When it comes to creating an audio system that sounds amazing, incorporating a digital signal processor into the system gives your installer the tools required to compensate for the majority of the limitations that vehicles impose. To maximize the benefit, a digital signal processor system design needs to take the features and benefits of a processor into consideration. In this article, we are going to explain some of the key differences between a system with and without a digital signal processor.
What is a Digital Signal Processor?
A digital signal processor, also called a DSP, is an audio processor that uses a microcomputer to make adjustments to a signal in the digital domain. In a stand-alone processor, the audio signal from the source unit is converted to a digital data stream using an analog-to-digital converter. Once in the digital domain, the processor can equalize, filter and even delay the signal. Most processors have six or more output channels to provide us with the ability to send different signals to dedicated amplifier channels. Each channel has a digital-to-analog converter that provides a conventional analog audio output.
Digital signal processors offer many benefits over their analog brethren. All the adjustments are handled in the digital domain, making the system impervious to errors because of differing passive electronic component values. The range of adjustability is much greater in a DSP compared to an analog processor, and because all the calculations are based on mathematical equations, the results are more accurate and repeatable. Such functions as signal delay can be performed much more easily in the digital domain than by using analog components.
Speaker Selection for DSP-based Audio Systems
Your choice of speakers and subwoofers is independent of the presence of a signal processor. The criteria for accuracy, clarity and output capability doesn’t change at all. What will change is whether or not you need passive crossover networks.
The job of a passive crossover is to split the audio signal coming from your amplifier into frequency bands that are suitable for the woofer and tweeter in your speaker set. It should go without saying that the tweeter won’t be able to reproduce mid-bass and midrange information accurately, and the woofer can’t handle high-frequency information. Passive crossover networks use a network of capacitors, inductors and resistors to split up the signal and send it to the appropriate driver.
To this point, we have been talking about component speakers. We can certainly build an amazing audio system that uses coaxial-style speakers. Coax speakers are very common when a speaker location in the dash can accommodate a four-inch driver, and many people choose coaxial speakers for the rear locations in their vehicles as well.
When we design an audio system that will be using a digital signal processor, we can use that processor to divide the audio signal before it is sent to an amplifier. The drawback is that you need additional amplifier channels. The benefit is that we have complete control over the crossover slope and frequency for each driver. This flexibility to adjust the interaction between drivers in adjacent frequency bands allows us to ensure that the output of both drivers sums accurately where they overlap. Done correctly, the transition from one to the other is smoother.
Speaker Placement Considerations
In most cases, we install upgraded speakers in factory locations in the doors. The tweeter is often placed at the top of the door, or in the dash. Depending on your vehicle, this may put the tweeter closer to the listening position, or farther away. Another consideration of installing an audio system in a vehicle is that we sit much closer to the left side of the car than the right. This means that the left-side speakers are perceived as being louder, and we hear the signal from them before we hear the one created by the right-side speakers. The result is a soundstage that is clumped to the left side of the vehicle.
All digital signal processors include the ability to apply a delay to the signal output from each channel. We can use this delay feature, along with some simple calculations, to allow you, the listener, to hear the output of both the left and right speaker at the same time. The effect is much like listening to a high-end home audio system where you sit equidistant from each speaker. Executed properly, your music will appear to come from a virtual soundstage that spans beyond the width of your windshield.
With some additional tuning, we can adjust the arrival time of the entire front stage to compensate for the distance to a subwoofer. When adjusted properly, the sound from the subwoofer will appear to come from the front of the vehicle, assuming you are using premium quality, low-distortion subwoofer.
Digital Signal Processor System Design Amplifiers
We mentioned that sound systems that are designed using a digital signal processor often require additional amplifier channels. Most manufacturers offer four-, five- and six-channel amplifiers, and several even have eight-channel amps. These multi-channel amps are ideal for actively filtered audio systems.
