Speaker pods and build-outs on A-pillars are becoming increasingly common in custom car audio installations. While some of these solutions look cool, the laws of physics can work against these cosmetic efforts to degrade the performance of your car stereo system. The subject of speaker installation could (and should) fill a book. In this article, we’ll look at the benefits and drawbacks of mounting speakers in a way that’s not flush with the surrounding surfaces.

Speaker Directivity

Before we dive into our discussion of speaker pods, we need to have a quick reminder about speaker directivity. At frequencies where a sound’s wavelength is below 1.75 times the speaker cone’s diameter, sound emanates equally in all directions. Crucial to this discussion is an understanding that the description “all directions” includes the area behind the speaker.

By way of an example, let’s look at a 2.5-inch midrange driver. Let’s assume for simplicity that the cone has a diameter of 2.5 inches. As such, a 5.4 kHz tone would have a wavelength equal to the cone’s diameter. A sound with a wavelength that’s 1.75 times the cone’s diameter would have a frequency of about 3.1 kHz. As we stated, sounds with frequencies at or below 3 kHz will radiate in a spherical pattern from the speaker’s center, including areas behind the speaker.

Sound Reflections Can Wreak Havoc with Your Music

Car audio system design combines a multitude of talents. The Product Specialist designing your audio system needs to have a firm understanding of the available speaker mounting options in your vehicle to create a speaker installation solution that will meet your expectations. The technician working on your car needs to know how to optimize each speaker’s performance in those locations to deliver measurably accurate performance. There’s no doubt that perfect execution is a combination of a thorough knowledge of the laws of physics and some artistic style.

If you look at home speakers, you’ll see that each driver is typically mounted flush with the enclosure’s front baffle. This decision doesn’t happen by accident. Because sound radiates rearward from the cone, it will bounce off this mounting surface. All these reflections combine with the speaker’s energy directly radiated, and both signals eventually arrive at your ears. When the baffle is even with the speaker, the results are quite predictable and usually acceptable.

What would happen if the speaker stuck out an inch or two in front of the baffle? The sound reflecting off the baffle may not add to the sound coming directly from the driver at all frequencies. This difference in pathlengths causes cancellations at some frequencies, making the speaker system very difficult to calibrate with an equalizer.

Calculation Frequency Response

Despite the belief that delivering great sound in a car or truck is magic, it’s easy to predict the frequency where reflections can become an issue in a car audio system. Imagine if a speaker pod is sitting 3 inches in front of your car’s windshield. This location results in the sound bouncing off of the glass traveling an extra 6 inches before it combines with the energy radiated directly from the speaker cone.

If we look for a frequency where one half of a wavelength is equal to our 3-inch distance, we find that at 2.26 kHz, the sound is one half-wavelength out of phase with the original source when it sums back together after reflecting off of the glass. At this frequency, the sounds will cancel each other out. The result is a notch in the frequency response of the system. This acoustic cancellation repeats at 6.7 and 11.3 kHz. Those last two will be inaudible as comb filtering at frequencies significantly above 1 kHz is difficult to perceive because the Q is of the notch is very high.

This phenomenon doesn’t just happen with midrange speaker pods on your dash. Without some compensation, differences in sound arrival times between the left and right speakers or front and rear speakers can produce the same effect. In home audio, placing a speaker so that the driver is 8.5 inches in front of a wall will produce the 400 Hz, 1.2 kHz and 2 kHz dips you see in the image above. The same thing happens at the frequency where sound created by the speaker bounces off of the floor and combines with the sound coming straight from the driver.

If you are working with a car stereo shop to design an audio system upgrade for your car or truck, it’s not difficult to minimize the effects of comb filtering by having your speakers mounted as flush as possible with the vehicle. Where there are front-to-rear or left-to-right pathlength differences, implementing signal delay or an all-pass filter in a signal processor from a company like ARC Audio, Audison or Audiotec Fischer can dramatically improve the way your music sounds. Placing your speakers in pods away from door panels, the windshield, side windows and the dash might not be an idea that’s as good as it seems.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

If you’ve looked carefully at the specifications of car audio amplifiers for any amount of time, then you’ll know that some designs make more power when they are connected to a higher-voltage electrical system. This type of amplifier is called an unregulated design. In the simplest of terms, it multiplies the provided battery voltage by a fixed amount to power the amp’s internal components. If that sounds complicated, don’t fret. We’re here to spell out why these amplifiers like extra voltage.

What Is an Unregulated Car Audio Amplifier?

Before we talk about regulated and unregulated designs, we need to define what’s known as rail voltage. Car audio amplifiers, in general terms, work with five different voltages. The most basic circuitry that turns the amplifier on and drives the output stage runs directly from the feed from your battery. The second pair of voltages, usually plus and minus 15 volts, is used for the signal processing and output device driver circuitry. Lastly, there’s what’s known as the rail voltages. The rails voltages are key to determining the maximum voltage the amplifier can supply to your speakers.

As discussed in our recent article about amplifier clipping, the maximum undistorted voltage an amplifier can produce is based on the rail voltage. When you drive an amp with more input signal, the tops and bottoms of the waveform become distorted, and significant harmonic distortion is added to the output signal.

