supplies in commercial and residential applications is that it is easy to change the relationship between voltage and current using a transformer. A transformer is a device that uses magnetic fields to increase or decrease the voltage to current ratio. For example, an ideal 2:1 transformer would convert 10 volts and five amps of AC to five volts and 10 amps.

George Westinghouse is credited with the popularization of the delivery of AC power to homes, thanks to being awarded the contract to supply power to light the 1893 World’s Fair Columbian Exposition. Westinghouse used transformers based on patents he purchased from Lucien Gaulard and John Dixon Gibbs. Gaulard and Gibbs invented the transformer in London in 1881.

The output of a generator in a nuclear, coal or hydroelectric plant is 20 to 22 kilovolts. This voltage is stepped up to between 155,000 to 765,000 volts using a transformer for distribution around the state or province. Most of the high-voltage towers you see along the highway or in clearings have around 500,000 volts flowing through the three power conductors.

Each city or portion of a city will have some type of electrical substation where the electricity from these high-voltage lines is stepped down to lower voltages for distribution around different neighborhoods. These voltages are usually in the 16kV range to maintain an adequate level of transmission efficiency over these short to moderate distances. Transformers in enclosures at the side of the road or installed underground convert that voltage to the 120V feeds that run to the electrical panels in our homes.

By way of an example, let’s look at 1 mile of 8 AWG stranded cable. According to the American Wire Gauge standard, 1 mile of 8 AWG copper wire will have a maximum resistance of 3.782 ohms and an ideal resistance of 3.6 ohms.

If we want 5,000 watts of power delivered through this mile of cable, there will be some energy lost to the resistance in the cable. If we transmit our power at 240 volts, there will be 20.83 amps of current flowing in the cable. With a resistance of 3.6 ohms, the cable itself causes a loss of 1562.5 and we lose 75 volts across the cable. Clearly, low-voltage signal transmission over long distances doesn’t work.

If we increase the voltage up to 16,000 volts, the power loss in the cable drops to 0.3125 watts and we only lose 1.125 volts to the cable.

High-voltage transmission lines are how electric companies can deliver megawatts of electricity over long distances with minimal power loss. At 500,000 volts, we can transmit 1 megawatt of electricity over 100 miles and lose only 720 volts. That’s 0.144 percent!

OK, enough about the relationship of AC power and voltage. Let’s talk about audio systems.

A First Look at Audio Signals

Unlike the 60Hz AC waveform that feeds our homes, audio signals contain voltage information that mimics the changes in air pressure that we would perceive as sound. In most cases, sounds are recorded using a microphone that works in the opposite way a speaker does. Sound energy moves a small diaphragm that includes a coil of wire. The coil of wire moves past a fixed magnet. The motion of the coil through the magnetic field induces a voltage in the wire. The distance the diaphragm moves determines the amplitude of the voltage signal. Louder sounds produce higher voltages.

Below is a picture of an audio waveform as seen on an oscilloscope. The person speaking said the word audio.

Understanding Power in Alternating Current Circuits

The basic concept of power in an AC circuit is the same as for a DC circuit, but some calculations need to be completed before we can apply Ohm’s law. We’ll look at the 120V, 60Hz residential power supply to explain the math in the simplest of terms.

To measure power, we need to look at the amount of work completed over a given period. In the case of a light bulb plugged into an outlet, the filament doesn’t care which direction current is flowing, but the amount of light and heat created depends on the amplitude of the voltage supplied. The work done by the bulb is calculated by the number of electrons that flow through the bulb for a given amount of time.

To determine the work done by an AC voltage, we need to calculate the value of that signal that does the same amount of work as a DC voltage. This value is called the RMS or root mean square value and is 1/sqrt 2, or 0.70711 for sine waves. For our 120V power feed coming out of the wall, 120V volts is the RMS voltage. The peak voltage is about 167.7 volts. To be clear, the value of 0.70711 only works for a sinusoidal waveform. The RMS value of a square wave is 1.0 and for a symmetrical triangle wave is 0.577.

By definition, the RMS AC voltage can perform the same amount of work as DC voltage of the same value.

The image below shows a single cycle of a sinusoidal waveform. The peak voltage is 167.7 volts, and the two orange lines define the RMS value of 120V.

Basic Understanding of Alternating Current Sources and Signals

For this article, the takeaway is that the audio waveforms on the preamp and speaker wires in our stereo system are alternating current signals. In the next article, we will discuss the concept of frequency and amplitude in more detail.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

In any discussion about understanding sound, the unit of decibels will undoubtedly become part of the conversation. Unlike almost all other units of measurement, the decibel is not a linear scale. That is to say, 1 decibel (also written as dB) is not one-tenth the amplitude or strength of 10dB. In this article, we’ll explain how the decibel scale works and present some reference information to help you understand how the decibel scale works.

