What does "24 on center" mean

I'm viewing a tutorial on soundproofing, and it shows the diagram below, with the red rectangle area being the noisy space to soundproof from, and the blue rectangle being the quiet space being protected. Then he says

instead of 16 inch on center we're gonna go with 24 on center

while pointing at the red arrow. What does that mean?

• Hello, and welcome to Home Improvement. If an answer is helpful, please click the large check mark next to it to accept. And, please take our tour so you'll know how best to participate here. Jan 31, 2020 at 11:45
• The 2 lines with an X in them that your red arrow is pointing to is a common building symbol for the location of a stud or studs.
– Jack
Jan 31, 2020 at 15:32
• @AlaskaMan "There are millions of place ...", would you please give a few of them that are quick and easy to understand for the popurse of soundproofing? Jan 31, 2020 at 19:08
• @zghqh hear is an example "modern soundproofing techniques in home construction" duckduckgo.com/… On google this search gave About 489,000 results (0.65 seconds) - Half a million, i was wrong. Jan 31, 2020 at 19:37
• @AlaskaMan Thanks. Actually I did google something like this, and then I choose some of the results that quick and easy to understand for me, and then I've read tutorial posts. I've watched tutorial videos. I add anotation on images. My questions come from this procedure. Jan 31, 2020 at 19:52

A common method for building walls is to use vertical studs (often the classic "2x4"s) to support the surfaces of the wall:

The standard spacing for these studs is 16 inches "on center", which means that the stud centers are 16" apart. This provides a good balance between strength and expense. 16" is also a common spacing for other building supports (beams and joists).

The tutorial is describing building an additional surface to block the sound, supported by studs. However, this wall will be supported by studs every 24" rather than every 16". I'm guessing the wider spacing is for two reasons:

• Loosen the support of this new surface, so that its vibrations won't be directly transmitted into the main wall and thus into the "quiet" space
• Reduced cost
• "Spacing" isn't really a great term. "Interval" would be better, as the actual space is 14-1/2". You know this, but it may not be obvious to others, who may attempt to do layout by leaving a 16" gap. Jan 31, 2020 at 13:57
• Thanks for your answer. a 2"x4" stud is actually 1.5" x 3.5", right? Jan 31, 2020 at 14:27
• So you mean 16" from the side of one beam to the side of the next beam so the centre spacing will be 18"... You failed to explain "On centre" which the OP asked. Jan 31, 2020 at 14:45
• The only problem with centers is actually finding the center of every single stud - while certainly doable, it's time consuming. Using one edge or the other is very quick and simple and the inter-stud spacing remains exactly the same. Jan 31, 2020 at 14:53
• @zghqh Yes the 2" in 2x4 is 1 1/2 inchs. So the center of the stud is 3/4" inch in from each side. In the photo above the studs are placed 16" on center. ( OC ) Meaning the center of each stud is placed 16 inches apart. That means the space between the studs is 14 1/2 inches. ( 16 minus 1 1/2" = 14 1/2 ) On a tape measure ( non metric ) you will see that the numbers 16, 32, 48 and on up sequentially are with in a colored box, usually red. This is to aid in laying out and marking the top plate and bottom plate of the wall so you know exactly where 16" OC is. Jan 31, 2020 at 18:27

"On-Center" is a term to indicate measuring from the center of one to the center of the next. This has the advantage of not getting into the detail of the actual width of the material being used. If you try to space a set of 2x4's by measuring between the side of one, to the side of the next, then you have to take into account the actual width of the stud. (24" - width) A "2x4" is a nominal size, the actual size is less, and that's just a detail in the bigger scheme of things. If you do "On-center" measurement that issue is brushed away.

• Right, and the point is that side to side spacing is problematic. On-center makes it clear what is intended. Jan 31, 2020 at 14:02
• It is a center to center term, but in the real applicatioin of building it, to get it precise, it will take no time at all to realize the same spacing can be maintained by going from edge to edge, using the same side of each stud as a reference. It does not matter which side of the stud it is either as long as it is consistent. This is referring to "setting a stud ahead" or "setting it back" This is done by simply setting the first mark for layout either back or ahead half the thickness of the studs. The rest of the layout is done at the recommended spacing.
– Jack
Jan 31, 2020 at 15:20