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Revisiting Sealed Subwoofer Enclosure Stuffing with SPL Measurements

Sealed Enclosure

A while back, we looked at how adding stuffing to a sealed enclosure affects its performance. It was clear from our measurements that the addition of Dacron lowered the system’s Qtc (Total Q). The original theory was that adding stuffing made the enclosure seem larger and let the driver play louder at low frequencies. Let’s revisit this test and add several acoustic measurements to quantify any changes in efficiency and output.

Results from Our Original Testing

Our original article determined that adding different amounts of stuffing to our 1.358-cubic-foot enclosure lowered the system Qtc. Without stuffing, the Qtc with our audiophile-grade 12-inch subwoofer was 0.9532. That’s a bit high for our liking but offers good efficiency. With 0.25 pound of Dacron added to the enclosure, the Qtc dropped to 0.9148. That’s still on the high side but getting better.

Moving up to a half-pound of stuffing had minimal effect on the driver, and the system stayed roughly the same at 0.919. Cramming another quarter-pound of stuffing into the enclosure made a truly beneficial change. The Qtc was now down at 0.8397. The lower Qtc measurement is better as it results in less resonance and a tighter, more controlled bass perception. In this capacity, stuffing with Dacron does have the same effect as installing the subwoofer in a larger enclosure.

The driver’s resonant frequency in the enclosure barely changed throughout the test. Empty, the system had an F3 of 43.35 hertz. With all the stuffing in place (0.75 pound), the resonant frequency dropped to 41.68 hertz. The difference would be negligible and doesn’t support the claims of stuffed enclosures playing lower.

Sealed Enclosure
The results from our original article on adding stuffing to a sealed subwoofer enclosure.

Round Two of Subwoofer Enclosure Testing

In this test, we’ll use the same enclosure and subwoofer and take several acoustic measurements under strictly controlled conditions. We’ve set the enclosure up in the middle of our lab and placed the Clio Pocket calibrated mic on the floor 50 centimeters in front of the enclosure. This configuration is similar to a typical ground-plane measurement, except the closer proximity to the enclosure will help to reduce the effect the room has on the measurements. A “normal” ground-plane measurement would have the microphone 2 meters from the enclosure. We will continue buying lottery tickets in hopes of financing our own anechoic chamber, but that might take a while!

All measurements are at the same output level. We’ll use 4 volts representing 2 watts of power into the subwoofer’s nominal 4-ohm load. With a drive level any lower than this, the background noise from the HVAC system starts to mess with the very low frequency measurements. Again – anechoic chamber, please!

Sealed Enclosure Stuffing Findings

If you look at the graph below, you’ll see the SPL measurements from the four test conditions. The red trace is the enclosure without any stuffing. The violet trace represents 0.25 pound of stuffing. The black trace represents a half-pound of filling. Finally, the amber trace is 0.75 pound.

As expected, the more stuffing there is, the smaller the bump at the top of the response curve. Why does this happen? Because polyester fiberfill reduces the resonance of the system. With less resonance, the driver returns to rest faster after the signal stops, and less distortion is added to the output.

Sealed Enclosure
Measurements of a sealed subwoofer enclosure with four different amounts of Dacron stuffing.

You’ll notice the difference between no stuffing and the tightly packed enclosure is relatively tiny. Indeed, the maximum difference is a total of 1.4 dB SPL, with the unstuffed enclosure being louder.

I generated a second graph referencing the first three measurements to the fully stuffed measurement. This analysis shows you how much louder the subwoofer is as there is less and less stuffing. While it might be noticeable, the difference is minute.

Sealed Enclosure
Some quick math to show you the difference between enclosure stuffing levels.

Sealed Enclosure Stuffing Summary

Unlike what many “old timers” will tell you, adding a large amount of Dacron (or similar) stuffing doesn’t significantly affect output, especially at lower frequencies. It certainly doesn’t cause the same improvement of the low-frequency production that you’d get from a larger enclosure. One consideration, though: If the crossover point for our subwoofer systems is, or should be, around 80 Hz, then a system with a flatter response will seem to be a bit louder at lower frequencies. With that said, we are talking about less than 1.5 dB SPL, so the whole thing regarding output amplitude is effectively irrelevant.

So, is it worth asking the shop building your sealed subwoofer enclosure to add stuffing? Don’t add anything if you’re a bass head and want the system to play as loudly as possible. If you’re into sound quality and want to reduce distortion around the resonant frequency of the subwoofer system a bit, then go for it. It’s not like the cost of some stuffing is significant.

