How to Connect a Subwoofer to an Old Amplifier

Sound technology and audio equipment are rapidly evolving in today’s Silicon Valley era. Hundreds of brands launch new and better gadgets every year. Yet, many of them deserve your attention. As a result, these advancements turn the older types obsolete. Soon, it won’t be enough just to dust out some classic woofer or amp. Simply put, they will be products from the distant past. So, due to the gap, we’ll encounter compatibility issues that did not exist before.

how to connect a subwoofer to an old amplifier
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For example, let’s take an older amplifier, leaving its other aspects aside. As it ages, it loses its sound quality and bass range. After a while, it devolves into a box that’s prone to overheating. If we attempt to use it, we’ll hear only whining noises and a total absence of bass.

However, buying a new amplifier is a good option; we can also ‘reinvent’ our old one. For this, we can take the stylish route and connect it to a subwoofer. But, before we can resort to such measures, we should know a couple of things about subwoofers and amplifiers. After all, it’s our ears we’re taking care of with this!

What a Subwoofer Does

what a subwoofer does

The Low-Frequency Champ

A subwoofer makes the heavier, low-frequency sounds more pronounced. While a regular speaker is a jack-of-all-trades for sound frequencies, subwoofers (or subs) specialize in a particular range. Specifically, most of them are at home around the 20-200 Hz frequency. However, some unique subwoofers can go lower even than 20 Hz.

So, these frequency ranges fall into their sub-categories. That’s why we refer to anything below 20 Hz as the ‘low’ frequency range’. Next comes the 100-1000 Hz, or the ‘lower-middle’ frequencies, followed by the ‘upper-middle’ ones between 1k-10k. Lastly, we call the range between 10-20k ‘high’.

No Distortions

Not every piece of audio equipment has the same output signal. Hence, you should use them for their general purpose. Also, don’t expect marvelous results outside those limits. For example, even full-range speakers with aural flexibility will underperform around frequencies lower than 50 Hz.

Deep bass can over-burden standard speakers at such ranges, resulting in irritating distortions. At this point, subwoofers come in to save the day. Since they differ from regular speakers, they will provide much clearer audio.

Types of Subwoofers

subwoofer type
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To figure out how to connect an old amplifier to a sub, we also need to know about the types of subwoofers. Once we figure out which subwoofer is in question, we are one step closer to solving the compatibility problem.

Active Subs

Active subs have their internal amplifiers. Hence, they do not need an external amp or receiver to work. This type of subwoofer may also have built-in equalizers. In practice, this means the frequency filters will impact the overall sound quality in practice.

Passive Subs

On the other hand, passive subs do not have internal amplifiers. Therefore, you’ll need to get one separately. They also do not have a built-in equalizer or frequency filter. TAs a result, it might be a little more challenging to restore a passive subwoofer.

The Two Types of Amplifiers

two types of amplifiers
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Depending on the type of connection they offer, there are two kinds of amplifiers. Let’s check out their ins and outs. 

With RCA or Sub-Outs

The first type is amplifiers with sub-outs. A sub-out is the output port that filters the audio. As such, it allows active amps to utilize the crossover function of the sub’s audio. In that way, it makes their job easier and boosts performance.

For a passive sub, a sub-out is sometimes necessary. However, we could also do without a sub-out. Only, in that case, we will need a low-pass crossover taking care of the sub-out’s job. In short, since a passive subwoofer does not have a built-in equalizer, an external component must do the filtration.

Without RCA or Sub-Outs

The second type of amplifier comes without a sub-out. Because of this omission, ff we use a subwoofer, we’ll have to get an audio filter component, i.e., a low pass crossover. As a result, the added number of elements will make putting everything together a hassle.

Five Ways to Connect Subwoofers to Old Amplifiers

amplifier and equalizer
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So far, we’ve covered a lot of ground regarding subwoofers and amplifiers. Next, we can dive straight into connecting them and making them tick. For example, consider these five convenient ways to re-configure your audio equipment.

1. Active Subwoofer With Speaker Input If Your Amp Does Not Have Sub-Outs

Old amplifiers may not have a dedicated subwoofer output. However, they should have a speaker signal out. And since your sub has speaker-level inputs available, you are in business.

Connecting the subwoofer with a vintage or old amplifier is relatively easy. Just take your amp’s speaker wires and pass them to the sub. Keep an eye on their polarity, though. Sometimes it may be defined, and you will have to manually connect the positive and negative ends to their respective slots.

This kind of connection allows for parallel links with the other speakers in the sound system. Also, if your sub has both speaker-level inputs and outputs, that is even better. This way, you can run the circuit through the subwoofers to the speakers, saving you some time. Then, the subwoofer’s internal circuit will convert the high-level speaker input into low-level RCA signals. The result is clean, quality sound.

If Your Amp Has Sub-Outs

It’s not usual for older amplifiers to have sub-outs. But on the off-chance that you got one of those, you’re in luck. Thanks to it, you can quickly connect the amp with a subwoofer using the RCA to RCA connection between them.

Just remember that it is always better to have more than one RCA cable set connecting your amp with the sub.

2. Active Subwoofer Without Speaker Inputs If Your Amp Does Not Have RCA or Sub-Outs

If your amplifier does not have a dedicated sub-out, you would’ve to use a line converter instead. Under this term, we refer to the RCA low-level line converters. Also, you might find them as RCA-speaker level adapters. As for their purpose, they convert high-level speaker sound signals from your amplifier into low-level RCA signals.

