How To Measure A Subwoofer
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Let’s say your current subwoofer is old and no longer produces quality bass. You’re thinking of replacing it, but you want to use the same enclosure. Where do you start? You may be wondering what size is my subwoofer? Well, you need to measure the subwoofer so that you can get a replacement that fits the enclosure. Read on to find out how you can measure a subwoofer quickly easily and correctly. 

To measure a subwoofer, use a tape measure or ruler to get readings of the subwoofer’s mounting depth, mounting height, and cutout diameter. You can then use these readings to get a correctly sized replacement.

Read on for more details. 

What Aspects Of A Subwoofer Should You Measure?

To determine the overall physical size of a subwoofer, you need to measure its diameter, mounting height, and mounting depth. Remember, subwoofer measurement goes beyond just whether you need a 10″ or 12″ sub. Here’s an illustration and description of each:

subwofer measurements how to measure a sub

Speaker diameter: The diameter is a measurement of a subwoofer across its frame, from one end to the next with the exclusion of any mounting lugs present.

Cutout diameter: This is a measurement of the subwoofer including the mounting holes. This is important for the surround and cone to clear the speaker’s mounting plane.

Mounting height: This is a measurement of that indicates how far the subwoofer’s front-end part projects from the front mounting plane. This way, you ensure the subwoofer doesn’t project too high.

Mounting depth: This is a measurement of the length of the subwoofer’s rear. This way, you can determine how far the speaker’s rear projects from the front mounting plane.

In this article on choosing a sub, the writer doesn’t go into much detail on selecting a sub except for exploring 12″ vs 10″ subs. You need to go beyond this, especially if you already have an enclosure. 

Method 1: Measure Subwoofer Dimensions

Step 1:  Remove the Subwoofer Driver from the Old Enclosure

Turn off the subwoofer and remove it from its enclosure or mounting. You’ll need a screwdriver to do this.

Take off the covers in the subwoofer’s front and then loosen the screws. Once you are done, pull the subwoofer out of the enclosure and disconnect the attached wires. Ensure the driver is completely detached from the enclosure.

Step 2:  Measure the Subwoofer’s Mounting Depth

With the subwoofer sitting upright, you can use either use a tape measure or ruler to measure the mounting depth in inches.

The mounting depth refers to the height from the back of your speaker to its mounting frame.

subwoofer mounting depth

Let’s get into how to measure subwoofer mounting depth. You can start measuring from the bottom up to the mounting frame which is the flat metallic or plastic plate around the cone.

You should also note two measurements, the subwoofer’s top and bottom mounting depth which refers to the measurement from the top and bottom of the counting frame. 

Step 3: Measure the Subwoofer’s Mounting Height

This involves measuring from the subwoofer’s mounting frame from the bottom to the highest projection point.

subwoofer mounting height

Place the subwoofer in a way that ensures the wide part of the cone faces up. Now, with the driver sitting upright, measure the distance using a tape measure or ruler. The measurement should begin from the bottom of the sub up to the flat metal or piece of plastic around the cone, known as the mounting frame.

When measuring from the mounting plate’s bottom to the highest point of the sub, look at it from the side to find out how far it extends from the mounting frame.

Please remember that you need this measurement to ensure your sub is kept safe. If the height extends too far, you could damage the sub. The sub shouldn’t be too tall for the place where you’re putting it.  If it is, then the subwoofer won’t sit flush, which can lead to serious damage.

Step 4: Measure the Cutout Diameter

This is how you measure the subwoofer’s diameter. Flip the subwoofer speaker upside down to ensure the cone’s widest part faces down. Now measure the driver’s widest point from one mounting hole to another. Record the dimensions so that you don’t forget them when you need the details later.

Subwoofer cutout diameter

Now let’s talk about how to measure a square subwoofer. Note that if the subwoofer isn’t round, you should take the measurements from the widest points of each side. If the sub has four mounting holes, measure the diameter from each mounting hole to the others diagonally across.

Method 2: Measure Mounting Holes

When you know the size of mounting holes of new subwoofers, you can choose a subwoofer that suits your enclosure.

However, the above method offers more value than this one since you can drill new holes to hold the new subwoofer, if necessary.

It’s a method that can help you as well, to measure your subwoofer accurately. If you want to try it out, here’s what you need to do:

Step 1: Determine the Mounting Hole’s Outer Diameter

Please find the most expansive area of the hole and position your measuring tape or ruler across it. Measure from one edge of the mounting hole to the opposite side.

Check the widest point on all sides in case the hole is not circular.

Step 2:  Determine the Hole’s Inner Diameter

This step is critical if you can notice recessed lips in the place where you intend to mount your subwoofer.

This issue often makes the mounting frame lay flush.  To measure the inner diameter, ensure you place your rule on one side of the hole. Determine the length by measuring straight across to the opposite side.

It’s important to note that subwoofer closures have a recessed lip. If the hole isn’t round, you should find the widest point on each of the sides.

If you’re dealing with a recessed lip, the cutout diameter should be slightly smaller or the same size. Otherwise, it won’t fit in the mounting hole. That could lead to severe damages.

Step 3: Measure the Depth of the Subwoofer Space

You should know how deep space you are placing the sub is to make the best buying decision. 

To measure it accurately, you should stick the rule inside the mounting hole and see how much it goes.  Once the ruler reaches the end of the surface, record the measurement. That’s how much you can get for your subwoofer.

Note that the mounting height of your new subwoofer should be shorter than the depth of the space. So, you should use the measurement to choose a sub that perfectly fits inside the enclosure.

Step 4:  Determine the Unique Features of the Screw Pattern

Check the pattern of your old enclosure. Determine the distance between the different screw holes to the ones that are opposite each of them. 

Find out the exact distances between the other screws. Write the findings down and compare the pattern to the ones on the new subwoofers you intend to use.

As already mentioned, if the screw pattern can’t match, you can always drill new ones.

Why Consider Impedance?

When you are thinking about replacing your subwoofer, impedance is another essential thing that you can’t forget about. It determines the load value that the sub sends to the amp.

Other than the physical size, ensure the replacement has at least the same load so the amp isn’t overloaded.

This is technical, but designers do the calculations and provide the impedance of every sub.  You have nothing to worry about, for that matter. You can find 2 ohms, 4 ohms, 8 ohms, or higher impedance subwoofers.

Wrapping Up

When considering buying a replacement subwoofer, you should consider the dimensions carefully, but you should consider other things as well such as whether the enclosure hole is recessed. Also, the enclosure size and the subwoofer’s shape should suit your needs. You can use the two methods above to do all this. Finally, you need to ensure the replacement doesn’t overpower your amp.