Upgrading a factory audio system is not as easy as it used to be. In the late 1990s and early 2000s, connecting an amplifier and a new set of speakers to a factory source unit would yield impressive, if not amazing, results. As automobile manufacturers put more focus on the performance of factory-installed sound systems, digital signal processing (DSP) became more and more prevalent. Equalization and signal delay built into factory source units and amplifiers allow inexpensive speakers to sound acceptable. This tuning works well for such speakers, but not for a set of premium aftermarket speakers. In the past few years, it has become common practice for reputable mobile electronics retailers to perform a series of oem sound system measurements in a vehicle we haven’t worked on before to ensure we understand how the factory entertainment system functions. The results of the measurements will determine the best path to upgrading the performance of the audio system.

Measure Twice, Cut Once

What do we measure, you ask? We need to quantify three items before a system upgrade can be discussed.

The first is frequency response. We need to know if the signal coming from the factory radio or amplifier has been equalized or filtered in any way. Equalization can help improve the performance of inexpensive speakers and compensate for the acoustic characteristics of your vehicle.

The second is voltage. If you have a high-power factory amplifier, then the interface we choose for your system has to be able to handle all of the voltage the amp can produce. Not knowing how much voltage is present in the speaker wires can lead to a system design that distorts at high volumes. This distortion will damage speakers.

The last thing our shop will want to analyze is the type of signal present. In most cases, the output of the amplifier is a BTL (Bridge-Tied Load), though some are single-ended. There is no right or wrong type of signal, but the information is required to ensure that they will use the appropriate interface solution or amplifier.

Depending on the vehicle and complexity of the factory sound system, we may have to complete several other tests. Signal routing tests are critical, especially if there is a center channel in the vehicle. Chimes, navigation prompts, parking sensors, up-mixers, active noise cancellation and systems that inject “engine noises” into the audio path have to be taken into account before the system design is complete.

What if We Do Not Measure Your System?

Imagine that you want to improve the sound in your audio system. You go to a car stereo shop and buy an amp and a set of speakers, determined to install them yourself to save some money. Even worse, you want to try to save a few more bucks, so you buy the equipment online and have it shipped to your house. Saturday rolls around, and you tear into your vehicle. You run wires to the battery and try to connect to the factory amp. After an hour or two in forums or Facebook groups, you think you have finally connected to the right wires. When you turn the system on, it sounds dull and lifeless.

What happened?

Many factory amplifiers have dedicated outputs for tweeters and midrange drivers. Connecting to one or the other limits how much information goes to your new speakers. Working with an experienced mobile electronics retailer helps you eliminate situations like these. A retailer that doesn’t already have the information can measure the response of each channel of the factory source unit or amplifier and provide a way to manage work with that information.

A more-typical result is that the high-frequency output from the new speakers is overwhelming. Many factory audio systems use a woofer in the door and a small midrange in the dash. These tweeterless factory systems require a moderate amount of high-frequency emphasis to sound acceptable. When you add a tweeter that can do a good job of reproducing these frequencies, the boost inherent to the system becomes overwhelming. You may be able to turn down the treble control on the radio, but it’s likely that the adjustment only compensates for the highest of frequencies, leaving you with an annoying frequency response bump around 4 or 5 kHz.

What We Do with the OEM Sound System Measurements

After the measurements are complete, our shop can recommend a solution to help ensure the success of your new system. If you luck out and have a simple factory source unit, you may only need a voltage adapter, commonly called a line output converter, to send an appropriate signal to your amplifier.

If a large amount of equalization is present from the factory amplifier, then an equalizer or digital signal processor may be adequate to compensate for the factory tuning. A calibrated microphone and audio analysis equipment is required to set up the new system. These devices are expensive, and it takes time to learn how to use them correctly to achieve acceptable results.

If you have a factory amplifier that includes crossovers or time alignment, then your interface options narrow. Several system integration processors on the market can automatically undo equalization and time alignment, then recombine signals from the subwoofer, midbass, midrange and tweeter outputs. There are also integration modules that will replace your factory amplifier and provide connections that will feed a signal directly to your new amplifier. Unfortunately for the Do-It-Yourselfer, these amplifier replacement modules need to be programmed for the year, make, model and trim level of your vehicle. This configuration process is not something that you can do at home.

Inquiring Minds Want to Know

Performing OEM system measurements are like preparing to have a cavity filled. Before your dentist starts grinding or drilling, he or she will take a series of X-rays so that they know exactly what they are dealing with. The same philosophy applies to constructing a subwoofer enclosure. You’d never see someone start cutting wood without having measured the car accurately.

