Understanding how to recreate music in our vehicles is a complicated science. Balancing speaker sizes and locations with the goal of recreating what the recording engineer heard in the mastering studio or, at the very least, making your system enjoyable isn’t always easy. We want to take a look at the physics behind sound and explain a few fundamentals of how sound works to help you understand the terminology used in the automotive audio industry and why a balanced system design with the proper equipment is crucial to creating an enjoyable and realistic listening experience.

What is Sound and How Does It Work?

At the most fundamental level, sounds are vibrations that travel through air and other mediums. These vibrations are detected by our ears, which in turn convert them to minute electrical signals that our brains interpret.

Because we have two ears, our brain can determine the location of a sound source by analyzing the arrival time and frequency content of what each of our ears hear. For example, a sound that is created directly in front of you will arrive at both ears simultaneously and with equal frequency response. A sound that is created directly to the right of us will arrive at our right ear before our left. The amplitude of the sound will be slightly higher in the right than in the left. Also, the high-frequency content of the sound that arrives at our left ear will be different. We learn as we grow up to correlate different visual cues with what we hear to develop a sense for where the sound comes from.

Recreating Sound and Music

Much like the way signals from our auditory nerves send electrical messages to our brains, sound waves (or vibrations) can move a microphone diaphragm to create an electrical signal that a recording device can store for playback at another time. The image below is an electrical representation of someone saying the word hello. You can listen to the original audio file by clicking here.

The image shows us a graph of voltage versus time, with voltage on the vertical scale and time on the horizontal. The amplitude (level) of the signal determines its intensity (or loudness). The speed at which the signal changes determines frequency. Understanding the interactions of simultaneous frequencies is fundamental to understanding why similar sound sources produce different sounds.

The graph below shows the average frequency content of the person saying hello. You can hear the audio file by clicking here

When a performer is singing or someone is playing an instrument, the sound of that instrument is determined by its harmonic content. For example, a Middle C on a piano and Middle C on a guitar are based around similar frequency content. The following recordings show the majority of energy at 261 and 522 Hz. Here is the Middle C note on the piano and here is the note on the guitar. You can see that the average harmonic content of each is quite different.

If we focus on just the main 261 and 522 tones with a steep band-pass filter set to 120 and 650 Hz, the two instruments start to sound very similar.

Filtered Piano Sound

Filtered Guitar Sound

As you can hear, the “sound” of an instrument depends heavily on its harmonic content and relative balance (amplitude) of that information.

Car Stereo System Frequency Response

So, why are we dwelling so much on the fact that sound of different instruments and performers is based heavily on harmonic frequency content? When it comes to time to design an audio system for your car, truck, boat or motorcycle, it’s important that the system performs evenly across the entire audio spectrum in order for your music to sound realistic.

To achieve this goal, you need at least a two-way speaker system. Because no single speaker can reproduce the entire audio spectrum (from deep bass to the highest highs) with good efficiency and dispersion, we dedicate different size drivers to different frequency ranges. In the simplest of systems, you’d have woofers (not to be confused with subwoofers) that play frequencies below about 3,000 Hz. For the top end, you’ll need tweeters to cover the frequencies above 3,000 Hz.

For even better performance, you may want to add a subwoofer to the system to relieve the woofer of the task of reproducing those frequencies below about 80 Hz and dedicate them to a larger speaker that is more efficient in that range. It also takes a lot of energy to reproduce bass information, so you’ll want a moderately powerful amplifier available to drive that subwoofer. If you have 25 watts of power available to drive your left and right speakers, 250 watts would be a good starting point for your subwoofer.

Creating an Amazing Mobile Audio System

The last step in creating a car stereo system that sounds good is to ensure that the placement of each of the speakers in the vehicle allows for equal and balanced frequency response from both sides of the car. This is crucial to creating a realistic listening experience. With that said, most of us start with a set of coaxial or component speakers in the stock door locations. This puts our listening position quite far off-axis to the left side driver as compared to the right. For most people, the sound isn’t too bad and they can live with the minor differences, especially if the tweeters are angled up and rearward to deliver similar high-frequency response.

If you want a truly enjoyable and realistic listening environment, consider adding a digital signal processor that allows your installer to fine-tune the output of the left and right speakers at all frequencies so that they sound the same. If your installer knows how to sprinkle in the right amount of time delay so that the output of the right speaker arrives at your ears at the same time as the left, well, chances are you’ll enjoy an impressive soundstage in the vehicle. Your music will be spread evenly from left to right, and with the right recordings, you’ll be able to pick out each instrument or performer and their relative location to one another cross this soundstage.

