Since the 1980s, car audio enthusiasts have been using large-value capacitors to improve the performance of their car audio systems. Aside from people believing that distortion damages speakers, few topics are as misunderstood as the benefit of adding a high-quality capacitor to your car stereo. So, let’s take a look at what a capacitor is, how it works and how it can be of benefit to a high-power car audio system.

What Is a Capacitor?

A capacitor is similar to a battery in that it stores energy between plates. Unlike a battery, the charge is stored directly as a difference in voltage (called an electrostatic field) and doesn’t require a chemical reaction to release energy. As such, capacitors can release large amounts of energy very quickly, whereas a battery releases energy at a slower rate. Another way to look at the difference between the two is that a battery is intended to be a source of energy, whereas a capacitor is used to store energy for a short period of time. Access to large amounts of energy storage is crucial to the performance of your car’s audio system.

In a capacitor, two or more plates are separated by a dielectric known as an insulator. This insulator prevents the metal plates from touching each other and draining the stored energy. When a voltage is applied to a capacitor, current will flow into the device until the potential of the electric plates matches the source voltage. If you connect a capacitor to a car battery, it will charge (very quickly) to the same voltage as the battery. If you disconnect the cap from the power source and connect it to a load, it will drain equally quickly.

The Capacitor Analogy

If you are into high-performance vehicles, then you may have heard of a small fuel storage canister called a swirl pot or surge tank. These tall, skinny tanks are added after the feed from the main fuel tank to act as a reserve for those instances when a vehicle is accelerating, braking or cornering such that the fuel in the main tank may slosh away from the pickup. Rather than starving and potentially damaging the engine, the fuel injectors or carburetor are fed from the fuel stored in this small reserve tank. The engine doesn’t know or care where the fuel is coming from so long as it has what it needs to keep running.

A capacitor in an electrical system works the same way. If a capacitor is installed across a load like an LED, it will provide current to the load when the supply voltage is removed until its stored energy has been depleted.

In most direct current electrical applications, capacitors are used as filtering devices to reduce the voltage peaks and dips in an electrical circuit. If you know how a DC power supply works, capacitors are a crucial component in converting energy pulses in a relatively smooth waveform.

Capacitors in Car Audio Applications

If you’ve ever looked inside a car audio amplifier, you’ll see two banks of capacitors. There is a small group of capacitors on the power input to the amplifier and a second set on the output of the switching power supply, also referred to as being on the “rails.” These capacitors are there for two reasons. They smooth the voltage ripples that are caused by the power supply switching devices turning on and off quickly. Secondly, they store energy. Power supplies, especially the switching style used in audio amplifiers, take a moment to react to sudden demands for current. During that time, without having capacitors present in the circuit, the rail voltage level would drop. The presence of the capacitors helps supply energy to the output stage for these sudden and dynamic bursts of energy.

If we look at how most amplifiers work at lower load impedances, it is the maximum current delivery capacity of the power supply that limits power. At 4 ohms, when pushed to their limit, amplifier output power is usually limited by the rail voltage. When we need twice as much current to drive a 2-ohm load, the power supply typically can’t deliver and the rail voltage drops. This is why many modern amplifiers don’t double their maximum power when the load impedance is halved. Capacitors don’t help in constant current draw conditions.

Benefits of Stiffening Capacitors

Think about everything we’ve stated. If you’re building a car audio system designed to play music at high volume levels, the current drawn by the amplifiers will vary dramatically. Capacitors are a perfect way to help fill in voltage drops that might occur when a battery or alternator can’t deliver enough current or when wiring and connections waste energy. For dynamic loads, capacitors can provide an audible improvement to your audio system.

The benefit of adding a capacitor is going to depend on the amount of power your electrical system can supply, how loudly you listen to the audio system and the efficiency of your amplifiers. If you listen at moderate volume levels, the system might only draw 20 or 30 amps of current. The stock electrical system in most vehicles can keep up without much fuss. If you listen really loud, you might draw 50 to 100 amps of current during the most dynamic parts of a song. In these applications, a capacitor will help maintain the voltage available to your amplifiers. The difference in performance between having a capacitor in a system or not is typically most audible in loosely or unregulated amplifiers powering midrange and high-frequency drivers. We can hear the clipping distortion from these amplifiers much easier than from a subwoofer system.

