When choosing a subwoofer system for your car or truck, picking the right products can be the difference between accurate and musical bass or a sloppy, boomy mess. Over the decades, small subwoofers have gained a reputation for being described as faster than those with larger cone diameters. Is woofer speed a thing? Can we measure it? Don’t fret; we’ll explain what you’re hearing.

Subwoofer Diameter vs. Frequency Response

Each high-quality subwoofer on the market is optimized to play a certain range of frequencies. For most companies, the engineers balance the design so that there is a good mix of efficiency and low-frequency extension.

Changes to the weight of the woofer cone and voice coil will dramatically affect how low a speaker will play. The graph below shows a 6.5-inch subwoofer and a 6.5-inch midrange, both with similar power handling ratings and excursion capabilities of about 9 mm.

The subwoofer output is down 3 dB at about 79 Hz, where the midrange starts to roll off at just over 130 Hz. The subwoofer cone assembly weighs about 50 grams, whereas the midrange cone assembly is about 20 grams. As is clearly evident, a heavy cone assembly will play lower, but you sacrifice efficiency. In order to play bass frequencies at high levels, you need speakers with more surface area. This is one of the main reasons why subwoofers are typically quite large.

The graph below shows the output of five different-size subwoofers from the same brand. Each subwoofer in this simulation is getting 150 watts of power.

It’s clear to see that efficiency increases as the subwoofer size gets larger. What’s harder to see in this graph is that the low-frequency cutoff gets lower as the subwoofer size increases.

The graph below shows the same five subwoofers with their outputs normalized to the same level. The -3 dB points are 80 Hz for the 6.5-inch, 85 Hz for the 8, 59 Hz for the 10, 54 Hz for the 12, and 46 Hz for the 13.5-inch woofers.

Frequency Response vs. the Perception of Speed

Maybe you’ve heard stories and jokes about someone building a system with a 15-inch sub for deep bass and a pair of 10-inch subs for “fast bass.” If all the drivers are being used below 80 Hz as subwoofers, then there’s no need to mix and match sizes.

If you’re listening to a recording of a drum kit and are hoping for a perfect recreation of the original sound, you need a subwoofer system that plays flat to just under 40 Hz to capture the fundamental of a kick drum. To play the floor tom accurately, your subwoofer needs to play down to about 60 Hz.

Imagine if you cut off the subwoofer at 60 Hz with a steep high-pass filter and attempted to play the kick drum recording. It would sound more like the tom with more emphasis on higher-frequency content. This is what happens when you compare the output of a small subwoofer with a larger one where the system hasn’t been equalized to deliver the same response. You won’t hear as much deep bass from the smaller speaker, so there will seem to be more emphasis on higher-frequency instruments.

This is the same reason why sealed (acoustic suspension) subwoofer enclosures are perceived as being “tighter” than vented (bass reflex) enclosures. The vented enclosures play louder and lower, changing the overall balance of the system.

Speaker Speed – What’s That?

In absolute terms, a small speaker can move faster than a larger speaker. This is the reason we have large woofers and small, lightweight tweeters. A speaker’s “speed” limit determines its upper-frequency response limit, not how accurately it can reproduce low frequencies. You’d never use a 12-inch subwoofer as a tweeter. So, yes, a big sub isn’t “fast enough” to be used as a tweeter. However, if you shave off a bunch of weight, it can move back and forth faster, and it becomes more efficient. Many PA systems and pro-sound speakers use 12-inch midrange drivers.

The Importance of Proper Equalization

When a professional installer finishes an installation, he or she will usually set the equalizer on a DSP as one of the final steps. Assuming the subwoofers in the system have the excursion capability, and there’s enough amplifier power, they will tune the system to deliver flat bass response, usually down to 30 Hz. In a scenario like this, most subwoofer systems, even with different-sized speakers (not in the same system, please), will sound similar. So, is subwoofer speed a thing? No, it’s isn’t. If you try to use a subwoofer as a midrange, well, then, you have system design problems.

If you’re planning on upgrading your car audio system, drop into your local specialty mobile enhancement retailer and talk with them about picking the best subwoofer for your car or truck. They can help you choose a size that will deliver the low-frequency output you want for the space available in 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.

For decades, stereo and multichannel amplifiers have offered the option of bridging to deliver significant power to a single speaker. Whether you refer to it as bridging, a bridge-tied load (BTL) or strapping, the process is the same. Curious how it works? Read on and we’ll explain.

How Most Stereo Car Audio Amplifiers Work

If you were to look at the signals on the positive and negative terminals of one channel versus the other, you are likely to find that they aren’t the same.

