808 bass kick / sub kick / low kick / bass slope ?

[iSanctvs]

Hi everybody !!
First, i'm sorry for my bad english :/
That's not my mother language

I've got a local Electrometalcore band, with electronics samples, we want to put in our music some bass kick / sub kick / low kick.

It ring like a big bass boom before for example a breakdown.
It make the music heavier. We can hear it in the music of Job For A Cowboy, Taking Your Last Chance, Hester Prynne ...

It's rather difficult for me to name this technic, the word doesn't exist in my language.

I think it exist 2 sorts of this sort of kick :
* a linear
* a descrendo, a sort of jump of an octave or 2 octave with a large portamento.
But this differences are very closed.

The perfect example is in this TYLC video at 1min35 & 2min20:
http://www.youtube.com/watch?v=ducSZehmYhg

I think this boom is a linear

An other example at 45sec :
http://www.youtube.com/watch?v=FLvG-z53pdc

And this boom is more like a slope, a "melodic decrescendo"

I'm searching first for this second sort of kick.
But i will not refuse both ^^

I've only found a sound, not very clean.
So, i'm searching for a very clean bass boom/bass kick / sub kick / low kick/ bass hit ... in .wav or .mp3.
Not more than 3 seconds.
I know the heavier attack of the kick is at the beginning of the sound.

Is somebody able to help me in my search ?
My request in total confused but it's pretty hard for me to explain.
I would be very very grateful if you would help me to find what i want

Cheers !