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.

If you’ve looked at an amplifier installation kit, you’ll see it comes with about 17 feet of power wire, a shorter length of ground wire and a fuse holder. The intent of this fuse holder is for it to be installed as close as possible to the positive battery terminal. As for the fuse size, should it be the same as the fuse in your amplifier? Likely not. Read on to learn why.

Overcurrent Protection Devices

When it comes to overcurrent protection devices in car audio systems, there are two main contenders: circuit breakers and fuses. Our extensive testing has revealed that circuit breakers, while effective, tend to waste a bit more voltage than their fuse counterparts. Moreover, there’s a risk of circuit breakers not opening when an overcurrent condition occurs. That’s why we strongly advocate using ANL and Mini-ANL fuses to safeguard our vehicles.

A fuse is a simple device in that it’s a piece of metal with a specific area through which all the current going to the load passes. We know that all conductors, be they copper, aluminum or an alloy, have a specific resistance for a given area. As such, fuses are sized so that their resistance will cause the fuse to melt when the current flowing through the device exceeds a certain threshold. Once melted, the current no longer flows to the load.

Why Do We Need a Fuse at the Battery?

When a local mobile enhancement retailer upgrades our vehicle with an amplifier, they run a large-gauge power wire to the battery’s positive terminal and ground the amp’s negative terminal to the chassis. In some cases, especially in vehicles built with aluminum or adhesives, the negative terminal must also go to the battery. The purpose of the fuse is to protect the battery from an overcurrent condition.

What could cause an overcurrent condition in the amplifier power wire? Well, if the wire comes loose from the amp and drops onto the vehicle’s body or touches the negative terminal, a lot of current will flow. Without a fuse, the wire will likely heat up quickly, the jacket will melt, and there could be a fire. Likewise, if the power wire is run across a sharp edge like a hole drilled in a piece of metal, that could cut into the wire and potentially short the wire to the ground. If you’re in an accident where the side of the vehicle is crushed, the power wire might be pinched by the folded metal and be shorted to the ground. Any of these conditions will result in a mess if no overcurrent protection device is installed at the battery.

Why Are There Fuses in Car Audio Amplifiers?

Contrary to popular belief, a fuse in a car audio amplifier isn’t to protect the amplifier. Fuses are there to protect the vehicle battery in the event the positive and negative power connections to the amplifier are reversed. Because of how the switching devices in a power supply work, there will be a short circuit if the power connections are reversed. With no protection device, the switching devices will explode violently. The fuse or fuses are not going to prevent damage to the amp if a single switching device fails during regular operation.

So, how are the fuses on an amplifier chosen regarding their current capacity? They need to be large enough to ensure that the amplifier can produce its full rated power without them blowing. We’ve tested a few amplifiers that will pop the included fuses when all channels on the amp are driven at full power into their minimum impedance with test tones. This scenario is different from playing music, so it’s not an issue.

What Size Fuse at the Battery?

To recap, the fuses on the amp protect it from catastrophic failure in the event of a wiring accident. What size should the fuse be at the battery, and what’s its purpose? The fuse at the battery protects the power wire. As such, it should be sized to prevent the wire from carrying more current than it can handle without overheating.

We know there are many official wire sizes, and that wire should be made of copper. However, we also know that there are many mystery wire diameters and that many inexpensive amplifier installation kits use copper-clad aluminum wire. Unfortunately, we don’t know how much aluminum is in these kits, so an educated assessment of the wire resistance is impossible.

The ANSI/CTA-2015 standard for car audio power wiring suggests we should have no more than 0.25 volt of drop across the wire. This will, of course, be for steady-state current requirements. Nevertheless, we’ll use it as a reference for our calculations. In terms of power wire length, we will provide data for 10- and 16-foot runs. Ten feet is likely adequate to connect an amplifier mounted under a seat to the battery under the hood. Sixteen feet is usually enough to mount an amp in the trunk. The table below shows the maximum current the wire can pass for the given lengths, resulting in a roughly 0.25- to 0.26-volt drop.

As you can see, the maximum current decreases with length. This is because the resistance increases, which results in more voltage drop.

While the above chart is logical, it is perhaps too optimistic about the reality of modern car audio system design. We know of many systems where a run of 4 AWG wire is subjected to well over 100 amps of current. Sure, the amp won’t see the full battery or alternator voltage, but the cable doesn’t melt and catch fire. So, here’s our recommended maximum fuse size chart.