Your sub can use these low-level RCA signals to run your subwoofer besides your speakers. Thus, you can also connect your speakers and sub in parallel with this kind of connection if you wish.

Just make sure that your amp and sub are both turned off when you connect them. Plug the power in only after the circuit is complete.

If Your Amp Has RCA or Sub-Outs

If your amplifier has a dedicated subwoofer out, the process is simpler. Just connect this RCA jack out to the sub’s input, and you are good to go. If there is space for two sets of RCA cables instead of one, you may even connect two at once. Such a combination can enhance the quality of the sound.

3. Passive Amplifiers With or Without Speaker Inputs

The General Problem

A passive subwoofer does not have its own amplifier or crossover. Hence, there are two things to take care of here.

Firstly, it will need an amplifier. That may not appear like a problem in this hypothetical situation since you already have an old amplifier in your hands. But here’s the catch: unlike the circuits we discussed above, you can not use the same amplifier for your speakers alongside the sub for this system to work. So, if you have some means of running your speakers without a parallel connection to the sub, you can connect the audio set-up this way.

The second problem would be the absence of a crossover or a frequency filter. Without this filter, your subwoofer might get high-frequency audio input alongside the low-frequency input. However, that is not a good thing. If you assemble the abovementioned combo without the low-frequency pass, your ears might suffer.

So another thing you have to do is get a low-pass crossover. A low-pass crossover can help you filter out the unnecessary noise from your sub.

If Your Amp Does Not Have a Dedicated Sub-Out

In this case, you will have to connect the amp to your sub using an RCA-speaker level adapter. On top of that, you will also have to use a low-pass crossover for quality audio. And as we discussed before, avoid using this circuit in parallel with other speakers.

If Your Amp Has a Dedicated Sub-Out

Again, if your amp has a dedicated sub-out, then it’s easy. The solution is a straight RCA to RCA connection, possibly with a Y-type RCA jack. Of course, since this is also a passive amp, you will have to run it through the low-pass crossover.

4. Connecting a Subwoofer With an Old Amplifier in a Stereo-System

You should consider another type of outlet if you use a subwoofer and an old amplifier in a stereo system: pre-out. So, if you are running a receiver with a set-up of stereo speakers and subwoofers, you may run into some problems. Namely, you may find that the built-in amp lacks the juice to run everything. So what do you do? Get some extra Hz power. This is where a pre-out comes in.

A pre-out is a port that gives you an unamplified signal. If the built-in amp can not handle all the load, it outsources some to the pre-out. From here, the connection runs to another amplifier. In this case, it would be your old one.

Presumably, this external amplifier of yours does not have an RCA sub-out, so you will connect it to your subwoofer using a speaker to RCA line converter. If your sub has speaker signal input jacks, it could also be a speaker-to-speaker connection. When the connection runs through the external amp, this amp shoulders the subwoofer’s heavy load of bass frequencies.

The sudden sound fluctuations and distortions indicate that your subwoofer might be underpowered. If present, they confirm the need for an external amplifier input, namely a pre-out.

5. Connecting Your Subwoofer to a Surround Sound System and an Old Amplifier

Stereo systems consist of at least two audio output units, typically the left and the right speakers. Surround sound systems go two steps further and have at least five different audio output units, including the subwoofer.

On modern surround sound A/V systems, you can have both pre-outs and dedicated LFE/ sub outs. Each of these two features is worth looking at. If you find the audio quality from your surround sound system sub-par, one possible reason might be the lack of power. There can be several causes for this.

Similar to before, one solution could be to re-direct some of the heavy lifting to an external amp. So, you can try and connect the receiver and the amp. Then, the port used as output from the receiver would be the pre-out.

As for the dedicated bass track output, modern surround sound receivers give the bass an edge by providing the subwoofer a separate audio track for low frequencies. As a result, the user can enjoy a more immersive experience. However, the subwoofer doesn’t spread the load over all the speakers. Instead, it takes the responsibility away from every audio output unit.

You can find the dedicated port for this under ‘X. 1’ channels, where X would be the number of speakers. Usually, the X is two for stereo systems. If that is the case, then the bass channel would be 2.1. Similarly, it would be 5.1 for five speakers.

Connecting Your Subwoofer With an Old Amplifier via Speaker Cables V/S RCA Cables

old amplifier connected to subwoofer
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We have analyzed the two main types of connections in this guide: speaker or high-level signal connection and RCA or low-level signal connection.

As is evident from our summary, connecting a subwoofer with an amplifier is effortless if both of them have RCA connections available. Also, some amplifiers have specified RCA outs for LFEs like subwoofers. That’s why this output is sometimes named subwoofer output.

We also mentioned that it would be better to have a set of RCA cables connecting your old amplifier to your subwoofer; if you have the luxury of having two. Usually, though, subs will only have a single RCA input.

Anyhow, connecting your amp and your sub via the speaker cables might be the preferable setup. Also, expect some slight lag when using a straight RCA connection between the speakers and the subwoofer. In that case, your speakers are running on a higher signal than the sub. As a result, you might hear some desynchronization.  Speaker cable connections can resolve this problem.

Furthermore, the lag between the two should diminish when running a parallel system. So, if the speakers and the subwoofer use the same high-level output signal, the audio will be clearer and less jittery. 

In Conclusion

This guide presented some practical ways to combine your outdated audio equipment and give it new life. By following our tips and tricks, you can indeed improve your setup and, at the same time, put some bucks aside.

However, there’ll always be newer intricacies when it comes to such technology. Therefore, remember to refer to our explanations whenever you encounter a different issue. In any case, the fundamentals will likely stay the same.

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