# Port location and diameter with flare



## aceinc (Oct 24, 2006)

I am building a box that has 2 - 5" nominal drivers. When I model it with winisd it tells me I need at least a 1-3/4" diameter port for the air speed to be .16 (vent Mach). I purchased the 1-1/2" flared port from PE (flare on one end only). Winisd calculates the air speed for a 1-1/2" port to be .21.

What kind of problems will I run into using just one of these? ie is .21 that bad?

Is it better to put the port on the front, or the back? 

If I put it on the back, how far from the wall of the room should the speaker be?

Should a flared port be longer or shorter, or the same length as a non-flared port to acheive the same freq?

Lastly, where do I measure the port length from? The end of the flare, the start of the flare...?

Paul


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## brucek (Apr 11, 2006)

> Lastly, where do I measure the port length from? The end of the flare, the start of the flare...?


See here

brucek


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## BoomieMCT (Dec 11, 2006)

aceinc said:


> What kind of problems will I run into using just one of these? ie is .21 that bad?


It depends on what you listen to and how loud. If send a low, loud signal to the speaker you may get some port chuffing. Or, you may not. I have built speakers with slightly undersized ports and haven't heard chuffing. Having a flare helps reduce this effect. Remember WinISD is calculating the port airspeed assuming full power at a specific freqency.



aceinc said:


> Is it better to put the port on the front, or the back?
> 
> If I put it on the back, how far from the wall of the room should the speaker be?


I'm not sure what the official answer on this is but I'd guess that a rear port will take better advantage of room gain (being closer to a wall or corner) whereas a front port would have more flexibility in placement. I have few "ideal" places to set up speakers in my house and I find rear ports to be boomy if not optimally set up. Like I said - this is just my personal experience.



aceinc said:


> Should a flared port be longer or shorter, or the same length as a non-flared port to acheive the same freq?
> 
> Lastly, where do I measure the port length from? The end of the flare, the start of the flare...?


Longer. I believe you measure the unflared part and add half the flare radius (not the port radius) of each port. So, if you have a 3 in straight pipe and add a flare with a 1/2" radius, your effective port is 3 1/4".


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## Bradley (Aug 2, 2007)

BoomieMCT said:


> Longer. I believe you measure the unflared part and add half the flare radius (not the port radius) of each port. So, if you have a 3 in straight pipe and add a flare with a 1/2" radius, your effective port is 3 1/4".


If that's the case, why does port length go down in WinISD if you switch from zero flared (or "flanged") ports to 2 flared ends? Likewise, in Collo's Boxnotes if you go from zero to 2 flared ends, the tuning frequency drops (as if effective port length has increased). This suggests each program is using port length to refer to the straight section without the flange, but I've read conflicting reports about that. So, I'm pretty confused right now. :scratch:

EDIT: Nevermind! I've had my head in my a$$ all day today about this... because I confused "flanged" with flared, or at least thought they were being used to mean the same thing. Oops! :duh:


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