In the simplest of systems, we can use a five-channel amp with a digital signal processor to power a set of tweeters, a set of midrange drivers and a subwoofer. For more complex systems, you may want dedicate midrange drivers on the dash and mid-bass drivers in the door, so you’ll need another pair of channels. If you like having rear speakers, tack on another pair of channels. You may find it ideal to combine a six- or eight-channel amplifier with a dedicated subwoofer amplifier to achieve the correct number of channels and precisely the amount of power you want.
System Equalization
Another huge benefit of using a DSP in the system is that it gives us the ability to equalize the signal going to each speaker to compensate for reflections and resonances in the vehicle. Speakers have different response curves at different angles. As a result, a speaker will seem to sound different depending on where it is installed.
System Flexibility
Another benefit of building a system that includes a digital signal processor is the ability to factor multiple configurations into the design. Many processors include multiple presets that can be accessed using an optional remote control or a simple switch. We could configure one preset to provide the driver with excellent imaging and a second configuration designed to be used when there are multiple people in the car. This second option would remove some of the signal delays. The accuracy and placement of the soundstage would suffer somewhat for the driver but improve dramatically for the passenger.
If you are designing an audio system upgrade from scratch, talk to your local car stereo shop about including a digital signal processor in the system and be sure to include an hour or two of labor in the quote for tuning the system once it’s installed. If you already have an upgraded system, drop into your local mobile enhancement retailer and ask them to demonstrate the benefits of a digital signal processor. When configured properly, a DSP can make your existing audio equipment sound better. We know you will be impressed!
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When you think of the stereotypical car audio system, most people imagine compact cars with large 
The monologue introduction to “Boom Boom Pow” by will.i.am builds to a crescendo from the 45-second mark, peaking with infrasonic information from :50 to 1:03. Content during this time extends solidly down to 7 Hz. There is another drop at 2:18, and the section from 3:13 to 3:42 contains a lot of infrasonic content. If your system is up to the challenge, this track has it all: a solid conventional bass line and enough content below 20Hz to make any true basshead happy!
Often referred to as Bass Check, “Hoods Run Down” by Lil Wyte is a rap song that starts with an introduction and the DJ plays five sequentially lower tones. The first is centered at 41Hz, and most factory sound systems can handle this one with no problem. The second “beat” is at 35Hz, and you are going to need at least a small sub to catch this one. The third drop is centered around 27Hz and will tax premium factory systems and aftermarket systems tuned to boom rather than rumble. Now things are getting fun! The second-to-last tone is centered at 20Hz and is going to be a workout for most vented enclosures. Pay attention; speaker damage may ensue! The last beat is centered around 16Hz. You are going to need serious cone area and power to feel this one with any authority. The rest of the song continues with a standard bassline with information around 30Hz. A good workout for your stereo and a nice gentle massage for the ride home.
Another classic rap track, “3 A.M.” features a steady bass line that extends down to around 30Hz, giving almost any sound system a chance to sound great. Interspersed randomly through the track are bass drops down to the single digits. There is lots of 9Hz content at the :57 and 2:01 marks. These don’t last long, but they are reasonably loud. You’ll hear 10-cycle beats at 0:37, 1:03, 1:54, 2:45, 3:11 and 3:37. There is lots of 50Hz content during these drops, so it might be hard to pick them out, but they are there.
This is more of a demo track than a song. Included on The Great Fantasy Adventure Album with main title themes from movies like Terminator 2, Clash of the Titans, Total Recall and The Abyss, “Jurassic Lunch” is a short 1:11 track at the end of the album. The track starts with birds chirping in the jungle. At the 13-second mark, a series of pulsations centered at 12Hz and 24Hz start. These continue to the 29-second mark, where harmonics are included that provide content above 30 cycles. It’s only then that you realize you are hearing the footsteps of the Tyrannosaurus rex stomping through the Jungle. Around the 39-second mark, you start to hear tree branches breaking with each step, and then at the 45-second mark, the roar of the Rex overpowers the track as he devours his prey. Of course, Kunzel included lots of bone-cracking and crunching around the 51-second mark. The Rex savors his meal from the 51- to 56-second mark, where he rewards himself with a giant burp that peaks with information down to 10Hz at the 59-second mark. This track serves as an awesome demonstration of a true subwoofer system.
