If there’s a single marketing statement that makes my eye twitch, it’s one that claims a specific subwoofer will “work” in a small enclosure. Contrary to many marketing claims, enclosure volume is directly proportional to low-frequency extension and sound quality. Let’s look at the math and how these tiny enclosures ruin the performance of your subwoofer.

The Backstory on Enclosure Volumes and Subwoofer Size

Many years ago, I flew to Edmonton, Alberta, for a distributor trade show. A friend graciously picked a few of us up in his pickup truck at the airport. As we drove toward the venue, I asked if he’d blown the subwoofer in the system. It didn’t produce any deep bass and sounded sloppy. He said that it was brand-new. I asked what subwoofer it was and what enclosure it was in. He told me it was a very popular name-brand sub (yes, I’m concealing the brand) and that it was in a 0.25-cubic-foot sealed enclosure. I thanked him again for picking us up.

The Relationship between Subwoofer Size and Enclosure Volume

For this article’s purposes, we will focus this discussion on acoustic suspension (sealed) enclosures. From 2-inch midrange drivers to 19-inch monster SPL subwoofers, the relationship between the cone area, suspension compliance (softness) and the volume of air in an enclosure is critical in determining how low the speaker will play. The correlation is so constant that many companies have tweeters that behave differently based on the air volume behind the diaphragm.

As a generalization, we can say that a larger enclosure will produce more low-frequency output. Since the goal of adding a subwoofer is to improve low-frequency extension, limiting this characteristic by putting a large subwoofer in a small enclosure is counterproductive.

Considering how it will sound is an even more important factor in designing a high-performance subwoofer system. We can analyze the calculated Qtc value of a subwoofer system (driver and enclosure) to see how well the cone motion is damped. Many car audio enthusiasts fail to consider this part of an enclosure simulation. This oversight results in subwoofer systems that sound terrible and perform poorly – like the one in my friend’s pickup truck.

We get the following qualifications if we look at the description of different speaker Qtc values from Vance Dickason’s Loudspeaker Design Cookbook.

Do you want the subwoofer to stop immediately after the drive signal is removed (Qtc = 0.5), or would you like a bit more upper bass output at the expense of slightly degraded transient performance ( Qtc = 0.707)? Perhaps you want a great deal of output at higher frequencies while sacrificing low-frequency output and cone control (Qtc > 1.0)? While there are simple algebraic formulae to calculate these values based on a chosen subwoofer’s Thiele/Small parameters and the volume of the enclosure, we’ll use our tried and tested BassBox Pro software to generate the volume, F3 or Qtc for our sample subwoofer.

Let’s Model Some Subwoofer Enclosures

We’ll start with a typical high-performance 10-inch subwoofer. This driver has a free-air resonant frequency (Fs) of 29 hertz, an equivalent suspension compliance (Vas) of 35.4 liters and a Qts value of 0.501.

While I like extremely well-damped bass, most car audio enthusiasts want a bit of boom and warmth, so let’s start with a target Qtc of 0.707 for our subwoofer system.

For the above enclosure simulation, the software tells us the subwoofer needs to have a net air volume of 0.833 cubic feet. The resulting F3 frequency will be 45.95 Hz. This is typical of a reasonably sized sealed enclosure for a 10-inch car audio subwoofer.

The manufacturer recommends an enclosure with a net internal volume of 0.53 cubic foot. Let’s see what modeling the driver in this enclosure tells us.

The 0.53-cubic-foot enclosure results in a system Qtc of 0.806 and an F3 frequency of 48.86. To put the latter value into perspective, the system output at 30 Hz has been reduced by 1.7 dB. Quite simply, the smaller enclosure isn’t as efficient at low frequencies. This is still a very reasonable enclosure design and will provide good output and reasonable physical power handling for the driver.

Let’s switch to looking at specific enclosure volumes. What happens if we cram this sub into a 0.4-cubic-foot enclosure, as is common with many pickup truck under-seat solutions?