When it is time to upgrade your factory audio system, visit your local mobile electronics specialist retailer. Ask if they know how your factory audio system is configured in terms of signal processing. If they don’t know, find out whether they have the equipment to measure the factory audio signals in your vehicle. Once you are comfortable with their level of expertise, you can enjoy the process of designing a fantastic sound system for your vehicle. You will be thrilled with the results!

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.

The adage that someone could write a book about a subject certainly holds true when it comes to a discussion of loudspeakers and their parameters. In fact, there are dozens of great books already available about the subject. This article provides an overview of some of the most commonly discussed speaker parameters.

What are Speaker Parameters?

Speaker parameters, often called Thiele/Small parameters, are a set of electromechanical measurements that can be used to define the low-frequency performance of a transducer. Using these parameters and a series of calculations, your installer can predict the performance of that speaker in an enclosure.

What Can We Determine from these Parameters?

Perhaps the most important set of calculations we can create is the output of the system. When we discuss the “system,” we are referring to the speaker itself and the enclosure in which we intend to install the speaker. Every speaker enclosure acts as a high-pass filter and reduces the low-frequency output of the driver. We gain physical power handling in return for this diminished output. Using a set of calculations, we can predict how much low-frequency information the system will produce.

Another important calculation is power handling. As mentioned, we need to control the movement of the speaker cone to prevent distortion and damage. We can predict how much the cone will move for a given amount of power in our test enclosure.

Resonant Frequency of the Speaker – Fs

In terms of analyzing the moving parts of the speaker, we need to know the frequency at which the compliance (springiness) of the spider and the surround combine with the mass of the cone and dust cap to store the most energy. At this frequency, the system alternately stores and subsequently releases the most energy for a given voltage input. If you were to swing a weight on a string suspended from the ceiling, the natural frequency at which it oscillates back and force would be equal to the resonant frequency of a loudspeaker.

Equivalent Compliance Volume – Vas

To understand how stiff the spider and the surround are, we compare them to an amount of air that would exert the same resistance to motion. Because air is easily compressed, a high Vas specification would represent a very softly suspended cone. Conversely, a speaker with a low Vas would have a very stiff suspension.

Electrical Q of the Driver at Fs – Qes

Understanding the Q (Quality Factor) can be somewhat difficult because it is a dimension-less value. In essence, the Q factor describes the damping characteristic of a resonant system. A higher Q represents less energy loss relative to the total energy stored in a system. A pendulum suspended from a low-friction bearing will have a high Q. That same pendulum, submerged in water, will have a much lower Q. An important consideration is that high-Q systems have less damping and, therefore, vibrate longer. The Electrical Q specification describes how much damping the voice coil and magnet assembly invoke on the moving cone.

As the voice coil moves past the magnet, it produces an electrical current. This current reaches its peak value at the resonant frequency of the driver and counteracts the current being provided by the amplifier. The net result is a significant rise in impedance at the resonant frequency.

Mechanical Q of the Driver at Fs – Qms

Just as the electrical characteristics of a speaker cause an opposition to cone motion, we have a similar effect from the mechanical properties of the speaker. Qms describes the mechanical losses resulting from the spider and the surround. A high Qms value describes lower mechanical losses, while a low Qms value describes higher losses.

Total System Q at Fs – Qts

This unit-less measurement is a mathematical combination of the mechanical and electrical characteristics of the speaker. In simple terms, we calculate Qts by dividing the total stored energy of the speaker by the dissipated energy in the speaker at resonance.

Compliance of the Driver Suspension – Cms

The Cms specification describes the stiffness of the driver suspension in meters per newton. A stiffer suspension will move less distance for a given amount of force applied to it.

Effective Cone Area of the Driver – Sd

This parameter describes the effective “size” of our speaker. We all realize that the cone will move air for us, but we also have to take into account the addition of the surround. It is commonly accepted that we can use a value of half the surround as contributing to the output of the driver.

Mass of the Cone and Moving Parts – Mms

The Mms specification describes the mass of the speaker cone and part of the spider and surround. Unlike the Mmd specification, Mms includes the acoustic load caused by the air in contact with the cone. In most cases, the values are similar, but as the surface area of the cone increases, so too does the value of Mms, relative to Mmd.

