When did acoustic suspension become infinite baffle?

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noah katz said:
I never much liked "acoustic suspension"; it's more marketing speak than a descriptive term.

"Air suspension" would be much more accurate.

"Acousitic suspension" been used by Villchur since the early fifties when the idea of a box colume much smaller than the Vas first appeared. I believe Villchur was the one who specified the 3 to 1 ratio as well.


noah katz said:
"Acoustic suspension is when the Vas/Vb ratio is less than 3. Infinite baffle is when the ratio is 3 or above."

Are you sure it's not Vb/Vas?

The acoustic suspension design, as outlined by Villchur, required a Vas/Vb ratio of 3 to 1 or greater.


noah katz said:
Either way, I disagree. In science and engineering, "infinite" is used where increasing a value has no further significant effect.

Even at Vb = 3 Vas, the total stiffness is 3 parts from the air and 1 part from the driver, giving Fc = 1.15Fs.
Strictly speaking, you're entirely correct. but the volume requirements to implements an Infinite Baffle become so great, people started fudging. And even Fc = 1.15 Fs only means that you have raised Fs two tenths of an an octave.


noah katz said:
To qualify as IB, I'd say Fc should be no more than 5% higher than Fs.
Not a bad standard to set. But to do it would require a box volume ten times the Vas. A 12 incher with a Vas of six cubic feet would require a box of sixty cubic feet to qualify. This is why people started fudging on the terminology.
 
"I believe Villchur was the one who specified the 3 to 1 ratio as well."

Actually, that makes sense if the idea is that the air spring dominates over the mechanical stiffness.

"But to do it would require a box volume ten times the Vas. "

Well, that's what people get when you try to build something infinite 🙂

IB is more aptly applied when there is no box, like using an attic or garage space for the back volume.
 
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