We now have a system Qtc value of 0.881 and an F3 frequency of 51.64 hertz. Bass output at 30 hertz is now down 3.2 dB from our original 0.833-cubic-foot enclosure. In real-world terms, we need twice as much for the sub to play as loudly as the same driver in a larger enclosure. More power means that your amplifier has to draw more current from the vehicle’s electrical system.

If you’re pondering the benefit of multiple subwoofers in a small enclosure vs. a single driver in an ideal enclosure, you’re starting to get the picture.

Let’s finish this by looking at what happens when our 10-inch sub is crammed into a 0.25-cubic-foot enclosure.

It isn’t hard to see that the sub doesn’t produce anywhere as much bass as it would from a properly sized enclosure. Specifically, the system Qtc is now at a very undesirable 1.034, and the F3 frequency is at 53.38 hertz. Output at 30 hertz is down by a whopping 6.2 dB compared to the original design. Our original 0.833-cubic-foot design only requires 70.4 watts to reach the same output level as this enclosure. Which do you think the amplifier and electrical system will prefer delivering?

What Does “Works in a Small Enclosure” Mean?

As we decrease the size of the enclosure, the air inside acts as a tighter spring and limits how much the woofer cone can move for a given amount of power. From a sound quality perspective, this tighter spring rings and resonates increasingly as enclosure volume decreases. Look at the increase in output around 90 to 100 Hz. This is caused by the woofer cone continuing to move (ring or resonate) once the input signal has been removed. This unwanted motion wasn’t part of the original audio signal and would be considered distortion. The subwoofer system will sound sloppy and is often described as a “one-note wonder.” In short, it should be avoided.

Let me put this into perspective for you in a different way. The graph below shows the output of a 6.5-inch midrange/midbass speaker mounted in the door of a car or truck. With no high-pass filter applied, it produces more bass (with the same power) at 40 hertz than the 10-inch subwoofer crammed into the small 0.25-cubic-foot enclosure. While a 6.5-inch speaker can’t handle 300 watts of power at 40 hertz, there are typically two in the vehicle. One hundred fifty watts is still a stretch, but I think you get the point. A subwoofer in a very small enclosure isn’t acting like a subwoofer – it’s more of a midbass speaker.

It’s not much of a stretch to say that stuffing subwoofers into microscopic enclosures is counterproductive. From a perspective of not failing, yes, they work. Do they sound good? No. Do they produce extended low-frequency output? No. Are these enclosures efficient? No. As such, do they make sense? No.

If you’re shopping for a subwoofer system for your vehicle, drop by a local specialty mobile enhancement retailer and work with them to choose a subwoofer system that will be efficient and offer excellent low-frequency extension. They should be able to show you computer simulations of how different drivers perform in an enclosure that works with the space you have available. If you want to hear those 35-hertz bass lines in your favorite music, proper subwoofer enclosure size and construction matter.

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.

I can’t even begin to count the number of times I’ve seen car audio speakers installed improperly in the doors, dash or rear deck of a car or truck. Many amateur car audio enthusiasts don’t understand that unlike home audio and Bluetooth speakers that come in an enclosure, the way that raw speakers are mounted in your vehicle plays a huge role in what they’ll sound like. Let’s do a few simple tests to quantify the importance of proper speaker installation.

Why Do Speakers Need an Enclosure?

When we talk about car audio speakers, 99% of the time we’re talking about a woofer or midrange driver that doesn’t have an enclosure. The days of the Pioneer Tune-Up and rear parcel shelf enclosures are long gone. If we look at one of these speakers, we will find that the basket to which the driver components are assembled is open on the back. The openings in the basket prevent air pressure changes behind the woofer cone as it moves forward or rearward. Many companies that employ Klippel testing to design their speakers will add vents under the spider mounting ledge for the same reason: to allow for more linear performance, especially at high excursion levels.

Because the back of the woofer cone is open, sound is created behind the speaker as the cone moves forward and rearward. The problem with the sound coming off the back of the cone, often called the “rear wave,” is that it’s opposite in polarity to the sound coming from the front. When the two sound sources mix, they cancel each other out.