Maximum Excursion Level – Xmax

This parameter is frequently misinterpreted as being the defining factor in the distance a speaker cone can move. Early calculations used a formula that subtracted the height of the voice coil winding from the height of the magnetic gap, then divided by 2. This calculation describes how far the speaker can move before the winding comes out of the gap.

Subsequent investigation shows that non-linear behavior elsewhere in the driver design could have a larger influence on the motion limits of the cone. This suggests that Xmax should be the one-way excursion distance that represents a distortion level of 10%. This performance-oriented specification is far more indicative of the useful operating range of a driver, but is much harder to ascertain.

Additional Parameters

In this article, we only describe the basic parameters that are commonly used in predicting the low-frequency performance of a loudspeaker. Other parameters, such as inductance, become more relevant at higher frequencies. Addition parameters such as Nominal Impedance (Znom), efficiency, sensitivity and the Efficiency Bandwidth Product (EBF) are derived through equations that use the specifications above.

Proper Design Requires Simulation

A woofer in an over-sized enclosure may bottom out and be damaged easily. A midrange driver crammed into a small speaker pod may have a significant frequency response spike and an associated distortion peak. The result is quite unfavorable.

Before you assume a subwoofer or speaker is suitable for the enclosure or mounting location you have chosen, it is worth asking your mobile electronics retailer to perform a simulation to ensure everything will function the way you want. They can work with you to ensure everything will perform optimally, and your system will sound great!

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.

Your automotive battery is one of the most important, and most often overlooked, electrical components in your vehicle. If your battery is not in good condition, you can be stranded, and other components in your vehicle may be damaged. This article discusses how batteries work and how to take care of them.

What is Inside an Automotive Battery?

Inside a typical car battery are six smaller energy-producing components called cells. Each cell contains a series of electrodes or plates. The positive plate of the battery is lead [eroxide (PbO2). The negative plates of the battery are pure lead in a soft, sponge-like state. The plates within each cell are arranged in alternating layers for a total of 16 components. All of the positive plates in a cell are wired in parallel, as are all of the negative plates.

Each cell produces roughly 2 volts of electricity. The six individual cells are wired in series with one another so the voltage generated by each cell adds together. The result is 12 volts.

Are You Ready for the Chemistry?

A diluted solution of sulfuric acid (H2SO4) surrounds the plates. The ratio of acid to water (H2O) is typically in the region of three parts of water to one part of acid.

When we connect a load to the external terminals of the battery, a chemical reaction starts to take place. Our diluted sulfuric acid mixture comprises H2SO4 and water (H20). As the reaction commences, the sulfuric acid splits into positive hydrogen ions (2H) and negative sulfate Ions (SO4).

When the hydrogen ions reach the lead peroxide plate, they absorb electronics from it and become a hydrogen atom. This process attacks the lead peroxide to produce lead oxide (PbO) and water (H2O). The lead oxide reacts with the sulfuric acid to form lead sulfate (Pb SO4) and water (H2O).

Negative sulfate ions move freely within the solution. As they reach the pure lead plate, they give up their extra electron and become what is known as a radical sulfate. As a radical sulfate cannot exist on its own, it will attack the pure lead plate to produce lead sulfate (PbSO4).

The action of positive hydrogen ions taking electrons from the lead peroxide plate, and the negative sulfate ions giving electrons to the pure lead plate produce an electron imbalance. These electrons flow through the external load to try and balance themselves. This process is how the battery provides power to our load (light, amplifier, heater or computer).

The Chemistry behind Battery Charging

When we apply an external DC source to the battery, we reverse the process. An external DC source such as an alternator or a battery charger feeds electrons to our positive lead sulfate-covered lead peroxide plate and the negative lead peroxide-covered lead plate. During the charging process, the density of the sulfuric acid solution falls, but we still have positive hydrogen ions and negative sulfate ions.

The positively charged hydrogen Ions more toward the negative terminal of the external DC source. Each hydrogen ion takes one electron from the negative plate to become a hydrogen atom. These hydrogen atoms attack the lead sulfate to produce lead and sulfuric acid.

The negative sulfate ions move toward the positively charged plate. When they get there, they give up their extra electron to become radical sulfates. This radical sulfate reacts with the lead sulfate, and forms lead peroxide and sulfuric acid.

We Can Simplify that a Lot!

In a nutshell, the negative terminal of a lead-acid battery has an over-abundance of electrons. When you connect a load to the battery, the electrons scramble through the load to get to the positive terminal. This electron flow is what allows the battery to provide energy to do work.

