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But in a 90 degree hard corner, the transition from pressure on one wall to the other is very abrupt. In reality, the corner introduces a pressure gradient, and in the case of hydraulic pressure a sheer force. That's why you never see hydraulic cylinders without rounded corners. Pneumatic pressure is more forgiving, and the tiny gradient creates a small pressure difference. Remember this.

The nearby pressure tries to equlibriate to the corner pressure. It would take more acoustic energy to pressurize the chamber with hard corners than say a cylinder or sphere of the same volume. Why? Sound pressure is oscillating pneumatic pressure; the chamber pressurizes, and relieves pressure into the vent in a ported box, and then reverses the process. For a given speaker "stroke" there is a defined amount of energy that is transmitted into the box volume. This energy is the same energy, that excites the port volume. Given the energy must be conserved, any loss of energy would result in less port excitation. This is where the loss of pressure energy in hard corners comes into play. In an acoustic circuit, it would equate to small resistors, one for each hard corner, especially the tri axis intersections. So he assumption that box rise was lowered is correct, though the volume displacement may have also been a factor in spl results. The size of the 45 is not critical, the more "round" the corner the better. Hard corners in a port will have a turbulent effect as well, but the oscillating air in the port doesn't see the same effects as in the pressure chamber. The argument that air " flow" is better in the box is not true.

I did one build, with decreasing box rise as much as possible the main goal. Dividing flat surfaces into equal "pressure chambers" and eliminating all hard corners were the two initial objectives.

Compared to the previous/initial build, where the volume was essentially the same with no 45s, the rise went from 2.7 times rise down to 2.3 times, at the minimum impedance.

A lot of variables other than just the internal geometry changed, so I can't say for sure that the decrease in rise was purely due to the angled corners. The frequency at the minimum impedance moved from 35 to 36, and the box volume as calculated by solidworks was about 0.1 cubes smaller. But same ports, same drivers, same baffle placement, even the same runs of speaker wire. Seems like there's some evidence in there to support the physics.

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you want the port to flow as smooth and easy as possible however you also want placements of sub vs port to create resistance. 1 big reason why port directly inline with the sub tend to have less than desirable results. always make the sub work to move that air but yet smooth line the airflow direction to. thats why for example so many suv boxes with subs up and port back work out so well. redirection of air flow causes self resistance yet still smooth out the airflow so static voids do not appear. a smoke machine really helps to show what im talking about. fill the box with smoke and run at low power and then you can see the area's that air gets hung up. make mods (45's or rounded edges) to free that trapped air.

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you want the port to flow as smooth and easy as possible however you also want placements of sub vs port to create resistance. 1 big reason why port directly inline with the sub tend to have less than desirable results. always make the sub work to move that air but yet smooth line the airflow direction to. thats why for example so many suv boxes with subs up and port back work out so well. redirection of air flow causes self resistance yet still smooth out the airflow so static voids do not appear. a smoke machine really helps to show what im talking about. fill the box with smoke and run at low power and then you can see the area's that air gets hung up. make mods (45's or rounded edges) to free that trapped air.

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41hz - 141.5db - 587 watts (7.41 ohms)

42hz - 141.9db - 561 watts (7.72 ohms)

43hz - 142.2db - 568 watts (7.11 ohms)

44hz - 142.3db - 595 watts (6.24 ohms)

45hz - 142.1db - 689 watts (5.41 ohms)

After adding the 45 degree angles

41hz - 141.7db - 668 watts (7.07 ohms)

42hz - 142.0db - 637 watts (7.40 ohms)

43hz - 142.3db - 633 watts (7.06 ohms)

44hz - 142.5db - 663 watts (6.15 ohms)

45hz - 142.5db - 757 watts (5.34 ohms)

The power delta in every result *should have* resulted in a +.6dB gain. Theoretically. And at these power levels, it probably should have.

I would like to see a retest with the original box after having removed the 45's and using the added power that the second test utilized.

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Sort of, except that the goal of the rear chamber in a sealed enclosure is only to absorb the rear wave energy of the cone, not to transfer the energy to a resonator. From this argument, the more sharp angles you can create in a sealed enclosure, the better.

Really though, the efficiency of the geometric shape used for the enclosure means more than the corner geometry alone. There is a lot of do***entation covering these variations, from trapezoids and cylinders even spheres. Each shape will shift the system a slightly and made for a different sound.

I agree, it seems like spl should have gone up more at certain frequencies even if it was a difference of 60-80 VA. I never tested my results by spl, just impedance alone.

41hz - 141.5db - 587 watts (7.41 ohms)

42hz - 141.9db - 561 watts (7.72 ohms)

43hz - 142.2db - 568 watts (7.11 ohms)

44hz - 142.3db - 595 watts (6.24 ohms)

45hz - 142.1db - 689 watts (5.41 ohms)

After adding the 45 degree angles

41hz - 141.7db - 668 watts (7.07 ohms)

42hz - 142.0db - 637 watts (7.40 ohms)

43hz - 142.3db - 633 watts (7.06 ohms)

44hz - 142.5db - 663 watts (6.15 ohms)

45hz - 142.5db - 757 watts (5.34 ohms)

The power delta in every result *should have* resulted in a +.6dB gain. Theoretically. And at these power levels, it probably should have.

I would like to see a retest with the original box after having removed the 45's and using the added power that the second test utilized.

Joined

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12,531 Posts

41hz - 141.5db - 587 watts (7.41 ohms)

42hz - 141.9db - 561 watts (7.72 ohms)

43hz - 142.2db - 568 watts (7.11 ohms)

44hz - 142.3db - 595 watts (6.24 ohms)

45hz - 142.1db - 689 watts (5.41 ohms)

After adding the 45 degree angles

41hz - 141.7db - 668 watts (7.07 ohms)

42hz - 142.0db - 637 watts (7.40 ohms)

43hz - 142.3db - 633 watts (7.06 ohms)

44hz - 142.5db - 663 watts (6.15 ohms)

45hz - 142.5db - 757 watts (5.34 ohms)

The power delta in every result *should have* resulted in a +.6dB gain. Theoretically. And at these power levels, it probably should have.

I would like to see a retest with the original box after having removed the 45's and using the added power that the second test utilized.

Or...use the same box w/o the 45's in it...do a test. Jot down results. Then add the 45's in it. Then do 2nd test. Then compare the 2 tests and see if anything is gained.

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1,519 Posts

again place the 45's in a manner of which will help increase air flow. some area's depending on the build might not need or even call for no 45's

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1,519 Posts

Which is why I was hoping others would have data to contribute as well =)

41hz - 141.5db - 587 watts (7.41 ohms)

42hz - 141.9db - 561 watts (7.72 ohms)

43hz - 142.2db - 568 watts (7.11 ohms)

44hz - 142.3db - 595 watts (6.24 ohms)

45hz - 142.1db - 689 watts (5.41 ohms)

After adding the 45 degree angles

41hz - 141.7db - 668 watts (7.07 ohms)

42hz - 142.0db - 637 watts (7.40 ohms)

43hz - 142.3db - 633 watts (7.06 ohms)

44hz - 142.5db - 663 watts (6.15 ohms)

45hz - 142.5db - 757 watts (5.34 ohms)

The power delta in every result *should have* resulted in a +.6dB gain. Theoretically. And at these power levels, it probably should have.

I would like to see a retest with the original box after having removed the 45's and using the added power that the second test utilized.

21 - 36 of 36 Posts

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