In a regulated amplifier design, the rail voltage is set to a fixed level that the amp attempts to maintain no matter what voltage is applied to the power terminals. If you’re sitting in a parking lot listening to music, your battery voltage may quickly drop to 11.8 or 11.9 volts. A regulated amp will draw extra current to maintain the target rail voltage. If you’re cruising down the highway, the alternator could easily produce 13.8 volts. In this case, the amp draws less current but maintains a fixed rail voltage.

In an unregulated amplifier design, the rail voltage is a function of the supply voltage. Let’s say the power supply produces +24 and -24 volts from a 12-volt feed, by way of an example. If the voltage drops to 11 volts, the rail voltage drops to +22 and -22 volts. If the voltage increases to 14 volts, we might have plus and minus 28 volts. This is a gross oversimplification of the process, but it gives you an idea of how things work.

The Power T1000X5ad five-channel amplifier from Rockford Fosgate uses an unregulated power supply design. Maximum output power increased by almost 30% when the supply voltage is raised from 12.6 to 14.4 volts.

Real-World Measurements

As with any technical subject, sometimes it’s better to look at a real-world example to more easily understand the concept. We dug up an older Class-AB stereo amplifier rated to deliver at least 80 watts per channel at 1% distortion when connected to a 4-ohm load and supplied with 14.4 volts.

Step 1 was to set the amp up on the bench and see how much power it makes with our supply voltages on their low setting. The D’Amore Engineering AMM-1 shows the amp could produce 74.5 watts per channel with a supply voltage of 13.58 volts.

Just under 75 watts is pretty good power for an amp rated at 14.4 volts. The next step was to increase the power supply voltage to 14.38 volts and leave the input signal at the same level. Now, our amp is producing 81.1 watts, and distortion has dropped to an impressive 0.009%.

With more rail voltage available, we can now increase the signal fed to the amp and further increase its power output until we reach a 1% distortion level again. Powered with the same 14.38 volts, the amp can now produce 85.3 watts. That’s more than 10 watts over the low-voltage level maximum output level.

Can We Correlate Amp Power with Supply Voltage?

It should be clear that when you have an unregulated amplifier in your car or truck, supplying it with as much voltage as possible allows it to make more power. I compared the power output of several high-quality amplifiers under different supply voltages. All made more power with more supply, but the ratio by which the specs increased varied from brand to brand. On average, one extra volt supplied to the power connections raised the maximum 1% distortion power output level by between 15 and 30%.

Knowing this information, the importance of having your amplifiers installed with large-gauge, all-copper conductors can’t be overstated. While there are places to save a few bucks when it comes time to get an amplifier installed in your vehicle, skimping on power wiring quality isn’t on the list. Drop by your local specialty mobile enhancement retailer today to find out what amplifiers are available to make your music sound amazing. And don’t forget: Make sure to feed them with all the battery voltage your vehicle can muster.

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.

Over the years, car audio speakers have been installed in seemingly endless combinations of panels, pods and baffles. Some look great, some sound great and some offer both. Sadly, not everyone understands the physics involved in choosing the ideal installation locations for speakers. This article will cover a few of the vital installation criteria that need to be considered when your local retailer is installing new speakers in your car or truck.

Every Speaker Needs an Enclosure

If a speaker were set on a table and music played through it, you’d find it doesn’t produce any bass and very little midbass. This is because there’s a nearly equal amount of sound produced from the back of the woofer cone compared to the front. If you wrap your hands around the speaker, the performance improves. If you mount the speaker in a baffle that separates the two sound sources (front and rear), you’ve eliminated back-wave cancellation.

Dash and Door Panel Installations

Of course, one of the most popular locations to mount a speaker is in the factory location in the dash or door of your car or truck in place of the speaker that came from the factory. This location typically provides excellent cosmetics as the vehicle retains its factory-like appearance. In many cases, such as a dash location at the base of the windshield, the speaker’s performance can be such that it delivers excellent frequency response throughout the entire listening environment.

Door Speaker Installation and Sound Deadening

If you have a speaker installed in a door location, your retailer may need to create a set of mounting adapters. A few factors need careful consideration during the design of these adapters. First, they need to be thick enough to ensure that the magnet assembly on the speaker’s rear won’t interfere with the window mechanism or glass. Second, the speaker’s front needs adequate clearance to ensure that the woofer cone can’t come into contact with the grille. Finally, the adapter needs to be made from a material that won’t be damaged by moisture. Most people would be surprised by how much water gets into the door when it rains or when a vehicle goes through a car wash. Common materials for speaker adapters include ABS and expanded PVC plastics. Wood is not a suitable material for use in the doors.

Most modern vehicles have openings built into the interior skin of the doors. These openings allow technicians to service the door handles and window mechanism. Unfortunately, these openings also allow the sound from the speaker’s rear to mix with the sound from the front. The easiest way to improve the performance of a speaker mounted in a door like this is to add a layer of sound deadening. The dense butyl material and foam will seal the openings and dramatically improve your speakers’ efficiency and sound quality.