What is Sound?

Sound is a vibration of air molecules that vibrates our eardrums. The eardrum passes these vibrations through to the middle ear through tiny bones called ossicles. The inner ear has a shape similar to that of a snail shell and contains microscopic hair cells that convert these vibrations into minute electrical signals. These signals are transmitted to the hearing nerve and subsequently to our brain. Each inner ear contains roughly 18,000 hair cells, all of which are said to fit on the head of a pin. Once a hair cell is damaged, it never grows back or repairs itself.

Understanding the Decibel

The decibel unit was created in the 1920s by Bell Telephone Laboratories to describe losses in communication cables used in early telephone systems. The original unit was MSC (Miles of Standard Cable) and was the loss of signal in 1 mile of cable at a frequency of 795.8 Hz that was equivalent to the smallest perceivable attenuation detectable to the average listener.

The Decibel and Sound Level Measurement

When discussing sound levels, the proper format is to use the unit dB SPL, dB(SPL) or dBSPL. The reference for any statement is the sound pressure as compared to 0dB. 0dB is defined as the perceived sound of a mosquito at a distance of 10 feet from the listener.

Because dB SPL expresses a ratio, sounds can be quieter than 0dB. Imagine if you will, you are in the space where the sound created by that original mosquito was measured. If we take away the mosquito, the space will be quieter. How much quieter depends on other sources of noise. Electrical noise created by lighting and noise caused by heating and cooling systems all contribute. If we eliminate as many noises as possible, the room will get quieter and quieter.

According to Guinness World Records, the quietest place in the world in 2012 was an anechoic test chamber at Orfield Laboratories in Minneapolis. The sound level in this room was measured at -13dBA. In October 2015, a team of engineers at the Microsoft head office in Redmond, Washington, smashed this record with measurements taken in the anechoic chamber in Building 87. A team of independent specialists measured a noise level of -20.35 dBA. The room is not only completely isolated from all sources of noise and vibration, but the walls are lined with large acoustic foam wedges design to absorb sound.

At the opposite end of the sound spectrum we have 191 dB SPL. This is the sound level where the air is pressurized to 1 Bar or 1 atmosphere. Linear sound cannot exist above this level because the low-pressure side of the wave reaches an absolute vacuum. There are louder noises (such as nuclear explosions), but they are examined as pressure waves rather than sounds.

All Sounds Are Not Perceived Equally

The human ear is not sensitive to all sounds equally. In 1933, the results from research into how our ears perceive different frequencies was published. Researchers Fletcher and Munson released a set of human hearing sensitivity curves that are based on frequency and amplitude. The curves were created by playing a pure 1 kHz tone and a tone at a different frequency alternately. The amplitude of the 1 kHz tone was adjusted until participants felt the level of the two were equivalent. The adjustment level was recorded and they moved to another frequency.

In 1937, similar testing was done by Churcher and King, but the results differed a great deal from the Fletcher Munson charts. Researchers Robinson and Dadson repeated the testing in 1956 with newer equipment. The resulting measurements were accepted and defined the ISO 226 normal equal loudness-level contours. These remained the standard until 2003 when new testing further revised the graphs.

What the curves tell us is that our hearing is most sensitive around 2 to 3 kHz, depending on amplitude. We are less sensitive to high-frequency information around 10 kHz and 150 Hz by about 20dB. We are increasingly less sensitive to sounds below 150 Hz, but this phenomenon decreases as volume increases.

How We Perceive Sound

Many statements about sound levels get thrown around the industry. Let’s talk about and clarify a couple of the most common.

3dB is twice as loud. No. No, it isn’t. A change of 3dB represents a doubling or halving of acoustic energy. It takes an amplifier twice as much power to produce a tone at 73dB as it requires at 70dB. The reality is, most listeners can just barely perceive a change in level of 3dB at all audible frequencies.

If 3dB isn’t twice as loud, what is? Based on extensive testing, it is agreed that a change in level of 10dB is considered to be twice or half as loud.

A Listening Test

Just for fun and education, below is a series of test tones to demonstrate our ability to detect differences in amplitude. These tests are created to make the differences as easily perceivable as possible.

The tones involve a sine wave at a frequency of 1 kHz recorded at a starting level of -10dB from the full scale in a 44.1 kHz, 16-bit uncompressed .wav file format. The amplitude (volume) of the waveform is decreased at one-, two- and three-second marks by varying amounts. For most, discerning the 1dB per step decrease is easy. Many will be able to detect the 0.5dB decrease per step. The 0.25dB decrease per step is difficult to hear.

