Can I add a subwoofer to stock headunit?
02-25-2006, 03:01 AM
#21
Registered User
It does roll off sharply below 100Hz. Probably 18dB per octave. I did not know this at the time but everything still turned out fine. My crossover points are a little different than I expected and the sub gain on my crossover and my amp channel are higher than the fronts. Now that I know it's becuase of the HU I may go back and re-tune the whole thing a different way knowing what's going on now but won't do that until I do my sound deadening. This would require re-tuning anyway.
There definately is 20Hz-whatever frequency response out of the non-stock HU. It just drops off sharply. If anyone runs across this other test that was done on it please post it here - none of us can find it
I'm still happy with what I've got. Had I known about this beforehand I would have probably not even tried to upgrade because reading about it sounds like opening a can of worms - but it isn't as bad as it looks like on paper! Many of us have kept the stock HU for our own cheap or paranoid reasons and can make a decent system. You definately have to boost the low end one way or another though.
There definately is 20Hz-whatever frequency response out of the non-stock HU. It just drops off sharply. If anyone runs across this other test that was done on it please post it here - none of us can find it
I'm still happy with what I've got. Had I known about this beforehand I would have probably not even tried to upgrade because reading about it sounds like opening a can of worms - but it isn't as bad as it looks like on paper! Many of us have kept the stock HU for our own cheap or paranoid reasons and can make a decent system. You definately have to boost the low end one way or another though.
02-27-2006, 04:43 PM
#22
Registered User
So the stock HU may roll off sharply below 80Hz. There is signal still there.
I've read that the basic rule of thumb (until I can measure this in my own car) for the transfer function of a car is that for all frequencies that occur outside the length of the car get a boost of about 12dB/octave. I measured the Z from trunk rear wall to where the windshield meets the dash to be about 103". Using the equation for wavelength=speed of sound/freq.
131Hz has a wavelength of approx. 103" So even though the HU is cutting about 18dB/octave below 80Hz the cabin is gaining it back at a rate of 12dB/octave below 131Hz. I know it isn't that simple but that's enough for now to make me sleep better at night
I first thought that the rolloff was to protect the stock speakers and make them sound better also at high volume. Maybe it's not the end of the world after all. In theory the cabin and HU almost cancel each other out to flat. If my car was tuned flat it would sound pretty thin with road noise in there. My sub gain is probably then set higher becuase there is not a one to one overlap described by me above and by my preference to have some clean bass hit me in the back of the head every once in awhile without going overboard
I've read that the basic rule of thumb (until I can measure this in my own car) for the transfer function of a car is that for all frequencies that occur outside the length of the car get a boost of about 12dB/octave. I measured the Z from trunk rear wall to where the windshield meets the dash to be about 103". Using the equation for wavelength=speed of sound/freq.
131Hz has a wavelength of approx. 103" So even though the HU is cutting about 18dB/octave below 80Hz the cabin is gaining it back at a rate of 12dB/octave below 131Hz. I know it isn't that simple but that's enough for now to make me sleep better at night
I first thought that the rolloff was to protect the stock speakers and make them sound better also at high volume. Maybe it's not the end of the world after all. In theory the cabin and HU almost cancel each other out to flat. If my car was tuned flat it would sound pretty thin with road noise in there. My sub gain is probably then set higher becuase there is not a one to one overlap described by me above and by my preference to have some clean bass hit me in the back of the head every once in awhile without going overboard
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