Is Leakage Desired In An Acoustic Suspension Speaker?

[gdmoore28]

OK, all my life in the speaker building hobby I've read and been told that an acoustic suspension design should have zero leakage - period. Then I run across a conversation on AK that proclaims that Henry Kloss and others designed their woofers to specifically leak air through the surround and the cone. I dismissed this out of hand, but did some research nonetheless. Seems that it's true, and that the patent holder, Vilchur, specified this leakage in his original patent application.

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/4630-ar-box-and-woofer-sealing/

My recent build uses 10" aluminum cone drivers with rubber surround and specified for sealed enclosures only. No air coming thru those. What's the deal?

GeeDeeEmm

[dcibel]

I can't speak for the "leakage by design", but acoustic suspension and sealed cabinet are not exactly the same thing. I believe the term acoustic suspension comes from when speakers were designed without the aid of computer simulation. An acoustic suspension speaker had a very loose suspension and relied on the back-pressure built up in the cabinet to aid in control of the cone.

100% sealed should never be a goal, you need the cabinet to be able to adjust to barometric conditions. Other than barometric equalizaion, I can't think of any other reason why some leakage would be a requirement. A aperiodic design may be another goal to reduce cabinet size.

[billfitzmaurice]

I can't speak for the "leakage by design", but acoustic suspension and sealed cabinet are not exactly the same thing.

True. Acoustic suspension was a specific combination of a very loose suspension and low Fs driver. It allowed use of a relatively small cabinet, with the small air volume providing most of the restorative force. That doesn't apply to the majority of modern sealed cabs. The closest you will find today to the classic acoustic suspension alignment will be with some sealed subwoofers. While all acoustic suspension cabs are sealed not all sealed cabs are acoustic suspension.

The issue that Vilchur addressed was not only the need for some air leakage but also that if there was too much leakage there would have been a loss of restorative force. With modern modeling software leakage from all sources are lumped together under the spec Ql.

[andy19191]

My recent build uses 10" aluminum cone drivers with rubber surround and specified for sealed enclosures only. No air coming thru those. What's the deal?

If you don't have any air leakage then the air inside the cabinet will be trapped at a fixed volume. When the atmospheric pressure outside the box changes the resting position of the cone will move in or out degrading linearity and limiting maximum excursion. The solution is to have something in the build that is not airtight or perhaps a tiny pin prick of a hole somewhere that is too small to squeak but will allow the atmospheric conditions inside the speaker to equalise with that outside.

PS Apologies I have repeated what dcibel said.

[fpitas]

My own experience is that it is very difficult to build a sealed cabinet that doesn't leak a tiny amount. Even a tiny leak will compensate for normal changes in atmospheric pressure.

[mzisserson]

Apriodic enclosures are intentionally lossy.

[Chris Roemer]

I think MANY (if not most) woofs/mids have enough "leakage" through/around the spider/voice-coil/and dustcap to eliminate any worries about barometric pressurization. A "sealed" system only has to act sealed, maybe down to 5-10Hz or so. I'd think that any ("normalinzing") leak that's slower than that wouldn't really affect the closed-box model.