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Subwoofers FAQ

JL Audio CS110-WXv2

The JL Audio CS110-WXv2 10" subwoofer in a sealed enclosure

Basic Questions

Subwoofer Construction

Connecting to an Amplifier

Basic Questions

Q: Which subwoofer will sound the loudest?

A: If you're looking for the sub that will deliver maximum SPL (play loudest), you need to consider sensitivity, enclosure type, and available power.

Start with a subwoofer with a high efficiency (sensitivity) rating housed in a ported or bandpass box.

Next, power the sub with an amplifier that has a power output that is within your sub's recommended power range (preferably in the top third of that range) or slightly higher. You'll achieve the slam you're listening for. Using an amplifier with a "bass boost" control can also help.

Consider a multiple subwoofer set-up, as well. It'll require more power, but will play louder.

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Q: Which subwoofer will sound the deepest?

A: To experience the lowest possible bass tones, select a large woofer designed for use in a sealed box. This type of enclosure is your best bet for driving your frequency response down.

Ample wattage is also a must if you want to hear those lowest bass notes. A woofer with a very low frequency response spec can help deliver extremely low notes. Additionally, larger woofers, because of their size and excursion capabilities, often have the ability to play deeper than smaller woofers.

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What hits harder?

Q: Which hits harder: one 12" sub or two 10" subs?

A: This is a popular question, and one that's difficult to answer definitively. There are so many factors that come in to play — power, enclosure type and size, as well as your specific vehicle and your individual perception. But, generally speaking, given adequate power, the two 10" subs will sound a little cleaner and punch harder because their combined cone surface area yields more sound pressure. The single 12" sub, however, may sound a little deeper.

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Q: Do I need an aftermarket stereo to hook up my amp and sub?

A: Although you’ll get cleaner sound using the unamplified “line-level” signal from an aftermarket stereo, there are a couple of ways to hook up an amp and sub to a factory system. With either, you’ll need to tap into your car’s speaker wires to get to the high-level signal the stereo puts out. You can then use a line output converter to lower the signal’s strength and send it on to the amp. Or you can get an amp or powered sub with speaker-level inputs and use the high-level signal directly.

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Q: How much power do I need?

A: The right answer to this question depends upon which subwoofer you choose. You'll find a recommended power range (in continuous or RMS watts) listed in the specifications for each subwoofer on this website.

The lower number is the absolute bare minimum amount of wattage you need to get acceptable results. Generally, more power is better because bass notes are power hungry. So, to really make your subwoofer deliver, we recommend choosing an amp rated in the upper third of your woofer's maximum RMS power range.

Your amp's RMS output can even exceed the woofer's maximum RMS rating, provided you keep an ear on the sound quality — when the bass starts to distort or "break up," you've reached the performance limit of your amp/speaker combination. Back the volume knob down a bit, and your woofer is safe; clean, high-volume sound will not damage your speaker.

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MTX Thunderform

MTX ThunderForms fit in out of the way places

Q: Subs for pickups — what do you have that will fit behind or under the seat?

A: We carry a large selection of subwoofers that fit in pickups. We highly recommend vehicle-specific loaded enclosures, which are designed to fit and blend in with a truck’s interior. Use our vehicle selector to find out if there’s one that’ll fit yours.

We also carry small powered and enclosed subs that fit under or behind the seat. You’ll have to measure the clearances in your vehicle to tell for sure, but you’ll probably find quite a few truck- and wedge-style enclosures that’ll fit.

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Q: If I put my subwoofer box in the trunk, will I be able to hear the bass?

A: Absolutely. The only situation that might prevent you from hearing bass from a trunk-mounted box would be if your trunk is sealed and soundproofed. Usually, bass travels easily through the materials separating the trunk from the passenger compartment. If you think you're missing out on bass because your seatback and rear deck material are blocking the sound waves, you can alleviate the problem by punching a few small holes in the rear deck and covering it with an acoustically transparent material.

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Box types

Q: What kind of box should I get — ported, sealed, or bandpass?

A: Which enclosure will be right for you depends on your preferences in music and bass sounds. See our article about Subwoofer Enclosures for a full explanation.

