Though it might surprise you, human hearing is significantly more sensitive to some frequencies than others. You can think of this phenomenon as our built-in frequency response. However, unlike a speaker or amplifier, variations are not something we want to compensate for in an audio system—at least, not directly. Let’s discuss how human hearing works with respect to different frequencies and why we need to compensate for this when making sound or product specification measurements. All of this will tie together perfectly with an explanation of weighting curves.

Human Hearing and Frequency Response

Did you know that human hearing is most sensitive around 3.5 kHz? This is due to the dimensions of the ear canal, which typically resonate between 2 and 5 kHz. Even a faint sound at 3.5 kHz is easy to detect. A sound might need to be 10 dB louder at 350 hertz to be perceived as having the same loudness.

In 1933, Harvey Fletcher and Wilden Munsen performed a set of measurements to quantify human hearing concerning frequency and intensity perception. Their paper, “Loudness, Its Definition, Measurement and Calculation,” included what became known as the Fletcher-Munson curves.

The lines on the chart are separated into amplitude levels called Phons. The Phon is the unit of measure used to describe sounds perceived as equal in intensity. As such, they follow the equal loudness level contours proposed by Fletcher-Munson and subsequent iterations.

It shouldn’t be surprising that the test equipment used to generate test tones wasn’t as precise in 1933 as it is today. Similar testing in 1937 by Churcher and King and again in 1956 by Robinson and Dadson produced significantly different results.

Introducing the Equal Loudness Level Curves

The International Organization for Standardization (ISO) took over the creation of reference loudness curves in 2003. A study by Tohoku University, Japan, and the Research Institute of Electrical Communication showed errors as large as 15 dB from the original data. These new tests became the ISO 226:2003 Standard. Don’t think it’s over yet. These have since been revised again to the ISO 226:2023 Standard.

Of course, the above curves are averaged across a wide selection of people of different shapes and sizes. Everyone’s hearing will be slightly different in the areas where it is most sensitive. However, this data provides an excellent overview.

If anyone references the Fletcher-Munson curves, they are at least four generations behind in their data. When discussing the perception of sound levels versus frequency, the proper reference is the ISO 226:2023 Equal Loudness Level Curves.

Interpreting Equal Loudness Level Curves

If you look at the 1 kHz point on each trace, you’ll see that this point coincides with the reference SPL value. So, a sound at 70 dB at 1 kHz is perceived as being at 70 Phons. However, it takes about 74 dB of energy at 1.5 kHz to seem as loud. Further, it takes only 67 dB of energy at 3 kHz to seem as loud.

What matters here are the extreme ends of each trace. We can make some generalized assumptions about human hearing based on the reduced sensitivity in these regions. Staying with the 70 dB trace, we would need to hear a sound that’s 83 dB at 10 kHz to be perceived as being as loud as 70 dB at 1 kHz. Further, a sound at 93 dB at 63 hertz is also perceived to be as loud as 70 dB at 1 kHz.

Though we haven’t consulted with an audiologist (yet), the issue is less about attenuation at opposite ends of the audio spectrum and more about an increase in sensitivity in the middle. As mentioned, the ear canal resonates around 2 to 5 kHz. Furthermore, the outer ear, called the pinna, also amplifies sounds in this frequency range.

The middle ear bones, the ossicles, are more efficient at transmitting mid-frequency sounds. An effective impedance mismatch between the air and the fluid in the cochlea further accentuates this frequency range.

There are additional mid-frequency sensitivities in the cochlea due to where different frequencies peak.

Audio System Equalization

We’ve seen many amateurs try to equalize their audio systems, more often in a home environment than in a vehicle, to compensate for the shape of these curves. That’s not the purpose of the information. Our perception of hearing is static. In short, we hear what we hear. We accept that the sound of a trumpet or saxophone is what it is. We don’t want to change that presentation to compensate for being more sensitive in one range versus another.

There is an exception to this statement. Regarding headphones and earbuds, flat response doesn’t sound accurate. This is because we’ve eliminated some of the frequency filtering caused by the pinna. As such, a modified response curve sounds best. The team at Harman International has devoted significant time and expense to creating a target curve for headphones based on similar experimentation that created the Equal Loudness Level Curves.