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.

Filed Under: RESOURCE LIBRARY, ARTICLES, Car Audio

Automotive Headlight Upgrades – Part 2: Terminology

Light Terminology

We talked about headlight bulb styles in the first part of our series on understanding headlight upgrades. In this article, we will briefly explain relevant light terminology to help you understand what lumens, lux, candela and watts mean. Knowing what these terms mean will help you make better bulb upgrade choices – and you’ll be less likely to be fooled by bogus light output claims.

The Importance of Proper Headlights

The forward lighting system on your car or truck is, or at least should be, designed to light up the road in front of your vehicle. The lighting should be bright enough to allow you to see and react to objects in your path safely. If your car needs two seconds to stop from 40 miles per hour, then your lights need to illuminate objects at least 117 feet in front of your vehicle.

Light Terminology
Rally racers add extra lights to their race cars to see better at night. Image: FIA World Rally Championship

The Candela

Long ago, a light source’s output was comparable to the light produced by a typical wax candle. A conventional wax candle produces 1 candela (symbol: cd) of light. It’s crucial to understand that this is the total light output of the light source in all directions. Put another way, no matter what direction you’re looking at a candle from, it produces 1 candela or 1 cd.

Light Terminology – Lumens

A lumen (symbol: lm) is the most commonly used descriptor of how much light a bulb produces. The lumen is the SI unit used to quantify luminous flux. Sadly, it’s also easy for this number to be irrelevant in describing how well you can see in front of you at night.

We have to detour a moment to make a super-technical definition. The term steradian, or square radian, describes a circular area on the surface of a sphere. A sphere (or ball) has a surface area of 4π steradians – or 12.5664 steradians. Expressed another way, 1 steradian is 1/12.5664 of the surface of a sphere. If you have a sphere with a radius of 2 meters, then 1 steradian represents 4 square meters on the surface of that sphere. It should be no surprise, then, that the total surface area of the sphere is 50.265 square meters and that 1/12.5664 of that is 4 square meters.

Light Terminology
A graphical representation of 1 steradian. By Andy Anderson – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=84111964

OK, now back to the lumen. One lumen equals 1 steradian of a sphere illuminated by a light source that outputs 1 candela. Think of this description as that of a flashlight pointing at the inside of a sphere. If the flashlight produces 1 candela of output and all the light is focused onto an area the size of 1 steradian, the result is 1 lumen of illumination.

If we back up and consider the light source to be isotropic or equal in output in all directions, then the light source must produce 12.5664 candelas to produce 1 lumen of flux over an area of 1 steradian. In theory, you need about 12 and a half candles to produce 1 lumen of luminous flux on an area of 1 steradian of a sphere with a radius of 1 meter. A 1-candela light source would produce 1/12.5664 of a lumen on the same area, or 0.0796 lumen.

When professional light bulb manufacturers measure a light source’s output, they use an integrating sphere. The inside of the sphere has a pure white reflective coating. The goal of the sphere is to average out any bright or dim spots to create an even distribution of light through the assembly. A calibrated electronic sensor measures the light level in the sphere to calculate the total light provided by the light source.

Light Terminology
A light-integrating sphere accurately measures the output of light sources. Image: Pro-Lite Technology Ltd.

When a company like Cree or Samsung creates an LED, they describe the output of the LED COB in lumens, or more accurately, lumens per watt (LPW). A high-quality LED COB produces about 133 lumens of output per watt. Most high-power LED COBs have a maximum power handling of about 3 watts. This efficiency means a 1-watt single LED COB can produce about 400 lumens. An aftermarket LED headlight bulb that uses one of these LED COBs on each side would produce 800 lumens. Compact assemblies with three or four COBs assembled into a single housing are available. These 12-watt LED COBs produce about 1,500 lumens. If a 12-watt COB is on each side of the bulb, it would theoretically produce 3,000 lumens.

Light Terminology
The ATOM bulbs from Lumens High Performance Lighting are rated to produce 3,000 lumens of “total raw light output.”

Light Terminology – Lux

Unfortunately, having an incredibly bright light bulb doesn’t directly correlate to proper road lighting. Understanding lighting terminology is crucial. The plastic lens on the front of the light assembly blocks a small amount of light. The design of the reflector at the back of the light assembly plays a considerable role in determining where that light projects. In a worst-case example, you could have a 3,000-lumen headlight bulb in a black box, and no light would be visible and, as such, the bulb would produce 0 lux.

