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 Multi-Way Conventional loudspeakers with crossovers

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diyAudio Member

Join Date: Feb 2004
Location: Los Angeles
Quote:
 Originally Posted by Ron E This is wrong. Change it slightly to: Vas represents the volume of air that when compressed [by a piston of the same diameter as the speaker] exerts the same force as the compliance (Cms) of the suspension in a particular speaker.
Good catch!

Stiffness is the real, physical parameter. But Thiele and Small (and Benson maybe?) wanted to get all the parameters into the same domain, so you could apply electric filter theory for design simulation.

Stiffness in Newtons/meter is not too helpful to designers. But mathematically transformed by the cone area, it becomes cubic meters.

Aha! That's like the volume of a box! So now we can apply standard capacitor formulas for the combined stiffness of speaker + sealed box. Since the mass stays the same* then a new resonance can be found from the mass + combined stiffness, and the new combined Q calculated as well.

(*Well, except for changes caused by the shape of the box, generally quite small. LEAP calculates that for you.)

 1st November 2010, 03:06 PM #12 kabennett diyAudio Member   Join Date: May 2010 I'm still trying to digest all these wonderful responses, but just wanted to take a moment to thank you all for them. This is without a doubt a phenomenal online community, and I hope to learn enough to be able to contribute something back.
 1st November 2010, 04:34 PM #13 Cal Weldon   Speakerholic diyAudio Moderator     Join Date: Jan 2004 Location: Near Vancouver You already have. You thanked those who took the time to help. __________________ planet10 needs your help: Let's help Ruth and Dave
speaker dave
diyAudio Member

Join Date: Nov 2009
Location: The Mountain, Framingham
Quote:
 Originally Posted by thetubeguy1954 David, I also want to thank you for your excellent explanation and analogies! It's the very first time I actually got a grasp on what Vas meant. Thetubeguy1954
Happy to help out.

Most of these concepts are pretty straightforward if carefully explained. A lot of other people have helped me out along the way and I'm happy to be able to pass a little knowledge along.

I think we could put together a list of terms and definitions, perhaps in a wiki approach. Maybe we should have a thread: "Could somebody please explain...?" and let various newbies ask any question and others take a crack at explaining it. Good questions and answers could be collected in an FAQ or "terminology" area.

Thanks to everybody else for the other excellent responses!

David S.

kabennett
diyAudio Member

Join Date: May 2010
Quote:
 Originally Posted by speaker dave I think we could put together a list of terms and definitions, perhaps in a wiki approach. Maybe we should have a thread: "Could somebody please explain...?" and let various newbies ask any question and others take a crack at explaining it. Good questions and answers could be collected in an FAQ or "terminology" area.
How about a sub-forum titled "Could somebody please explain...?" (instead of a thread), and then particularly useful and lucid and evolved/edited threads could be made sticky, making for a quick reference for those of us deficient in knowledge, memory, or both....

What do you think moderators?

jcandy
diyAudio Member

Join Date: Feb 2009
Location: San Diego
Quote:
 Originally Posted by sreten Vas is simply the the equivalent box volume of the drivers suspension. If the driver is put in a sealed Vas box, Fs goes to Fbox and Qts goes to Qbox by multiply by 1.414 (root 2). In a sealed 1/3 Vas box, Fbox and Qbox are double Fs and Qts.
I think this is a great post. This analogy can be extended to see how Fc (speaker in closed box) improves only marginally for Vbox > Vas. Let a = Vbox/Vas:

a=1/3: Fc = 2 Fs
a=1/2: Fc = 1.7 Fs
a=1: Fc = 1.4 Fs
a=2: Fc = 1.22 Fs
a=3: Fc = 1.15 Fs
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arjunm009
diyAudio Member

Join Date: Aug 2014
Quote:
 Originally Posted by speaker dave The term Vas came into common use because it was a way for Thiele and others to generalize a woofer without worrying about its particular diameter. That is, a design with the woofer/box system defined partly by Vas would work the same whether it used 10" diameter or 6" diameter. (At least for small signal performance.) Not sure about the Eminence definition but the first definition you gave is correct: the volume of air that has the same compliance as the driver suspension. Picture a box with a piston on the front that you can press to compress the air inside the box. Since you are compressing the air to a smaller volume, there will be a restoring force. If the box is very large a given "distance of press" will compress the inside air a small percentage and the restoring pressure will be weak. As the box gets smaller the enclosed airspring gets stiffer and the restoring force greater. Some particular volume of air would have a stiffness equal to any given woofers stiffness. Another way to think of it is: "Take away all of the suspension of the woofer and find a box of just the right size to give it back the same stiffness." (or return it to the same resonance) The size of that box is equal to Vas. David
Then when designing enclosures, does it mean to have a box volume appropriate to the value of Vas?

At some places, there is a recommended enclosure volume mentioned for sealed and ported. But they are all generally different from Vas.

godfrey
diyAudio Member

Join Date: Nov 2009
Location: Cape Town
Quote:
 Originally Posted by arjunm009 Then when designing enclosures, does it mean to have a box volume appropriate to the value of Vas?
Yes, among other things. Fs and Qts in particular have to be taken into account as well.
Quote:
 Originally Posted by arjunm009 At some places, there is a recommended enclosure volume mentioned for sealed and ported. But they are all generally different from Vas.
Yes, box volume is often different to VAS, depending on the other driver parameters and the desired result.

 10th September 2014, 06:15 PM #20 fastbike1   diyAudio Member   Join Date: Aug 2009 Location: North Texas, USA Vas and box volume are virtually never the same. __________________ I was so much older then, I'm younger than that now.

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