Windows 7: Batch processing (xlsx to xlsb) in Excel 2010

Sorry.So the 44 subfolders contain around 1800 xlsx files?
Is the "1 specific folder" in the subfolder named the same?
Is that 10-30 files in each "1 specific folder" or all up?
Do the files that need converting have anything in common. eg tag, dates?
Can you do a search in Explorer and return those specfic files or sort returned files so there grouped?

Yes, the "1 specific folder" you bolded is named exactly the same.
And yes, this "1 specific folder" contains 10-30 files.
Well, the files have something in common, but there are files named the same in other folders, which I don't want to be converted.
So no, I can't (at least I can't think of a way how I could) search for the specific files only.

If there's only 10-30 files in one folder that need converting it wil probably be easier just to copy the paths one by one.

Otherwise does the "1 specific folder" named exactly the same exist in multiple subfolders and contain only the files to be converted?

Draw me a better picture, eg.
Main Folder
-Sub1
---FolderW
-----Files (don't convert)
---FolderX
-----Files (don't convert)
---Specific Folder
-----Files (All Convert)

-Sub2
---FolderY
-----Files (don't convert)
---FolderZ
-----Files (don't convert)
---Specific Folder
-----Files (Some Convert)

I don't think so. Like I said, altogether there are like 1800 xlsx files. The "1 specific folder" contains 10-30 files. So I have about 90 of those "1 specific folders". Therefore copying the paths one-by-one is too time consuming.

Yes Exactly. The "1 specific folder" has the same name in every of the subfolders. This "1 specific folder" contains only files which need to be converted (10-30 files).
So if it's possible to search for all of the folders named like the "1 specific folder" and to convert all the xlsx files it has in it, that should do the trick.

*edit*
just saw your edit after posting. I'm going to prepare a better picture for you. just one sec...

First try this,

^works, BUT returns the path of each xlsx file. What I need for the macro strollin posted, is the path of the "specific folders" only.

My mistake again.
Just open the main folder in Explorer and search for "Specific Folder".
Select all folders, hold shift and right click.
Click Copy as Path
Paste into notepad

Edit > Replace
Find: "
Leave Replace blank and Replace all

Edit > Replace
Find: Specific Folder
Replace: Specific Folder\
Replace all

I tested the macro and it won't work if the path contains the quotes.

Edit: Just paste straight into Excel and do the second Replace

ah right, I could have thought of that myself. :\
Thanks a lot!
Rep added to both of you, Duzzy and strollin!

(I'll run the macro while I'm away, I'll report back if everything went fine)

I don't think anyone can provide you with a 1-click solution, whatever method you use will require you to put in some manual effort.

The macro could be modified to add the backslash which would eliminate the need for the second Replace. Replace this line:

with this:

Either way, all the paths in the list need to be consistent.