PCV for ports

[PoorboyMike]

Just a few questions (probably stupid) about pcv fittings.

What affect would a Y-fitting have on overall port length? If you put the Y inside the box so you had 2 inlets and 1 outlet, could you run a shorter port for a given tuning, or would it actually need to be longer?

2nd, I notice some guys don't recomend elbows for ports when trying to get a long port in a smaller box. Instead of 90s, would 45 or even 22 1/2 degree elbows cut down on some of the problems? You wouldn't be able to stuff as much port in a box, but it could give you a couple extra inches over a straight pipe without as sharp of a bend as a 90.

And, since 6" flares are no longer available, how would a 10X6 coupler work for a flare? If not so well, would I be sacrificing much sound quality by going to a 4" precision flare from PE?


I'm just looking for some options for my upcoming sub project. Since I can't seem to make up my mind about sealed or ported, I'm considering doing a convertable box, but I really don't want to make it any bigger than 110 liters. The driver will be a BP1503.

[SteveCallas]

I don't know about the Y fitting, but what about just making a flair on what I assume will be MDF? You can either use a large roundover bit or do it by hand with a file and some sand paper.

[Bent]

the Y-fitting is an interesting idea though, a dual 6" to a 10"?
or dual 4 inch flared to a 6 inch?

hmm????

[PoorboyMike]

the Y-fitting is an interesting idea though, a dual 6" to a 10"?
or dual 4 inch flared to a 6 inch?

hmm????

I thought it seemed interesting too. There are a lot of options as far as sizing too, I just don't have a clue how any of them would work.

Another thing I thought of as I was laying in bed with the jitters from this darn cold medicine is stepping up or down the size of the port a couple of times with reducers. Exhaust companies do this to increase the flow of header pipes. The only problem is, I have no idea how this would apply to speaker ports.

[dyazdani]

I have never thought about the Y fitting. If I had to guess, I would say that it would increase the "effective" diameter of the port therefore requiring a slightly longer port tube. If you had two ports entirely, you would divide your box volume in two and then do the calculation. I ended up doing that on my last box, it worked well and allowed me to arrange the ports a little easier.

Stepping down the diameter of the port (again a guess) would effectively decrease the overall port diameter and require a shorter port. However, you would have to see about port noise due to the increasing velocity of the air as it exits the port.

I have not seen a calculation for a port tube with varying diameters. Maybe in the 2nd case, you could take an average of the beginning and ending diameters.

A standard formula can be found here.

I'm not an expert at this, so hopefully one of the many geniuses here will give you a more thorough answer.

[Bent]

at what point (speed) does port noise become a problem?
Unibox indicates a coupla different velocities on it's graphs, but what is really not acceptable?

[dyazdani]

I haven't used UniBox so I'm not sure what units the graphs are in. If I remember correctly, WinISD's are in meters/s in which case I believe they suggest to try and keep it below 20 m/s.

The same link in my other post also gives a formula to calculate the minimum port diameter to prevent port noise.

Flaring the ports also helps with this...

[Dennis H]

Elbows are fine. Plenty of designs use folded ports, usually made out of wood, e.g. all the transmission line designs out there.

A Y would make things worse, not better, as you would be doubling the area, requiring longer pipes, but chuffing due to air velocity would still be determined by the narrowest point.

[PoorboyMike]

Elbows are fine. Plenty of designs use folded ports, usually made out of wood, e.g. all the transmission line designs out there.

A Y would make things worse, not better, as you would be doubling the area, requiring longer pipes, but chuffing due to air velocity would still be determined by the narrowest point.

So you're saying if you use a 4" flared port for half the length and step up to a 6" with a flared exit for the rest of the port, that you would still get the same amount of chuffing as you would using 4" double flared the entire length?

I'm just trying to come up with options to make a reasonably sized convertable box. I realize the ported box size wont be optimal, but it will still give an increase in output over the sealed design. And I'm sure both of them would be considerably better than what I currently have.

Is this worth even trying?

[ThomasW]

Is this worth even trying?

Probably not.

Ideally the port shouldn't have bends since they change the 'spring' loading of the air mass. Now obviously lots of people use elbows, but if goal is to get the absolute best performance and length isn't a problem use straight port.

Other rules are, keep the port at least the diameter of the port away from any interior walls (this is to avoid chuffing). And of course use the absolutely largest diameter port that box size will allow...

[TacoD]

Don't make the port to long, otherwise you get a horn / TL loudspeaker. Or something inbetween.

[Dennis H]

So you're saying if you use a 4" flared port for half the length and step up to a 6" with a flared exit for the rest of the port, that you would still get the same amount of chuffing as you would using 4" double flared the entire length?

Right. More or less the same amount of chuffing but the pipe would need to be longer because of the 6" diameter part. You waste space in the box because of both the extra diameter and the extra length. If you have that much room to waste, a 5" pipe all the way would be about the same length and volume and would have less chuffing.