If your car audio system is designed to play test tones, as you’d find at SPL (Sound Pressure Level) competitions, capacitors are of little value. They might reduce some regulation issues from a high-current alternator and help with the initial demand for energy when you burp the system. After 100 milliseconds or so, they do nothing of significance to make an audio system louder over long periods of time.

If you’re looking for the best possible performance from a high-power car audio system, drop by a local mobile enhancement retailer and ask them about adding a high-quality stiffening cap to your sound 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.

Two factors limit how loudly a car stereo system can play: how much power you have to drive the speakers in the system, and the maximum output capabilities of those speakers. We see a lot of amateur and poorly executed audio system installations that play good and loud when the volume on the radio is barely over a quarter of its maximum output capability. What does this mean in terms of system configuration? It indicates that the sensitivity controls on your amplifiers or integration processors haven’t been configured properly. Why does it matter? Let’s have a look!

Audio System Gain Structure

Gain control on a car audio amplifier exists for two reasons. First, it allows that amplifier to produce its maximum rated power with various input voltages. Suppose you had an old or inexpensive source unit that could only produce 1.5 volts of signal on the preamp outputs. In that case, a setting somewhere in the middle of the amplifier’s sensitivity range might be appropriate. If you have a modern high-performance source unit that can produce 5 volts of output, you can likely drive the amp to full power with the gain control turned most of the way down.

The second purpose of the gain (or sensitivity) control is to balance the output of speakers in the system. If you have one amp for your subwoofers and a second amp for the front and rear speakers, the sensitivity controls can ensure that the system’s balance of bass to midrange and high-frequency information is correct. This process can be tricky as it usually leaves some subwoofer amplifier power on the table or, if executed incorrectly, might cause the amp driving the midrange and high-frequency drivers to clip.

What Happens with Too Little or Too Much Gain?

To keep the conversation simple, let’s consider a simple two-channel amplifier running a pair of full-range speakers. What happens if the gain on this amp is set too low? For context, the amp might be set to require 5 volts of input when the source unit can only produce 2 volts; the amp won’t make all the power it’s capable of producing. Assuming the source unit doesn’t distort at full volume, that amp could be turned up a little bit so that it just reaches the point at which it clips the output signal when the recording level goes 0 dB FS.

At the other end of the spectrum, we have a condition where the amplifier gain is too high. It might be set to 0.5 volt when the source unit can produce 4 volts of output. What happens in this scenario? If the listener is paying attention, they should only be able to turn the radio up about three-quarters of the way to get the maximum power possible out of the amplifier. In most situations, listeners tend to continue cranking the volume well past when the amp clips, sending significant extra power to the speaker in the form of harmonics. Not only does this sound terrible, but it can damage small drivers.

There is a scenario where an amplifier should be set to have a little more gain that would be mathematically ideal. In a perfect world, assuming all music was recorded such that it reached the maximum allowable level on the recording media (which should be 0 dB FS), an amp should be set to clip with a test tone at this level. Unfortunately, and especially with older recordings, sometimes the recording level isn’t all the way up. If the recording only reaches -5 dB FS, then we need more gain on the amp to play this music back at the loudest level possible from our amplifier. This scenario requires what’s known as gain overlap. We set the amp gain a little higher than would be deemed perfect so that quiet recordings can still be played loudly.

The Problem with Too Much Amplifier Gain

If you know what to listen for in terms of distortion from an amplifier, then having some gain overlap is OK. If you hear the amplifier clipping, you can (and should) turn the radio volume down until it stops. What happens in a case of having WAY too much gain? Amplifiers don’t know the difference between background noise and an audio signal. If the volume on your radio is adjustable between 0 and 40, but the system is screaming loud at 20, then the gains are likely too high. In this scenario, the background noise produced by your radio and the noise in the input stage of your amplifier will likely be audible all the time. This noise will sound like hiss or static – similar to what you hear when tuned to a radio frequency where no signal exists.

