Wiring several subwoofers into a single home theatre receiver

The idea of running more than one subwoofer from a single amplifier used to be the reserve of high-end custom theatres, but the gear and the know-how have trickled down to the point where most enthusiasts in Sydney, Melbourne or Brisbane can pull it off over a weekend. Two or three subwoofers, placed thoughtfully, can fill in the dips and peaks that a single box leaves in a typical rectangular lounge, giving you bass that feels even whether you are sitting on the couch or standing in the kitchen.

Before you start drilling holes in the gyprock or buying extra cabling from the electronics aisle at Jaycar, it pays to understand what your existing receiver can actually push out, what sort of subs will play nicely together, and where to put them so they reinforce rather than cancel each other. This guide walks through the practical side of the job in plain language, with tips that suit Australian homes, our 240-volt mains, and the way our open-plan living rooms tend to behave acoustically.

Why run more than one sub at all

A single subwoofer has to fight the room it sits in. Long, narrow Australian homes with timber floors and high ceilings often leave the sub playing hot in one corner and disappearing in the middle of the couch, which is why two or three boxes make a real difference. Adding a second or third sub doesn't make the bass louder in the obvious sense; it smooths out the response so everyone in the room hears roughly the same level of low-frequency energy.

The technical reason comes down to modal behaviour. In a room of about four metres by five metres, the lowest notes from a sub bounce around and create peaks at some seats and nulls at others. A second sub placed elsewhere excites those modes differently, and the peaks and dips average out. The end result, in practical terms, is cleaner dialogue rumble, tighter bass in music, and explosions that feel solid from any seat.

There's also a reliability angle. Two subs each doing half the work generally run cooler and last longer than one sub straining at the limit, especially during a long session on a stinking hot Adelaide arvo when the air-conditioner is also working overtime. Audio hobbyists often swap tips online, and broader resources such as the Steve Platt dating feature reflect the wider community side of the scene where enthusiasts gather.

Checking what your receiver offers

Modern AV receivers usually have one or two RCA subwoofer outputs on the back, often labelled "Sub Out" or "Subwoofer 1" and "Subwoofer 2" near the HDMI cluster. A receiver with two outputs is the easy case: you run an RCA cable from each output to its own sub, and the receiver's own bass management does the rest. Brands such as Denon, Marantz, Yamaha and Onkyo sold through Australian retailers typically include this dual-sub feature from the mid-range up.

If your receiver only has a single subwoofer pre-out, you have a few options. The cheapest is a simple RCA Y-splitter, which forks the mono signal into two leads so both subs receive the same feed. This works fine when both subs are identical and you want them to behave as a matched pair. For setups with mixed brands, a small active subwoofer distribution amp from a place like Jaycar can give each output its own level trim and sometimes a delay adjustment, which helps if the subs are different distances from the main seat.

It's worth checking the receiver's manual before buying anything. Some lower-priced models multiplex the two outputs and only run one at a time in certain listening modes, while higher-end units like the Anthem MRX series available through local distributors treat them as fully independent channels with separate room correction filters.

Cables, connectors and signal types

Most consumer subs use a single RCA line-level input, and the standard lead is a shielded coaxial cable with RCA plugs on each end. For runs under about five metres, a decent gold-plated lead from the cable bin at Bunnings or any audio shop will do the job without any hum. Longer runs, especially in older Brisbane and Melbourne houses with chunky brick walls, can pick up mains buzz, so a properly shielded cable with solid foil and braid is worth the extra few dollars.

If you happen to be running pro audio subs or higher-end home units, you'll sometimes see balanced XLR inputs instead of RCA. In that case you can use XLR cables directly, or run RCA from the receiver and adapt to XLR at the sub end. Keep the cable lengths matched between subs of the same brand so the timing stays consistent.

Stereo RCA leads work fine for subwoofer duty because the bass content below about 80 Hz is essentially mono in almost every film and album. You don't need fancy directional cables or audiophile nonsense; you need a solid conductor, good shielding, and plugs that stay put when you nudge the sub six months later.

Placement around an open-plan lounge

Where the subs physically sit matters as much as how they are wired. In a typical open-plan Aussie living area with the kitchen flowing into the family room, the corner-loading trick still works well for the first sub: shove it near a wall corner about a third of the way along the longer wall, and let the boundary gain lift the very low notes. The second sub should go somewhere that excites different room modes, which often means the opposite end of the room, beside the couch, or even along the short wall if space allows.