Analyzing Headphone Target Frequency Response

There are two critical pieces of information to extract from the above response graph. First, we can see the boost around 3.5 kHz that coincides with the boost the pinna of our ears adds. Without this, headphones would sound dull and flat. Second, there is a boost in low-frequency information. Part of this will be due to the Equal Loudness Level Curves, and part will be listener preference. We all know that many people prefer bass information boosted in their listening systems. The Harman headphone curve combines the science and mechanics of human hearing with extensive listener preference. They even have details on the percentage of people who prefer more bass and less bass.

Harman uses very specific test equipment to measure headphones. Specifically, a head and torso simulator accurately and repeatably simulates how humans perceive sound.

It’s worth noting that Harman has revised its target curve from the one shown above. Unlike this first iteration, they are not releasing this new curve to the public for endless debate and whining (insert sarcastic wink here!). They will use it to fine-tune the performance of their AKG, Mark Levinson, Harman Kardon, and JBL consumer and professional products.

Speaker Evaluations in Free Field Conditions

If we measure the frequency response of a conventional loudspeaker using a sine sweep or pink noise, we should end up with a fairly flat line, assuming the speaker can play from 20 Hz to 20 kHz with good accuracy. Most floor-standing home speakers roll off below 30 Hz. It would be best to have a dedicated subwoofer to fill in that bottom octave.

The chart below represents a nearly perfect speaker’s ideal frequency response. Do you think if we suck up to KEF enough that they will loan us a set of Blade 2 Meta to use as our reference review speakers? Here’s hoping!

As noted in Stereophile Magazine’s review of the Blade 2 Meta, the boost in the bass is primarily due to the close-micing technique used for measurements.

A-Weighting Curves in Measurements

Let’s get to the nitty-gritty of this article. Look at the Equal Loudness Level Curve chart above and analyze the 40-phon trace. Information similar to this was used to create what’s known as the A-weighting curve. This curve is intended to be applied to a sound pressure measurement so that the energy in the measurement correlates to how we hear. It was actually the Fletcher-Munson 40-phon curve that was used to create the A-weighting curve. Thankfully, the ISO 233-2032 40-phon curve is quite similar.

To show you the same data in a format you might be more familiar with, we dug out the Sony XM-4ES amplifier we reviewed a few years back. We performed a frequency response test with all the settings flat and again with the A-weighting filter activated in the QuantAsylum software.

 

Where We Use Weighted Measurements

The ANSI/CTA-2006-D standard for measuring car audio amplifiers calls for applying the A-weighting curve to the measurement after the reference level is set. Up to this point, we’ve shown the measurements as unweighted. The result is slightly lower values, indicating the presence of more noise. As we move to further comply with ANSI/CTA-2006-D, we’ll start using the A-weighting curve to evaluate the signal-to-noise ratio of the source units’ amplifiers and signal processors we test.

We can see that the Signal-to-Noise Ratio measurement of this Sony XM-4ES amplifier is specified as being 71.23 dB.

Now, if we turn on the A-weighting filter and apply it to the measurement, the low- and high-frequency information is attenuated, which reduces its effect on the measurement.

The QuantAsylum software has revised the SNR measurement to -76.11 dBA. The addition of the letter A after dB indicates the use of A-weighting. Given the published measurements on the CTA TECH website, which show -76.5 dBA for the XM-8ES and -80.8 dBA for the XM-6ES, we are comfortable saying our data aligns with those numbers.

So, the next time you see a signal-to-noise ratio measurement with the amplitude specified in dBA, you will understand how and why that rating system is used. Finally, a higher SNR number means that the noise is further below the test signal. A level of -75 dBA is about the minimum you’ll want to consider for an amplifier in a car audio system that will drive midrange and high-frequency speakers.

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.

A reader requested that we compare the sound quality performance of wired and wireless Apple CarPlay. This is a great idea, as very little information is provided about the communication standards used to send audio signals wirelessly to a source unit. So, let’s look at distortion characteristics and frequency response to see if there is a performance difference.

The Test Configuration

While our lab has an impressive selection of car radios, we didn’t have one that supports both wireless and wired CarPlay. We contacted our friend Lee Mattason at Burlington Radioactive for help. He graciously lent us a Kenwood eXcelon DMX908S to make some measurements. If you live in the Golden Horseshoe region of Southern Ontario and are looking for a car, boat, or motorcycle audio upgrade, Lee and his team are a great choice.