Why Not Use a Smaller Battery Fuse?

Could you use a smaller battery fuse than we’ve recommended? Absolutely. However, there’s an interesting reason why you might not want to. As mentioned, fuses have a specific resistance that causes them to blow when a specific amount of current passes through them. Fuses rated for larger amounts of current have less resistance. As such, less voltage drops across the fuse, and more is available to feed the amplifier. More voltage will result in the amplifier being able to produce more power before it starts clipping.

Fuse Location

Decades ago, the International AutoSound Challenge Association established a rule that said the fuse in a car audio system should be within 14 inches of the battery. Sadly, many people took this to mean that the fuse should be 14 inches from the battery. In reality, the fuse should be as close as possible to the positive terminal to provide maximum protection. Having a fuse 10 to 12 inches away might not provide adequate protection in a front-end collision.

We like the idea of fuse holders that are integrated directly into battery terminals. This design provides the most protection possible should something go wrong.

Ensure that Your Car Audio System Is Protected

While most professional car audio installers know how to adequately protect your vehicle from damage because of a short-circuited power wire, some might need guidance. Before you let anyone work on your vehicle, discuss what type of overcurrent protection device will be used and where it will be installed. A proper battery fuse is crucial to preventing additional damage should something go wrong.

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’re looking for the best performance from your car audio system, the limitations of Bluetooth sound quality might be holding you back. Even if you’re streaming lossless or high-res files from Tidal or audio files stored directly on your phone, wireless connections to a car audio source unit are often optimized for bandwidth, not audio quality. Let’s make some simple measurements to demonstrate what happens when you’re using Bluetooth or Apple CarPlay to connect to your radio.

Some Background on Bluetooth Audio Streaming

As we’ve explained previously, Bluetooth is not an audio streaming solution. Specifically, it was designed as a low-power, short-range wireless communication solution that would replace serial cables. Imagine walking up to a printer to get a hard copy of a document rather than having to connect a serial, parallel or USB cable. Though initially developed in the mid-’90s, Bluetooth communication didn’t become popular until around 2004. Now, Bluetooth is everywhere. We use it to connect the controllers to our gaming systems. We use it to connect a mouse or keyboard to a computer. Of course, streaming music from a smartphone or media player to a car radio is also common.

Bluetooth uses different sets of instructions, called profiles, to perform different tasks. For instance, when your smartphone connects to your car radio, it might use the Phone Book Access Profile (PBAP) to download your contacts into the radio. The Hands-Free Profile (HFP) allows the microphone in your radio to send audio out to the person calling you and let their voice play through the car speakers.

Pertinent to this discussion, the Advanced Audio Distribution Profile (A2DP) is used to stream music to the radio. The devices also use the Audio/Video Remote Control Profile (AVRCP) to allow the radio to change tracks and display song and artist information. A lot happens when you connect your phone to your radio wirelessly.

Within A2DP, there are several different CODECs. A CODEC is software that compresses and decompresses data for transmission across bandwidth-limited connections. You can think of a CODEC as a real-time file compression or ZIP process like we use to send large programs over the internet. The data is analyzed and compressed, then transmitted. The receiver decodes the data and attempts to restore the original information. This is where we lose some quality and accuracy. CODECs, like audio formats like MP3, are inherently lossy. This means you don’t get an exact replica of the original file out of the system. It’s pretty good, but it’s not perfect.

For this article, we’ll use an Apple iPhone and the Sony Mobile ES XAV-9000ES multimedia receiver we recently tested to evaluate audio streaming performance. Apple smartphones are limited in their streaming capabilities as they only support the SBC and AAC CODECS. The Low Complexity Subband Coding (SBC) CODEC is basically the industry standard. Almost all streaming-capable Bluetooth devices will have SBC built in. The Advanced Audio Coding (AAC) CODEC offers better performance than SBC. It’s worth noting that Apple has not adopted Qualcomm’s aptX or Sony’s LDAC, both offering even better performance. If you have to stream audio, an Android-based smartphone is a better-sounding choice. Nevertheless, we’ve got what we’ve got, so let’s see how it performs.