Lux (symbol: lx) is the SI unit of luminous flux per unit area. The lux is the unit that quantifies light intensity as the human eye perceives it. Thankfully, unlike the whole steradian thing (sorry about that), the lux uses an area of 1 square meter. One lux equals the illumination of 1 lumen of light over 1 square meter. If all the light from a 100-lumen light source illuminates 1 square meter, the light intensity would be 100 lux.

Light Terminology

How do all these numbers relate to headlight bulb ratings and how well you can see the road once the sun sets? With modern LED headlights like you’d find on an Audi, Mercedes-Benz or Genesis, the optics are designed to work specifically with the LED COBs light emission pattern. Every aspect of the light source is optimized to produce a specific beam pattern on the road. If you upgrade your headlights from a halogen bulb, HID or LED aftermarket bulbs must work with the existing reflectors and lens. The upper cut-off for the low beams must be accurate, and the light distribution pattern needs to remain the same. These criteria are crucial for your safety and the safety of those you share the road with.

Light Terminology
The Genesis G70 sedan features LED headlights. Image: Genesis.com

Companies such as Rigid Industries and Baja Designs that manufacture aftermarket off-road and work light solutions provide light output levels in lux. Both companies describe the distance from the light where they produce a fixed illumination level. Of course, the two companies don’t use the same descriptions, so you have to do some “figurin’” to determine which is best for your application.

Light Terminology
Extreme Audio near Richmond, Virginia, upgraded this Mercedes-Benz Sprinter with a Baja Designs LP6 PRO amber light pod set.

Watts, Power and Light Output

The SI unit watt describes the work done over a fixed time – usually one second. One amp of current flowing through 1 ohm of resistance in electrical circuits produces 1 watt of heat energy. To calculate watts in direct current (DC) circuits, you can multiply the voltage times the current. If you apply 12 volts to a light bulb and 2 amps of current flow through the circuit, then the work done is 24 watts.

When all we had were halogen bulbs, a bulb that drew more energy would typically produce more light. The low beams on most cars and trucks used 35-watt bulbs, and many used 55-watt bulbs for the high beams. Unfortunately, those numbers don’t correspond to light output regarding HID and LED replacement bulbs. A 15-watt LED bulb produces significantly more light than a 35-watt halogen bulb. Many HID kits were marketed with 35- or 55-watt ratings, making three or four times as much light as halogen units. The bottom line is that looking at HID or LED headlight upgrades and comparing them by the energy they consume won’t be effective.

Light Terminology
Morimoto Elite HID kits are available in 35- or 50-watt configurations. Image: The Retrofit Source.

Research Your Headlight Upgrades

A forward lighting system that functions accurately and reliably is the top vehicle safety consideration once the sun sets. If your headlight bulbs are worn out, the lenses are foggy, or the lights aren’t aimed properly, your risk of getting into an accident increases dramatically. Now that you understand automotive headlight terminology better, you can make better purchasing decisions. Drop by a local specialty mobile enhancement retailer today to find out about the upgrades they have available to improve the lighting system on 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.

Filed Under: RESOURCE LIBRARY, ARTICLES, Lighting

How Do I Know if My Car Audio DSP Is Adjusted Properly?

DSP Adjustment

It should go without saying that a car stereo system designed around multiple amplifier channels and a DSP is the easiest way to get great sound in your vehicle. The technician working on your vehicle has complete control over the output level, sound arrival time and the frequency response of each speaker in the system. The result should be a sound system that is as optimized as possible – assuming the calibration process is executed properly. There are still many misunderstandings about what a DSP can and can’t do. This article will provide a few things to listen for to help you determine whether your DSP has been adjusted properly.

What Is a DSP?

What is a digital signal processor? Though we have covered the topic extensively, we’ll offer a quick “too long; didn’t read” for those new to our magazine. A DSP is a computer chip optimized to perform many calculations quickly and repeatedly on a sequence of digital samples. These samples are typically a digital representation of an analog signal. In the case of our car audio systems, the analog signals are the left and right channels of the audio recording. DSPs are common in other applications, including video processing and radio frequency transmission analysis. Modern recording studios and live venues use DSP-based mixing consoles.