We are going to perform two different tests using four connectivity criteria. We will analyze sound quality by playing a 0 dB 1 kHz test tone and then analyzing it for harmonic content. The second test will evaluate frequency response by analyzing a white noise track. In both cases, the test tracks have 44.1 kHz sampling rates and are stored with 16 bits of depth. To ensure Apple didn’t alter the file while uploading it to the phone, we used the Onkyo HF Player and copied the tracks as files to a specific folder on the iPhone. The device is an Apple iPhone 14 Pro running iOS 18 Beta 2. Please don’t ask why the owner tries beta software on this phone—it’s a terrible idea.

The four communication methods we’ll use are playing the files from a USB memory stick, over a Bluetooth connection, through Apple CarPlay with the phone connected to the radio with a Lightning cable, and finally, using Wireless Apple CarPlay.

USB Media File Playback

The first test is to play the 1 kHz test tone track directly from the USB stick. We’ll note that with all the audio settings turned off and the source-specific levels flat, we saw an output of 4.539 volts on the front RCA output. The signal had a THD+N measurement of 0.01086%, which is excellent for a consumer-grade source unit. The signal-to-noise ratio (SNR) came in at -85.39 dB, unweighted.

Next, we have a 10-minute white noise track. We cranked up the averaging on the QA403 audio analyzer to produce as flat of a measurement as possible. The goal in interpreting the data below is to average the frequency response in your mind. We’d call this flat from below 20 Hz to 22 kHz on the top end. This is precisely what you’d expect from this measurement.

These measurements will serve as a solid baseline to compare with other playback media.

Bluetooth File Playback

We all know that the iPhone isn’t the go-to for Bluetooth sound quality. The use of Bluetooth 5.3, specifically with the SBC codec, really limits performance compared to an Android-based device that offers something spicier, like LDAC or aptX HD. For now, this is the test, and we’ll hunt down an Android phone and give that a go in a future article.

Let’s start with the distortion measurement. In a word, we can sum this up as being subpar. We can see all sorts of artifacts and harmonics starting at -46 dBV. This gives us a THD+N specification of only 0.14655% and a signal-to-noise ratio of 56.83 dB.

In terms of frequency response, the curve remains nice and flat, so overall, music would sound generally the same. The increase in distortion shown above hampers clarity and could add some emphasis. However, the raw amplitude measurements are similar. Looking closely, you can see that the high-frequency information rolls off at about 17.5 or 18 kHz. None of us can hear anything above 18 kHz, so that’s not a massive concern.

Wireless Apple CarPlay

We deleted the Bluetooth pairing from the radio and phone and reestablished it to turn on Apple CarPlay. We were cautious in all the tests to ensure the communication used our desired method.

Starting with the 1 kHz tone, we can see that the Wireless Apple CarPlay connection uses Bluetooth to transmit audio to the source unit. The distortion numbers are slightly worse at 0.15072%, and the SNR is -56.62 dB unweighted. If you are fanatical about sound quality, this isn’t the best way to get music from your phone to your radio.

Using Wireless CarPlay, the high-frequency information is attenuated a little more than when using a Bluetooth-only connection. We’d say the audio information stopped around 17-17.5 kHz. Once again, this won’t be audible to most people. However, it’s repeatably measurable and very real.

Wired Apple CarPlay

Last but certainly not least, it’s time to see how the combination works with a wired connection between the iPhone and the Kenwood radio. We deleted the phone pairing from both devices and plugged the phone into the micro-USB port on the back of the chassis.

For the 1 kHz tone, we saw a THD+N measurement of 0.01042%, which is the best of this test session. The signal-to-noise ratio came in at -85.21 dB. Both numbers are inconsequentially different from the original USB test. Nobody would be able to hear the difference in clarity or background level between Wired Apple CarPlay and playing an audio file from a USB memory stick.

We also have the spectral analysis of the white noise when played over a wired CarPlay connection. It looks nearly identical to the wireless connection. Again, even a variation from 17.5 to 20+ kHz isn’t audible to humans. Your pet cat, Fluffy or Wayne, or the neighborhood bat might disagree.

