My Findings...

[Raptorman]

commenting to tune in.

[DubNDodge]

+1

[oldsoundguy]

Hopefully the testing will be done before I am ready to build my next box.

[Wicks]

Holy shit, best thread I've seen in a long time.

Science makes me happy

Love to see where this goes.

[Krakin]

To help some people get some back ground knowledge on ports I'll try to explain them. An average person would think that the output of a port is 180 degrees out of phase, because as the driver is being pulled back into the enclosure it would in turn push air out at the same time.

The reason a ported speaker works is because the air in the port causes a 180 degree phase shift in the air behind the driver. When the air comes out of the port, at least at the tuning frequency, it is in-phase with the front of the driver, giving a boost to the output.

As air in the core of the port becomes turbulent, this phase shift decreases, thus reducing the in-phase contribution made by the port. The total output of the box no longer rises at the same rate as input power is increased, and the port is said to be compressing. Eventually the port acts as a mere hole in the box, short circuiting the acoustic output of the driver and allowing excursion to become uncontrolled.

[Triticum Agricolam]

I haven't gone through the paper on AES yet, but there was a work done on the flaring and maximizing the performance from ports that suggests that you should make the flare radius of the port equal to the length of the port.

Like this,

"The ideal port shapes for high-velocity inlet and exit air streams are different, and the best solution is one that balances both."

It would be cool to see something like this done, if you are interested in it.

The article: http://www.aes.org/e-lib/browse.cfm?elib=11094

I've looked at this paper as well, my big question about port shapes such as what it is the picture is how do you even begin to calculate what the proper size/length should be to get your desired tuning?

[Krakin]

Shoot if I knew lol, I would say to start with half way through the radius and work from there.

[Guest]

following this thread...

[Dwn4BassAlan]

WARNING: The following post contains actual scientific test results. No anecdotes allowed.

So first a little background. I'm employed as a professional fuck-off. I race for a living, and design/develop and build racing engines. What does this have to do with subwoofers/enclosures?

Airflow. I'm an airflow guru. I've been porting cylinder heads for years. You learn that air does NOT act as you would intuitively think it would.

For the last few months, I have been applying my knowledge and testing procedures from cylinder head airflow to subwoofer enclosures.

I will share some findings, but please understand that I can't share everything I've found, all at once. There is some findings that need to be further tested.

1. 45's in boxes.

Seems pretty straightforward, right? WRONG. I know that air never likes to turn more than +/- 14deg in any direction.

So I made a port with 1 90deg turn. I used a flow bench capable of pulling 60" of vacuum, but pulled 28" WC for all testing.

I tested ports with the same CSA (cross-sectional area), 4 in total on the first round of testing. The numbers were recorded.

I then put 45's in the port, both inside and outside corner, while keeping the CSA the same throughout the port.

Well, on average, ports with 45's flowed, on average, 14% WORSE than ports with 90deg corners. And yes, all variables were held constant.

I then used a pitot tube to do a velocity profile. The flow was it's fastest just after the first 45, which indicates choking and turbulence near the boundary layer. These findings were confirmed by doing a smoke trace as well as a wet flow analysis.

So, in this rudimentary test, it appears 45's to be a hindrance rather than helpful.

Yed, I did test an idea that improved flow significantly over both 90 and 45s. That will be my next post, as it is 4am and time for coffee and a pastry.

I have conducted many other tests, and I will post them in the following days as I find the time. Also, please forgive me if I don't share everything in public, as I feel I've learned some groundbreaking things.

Btw, I am not a box designer. I pay other for that. People who are smart enough not to say "oh yeah, dd's love big ports, brah"

For people who would like other tests performed or would like to speak in private, you can pm me and I will give you my cell number.

More in a bit...

Hey, change your profile picture to your real face, Bill..........We know it's you....

I'll suggest one of your better shots for you:

[Dwn4BassAlan]

Sorry to break it to you guys but you're literally wasting all of your time even considering all of this.

Have you already forgotten that, from the mouth of Dr.Subwoofer himself, we know for a fact; 30Hz is the BEST thing you can possibly tune to. There is no way to refute that evidence, so just save yourselves some time and energy and tune to 30.

Good thing I remembered, might have actually tried like, real science or something, with tests. Ew. Don't even like to think about that. :D

lol