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Q: Will there be a difference in sound if the vent is on the middle, bottom, top, or off to the side?

A: Generally, it doesn't matter where on the box the port is, as long as the air coming from it can flow freely. Where the port aims in your car, however, can make a big difference.

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Q: What's polyester fiber stuffing, and how will it affect my subwoofer's sound?

A: You're probably already familiar with Dacron polyester fiber-fill — chances are you've slept on a pillow stuffed with this material. But you may not realize how polyester fiber stuffing can help your bass.

Stuffing your enclosure with the right amount of polyester fiber can make your box behave like it's larger than it really is. This comes in handy if the volume of the box you've built turns out to be a hair shy of the cubic air space recommended for your subwoofer. Depending on how much stuffing you use, you can actually vary perceived box volume by as much as 30%.

You can also "stuff it" if you simply don't have room in your vehicle for the larger box your sub demands. And adding polyester fiber stuffing to any enclosure can clean up your bass by minimizing unwanted box resonances — and at a reasonable cost.

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Subwoofer Construction

Q: What difference do cone materials make?

A: Subwoofer cones, like speaker cones, are made of treated paper, synthetics (like Highly Oriented Polyolefine) or composites (like aluminum or injection-molded quartz). Paper tends to be less durable, but, because it's so lightweight, it responds quicker than other materials. They all work well and sound great, so you need to experiment with different sounds to find the sub that's right for you.

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Q: Are square or triangular subwoofers better than round ones?

A: "Better" is a relative term, since the bass you prefer might differ from someone else's taste. If you're into imaginative looks and style, square and triangular subwoofers might be for you. They'll definitely catch the eye! These woofers also reproduce bass extremely well (Kicker's square woofers are big on the competition scene), though traditional round woofers tend to play more accurately. The triangle-shaped woofers might be convenient if you're short on cargo space, since triangular boxes fit into places where standard boxes just can't go.

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Q: What's a dual voice coil sub?

A: A dual voice coil subwoofer has two separate voice coils (each with its own connections), offering more flexibility in system wiring than a standard sub. The DVC sub can be wired in three different configurations: parallel, series, or independent. This way, you can wire the subwoofer according to your system design and preferences. Check out the article on dual voice coil subwoofers for more information.

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Dual voice coil sub

This MTX subwoofer has two sets of speaker connections, which means it has two voice coils

Connecting to an Amplifier

Q: Should I use a mono amplifier or a multichannel amplifier to power my subs?

A: Because mono amps tend to be Class D amplifiers, they are a good choice for powering subwoofers — Class D amplifiers have a high power-to-heat ratio and excellent efficiency, which are exactly what you want when dealing with power-hungry low frequency signals.

Most mono amplifiers are designed to run at 2 ohms; some are even 1-ohm stable. Multichannel amplifiers, on the other hand, are typically designed to work with a 4-ohm load. This is an important difference when using your amp to power multiple subwoofers, because you won't be able to bridge your multichannel, 4-ohm stable amp to power multiple subs that present less than a 4-ohm load. Instead, use a mono amplifier to power a 2-ohm load — two 4-ohm subwoofers, or 2, 2-ohm dual voice coil subwoofers, for example. You'll be able to push your subwoofers with the mono amp's maximum power, without running at a dangerous impedance.

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Q: What are the benefits of hooking up two subwoofers to a mono amplifier? How would I wire them?

A: The benefits of hooking up two subs to a mono amplifier are the same as hooking up any other number of subs to a mono amp: you can push the subs with more power at lower impedances. Because lower frequencies are less directional (i.e. it's more difficult for your ears to determine where low frequencies come from than highs), bass is often transmitted in mono. Mono here refers to a single channel (as opposed to stereo, or two channels), not one speaker.

Most mono amps have two sets of speaker terminals for convenience of installation: if you are hooking up two subs to the amp and using large-gauge wire, it gives you a place to attach the wires without having to trim them, appearing as if each subwoofer gets its own terminal. But in reality, these terminals are actually tied together inside the amp — both positives are going to the same place inside the amp, as are both negatives. If you are using more than two subs, then you simply use parallel or series wiring (or a combination) to get as close to the minimum impedance of the amp as possible (see our subwoofer wiring diagrams for more information).

