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.

Decades ago, it took about $40 in parts, on top of the cost of a new car radio, to give yourself improved sound quality and more features. A simple wire harness adapter would let a single-DIN radio connect right to the factory radio harness behind your dash. Add an antenna adapter and you were likely on your way.

Fast-forward to the 2020s and modern infotainment systems often include climate controls, backup camera displays and vehicle information like tire pressure. Let’s take a detailed look at how things have changed when it comes to upgrading the radio in cars and trucks.

The Platform: Jeep Grand Cherokee

We’ve chosen the Jeep Grand Cherokee as the platform for our example. Why? Because we know what’s required to upgrade both classic and late-model versions of this vehicle.

We’ll start by talking about a 1998 model year Grand Cherokee, also known as the ZJ Chassis code models. These sport utility vehicles came with one of Chrysler’s infamous DIN-and-a-half radios. If you bought a premium model, you might have had a CD player and a cassette player along with three bands of equalization.

If you wanted to upgrade the vehicle with a new single-DIN CD receiver or one of the rare-at-the-time flip-out multimedia receivers, all your installer would need was a mounting adapter plate and a wire harness adapter.

2010 Grand Cherokee Radio Upgrades

Let’s jump over the second-generation Grand Cherokee and look at the popular WK platform covering 2005 through 2010. Chrysler was still rocking versions of their DIN-and-a-half radios in most models. Some models had a touchscreen navigation radio after 2008 that could be swapped out for almost any aftermarket double-DIN multimedia receiver. By the way, the REC version of the navigation radio used a DVD to store map data. Can you imagine how long that would take to plot a route somewhere? Premium models included a Boston Acoustics-branded system that didn’t sound too bad for the time.

If you wanted to upgrade this radio to a double-DIN, you had to have the oversized dash trim piece, a mounting adapter plate, a digital radio replacement interface to communicate with the data network in the vehicle and an antenna adapter. You would probably also want a steering wheel control interface to use the volume and track selection buttons on the back of the steering wheel with your new radio.

You will likely need to spend over $300 on parts and accessories on top of the cost of a new multimedia receiver to upgrade the radio in one of these Grand Cherokees. With that said, if your Jeep didn’t come with navigation or you wanted to play digital audio files from an iPod or USB stick, the investment was worth every penny!

2015 Grand Cherokee Radio Upgrades

OK, let’s look at something modern and just about current. The WK platform Jeep Grand Cherokee was built between 2015 and 2021. Like most other car companies, Chrysler finally gave up on the stand-alone radio and went to a large display and hide-away module. If you have a 2015 or 2016 Grand Cherokee, you likely don’t have Apple CarPlay, and you’ll want to upgrade it. The problem is that the climate controls are integrated into the big touchscreen in the center of the dash. Fear not; the aftermarket audio industry is here to help! PAC has a dedicated dash kit, wiring, interface and climate control upgrade solution called the RPK4-CH4103. This kit allows you to install any double-DIN radio to get the entertainment and productivity features you want. It even works with the factory backup camera.

If you read the caption on the above image carefully, you’ll notice that we said “almost everything.” Yeah, it’s not over yet. If you’re connecting a new radio to the factory-installed amp and speakers, you should be good to go. Suppose you’re upgrading the system with new speakers or a subwoofer. In that case, your installer might need to deal with the Active Noise Cancellation (ANC) system built into the factory amplifier. Thankfully, PAC has a cable to disable that called the ANC-CH01.

Plan on at least $500 in parts to get a new multimedia radio into a 2015 through 2021 Grand Cherokee.

Premium Aftermarket Radio Integration

Before you get the idea that it’s just the Grand Cherokee that gets this fancy, let me assure you that there are dozens of similar solutions for other makes and models of cars and trucks. The 2015 through 2019 Ford F-150 and Super Duty trucks, 2003 through 2007 Honda Accords, 2010 through 2012 Cadillac SRX, 2016 through 2021 Honda Civics, 2011 through 2014 Dodge Chargers, 2011 through 2019 Ford Fiestas and 2010 and newer Mustangs all require some sort of climate control solution when you want to upgrade the radio.

We didn’t even scratch the surface on vehicles that use MOST, A2B, AVB, SPDIF, TOSLINK or data-bus controlled amplifiers. Thankfully, a local specialty mobile enhancement retailer will have access to all the components needed to let you pick nearly any radio you want for these applications. Drop by a store today and see what new radios are available to upgrade your vehicle’s technology and entertainment options.
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 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.

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