The Best Subwoofer for Under $100?

I love bass, and I mean the deep stuff below 20 Hz that makes you think your house is in an earthquake. The problem is that commercial subwoofers that get there cost a lot, a lot of money. Even DIY subs struggle to stay flat down to about 20 Hz unless you build something really big. So I sat at my computer asking the usual question: can I do it cheaper? Here's how I got to around 22 Hz for about $80 in drivers.

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Jump to: Why the GRS 10SW-4 · Isobaric clamshell loading · The impedance problem · The finished box · Versus the Ultimax 18

The $20 driver that modeled too well

I knew something like the Ultimax 18 could easily hit my goals, but it was out of the price range I wanted. I wanted to keep the subwoofer under $100. Then I found the GRS 10SW-4. At the time, one of those subwoofers was right around $20, and when I modeled it, it gave me an F3 of 22 Hz.

I didn't quite believe it, so I ordered one in, tested it, broke it in, and my results actually mirrored the model, with a little better response. The F3 is the point where the response is down 3 dB, and the goal is to get it as close to 20 Hz as possible. At 22 Hz, this fits the bill.

Six cubic feet is a lot of couch

So why use four of them instead of one? When you model it, one GRS 10SW-4 needs six cubic feet to hit 22 Hz. That's big. For comparison, an 18-inch sealed subwoofer uses about four cubic feet.

The clamshell trick

The trick is isobaric loading: two of the same subwoofer wired together to act as one. There are a couple of ways to do it, and I chose the clamshell method. The subwoofers face each other, face to face, and get wired out of phase. When the signal comes, one pushes while the other pulls, so they move in the same direction and act as one subwoofer. You get more power handling, and the box size drops by half. Now two 10-inch subwoofers only need three cubic feet.

Then the ohms got in the way

There was one more problem: adding a second subwoofer changes the impedance. A typical subwoofer is 4 ohms, and my amplifier is 4 ohms. Add a second subwoofer and you either double the impedance to 8 ohms or halve it to 2 ohms. My amplifier can't handle 2 ohms, and at 8 ohms I'd only be using about half the power I'd get at 4 ohms.

I could have bought a different amplifier, but this is a budget build and I wanted to use what I had on hand. With subwoofers this cheap, it's much cheaper to add subwoofers than amplifiers. Going to four drivers let me use the whole six cubic feet, still tune it flat to 22 Hz, and keep the amplifier I already had. A win-win.

The finished box (and an end-table disguise)

The build footage didn't come out, but the finished sub has two 3-inch ports, bracing inside, and a cutout for the plate amplifier on one side. It looks a little weird, because instead of a cone you see the back of a subwoofer and its magnet. With the GRS, the back end is nothing special to look at.

If looks matter to you, put feet about 6 inches tall on the side where the baskets are, and add a top, like an oak top. Believe it or not, that's perfect end-table height. Stick it next to your couch and no one would know it's a subwoofer, unless you turn the bass on. On a 20 Hz test tone, the bass shook my camera tripod even with the camera way back on a 50 mm lens.

The $80 sub versus a sub three times the price

I compared it on paper with the Ultimax 18. The Ultimax 18 is a better subwoofer through and through, but it's also over three times the price. In WinISD, the Ultimax 18 takes about 1,000 W before it hits its mechanical limits, and the GRS setup is supposed to take around 480 W. There's a sensitivity difference too, so here's how the SPL compares at those wattages:

• ISO-100 (GRS): about 112 dB at 480 W, flat all the way down to an F3 of about 22 Hz.
• Ultimax 18: a better F3, with a rise around 30 Hz that gives it about 118 dB.

For a third of the price, 112 dB in the 20 Hz range is really good, and I can't think of another budget subwoofer that does it. Realistically, if you're building an $80 sub, you're probably running something closer to 250 or 125 watts, not 500. Even at those wattages it can still hit over 100 dB.

Temper your expectations

That's not to say you'll get the same sound quality as an Ultimax 18. These are still going to be a little noisier than other subwoofers. Their motor structures are inexpensive and very basic. But if you're after that deep, low bass for movies and music, I know these can get you there.

Prefer to watch it on YouTube? Here's BEST Subwoofer for under $100? Will Shake your House! ISO-100 Mega earthquake on the Toid channel.

Want deep bass without a separate sub?

If you'd rather build bass into the speakers themselves, the Dinas plans put a subwoofer inside each compact cabinet. You can also browse all of my DIY speaker plans.

Keep building: The Dinas: Do I Need a Subwoofer? · DIY Attempt at $14,000 JTR Speakers · all my DIY projects

Parts Used and Mentioned

Here's the subwoofer and ports I used, plus the budget plate amps and the Ultimax 18 I mentioned. Prices change, check the current price.

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Prices change, check the current price.