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Total Equivilent Length of a 90 in a port?


Markous

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Let me start off by saying i am looking at this question as a person who is a pipefitter with 18 years experience in my trade (Nearly 10 years as a Canadian Red Seal Journeyman)

I am curious about the total equivalent length of 90 degree elbows (round) or bends (L shaped) in ported designs of subwoofer enclosures.

In trade school i was taught that the change of direction caused by a 90 degree turn creates resistance in the flow of whatever medium should be passing through it.

As an example, the resistance to flow with water in a normal radius 6" ninety degree elbow has a total equivalent length of 14" of a straight run of the same size (#'s from a chart i found on google images)

I would think this should be a factor to be considered in designing a ported system yet i've yet to see any mention of it in my time spent in the car audio hobby/habit/addiction/disease

Not sure if sound waves care if they are going straight or through a curve? but wouldn't the air that is transmitting the wave be affected and in turn affect the sound wave?

Figured i start this topic for discussion and learning purposes.

 

 

'07 Ford Ranger - DM-608 I E700.4 I SA-CX6.5 v2 I SAZ-1500D 15th (x2) I Zv6 12" D1 I SB500-34 I JP40 I

On 5/21/2015 at 7:07 PM, boom50cal said:

of course he gives no fucks. it's a ford ranger.

only bad mother fuckers drive ford rangers

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The total length of a 90 is measured straight down the middle. As for the air being restricted, I have seen people do two 45s instead of a 90 but I don't know if it really gains anything. The air moving in an out of the port is not necessarily the sound, the sound waves propagate through the air in the port. The fact that the air in the port is moving is a byproduct. Like when a port is tuned to 30hz and 10 hz is played. Lots of air but not much sound.

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Thank you for the comment STM, i am aware of how the port length is determined by the centre line measurement.

I am curious though, if the resistance to airflow caused by the change in direction(s) by using one or more 90's is a factor that is overlooked in determining the physical dimension.

I might be "06chargering" (sorry guy, had too, LOL!) this thought in my mind but it something that has, not bugged me but rather made me curious as a tradesman.

I haven't seen it discussed before it may be a non-issue but i know how technical i like to be sometimes and wanted an answer/explaination

 

'07 Ford Ranger - DM-608 I E700.4 I SA-CX6.5 v2 I SAZ-1500D 15th (x2) I Zv6 12" D1 I SB500-34 I JP40 I

On 5/21/2015 at 7:07 PM, boom50cal said:

of course he gives no fucks. it's a ford ranger.

only bad mother fuckers drive ford rangers

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There still is resistance in a direction change though, albeit a possibly negligible amount to be a factor.

'07 Ford Ranger - DM-608 I E700.4 I SA-CX6.5 v2 I SAZ-1500D 15th (x2) I Zv6 12" D1 I SB500-34 I JP40 I

On 5/21/2015 at 7:07 PM, boom50cal said:

of course he gives no fucks. it's a ford ranger.

only bad mother fuckers drive ford rangers

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1 hour ago, Markous said:

There still is resistance in a direction change though, albeit a possibly negligible amount to be a factor.

Never said there wasn't...

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There was no intent to offend (probably to strong of a word for what i'm trying to say) with my reply to your post.

I'm sorry (Canadian thing) if it was taken that way.

 

 

Off to google and do what i should have done first, some of my own research into this.

'07 Ford Ranger - DM-608 I E700.4 I SA-CX6.5 v2 I SAZ-1500D 15th (x2) I Zv6 12" D1 I SB500-34 I JP40 I

On 5/21/2015 at 7:07 PM, boom50cal said:

of course he gives no fucks. it's a ford ranger.

only bad mother fuckers drive ford rangers

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This flue gas (air & combustion products) chart shows pipe sizes and total equivalent length of a straight run in inches. I can imagine the bends in a  hard L, C or labyrinth style being even more restrictive than these numbers.

table1.jpg

I don't mean to irritate with bumping this thread but i am hoping someone can explain what i feel is a factor in design that i haven't seen addressed before.

'07 Ford Ranger - DM-608 I E700.4 I SA-CX6.5 v2 I SAZ-1500D 15th (x2) I Zv6 12" D1 I SB500-34 I JP40 I

On 5/21/2015 at 7:07 PM, boom50cal said:

of course he gives no fucks. it's a ford ranger.

only bad mother fuckers drive ford rangers

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I work at a service company as an HVAC tech and installer but we also do plumbing installs and repair so im a little familiar with being conscious of resistance within pipes/plumbing. Im sure there is definitely an amount of added resistance as the air flows in and out of the port through a bend of any kind. As to how much is speculation IMO. Best thing to do as we all know is to make the bend smooth as possible, through kerfs, elbows for aeroports, 45s in slot ports etc. I just finished building a basic design slot port box for 2 alpine type s 10's to put in my wife's Camry, and i did not add any 45s in the port corner, i just rounded off the sharp corners of the boards in the slot port. No port noise that i can hear personally. Its just a daily driver simple system though. 

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Not sure if Im answering this the way you are expecting, but the length of a 90 degree bend is usually taken from its center line (for car audio purposes), and its affect on the equivalent length of the port is probably small.  However, I'm skeptical that with ALL OTHER FACTORS combined that the equivalent port length difference by adding a 90 degree bend would cause more error than incorrectly stated TS Parameters.  Or the inaccuracy of the Torres calculator.  

On 12/31/2017 at 2:04 PM, Markous said:

There still is resistance in a direction change though, albeit a possibly negligible amount to be a factor.

This.  Air isnt very dense, so the drag along a smooth wall at 30m/s or less should be negligible.  

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