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Bridging an amp

Bridging an amplifier

Q: What is "bridging" an amplifier?

A: Bridging combines two of an amplifier's channels into one channel, in order to get more power. For example, a 2-channel amp that puts out 75 watts RMS per channel at 4 ohms may be able to put out as much as 200 watts RMS at 4 ohms into one channel when bridged, which could be great for running a subwoofer. There are no formulas for determining how much power you gain when you bridge an amp's channels — every amp is different. Most 2- and 4-channel amplifiers can be bridged so they can conveniently be used in a variety of situations and systems. For example, you could use a 4-channel amp to drive your left and right speakers with two of its channels, and drive a sub with its other two channels bridged together, saving you the need to buy a separate sub amp.

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Q: Are there any problems in bridging an amp?

A: A disadvantage in bridging amplifiers is that you must be careful not to hook up too low of an impedance load, or you could damage the amp. Amps that work with loads as low as 2 ohms per channel usually can safely drive loads only as low as 4 ohms when bridged. The danger in driving an amplifier with an impedance load that's too low is that the amp could overheat and burn out. You should always check the bridged minimum impedance specification before connecting a bridged amplifier to a low impedance sub or speaker system.

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Q: Can I bridge my mono amplifier?

A: No, you cannot bridge a mono amp because there is nothing to "bridge." Bridging means combining two amp channels together into one, in order to get more power. If you only have one channel, there's nothing to combine it with.

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Q: What do I need to know about impedance when wiring subs to an amplifier?

A: Impedance is the amount of resistance speakers provide to the current flowing from the amplifier. Every time you halve the speakers' impedance — switching from a 4-ohm to a 2-ohm sub, for instance — you effectively ask the amplifier to double its output. Some amps can handle this lower impedance, some cannot. The key thing to know about impedance, then, is how to match your speakers to the capabilities of your amp.

The typical car stereo amplifier is stable down to 4 ohms in mono (or bridged) mode or 2 ohms in stereo. Some high performance amplifiers can operate safely with loads as low as 1/2-ohm in stereo (1-ohm mono). If you're designing a subwoofer system, ask yourself the following questions:

  1. How many subs do I want? More subs = more cone surface area = more air moved = big bass! Balance this equation against the amount of room in your vehicle.
  2. How much power do I want? If you're powering your vehicle's speakers with your receiver, you'll need less power for your subs. If you use a multi-channel outboard amp for your speakers, you'll need more power for your subs.

Check out suitable amps in your price range. Once you've found the right amplifier, look for subwoofers that complement your amp in terms of power rating and impedance. Most subs are rated at 4 ohms, but 2-ohm, 8-ohm, and dual voice coil subwoofers have become commonplace, so it's easy to find speakers that will bring out the best in the amp you've chosen.

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Q: How many subwoofers can I hook up to my amplifier? Can I bridge my amp and run two in parallel?

A: A well-made stereo amplifier that is stable to 2 ohms should be able to handle up to four 4-ohm woofers (two subwoofers wired in parallel to each channel).

If you want to bridge a 2-channel amp to one channel, it's best to only connect one 4-ohm woofer. The minimum impedance for the bridged (mono) output of a 2-channel amp is usually 4 ohms. Mono subwoofer amps, like the Kenwood KAC-5001PS, are stable down to 2 ohms, allowing you to hook up two 4-ohm subs in parallel.

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Q: What crossover point should I choose?

A: When we set up systems at Crutchfield, we usually start with a low-pass crossover point around 80 Hz. Through trial and error, we've found that higher crossover points tend to emphasize the source of the bass instead of the overall musical experience. In other words, you can tell the bass is coming from a box in the trunk.

A crossover point between 60 and 80 Hz focuses the power of your subwoofer amplifier on your music's deepest notes (the ones you feel) and helps make the bass you hear seem like it's coming from the front of the vehicle along with the rest of the stereo image.

Your own preferences are also important. If you prefer a hard-hitting mid-bass boom, or if your front speakers or subwoofers are small, a crossover point of 100 or even 120 Hz is appropriate.

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