When we apply a voltage to the battery that is higher than its resting voltage the electron flow reverses. The sulfate layers on the plates are converted back to lead and sulfuric acid.

Battery Charging: Calm Down – What’s the Rush?

About the worst thing you can do to a car battery is to rush the charging process. If you rush the recharging chemical reaction, the lead sulfate will heat up and adhere permanently to the lead and lead peroxide plates. Once it is stuck there, we can no longer use that area of the plate to flow electrons, and we have reduced the effective size of the battery.

You probably have heard the expression “a battery is never the same after it has been killed.” This statement is very true if the battery is not charged gently and thoroughly.

When you want to recharge your battery properly, keeping the process slow will allow the chemical reaction to take place at a controlled rate. If you are using a high-quality, computer-controlled charger (and you should be!) there are two major charging stages. The first stage is called bulk charging. The charger will maintain a constant current flow to the battery by adjusting the applied voltage.

How do you know if you are charging a care battery too quickly? Standard flooded batteries should not exceed roughly 120 degrees Fahrenheit during charging. We suggest that slower and cooler is always better. An absorbed glass mat (AGM) or gel battery should not exceed 100 degrees.

Once approximately 80% of the used energy has been returned to the battery, the charger will switch to the absorption stage. At that stage, the charger provides a constant voltage to the battery and the current flow diminishes as the battery reaches full charge.

How to Calculate Maximum Battery Charging Rates

A relatively large car battery may have a capacity of 70 or 80 amp-hours. This specification means that under ideal conditions, you can draw 1 amp of current from the battery for 70 or 80 hours. After that time, the battery will be considered dead.

To find the ideal charging rate for our 70 amp-hour battery, we divide this specification by 10 to get seven amps. The battery should be able to accept 7 amps of charging current without overheating. It is worth noting that, if the battery is completely discharged, it will take 10 hours to charge it. Remember, slower is better when it comes to charging batteries.

Taking Care of Your Car Battery

Some of us who are more fanatical about the care and maintenance of our car batteries will connect them to intelligent battery chargers several times a year. One rule of thumb is to charge your battery fully after each oil change, or four times a year. You should increase this frequency if you make short trips that do not provide adequate charging time. Likewise, time spent playing your audio system with the engine off can drain a battery very quickly. If you have been out with friends and your car battery has been depleted, put it on a high-quality charger overnight.

If you can access the acid solution in your battery, ensure that it is at the proper level, or at the very least, is covering the lead plates completely. A hydrometer should be used to confirm the specific gravity of the solution, but if it is low, adding distilled water is better than doing nothing. That little green “eye” included in some batteries is a hydrometer. When it disappears, the chemical balance within the battery is off and it needs to be charged.

Your local mobile electronics retailer may have a battery load tester that they use before every remote car starter they install. If you are concerned about the condition of your battery, ask them to check it. Being stranded due to a dead battery when the temperatures get cold is frustrating if you are trying to get home or to work.

Ensure the battery terminals and connections to your vehicle are clean and secure at all times. A loose connection can have a dramatic adverse effect on the functionality of your electrical system.

If you need a new battery, check with your local mobile enhancement retailer first. They often have extensive experience in upgrading batteries and can help you choose a solution that will ensure your car is ready to go every time you turn the key.

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.

If you spend any time reading car audio discussions on Facebook or in forums, then you will have undoubtedly come across comments involving the supposed drawbacks of using RCA Y-cables. There seems to be a lot of misconception or misunderstanding about how preamp signals works, and this misinformation leads to comments that aren’t always accurate. Let’s take (more than) a few minutes to clear things up.

Understanding Preamp Level Audio Signals

The audio signal that connects your source unit to your amplifier is both very weak and quite small. The voltage of the preamp signal is rarely above 10% of the maximum voltage capability of your source unit for several reasons. Firstly, the signal level is directly proportional to the output of the system. When the volume is low, the signal is low in amplitude.

The second factor that contributes to the microscopic amplitude of the preamp signal is known as the Crest Factor. By way of a formal definition, the Crest Factor is the ratio between the peak signal amplitude and the RMS value of a waveform. For a pure sine wave, this value would be 1.414. For music, the Crest Factor value is much larger.

We analyzed a few different songs to come up with some relatable numbers. The new song Run by the Foo Fighters has a maximum amplitude of +0.15 dB and an RMS amplitude of -12.7 dB over the entire track. To keep the math simple, let’s call it 13 dB, which is a ratio just shy of 20:1. We also analyzed Heathens by Twenty One Pilots and found that it has a Crest Factor of 10.5 dB, or just about 11.25:1.