DSP Adjustment
Escort’s M14 radar receiver uses an Analog Devices Blackfin DSP to pick out police radar signals and reject noise.
DSP Adjustment
The Vista One Carbon is a high-end DSP-based mixing console ideal for live, broadcast and studio applications.

How Is a DSP Used in Car Audio Systems?

In car audio applications, a DSP serves many purposes. A DSP can combine signals from multiple sources, adjust levels, apply equalization and frequency filtering, and add delay to a signal. In short, it helps the technician connect to a factory-installed stereo, optimize the signal to each speaker and compensate for your vehicle’s acoustics.

If your car stereo uses an aftermarket head unit, your installer will likely connect a DSP directly to the radio’s preamp outputs using RCA cables. Suppose you have a vehicle that uses a digital interface between a factory-installed head unit and an amplifier like A2B, MOST, AVB or a SP/DIF connection. In that case, you may have an interface that feeds a digital signal to your DSP over a fiber-optic cable. Finally, many audio system upgrades require recombining signals from multiple factory-installed amplifier channels and removing any processing to create a full-bandwidth signal. A high-quality DSP can help with this.

After the audio signal is in the DSP, the first order of business is to route that signal to the appropriate output channels. You don’t want the left-channel signal from the radio going to the right-side tweeter. Also, you’ll likely want the signals from both the left and right channels going to the subwoofer signal. All reputable DSPs have a signal-routing mixer to perform these tasks.

Next, the technician configuring the system must filter the signals to each speaker. You don’t want bass information going to a tweeter or midrange information to a subwoofer. A properly trained technician knows which high- and low-pass crossovers to apply to the speakers in your vehicle based on their design, directivity characteristics and the speakers that are operating in adjacent frequency ranges.

The last step is for the technician to use a calibrated microphone system and measure each speaker’s acoustic output at the listening position. Using that information, they can adjust the equalizer to smooth out any peaks or dips caused by reflections in the vehicle. Finally, the output level of each speaker is adjusted to ensure that the transition from one driver to another is smooth.

DSP Adjustment
The Audison bit-Tune is an acoustic real-time audio analyzer that uses a microphone array to capture accurate information.

Auditioning Overall Tonal Balance

While a DSP often seems like some mystical black box of audio voodoo, they are quite simple devices. Yet they do have an extensive list of functions and require training and a thorough understanding of the laws of physics to implement properly. A DSP is effectively mandatory if your goal is realism and accuracy from a car audio upgrade. That brings us to the question, how would a consumer know whether the DSP in their car or truck is adjusted properly?

The first thing to listen for is a smooth frequency response. There shouldn’t be emphasis or deficiencies in any frequency range. For example, if the letters S and T seem overly prominent, the equalizer bands around 3 and 5 kHz might need adjustment. If voices are boomy or chesty, there might be too much output around 200 Hz. The bottom line is that if every genre of music doesn’t sound right, then the DSP needs more adjustment.

An idea offered by long-time car audio competitor Harry Kimura is to listen to a well-engineered piano recording. The lowest note on a piano has a fundamental frequency of 27.5 hertz. That’s well below what an audio system without a subwoofer can reproduce with any authority. The highest note has a fundamental frequency of 4.186 kHz. It’s crucial to remember that each note includes several octaves’ worth of harmonics to give the instrument its “sound.” There’s still important audio information beyond 12 kHz from this 4.186 kHz note. If someone plays a scale from the highest to the lowest notes, each should be reproduced by your car audio system with the same volume or intensity. If something is too loud or quiet, the DSP’s equalizer needs adjustment.

DSP Adjustment
The Rockford Fosgate DSR1 DSP has eight output channels and includes an iDatalink Maestro AR interface.
DSP Adjustment
The bit Nove DSP from Audison includes six analog inputs, two digital inputs and nine outputs for extremely flexible audio system design.
DSP Adjustment
The compact ARC Audio PSM-Pro DSP includes audio processing features typically found only on high-end models.

What about the Bass?

We can confidently tell you that a car audio system that plays the bottom two octaves of a piano at the same level as middle C won’t be much fun on the road. It might be super-accurate, but the bass will be drowned out when competing with wind, road and exhaust noise. The subwoofer in your car audio system should be 8 to 12 dB louder than the midrange for the system to be enjoyable while in motion. If you’re a basshead, fill your boots!

