How to Connect a Subwoofer to An Old Amplifier?

Being a music fan can mean a lot of things. It can be that you appreciate a good song or know the specifics of music production that render something great. It can also mean knowing what makes a great audio setup.

Any true fan of music will tell you that to really get the most out of any audio system, you need a subwoofer. You may be able to live without one if you only like certain music, such as classical or orchestral, but even then, you’re losing the full experience.

After all, there are still drums in classical music, and even the biggest music snobs in that field are prone to slipping into something more contemporary once in a while (even if they’d never admit it). The experience of hearing drums and bass without a subwoofer is an underwhelming one.

But there are other problems as well. For one thing, there are frequencies your speaker isn’t going to be able to produce. The subwoofer takes the pressure off the rest of the system, trying to produce that frequency, giving you better sound and keeping your system running better.

Most modern subwoofers contain built-in amplifiers, but you can still find subs without this feature.

In this blog, we’ll explain how to connect a subwoofer to an old amplifier, but before that, let’s understand the principles at play in both of them.



What Is a Subwoofer?

What is Subwoofer

It may be strange to think about, but humans are capable of hearing the vibrations carried in the air from a range of 20 Hz. That frequency is divided into four subsections.


20Hz – 100Hz are low frequencies.

100Hz – 1kHz are low to mid-range.

1kHz – 10kHz are high mid-range.

10kHz – 20kHz are high frequencies.


Each section has different kinds of speakers that are specifically made to create the best sound. Subwoofers are made to provide the best low-frequency sounds. Depending on how you’re trying to use them, they can cover 20 Hz – 200.

If you’ve ever watched a movie with subwoofers, you probably have some idea of what they are capable of doing, particularly if the film has a lot of explosions or shootouts.



Types of Subwoofers

There are two kinds of subwoofers that exist – active and passive.

Active subwoofers will have their own power supply independent of the amplifier. To get them working correctly, all they need is the right signal from the amp.

As you may have figured out, a passive subwoofer must be connected to the amplifier for it to be powered. It will only be as good as the amplifier to which it’s hooked.  If you’re using a stereo system, it will have two or more channels.

Stereos with only one channel are not optimal, as you aren’t going to hear much bass through a single feed. A good subwoofer will reach the low notes on a song that your speakers are unable to.

Subwoofers can be front-firing, with the main drive facing the front or down-firing. Front-firing subwoofers are ideally placed close to the main speakers, enhancing the sound already emanating from them. On average, the front-firing subwoofers are preferred, particularly for music.

If the subwoofer has ports leading into the circuits inside, it’s known as a ported subwoofer. If it doesn’t have ports, it’s a sealed subwoofer. Sealed subwoofers are preferred as they are usually cheaper, and they also provide clearer, more pronounced audio quality.

Recommended: Mono vs. Stereo Sound: Differences Explained



Do Subwoofers Work Better With Old Amps or Modern Receivers?

One might assume that modern subwoofers work best with corresponding technologies; however, the answer to that question is a little more complicated than that. The sound quality from a subwoofer is going to depend on a lot of various factors.

If you just happen to have an old amp lying around and want to connect a subwoofer, you should be able to do so. However, that doesn’t mean every old amp is going to get you the ideal sound you’re looking for with the addition.

You can also easily purchase vintage amps at specialty stores. These will obviously be of better quality than what you have lying around in your house or garage, but they will cost a lot more than what you might be willing to pay. Though for some, no cost is too great for the nostalgic trip.

Buying any item used, however, is obviously a risk.  Modern receivers are just going to be better equipped for a subwoofer’s specifications, but that doesn’t mean that a perfectly working old amplifier may produce exactly the sound you’re seeking.

There is one caveat, however. Vintage receivers do not come with the equalizers that modern amps have, so when you raise the volume on the receiver, the bass will go to levels that it should not reach. This can cause the sound to get quite unpleasant, so there are certain volume levels you should never go over when connecting a sub to a vintage receiver.



How To Hook An Active Subwoofer To An Old Amplifier

Old Amplifier

Some older amplifiers are going to have different outputs than modern ones. Many will have a simple mono output. Simply find the matching port on your subwoofer and use it as the signal source from sub to the amp. It’s a great, vintage feature, and it’s one that still works with subwoofers without much issue.

However, some older amplifiers don’t have such ports, so this may require a little improvisation on your part. First, your amplifier needs a few things to make this possible.

It’ll need two speaker outputs in order to play sets A and B simultaneously. The active subwoofer, on the other hand, needs a high-level input option.

If your amp and sub have both of these things, that means you’re in business. Set A on the amplifier to connect to your regular speakers. The B line should be connected to your subwoofer’s high-level input. When you play them simultaneously, you should hear that extra bass kicking in.

For most amplifiers, there are even markings for where you should plug in your subwoofer. The B line will often read, “subwoofer output.”

It’s even easy to turn it off. Simply shut off the B channel on your amp.



How To Hook a Passive Subwoofer To An Old Amplifier

Passive subwoofers are far less complicated to hook up to older amplifiers. Passive subs have pass-through connectors that allow you to connect the subwoofers before you connect the speakers.

You can connect the passive subwoofer to the amp by treating it like a loudspeaker, hooking it directly into the speaker connectors.



How To Connect Your Stereo System to A Subwoofer

If you do this correctly, you can boost the sound on your entire speaker system. The way a subwoofer can improve a stereo’s sound goes beyond just boosting the bass levels. It will give the system a more pronounced, sophisticated sound. But the actual job of connecting the two is slightly different.

To make this connection, there are no features that allow for bass management. The subwoofer’s high-input connection will be used for this. Run the speaker outputs between your sub and your stereo using the output jacks. This will double the connection, giving your stereo the complete subwoofer effect. This includes bass, midrange, and treble.



Connecting a Subwoofer to a Vintage Amplifier Without an Out

Vintage Amplifier

Some vintage amplifiers may not have an out for a subwoofer. In cases such as this, it is possible to connect your subwoofer and amplifier still. Depending on the brand name, the amplifier should have an out labeled “Preamp” or “pre-out,” depending on the brand name. Subwoofers with only one RCA input will require a Y adapter.

If your amp lacks an output labeled as such, it’s still possible to treat your subwoofer as though it was just another speaker. Simply use speaker wires to plug the sub into the speaker output. This means you will have to run the front-right speaker and front-left speaker into your sub.

Recommended: How to Connect a Mixer to an Amplifier



What The High-Level Signals Do To Your Connection

When connected through its high-level signals, the subwoofer will see the same signal with the other receiver. So there’s no lag. When you connect it through an RCA output jack, the sub-signal won’t be synched as precisely, so you may experience some time lag.

For most people, the slight loss in sound quality is almost inaudible, but it can be a particular annoyance for those with training in the field. Even amateurs would be able to notice the difference if they heard the same sounds played back-to-back.

But when you connect your subwoofer to your speakers, they are receiving the signal at a very similar frequency in terms of damping and tonal balance. This results in the bass being given off simultaneously from both objects, covering up any lag to the human ear. This is especially important if you’re producing music in a studio, as synching is critical.

Now that you know the many options available to plug your subwoofer into a vintage amplifier or receiver, you should get the sound quality you desired. Vintage amplifiers hold a special place of nostalgia, and sound often triggers that reverie.


How to Connect a Subwoofer to An Old Amplifier Pin



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Is a musician and journalist with over 13 years of experience writing for some of the music world's biggest brands. Ray loves getting nerdy about everything from guitar gear and synths, to microphones and music production hardware.

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