Track 1

1 kHz, decreasing in amplitude by 1.0 dB at one-second intervals

Track 2

1 kHz decreasing in amplitude by 0.5 dB at one-second intervals

Track 3

1 kHz decreasing in amplitude by 0.25 dB at one-second intervals

Now, based on your results, does this test disprove the above statements about 3dB and 10dB differences? Not at all. As mentioned, the tests are designed to make the perception of level changes very easy. If you were to listen to a song, then play the same song again five minutes later after adjusting the volume up or down by 0.5dB or 1dB, most people wouldn’t be able to detect the difference.

We’ll revisit the decibel in future articles and explain how different rating curves affect the numbers we read when looking at audio equipment noise measurements and specifications. Until then, we hope you enjoyed this article and the test tracks.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

There is nothing worse than turning up your music only to hear your car speakers or subwoofers rattle and buzz because they are damaged. Well, there is something worse: You could turn up the volume and hear nothing at all. We hear stories about people damaging their car speakers all the time. In almost every case, the issue is over-powering them because of unwise adjustments to the sound system. In this tongue-in-cheek article, we’ll discuss the five fastest ways to blow your car speakers. Let’s be clear: We don’t want you to damage your speakers and, more importantly, your hearing. The reality is, this is a list of five things NOT to do to your car stereo system. We hope you enjoy!

1. Turn Up the Gains on Your Amps

When a mobile electronics specialist installs an amplifier in your vehicle, the gain control (also called the sensitivity control) should be adjusted so that the amp will produce its maximum power when the volume on the source unit is turned up all the way. Some installers provide a little extra range on the volume so that quiet recordings can still play loudly. This is called gain overlap.

The amount of power your amplifier produces is fixed. That is to say, no amount of knob-turning, button-pushing or amp-gain-tweaking will allow it to produce more power. Turning up the gains on your amp only causes the amp to produce full power with a lower input voltage from your source unit. There is no benefit to this, and depending on your system, could introduce more background noise.

If you think your system doesn’t play loudly enough or seems to get too loud with only a little turn of the volume, go back to your installer and have him or her check the settings on the amp while playing the music you enjoy.

2. Crank the Bass Boost!

Perhaps the most dangerous control on an amplifier, besides an improperly set gain control, is the bass boost control. In all cases, this single-band equalizer increases the output of the amplifier around a specific range of frequencies — usually in the 40 to 50 Hz region. What the control doesn’t do is increase the maximum available power from your amp. If your audio system is configured to produce full power with the volume on your radio turned up all the way, turning up the bass boost on an amp or processor will cause the amp to distort at the frequencies that you have boosted. It won’t make the system play any louder.

If you turn the bass boost up 10dB, then you need to turn the gain control by an effective 10dB to keep everything equal. Perhaps it’s easier to leave it alone?

3. Wire the Amplifier To Below-Spec Impedance

If you have multiple subwoofers with dual voice coil designs, a variety of options are available to wire them to your amp. The voice coils can be wired in series, in a series-parallel configuration or all in parallel. The maximum amount of power an amplifier produces is dependent on the voltage and current provided by the amp. Lower load impedances will typically cause an amp to produce more current and consequently more power. With that said, there is a limit. All amplifiers have a minimum load impedance rating. This means the manufacturer has designed the amp for a specific current limit that won’t over-tax the power supply transformer and the power supply and output switching devices.

Changing the way your subs are wired to something that is beyond the specification of your amplifier may allow it to produce a little more power, but in the case of most amplifiers, all it does it make the amp run much hotter because the efficiency is reduced. If your amp was producing 1,000 watts and rewiring it made an extra 50 or even 100 watts, well, that difference is almost inaudible.

4. Adjust the Tone Controls or EQ on Your Radio

If your radio has an equalizer or simple bass and treble controls, turning them up will make different frequencies of your music louder relative to others. With that said, it won’t make a properly configured and tuned audio system play any louder. Just like the bass boost on an amp, equalizers and tone controls affect the signal level at specific frequencies.

Another common problem with adjusting equalizer controls in a source unit is the ease of distorting the output signal. The preamp signals from radios are rated for a specific amount of voltage, usually 2, 4 or 5 volts RMS. Turning up the tone controls on the deck could cause the signal coming from the radio to distort and make your music sound horrible.