The Source of Sound

The second criterion to listen for is staging and imaging. Imaging refers to the ability of an audio system to render the sound of specific instruments accurately on a virtual soundstage. Think of yourself listening to a live acoustic music performance. A four-piece jazz band with a drummer, pianist, upright bass player and lead singer would be a perfect example. No matter where you sit in the audience, the sound source from their instruments is easy to detect. You’d know if the lead singer walked across the stage while performing, even if you didn’t see them.

In your car audio system, you should be able to pick out the specific instruments in a well-recorded track. If the singer and drummer were in the center of the stage, they should sound like they are in the center of the dash or windshield. If the bassist is on the left, then the sound should come from in front of the steering wheel. If the piano was on the right side of the stage, it should sound like it’s coming from the airbag on the right side of the dash.

Here’s a good example of what you should hear if the system has a solid soundstage and good imaging. “Listen to Money for Nothing” by Dire Straits. At 1:12 into the track, Pick Withers’ drums pan from the far right to the center. Each drum appears to have a dedicated microphone, and their signals are panned to fill the soundstage. As he hits different drums, the sound source should move. The system isn’t configured correctly if the drums are a big blurry mess.

DSP Adjustment
Dire Straits’ Brothers in Arms album is a popular choice for auditioning high-end audio systems because of its excellent recording quality.

How Do You Want Your System to Sound?

The above description assumes you wanted your car audio system calibrated as though you were in the audience. The other option is to have the system configured as though you were on stage with the performance. In this scenario, the sound in your car would be more like what you’d hear when wearing headphones. The vocals and drums might be in the middle of your head. The bassist would be to your left, and the piano to the right. Some call this a “club” sound, where music comes from around you. The product specialist you’re working with to design your mobile audio system should ask you about your listening preferences during the client qualification process.

A car audio system with high-quality amplifiers and an excellent DSP will offer better focus for each instrument. We call this better imaging. We’ve heard many factory-installed audio systems where the center-stage vocals came from a space the size of a large pizza. The best aftermarket systems we’ve listened to reproduced that same track from a point in space the size of a tennis ball. It’s not just equipment that achieves this goal. The technician adjusting the DSP needs to know what to look for and what to ignore in the acoustic measurements to get this right.

DSP Adjustment
In the audience or on the stage – the shop installing your DSP must ask how you want the system configured. Image: mcmillanpazdansmith.com

What Can’t a DSP Fix?

There are some product and installation issues that a DSP can’t resolve. If you’ve chosen speakers with resonance and distortion issues, the DSP can’t remove that harmonic information added to your music. If you find the high-frequency response harsh or fatiguing, you are probably hearing harmonic distortion from your speakers. The only solution is to switch to better-designed speakers that include distortion-reducing designs and technologies.

The same goes for sloppy midbass. If a rim hit on a tom drum sounds like a thud or bump rather than a sharp crack, you may have a speaker or amplifier distortion problem. Audio components (primarily amplifiers and speakers) with high levels of intermodulation distortion typically cause muddiness or unwanted warmth in the lower midrange frequency range. No amount of DSP adjustment can fix this.

DSP Adjustment
An example of an exceptional intermodulation distortion measurement from a DSP-equipped car audio amplifier.

Learning About High-Quality Audio Systems and Accurate DSP Adjustment

This article kicks off a series on how to listen to audio systems and components from a technical perspective. We’ve noticed that many consumers think certain products “sound really good” when they are, at best, mediocre. We hope that educating everyone about what to listen for when auditioning speakers and listening to demo vehicles will help people purchase solutions that offer the best performance possible for their investment. As you learn what high-quality car audio upgrades sound like, use that information when working with a local specialty mobile enhancement retailer to pick the best upgrades possible.
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.

Filed Under: RESOURCE LIBRARY, ARTICLES, Car Audio

Do I Need a Line Output Converter To Add a Car Amplifier?

Output Converter

We’ve talked at length about how car audio line output converters work and have even compared a few to see which sound best. We skipped over a discussion on whether a car audio amplifier upgrade needs a line-output converter. Let’s dive in!

What Does a Line Output Converter Do?

A high-quality line output converter serves three purposes. First and foremost, it can reduce the voltage from a radio or amplifier output to something acceptable on the preamp input of an amplifier. Second, it converts a bridge-tied load (BTL) signal to a single-ended signal that works with all amplifiers. Thirdly, it can provide a remote turn-on signal to activate an amplifier when you turn on a factory radio.

