Key takeaways
- Not every soundbar can drive a third party subwoofer. Check for a dedicated subwoofer pre-out RCA jack before buying anything.
- Without that jack, the only subwoofer that will pair is the soundbar's own matched wireless unit, regardless of brand preference.
- Gain, phase, and crossover on the subwoofer's own controls do the actual blending work once the connection is made.
- Confirm the match by listening for a smooth handoff between the bar and the sub, not a visible bump at one frequency.
- A mismatched crossover setting, not a faulty subwoofer, is the most common reason a new addition sounds worse than the bar alone.
You already own the soundbar. What sits in a box in your hallway right now is a subwoofer from a completely different brand, an SVS SB-1000 Pro bought on sale, and the soundbar’s own companion app has no idea it exists.
That is a normal position to be in, and it is fixable in most cases, though not all. The honest first step is finding out whether your specific bar has any way to feed a third party subwoofer a signal at all, before worrying about cables, gain, or placement.
What you need before you start
You need the soundbar’s own manual or spec sheet, checked for a port labelled subwoofer out, sub out, or LFE out, usually a single RCA jack on the back panel. You need an RCA cable, and you need the subwoofer itself to have a line level RCA input alongside its own power connection.
You do not need to match brands for this to work. Unlike wireless rear speakers, which pair only within a single ecosystem in almost every case, a wired subwoofer connection through a dedicated pre-out is a simple analogue signal, and any powered subwoofer with a compatible input can receive it.
Set aside twenty to thirty minutes for the whole process. Most of that time goes toward tuning gain, phase, and crossover by ear rather than the physical connection itself, which usually takes under five minutes once the right cable is in hand.
Checking whether your soundbar can even drive an external sub
This is the step most people skip, and skipping it is why some third party subwoofer additions never work at all. Many all in one soundbars are closed systems: they pair only with their own matched wireless subwoofer and have no output jack for anything else.
Other models, particularly those marketed as supporting an additional or external subwoofer, do include a dedicated RCA pre-out specifically for this purpose. Check the rear panel photo in the product listing or the printed manual rather than assuming either way.
If your bar has no sub-out jack and no exposed speaker terminals, there is no reliable way to add a third party subwoofer to it directly. The honest options at that point are the brand’s own matched wireless sub, or routing bass to a separate subwoofer independently through the TV rather than the bar.
If your bar genuinely has no path for this, how a built in subwoofer trade off actually works is worth reading before assuming an external unit is the fix, since the built in driver may already be doing more than expected.
Connecting the two properly
Run a single RCA cable from the soundbar’s sub-out jack to the subwoofer’s line level input, keeping the run as short as reasonably possible to avoid picking up interference from other cables nearby, particularly power cables running in parallel.
Place the subwoofer according to normal placement principles rather than wherever the cable happens to reach. Where to put a subwoofer in any room covers corner loading, distance from walls, and the trade offs of each position in more detail than cable length alone should decide.
Power on both units and confirm the subwoofer is receiving signal, usually shown by an LED changing colour or a brief flicker when bass heavy content plays. If nothing changes, check the cable connection at both ends before assuming a fault.
Leave a metre or so of slack in the cable rather than pulling it taut across the floor. A cable under constant tension at the RCA connector is a common, slow cause of an intermittent connection that shows up as bass cutting out weeks later rather than immediately.
Setting gain, phase, and crossover so they do not fight
The subwoofer’s own gain control sets its output level relative to the bar. Start low, around a quarter turn from minimum, and raise it gradually while playing familiar content, rather than guessing at a setting and correcting by ear afterward from too loud.
Phase, usually a simple 0 or 180 degree switch on the subwoofer itself, corrects for cancellation between the sub and the bar’s own bass output. If bass sounds thinner with the sub on than with it off, flip the phase switch. That single change fixes the majority of cases.