This remake of “White Rabbit” by Jefferson Airplane features the required tuned PVC tubing percussion that has made Blue Man Group so unique. Though this track doesn’t share the intense infrasonic peaks of our other suggestions, it maintains an impressive level of 15-cycle content throughout the almost three-minute-long track. There is very evenly dispersed mid-bass energy in this track as well — a great challenge for your door speakers.
Another fun track from The Great Fantasy Adventure Album is the Terminator theme. This haunting track is full of special effects and mechanical sounds that remind listeners of the end scene of Terminator 2 as the machine slowly lowers himself into the mass of molten steel in the refinery. While most of the percussion comes from kettle drums in the 47-48 Hz range, the closing of the track features an explosion that starts at the 3:11 mark and peaks with 11Hz information from 3:14 to 3:16. A fitting ending to a great track.
This track goes back, waaaay back! Scholars think that Bach wrote this classic piece of organ music between 1704 and 1750 (when he died). Even those who don’t listen to classical music recognize this track. Don Dorsey released Bachbusters, a synthesizer-based take on some of Johann Sebastian Bach’s greatest pieces, in 1985. The album took first place on the Billboard classical music chart and has been popular with 
There had to be some dubstep in this list somewhere, right? “Centipede” is a somewhat creepy track that is full of fun bass. While the focus of the bass line is around 40Hz, the track contains content with good output levels down to the 10Hz range. While we doubt most clubs could reproduce this infrasonic information with serious output levels, the sensation of listening to this in a well-designed mobile audio system would be fantastic. It’s also really loud: The VU meters remain pinned at the 0dB mark for the majority of the track.
Another all-time-classic classical recording is Tchaikovsky’s 1812 Overture. This recording is known for its jaw-dropping cannon blasts at the end. When played back on a vinyl record, all but the very best turntable configurations will result in the needle jumping out of the track as the cannons go off. The first five cannon blasts appear at 12:36 into the track. The second and most impressive group begins at 14:41, with the blast at 14:55 containing low-frequency energy that extends down to nearly DC levels. Call it one to two Hertz if you want – it makes no difference.
“Purple Lamborghini” won a Grammy Award for Best Song Written for Visual Media. This rap track contains a bass line that is centered around 38Hz for the majority of the track. But the fun doesn’t stop there: Four times in the track, the bass sweeps from 50 down to 22Hz with impressive output. The video features Rick Ross, Skrillex and none other than Jared Leto in full Joker garb.
“Put On” makes our list with what we’ll call an honorable mention. The track doesn’t dig hard into the infrasonic region but contains four drops that repeat through the entire track. The first is up at 55Hz and is classic rap music bass. The second is at 44Hz and the third is at 36Hz, giving your body a nice massage. The last is centered around 27Hz and will give your subwoofers a good workout. We included this track because the 27Hz bass line appears no less than 22 times in this 5:21-second track.
The second of our three Honorable Mention tracks is “This Means War” by Avenged Sevenfold. This rock track opens with well-recorded percussion and guitar. At the 25-second mark, there is a rumble of thunder with great content down to 20 Hz that slowly fades to the 30-second mark. The remainder of the track only gets down to about 40Hz, but the kick drum is well-recorded and the entire track is well worth listening to.
Another honorable mention is Lorde’s “Supercut.” Though the main bass line remains focused between 40 and 60 Hz for the majority of the track, the section of the song from 2:34 to 3:05 has a surprising amount of information that extends down to 10 cycles at a moderate level.
Winning our “what the heck is that doing there?” award is “Supermarket Flowers” by Ed Sheeran. This track features Sheeran accompanied by a piano for the majority of the track. At the 2:08 mark, a synthesizer comes in to add some a gentle bass line to the track. The lowest notes are 28Hz at the 2:32 mark. While not the infrasonic content we were searching for, this remains a nice surprise in what would be described as a nice song.
