Polk PSW10 drawing inward on hits

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Finn.OS

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Joined 2025
#1
Hello thread goers, i need some help figuring out why my subwoofer is drawing inwards during and after hits of bass. If there is a part where the sub hits and holds a frequency between 30-60hz, the sub kinda recedes into the enclosure. not sure if it’s an optical illusion or if it’s supposed to happen but i just wanted an answer. thanks
video of it happening
 
#3
Looks totally normal to me. Speakers, vibrations work in both directions. A driver cannot continually pump forward. In a sealed cabinet you'd eventually create a vacuum.
The efficiency of a ported system is largely down to capturing a driver's rear output, the port reversing the phase of the selected frequency window. Around Fs the port is using the energy of the negative stroke to power the resonator.
There are nerds and techs who can explain this far better than me.
 
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#6
all these seem to make sense, I was honestly just curious what could be the cause or if there was even an issue to begin with. I haven’t noticed a difference in sound quality when changing the sub input from rca to wire inputs so who knows, thanks!
 
#7
Rectification is evident where an AC signal becomes biased away from zero. If it happens significantly it could be a problem. It may be caused by distortion. Distortion could be electrical or mechanical. As suggested it may be from a port that can't draw air in as fast as it can be pushed out. Perhaps it has a connection to the port size and it can't support movement at high velocity.

As mentioned, member @stv has good port information on this thread - https://www.diyaudio.com/community/...sonance-absorbers-and-port-geometries.388264/
 
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#8
As indicated, I'm just a novice but I doubt a driver's behaviour outside of a cabinet is particularly relevant. At high output the diaphragm’s movement is influenced by the difference of internal and external air pressures.
Try blowing up a balloon without sealing the aperture between breaths.
 
#9
Surtsey said:
As indicated, I'm just a novice but I doubt a driver's behaviour outside of a cabinet is particularly relevant
Click to expand...

It is absolutely relevant.

Klippel analysis of drive units and advanced simulation tools have resulted in much lower distortion transducers, and pinpointing the different mechanisms for different distortions.

The difference in pressure of a 1 cubic foot sealed box with an 50.84 square inch piston ( Dayton UM-10 ) with the driver at 19 mm xmax inwards is 0.33 PSI higher than static. If the box were increased to 3 cubic feet, the difference in pressure would be 0.11 PSI.

If the difference of a fraction of a PSI resulted in a DC offset, daily fluctuations of atmospheric pressure would result in sealed subwoofers looking somewhat bulged out during daily low atmospheric pressure conditions and bulged inwards during high atmospheric pressure.
 
#10
diyuser2010 said:
The difference in pressure of a 1 cubic foot sealed box with an 50.84 square inch piston ( Dayton UM-10 ) with the driver at 19 mm xmax inwards is 0.33 PSI higher than static. If the box were increased to 3 cubic feet, the difference in pressure would be 0.11 PSI.
Click to expand...

Exactly.
PSI = POUNDS PER SQUARE INCH.

50.84 x 0.33 equates to around 17lbs. Load 8 bags of sugar onto the cone, tell me if it moves.
 
#11
Surtsey said:
Load 8 bags of sugar onto the cone, tell me if it moves.
Click to expand...

Of course it is going to move with 17 pounds of sugar piled onto it. I am well aware of what PSI stand for, no need to shout it out. It was a hypothetical example of a mythical 1 cubic foot sealed box. ( not that I'd ever build one )

Maybe we could re-run some numbers with a 12 cubic foot box, one that would be worthy of calling a subwoofer.

Besides, the Polk PSW10 mentioned is a ported subwoofer. At tuning, the pressure is higher internally than a sealed box.
 
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