If you can hear a hiss from your audio system and you can’t turn the radio volume up to 37 or 38 (out of 40) and still have everything clear, then you need to go back to your installer and have the gain structure set properly. This hissing noise is also often called floor noise, background noise or fuzz. Any noise or distortion detracts from the listening experience, just as static or improper color or contrast adjustments on a video display would detract from watching a movie.

The secondary problem with having too much gain is that you have dramatically reduced the number of volume levels you have available. If you always listen loudly, perhaps this doesn’t matter, but it’s still a consideration. If your system makes as much power as possible with the volume halfway up, you might only have 20 volume levels instead of 38 or 39.

How To Know Your Car Audio System’s Gains Are Set Correctly

If you’ve chosen high-quality amplifiers and a good source unit, you shouldn’t hear much, if any, hiss from the sound system between tracks. If your audio system includes internet-brand bass-head amplifiers, high-efficiency PA speakers and things aren’t set up properly, you’ll likely be able to hear background noise at even moderate listening levels. Your installer can maximize the signal-to-noise-ratio capabilities of your system by setting things properly, but no configuration settings will overcome the poor performance of low-quality products.

When it’s time to upgrade your car audio system to something that sounds amazing, works properly and doesn’t add noise or distortion to your music, drop by a local specialty mobile enhancement retailer to find out what’s available. You might find that high-quality products cost a little more, but at least you’ll be investing in something that sounds good and can be part of your car audio system as it grows and improves.

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.

When it comes to car audio subwoofer upgrades, infinite baffle installations have been around for as long as subwoofers have existed. The science behind a subwoofer installation that doesn’t use a compact enclosure is quite simple. As with any subwoofer system design, some benefits and drawbacks need to be considered. Strap on your thinking caps; we’re diving in!

What Is an Infinite Baffle Subwoofer Installation?

Most of us are used to looking at acoustic suspension (sealed) and bass reflex (vented) enclosure options for the subwoofers in our cars and trucks. Enclosures with passive radiators are a version of a vented enclosure, so they fall under the same category. An infinite baffle subwoofer system uses the trunk of a sedan or coupe to prevent the sound coming off the back of the subwoofer from mixing with the sound from the front. To be clear, a trunk, in this reference, is not the same as a hatchback’s cargo area. Your installer must seal the area behind the rear seats and under the parcel shelf, then mount the subwoofer on this baffle. Separating the trunk from the vehicle’s interior is crucial as we don’t want any energy on one side of the baffle to mix with sound energy on the other.

Over the decades, many companies have offered subwoofers designed for these installations. The Kicker Freeair, JL Audio IB series and the OZ Audio H series are some classic infinite baffle subwoofers that we older car audio folks remember. Most companies that offer high-performance marine subwoofers still have models designed to be used without a compact enclosure. Many factory-installed subwoofers use infinite baffle installations as they add very little weight to the vehicle.

Classically, these subwoofers designed for infinite baffle applications had a stiffer-than-normal suspension that helped to control cone motion without the added compliance of an enclosure. As a result of that, the Qts value of these drivers was higher than a sub designed for a small enclosure. With that said, any subwoofer or speaker can be used in an infinite baffle application – with some performance limitations.

Benefits of Subwoofers without Enclosures

If your installer has to build an enclosure for the subwoofer you want to use in your car, that will add some weight. It’s not uncommon for a well-constructed enclosure with a pair of high-performance subwoofers to weigh well over 60 pounds, with many approaching 100 pounds. Added weight in your vehicle is the enemy of fuel economy, acceleration, handling and braking performance. An infinite baffle installation may require a single sheet of wood to seal the area behind a seat. It’s not without some additional mass, but it might be less than a typical enclosure.

Every subwoofer enclosure can be modeled as a high-pass filter using Thiele/Small parameters and software. The primary purpose of an enclosure is to prevent the front and rear waves from mixing and canceling each other. The second purpose of an enclosure is to add compliance to the cone assembly, so it isn’t damaged at high power levels. A subwoofer used in an infinite baffle installation has barely any compliance-based low-frequency filtering applied to it. As such, they can produce impressive amounts of infrasonic energy and are pretty efficient relative to an acoustic suspension design.