Conclusions on Apple CarPlay Audio Playback Quality

Based on this specific test, we’d say there is an audible difference in clarity between wired and wireless connections. Whether you are using Bluetooth or Wireless Apple CarPlay, you leave a significant amount of audio clarity performance on the table compared to Wired CarPlay or a USB memory stick. However, this is a single test with one specific radio and phone combination. It’s possible that an Android phone would fare much better wirelessly. We’ll make that test happen soon!

It’s also worth noting that the clarity difference might be easy to hear when sitting in the car with the engine off but much harder when you’re driving down the Interstate. Background noise masks a lot of distortion. However, we’d use a wired connection every chance we could.

If you are shopping for a new radio with Apple CarPlay and Android Auto, drop by a local specialty mobile enhancement retailer and ask what they have that will fit your vehicle. Be sure to bring your phone to connect it and ensure the radio works exactly how you want.

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.

Unlike home audio systems, car stereo upgrades have to withstand harsh conditions. Your car, truck or SUV subjects your system to vibration, bumps and massive temperature changes. At home, as long as there isn’t a flood, everything should work fine for decades with regular dusting. Your car stereo system might not be quite as foolproof. Let’s look at five quick and simple tips to ensure that your system works great

1. Radio and Touchscreen Maintenance

The device you will interact with the most is, of course, your car radio. If you have a multimedia receiver, then the touchscreen and volume knob will be the primary contact points. A slightly damp cloth is likely the best way to keep these items looking good. If there’s something stubborn on a touchscreen, a product like Whoosh! is a perfect choice. Spritz a little of this cleaner on a soft microfiber cloth, and you’ll be able to get it looking like new. You can wipe any dust off the instrument cluster while you’re at it.

Never spray any liquid directly on the screen. If dust is caught in the corners of the screen, pick up a makeup brush from a dollar store. These are soft enough to prevent any damage to the screen. This cleaning process also works great for laptops and smartphones.

While checking the screen, make sure the radio is still solid and secure in the dash. Push on the corners of the chassis (not the screen) with a finger. If it moves, something might need tightening behind it. Please drop by the shop that did the installation and book an appointment to have them check it out.

2. Amplifier Maintenance

In most cases, a well-designed amplifier will happily play without trouble for years or even decades. You will want to start by ensuring that the amplifier or amplifiers remain secure in the vehicle. Once again, please give them a gentle push or tug. If they move, get with the shop that installed them.

Next, inspect the amplifier and the area around it for signs of water damage. If an amp is mounted in the corner of the trunk, water from a leaky seal can cause problems. Water and salt damage from slushy boots can cause trouble if the amp is under a seat. If you see signs of water on the amp, find out where it came from. Make sure everything is dry, especially a wooden amp rack.

Check all the wiring to and from the amp. Do the connections look solid? Do you see any signs of excessive heat? If anything looks like it might be loose or if plastic has started melting, consult with the installer immediately. Some types of wiring, especially copper-clad aluminum, can loosen over time and cause poor connections. Terminal blocks can get very hot when these connections get hot, and plastics will melt.

3. Power and Ground Connections

Though this is an extension of an amplifier inspection, pop the hood and look at the connections to the battery. Pull on the power wire (gently). If any connectors move, then something needs to be tightened.

Check the fuse holder. Is it still secure? Was it ever secure? The electrical connections will be stressed if it’s flopping under the hood. Make sure a reputable shop mounts the fuse holder securely.

Check the ground connection in the trunk or under a seat. These are notorious for corroding, resulting in amplifier failure from power starvation.

If you see any signs of green, white or blue corrosion on the wiring or battery terminals, there might be an issue with the battery or water getting into the wiring.

4. Subwoofer Enclosures

While the other items are likely safe to check once or twice a year, this one should be done every month. If you have a subwoofer in the trunk or cargo area of your car, truck or SUV, make sure it’s secured solidly to the vehicle. In the event of a severe accident, a subwoofer enclosure flying through the vehicle could be enough to seriously injure you or a passenger.

Using a simple hook-and-loop fastener isn’t enough. In an accident, forces from the deceleration can easily exceed 10 or even 20 Gs. This would make a 30-pound subwoofer enclosure act like it weighs 300 to 600 pounds. Little plastic hooks (on the hook-and-loop fastener) won’t keep it in place.