A neat trick is the "sub crawl": put the sub where your head normally sits, play a bass-heavy track, then crawl around the room edges listening for where the bass sounds smoothest and loudest. Swap positions with the sub and you have found a great spot. It looks ridiculous, but it works in a fibro cottage in Fremantle as well as it does in a brand-new build in Kellyville.

Be careful with timber floors on stumps, which is common across Queenslanders and many older Adelaide and Perth homes. The sub can rattle the floor enough to annoy the neighbours downstairs in a duplex, so a dense isolation pad under each sub is a worthwhile spend. The same goes for placing subs on built-in cabinetry, which can colour the sound and shorten the life of both the cabinet and the sub. Once the subs are settled, it pays to match the picture side of the system with the same care, and a resource such as this projector calibration walkthrough covers the display end of the home theatre setup.

Tuning phase, polarity and crossover

Once the subs are in place, the receiver's room correction will handle a lot of the heavy lifting if you are running Audyssey, YPAO, MCACC or DCAC. Run the calibration with the supplied microphone from the main seat first, then re-run it with the mic at a couple of other spots if your receiver supports multiple measurements, so the system averages the room rather than chasing a single sweet spot.

The crossover point matters too. Set the main speakers to "small" and pick a crossover frequency that suits them, usually 80 Hz for most floorstanders and 100 to 120 Hz for smaller bookshelf units. Letting the receiver send everything below that point to the subs takes a load off the main amps and gives the subs something coherent to work with.

Phase is the bit that confuses most people. Start with both subs set to 0 degrees and listen, then flip one to 180 and listen again. The setting that gives louder, tighter bass at the main seat is the right one. Some subs also offer a continuously variable phase dial between 0 and 180, which is handy when the subs are different distances from the listening position. If the receiver supports individual sub distance settings, measure each sub's distance accurately with a tape rather than guessing.

For tricky rooms, calling in a professional calibrator with the right gear is worth the visit fee. Local installers, audio clubs in the state capitals and broader resources such as reformed matchmaking service often list experienced hobbyists who are happy to lend an ear or a measurement mic for an afternoon session.

Common mistakes and quick fixes

Hum is the classic bugbear. A ground loop between the receiver and the sub often shows up as a low buzz that rises with volume. Check that both units are on the same power circuit, ideally fed from the same double-GPO on the wall, and avoid using the receiver's pre-out and the sub's high-level speaker inputs at the same time. A cheap ground-loop isolator on the RCA lead is the standard fix if the problem persists.

Another common slip is running the subs at full gain and using the receiver's trim to control level. It is much cleaner to set the sub's own volume to about a third, let the receiver trim them up, and use the master volume for everyday listening. This keeps the subs in their linear operating range and reduces port noise.

If the bass suddenly disappears after a firmware update or a power outage in your street, the receiver may have reset the subwoofer output to "off" or reassigned bass to the main speakers. Dive into the speaker configuration menu, confirm the subs are enabled, re-run room correction, and you will usually be back in business without any further drama.

For Australian homes that suffer from heat-driven amp shutdowns during a long session on a forty-degree Sydney day, make sure each sub has at least a handspan of clearance behind it for airflow, and avoid stacking gear in a sealed cabinet. Between marathon test sessions, stepping away for a light meal such as a green sprout salad recipe keeps the brain ticking over and often reveals the placement error that was bugging you all afternoon.

Handy additions worth picking up

• A roll of quality shielded RCA subwoofer cable, long enough for the planned runs.
• A basic Y-adapter or a small active subwoofer distribution amp if your receiver has only one sub output.
• Isolation pads or dense foam mats for each sub, especially on suspended timber floors.
• A compact SPL meter or phone-based calibration app to double-check the levels after auto-calibration.
• Spare mains leads and a small powerboard with surge protection, rated for 240 volts and the Australian plug standard.
• Cable ties, labels and a cable channel kit from Bunnings to keep the runs tidy and pet-proof.

Documenting the install online is half the fun for many people. A simple walkthrough such as a Weebly video background guide helps when you want to share build photos or short video tours of the finished theatre, particularly if you are running a small blog to track upgrades over time.

For homes with tricky acoustics, a final sub crawl after the room correction has run will often reveal one more seat where the bass still feels weak. Moving the offending sub by as little as fifteen centimetres, or swapping its phase switch, can lift the response without any further electronics. Patience pays off here, and so does taking measurements with a phone-based SPL app if you don't have a dedicated mic.

Finally, remember that every extra metre of cable, every extra box and every extra connector is another potential failure point. Keep the signal chain as short as practical, label everything as you go, and take photographs of the rear of the rack while the cables are tidy.