Port area per cube question??

[Jessica]

I keep seeing power as one of the port area calculations. Power is really not part of the equation, unless you model the entire system to see what the sub is actually doing. In other words, the the same driver (or even 2 different subs with same cone area and Xmax) may reach Xmax with 100 watts in alignment X, but it may take 200 watts in alignment Y. Assuming the same tuning frequency, they both require the same amount of port area.

Port area is based on air velocity through the port, which is determined by driver surface area, Xmax, and tuning frequency.

Small ports do NOT have more bandwidth than larger ports, unless they are way undersized and begin to act in a non-linear fashion. This scenario is not a valid argument. It would be like puting an 18" sub in 1 cuft and saying it didn't have good low end response.

So what makes some low tuned boxes peaky?

mine, 8 cuft, 129 sqin of port and tuned to 32ish unloads like a mofo quick under tuning, drops of quick above about 60hz. (4 sa-12's) Maybe its the car but even with 2 12's in the hatch as apposed to the wall it was still peaky.

this is to the ear of course, never metered it.

edit: under tuning i can play down to about 27 or 28hz with no ifs, thats what i mean by unloading quickly under tuning

[bkolfo4]

So you said lower turning frequency, not port area. I will assume you mean less port area.

Playing below tuning frequency, is like the example of playing an 18 inch woofer in a one cubic foot enclosure. You are really not supposed to do it. The results are going to vary based on the entire system and it's reaction inside the vehicle.

In theory, if the port area is correct, the driver should unload below tuning frequency.

You should not be designing your system with a turning frequency that you want to play below.

[Jessica]

No I mean lower tuning. You would surprised how many boxes are tuned in the 40's. Not that many people tune in the 30's as compared to the whole

[Krakin]

Below the resonance the reflex of the system backs off from loading the driver. Since it is only venting back-pressure from the driver it is acting no more than a hole in the baffle, which in turn causes cancellation with the speaker's front output. This in turn rolls off the output at an insane 24 dB/octave, or 200 times less output every 1/2 of the last frequency. The port also no longer limits excursion or suspension that would normally be provided at or above resonance. This can easily cause the driver to bottom out, or smack against the backplate.

[bkolfo4]

And your upper frequency response has more to do with the driver being used, the crossover settings, the alignment that you have the driver in, and the vehicle peak. If the peak is really high due to the alignment, and/or car, the frequencies above the peak are going to sound much lower. Port size should not affect this, unless once again it is sized so incorrectly that the port is not operating correctly.

[Jessica]

I get how unloading works.

My question was about peakyness and port area.

[Kyblack76]

My issue, is adding more and more power, and seeing nil on the meter.... like nothing, Brian.

ALso, a lil issue of subs getting hot... that sort of deal.

My understanding NOW, is that my enclosure is to large....

ill work to SHRINK.

[bkolfo4]

A large peak is caused by the system alignment and the vehicle resonant frequency, not the amount if port area.

The same sub in one alignment might have a nice flat response, while another alignment might have a 5 dB peak just above tuning, regardless of port area.

Bottom line - if port area is changing your frequency response, it is because the port is not sized to operate like it should. . .back to unpredictable results due to a poor design.

[bkolfo4]

My issue, is adding more and more power, and seeing nil on the meter.... like nothing, Brian.

ALso, a lil issue of subs getting hot... that sort of deal.

My understanding NOW, is that my enclosure is to large....

ill work to SHRINK.

And when you shrink it, you lose efficiency and alter your frequency response.

I personally never alter enclosure designs just to allow more mechanical power handling. You can control mechanical with the SSF.

You select the sub based on your goals, design the enclosure based on the sub you selected and the desired frequency frequency response, and then power it accordingly.

Still running the SP4's? How much power?

[Kyblack76]

A large peak is caused by the system alignment and the vehicle resonant frequency, not the amount if port area.

The same sub in one alignment might have a nice flat response, while another alignment might have a 5 dB peak just above tuning, regardless of port area.

Bottom line - if port area is changing your frequency response, it is because the port is not sized to operate like it should. . .back to unpredictable results due to a poor design.

Hmmmm

I have no large peak.. im flat as balls, and, i seem to not BE WHERE i thought i should be. If ya feel me.

I added another alt, for elc, and then another amp. Wired them both down, and saw no gain.

I suspected the port...

Now, ..... i feel i need to SHRINK like a boss..... like.. many cubes....

Thanks Brian.