While you’re inspecting the subwoofer enclosure, push gently and evenly on the subwoofer cones. They should move smoothly. If their motion is rough or scratchy, you have overheated the voice coil and damaged the speaker. Don’t replace the subwoofer with an identical model. Clearly, you need something that’s more capable in terms of power handling and output capability.

5. Speakers

Without taking your car or truck apart, checking the condition of your car’s audio speakers can be difficult. The best test is to give them a listen. Put in some good earplugs and play music with a lot of bass at a moderate volume level. Long, drawn-out bass notes from an organ or bass guitar are better than drums. Get up close to the speaker and listen for buzzes and rattles. These could be signs that the cone is interfering with the grille or that the surround has failed. The speaker could also have come loose from its mounting. If you hear anything abnormal, have the installer check it out.

Please never do this without proper hearing protection. You only get one set of ears, and if you damage them, you’ll regret it for the rest of your life.

Car Audio System Maintenance Improves Longevity

Thoroughly inspecting your car’s audio system should take about 10 to 15 minutes. If anything seems even the slightest bit abnormal, return to the shop that installed it and have it inspected. Fixing a loose connection now could prevent you from having to replace an amplifier later.

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.

One of the most common questions we receive is whether you can use car audio products, like radios and amplifiers, in the home or shop. The answer is a resounding yes! However, the real challenge lies in finding a suitable power supply, especially for high-power amplifiers. We’ve recently dedicated a significant amount of time to researching power supplies for an upgrade to our lab. Understanding what a power supply is and how it works is crucial.

What Does a Power Supply Do?

What does a power supply do? Typically, it takes a voltage like the 120-volt AC we have in our homes, shops, and offices and converts it to something we can use to power an electronic device. A laptop computer might have an 18- or 20-volt DC power supply. A desktop computer power supply provides +12V, -12V and +5V. Some even supply 3.3 volts and -5 volts DC. The little wall adapter that used to come with an iPhone provided 5 volts – the standard for USB charging.

It should be clarified that there are many types of power supplies. For example, an X-ray machine might need 200,000 volts, mass spectrometry systems may need 30,000 volts, and the microwave oven in your kitchen around 2,100 volts, but some are as high as 2,800 volts. Not all power supplies step the supply voltage down, and not all produce DC voltages.

If you thought we were talking about the power supplies that are part of an amplifier, sorry to mislead you. They also do a voltage conversion. They take the 12 to 14 volts available from the vehicle’s electrical system and convert it to the rail voltages in an amp. This might be +20 and -20 volts for an 800-watt subwoofer amplifier.

How Are Power Supplies Rated?

Power supplies are rated based on the total current they provide, or more specifically, wattage. For example, a multi-outlet USB-C charger for a modern smartphone might deliver 40 or 60 watts of power. A USB port might be rated for 3.1 amps of current, which works out to 15.5 watts. Some USB-C devices can charge at 20 volts and 5 amps of current, which is 100 watts.

If you’ve shopped for a new power supply for a computer, you’ll see supplies are available in power delivery ratings from 500 watts up to about 1,650 watts. The latter is the upper limit of how much power a device can draw from a 120-volt wall outlet. The math there is 120 volts times 15 amps equals 1,800 watts. Drop in 90% for efficiency, and you have 1,620 watts. Suppose you have a liquid cooling system, several case fans, RGB lighting, a CPU that needs lots of power, a beefy video card and several external drives. In that case, you need a power supply large enough to ensure that it all runs reliably.

Refocusing on car audio equipment, it’s not uncommon for us to install a subwoofer amplifier rated for 1,000 watts of power. Assuming it’s of reasonably good quality, that amp might draw 1,175 watts of power from the vehicle charging system. At 13.6 volts, that would be 86.5 amps of current. As an aside, if the amp isn’t efficient, it might draw as much as 120 amps to produce the same output. Amplifier efficiency is crucially important.

Let’s say you want to run this 1,000-watt amp in your living room to power a pair of car audio subwoofers in a ported enclosure. It would be best if you had a 100-amp power supply. We’ve been researching these extensively for the last few months as part of an upgrade to our lab. If you want a true 100-amp, 12-volt (1,200-watt) power supply, you’ll likely need to connect it to a 20-amp circuit. Be very wary if the supply claims it can produce 100 amps from a 15-amp circuit.

