Kinda complex quesiton about port velocities

[vehementSPL 10+ year member]

Ok . I have a wall and it is pretty underpowered right now so the port velocity isn't very high. Well when I metered the truck the pressure inside the cabin even near the ports is 4db higher than in the ports. Metered a few times same thing every time. Now i am curious how this affects the metering of the vehicle? does it cause any cancellation waves etc etc. I just think it is kinda odd to have lower spl in the port by 4 db than in the car. . But there again just how does it affect the system's metering if any on a LAB. Thanks

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[skateboardkid 10+ year member]

Well that is kinda weird, how big is the box in cubic feet and how much port area do you have, plenty of people would love to have it meter 4 dbs higher than in the port inside their vehicle..

sounds like port velocity is real low and it is pressurizing the cab real well, up the power x4 and see what the #'s do.

 

[Ed Lester 10+ year member]

for SPL you do not want high port air velocity. You want to be able to levitate objects in the port by having even pressure and velocity both exiting and entering the port.

How deep is the port? And where in the port is it 4 dB down? This may be a normal occurance when the meter is placed in an area of the port where the air exiting and air entering is not equal, like the mouth of the port.

 

[vehementSPL 10+ year member]

I realize it is too low due to the underpowering of the subs currently till I up the power. And port is about 16 inches deep and anywhere in the port. doesn't matter. But I do mean IN the port not in the opening

 

[vehementSPL 10+ year member]

Well I know the termlab is famous for murdering feelings if you have any cancellation and I wonder if that low port pressure could cause some

 

[Haunz 10+ year member]

for SPL you do not want high port air velocity. You want to be able to levitate objects in the port by having even pressure and velocity both exiting and entering the port.

WAT ?

that makes no sense..

 

[15nissen 10+ year member]

Well I know the termlab is famous for murdering feelings if you have any cancellation and I wonder if that low port pressure could cause some

Its because your wall is whisper quiet. Its not a pure ground pounder that everyone strives to have for that all day low end rattle rattle.

The term-lab doesn't lie

 

[Ed Lester 10+ year member]

Its true.

You want your air velocity to travel perpendicular to the port. If you have high air speed blowing out of the port, that means that your port in unloading and not helping with SPL but rather it is hurting it.

 

[Ed Lester 10+ year member]

16 inch long port in a wall is kind of long. do you have any pics?

Most SPL only walls are tuned pretty high and the ports are never longer than the thickness of the baffle which are usually about 6 inches thick.

 

[Louisiana_CRX 5,000+ posts]

If your really serious about getting louder you can add a Tornado Fuel Saver inside your aero or round port to increase the airflow...I've heard of gains up to 3 dbs...1.5 db plus is typical....under most applications which you would notice....a lot of the big boys run these in competition vehicles //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

 

[chunky cumz 10+ year member]

well this is gonna bring up another thing then, as i read this... in a very small vehicle then should the ports face forward or back then?

 

[Louisiana_CRX 5,000+ posts]

well this is gonna bring up another thing then, as i read this... in a very small vehicle then should the ports face forward or back then?

depends on what your looking for..and vehicle....there are way too many variations....

 

[chunky cumz 10+ year member]

depends on what your looking for..and vehicle....there are way too many variations....

you goin to usaci finals this year?

 

[Ed Lester 10+ year member]

well this is gonna bring up another thing then, as i read this... in a very small vehicle then should the ports face forward or back then?

really depends on the geometry of the vehicle.

Usually, if you have the port face forward, you want to have the airspace behind the port totally sealed off from the listening environment. This is like a trunk car with the box in the trunk and port firing forward and having to totally seal off the trunk area.

But in hatch backs and SUVs, you cant do this without building a wall so without a wall, these cars usually perform best with ports firing back or up.

I recently tested the HHR as having subs firing to the side and ports up yields the highest SPL and subs up, ports back is the second best.

I can put my sensor in my box behing the subs and get over 165 dB. I can then put the sensor in the port and barely get 150 dB, then at the dash I can get 152.6 dB

 

[Haunz 10+ year member]

Its true.You want your air velocity to travel perpendicular to the port. If you have high air speed blowing out of the port, that means that your port in unloading and not helping with SPL but rather it is hurting it.

I think what you are attempting to explain is that smaller ports with higher velocities give greater losses due to drag...

I'm not 100% sure why the OP is measuring SPL at or inside the port... but for port wars having a high port velocity port is desirable... velocity ~ amplitude