In amplifiers that are bridgeable, a popular configuration is to have the Left Positive and Right Negative speaker connections connected to the ground plane (a virtual ground, not the same as the chassis ground) inside the amp. The other two connections receive audio signals from the output devices.

When the signal on the Left Negative speaker terminal on the amp in the image above moves positive, the speaker will cone will move inward. When the signal on the Right + speaker terminal on the amp moves negative, that speaker will also move inward.

Common Amplifier Bridging Configuration

When your installer wires a single speaker to your amplifier in a bridged configuration, he or she only uses the terminals with signal on them. Because the signal on one channel is inverted relative to the other channel, the voltage present across the speaker terminals has the potential of being twice what is available on a single channel.

How Much Power Does a Bridged Speaker Receive?

The amount of power an amplifier produces is determined by the voltage the amp can produce and the impedance of the connected speaker. This statement assumes that the power supply in the amp can provide adequate current to the load.

In our example amplifier, let’s make the assumption that the positive and negative voltage rails are set at +21 volts and -21 volts. The output voltage on each channel can swing between plus and minus 20 volts relative to ground. The maximum power this amplifier can produce per channel when connected to a 4-ohm speaker is calculated using the maximum output voltage squared, divided by the load impedance. In this example, we have 20 volts squared divided by 4 ohms. This works out to 100 watts.

If you have a 4-ohm speaker wired in a bridged configuration, it can receive a maximum of 40 volts. This is because the signal on the positive speaker terminal goes in the opposite direction as the signal on the negative terminal. If we apply the same math, we get 40 times 40, divided by four, which is 400 watts.

What’s With Amplifiers ‘Seeing’ a Load?

You will find that most people in the audio industry refer to amplifiers “seeing” a load. In our original two-channel stereo wiring configuration, each channel has a single 4-ohm speaker connected to it. As such, each channel sees a 4-ohm load. When we bridge an amplifier, you will note that the minimum impedance for this configuration is double that of each individual channel. Our model amp can drive a 4-ohm load for each channel, but only a single 4-ohm speaker when bridged. Have you ever wondered why?

While amplifiers are designed to increase voltage, the amount of current their power supply can pass to the output devices is often a limiting factor. If we look at a single channel of this amp when connected to a 2-ohm load, the amp needs to provide 10 amps of current to the 2-ohm speaker when the output is at 20 volts. If we were to wire that 2-ohm speaker in a bridged configuration, we now have a maximum of 40 volts across its terminals, and we’d need 20 amps of current from each side of the amp. If the amp isn’t capable of delivering 20 amps per channel, it will either distort, overheat, go into protection or become damaged. If we wire a 4-ohm speaker in a bridged configuration, each channel only has to produce 10 amps of current.

Audio Signals When Bridging an Amp

For a speaker connected in a bridged configuration to function optimally, you will want to make sure that the audio signals going to the left and right channels are identical. Many high-quality amplifiers will have a mode selection switch that will let you select from Stereo, L+R or Mono operation. In the Stereo setting, the signal from the left RCA input goes to the left output channel, and the right RCA input goes to the right output channel. When you select L+R, the signals from both the left and right inputs are mixed together inside the amp and sent to both channels. Finally, in most applications, the Mono option uses only one of the input terminals and feeds that signal to both speaker outputs.

Bonus Amp Information

Back in the ’80s and ’90s, most car audio amplifiers were quite large. They were designed to produce lots of current because, well, size and heat weren’t an issue. When you connected a single 4-ohm speaker in a bridged configuration, most of these amplifiers would produce roughly four times as much power as that speaker would receive if connected to a single channel.

As amplifiers have become smaller, the size of their power supplies has decreased dramatically. As such, many compact amplifiers can’t deliver the current required to quadruple power. You’ll see ratings like 65 watts per channel when connected to a 4-ohm speaker, but only 95 watts per channel when driving 2-ohm speakers. In this example, the amp would only produce 190 watts when bridged as opposed to the 260 watts (four times 65 watts) you might have hoped for. This doesn’t make the amp necessarily sound worse; it’s simply a trade-off based on the desire for smaller chassis sizes and lower prices.

Upgrade Your Car Audio System with a Bridgeable Amplifier

If you’re considering upgrading your car audio system with a subwoofer and you have a two-channel amplifier, your installer is likely to choose to wire that sub in a bridged configuration. In most cases, with a high-quality amp, you’ll get all the power you need to crank your music up to concert volume levels. If you’re shopping for an amp, drop by your local specialty mobile enhancement retailer to get some advice on the solution that is best for your application.

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.