Finally, because there is no enclosure, there is no additional compliance that might cause the subwoofer to continue to resonate after the audio signal stops. This phenomenon is quantified by the Qtc value of a subwoofer system. As we’ve mentioned in other articles, a Qtc of 0.5 is considered ideally damped and will deliver the best transient response with good low-frequency efficiency. Enclosures with a Qtc of 0.707 are considered a Butterworth response and have a flat frequency response in the upper range with minimal low-frequency cut-off and acceptable transient performance. Above 0.707, power handling and efficiency increase while transients and low-frequency output performance are degraded. Most car audio enthusiasts who want a “sound quality” subwoofer system shoot for a Qtc around 0.7.

It’s straightforward to see that the high Qtc enclosures dramatically reduce low-frequency output. The green enclosure is predicted to produce 103.7 dB SPL at 30 hertz when driven with 500 watts of power. The yellow enclosure produces 109.1 dB SPL at the same frequency and power, while the red enclosure produces 111.0 dB SPL. The red enclosure would only need 93 watts to produce the same output as the tiny green enclosure. For reference, for the 10-inch driver we used in this simulation, the red enclosure has a net internal volume of 6.95 cubic feet, the yellow enclosure has a volume of 0.77 cubic foot, and the green enclosure is tiny at 0.25 cubic foot.

Effectively, the 9-cubic-foot enclosure isn’t an enclosure. It is large enough that it has almost no effect on the subwoofer’s frequency response. I added a 20-cubic-foot enclosure simulation to the graph, and the response is effectively the same through the audible range.

This would be a simulation of an infinite baffle application for this subwoofer. If you love those deep organ pedal notes and synthesizer beats, then this is a great option – maybe.

The Primary Issue with Infinite Baffle Enclosure

Do we ever get something for free when designing a subwoofer system? This infinite baffle application produces excellent low-frequency output, but at what cost? The answer is power handling. Recall that we put subwoofers in enclosures to help limit cone travel. You don’t want the voice coil former smashing into the back of the T-yoke or ripping the spider off the voice coil former, right? Designing a subwoofer enclosure that will sound great, offer excellent low-frequency extension and handle significant amounts of power is a tricky balance.

The above graph tells us that this driver, which has an Xmax specification of 17.6 millimeters, will reach its excursion limit at around 50 hertz when driven with 500 watts of power for the red and yellow enclosures. The subwoofer may be damaged if played with that much power at lower frequencies. The ultra-compact dimensions of the green simulation add enough compliance that the driver never bottoms out with 500 watts of power. Checking power handling at different drive levels and frequencies is crucial in designing a subwoofer enclosure.

Here’s the same graph with the input power reduced to 220 watts. We can see that the yellow and green enclosures are safe in terms of preventing the driver from bottoming out.

So, how much power can this 10-inch subwoofer handle in an infinite baffle application?

Depending on whether or not your amplifier or signal processor has an infrasonic filter, you are limited to between 55 and 60 watts of power and very low frequencies before the sub will bottom out. You can probably get away with 100 watts with most music without any problems. Driving the sub with 100 watts of power is still enough to produce 104 dB of output at 30 Hz, and this doesn’t take into account the transfer function/cabin gain of the vehicle, which should add at least another 10 dB. You aren’t going to set any SPL records, but it should be loud enough for most listening situations. You can always add another driver or three to increase the output capability of the system.

When considering driver excursion and sound quality, remember that distortion increases with cone excursion levels. If you want to listen to your music at high volume levels, use more drivers, so they don’t have to work as hard. Two 10s would be better than a single 10. Two 12s of equal caliber would be better than two 10s.

Infrasonic Filters Can Help

If you don’t need to reproduce the very lowest of frequencies, implementing an infrasonic filter in a digital signal processor is a great way to limit subwoofer cone excursion in an infinite baffle application. The advantage of adding a low-frequency high-pass filter in a DSP is that you can monitor the subwoofer’s response on an RTA and quickly adjust the crossover frequency and slope to deliver a smooth in-car response curve.

Is an Infinite Baffle Subwoofer System Right for Me?