5. Buy the Wrong Amplifier

All speakers and subwoofers have power ratings. In almost all cases, this rating is the amount of power that the speaker can manage from a thermal standpoint. You see, speakers are notoriously inefficient. More than 95 percent of the energy fed into a speaker is converted to heat. If you feed a woofer 100 watts of power, 95 watts go into heating the voice coil and motor assembly and less than 5 watts are converted into acoustic energy.

If you buy an amplifier that produces more power than a speaker or subwoofer is rated to handle, you will overheat the voice coil assembly, and it will fail.

At the opposite end of the spectrum, having too little power can also cause problems. Let’s say you have a coaxial speaker rated for 70 watts of power and you are using an amplifier rated for 50 watts. You’d think that you are pretty safe, right? If you push that amplifier to the point that its output signal reaches clipping, the amp will produce a great deal more high-frequency energy. The additional energy can cause the tweeter to heat up and possibly fail.

Another consideration about amplifiers is that most can produce 150 percent to 200 percent of their rated power as extra energy when pushed into clipping or distortion. So, a 50-watt amplifier can easily produce 75 watts of distorted power and still damage that 70-watt speaker.

Make sure you have enough power to enjoy your music at the listening levels you want without having to push an amp to the point of distortion.

If you have any questions about purchasing the right products for your mobile audio system, visit your local mobile electronics specialist retailer. They will ensure you get the right solutions that are configured so your car audio system sounds great and will last for years.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

Shopping for car audio upgrades is as personal as shopping for a new car or new shoes. Each of us likes something different, has a different budget and different performance and style preferences. In the case of a new car, your options range from a solid and reliable daily driver in the $14,000 range to luxury and exotic vehicles costing well over $100,000. When it comes to a new radio, speakers, an amplifier or a subwoofer upgrade for your car, the price point differs just as much, as do the features and performance levels. In this article, we will provide some tips to prepare yourself to buy new car audio upgrades and ensure they are installed and configured reliably.

Shopping Online or at a Store

A discussion about online shopping opens a monumental can of worms. One of the biggest differences between buying from an online retailer and a local independent specialist will be the level of after-sales service and support. If you buy new speakers online and you have a problem with them, you can try contacting the supplier. About all they can do is offer to let you send the speakers back (at your cost) and they will send you another set. When you deal with a local retailer, someone can go to your car and listen to the problem. The issue may not be the speakers at all. It could be the source unit, an amplifier or an installation issue. Likewise, if you buy something online and it doesn’t fit your vehicle, you will have to send it back (again, at your expense). If you buy speakers from a local shop, they can make sure you get the right size and that the units they install function perfectly.

Do-It-Yourself Installations

Make no doubt, most of the installers, technicians and fabricators who work at mobile electronics retailers got their start working on their vehicles in their driveway. In some cases, this passion for working on cars and trucks grew to include their friends’ vehicles, while others sought out training from companies like Installer Institute, Kingpin University, Mobile Solutions, or in the good old days, Mobile Dynamics. Whether an installer had formal training or extensive hands-on experience, most of them have continued to hone their skills and knowledge through ongoing training to deal with data network integration, handle factory audio systems with advanced tuning and learn about new cool and unique fabrication skills.

Whether you decide to pay for the expertise of a professional or attempt to install something yourself comes down to your comfort level. If you feel you can do the work safely and reliably, then, by all means, give it a try. If you don’t know how to access and confirm the correct wire connections, make electrical connections securely and safely and mount equipment in a way that ensures maximum performance and reliability, then ask your local shop to do the work. Don’t get in over your head, though; it’s easy to break plastic trim panels or short wires and damage electronic modules.

Preparing to Go Shopping

When it’s time to head out and shop for new audio equipment for your vehicle, you’ll need to bring a few items with you and do a little planning. First, you need to decide on a budget. How much money do you want to spend on the product? Set yourself two levels for this decision: an ideal price and an absolute maximum price. What if you’ve allowed $800 for a set of speakers, but you hear a set priced at $1,000 that sounds amazing? Leave yourself some wiggle room.

Set a budget for accessories as well. Here are some common accessories required for some of the major audio system upgrades:

Source Unit

• Mounting Kit
• Wire Harness Adapter
• Antenna Adapter
• Vehicle Integration Module *

Speakers

• Mounting Adapter
• Speaker Wire
• Sound Deadening
• Acoustic Coupling Rings

Subwoofer

• Subwoofer Enclosure
• Speaker Wire
• Mounting Screw/Hardware

Amplifier

• Power Wire
• Fuse Holder
• Interconnect Cables
• Remote Turn-On Wire
• Vehicle Integration Module *

 

*Many new vehicles use data connections between the factory radio and amplifier. To upgrade either of these components, you may need to purchase a data interface module. These modules need to programmed for the specific make, model and trim level of your vehicle to function properly.