Bluetooth Audio Testing Criteria

When it comes to audio playback, the most crucial criterion is frequency response. Changes to any part of the amplitude of our music can easily be perceived as detrimental. As such, we created a four-minute white noise track. We’ll play this from the phone and then analyze the radio output to see how the stream affects the quality.

Next, we want to quantify accuracy. The most straightforward test is to play a single-frequency test tone and analyze the radio’s output to see whether it added any unwanted harmonic content. We’ll use a 1-kHz test tone for this evaluation.

Lastly, we’d like to measure intermodulation distortion using the CCIF standard. I’ll fully admit that I wasn’t sure whether this test would be possible, as I didn’t know whether the radio would reproduce audio information up to 20 kHz. As such, I created a similar test with tones set to 10 and 11 kHz. Any sidebands and products will be very visible.

Loading the tracks onto the iPhone made me want to bathe with a porcupine family. As much as I enjoy some parts of the Apple ecosystem, using iTunes to load music onto the phone when Android devices are as simple as copying and pasting is infuriating. Ultimately, I used a player called Onkyo HF Player. It was easier than iTunes and supports high-res files. We kept all our test files to 44.1 kHz sampling rates with 16-bit depth.

Bluetooth Audio Quality Measurements

I started by playing the test files directly from the USB memory stick. The Sony is an excellent source unit, and the results are very good for a radio of this caliber.

In terms of frequency response, the 44.1-kHz test track was rendered with smooth response past 20 kHz, just as we would expect for a radio that supports high-resolution audio.

Next, I played the 1-kHz test track. Just as when I reviewed this radio, the performance was excellent, exceeding the limits of the test track itself. Our calculated total harmonic distortion based on the second through fifth harmonics is an impressive 0.0014%, or -97.3 dB.

Finally, we have our custom intermodulation distortion track. It’s tricky to turn this information into a single value, as there are two pieces of information we want to extract. First, we want to look at the amplitude of the f2-f1 frequency. In our USB-based measurement, we can see that 1 kHz is at a level of -93.65 relative to the two test tones at 6.47 dBV. This alone works out to an IMD of 0.0021%, which is very good.

Next, we want to look at the amplitude of the sidebands adjacent to the 10- and 11-kHz tones. The 9- and 12-kHz tones are somewhat high at -66 dB below the reference signal. The third-order sidebands are at -72 dB, and the fourth is at -85.5 dB. If we add these amplitudes and compare them to the reference, we get an IMD of 00776% or -62.2 dB. This isn’t terrible.

Bluetooth Streaming Audio Test

Now, let’s repeat the test by playing the same tracks on the iPhone using the Bluetooth connection to the radio. First, we’ll check the frequency response with the white noise track.

Though subtle, the wireless connection now excludes audio information above roughly 19 kHz. This is still pretty good, and most importantly, the information below remains ruler-flat.

Next, we have the harmonic distortion evaluation with our 1-kHz test tone.

Here, it’s clear that a lot of unneeded information has been added to the playback. It’s not a disaster, as the overall amplitude is fairly low. The harmonic content is -75 dB below the fundamental frequency, equal to 0.017% THD. In short, this transforms the high-end Sony radio performance into a regular consumer-grade product. Based on our listening tests using Bluetooth connections, this jibes with what we’ve experienced.

Finally, let’s look at the intermodulation distortion performance.

Once again, we can see that a lot of garbage has been added on either side of the test signals. The f2-f1 is at basically the same amplitude as from the USB playback test. The second- and third-order sideband peaks are also at similar levels, but the noise around -70 to -80 dBV becomes an issue.

You can see there’s a mirror image of the side-band distortion added to the output centered around 30 and 50 kHz. If, indeed, there is any validity to claims about the importance of audio content above 20 kHz, this unwanted information would be detrimental. In short, the intermodulation distortion is a bit worse in terms of the effects on audibility.

Conclusions on Bluetooth Audio Quality

Based on these tests, there’s a subtle but audible difference in sound quality when streaming music over a Bluetooth connection compared with playing the same tracks directly from a USB stick. If you’ve invested in a high-quality source unit or digital signal processor but are transmitting audio wirelessly, you are doing yourself a disservice. The difference isn’t as significant as moving from consumer-grade to audiophile speakers, but where every step in the audio chain matters, Bluetooth remains a weak link.

We’ll start looking for a phone that supports the LDAC codec so we can repeat this comparison.

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.