Why Do My Subs Play Well Below Port Tuning?

[kryptonitewhite]

i figured it was something to do with transfer functions, but i wanted to know details=)

port is NOT LOADED, it is in an armrest, firing straight into the cabin, and at ~18sqin/cube, its friggin massive

amp gains/setting are untouched from last install, subwoofer volume on deck is low for break in (like -8 when amp does full potential at 0, subs cant really take full power, so its going to be staying lowish, till i get L7's)

and the subs, i dont know how much they can be loading off glass about a foot away, thats what was bugging me, that it seems so darn open, i knew cabin gain had something to do with it, but jeeze, playing 15-20hz below tuning is kinda strange IMHO.

Ive been told to tune to 32-33hz for daily, but come on, if i get more spl out of 42, and it can still play high 20's, what could possibly be the upside of tuning low?

edit: 2 pics so ya'll know what i mean, i know i cant explain worth a shit

port:

subs:

i know its ugly, im cleaning it up when i go home, it was a day before going back to college cuz i need bass job, in the middle of the night in snow

thats gotta b the most interesting install ive seen in a grip

Edited January 27, 2009 by kryptonitewhite

[anubis]

if u dont mind i might try to do something like this setup in my sunfire

[BigPimpin91]

If your box is ported into the cabinet like that..

All the sound comes from the port when you drop below tuning.

So you get all of the sound blasting out of the port.

[aznboi3644]

actually below tuning not all of the sound is coming from the port....the only time most of the sound emanates from the port is right around the tuning frequency.

[raytard]

i think aznboi is right on that one, and when you model excursion v. frequency in something like winisd, it does give you a drop in excursion right around tuning freq

thanks for the comments on the interesting idea, and feel free to try it if you'd like. make sure you wear some safety goggles and have someone standing by with a wet towel, and a few extra grinding disks, i took a fresh one down to a nub in no time

I get what youre saying boon, thankyou. I figured it was something along those lines, but just didnt realize how severe the difference in in car v. free air responses could be. If we have a slow day at work I'll break out a sealed sub and our trusty AC mic and see what kind of transfer function I can find, and see how it compares to the vented response, which may be cool for everyone on here, just to see how stuff works in real world applications, because this really has me intrigued.

I also have to make it prettier, im about to just cut a big square out of my rear deck and cover the entire thing in grillcloth and put it back on, i'll sprayfoam it when i get back to work and buy my L7's. Put the armrest back in and maybe flectone the port too, just to make it pretty

[raytard]

honestly the reason i asked this question is because it was LOUDER under tuning freq than at or above it, which seemed just so utterly wrong to me i had to ask whats up.

turns out when my girl was carrying the amp from my room to the garage for me, she basically had her finger on the knob for the DBO, or dynamic bass optimization control of the amp (fancy jbl bass boost with attenuation point) it had like 12db of boost a like 25 hz

so, turned that junk off, sounds much more normal now, still plays very low, but now is peaking more around the 43ish hz i was expecting, and sooo much smoother, volume is very much more constant