If you were to put a 6.5-inch woofer on a table and feed it a 150-Hz test tone, you wouldn’t hear much. When a speaker is mounted in an enclosure, the rear wave sound is trapped in that enclosure and doesn’t cause this cancellation. This phenomenon is most critical at bass, midbass and lower midrange frequencies. Subwoofer enclosures are slightly different in that they also control cone motion at low frequencies – but that’s an entirely different discussion. If we were to mount a speaker in the middle of a wall in our home, there is no way for the sound coming from the back to mix with and cancel the sound from the front. If there is, the sound likely has to travel a long distance, and it will lose enough energy that it becomes effectively irrelevant. We call this an infinite baffle installation because the wall acts as a divider to prevent the two sounds from mixing.

Car Door Speaker Installations

When a speaker is mounted in a car door, the metal or plastic on the inside door frame must act as this baffle. If the speaker isn’t sealed against the mounting surface, sound from the back can leak through and cancel with the sound from the front. If the mounting surface has holes in it, the same thing happens. Investing in a layer of sound deadening material on the inner skins of your vehicle’s doors is an excellent investment. Even holes for wiring and fasteners can allow cancellation. If you have a speaker with a dozen holes in the mounting lip to allow it to bolt into several different fastener locations, making sure those are sealed is also essential.

Testing Speaker Installations

I scrounged the lab for a reasonable quality speaker to do this test. I found an old 6.5-inch woofer from a Clarion SRD1700S speaker set I had in one of my vehicles. If you know your car audio speakers, you’ll likely recognize the company that built these drivers for Clarion.

For the first measurement, I set the speaker in my test enclosure and connected the test leads to the amplifier. As you can see from the image below, the speaker certainly wasn’t “installed” properly. Sadly, this mimics many installations I see pictures of all the time.

I set my Clio Pocket microphone at an arbitrary distance of 7 inches from the speaker. I chose this close proximity as I didn’t want the acoustics of my lab to affect the measurement. Yes, I bought lottery tickets, and I WILL build an anechoic chamber if I win big!

As you can see, the response from 140 Hz to 900 Hz is relatively flat; then there’s a massive 13 dB spike around 1.6 kHz. If you listened to this speaker, you’d be disappointed.

Better but Still Terrible Speaker Installation

The next test had the speaker held in place with two screws, but neither was tightened to where the speaker was pulled up tight against the mounting surface. This simulates an installation where there are severe leaks around the speaker.

The violet trace in the frequency response chart below shows that there has been an increase in output of about 5 dB SPL at all frequencies below 700 Hz. There is still an 8 dB difference between 1 and 1.7 kHz, which is less than ideal but not as disastrous as the original measurement.

Some quick math shows us that this 5 dB increase in output is equivalent to going from 10 watts of power to 31.6 watts to produce the same increase. Put another way, we could feed this second installation with 10 watts of power or the first with 31.6 watts to produce the same output in the mid-bass and lower midrange region. Since we know that all speakers produce more distortion at higher excursion levels, a free gain in efficiency of 5 dB SPL is a better choice.

OK, time to do this properly. I tightened the screws to pull the speaker tight to the baffle. In each measurement, I moved the microphone to ensure that I was getting a reading at the same distance from the cone and that any variances in the measurement could be attributed to the installation and not my testing configuration. You can see how much things improved in the frequency response graph below.

The speaker has picked up another 2 to 3 dB of output compared to the mediocre installation. If we fed this speaker 10 watts of power, the mediocre installation would need about 20 watts to produce the same result. The poor installation would need 63 watts. Very few 6.5-inch speakers would survive being fed more than 60 watts of power at bass frequencies for very long.

Proper Speaker Installation Ensures Reliable Performance

How your speakers are installed in your car or truck is critical to the performance and longevity of your audio system. An investment in having the shop you’re working with create high-quality mounting adapters (as needed) and install sound deadening for speaker installation is worthwhile. Proper installation can dramatically improve the performance and efficiency of your entire 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.