A Look at Speaker Pods and Enclosures

A common error we see in custom A-pillars and speaker pods is the use of an enclosure that’s too small for the chosen speaker. Even a 4-inch midrange that will play down to 125 Hz needs a certain volume of air in the space behind the driver so as not to affect the overall compliance of the system. If a speaker pod is too small, the system’s resonant frequency will increase and, beyond a certain point, so will the distortion added to the signal. Let’s look at a few examples.

It’s quite common to see 6.5-inch coaxial speakers mounted in small enclosures in an amp rack or subwoofer enclosure. Let’s look at a speaker like the BLAM Live-Series LW 165 C 6.5-inch coaxial speaker. Based on the manufacturer’s Thiele/Small parameters, the small sealed enclosure that would be acceptable for this driver would have an internal volume of about 0.3 cubic feet. This enclosure yields a system Q (Qts) of 0.707 and a-3 dB frequency of about 90 Hz.

Where we get into trouble is when an enclosure isn’t large enough. We recently saw a post where a fabricator crammed a driver similar to this into a pod that “was just big enough to house the speaker.” Let’s make this an extreme example and say the interior dimension was 5.5 by 5.5 inches with a depth of 2.5 inches. That’s a mere 0.017 cubic feet.

To prevent this, every speaker larger than about 2.5 inches in diameter should be modeled using enclosure simulation software to ensure that the planned enclosure won’t be detrimental to the system’s overall performance.

System Directivity

The last topic we’ll mention is directivity. Every speaker, from every brand and of every size, is subject to a phenomenon called directivity. In short, directivity describes how directional the sound of a speaker is. At relatively low frequencies, the sound created by a speaker radiates in a sphere from the cone.

As frequency increases, all speakers become more directional. The frequency at which this starts to happen depends on the diameter of the speaker cone. The chart below indicates (in green) maximum frequencies that radiate evenly in all directions. Frequencies in the red zone are only audible directly in front of the speaker.

Knowing about directivity, it’s important to choose speakers that will sound good in your vehicle’s available locations. For example, a component speaker set with an 8-inch woofer and a tweeter that only plays down to 4 kHz may not deliver good audio performance between 3 and 4 kHz if the listening position isn’t directly on-axis with the speaker. If you can add a midrange driver to the system, you may be better off choosing a 6.5-inch set.

Car Audio Speaker Installation Is Crucial

As you can see from the above, working with an experienced specialty retailer is vital to your car stereo system’s performance. Unlike buying home stereo speakers, where the crossovers and enclosures are designed in a controlled environment, car audio installation experts have to use their knowledge and training to create a speaker system from scratch. The tools and training they offer can be the difference between music that sounds realistic and an audio system plagued by distortion and poor frequency response.

Lead-In Image Credit: Musicar Northwest in Portland designed these enclosures to house a set of Morel tweeters in the doors of this 2009 Ferrari F30 Spyder.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

If you’ve asked your local specialty mobile enhancement retailer about upgrading your car stereo in recent years, they may have told you that they will need to add load resistors. While seemingly new in concept, the purpose of these resistors is simple. They’re often needed to ensure that the factory-installed amplifier in your car, truck or SUV continues to function the way it was designed.

Modern Car Audio Systems and Class-D Amplifiers

Most modern car audio amplifiers, especially those installed by a vehicle manufacturer on an assembly line, use Class-D output circuitry to provide a balance of sound quality and amplifier efficiency. Automakers are fanatical about reducing fuel consumption. If an electronics supplier can deliver an amplifier that draws less current, there’s less load on the alternator, and the engine has to do less work.

All Class-D amplifiers use a filter circuit on the switching devices’ output to remove high-frequency noise caused by the MOSFETs switching off and on. The output of the filter is the original audio signal. These filters typically comprise a capacitor and an inductor. The value of these components is based on the load (speaker) impedance the amplifier is designed to drive. If the values are incorrect, high-frequency audio information may be attenuated, or too much noise might be allowed into the output.

Upgrading a Mobile Audio System

If you visit a local stereo shop and tell them you want to upgrade your audio system, they’ll likely suggest new speakers and an amplifier. In many cases, the shop will use the factory amplifier’s output to feed to the new amp. All good so far.

When the speaker is disconnected from the factory-installed Class-D amplifier, the filter circuit that was designed for a 2- or 4-ohm load isn’t going to function correctly. The signal presented to the capacitor and inductor will cause an oscillation, and a great deal of high-frequency noise may be added to the signal.

Another issue is that these oscillations in the output filter network may become quite significant in terms of their voltage. These voltages can damage components in the amplifier. Companies like Dodge, Chrysler and Ram have circuitry in their radios and amplifiers that prevents them from producing any output if their original speaker isn’t connected.

Upgrade Your Car Stereo Today for Better Sound!

If you can’t turn the volume on your factory-installed car stereo system up without the system distorting, drop by a local car stereo retailer and ask about upgrading your audio system with new speakers and a more powerful amplifier. If they mention that the upgrade will require load-resistors to prevent noise or hiss, now you know why.

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.