Experience Amazing Audio in Your Car Today!

Now that you have a basic understanding of how sound, works, it’s time to upgrade your car audio system. Drop by your local mobile enhancement retailer and ask about a subwoofer, a DSP-equipped amplifier and new speakers. The difference you’ll hear with each of these upgrades will blow your mind and put a smile on your face.

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.

We’ve written several articles about speaker power ratings over the years, but the topic seems to be one that very few people understand fully. This article will serve as the reference guide for how premium and reputable manufacturers rate the power handling capabilities of their speakers. We’ll start by looking at the physics of speaker design regarding how they cope with the heat created by the power from your amp, then explain how pink noise is used to create power ratings.

Loudspeaker Efficiency and Power

Unfortunately, loudspeakers are notoriously inefficient. A high-efficiency 8-inch midrange driver used in a public address speaker can only transform about 1.3 percent of the power from the amp into acoustic energy. The remainder is converted to heat in the voice coil and, subsequently, the parts around the coil such as the magnet, T-yoke and cone.

Speakers designed for car audio applications are often significantly less efficient because they need to operate over a wider frequency range. For a midrange driver with a sensitivity rating of 90 dB 1W/1M, the efficiency is a paltry 0.63 percent.

Think about how much heat a 100-watt incandescent light bulb generates. Below is a thermal image of a 100-watt bulb that has been turned on for only 60 seconds. The glass base of the bulb has already reached a temperature of more than 90 degrees Celsius or 195 degrees F. It’s clearly too hot to touch and will only continue to get hotter. Quick research shows that incandescent light bulbs have an efficiency of about 2.2. This lack of efficiency makes them a great analogy in terms of comparing heat generation to that of a loudspeaker. We’ll get into the logistics and reality of feeding that much power into anything but a subwoofer shortly.

How Speakers Handle Heat

Heat in a speaker is generated in the voice coil winding. Whether it’s copper, aluminum or a combination of both, all that heat is focused on that relatively tiny coil of wire. The only component that comes into direct contact with the voice coil is, not surprisingly, the voice coil former. In car audio speakers, voice coil formers are made from materials such as kraft paper, synthetic insulating papers such as 3M TufQUIN, aramid fibers such as Nomex and Bondex, and aluminum. Each of these materials has different insulating and thermal conductivity properties.

The next speaker component that has to handle the heat from the voice coil is the top plate. In most cases, the top plate is a piece of steel that is affixed to the magnet (or magnets) to focus the magnetic field on the voice coil. Though the top plate doesn’t come into contact with the voice coil, the two components are very close to each other. The majority of the cooling for the speaker’s voice coil can be attributed to heat being transferred away into the top plate and subsequently the motor structure. Many loudspeaker manufacturers go to great lengths to ensure there is significant airflow around the top plate to further enhance cooling, especially on subwoofers.

The T-yoke, the part of the motor structure that completes the magnetic field loop, is also important in helping to draw heat away from the voice coil and the former. The T-yoke resides inside the voice coil former in most designs.

Subwoofer Voice Coil Diameter and Power Handling

The ability of any device to handle heat is determined by its size. A 1/8-watt resistor is much smaller than a 1-watt resistor. Generally, the size of a component determines the amount of surface area and the ability to transfer heat into the air. In speakers, the diameter and length of the voice coil winding in a subwoofer are a good indicator of how much heat and, subsequently, how much power the speaker can handle.

By way of an example, looking through a popular subwoofer manufacturer’s product range, we see that their subwoofers with a 2-inch diameter voice coil are rated for 250 watts; stepping up to a 2.5-inch diameter coil increases the power rating to 500 watts. Their subwoofers with 3-inch coils are rated at 600 watts, and their competition-level woofers have massive 4- and 5-inch diameter coils rated for 2,500 and 3,000 watts, respectively.

Keep in mind, the physical size (height) of each of these voice coils was not provided, so it’s safe to assume that the jump to more than 2,500 watts of power handling comes with a significant increase in coil winding height and associated surface area.

