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View Full Version : Subout - cutoff freq.



CKY
12-21-2004, 07:06 PM
I own a Pioneer DEH-P5630MP and i started a "flame" with a guy from a local shop who kept telling me that i need to use the xovers from the amp , because the HU sub out doesn't cut the high freq (although i can select a cutoff freq of 50,80,100,125Hz). So he told me to change my current setup : Crossovers from the amp set to minimum (320Hz) with 100Hz or so from the HU.
As i own a JBL GTO75.4 , i run 4 channels bridged into 2 , each one going to a coil of a Alpine TypeR 1241D. But can you make a perfectly identical crossover freq. setup on both channels to prevent having different signals going to the coils ?

So i burned a CD with a 150Hz tone , set the amp crossovers to min (320hz) and selected 100Hz subout cutoff from my HU ... surprise ... the sub was recieving that freq :scared:

WTF ?

Somebody please explain it to me :thumbsup: Thanks !

JoseMCeee
12-21-2004, 08:35 PM
I still dont completly understand the whole xover thing cuz i set mine to 100 hz and i stil hear the beeping coming out of the subs when im settin my comps with a 1khz tone. But Im sure it should completly if not almost completly cut out the frequencies that it is supposed to. But those frequencies that are cut off by the xover should sound very very light so its not something to get excited about. And o yea, I dont think the HU completly cuts off the frequencies. Im not sure why u wouldnt want to use the xover on the amp if thats what its there for.

CKY
12-22-2004, 11:25 AM
Im not sure why u wouldnt want to use the xover on the amp if thats what its there for.

because i dont know "how much" freq. difference coming to the voice coil would damage the sub ..... because you set the xovers by eye .... what if i set one channel(going to a VC) to cut over 80Hz and the other one over 70Hz ? and what if a song plays a let's say 75Hz line ?

Would this really affect the sub or are we talking to "long-term" damage ?

thismightbepat
12-22-2004, 02:36 PM
I'd also like an explanation for this. My x-over on my components' amp is set to around 120hz, yet when i play a 50hz test tone (without the sub amp on so I can tell for sure), the speakers still produce noise.

ANeonRider
12-22-2004, 03:39 PM
It is because the crossover doesn't block the sound like a wall, each crossover network has an associated slope (i.e. -6dB/oct). Read more on crossovers on www.bcae1.com

squeak9798
12-22-2004, 03:50 PM
ANeonRider hit the nail on the head. Keep in mind that a crossover (highpass, lowpass, subsonic, etc) ISN'T a brick wall. It doesn't just kill the frequencies above the crossover point. It attenuates (which means to reduce the amplitude of) the frequencies above or below the crossover point at a predetermined slope (or rate). For example, a lowpass set to 50hz with a slope of 12db/oct (12 decibels per octave) attenuates frequencies above the crossover point at a rate of 12 decibels per octave. Everything below the crossover point (in the case of lowpasses) pass through unfiltered. So, you still hear some of the frequencies above 50hz because they haven't been attenuated to an inaudible level. The farther away from 50hz the frequency is, the quiter it will be. The same applies to highpasses (only, in HPF the frequencies below the xover point are attenuated) and subsonic filters.

Nikuk
12-22-2004, 04:18 PM
24dB/octave filters :D

squeak9798
12-22-2004, 04:23 PM
24dB/octave filters :D


Pfft....the old Sony 4000X (or whatever) had like 72db slopes on the lowpass. Now that is getting pretty **** close to a brick wall.....LOL

Nikuk
12-22-2004, 06:50 PM
Pfft....the old Sony 4000X (or whatever) had like 72db slopes on the lowpass. Now that is getting pretty **** close to a brick wall.....LOL

:eek: Good lord... that'd be kinda fun.... but then again, I'm alil twisted.