I have been in the game alittle while.. I have been away from the forums for sometime but......
I am building a ported box and im wondering on a slot port does the "tunnel have to be straight or would it hurt to be bent... anyone know I have a rise in the trunk and was wondering if i could angle the box over that rise give a straight then up angle to the box sort of like _____/ not quite as drastic bend....
I build slot port enclosures with right angles in the ports nearly 40% of the time. go for it man!
You can bend ports as many times as you like as long as you take your measurements correctly when it comes to port length. The key is that you have to use the center line of the port as your port length. As you build your 90 degree bend, the outside boundary is longer than your inside boundary so you have to take that into consideration for correct tuning.
The following picture shows how to properly measure slot port lengths when you have to bend the overall length. The measurement A is taken from the outside edge of the port opening and ends at 1/2 of the port width from the back of the box, since the port should be the same width the entire length. Measurement B is taken from 1/2 the port width from the side to 1/2 the port width past the end of the port baffle. The end of the port should be no closer than 3 times the width of the port from the next side of the box.
]Measu wrote:
ement B is taken from 1/2 the port width from the side to 1/2 the port width past the end of the port baffle.
Actually the measureable port length ends exactly where the physical port ends (re: left side of B in pic above). The acoustical port extends farther but can't be seen and is not guessed at for measurement. If the example shows a 3" wide port, the measurement as shown in the pic would be 1.5" too long.
Measure long port side length total, measure short length total. Find the middle ground between the two measured lengths for port length.
]The e wrote:
d of the port should be no closer than 3 times the width of the port from the next side of the box.
One times the port width is sufficient.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Just taking what I was taught by the techs from JL about the tuning length and port clearance.
Yes, that is exactly what JL says about end correction factor. The dilemna occurs when one is using a software program to model the port and enclosure. End correction factors are built into the programs. But if someone was calculating the formula (see the above link) without the aid of modeling software, he would add the correction factor as JL notes.
The part about leaving three times the port diameter away from the end wall has got me stumped, though. https://www.diysubwoofers.org/faq.htm says this:
2.03 - Where should I place the port(s)?
If your system calls for the use of ports, these can be placed on any side of the enclosure, once the intended location meets the following requirements:
1. The exit of the port should be at least one port diameter away from any external surface.
2. The entrance of the port should be at least one port diameter away from any internal surface, including the driver.
I've known it to be "at least", but I haven't heard of using three times width as a rule.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
I thought the same thing, that the end should be at least ONE port width away from corresponding walls, so when the JL tech told me at least three, I took the advice and built accordingly. However, since the advice was asked for a very special occassion, I followed suit, and the rest of the boxes I have built, I used the old "one width" rule without problems. So when I posted earlier, I was spreading the advice of the professional, and leaving my own unproven theory off the website. :)