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RSDXzec
06-02-2012, 05:50 AM
I used winisd to make my box and decide my port length. Tuned at 25.5hz my box port length by winisd is 24.7", this is the same measurement given on this port calculator Port Length Calculator (http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm)

But the port calculator has the option of slotted port or not, and with a slotted port it gives me a length of 20.3". My box is a slotted port and I made it 24" long, so did I tune my box wrong? Or what's with the option on whether or not it's a slotted port, how does it matter?

Cheers.

Moble Enclosurs
06-02-2012, 12:55 PM
Well, slot ports usually utilize a wall or two or more to create the ports physical form. A square port has the same output characteristics as a round port with the exception of less even resonance control, so square ports have more resonance changes when the sound exits, and can change phasing. BUT for length, this is mainly because of the wall where a corner lies. The square port does not have the ability to build up pressure AT the throat of the port, like a slot port does, if it is a constant port. Therefore tuning may be a bit different, and therefore lengths may need to be adjusted.

But these differences are very minor in the audible sense. Unless you are worries about SPL scores, they are not very noticeable. BUT I will say, that using a square port will likely give more of a peaky response compared to a slot port more to a 1:1 hxw ratio because the output characteristics of each (when comparing the two of a square and a slot 1:1) are very different. When the slot port becomes more of an 8:1 ratio, it begins to act more compressed than coupled EVEN THOUGH the square area remains constant. This is due to the high pressure in the corners. The further away the pressure areas are from each other, and the more symmetrical the output is, the smoother the output will be.
The good news for us is...we are dealing with vehicle cabin volumes and low to very low frequencies. That being noted, we can pay less attention to those types of changes when dealing with high power applications.

So, in general, the differences of lengths are minor, and an average of the two can be used for any doubts of its accuracy. The audible output will be similar for both if the ratios are kept under control. Hope that helps!

RSDXzec
06-05-2012, 08:35 AM
Well, slot ports usually utilize a wall or two or more to create the ports physical form. A square port has the same output characteristics as a round port with the exception of less even resonance control, so square ports have more resonance changes when the sound exits, and can change phasing. BUT for length, this is mainly because of the wall where a corner lies. The square port does not have the ability to build up pressure AT the throat of the port, like a slot port does, if it is a constant port. Therefore tuning may be a bit different, and therefore lengths may need to be adjusted.

But these differences are very minor in the audible sense. Unless you are worries about SPL scores, they are not very noticeable. BUT I will say, that using a square port will likely give more of a peaky response compared to a slot port more to a 1:1 hxw ratio because the output characteristics of each (when comparing the two of a square and a slot 1:1) are very different. When the slot port becomes more of an 8:1 ratio, it begins to act more compressed than coupled EVEN THOUGH the square area remains constant. This is due to the high pressure in the corners. The further away the pressure areas are from each other, and the more symmetrical the output is, the smoother the output will be.
The good news for us is...we are dealing with vehicle cabin volumes and low to very low frequencies. That being noted, we can pay less attention to those types of changes when dealing with high power applications.

So, in general, the differences of lengths are minor, and an average of the two can be used for any doubts of its accuracy. The audible output will be similar for both if the ratios are kept under control. Hope that helps!

bit of a late reply, but I read over it a couple of times, and when you talk about square ports I'm not sure if you're just referring to ports with the same LxW or even rectangular ports that don't use the box wall.

Been a little busy, but in about 2 weeks I'll be starting a new box design and I'm pretty keen to get started. I'll be going with round ports for this one.

madcad95
06-05-2012, 10:00 AM
From what I understand is that slot ports need to be a lil shorter due to the 3 sides of the slot port being part of the box and the fact they are longer then the 1 side that's not makes the port longer naturally.

Moble Enclosurs
06-05-2012, 10:46 AM
bit of a late reply, but I read over it a couple of times, and when you talk about square ports I'm not sure if you're just referring to ports with the same LxW or even rectangular ports that don't use the box wall.

Been a little busy, but in about 2 weeks I'll be starting a new box design and I'm pretty keen to get started. I'll be going with round ports for this one.

Nice! Yea, what I mean by square is not based on hxw=1:1 I mean by the use of a "squared" port without wall reenforcement. In other words, a "floating" slot. :D

Moble Enclosurs
06-05-2012, 10:48 AM
From what I understand is that slot ports need to be a lil shorter due to the 3 sides of the slot port being part of the box and the fact they are longer then the 1 side that's not makes the port longer naturally.

Kind-of yes. The parts that matter in the dimensions difference of length is the part that can be either considered compression volume OR port length, not actually the loading area of the port even with the 3 walls, but the area just before the throat of the port. :D So, yes, pretty much the deciding factor and this is usually where that corner is that I was referring to that changes the resonance's and such. It all works together.