dumb question about flared vents

Hi there Gonar,

A flared port shares part of the air in the flare with the surrounding air, meaning that the port appears shorter.

The generally accepted adjustment is to subtract half the flare radius from the physical length to obtain the effective length. If both ends of the port are flared, the adjustment is done for each flare



The PSP ports have a flare radius of around 30mm (or 1-3/16"), so for a port with a flare on each end , the overall physical length is the WinISD length plus 30mm (or 1-3/16")

regards
Collo

If you want more port length for the sake of accuracy, you could use two ports instead of one. Each would then be twice as long (or at least very close to that).

A quick check with WinISD - 3.8 cu.ft / 25hz / single 3"

Your effective length of 5.43" is what you get if you flange both ends.

The normal mounting method is to leave the inside end free, so you select "One Flanged end" for the end correction. This gives you a required length of 5.79"


Another check is to use the calculator on the PSP website
It gives a "Straight port length required" of 5.83" - they must be using a slightly different equation to what winISD uses.

Now adding the adjustment for flares to find the overall physical length:
WinISD plus 1/2 flare radius gives 5.79 + 1.19 = 6.98
PSP website gives "Flare length port required" = 6.83"


PSP are adding 2 * 1/2" for their flare adjustment, which is what you would normally use for a 1" flare radius. I know that their new 6" ports use a 1" radius, so perhaps they have dropped their other products to that size as well - it would be interesting to get some feedback from people who have recently bought their products.

If that is the case then the WinISD method gives:
WinISD plus 1/2 flare radius gives 5.79 + 1 = 6.79 .... essentially the same as the PSP method.


The Installation Instructions on the PSP website for 3" ports suggests that each flare and connecting ring adds 3" to the length. This gives you somewhere between 0.98" and 0.83 for your straight section.

They suggest using ordinary ABS adhesive or similar type glue

The difference is less than 4 mm. Do you really believe the port structure and tuning frequency is going to be that accurate at the end of the day?

I look at comparisons such as Collo showed above as verification, not as a problem with which one to use. You have verified the size, so if you can possibly construct this port precisely so that if falls into that range then you have done well.