Beyond the features and design of a subwoofer, no single factor affects the performance of a subwoofer system more than 
As you can see, above 60Hz, the smaller enclosure is a little bit louder but remains within a decibel or two. Below 50Hz is where things start to vary more. The larger enclosure is 2.15 dB louder at 35Hz and 3.35 dB louder at 25 Hz. While it might not appear dramatic, 3dB is the equivalent of having twice as much power driving the subwoofer. However, this increase in efficiency comes with no thermal power handling penalty.
Once again, above 60Hz, there is minimal difference in the excursion between the two drivers. Below that, the larger volume of air in the big enclosure has less effect on the stiffness of the subwoofer system. The result is the subwoofer moves farther for each watt of power. If you compare the excursion graph to the frequency response graph, the efficiency levels are directly correlated.
The second popular option for a subwoofer enclosure is a 
Now, while most vented enclosures are larger than their sealed brethren, the benefit is often an increase in output that is potentially more than having two subs in a sealed design. In fact, this vented design is louder from 20 to 60Hz than three identical subs in an enclosure that is 50% larger (1.8 cubic feet).
This reduction in cone excursion increases physical power handling and also reduces distortion – as long as you have designed and constructed the vent properly. Vents need to have a large enough area so that air velocity in the vent is kept to a minimum. The mouth of the vent also needs to have a large radius
Bandpass enclosures are called that because they not only act as a high-pass filter but as a low-pass filter as well. A typical bandpass enclosure features two chambers. The woofer is mounted between these chambers. In a single-tuned enclosure (often referred to as a fourth-order bandpass or single- reflex bandpass), one of the chambers includes a vent from which all the sound is created. A benefit of this design is the ability to feed that vent through an opening in a rear parcel shelf or similar to ensure coupling with the interior of the vehicle.
The second bandpass enclosure design is a Double-tuned design where both the front and rear chambers are vented. In a Series-tuned bandpass enclosure, the large rear chamber vent feeds into the front chamber. In a parallel-tuned design, the vents from each chamber feed directly into the listening area. Double-tuned bandpass designs are often referred to a sixth-order or dual-reflex designs.
A quick note on “basic” subwoofer systems. Over the years, we’ve seen a LOT of retailers offer “bass packages” that include a sub, amplifier, enclosure and often a wiring kit. In the majority of these packages, the retailer has paired an inexpensive sub with an inexpensive amp and a sealed subwoofer enclosure to minimize the total cost of the system. When you are limited in 
No single upgrade to an audio system offers a larger improvement in sound quality than the addition of a 
In the simplest of terms, a subwoofer is a large speaker designed to play frequencies below 100 Hz at relatively high output levels. Subwoofers are most commonly available in 10- and 12-inch sizes, but 6.5-, 8-, 13.5- and 15-inch subs are also readily available.
Picking “enough” subwoofer depends on several factors. How loud is loud enough? How much space can you afford to give the subwoofer system? How powerful of an amplifier can your vehicle’s electrical system support? It can be difficult to choose the right sub based on these criteria, especially since different vehicles offer different amounts of cabin gain. Would a single 10-inch sub in a sealed enclosure in the back of a Honda Fit be a suitable solution in a Cadillac Escalade or short-cab Ford F-150?
The next step is to decide 
If you want something truly unique, then ask about including LED lighting in the enclosure. You can choose to have a Lexan or Plexiglas window added and illuminate the interior of the enclosure or add acrylic plastic accent pieces that light up. Upgrades at this level are often combined with enclosures finished with multiple materials – different colors of vinyl can provide amazing cosmetics.
The next step, beyond a simple wooden 
Companies like JL Audio, MTX and Kicker offer subwoofer systems designed for specific models of vehicles. These enclosures are designed to offer impressive performance while minimizing how much space they use. Some companies construct these enclosures from fiberglass in large molds, while others use thick plastics. In most cases, while these enclosures are visible once installed, they are available in materials that match the color of the vehicle interior. An application-specific enclosure is a great way to add amazing bass to a vehicle quickly and efficiently.
You’ll note that we haven’t discussed the specific features of subwoofers that differentiate one from another. This omission is quite deliberate because we will dedicate an entire article to that topic. In the meantime, it is worth discussing the difference between a conventional subwoofer and a shallow-mount design.