Most car audio amplifiers can only accept up to 5 or 6 volts on their preamp inputs. This voltage is equivalent to the output of an amplifier that produces a maximum of 9 watts of power into a 4-ohm load. Since most car radios can produce at least 20 watts, equivalent to just under 9 volts of signal, we need circuitry to reduce that level and not over-drive the input stage on the amplifier.

All car radios we’ve tested use the bridge-tied load speaker output configuration. This speaker driving method allows a radio to provide more power than a single-ended design without needing a dedicated switching power supply. If you’ve asked a technician to install an inexpensive or poorly designed amplifier, it will likely need a single-ended signal.

If you have a factory-installed radio in your car, truck or SUV, the chances of a wire going live only when the radio is on is quite unlikely. You’ll need a way to tell the new amplifier when it’s time to wake up and get to work. A good-quality line output converter can do that.

Modern Amplifier Features – Automatic Turn-On Circuits

If you look at most high-quality amplifiers on the market, you’ll see they include some sort of remote turn-on detection circuitry. Some of these circuits monitor the input connections on the amplifier for a presence of an audio signal. This is usually called a signal-detect turn-on circuit. Others look for the 55 to 6 volts of DC offset found on the output of BTL amplifiers as would be used in a car radio. These circuits are called DC offset or BTL detection solutions.

Output Converter
The DPower 1 from Hertz includes their ART Auto Turn On/Off Circuitry to simplify installation.
Output Converter
The XM-4ES from Sony’s Mobile ES line includes a switch that will activate the remote turn-on detection feature.
Output Converter
Rockford Fosgate’s Prime-Series R2-300X4 four-channel amplifier includes an Auto Remote Turn-On option.
Output Converter
X2-Series amplifiers from ARC Audio include both signal and DC offset detection remote turn-on circuits for maximum installation flexibility.

Car Audio Amplifier Differential Inputs

Decades ago, car audio amplifiers used the same single-ended RCA input circuitry as a home stereo receiver. Reputable car audio equipment manufacturers realized that switching to balanced differential circuitry inputs dramatically reduced the chances of ground loops that could cause unwanted engine noise in an audio system. This balanced input circuitry also helps eliminate any unwanted noise that the interconnect cables might have picked up as they run through the vehicle.

We’ve written a few detailed articles on the importance of balanced differential inputs and how to test an amplifier to make sure it has this feature. Don’t bother with amplifiers that don’t use differential inputs. You’re only asking for headaches and noise.

Too Much Preamp Voltage

It’s not often you hear the phrase “too much voltage” in the context of car audio discussions. With that said, if you feed too much signal to the RCA inputs on an amplifier, both the input and output can add huge amounts of distortion to your audio system. This distortion is called clipping.

Designing a car audio system upgrade requires an understanding of how the factory-installed audio system works. Your installer might need to take frequency response and amplitude measurements before recommending products. Some factory-installed subwoofer amplifiers can produce just shy of 40 volts of signal.

If you’re shopping for an amplifier to add to a factory-installed radio or amplifier, choose one that can accept a wide range of voltages. Some amplifiers have dedicated speaker-level input terminals. Others have a switch that attenuates the signal on the RCA jacks. Some DSP-equipped amplifiers have digitally selected input voltage ranges.

Output Converter
The Audison Forza AF M4D four-channel amplifier can accept up to 22 volts of signal on its speaker-level inputs.
Output Converter
Sony’s Mobile ES Amplifiers will accept up to 16 volts on the RCA jacks when set to their high-voltage range.
Output Converter
Rockford Fosgate’s Punch-Series P600X4 amplifier can accept up to 12V on the RCA inputs without any switches or adapters.
Output Converter
The Blackbird DSP amplifier from ARC Audio will accept up to 32 volts on the RCA inputs. Four input ranges are selectable in the ARC DNA software.

Questions To Ask When Purchasing Audio Upgrades

If you want to add an amplifier to your car audio system, you’ll want to ask the product specialist you’re working with some questions. Aside from everything we’ve suggested in our Buyers Guides, you need to know what accessories they plan to use for the installation. If they say you need a line output converter, ask what it would cost to move up to an amplifier that can accept the full signal from the source unit and turn itself on and off automatically without any adapters. The chances are good that the higher-quality amplifier won’t just simplify the installation but will likely sound better. If they insist a line-output converter is still required, ask 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.