Setting the crossover frequency correctly determines where the subwoofer takes over from the bar, typically somewhere between 80 and 120 Hz for most living room setups. Too low a crossover leaves a gap neither unit fills. Too high asks the subwoofer to reproduce frequencies where its location becomes audible rather than blending in.
| Setting | Typical starting point | Sign it is wrong |
|---|---|---|
| Gain | Quarter turn from minimum | Bass louder than dialogue, or barely audible |
| Phase | 0 degrees | Bass sounds thinner with sub on than off |
| Crossover | 80 to 100 Hz | An audible gap or a boomy overlap between bar and sub |
Confirming the match actually worked
Play a scene with a clean bass line or a low frequency effect you know well, and listen specifically for a smooth handoff rather than an obvious jump in level at one particular frequency, which usually means the crossover or gain still needs adjustment.
Walk around the room while it plays. A properly matched subwoofer should sound like an extension of the main bar, not a separate, locatable source you can point to. If you can easily tell exactly where the bass is coming from, gain is probably too high or the crossover is set too high.
How wattage figures actually translate to real output is useful context here too, since a subwoofer with a modest wattage rating and a well sized driver can still outperform a higher rated unit with a smaller one, once properly matched and set.
What to do when the two subs fight instead of blend
If your soundbar has its own built in or bundled subwoofer as well as the new third party one, running both at once often causes phase cancellation, an audible dip in bass rather than an addition, since the two are not naturally in step with each other.
Most bars let you disable the original subwoofer’s output once an external one is connected through the sub-out jack, either in the companion app or through a rear panel switch. Check the settings menu for an option labelled internal sub or built in bass before assuming both must stay active together.
If bass still sounds worse with the third party sub added than the bar sounded alone, disconnect it and reintroduce gain, phase, and crossover changes one at a time rather than all at once, so each adjustment’s effect is clear before the next one is made.
Give each single change a full evening of normal viewing before judging it. A setting that sounds slightly off during a two minute test clip sometimes settles once your ear adjusts, and a setting that sounds fine on one scene can reveal a problem on a completely different piece of content an hour later.
The buying mistakes that waste money on soundbars generally apply here too: deciding on the subwoofer question before spending on either unit avoids most of this troubleshooting entirely, but once you own both, patience with one setting at a time gets you there.
SVS documents recommended gain and crossover starting points for its own powered subwoofers on its own product support pages, and checking a specific model’s own guidance is worth doing before relying purely on the general starting points above.
Questions readers ask about this
No. Only soundbars with a dedicated subwoofer pre-out RCA jack, sometimes labelled sub out or LFE out, can drive an external subwoofer directly. Bars without that jack are closed systems that only pair with their own matched wireless subwoofer, regardless of what else you connect.
Somewhere between 80 and 100 Hz suits most living room setups, handing bass below that point to the subwoofer and everything above it to the bar. Adjust upward if a gap is audible, or downward if the transition sounds boomy or overlapped, then fine tune from there by ear.
This is almost always a phase issue, where the subwoofer's output is arriving out of step with the bar's own bass and partially cancelling it. Flipping the phase switch on the subwoofer, usually between 0 and 180 degrees, resolves the majority of these cases immediately.
Usually yes, if the bar allows it through its settings menu or app. Running both simultaneously without disabling either one often causes phase cancellation, an audible dip rather than an increase in bass, since the two were never designed to work together.
Generally not through the bar itself. Without that jack, your only supported option is the brand's own matched wireless subwoofer. A separate subwoofer connected directly to the TV, independent of the soundbar, is possible on some setups but is a different project entirely.
About the author
Rahul Gupta
Rahul Gupta has spent nearly a decade quietly wiring living rooms, testing soundbars in every awkward apartment layout imaginable, and untangling the kind of HDMI handshake problems that make people give up on Atmos altogether. He writes here about what actually works when you get the boxes home—not what the spec sheet promises. If a piece of gear on this site earns a recommendation, it earned it in a real room with real furniture, not a lab.