Linear Versus Switching Power Supplies

Decades ago, the standard for car audio power supplies for display boards was the Orion PS 100A. This thing weighed what felt like 90 pounds and could pop a 15-amp circuit breaker at will. However, it provided clean and reliable power to ensure that the subwoofer amplifiers on display boards sounded awesome. Specifically, this was a 100-amp supply with current limiting and output voltage adjustments.

The massive weight of the supply was attributable to the giant transformer inside it. This was a linear power supply, so the transformer needed to be massive to deal with the vast amounts of current that would flow through it.

These days, you can get a 1,400-watt (100 amps at 14 volts) power supply that fits inside a computer case. You could fit two of them in a typical backpack. These are also available as 1U-sized rack-mount units, just like a processor in the effects rack for a band. So, why are power supplies smaller now? Most of them are called switch-mode supplies. They work differently than their linear cousins. As expected, they have their benefits and drawbacks.

Linear Power Supply Operation

Let’s discuss how a linear power supply works without getting into university-level electronic design. We’ll be talking about supplies that take the 120-volt AC power from the wall and convert it to something like 13.6-volt DC to power car audio equipment.

Power supply operation is quite simple. The process starts by taking the 120-volt AC and passing it through a transformer to reduce the voltage. The transformer’s input and output will be a 60-hertz sinusoidal waveform.

After the transformer lowers the voltage, we feed the AC waveform to a rectifier. This circuit, typically comprised of four diodes, inverts the negative half of the waveform, producing a positive voltage with lots of ripples – it sort of looks like waves in an ocean.

From there, the noisy DC signal passes through the filter stage, which typically consists of a few large electrolytic capacitors. As we should know from talking about passive crossovers, capacitors oppose changes in voltage. As such, they smooth out the ripples to produce a fairly clean DC voltage.

Finally, we get to the regulation stage. In a linear power supply, this stage is usually handled by a single large or multiple medium-sized transistors. This circuit works as a variable resistor, ensuring that the output voltage stays at a set level. The transistor adds resistance to the circuit based on a feedback loop to ensure that we get our desired 13.6 volts.

Benefits and Drawbacks of Linear Power Supplies

You might choose a linear power supply for high-current applications for two reasons. First, they’re usually relatively quiet regarding electrical noise on the output signal. We call this noise ripple, as once again, it’s like small waves in a lake. Second, linear power supplies offer excellent transient response. They can keep up with sudden power demands quite well, making them ideal for high-current audio applications.

Unfortunately, with the good comes some drawbacks. Linear power supplies are large, expensive and inefficient. They waste significant energy as heat because of the regulation transistors operating as variable resistors to maintain the chosen output voltage. Second, the power supplies require huge, heavy and expensive transformers. This is primarily because of their inefficiency. If they waste 70 to 80% of the power they consume as heat, the transformer must supply large amounts of energy to have enough left over for the load (amplifier).

Switch-Mode Power Supplies

The other type of power supply available is a switch-mode power supply, or SMPS for short. These are, by far, the most popular type of power supply you’ll encounter. Their operation philosophy is similar to that of a linear supply, but rather than wasting energy with a resistive regulation stage, they use pulse-width modulation to control the power going into the transformer.

An SMPS starts with a bridge rectifier that inverts the negative side of the input sine wave. Violet is the 120 VAC input, and green is the rectified output.

Electrolytic filter capacitors smooth the signal before it’s passed to a transistor or MOSFET driven by a pulse-width-modulated control.

The next step is to chop up the signal into tiny pieces again so we can pass it through a transformer to reduce the voltage. Why not just do this at the beginning? Well, the pulse-width modulating controller is fed by a signal from the circuit output. It decides how much duty cycle is needed to deliver an appropriate voltage and current. So, rather than all of the input voltage going to the transformer, we can feed minute amounts of power if there is no load or moderate amounts if there is a heavy load. Because the PWM control will determine the circuit’s power, we aren’t wasting energy through a resistive regulator like the linear supply. As such, the transformer can be much smaller and operate more efficiently.

