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post #3991 of 3994 Old Today, 09:33 AM
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The Helmholtz resonator reference reminded me of Tom Danley's trip to the pyramids to measure the sound inside using a microphone and an accelerometer.

The Great Pyramid: Early Reflections & Ancient Echoes
TestTones, Indiana Jones and the Lost Knowledge of Yore

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post #3992 of 3994 Old Today, 11:24 AM - Thread Starter
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Quote:
Originally Posted by 3ll3d00d View Post
Since the driver is barely moving at this point, isn't it more likely that a port produces greater pvl per SPL than a driver? If we assume the driver doesn't contribute in the ported system, you could test this by applying a bandpass filter to a sub so as to coerce it into the same FR as the port has alone. Compare the tr results when playing a sine wave (or noise band limited to the port output passband?) and see which one wins.
I believe I've already performed this test as documented in post 5 below:

http://www.avsforum.com/forum/113-subwoofers-bass-transducers/1488059-your-home-theater-ulf-score.html#post23676274

The results support the hypothesis as I recorded more Tactile response with the vibration meter with the ported design.

But you're right, it could be because the port is contributing more pvl per spl compared a sealed design at those frequencies. I don't understand the physics enough to explain why if that was the case, but definitely a possibility.
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post #3993 of 3994 Old Today, 11:42 AM - Thread Starter
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One other note about pvl...

It is directional. That being the case, subs where the port fires up or down or a different direction than the driver, may not be able to optimize tactile response...above tune, the driver produces the lion share of pvl, but near tune the port does. If they aren't firing the same way, you may lose TR.

Directionality is an easy one to test...for those with nearfield setups, turn your sub so that the driver is facing in the opposite direction of your seating...Tactile Response will drop significantly even if calibrated with the same spl.

Of course boundaries could also come into play, and perhaps dual opposed boundary loading might be a sweet spot as I know @coolrda experienced a difference when he went DO behind his seating...
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post #3994 of 3994 Old Today, 11:52 AM
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Quote:
Originally Posted by dominguez1 View Post
But you're right, it could be because the port is contributing more pvl per spl compared a sealed design at those frequencies. I don't understand the physics enough to explain why if that was the case, but definitely a possibility.
I wonder whether different port configurations behave differently too? e.g. 1 big port vs 3 smaller ones.
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