trading off port area for tuning freq and box volume or vice versa

[ROLEXrifleman]

Ended up cutting my port size down by .5" to make the subs fit. Went from 57^2 29Hz with 4.5 cubes to 51^2 27hz and 4.7 cubes.

Even with the 57^2 hair tricks seemed a pipe dream so I'm not feeling too bad seeing as I dropped my tuning freq and ended up with a slight gain in box volume.

I think it will play low, so in that case mission accomplished.

[TRTC360]

not exactly 100% sure what the actual question is here, but if i'm reading it correctly, yes i'd sacrifice port area to gain box volume and lower tuning.

[ROLEXrifleman]

Not realty a question, more thinking out loud than anything trying to drum up some good conversation vs. some of the other crap we've been reading lately.

[DylanBunch]

i had an x 18 for a couple months and the day before i sold it i made the port thinner just by cutting two pieces of mdf the same dimensions of my original port pieces and screwing them together, my port area went from 100" to 89" and honestly it felt a tad louder or maybe just louder on a wider range. I believe the box volume stay the same since the original port pieces were still in place but it definitely sounded a lot better. Also lowered my tuning frequency from 35 to 32

[Krakin]

The lower the tuning the lower the required port area.

In your design you were pretty far below the audiophile consideration of the minimum required for full xmax, but you really don't have much more of and option unless you want to get really creative. And I remember you didn't.

[Krakin]

I don't remember the exact piston area of the JL12w7's but they have a larger surround than commonly seen right?

If so you shouldn't be too bad.

If you want I can also try and figure out the required flare, which will help a lot.

Edit: I also only have tried it with round ports so converting to slot could be off.

[Omega5002]

Larger volume > Larger port

[FeelDaBass]

The lower the tuning the lower the required port area.

In your design you were pretty far below the audiophile consideration of the minimum required for full xmax, but you really don't have much more of and option unless you want to get really creative. And I remember you didn't.

I have to ask since this thread is just for conversation... What would an audiophile consider as a minimum required for xmax with a T1D215 (1000 rms) off a T1500bdcp @ 4 ohms? My box is ~3 cubes between 34 and 35 hz with 2.75" port by 12.5" height 20 inches long?

[Krakin]

The lower the tuning the lower the required port area.

In your design you were pretty far below the audiophile consideration of the minimum required for full xmax, but you really don't have much more of and option unless you want to get really creative. And I remember you didn't.

I have to ask since this thread is just for conversation... What would an audiophile consider as a minimum required...

First let's define why you need to have a certain amount of area for certain applications. The port area is determined the amount of and the maximum velocity of air that will be trying to move through the port of a box.

The variables that need to be know to figure this out are:

• Effective Piston area in square centimeters (Sd)
  • Sd = π*(Dia/100)^2/4

• Xmax is the maximum linear excursion of the driver in meters
  • (conservatively) Xmax = (the voice coil height minus the top plate's thickness) / 2

• The maximum linear volume displaced by the driver (Vd)
  • ​ Vd = Sd*Xmax/1000

• Tuning frequency in Hz (Fb)

• The number of ports (Np)

• And finally the minimum port area in centimeters (dmin)
  • Dmin = 100*(20.3*(Vd^2/Fb)^0.25)/Np^.5

There are some more formulas and most of them require calculus (which I don't feel like doing at 1:20 am)

The amount required to completely eliminate the "chuffing" or "fluttering" sounds that an enclosure can make when there is not enough port area.

Don't let the saying "round ports are more efficient" throw you off course. Yes they are more efficient, but some people think of this as a way of it being okay to lower area. That is just contradicting running round ports.

Just really loosely your dmin for a T1D215 at 34-35Hz should be around 58-59 in².