DeadlySones

iTrader: (4)

My deck has a crossover, for lets say sub ... adjustable 6, 12, 18db and the amp also has 12/24db. If you run both deck and amp at 12db, does that add to a 24db slope or is it still only a 12db slope??

MTT

iTrader: (17)

if both have the exact same slope there will be no change.
(12db@deck and 12db@amp = 12db at the speakers)(if the frequency is the same obviously)

if each has a different slope, the sharpest of the two slopes will be used(12db@deck and 24db@amp = 24db at the speakers.)(also frequency dependent)

DeadlySones

iTrader: (4)

That's exactly what I needed to know. Thank you!!

MTT

iTrader: (17)

Just want to add that many people, including lots that know more about car audio than me, will argue that the slopes actually combine, so a 6db at the deck and a 12db at the amp will result in an 18db actual slope at the speaker.

While they maybe right and I am completely off my rocker on this one, I did spend the better part of a weekend measuring this with an RTA and came to the conclusion I posted above.

/disclaimer

DeadlySones

iTrader: (4)

Either way, thanks!! It's a starting point. I have no highs installed right now so I'm thinking I should be able to hear something when I change these settings. Gonna try deck Xover off, amp @ 12db and listen for audible highs through the sub. I know they will be faint but I should be able to hear something. Then I'll switch the deck on to 12db and see if any thing changes. Then I'll switch the deck off again and switch amp to 24db and listen again. Then finally I'll switch the deck back on one more time just to see if anything changes. Gonna have to try it.

BigRedGuy

iTrader: (11)

Please do.....as far as I know the slopes do combine.....ie. -12db at the deck @ 40hz + -12db @ 40hz at the amp will give a -24db/octave slope @ 40hz at the speaker......phase does not change in this example but using -6db or -18db with a -12db will reverse the phase of the output.

Would one of the nit-pickers be so kind as to step in and clarify this??......thx.....

sirsleepsalot

iTrader: (1)

I'll have to agree with the fact that the slopes do add up.

Think of it this way, your amplifier will attenuate -12db / oct @ given frequency, regardless of the signal being sent to it.

If that signal already has a -12db / oct @ same frequency, then logically, it can't do anything but add up since the reference signal already has the filter added to it.

DeadlySones

iTrader: (4)

Thanks everyone, I'm going to have to say that yes they do add up. I don't have any fancy RTA equipment, but have no highs right now So I was able to play with this a bit. Playing Dope Boy by Gorilla Zoe there is a long part at the beginning that has no bass. When I turn that song up with no highs, amp set to -12db @ 80hz I can hear the lower words barely, when I added the -12db from my deck it was considerably less noticeable (-24db) then when I switched the deck back off and amp to 24 db did not notice much change, but when I turned my deck back on to 12 db I could not hear any part of the strange higher sound. Basically -36db cut. Assuming that the frequencies settings where almost exact.

So, with that being said .... I too believe that they must add up. Now can someone explain how 6, 18db reverses the output phase. Am I safe using 12, 24, 36db? I know I read somewhere before about this. I'd just like to apply some of this knowledge. Is running 36db sub and 24db on highs good, or should I run both at 24db? How can I use this phase shift to my advantage when running mids and tweets separately?

Any documentation I can read about this would be greatly appreciated.

sirsleepsalot

iTrader: (1)

Basicaly, for every 6db you add on, you get a 90 degree phase shift

6db / oct = 90
12db / oct = 180
18db / oct = 270
24db / oct = 360 (0)

and so on and so forth...

DeadlySones

iTrader: (4)

Awww, cool. I didn't know that. THANKS!!