You’d think it’d be easy to choose an amplifier of a specific power rating to work with a 500-watt subwoofer. In reality, we need to consider several factors, particularly performance and reliability. Let’s take a detailed look at the complexity of choosing the perfect amplifier for your car audio subwoofer system.

The Myth and Mystery of Car Audio Amplifier Power Ratings

Let’s start by talking about amplifier power ratings, since this is an area the BestCarAudio.com editorial team is moderately obsessive about. Measuring practical amplifier power production requires rules. The industry standard for power measurement is defined in the ANSI/CTA-2006-D Testing and Measurement Methods for In-Vehicle Audio Amplifiers standard. Without getting too into the details, this standard requires that the audio signal be reproduced with no more than 1% total harmonic distortion and noise into a specified load and that the amp be powered with 14.4 volts. More supply voltage, which usually results in more power being produced, would be cheating. Not specifying THD+N in the rating is also cheating.

If you’re shopping for an amplifier for your subwoofer, you need to know how much power it will actually produce in your vehicle. You’ll know you’re in good hands if you see the CTA-2006 quoted in the specs. Some companies will specify identical or similar criteria but forego the standard. That’s odd but fine. Further, some companies under-rate their amplifiers’ power production capabilities. While this is often good regarding a value proposition, it might mean you have enough power to damage a subwoofer. Sadly, some companies flat-out lie about how much power their amplifiers can produce, and that’s a problem.

Subwoofer Power-Handling Ratings

If making sense of amplifier power ratings gave you a headache, try dedicating some time to figuring out subwoofer power ratings. The ANSI/CTA 2031 Testing and Measurement Methods for In-Vehicle Loudspeaker Systems and the ANSI CTA-426-B Loudspeaker, Optimum Amplifier Power standards describe a test where a speaker must play a test signal for a minimum of eight hours at a specific average power level without inducing any damage to the driver.

Variability and accuracy in providing real-world specifications are once again an issue. If you look at subwoofers from reputable brands, you’ll see that drivers with standard component features typically have similar power ratings. For example, as you move up through this company’s subwoofer series, their power ratings, which are specified as being CTA-2031-compliant, increase in proportion to voice coil diameter. The chart below gives you an outline of the relationship between voice coil size and power handling.

While venting under spider mounting ledges, vented pole pieces and vented formers can help, it’s unlikely you’ll find a subwoofer with a 2-inch diameter voice coil that can handle more than 500 watts of power for eight hours. Nevertheless, many companies make these claims.

So, how do you know what’s reasonable regarding power-handling ratings? The chart above is a good guideline, but some subwoofers might have small-diameter four-layer voice coils or designs with added length that also help dissipate heat. The mobile enhancement retailer you’re working with will have a good idea of how much abuse their subwoofers can take.

What Happens When a Sub Gets Too Much Power?

Because speakers and subwoofers are notoriously inefficient, most of the power sent to them is converted into heat. Usually around 99% is wasted in heating the coil, voice coil former, top plate, T-yoke and magnet. As we explained here, bigger subwoofers with heavier cone assemblies are often less efficient.

No matter what features are included in a subwoofer design, once the voice coil gets too hot, it will melt the varnish or adhesive that holds the assembly to the former. When this happens, the coil usually unravels and physically interferes with the top plate. The coil often rubs for a while rather than failing instantly. Nevertheless, the damage is permanent.

Another consideration in matching an amplifier to a subwoofer is physical power handling. It’s easy for someone unfamiliar with how to model a subwoofer in an enclosure to design a solution with physical power-handling issues. Subwoofers need enclosures to limit cone travel. When an enclosure design is incorrect, a subwoofer might bottom out, and the former will run into the back plate, or the spider might be stressed and damaged where it attaches to the cone.

The Power vs. Frequency graph above shows that a subwoofer rated to handle 500 watts of power can only handle just over 400 watts around 42 hertz because of the design of this seemingly simple 1-cubic-foot vented enclosure.