Choosing a New Source Unit

When it comes to source unit upgrades, the first thing you need to find out is whether or not you can replace the factory radio in the vehicle at all. Vehicles such as BMW, Mercedes-Benz, Mazda and many new Nissan vehicles have source units that can’t be removed.

Once you have determined that you can replace the radio, you need to determine the features you want to add. These will depend on how old your vehicle is. Many new radios include Bluetooth for hands-free calling and audio streaming, HD Radio tuners and playback of MP3, WMA, AAC, WAC and FLAC digital audio files. If you choose a multimedia radio, the system may also play MPG, AVI and MKV video files, and it may include an input for a backup camera. Navigation is a very popular feature on multimedia radios, as is smartphone integration. Features like Android Auto and Apple CarPlay have been the most popular reason people upgrade their radios over the last few years.

Speaker Upgrades

Perhaps the most important component in an audio system is the speakers. Speakers are the only link between your music source (radio, USB stick, streaming service or smartphone) and your ears. The quality of your speakers will determine the accuracy of your audio system. A speaker that produces a lot of distortion will color your music, detracting from the detail and realism of the listening experience.

Auditioning speakers can be difficult, especially in an environment other than a car. What you can tell is the difference between one speaker and another. Listen for clarity and detail rather than overall tonal balance. Does a brush on a cymbal sound real or like sandpaper on a piece of steel? Do the highs blend realistically with the midrange and midbass region? Is the bass taut with great impact or sloppy and resonant? The differences you hear on a display board will remain consistent once the speakers are installed in your vehicle, even if the overall tonal balance changes.

Amplifiers and Processors

Choosing one amplifier over another can be difficult. Most people buy amplifiers based on power ratings. You don’t need a 400-watts-per-channel amp for your midrange drivers; 50 to 100 watts is usually quite adequate. For subwoofers, well, power is fun. Too much power can lead to damaging your speakers. If you never, ever want to damage a speaker, choose an amp rated for half of the continuous power rating of your speakers and subs. If you can control yourself and know when to turn down the volume if you hear distortion, you can choose an amp that offers the same power as the speaker is rated for. Use only the continuous power ratings on your speakers, not those bogus “max power” numbers.

Signal processing has become a lot more important and readily available in the last few years. As more and more shops learn how to quickly and efficiently tune an audio system using a DSP, consumers continue to reap the benefits of improved accuracy and realism from their sound system. If your budget can handle it, include a digital signal processor in your upgrade and make sure the system is designed to maximize the features offered by that unit.

What to Bring With You

When you go shopping, bring one or two pieces of music that you know well. Before you leave your house, listen to that song on as many different sources as possible: your home theatre system, a portable Bluetooth speaker, headphones with your smartphone and your existing stereo. Think about what is different between each experience so you can listen for those elements as you audition new products.

It will sound strange, but bring the vehicle you want to upgrade with you. Don’t bring your wife’s car. Many shops will want to look at your vehicle to confirm speaker sizes and the available space for equipment installation, and some salespeople will want to sit in the car with you to learn more about how you listen to your music. Seeing EQ or tone control adjustments you have made can provide a great deal of insight into future upgrades.

Choosing the Right Retailer

Not every car stereo shop is ideal for every type of project. Needing a new radio in a 1990 Honda Civic does not require the same skill as fabricating a set of speaker pods for in the A-pillars of a Tesla Model 3. Part of your shopping process is to quantify the skills and capabilities of the shop to find out whether they have the experience and tools required to do the work you want. Specialist Mobile Electronics retailers have typically invested tens of thousands of dollars in tools and training so that their staff is ready to take on any challenge.

You can also learn a lot about a shop by the kinds of questions the sales teams ask you and the type of information they provide. If the salesperson is reading features off of the box the product comes in, they may not be genuinely qualified to provide you with the exact solution you need. True experts in the industry dedicate hundreds of hours each year to learning about the products they sell to make sure they offer excellent value and reliability.

The Bonus Buying Experience

If the shop you are visiting has a demo vehicle, ask to have a listen. Even if you have a modest budget, you can learn a lot about the shop’s capabilities by listening to a demo car and looking at the work they have performed. Looking at wiring around amplifiers and the battery is a great way to understand their level of commitment to doing great work.

We could go on for another 10,000 words about how to shop for car audio equipment. This article serves as a primer for the experience and to give you a few ideas about what to look for. Visit your local mobile electronics retailer and listen carefully to their advice.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.