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In Reply to: RE: in defense of my system posted by K-Bob on May 02, 2017 at 11:07:06
One of the nice things about physics is that it works reliably. :) With regard to woofers, or so-called "subwoofers", there is no substitute for diaphragm (cone) area, because it all comes down to excursion and output. To produce a given amount of output at a given frequency, the cone must move a certain distance. The smaller the cone, the farther it has to move in order to produce the desired output. That's why larger woofers beat smaller woofers every time for good low bass.There are very reliable formulae for calculating the required excursion based on the driver size, the frequency and the desired output. You can look at it from basically two perspectives: acoustic watts, or SPL. (SPL is a little more involved, since it is distance and room dependent.) I have them somewhere, but then I'd have to go upstairs and find them, and I'm too lazy to do that right now. :) It's easy enough to google it if you're interested, or maybe somebody like Tomservo or Bill Fitzmaurice or Presto has it handy and will post them.
:)
Edits: 05/03/17 05/03/17Follow Ups:
Here is an online calculator which will do max SPL:
I'm curious as to what diameter to use for the subwoofer. I have Rythmik 12-inch subwoofers but the diameter of the aluminum diaphragm is only 9-inches. Likewise, the woofers in my main speakers are called 10-inch woofers but the aluminum diaphragms measure only 7.5-inches in diameter.
Thanks,
John Elison
It's SOP to give a driver size including the basket. The only exception I've seen is the British company ATC who often gives the actual driver size.
You need about 1.25" per side for basket and surround on to connect the cone to basket. That measurement obviously decreases as the basket gets smaller. But not by that much!
The 8" or 10" or 12" size is basically just nomenclature for the speaker company to fit a hole size.
So a 8" is really only a 5.5" cone.
But what always got me is the size of the standard 6.5" "woofer".
I think it's probably better to take a physical measurement. It's pretty easy to use a ruler and measure the diameter of the actual moving diaphragm. On the other hand, it might be even more appropriate to include a portion of the surround in that measurement in order to more accurately estimate the effective piston diameter.
General audio terms so a 12" is a 12" is a 12" I would think. By the way, a cone driver is typically measured to the outside of its basket.
Martin
This still does not take into account how much of the speaker is actually vibrating.
Actually, a 12-inch speaker is really a 9-inch speaker for the purposes of moving air because the diameter of the moving diaphragm is only 9-inches. Therefore, measuring to the outside of a speakers basket might be good for designating speaker size, but it is not the correct measurement to use for calculating SPL. That's all I'm saying.
Consequently, I would need to see the algorithm in the SPL calculator in order to understand how it works and which speaker size designation to use.
Best regards,
John Elison
What you're looking for is the Effective piston area.
AFAIK you are correct, this does not include the surround. Only the cone itself.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
ok after looking at the calculator I see why you're confused, it would seem you're meant to measure the actual cone diameter, but is that to include the surround?But without knowing it's Xmax it's useless anyway, and if you have that info more than likely you also have the manufacturers measured max SPL as well. Even with all the sites required info plugged in it's still only a very rough estimate without all of the cones parameters (surface area, contour, etc) taken into account.
Martin
Edits: 05/04/17 05/04/17 05/04/17
Cool calculators.
--
Mucking around the low-end since 1986.
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