Subwoofer driver sizes
Subscribe to Ask Paul Ask a QuestionWhat difference does the subwoofer's driver size make? Is an 8", 12", or even larger woofer alright to use in a smaller room?
COMMENTS
Leave a Reply
You must be logged in to post a comment.
What difference does the subwoofer's driver size make? Is an 8", 12", or even larger woofer alright to use in a smaller room?
You must be logged in to post a comment.
Dear Paul,
I listen to you daily and you have pushed my understanding of my favorite hobby beyond my imagination. I love it and please keep it up.
In your discussion on subwoofer driver size you stated that based on square inches (footage) of the driver two 8 inch drivers move more air than one 12 inch driver. I get that but it raised another question in my head. Are two 8 inch drivers faster than one 12 inch driver and does speed of the driver movement have any impact on the deep base sounds that come from a subwoofer.
Thank you for all the information you have shared with me via your videos, books, and Copper.
Correction alert: Area of circle equal pi times radius squared. https://www.google.com/search?q=area+of+a+circle&rlz=1C1CHBF_enUS837US838&oq=ar&aqs=chrome.0.69i59j69i57j46i433l2j46j69i60j69i61j69i60.5000j0j7&sourceid=chrome&ie=UTF-8
8″ woofer area is 50.7
12″ woofer area is 113
Just sayin..
Truth be told, it all depends on how stiff the cone is in the woofer driver.
A stiffer cone no matter the size, will move more air then a cone that’s not so stiff and or thick.
A thin cone, will have flabby bass if you try to drive it down too low of a frenclicy.
As chucko points out, the nominal area of two 8″ woofers is less than one 12″ woofer by a factor of (2 x 8 x 8) / (12 x 12) = 0.89.
The effective area of the cone (Sd) is less than this nominal area because the surround doesn’t move as far as the cone. Looking at Volt drivers as an example, the effective area of their 8″ bass driver is 33 sq. in. while the effective area of their 12″ bass driver is 74 sq. in. This is pretty much the same factor where (33 + 33) / 74 = 0.89. Looks like the surround doesn’t change the basic idea.
What does change is that peak output depends on volume displacement, not on area. All things being equal, displacement increases as the cube of the diameter, not the square. Using our Volt units as an example, the 8″ displaces 48 cu. in. while the 12″ displaces 183 cu. in. There is truly no replacement for displacement. Even if you don’t need this enormous excursion, the larger unit is likely to be more linear at normal levels.
Yes, this is basically correct. When measuring the cone area (Sd), the convention of measuring from the apex of the surround is used. This is also the case when looking at mass (where 1/3 of the mass of the spring formed by the surround and spider contribute to the moving mass).
There are different frame/surround/cone sizes within a given driver size but two 8″ drivers are roughly equivalent to a 12″. The 8″ drivers we designed have a little over 200 cm^2 of cone area each. We designed them for high excursion (~14 mm one way at 70% BL), and with a large 2″ coil, more so than a lot of hifi woofers, so that they are as linear as possible at more moderate levels.
One of the benefits of using multiple 8″ drivers is that, while the displacement limited output may be similar to an equivalent larger driver, it is easier to to get much higher power handling and lower thermal compression, lower modulation distortions by splitting the power among multiple drive units, which is especially important when using them over a wide bandwidth.
Paul I’m not sure two 8″ woofers equal more than a 12″ woofer. You would think 8 plus 8 equals a 16″ woofer, but if you take the area of a 12″ woofer versus two 8″ the 12″ might have more area because you are adding 4 more inches to the outer area of the woofer which gives it much more area than adding a second 8″ woofer. If you were to cut up the area of the 8 inch woofer diaphragm and tried to use that area to add 4 inches to the outer part of an 8″ woofer I don’t think you would have enough area to make it into a 12 inch woofer let alone a 16″ woofer. We need to look up the Pi formula for two 8″ circles versus one 12″.
OK I just looked it up. The area of a 12″ circle is 113.10 and the area of a 8″ circle is 50.265. So indeed a single 12″ woofer is bigger than two 8″ woofers.
In square inches that is.
https://www.calculateme.com/shape-area/circle/12-inches
A single 18″ woofer is also slightly bigger than two 12 inch woofers. Basically two 8″ woofers are almost equivalent to a 12″ woofer and two 12″ woofers almost equivalent to a 18″ woofer. A 24″ subwoofer is about the same as four 12″ woofers in square inch area. Two 6″ woofers are about equal to a 8″ woofer. I made this point before months ago, I guess nobody was paying attention.