Picking the Right Amplifier for Your Car Audio Subwoofer

This topic is more complicated than it appears on the surface. Let’s simplify things a bit so you can head to your local specialty mobile enhancement retailer with a plan. Don’t skimp on subwoofers if you want your audio system to play at high volume levels. Choose high-quality drivers with real power ratings. Then choose a high-quality amplifier with a similar power rating. So, if you have a 500-watt subwoofer, then an amplifier capable of producing 500 watts into the current load impedance for that driver is a good choice.

What happens if you have less power than the sub can handle? Not much. The sub won’t play as loudly. If you push the amp to clip, that will put more heat into the voice coil, but it won’t make your music any louder. Make sure the shop that installs your amp and subwoofer has the tools and training to set the sensitivity controls on the amplifier properly. What if you have too much power? Well, it’s easy to put too much heat into the sub. If you are listening to music, a 650-watt amp on a 500-watt sub isn’t a recipe for instant disaster. You have to use that extra power for something bad to happen. For example, if you’re playing test tones to measure maximum SPL readings, you might be in trouble.

If you want the subwoofer system to sound great and last for decades, use a high-quality subwoofer amp and lots of drivers, then under-power the subs. If you have four 500-watt subs, choose a 1,000- to 1,200-watt amp. This will produce lots of bass but will never push the subwoofers near their limits. This reduced drive level not only allows the subwoofers to last longer, but they will sound better. Of course, don’t compromise on a proper enclosure design only to increase the number of subwoofers in the system.

One last thought: If you want your music to sound the best it can, focus on choosing an amplifier with excellent distortion ratings rather than focusing on power. Power ratings aren’t in any way related to sound quality. Some of the most powerful amps we’ve seen sound terrible. Choosing a high-quality amp that produces 500 watts of power will produce better bass than an inexpensive or poorly designed amp that produces 800 or 1,000 watts.

Your local specialty mobile enhancement retailer should be able to help you choose the correct number of subwoofers to deliver the kind of bass response you want and match them to an amplifier that will sound 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.

For as long as I can remember, car radios have had their “maximum power” ratings all over their packaging and often right on the face of the radio. These numbers are not only useless in terms of an ability to reproduce music with any sense of quality, but I have always questioned whether they are even possible. Let’s measure how much power a conventional car audio head unit can produce.

Car Audio Head Unit Amplifiers

Most car audio source units use an all-in-one four-channel amplifier integrated circuit (IC) to power the speakers in the vehicle. These ICs are typically driven directly by the supply voltage to radio with something on the order of 12 to 13.5 volts.

Some quick research shows that these units have a “power rating” of 50 watts by four. As a reader of BestCarAudio.com, you know supply voltage and distortion measurements are critical in quantifying a power measurement. The spec sheet for these little amps includes that information. Many are rated at 50 watts by four at 10% THD when powered with 15 volts. If ever there was a “that’s not useful” specification, this would be it.

When comparing car audio amplifier power measurements, the ANSI/CTA-2006-C standard defines the maximum noise and harmonic distortion to be equal to or less than 1%. Second, we use a maximum supply voltage of 14.4 volts – even if that number is a bit optimistic.

Is a Rating of 50 Watts per Channel Possible?

You might not know it, but 10% distortion from an amplifier playing a pure test tone starts to look a lot like a square wave. Let’s assume there is very little voltage loss due to the components in these amplifier ICs, then do some basic math. To calculate power, we square the voltage across a load, then multiply that number by the load’s impedance. As such, 15 times 15 is 225. Dividing 225 by four gives us 56.25. If the amp could produce a pure square wave, it could produce 50 watts of power.

Let’s back things down to something realistic and consider what power that amp might make if the output waveform was a sinusoidal signal. To convert a square wave to a sine wave, we divide it by the square root of 2. In our theoretical “perfect efficiency” amp example, we now have an output voltage of 10.6 volts, which the math says is 28 watts per channel.

