Car ACOUSTICS Problem (no 75Hz!)

[Mannequinhead]

Hey Folks,

I have a strange problem that I don't know how to start solving. After going through several of the planet's best subwoofers, manufacturer recommended amplifiers, and experimenting with different types of sealed/ported enclosures, the bass has always still sounded like it has a strange hole in it to me. After a year and a half of troubleshooting, I believe it's safe to say that I found the problem: the acoustics of my car cancels out 75Hz! I've confirmed that the subs/enclosure perform an even sine wave sweep from 30Hz-100Hz inside the house and even in the car when the trunk is open. But when I close the trunk, sit inside the car, and run a sine wave sweep...30Hz-50Hz sounds amazing, but then a dropout occurs that focuses where 75Hz almost completely disappears, and then it sounds good again around 100Hz and well over any crossover point I'd choose. The acoustics of the car just seem to be prohibiting a frequency band focused on 75Hz from sounding. The new Pioneer 6X9's that I recently put in to help with mid-bass seem to suffer from the same problem. Has anyone ever experienced this or have any recommendations?

For what it's worth, the car is a gorgeous 1970 Mercedes 280S. The current subwoofer setup is two JL Audio W7-series twelves powered by two perfectly matching JL Audio HD750/1 amps. The current enclosure is an Attrend ported box that almost perfectly meets the manufacturer's spec for airspace.

Help!!!

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[Jeffdachef 5,000+ posts]

Atrend is your problem right there.

 

[macsdad 10+ year member]

Prefab sealed is usually not too bad, but a prefab ported box, hellnever!!!! You are in desperate need of a properly built box, properly tuned for your set up dude. And I will say it first, and nicer than some of the others. Why invest in those subs, to turn around and put them in a schitty prefab box dude? But seriously, you need a custom built box, well worth it.

 

[garychoffmann 10+ year member]

Does the mercedes have any noise cancelation designed into the car to limit road noise?

 

[XxAndreaxX]

i have a similar problem with 20-40hz, when window is closed, that freq is almost canceled. open window, makes that double that loud.

above 60hz, mine also has some kind of gap, but its rather the speaker itself, and I don't mind, I don't like midbass.

because same enclosure, previous speaker was doing well at midbass and bad at low bass

 

[El-Camino]

Firstly, good job finding the issue. It has probably nothing to do with the car environment and more to do with the rest of the system. Your midbass speakers share some of the frequencies as the sub and at some point there needs to be a filter that fades out the sub and introduces the midbass hench crossover. At the crossover point, typically there is a 3db dip in the response and a phase change. A 12db per oct high pass typically gives a 90 degree phase shift. There is a lot discussed and documented about this issue in the audio world. The point is, it is more likely that you have a phase problem at that frequency caused by a crossover setting and or phase issue. Try reversing the phase on the sub or the mids and try different crossover settings and report back.

El-Camino