A subwoofer's cutout diameter is the hole the cone and basket drop through. The bolt circle diameter is the ring the mounting screws sit on, and it is always larger than the cutout. Reverse the two and the mounting tabs land inside the hole, so the driver will not bolt down. Both numbers, plus mounting depth, are printed on the driver's datasheet, and getting all three right is what makes a subwoofer actually fit its baffle.
- Cutout diameter is the hole the cone drops through. Bolt circle diameter is the ring the screws sit on, and it is always larger than the cutout
- Three measurements decide fit: cutout diameter, bolt circle diameter, and mounting depth. All three are on the driver's datasheet
- Typical cutout is about 9.1 inches for a 10-inch sub and about 11.2 inches for a 12-inch, but it varies by model, so use the datasheet, not a rule of thumb
- We cut both the cutout and the bolt circle from the driver's published mounting template on the CNC, so the holes land exactly where the driver expects
This is a mounting deep dive in our how a CNC subwoofer enclosure is built series. For the depth side of fitment, see shallow-mount subwoofer boxes.
What Is the Difference Between Cutout and Bolt Circle Diameter?
They are two different circles on the same baffle. The cutout diameter is the round hole you cut so the cone and the back of the basket can move freely. The bolt circle diameter, sometimes called the mounting hole diameter, is the larger imaginary circle that the mounting screw holes sit on, spaced evenly around the cutout. The driver's mounting flange bridges the gap between them.
So a subwoofer sits in the baffle like this: the cone drops through the cutout, the flange rests on the baffle face, and the screws pass through the flange into the bolt circle outside the cutout. Get either circle wrong and the driver will not seat correctly.
Diagram: Cutout vs bolt circle on a subwoofer baffle
The cutout is the cone hole; the bolt circle is the larger ring of mounting holes around it.
Why Is the Bolt Circle Always Larger Than the Cutout?
Because the screws have to land in solid baffle, outside the hole. The mounting flange sits on the baffle face around the cutout, and the screw holes are in that flange, so the circle they form is necessarily bigger than the hole the cone passes through. There is no driver where it works the other way around.
This catches people who reverse the two numbers off a spec sheet. If you cut the cutout to the bolt circle figure, the hole is too big and the flange has nothing to land on. If you set the screws to the cutout figure, they fall inside the hole with no material to bite. Either mistake means starting over with a new baffle, which is exactly why we cut both circles from the driver's own template.
What Cutout Size Does My Subwoofer Need?
Use the datasheet, because cutout sizes vary by model. There is no single universal cutout for a given sub size, but the typical ranges below get you in the ballpark for planning. For the actual cut, every quality driver publishes its exact cutout and bolt circle, and many publish a printable mounting template (JL Audio).
| Sub size | Typical cutout diameter | Notes |
|---|---|---|
| 8-inch | ~7.1 inches | Varies by model |
| 10-inch | ~9.1 inches | Common value 9.125" |
| 12-inch | ~11.1 to 11.2 inches | Varies by model |
| 15-inch | ~13.8 to 14 inches | Varies by model |
Typical cutout ranges for planning only. The driver's published cutout and bolt circle are authoritative; verify on the datasheet before cutting (Crutchfield).
One more reason to trust the datasheet over a chart: a shallow-mount 10 and a deep competition 10 can have different cutout and bolt circle figures even though both are nominally ten-inch subs. The nominal size names the cone, not the mounting pattern.
Don't Forget Mounting Depth
The third fit measurement is depth, and it ends more builds than the other two. Cutout and bolt circle decide whether the driver bolts to the baffle. Mounting depth decides whether the basket clears whatever is behind the baffle, like a seat back, a window mechanism, or the box's own rear wall. A driver can fit the holes perfectly and still foul on depth.
Measure all three before you cut or buy, and measure depth with the panel in its real installed position. For depth-limited spaces and shallow drivers, the fit math is its own subject, covered in our guide to shallow-mount boxes.
How Proline X Cuts the Baffle
We cut both circles from the driver's published mounting template, on the CNC, so the cutout and the bolt circle land exactly where the driver was designed to sit. There is no hand-marking and no guessing from a spec sheet that might be misread. The template defines the geometry, the ShopSabre cuts it, and the same model comes out identical every time.
On driver-specific boxes we go a step further and set threaded inserts on the bolt circle, matched to that driver's bolt pattern, so the sub bolts to metal threads rather than into bare MDF. Cutting the bolt circle to the template is what makes those inserts line up with the driver's mounting holes on the first try.
Frequently Asked Questions
What is the difference between cutout and bolt circle diameter?
Is the bolt circle bigger than the cutout?
What size hole do I cut for a subwoofer?
What three measurements does a subwoofer need to fit?
Why won't my subwoofer bolt into the box?
Want a Baffle Cut Exactly to Your Driver?
We cut the cutout and bolt circle from your driver's published mounting template on the CNC, and set threaded inserts to the bolt pattern on driver-specific boxes, in our Tullahoma, Tennessee shop. The driver bolts in the first time.
Send us your driver and we will spec the baffle. Contact us with the details, or browse the Proline X enclosures and the full subwoofer enclosures collection.
About the Author
Scott Welch is a Multi Time IASCA National and MECA World Sound Quality Champion, an active SQ judge since 2019, and the owner of Audio Intensity in Tullahoma, Tennessee. He cuts every Proline X enclosure on the shop's CNCs and tunes every customer system before it leaves. Audio Intensity is the original US importer for Goldhorn DSP and an authorized dealer for Prodigy, Crescendo, Image Dynamics, Wavtech, Tru Technology, and more.