Filed Under: Driver Safety, ARTICLES, Car Audio, New Category Name, PRODUCTS, RESOURCE LIBRARY, UTV Audio, Vehicle Security, Vinyl Graphics, Vinyl Wraps, Wheels and Tires, Window Tint

How Is the Power from My Amp Divided Between My Subwoofers?

Amp Power

We see a lot of questions like “My car audio amp can produce 800 watts; how much power does each of my subs get?” If you aren’t versed in the calculation basics of Ohm’s law, the answer might not be intuitive. Let’s dive into the math and logic that will let us calculate how the power from an amplifier is distributed through multiple speakers or subwoofers.

How Much Power Does an Amplifier Produce?

Without going off about the unimportance of power production versus amplifier quality, we should discuss what determines how much power an amplifier can produce. Most car audio amps use a switching power supply that is designed to chop up and boost the 12 to 14 volts from the battery and alternator, then regulate it to fixed DC voltages that drive the output devices in the amplifier. We refer to these as rail voltages, and they determine the maximum voltage available to the speaker terminals and, ultimately, the speakers or subwoofers.

If we use the example of an amplifier with +30- and -30-volt rails, we have a maximum theoretical voltage of 60 volts that we can apply to the speaker. Ignoring some losses through the output devices themselves, this amp could provide 900 watts into a 4-ohm load. The formula to calculate power given voltage and resistance is P = V^2/R.

Unless the amplifier uses a stiffly regulated power supply design, the rail voltages are typically a fixed multiple of the supply voltage. We’ll ignore some losses and say 30 volts is 2.08 times the supply voltage of 14.4 volts. If the supply voltage drops to 12 volts, our rail voltage would then drop to 25 volts, and we’d only have 50 volts we could use to drive a subwoofer. Our maximum theoretical power is now only 625 watts. This example highlights the importance of ensuring that the most possible voltage is delivered to your amplifier and why you should never skimp on power wiring.

How Amplifier Power Is Divided into Multiple Subwoofers

Our example so far has discussed a single 4-ohm load. What if we have two 8-ohm subwoofers wired together to the amp? How much power can it produce? The answer depends on how the subwoofers are wired. If the subwoofers are wired in parallel to get a net load impedance of 4 ohms, then the amp would produce 900 watts – the same as with a single 4-ohm load. Because both loads are identical, that 900 watts of output is shared evenly between the drivers, with 450 watts going to each.

Now, what happens if we decide to wire the subwoofers in series? An 8-ohm subwoofer wired in series with another 8-ohm subwoofer gives us a net load impedance of 16 ohms. Our amplifier can only produce 156.25 watts into a 16-ohm load. As both subwoofers have the same impedance, the power to each sub is divided evenly, with each receiving 78.125 watts. It’s very unlikely that we would want to run an amplifier at 16 ohms, even though it might be quite efficient.

The amount of power an amplifier produces depends on the maximum unclipped voltage it can produce on the speaker outputs, the impedance of the speakers connected to the amp, and how much current the amplifier can supply to the speakers. Why is current a consideration? What if we connect a 2-ohm subwoofer to our example amplifier? Theoretically, the amp should be able to provide 1,250 watts. In order for this to happen, the amplifier needs to be able to supply 25 amps to the load. That formula is I = P ÷ V, where I is current in amps, P is power in watts and V is voltage. For a well-designed, high-power amplifier, 25 amps isn’t an unreasonable amount of current.

What happens if we connect a 1-ohm load to our amp? The theoretical power jumps to 2,500 watts, and the amplifier would need to be able to supply 50 amps of current to the load. If you’ve looked at amplifier specifications where an amplifier’s power output capabilities don’t roughly double as the load impedance is divided by two, it’s likely because the amp can’t provide the required current into the lower impedances.

Amp Power
Four ARC 8 subwoofers powered by an X2-1100.5 by Speed of Sound in Memphis, Tennessee.

Why the Confusion about Amp Power Ratings?

Over the decades, we’ve been taught to think that amplifiers double their power when the load impedance is cut in half. An amp that produces 300 watts into 4 ohms should produce 600 watts into 2 ohms and 1,200 watts into a 1-ohm load. The massive “cheater” amps that were popular in the 1980s and ’90s were often rated similarly to this. However, things have changed significantly.