Benefits and Drawbacks of Switch Mode Power Supplies

As we mentioned above, the most significant benefit of a switch-mode power supply is that only the power required by the load passes through the transformer in the middle of the circuit. This means the supply operates much more efficiently, so the parts and case can be much smaller. Switch-mode supplies can easily be 90% efficient, wasting only 10% of the input energy as heat.

As happens with electronic circuits, there are drawbacks as well as benefits. Switch-mode supplies have more noise or ripple on the output. Looking closely at the final waveform above, you can see some bumps in the output. These aren’t there by accident. It’s not uncommon to have half a volt of noise on the output of a high-power switch-mode supply. Most good quality car audio amplifiers have an inductor and capacitors on the input power connections to filter this noise. However, not all do.

The second drawback is that there are many components (or blocks) between the output and the feedback signal to the PWM controller before the transformer. If an amplifier suddenly demands a large amount of power, the output voltage can droop, dip or sag before the supply can bump up the pulse width and compensate. You can consider this a slow response time. Switch-mode supplies aren’t the best choice if you want the best impact at maximum volume from an amplifier.

Picking a Power Supply for Car Audio in the Home

The explanation of power supply operation was more detailed than planned. Nevertheless, now you have the information. In terms of picking a supply to use a radio in your home or garage, you need something that can provide about 180 watts of power, or 15 amps at 12 volts. We’d suggest finding a 14- or 15-volt supply. Most car radios are acceptable up to about 16 volts, so the extra voltage means the radio will draw less current.

If you want to power a large subwoofer amplifier, you’ll need to figure out how much current the amplifier draws at maximum power at the load you plan on using. You can often use the fuse ratings on the amp as a guideline. For example, if the amplifier has 80 amps worth of fusing, you’ll need a supply that can deliver about 14 volts and 80 amps of current, a little over 1,100 watts. A solution like the Stinger SPS70 would be a just-adequate solution. We’ve used a pair of SPS80 supplies on the BestCarAudio.com test bench for several years with good success.

Now, why are there much more expensive power supplies available? For example, the go-to for car audio displays has been the Samlex SEC-100BRM. This supply offers 100 amps of current but might cost twice as much as the Stinger. Why? Well, it provides better voltage regulation under dynamic loads. Further, there is less noise in the output signal. The BestCarAudio.com lab has a Samlex supply for making noise and distortion measurements on high-end amplifiers.

Some Bad Ideas to Avoid

We’ve encountered several conversations online where the original poster planned on using a car battery in their home to provide supplemental current to the amplifier. In spite of our warnings about hydrogen gases being released during charging, they planned to proceed with this bad idea. Please don’t put a car battery in a living space. If you want to supplement the instantaneous power delivery to an amplifier, add a high-quality stiffening capacitor. Suitable stiffening capacitors are hard to find, but they are out there.

Finally, be very careful with the wiring. Car audio amplifiers can consume massive amounts of current. A loose connection can heat up and cause damage quickly. Honestly, you’re much better off buying used DJ or PA gear. You can pick up a used QSC or Crown amp from the Facebook Marketplace for less than you’d pay for an entry-level power supply. This solution is also dramatically more efficient and safer. I know, bummer, eh?

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.

Even though most car audio speakers are chosen without regard for genuine performance, our goal of educating consumers remains steadfast: If you’re searching for a high-quality car audio system, understanding how speakers work and what differentiates the great from the mediocre is essential. In this article, we’ll explore the topic of speaker inductance, what affects it and why it matters to what you hear.

What Are Inductors?

As an introduction, you should review our full article on how inductors are used in car audio systems. This will give you a good overview of how they work.

In short, an inductor is a coil of wire that opposes the flow of alternating current. Direct current can pass through an inductor nearly unhindered. However, the magnetic field created in the inductor resists the change in polarity associated with AC signals. As such, inductors act like a frequency-dependent resistor to AC. We can use this characteristic as a benefit to limit the high-frequency information sent to a speaker or reduce noise in an electronic component.

In this article, we’re going to talk about speaker inductance. Unfortunately, the voice coil in the center of a speaker is also an inductor. It’s a tightly wound coil of wire wrapped around a magnetically conductive core. Aside from a small air gap, it’s no different than the inductors we use in passive crossovers.

What Does Inductance Do?