High-Frequency Speaker Voice Coil Sizes

Talking about power handling in anything but a subwoofer is going to require some common sense. Think carefully about the power handling ratings on a midrange speaker. We’ll look across another popular brand and see how their voice coil diameters relate to the power handling specifications of several of their 6.5-inch midrange speakers. This brand has a driver with a 1-inch coil rated for 70 watts, and a 1.25-inch coil is rated 80 watts in one series and 100 watts in a higher-end solution. The different power ratings on the 1.25-inch coils demonstrate how the overall height of the winding affects thermal capacity.

Now, let’s talk about tweeters. Tweeters in car audio applications are extremely small and, frankly, quite fragile. The voice coil windings in tweeters are made from very fine wire, often smaller than 24 gauge. Even with a diameter of 1 inch on a soft-dome tweeter, they can’t handle much power. So, how do manufacturers come up with ratings of 100 watts or more for their tweeters when we know a midrange driver with a voice coil winding that’s at least five times as tall can only handle 100 watts? The answer lies in how manufacturers test their speakers.

What is Pink Noise?

Before we get into the explanation of how speaker power handling is rated, we need to take a close look at something called pink noise. Pink noise is an audio signal comprised of random frequencies from just above 0Hz to the upper limit of the audio or computer audio file format. For a conventional CD-quality .wav file, this would be 22.05 kHz.

In pink noise, each octave contains an equal amount of noise energy. This means that the octave from 100 Hz to 200 Hz contains the same amount of noise energy as the octave from 1 kHz to 2 kHz. The power in each octave is also inversely proportional to the frequency of the signal. Though this is a rough approximation of how the math works, there are 100 Hz between 100 Hz and 200 Hz whereas there are 1,000 hertz between 1 kHz and 2 kHz. In a pink noise signal, the 1-to-2 kHz band is spread over 10 times as much space.

Here is what the spectral analysis of a pink noise audio signal looks like:

You can see that above 20 Hz, the level of the signal decreases at a rate of -10 dB per decade as frequency increases. This means that there is 10dB less signal energy at 1 kHz than at 100 Hz. When we relate this reduction in signal strength to power from our amplifiers, the ratio is also a factor of 10.

If we are playing pink noise through an audio system, and the amplifier sensitivity controls are set to produce 100 watts of power at 20 Hz, at 200Hz, the amp will be producing 10 watts. At 2 kHz, the amp will be producing 1 watt, and at 20 kHz, the amp delivers 0.1 watt of power to our speakers.

Power Density in Music

Another topic we should discuss before getting to speaker power ratings is how audio energy is distributed in the music we listen to. We looked at six audio tracks and analyzed their spectral content in Adobe Audition in the same way as the pink noise waveform above. The results are shown below:

As you can see from this moderately diverse selection of music tracks, the audio energy is distributed similarly to our pink noise track. For this reason, many manufacturers use pink noise signals to test the power handling capabilities of their speakers.

How Speaker Power Handling is Tested

Depending on the brand, different companies use different processes to test the power handling capabilities of their speakers. It should be noted that some companies have detailed specifications for their testing procedures while others rely simply on data provided by their suppliers, and others guess based on the size of the voice coil used in the design. This is one of the key differences between companies that put significant effort into the design and development of their products and those that pick solutions from a catalog and have their name stamped on the basket and dust cap.

A properly engineered speaker testing process involves several steps. We’ll use a subwoofer for the first example. The technician performing the test would set the output of the amplifier using a sine wave audio track to represent a voltage level that equates to the power level they want to test. For a 4-ohm subwoofer that is to be tested at a power level of 200 watts, the sine wave voltage should be 28.28 volts rms or 40 volts peak-to-peak. Once this amplitude is set, pink noise that equates to an equal amplitude at 20 Hz is played to test the driver.

Once the levels are set and the speaker is mounted in the test fixture, this pink noise track is played at a continuous level until the speaker fails, or an adequate time has passed. Many companies use eight to 10 hours as a minimum test time and some extend this to 100 hours. After the temperature stabilizes in the speaker, the extended time test can help to confirm the suitability and reliability of chosen adhesives and materials used to build the speaker. In essence, it becomes a physical test as well as a power handling test.

Though it varies from brand to brand, in order for the speaker to pass the test, the Thiele/Small parameters of the driver must not have changed by more than a predetermined amount from those before the test began. A significant change in electromechanical properties indicates that something may have been damaged during the test and that too much heat was generated.