If we think about the highest voltage possible on our preamp signal as being 4 volts, then the average voltage for the above track would be 200 millivolts and 355 millivolts respectively. The peak of 4 V only happens when the volume is at maximum. Don’t forget that.

Scotty, We Have No Power!

Another characteristic of our preamp signal is that it contains almost no current flow. As with any electrical circuit, the amount of current flowing through the circuit is determined by the voltage in the circuit and how much resistance there is. The output impedance of most head units is between 300 and 500 ohms. The input impedance on most amplifiers is about 10,000 ohms.

Using our maximum voltage of 4 volts, and a resistance of 10,500 ohms, the maximum current in our circuit will be 0.381 milliamps. If we consider that the average signal amplitude is about 275 millivolts, then we have an average current flow of 0.0275 milliamps. That is nothing.

What does an RCA Y-cable Do?

An RCA Y-cable allows you to connect a single RCA output to two RCA inputs. Typical applications for Y-cables are a single subwoofer output RCA on a source unit or processor and the need to feed a pair of inputs on a subwoofer amp. Another common application is a source unit with only a single left and right RCA output; you want to use a four-channel amp that doesn’t include a two-input/four-input switch.

Please Don’t Believe the Hype

The biggest myth about the use of Y-cables is that they dramatically reduce the signal going to each input. To prove why this is not true, we need to understand how a voltage divider circuit works. Yes, it is time for a little physics and math.

In an ideal situation, when we have a signal source and a single load, all the voltage developed by the source appears across the load.

If we have multiple loads, the voltage produced by the source is divided among the loads when they are wired in series. In the image below, we have two loads in series with our single signal source.

If the resistance value of the two loads is the same, then the voltage produced by the source is divided equally across the loads. Half the voltage can be measured across each load. Using our 4 V preamp example, we would see 2 V across each load. However, what happens when the load resistance is not the same? We have to do some math to determine how much voltage is across each.

Let’s label the loads. The load on the left will be called Rs. This is the resistance of our source. For this example, we will use a value of 500 ohms. The load on the right will be our amplifier input resistance of 10,000 ohms, and we will call it Ra1.

We have 4 volts being produced by the source and a total circuit resistance of 10,500 ohms. We can calculate that the current flowing in the circuit is 0.0381 milliamps using Ohm’s law. Knowing the current in the circuit allows us to determine how much voltage is dropped across each resistance. For our source load, we have a resistance of 500 ohms with a current of 0.381 milliamps to produce 190.476 millivolts. The rest of the 4 V source signal or 3.809525 volts appears across the load.

Let’s wire another amplifier in parallel with our first amplifier. This is the same effect as using a Y-cable. Our second amplifier will be called Ra2.

Now it is math time again. This time, our circuit has a total resistance of 5500 ohms, and as such, has a current of 0.7272 milliamps flowing in it. The voltage dropped across the source has increased to 0.363636 volts, and each amp is seeing 3.636 volts. That seems like a noticeable difference, doesn’t it?

The Decibel Scale Changes Everything

Between the two examples above, we have seen a decrease in voltage at the amplifiers by 4.772%. Does that mean our music is almost 5% quieter? No. When we talk about the ratio of voltage to volume, we need to take into account the decibel scale. Our decrease of 4.772% percent in voltage works out to -0.405 dB less output.

Before you get your knickers in a knot, you can fix that by turning the gain on your amplifier up by that amount.

A Worst-case Mathematical Example

This example was a worst-case scenario. What if you have a source unit with a lower output impedance? Some head units have an output impedance of 300 ohms. For that head unit, with the same 10,000 ohm input impedance on the amplifiers, the change in output by using a Y-cable would be -0.2493 dB. If you have a premium line driver in your system, the output impedance may be as low as 50 ohms. In this scenario, the loss is a paltry -0.0431 dB.

What did we learn from this? If you need to connect many amplifiers to a single source, then choose a source with a low output impedance.

RCA Y-cables as a Solution are Not Evil

If your system requires that you use a set of Y-cables to distribute the audio signal to multiple amplifiers, then go right ahead. Once your installer sets the sensitivity controls on your amps, you will never, ever know they are there.

If you have any questions about the design of your audio system or what to know about how your installer will be wiring it, talk to the salesperson and your local mobile electronics specialist retailer – they would be happy to explain things to you.

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.