Let’s back this down to a more reasonable test voltage of 13.2 volts – something we might see while driving in an average, everyday car or truck. Our amp IC can now theoretically produce 21.78 watts.

If we dig back into the datasheets for a real amplifier IC, we see that they have a rating of 20 watts per channel with 1% THD when supplied with 14.4 volts. It almost makes sense.

Why Worry About Head Unit Power Ratings?

I’ve seen many instances of car audio enthusiasts asking how to upgrade their sound systems. One of the first suggestions is to purchase new speakers and an external amplifier. Many compact four-channel amplifiers will fit in a dash, under a seat or in the center console of a car or truck. These amplifiers are typically rated to produce 45 to 50 watts per channel. On many occasions, I’ve witnessed ill-informed owners state that this power rating is the same as their head unit. This statement is incorrect because the numbers aren’t stated with the same supply voltage and distortion ratings. If we want to use Maximum Power head unit ratings, these compact amplifiers would produce around 100 watts per channel. Nevertheless, we don’t deal in inflated numbers.

Testing Power from a Car Audio Source Unit

I dug through the cupboards in my lab to see if I had an older source unit and found a high-quality marine radio from around 2010. Let’s set this up on the BestCarAudio.com test bench to see what it’s capable of in terms of power production.

I created a test disc with various 1 kHz test tones in hopes of hitting an output level that contained exactly 1% total harmonic distortion and noise. Yes, a compact disc. Do you remember those round discs that store data? To keep the test simple and reliable, I will only drive one 4-ohm load during the test as I don’t want to overheat anything or damage this “vintage” piece of car audio history. Hahaha. Nevertheless, the disc has 40, 30-second long 1 kHz sine wave test tracks recorded at 0 to -4.0 dB FS in -0.1 dB increments. Yeah, this took a moment to create. Driving only one channel will allow me to use my small variable-voltage power supply to see how different supply voltages affect maximum power production.

The graphs above show how a single channel behaved when driven to an output level as close as I could get to 1% THD+N. The deck produced a waveform with a 7.16 volts RMS amplitude at this level. That works out to 12.81 watts. That’s most certainly not 20 or 45 watts.

Just so you know what you’re looking at on the waveform (oscilloscope), the yellow and teal traces are the voltages on the positive and negative speaker wires. The violet trace is the sum of those voltages calculated by the scope. This is what the speaker “sees” in terms of power.

Let’s up the supply voltage to the same level we’d use on a good quality car audio amplifier to see what happens.

At 14.4 volts, the output has increased to 8.66 volts RMS, which works out to 18.75 watts. This is now getting into the realm of the 22-watts-per-channel rating. Can we get closer by supplying it with 15 volts?

Supplying the deck with 15 volts resulted in an output of 8.99 volts RMS, which works out to 20.2 watts.

And In Today’s News, 20 Watts Isn’t 50 Watts

Over the years, I’ve tested dozens, if not hundreds, of source units. Most don’t make 20 watts of power per channel – they are typically between 14 and 17 watts.

Where am I going with this information? I want it to be clear to those wishing to upgrade their car audio systems that even a 45-watt-per-channel compact amplifier would be a significant upgrade over the power available from a head unit. For head unit manufacturers, please stop printing 45Wx4 on the packaging. It just isn’t a realistic rating.

Genuine High-Power Head Units

Before I wrap up, I have to note that some source unit manufacturers have gone the extra mile by including a small switching power supply and a high-power Class D amplifier in their source units. These radios can produce around 45 watts of power per channel using standard CTA-2006-C compliant distortion and supply voltage specifications. You’ll know when you’re talking about these radios because their installation requires running a larger-than-normal power and ground wire to a high-current power source in the vehicle. These decks usually include that 100-watt-per-channel rating I mentioned earlier.

Upgrade Your Head Unit for Better Sound

If you have a typical car audio source unit that makes around 15 to 18 watts of power per channel, upgrading your stereo system with a high-performance amplifier can dramatically improve both output capability and sound quality. Drop by your local specialty mobile enhancement retailer today to find out about the 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.