How Midrange and High-Frequency Speakers Are Tested

Because midrange drivers and tweeters can’t handle high excursion levels, they are tested in the same way as a woofer, but the test signal passes through a high-pass filter. Here’s an example:

Let’s say we want to test a 4-ohm tweeter, and we want to use the above standard to test it for 100 watts of power handling. That equates to a sine wave level of 20 volts rms or 28.28 volts peak-to-peak. The test begins with the amplifier calibrated to produce 20 Vrms using a sine wave while not connected to the speaker. Once the level has been set, pink noise is played through whatever high-pass filter the manufacturer specifies. For the purpose of this example, let’s say the filter is set at 2 kHz.

This is what the spectral analysis of the test signal will look like.

 

The average peak level of the test signal is now about 20 dB lower than it was at 20 Hz with a full-bandwidth signal. In terms of audio signal power, we have 1/100^th as much power. Or 1 watt.

Are we saying that a tweeter rated to handle 100 watts of pink noise power, tested above 2 kHz, is only tested with 1 watt of power? Absolutely! That’s exactly how it works. Think about the physics of music. We want the audio produced by the tweeters to be balanced with that of the midrange drivers and the woofers or subwoofers.

In the real world, that tweeter can likely handle a lot more than just 1 watt of power. It may be able to handle 10 watts. Does this mean that it would be a good idea to rate the driver as being able to handle 1,000 watts of pink noise? Not likely. You know that someone who doesn’t understand how pink noise works is going to use a sine-wave track to set the gains on their tweeter amp and try and feed 63 volts (1,000 watts) into the tweeter. Of course, these same people will also call the speaker manufacturer and complain that the tweeter is “broken” and all they were doing was setting gain controls.

What’s the Point of Power Handling Specifications?

Speaker power handling ratings that use pink noise are based on criteria established for full-range home speakers. The tests mimic what the speakers would experience when listened to a high volume levels and are intended to indicate what amplifier power rating would be suitable to get the most from the speakers without damaging them. This specification doesn’t take into account what happens when an amplifier is driven into clipping – we’ll touch on that another time.

For now, the takeaway of all this is that setting up an audio system should start with setting the sensitivity controls on your subwoofer amp, then bring up the midrange and tweeter channel levels to create a balanced system. Odds are, you aren’t going to come anywhere close to maximum power from the mid and tweeter amps. Oh, and you don’t need a 150-watt amp to drive your tweeters.

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.

It’s hard not to notice that almost every reputable car audio manufacturer now offers several ultra-compact amplifier solutions. These amplifiers are small enough to fit in the pocket of your jeans and help make installations easier when space is tight. While diminutive, they can deliver an impressive amount of power to upgrade the signal to your factory speakers or let aftermarket speakers transform your mobile sound system into an amazing listening experience. In this article, we’ll talk about how companies can cram so much power into such a small package and look at how these amps differ from conventionally sized solutions.

What is an Ultra-Compact Amplifier?

While small amplifiers from companies like Sony, Soundstream, Rockford Fosgate and Linear Power have been around for decades, most of these early solutions were limited to around 20 watts of power per channels.

One of the first modern high-power compact amplifiers to make its mark in the industry was the Alpine Power Pack KTP-455U. Measuring roughly 8 by 2.5 by 1.5 inches in size, this four-channel amplifier could deliver a real-world 45 watts per channel into 4-ohm loads. Alpine marketed this amplifier as an easily integrated solution to upgrade a factory or aftermarket radio and deliver almost three times as much power to your speakers.

A few years later, Rockford Fosgate introduced its Boosted Rail Technology series of amps. These amps use a unique and creative power supply design that was different from all the other solutions on the market. From a power-production perspective, the four-channel PBR300X4 could crank out 75 watts of power into a 4-ohm load and had a footprint of only 6.75 by 4.25 inches.

Fast forward five years, and there are dozens of companies with small, high-power amplifiers available. You can choose from four- or five-channel solutions to upgrade your sound system, and most offer a roughly 300-watt subwoofer amp to add big bass without taking up much space. Several models include water-resistant designs that make them ideal for marine, motorcycle and powersports applications.

Big Power in an Amazingly Small Package

Amplifier size is determined by two factors: how much space is required to house the components needed to make the amp work, and how much heat sink does the design need to dissipate heat reliably under all conditions.

