I just did this job on my sealed subwoofers (2x 150 liters), I guess I won't hear any difference but it seemed reasonable to me.
But I used a somewhat higher measurement than suggested for the SL cabinet (50 liters), 1.25mm, I guess it won't alter the Q ...
Subwoofer design
" The box is completely sealed except for a small pin hole (<1 mm diameter) to equalize internal with external static pressure and to prevent displacing the cone from its normal resting position."
But I used a somewhat higher measurement than suggested for the SL cabinet (50 liters), 1.25mm, I guess it won't alter the Q ...
Subwoofer design
" The box is completely sealed except for a small pin hole (<1 mm diameter) to equalize internal with external static pressure and to prevent displacing the cone from its normal resting position."
Funny, scientists go to great lengths to design and build sealed chambers that will hold pressure exactly where they want it. Takes some real work to do that.
While speaker designers only want pressure wave generated by the moving parts to hold for small moments to meet requirements to drive a sound wave. No attempt made to totally seal the driver. Just not likely to be a real problem needing a solution. IMHO, but believe what you wish and DIY to any degree that makes you happy.
While speaker designers only want pressure wave generated by the moving parts to hold for small moments to meet requirements to drive a sound wave. No attempt made to totally seal the driver. Just not likely to be a real problem needing a solution. IMHO, but believe what you wish and DIY to any degree that makes you happy.
The gap in the voice coil is completely permissive for the passage of contained air, but it cannot then go outside through the dust cover.
Probably very little, but enough to move the VC / cone away from the ideal resting point
I built the box myself, there is no air passage through it.
The vanishing points can only be three.
Seal the basket gasket against the baffle.
The dustcap.
The wing.
All are imperfect, yes, but it is not about descending 500 meters in an underwater capsule.
Using waterproof cones and mounting gaskets, it is possible (though unlikely) to make a completely air tight cabinet.
Air pressure (AKA barometric pressure) normally can vary from 980 millibars which equals 14.21 pounds per square inch to 1050mb, which is 15.23psi, a net difference of 1.02psi. Looking at current pressure maps shows readings from 991mb to 1024mb at one point in time on just one continent.
A 15" has around 133 square inches of cone area, 133 x 1.02= 135.66 pounds, assuming you seal the cabinet in the middle of the range, there is still about a 68 pound pressure swing that can be expected, more with extreme storm conditions which seem to be happening with more frequency.
Assuming 68 pounds of pressure on the cone does not actually tear the surround, it can certainly result in an offset great enough that the coil will easily bottom out, as well as the attendant distortion and sensitivity loss of a driver forced to operate with it's coil pushed out of the magnetic gap, whether rearward or forward offset. Good reasons why "sealed" cabinets are never designed to be "air tight".
Art
It's what I've wanted to avoid ....... but I'll tell you that I was a bit worried when I tried to push the cone in, there was a lot of resistance there.
There still is, but now I sleep easy because an insignificant 1.25mm hole will compensate the atmospheric pressure inside with that outside.
I'm not interested in knowing what it is, but it's always the same.
Thanks for the data, I was just thinking about what would happen in my cabinets when after a few days sweltering hot, the rain suddenly comes and the air gets cold.
Acoustic Research said that their cabinets were designed / built with special materials to prevent leaks, and it became popular as pneumatics suspension
I am aware that they are different concepts, sealed and pneumatic, my speaker would not work for the second case ...
Unless the cone was obviously pushed out from excess internal air pressure when you tried to push the cone in, most of the resistance you felt pushing the cone in was due to the suspension compliance (springiness).
You can verify that by pushing the cone in, waiting a bit for any air displacement to occur, then temporarily covering the 1.25mm hole.
My guess is the cone will still return to it's normal static position.
P.S.
Acoustic Research (AR) cabinets and drivers were leaky without pinholes, but still sealed enough to be considered "acoustic suspension", sometimes called "air suspension", though never "pneumatic suspension" in the USA. Their cones suspension had very little "spring resistance", almost all the resistance was from the (99.9%) enclosed air.
Art
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