Sound system in car does not play 100-200 Hz

[Mote]

We tried to improve my friends Subaru Legacy '04 sedans sound system by adding a closed box 10" subwoofer. Box is quite small 35 litres, element is made by quite unknown company - Sioux.

I burned 1000Hz to 20Hz sweep to cd, played it through subwoofer in house and recorded the result with microphone to computer. Played nicely down to 40Hz.

Now we installed box into the trunk of the car. Element is facing rear seat, armrest on the back seat is down, allowing the bass to go to interior of the car.

We placed microphone on the drivers seat headrest and played 1kHz to 20Hz sweep through cars audio system. Result was pretty bad, 200-100Hz did not show up at all on analyzer, other frequencies played at normal level.

Should we build another (inverted) box for element or replace cars original speakers? Any ideas at all?

[chris661]

Swap the wires to the subwoofers.

The subwoofer is cancelling the output from the other speakers.

[Mote]

How obvious
Will try that. Howcome I did not think of it?

[Perry Babin]

If reversing the polarity of the speakers doesn't help, turn off/disconnect all other speakers playing near 100Hz. If there is still a dip in the output, the problem may be in the vehicle.

I'm assuming that you're using the same signal source/amp. If not, are you sure that there isn't a crossover or equalization that's causing the problem?

[Mote]

We can measure it again next weekend hopefully. He switched the subwoofer wires and said that bass got a bit louder. So I hope the problem is solved.

The car has factory head unit, 6 speaker sound system consisting of 2 tweeters, 4 4" speakers in doors and thats it. I doubt that these will play under 100 Hz.

Amps input signal is taken from rear door speaker because factory head unit does not have RCA output. We use a Rockford Fosgate amp and its Hi level input. We tried different settings on the amps filter section, full, LPF with different crossover frequencies but nothing helped.

[JRace]

If you still get the `100-200Hz hole, then push the balance control all the way to one side (or the other, it don't matter).
Then if this gives you the bass you were missing, then swap the HI-Level input leads.

[amc32]

If all else fails! Your problem may be an acoustical problem because of the orientation of the subwoofer. If the output of the subwoofer isn't coupled completely into the car, while the subwoofer are facing forward, very rarely will you achieve optimum performance without a null in freq. response. Try turning the subwoofer around or reposition in the corners of the trunk to allow the sub freqs. to load better

[Mote]

We changed the orientation of the subwoofer as well. Subwoofer facing backward with different distances from the backseat had some effect but the hole was still there.

[ppia600]

Could just be equalization of the oem deck trying to make up for a bump in the car's peak resonances. Maybe try using the front speakers as the hi level source. Does his legacy have the oem amp/subwoofer box under the driver seat? You could use the output of that amp and just remove the woofer.

[Mote]

This Legacy does not have oem amp/subwoofer.
Anyway switching the wires did the trick. Friend is happy