One of the biggest technological advances that have allowed amplifiers to become so small is surface-mount devices. Thanks to subminiature resistors, capacitors, diodes, transistors and microcontrollers, circuits and their components can fit in half or a third of the space they used to require. Think about your smartphone — it has more processing power than desktop computers from 10 years ago, yet fits comfortably into the palm of your hand or a shirt pocket. By comparison, the computers that took the space shuttles into orbit ran at about 1.2 million instructions per second (MIPS) and had a total memory of a couple of megabytes. The Apple A11 processor found in the iPhone X can manage a jaw-dropping 600 billion instructions per second. With that said, the Apple CPU isn’t designed to handle the rigors of outer space and prolonged exposure to radiation — so keep that in mind if you’re planning a trip to Mars with our buddy Elon Musk.

The surface-mount Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) used in the power supplies of these ultra-compact amplifiers have also allowed the amps to shrink in size dramatically. You can fit four of these devices on the end of your finger, and each one is capable of passing 50 amps of current. Thirty years ago, a single 50-amp transistor would have been bigger than all four of these modern devices.

Another technology that has reduced amplifier sizes is multilayered circuit boards. Four-layer boards provide significantly more options for connectivity among the devices in the circuit and reduce the space required for signal traces.

Finally, high-speed Class-D amplifier designs help to reduce current consumption in the output stage of the amp. Class-D audio amplifiers operate by switching the output devices on and off at extremely high speeds, and varying the duty cycle (on vs. off periods) recreates the original audio waveform. Because the devices are either on or off, they spend less time acting as a resistor and, subsequently, waste less energy as heat.

Are Compact Amplifiers the Perfect Solution?

With any benefit, there are often drawbacks. For ultra-compact amplifiers, three limitations need to be considered: cooling capacity, features and noise. As we mentioned earlier, fitting lots of parts into a small package is much easier, thanks to surface-mount devices and multilayered circuit boards. The drawback of a small amp is that it still needs a heat sink to the cool the switching devices. If we reduce the heat-sink area for a given power level, the amp will be more prone to overheating when pushed hard. You might be fine for one or two songs, but you likely won’t be able to jam on these at full-blast on a hot summer’s day in Arizona or Texas without them going into protection.

The features included with an amplifier are often based on the space available for controls and switches. If you want high- and low-level inputs, adjustable high-, low- and bandpass crossovers, infrasonic filters, signal summing, individual sensitivity controls, bass-boost circuits and remote level controls, you need lots of space. In an ultra-compact amplifier, that space simply doesn’t exist. As such, most of those features won’t be found on this class of amplifiers.

Finally, we need to talk about noise. Noise, or more specifically, signal-to-noise ratio (S/N Ratio) describes how much background noise (heard as hiss) is added to an audio signal when it passes through a device. The power supply and Class-D output stage of an amplifier produce a lot of high-frequency electrical noise. In a conventional and physically large amplifier design, these noisy circuits can be located physically and electrically far away from the sensitive input and signal gain stages of the amp. When we shrink an amplifier’s size by 30 percent, everything is much closer and thus more of this noise is added to the output signal.

Let’s look at five different four-channel Class-D amplifiers to compare noise levels relative each amplifier’s physical size.

Comparison of Four-channel Amplifier S/N Ratio

Amplifier Footprint Power / Channel S/N Ratio at 1 Watt
Square Inches Watts A-Weighted

Amp 1 26.76 50 >68 dB

Amp 2 41.99 70 >70.4 dB

Amp 3 60.41 75 >84 dB

Amp 4 68.07 75 >84 dB

Amp 5 89.03 150 >88.2 dB

As you can see, larger amplifiers add less noise to the output signal. While none of these specifications is atrocious, you will be able to hear a little hiss from the first two amps between songs and likely won’t on the top three amps. Of course, the third amp has a 50 percent larger footprint (length times width) than the second amp, so pick your poison appropriately.

Ultra-Compact Amplifiers Offer Unique Installation Solutions

If you are trying to add an amplifier to a motorcycle or a side-by-side and finding space for the amplifier is a concern, then, by all means, choose one of the many ultra-compact amps that are available. With that said, if you have a little extra space, larger amps offer better noise performance and more features. In this case, you get an audible improvement in performance by investing a little more money.

If you are interested in upgrading your mobile sound system, drop by local specialist mobile electronics retailer and speak to one of their product experts. They can provide you with several options to dramatically improve the sound quality and volume level of your existing system.

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.