Let’s look at an example of a modern high-quality subwoofer amplifier like the Rockford Fosgate T500-1bdCP. This amp is rated to produce 300 watts into a 4-ohm load, 500 watts into a 2-ohm load and 500 watts into a 1-ohm load. We can tell from the 4-ohm rating that the amp likely has rail voltages of roughly plus and minus 17.5 volts. Knowing how Rockford Fosgate under-rates their products, the rails are likely running at 19 volts, and that amp would produce roughly 360-ish watts into a 4-ohm load. Nevertheless, let’s stick with the 17.5-volt rails for this discussion. Running a 2-ohm load should then produce just over 600 watts. It’s clear that current delivery into the lower impedance is the limiting factor if the amp is rated for 500 watts. Our math says the amp is limited to about 17.5 amps of current into the speaker load. That’s why the amp doesn’t produce more power into a 1-ohm load.

Amp Power
Three ARC Audio SW10 subwoofers powered by a 1,000-watt ARC 1000.2 amp. Each sub gets 333 watts of power.

Current-Limited Amplifier Design Considerations

Why would a manufacturer of high-quality audio products make a design decision to limit how much current one of their amplifiers can produce? The first consideration is heat management. We’ve tested many Rockford Fosgate amplifiers in the past few years. Their high-mass heatsink designs typically allow their amplifiers to run at maximum output continuously for at least 30 minutes if not more.

While 30 minutes doesn’t seem like a long time, for car audio amplifiers, that’s an amazing performance. We’ve seen compact amplifiers from supposedly reputable brands that overheated and shut down in less than three minutes at their maximum undistorted output. Some Brazilian amplifiers we’ve tested shut down in less than two minutes at full power. Reliability is as important as audio quality – you don’t want your music to stop playing because a poorly designed amplifier overheats.

The second reason for the limited-current design is that the output when driving a 4-ohm load is higher. In a classic design that is closer to doubling its power, the amp would only make 125 watts into 4 ohms if it made 500 watts when driving a 1-ohm load. Amp design is much like speaker design in that you have to trade one performance factor for another. As such, it’s not really a “current limited” design; it’s just optimized in a different way than the car audio industry is used to.

Amp Power
The T500-1bdCP not only sounds great, but its thermal management helps ensure reliable operation.

Guidelines for Amplifier Power Distribution

Here’s the takeaway in terms of figuring out how much power each subwoofer or speaker connected to an amp will receive. First, determine what your net load will be to the amp. Our article about “Ohms and Loads” can help you with that. Next, look at the amplifier’s published specifications to determine how much power the amp should make. If the specifications aren’t compliant with the CTA-2006-D standard, be wary of their accuracy. Finally, divide the expected power from the amp evenly among the subwoofers connected to the amp.

The above comes with a caveat: All the speakers or subwoofers must have the same impedance. We strongly recommend not mixing and matching drivers with different impedances on the same amplifier channels.

A single 4-ohm subwoofer on our T500-1bdCP would receive 300 watts. A pair of 8-ohm subs wired to a 4-ohm load would result in the amp producing 300 watts, and each driver would get 150 watts of power. If we run a single 2-ohm sub on the amp, it would get 500 watts. If we ran two 4-ohm subs wired in parallel, the amp would produce 500 watts, and each subwoofer would get 250 watts of power. A single 1-ohm sub would get 500 watts. A pair of 2-ohm subwoofers wired in parallel would get 250 watts each. Four 4-ohm subs wired in parallel would result in the amp producing 500 watts, and each sub would get 125 watts.

One last word of advice: Loading your amplifier down to lower impedances in hopes of it making more power will dramatically reduce its efficiency and likely shorten its lifespan.

Upgrade Your Vehicle with a Subwoofer System Today!

We’ll circle back to the beginning of this article to remind everyone that power production has no correlation to audio system quality. You could have a 2,500-watt amplifier, but a better-designed 1,000-watt amplifier might sound better and produce bass that is more accurate.

If you have several subwoofers and want help choosing a great-sounding amp for them, drop by a local specialty mobile enhancement retailer and find out about the solutions they have available. They can explain the options for wiring the subwoofers you have or suggest solutions that will offer amazing performance.

Lead-In image credit: Thanks to Bing from Simplicity in Sound in Milpitas, California, for providing the photo of the four Sony Mobile ES XS-W104ES subwoofers.

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.

Filed Under: RESOURCE LIBRARY, ARTICLES, Car Audio

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