If you consider yourself one of the stereotypical bassheads, then an infinite baffle car audio subwoofer installation is likely unsuitable. That said, four 15s or a pair of 18-inch drivers in this application can move a lot of air! Those same subs would be MUCH louder in a well-designed, well-constructed bass reflex enclosure. Suppose you like the bass in your car audio system to blend nicely with the midbass so bass guitars, piano and percussion sound realistic, and you have a vehicle with a dedicated trunk. In that case, an IB subwoofer solution might be perfect for you! Drop by a local specialty mobile enhancement retailer and talk to them about the subwoofer system options available for your vehicle.

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.

Who wouldn’t want to buy the loudest, most efficient speaker possible to upgrade their car audio system? A speaker that does a better job converting electrical energy into sound reduces the load on the vehicle’s electrical system, right? Well, efficiency is just a single parameter in the myriad values that describe how a speaker works. Let’s take a super-techy look at how speaker efficiency is calculated and explain how it relates to audio system design and performance when upgrading your car audio system.

All Speaker Parameters Matter

I read an article the other day in Stereophile magazine about a company called NWAA Labs. They built an anechoic chamber in a retired nuclear power plant. Aside from the stunning background noise level of -43 dB SPL at 1 kHz, the facility can provide accurate frequency response measurements from 25 Hz to 10 kHz. On the topic of speaker measurements and correlation specifications, Ron Sauro, owner of the NWAA Labs facility, said, “You have to spend some time learning how to look at the different measurements and determine how they all integrate with each other. You have to integrate them in your brain and understand that if you take this particular parameter and combine it with this other parameter, it’s going to give this type of result. That takes time and experience. You can’t just throw a graph out there and expect that somebody who has absolutely no experience integrating these measurements will understand what they’re seeing.”

Keep this in mind as we move through the article.

Calculating Speaker Efficiency

The relative low-frequency performance of a typical moving coil loudspeaker can be predicted using a set of electro-mechanical values known as the Thiele/Small parameters. Looking at a set of speaker Thiele/Small parameters, you will likely see efficiency values. The first will be n0 (lowercase n with a subscript 0). This calculated value provides a percentage efficiency (when multiplied by 100). The formula to calculate n0 is (9.7822 x (10^-10) x Vas x (Fs^3)) ÷ Qes. The Vas parameter is the equivalent compliance in liters, and Fs is the resonant frequency in hertz. Qes is the electrical Q of the speaker and is stated without units as it’s a ratio. In simple terms, this calculation tells us how much of the power sent to a speaker will be converted to sound and how much will be wasted as heat.

The first thing you should notice is that resonant frequency plays a significant role in the calculation as its value is cubed (multiplied by itself twice) in the numerator of the formula.

You might also be wondering why the driver’s area doesn’t appear to play a significant role in driver efficiency. It does. It’s just buried a little bit. The formula to calculate a speaker’s equivalent compliance (Vas) is 0.00014 x Sd^2 x Cms, where Sd is the effective radiating area of the driver in square centimeters and the Cms is the compliance of the driver suspension in millimeters per Newton. So, a larger driver or a more compliant (softer) suspension both increase the Vas of the driver. With the Vas in the numerator of the efficiency calculation, we know that more cone area and a softer suspension increase efficiency. So far, this is all very logical.

Working against driver efficiency is the driver’s calculated electrical Q (Qes) as it’s in the denominator. If we look at the formula to calculate Qes, the whole topic starts to make even more sense. The formula to calculate Qes is Re ÷ ((BL^2) x Cms x 6.283 x Fs). Looking at this equation, we have the DC resistance of the voice coil (Re), the driver’s BL product and the resonant frequency of the speaker (Fs) as the key considerations. Increasing resonant frequency will lower the Qes, raising the efficiency in the previous formula. An increase in the motor force BL (which is the product of the strength of the magnetic field multiplied by the length of wire in the field) also lowers Qes and raises efficiency. A more compliant speaker suspension lowers the Qes and boosts efficiency. Finally, increasing a speaker’s voice coil DC resistance, logically, increases the Qes of the driver and reduces the efficiency.

Look at the Big Picture!

