sealed cabinet; should it be totally air-tight?

nadams

On Polk's sealed cabinet speakers, should they be totally air-tight? On both of my Monitor 10's, if I push the PR in, the active drivers will push out, but then slowly go back to their resting position. If I then let go of the PR, the active drivers will pull in, and slowly return to resting.

Is this the way they're supposed to be? Or could the seals around the speakers be wearing out?

madmax

No. I believe air escapes through the speaker cones over time anyway. So long as air leaks slowly enough the drivers won't notice the leak. A good example was a car sub box (2 drivers in a single box) I had one time. Every effort was made to seal it even though it really doesn't matter. In the end you could push one in, the other one came out then slowly sank back in.
madmax

Tour2ma

Interesting question...

max,
I am sure some materials are air permeable to some extent, but not be so porous that a sizable leak occurs in seconds (which is what I read into nadams' observations).

With all externally removable parts, e.g., drivers, gasketed and all wood/ MDF joints glued (I presume), a good seal is certainly the goal. Is the goal a perfect seal? I doubt it, but a "practically perfect seal" would seem a resonable goal...

minutes later...
Just checked my SRS's and...
Pushing and holding the PR produced an immediate thrusting out of all MW's followed almost immediately by the MW's retreating about half-way back to their "resting" position.

Held the PR in for 30 seconds and the MW's stayed at half-way point until I released the PR. At release the MW's returnde to their resting position, they did not "suck in " as nadams described. This indicates a pretty damn good seal.

Maybe the MW's retreat is just giving back the momentum they had being thrust out???

more minutes later...
Just checked my 10's and much less MW "retreat", although I saw a little. The 10's seemed tighter to me...

Need Matt or Stu in on this....

tryrrthg

For sealed subwoofers my understanding is that you want absolutely NO air leaks. Air leaks could cause nasty "farts" (as some people call them). I believe an air leak in a sealed cabinet would cause similar results at port chuffing - not enough "breathing room" I would imagine the same would hold true for sealed speakers...

nadams

Good information, everyone. I think that what I'm seeing would not effect sound too much. A quick bass beat would be over before too much air would be able to escape. When I get home, I'll check to see if they go all the way back to their resting position or not.

madmax

Originally posted by Tour2ma
Interesting question...

max,
I am sure some materials are air permeable to some extent, but not be so porous that a sizable leak occurs in seconds (which is what I read into nadams' observations).


Well, thanks for correcting me again. I'll leave it up to you guys.
madmax


Edit: you may want to check and see what type of coil cooling system your particular drivers have. Many pull air from one side of the cone, usually the front, across the coil and exit the air at the back. The more the cone moves the more air is pumped over the coil.

George Grand

A certain amount of air leak is expected, and not harmful to the sound of sealed-box systems.

George Grand (of the Jersey Grands)

RuSsMaN

Maybe they need the fluid checked and refilled, since they are fluid-coupled speakers.

Cheers,
Russ

madmax

If you turn them upside down the ferro-fluid will leak out. :eek:

Tour2ma

max,
My apologies for tweeking your beak above... Went into my full-blown analytical mode, which forces the limited sensitivity I posess out the window.

Actually followed up on this with Polk Paul this past weekend, and the seal should be substantially air tight, but perfect is not required. Per Paul, unless there's an obvious tear in an MW/ PR surround, the tweeter is a more likely escape route.

nadams

Thanks, tour!

Tour2ma

U B Welcome...