What is a Passive Subwoofer? Pros and Cons

Except you absolutely haven’t heard the name before, a subwoofer is a sound device almost everyone wants to have in their collection. The music lover, DJ, movie freak, car owner – everyone who listens to some sort of sound. You want a better sound system? Get a subwoofer – or so it goes.

What is Passive Subwoofer
PascalSijen, flickr.com

Let’s go over it again. What is a subwoofer?

If you’ve rummaged through this site a little, you’ve probably gotten the gist of this subwoofer story. It’s a type of loudspeaker. But while other loudspeakers produce loud sound (more like treble), the sub produces deep sounds (also called low frequency sounds). They are designed to work with loudspeakers in other to transmit complete sound – i.e. both the high and low pitches.

If you prefer videos, this video explains What is a Passive Subwoofer

A subwoofer is not just any woofer system. Woofers produce low-frequency sounds like those within 40 and 80 Hz. But a sub produces much lower sounds – 20 Hz. It’s actually wrong to call a low-frequency system with a response that is above 20 Hz a subwoofer.

You can tell when a sub has been set well and when there is a lapse. If there is a lapse, the bass output will not be smooth. You’ll hear a lot of deep noise re-echoing at each other. Well-tuned subs, on the other hand, give out deep and rich sound.

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When Ken Kreisel from M&K (Mill operator & Kreisel Sound) made the first sub in 1973, it was for a chronicle studio. He built it into a 3-speaker structure, and it was used to blend the Pretzel Rationale collection of Steely Dan. M&K officially started in Beverly Hills in 1974 bringing subwoofers into mainstream cinema business and into home theaters. They became widely known in the 1980s and Kreisel has been leading the revolution.

Subs come in two varieties. They are passive and active subwoofers. The difference between them lies in their ability to power themselves or not. Both have their high and low points. Even though active subwoofers are easier to deal with, they don’t exactly produce better bass. The ability to give out clean, deep bass depends on the accuracy of the sub. You just have to be sure that your sub is set correctly.

In all cases, you need to run your subwoofer into a receiver for it to produce sound. The process of connecting your sub depends on the type that you are using.

Active Subwoofers

You can also call them powered subwoofers. An amplifier is built into an active sub. It can function as a speaker by itself, without being attached to another amplifying device. So, this is like bringing a sub and an amplifier into one cabinet so that they function together. What this means is that you don’t have to run a lot of wires to link it with your surround sound preamp or with the receiver in your home theater.

You can’t limit an active sub to the performance of the receiver they are linking to. They also do not make power demands from a connecting receiver which means that other connecting speakers (like tweezers) can get enough power.

Our focus is on passive subwoofer. Why should you consider a sub that cannot power itself when it’s easier to set an active sub?

Video: What is a Passive Subwoofer?

Here’s why you should choose a passive system or an active system

Passive Subwoofers

A passive subwoofer needs an external amp before it can function. All the power that it uses has to come from an external device. Many passive subwoofers are used in cars. A passive sub is usually a box with holes where the driver(s) sit, and a wire sticks out behind that can link with speaker wires. It’s possible to find a passive sub that has other components that help it to keep away the high frequency. This doesn’t make it a powered sub.

When you use a passive sub, the receiver that links with it should have enough power to carry its heavy bass needs and still deliver effectively. That’s because subwoofers require a lot more power to function than any other speaker does. Low frequency sounds take a lot of electrical energy. The deeper the bass, the more the sub needs.

Before you can set up a passive sub, you should be able to tell the range of its frequency and how much power it needs. That way, you’ll be able to know the right amplifier to connect it with. That’s because, if you get it wrong, you’ll have wasted a good time doing nonsense (except, maybe, learning the hard way). The good thing is that if your efforts produce the right result, you may just have a better system than a powered sub. Your frequency calibration and power control will be a lot more customized to your needs.

One way to differentiate a powered sub from a passive sub is by their connection port. While a passive sub comes with just the speaker connection jack, a powered sub will have subwoofer line (also called High Level) input. So, to connect to a passive sub to a receiver, you need speakers. You have to connect the sub as if it is a regular speaker.

The external amplifier that connects with your sub should have a Line Input jack. In this case, when connecting, you have to run your wires from the home theater’s subwoofer output (it may be an AV preamp) into the amplifier’s line input. It’s the speaker output of your external amplifier that you run to a passive sub’s speaker terminal.

The major place you will find a passive subwoofer used for home theater installation is when the design is to fix the sub on the wall. There are situations when a home theater system has its own passive sub.

A passive subwoofer will function better if it is placed in a room that doesn’t have a lot of space. That way, it won’t put a lot of demand on the amplifier that is powering it. You’re likely to find one that is built for a specific speaker. Running a sub and its speaker together will ensure that you have better sound.

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What are those Pros and Cons of a Passive Subwoofer?

A passive subwoofer has its advantages and concerns. Learning about them will help you make good choices with your subwoofer.

Pros of a Passive Subwoofer

  • With an amplifier that has many channels on it, you can power more than one passive sub in your home theater. This lessens the cost of getting more than amp for your subs.
  • The cost of a passive sub is easier to handle. It’s also easy to build one if you want to. Because they come in large boxes, you tend to have a lot more options for positioning the driver and the connecting ports.
  • Even if the sub comes with a specified amplifier, replacing it is with another external amp easy as the passive subwoofer can work with any amplifier.
  • You don’t need a direct power outlet to run a passive subwoofer. In fact, it’s okay to run long wires into it so that it is very far from the amplifying device. This reduces the possibility of the sub catching fire.
  • The wires you use for your sub are all easier to handle. If you’re using long speaker wires, they cost far less than subwoofer cables. Also, you’ll find it easier to hide flat wires than to hide cables.
  • The way passive subs are built, they have a better ability to reach lower frequencies than powered subs. You can even find those that their speaker output has a passive high pass.
  • Passives subs are the right choice for adding bass into small speakers. You can regulate the bass to fit the speakers. With a dedicated amplifier, you can even power the speakers conveniently. The other side, though, is that you have to make sure that your amp can supply enough power to the speakers and the sub to keep the bass up while sustaining itself. Of course, what determines enough power depends on the needs of the speakers and how big the room you are setting up is.
  • Passive subs can reach down efficiently to the low ends of your sound. So, when they are connected to home theater, they produce very clear bass to enhance the sound playing out.

Cons of a Passive Subwoofer

  • If your passive subwoofer comes with its dedicated external amp, then you probably may pay more to get the amp. You may even find that the amplifier costs more than the subwoofer does.
  • If your passive sub’s crossover and output are not adjusted well, you may have sonic issues.
  • Even though your passive sub may give out better bass when you adjust it well, the process is more complex than it is for powered subs. There’s the sub, there’s the external amplifier, and there’s the cable. You’ll have to run a lot of cables to get your job done.
  • Passive subwoofers don’t come by themselves often. You’ll get them as part of a home theater system. This makes the cost of getting one go up. You’ll end up paying more to acquire the entire components.

A Little More on Subwoofers

Some full-range speakers have a subwoofer built into them, with an amplifier them powers them. The amplifier is usually dedicated to the sub so that the major amp does not have to bear the load of the sub. Such speakers need to be plugged into a wall outlet.

As a reminder, having a subwoofer integrated into your musical system doesn’t automatically translate to super sound. If the subwoofer isn’t set up properly, designed effectively, or is built for home theaters, it will only make a mess of your system.