Let’s step back and look at this as a whole. More cone area increases efficiency. A more compliant suspension increases efficiency. A higher resonant frequency increases efficiency. Lower voice coil resistance increases efficiency. Now, think about what we’ve described. This doesn’t sound like a subwoofer to me. A 10-inch midrange driver with a very compliant suspension would be efficient, right? A perfect example would be the Hertz SV 250.1 SPL midrange. This driver is part of the SPL Show series and has a calculated n0 of 3.347%, a 1-watt/1-meter efficiency of 97.39 dB SPL and a 2.83-volt/1-meter efficiency of 101.2 dB SPL.

Rockford Fosgate has a similar 10-inch midrange driver called the Punch Pro PPS4-10. The Punch Pro 10-inch has a much lower resonant frequency (53.5 hertz compared to 90 for the Hertz) but also has a more compliant suspension (35.2 liters compared to 20 liters), so its efficiency is 2.48% 96 dB at 1-watt/1-meter. The trade-off between the two is that the Rockford Fosgate driver has about 50% more excursion capability at 4.6 mm vs. the Hertz at 3 mm. The extra weight of that taller voice coil winding would have contributed to the change in efficiency.

Enclosure simulations predict that the Punch Pro driver will give us a more midbass output at the expense of a few decibels of efficiency. If you don’t have dedicated midbass drivers in your system or subs that can play above 250 hertz, this would be the best option for your audio system. If you have midbass drivers in the system, then the added efficiency of the Hertz driver is beneficial. Remember what we said before we started this discussion: Every speaker parameter interacts with others, and no single consideration outweighs any other. One of these drivers isn’t “better” than the other as they fit a different application.

When it comes to speaker design, the low-frequency output is the typical trade-off for increased efficiency. A higher Fs value will mean less deep bass. A stiffer (less compliant) suspension also means less deep bass.

Modeling a Hypothetical Speaker

Let’s start with the Hertz SPL Show SV 250.1 speaker and do some simulations in BassBox Pro. I chose this driver because I have a complete set of Thiele/Small parameters for it.

We’ll model the driver in a 3-cubic-foot sealed enclosure as this replicates a typical car or truck door installation. The software predicts an F3 frequency of 190.1 Hz and a peak SPL of 118.2 dB SPL at 870 hertz.

What if we had a hypothetical driver with a similar design but with a lower resonant frequency because of a heavier cone assembly? I changed the resonant frequency value from 90 to 70 hertz and kept the Vas the same at 20 liters, the voice coil resistance the same at 3.3 ohms, then let BassBox Pro recalculate the remainder of the parameters.

Our efficiency has dropped from 3.347% to 1.575% or 97.39 dB at 1 watt to 94.12 dB. In the same application, the -F3 frequency of the enclosure is now 109.2 hertz, and the peak SPL is 114.9 dB with 100 watts of power. There are two ways to look at this new driver: It’s not as loud in the midrange, which is the scientifically correct observation. The other way to look at it is to say that it produces more bass relative to the maximum midrange output.

If we look at the predicted frequency response relative to the peak output, we see the second description of a driver that produces more bass relative to the midrange energy.

In reality, your installer could use a digital signal processor to attenuate the midrange output of the more efficient driver to produce a similar real-world response. This method has the benefit of requiring less power to reach the same midrange frequency output levels. Could you boost the bass response in the original driver to yield the same thing? Sure, but you will need to consider that the driver still has a maximum power handling and excursion rating, so there is a limit to how much power you can send the speaker at low frequencies. Bottom line: It’s six of one, a half-dozen of the other.

We could go on and on for a week simulating and comparing different drivers with different parameters to find one that gives us the midbass and midrange performance we want so that the speaker’s output will blend with the subwoofer system we have in mind. Here’s what you need to know: Driver efficiency increases aren’t a free lunch. You rarely get more output without some other aspect of the design changing. If the engineer developing the driver knows how to offset a motor strength gain to maintain low-frequency performance, they will likely come up with something impressive.

Drop by your local mobile enhancement retailer today to find out what they offer in terms of high-efficiency drivers, and be sure to ask them about what’s best to use with your existing audio 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.