As mentioned in the article linked above, inductor reactance, or opposition to the flow of AC signals increases as frequency increases. This results in less current flow. As such, if we have a speaker with a very inductive voice coil, less current will flow through the speaker at higher frequencies. This means the speaker produces less sound at high frequencies as the magnetic field that’s formed is weaker. Again, this is identical to wiring an inductor in series with a speaker to create a crossover.

Subwoofers have the largest voice coils and, as such, typically have relatively high inductance values. As the number of layers in a voice coil increases, so does the inductance. For example, a 1.5-inch voice coil with four layers might measure 3.7 millihenries.

If a speaker designer wants to increase power handling, then a voice coil with more layers of wire will do the trick. The drawback is that the winding will have more inductance and, consequently, less upper bass and midbass output. The inductance also starts to cause a phase shift if the output of the signal as it behaves as a first-order low-pass filter. At the point where the inductance reduces output by 3 dB, the signal will be shifted by 90 degrees. This phase shift complicates getting the midbass to blend with the woofers.

The same thing happens with midrange speakers. If the design engineer wants more power handling, the driver needs a larger voice coil winding. The differences in inductance can be quite staggering and have a clearly audible effect on upper midrange output and how the driver blends with the tweeter.

Woofer Voice Coil Inductance

Let’s do some math in a spreadsheet to simulate what different voice coil inductances do to affect subwoofer output. We’ll start with a low-tech, high-power handling driver, as you’d find from popular internet-only brands. We quickly found a 4-ohm subwoofer rated for a few thousand watts of power handling with a voice coil impedance of 5.5 millihenries.

When manufactured by a reputable brand, a typical consumer-grade subwoofer rated for around 500 to 700 watts of power has around 3.7 millihenries of inductance. Now, if a company is serious about sound quality, it will add inductance-reducing features like a copper or aluminum shorting ring and a copper T-yoke cap. Drivers like this might only have 0.33 millihenry of inductance.

The chart below shows how the voice coil inductance attenuates the output of the three woofers. This graph doesn’t consider the cone’s mass, which, if significant, will also attenuate midbass and midrange output.

If we refer back to the discussion about a -3 dB point, we can see that the high-inductance woofer is -3 dB at a really low frequency of 47.8 hertz. The typical speaker with an inductance of 3.8 millihenries plays out to 71 hertz. Finally, the speaker with the inductance management features is flat-out amazing at 795 hertz.

Translating Measurements in Sound

So what do high-inductance subwoofers sound like compared with the low-inductance designs? It should come as no surprise that they don’t sound as tight. The reduction in midbass output attenuates upper bass frequencies. As mentioned, this complicates getting the subwoofer to blend with the woofers in the doors. For example, kick drums or large floor toms lack attack or impact. The low-frequency thud of a kick drum might be clear, but the higher-frequency information of the hammer hitting the skin will be lessened. Yes, we can equalize the system to play these frequencies at higher output levels, but the clarity of a high-inductance subwoofer simply outperforms low-inductance designs.

Inductance in Midbass Drivers and Woofers

The same inductance criteria that affect subwoofers can also reduce the upper midrange clarity of woofers and midrange drivers. Most audio system target response curves call for a flat response out to 3 or 4 kilohertz. We can see from the graph below that high-power-handling speakers without inductance management features like shorting rings start to roll off well below where they would cross over to a tweeter.

The green trace is a 6.5-inch woofer with an inductance of 0.43 millihenry. This a robust driver with a 50-mm voice coil and a continuous power handling rating of 150 watts. The second trace in blue represents a 6.5-inch woofer with a measured inductance of 0.24 millihenry. Finally, we have a third 6.5-inch woofer with an inductance of 0.13 millihenry. This driver has a copper pole piece cap and an aluminum shorting ring under the top plate. Based on their inductance, these drivers have -3 dB frequencies of 620, 1,100 and 2,100 hertz.

Start Your Speaker Shopping with Research

If you’re shopping for truly magnificent-sounding speakers, start the process with some research. Create a table of speaker options in the sizes you want, then look up their voice coil inductance. Of course, this is not the only feature to consider. A low Total Q (Qts) can also tell you a lot about how a speaker will sound. So can frequency response charts. Once you have a short list of car audio speakers, do some listening evaluations at local specialty mobile enhancement retailers. This head-start will help you choose a speaker system that sounds genuinely amazing.

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.