Observation about subwoofer positioning...
Thread Starter
500 Watt CAFz'r
Joined: Sep 2002
Posts: 679
Hey, I've noticed that in my car, if I have the subwoofer facing forward firing into the cab I get barely any bass output. But if I have the sub facing back in the trunk I get great bass output. I've tried this with many different subs, different positions and everytime I have the sub facing the passengers I get no output. Why is this? I see trucks with subs in there cabs and they get great output as well as cars with subs facing forward. Can anyone shed some light on this?
By the way it's a Buick Century with the back seats taken out.
By the way it's a Buick Century with the back seats taken out.
50 Watt CAFz'r
Joined: Dec 2003
Posts: 268
There are couple of reasons for the senario that you are seeing one is that you are loading the woofer two is that lower frequencies need a longer wavelength in order to play now you are making for a longer wavelength by causing frequencies to travel the distance to the back and then to the front of the car. To see more on loading there is a post in install about woofer placement.
1000 Watt CAFz'r
Joined: Mar 2001
Posts: 1,626
I have mine facing forward *BUT* the trunk is sealed off from the cabin, eliminating any chance of cancellation from out-of-phase backwaves. This is the proper way to face a subwoofer forwards, that way you eliminate any trunk rattles and still get great bass.
Guest
Posts: n/a
"...now you are making for a longer wavelength by causing frequencies to travel the distance to the back and then to the front of the car..."
Think about that for a while and you will see why it cannot be.
The real deal is CANCELLATION. The woofer generates a wave and it radiates in a spherical pattern about the box unless blocked by the floor or whatnot. This means that a wave travels toward the front of the car and toward the back of the car at the same time.
The woofer travelling to the rear is the problem. It will reflect off the back of the trunk (nowhere to go right) and head toward the front again OUT OF PHASE compared to before it reflected. When it reaches the same plane as the woofer it will now cancel out the frequency that corresponds to the wavelength from the baffle to the back of the trunk. Make sense?
In most cars when the woofer is against the back seat the frequency corresponding to the distance from the seat to the back of the trunk is in the 70hz range and you get cancellation at 70hz. This is an important range of music for your woofer and you WILL notice it missing.
Turn the box around though and the cancellation frequency goes up to 130-140hz and is above the woofer's range. Problem solved.
As Chaos alluded to, if you totally block off the trunk from the cabin of the car then this is a very small or non-issue. Aside from looking fricking deadly, that is the sole purpose of the baffle shown here: http://images.cardomain.com/member_i...882_5_full.jpg
Think about that for a while and you will see why it cannot be.
The real deal is CANCELLATION. The woofer generates a wave and it radiates in a spherical pattern about the box unless blocked by the floor or whatnot. This means that a wave travels toward the front of the car and toward the back of the car at the same time.
The woofer travelling to the rear is the problem. It will reflect off the back of the trunk (nowhere to go right) and head toward the front again OUT OF PHASE compared to before it reflected. When it reaches the same plane as the woofer it will now cancel out the frequency that corresponds to the wavelength from the baffle to the back of the trunk. Make sense?
In most cars when the woofer is against the back seat the frequency corresponding to the distance from the seat to the back of the trunk is in the 70hz range and you get cancellation at 70hz. This is an important range of music for your woofer and you WILL notice it missing.
Turn the box around though and the cancellation frequency goes up to 130-140hz and is above the woofer's range. Problem solved.
As Chaos alluded to, if you totally block off the trunk from the cabin of the car then this is a very small or non-issue. Aside from looking fricking deadly, that is the sole purpose of the baffle shown here: http://images.cardomain.com/member_i...882_5_full.jpg
Thread Starter
500 Watt CAFz'r
Joined: Sep 2002
Posts: 679
Thanks, that definitely helps explain alot. So can cancellation take out a whole range of frequencies? With the woofers forward I got basically no bass output so 30-80Hz was cancelled?
With my sub box in it's current position, which is facing back and in the middle of the trunk I get poor response around 60-80, so I'm probably getting cancellation.
When I get the car back tonight im going to try and put the box all the way to the back of the trunk and face it towards the cab, hopefully I'll get my normal bass repsonce with less rattling and maybe gain some freq. response.
With my sub box in it's current position, which is facing back and in the middle of the trunk I get poor response around 60-80, so I'm probably getting cancellation.
When I get the car back tonight im going to try and put the box all the way to the back of the trunk and face it towards the cab, hopefully I'll get my normal bass repsonce with less rattling and maybe gain some freq. response.
50 Watt CAFz'r
Joined: Dec 2003
Posts: 268
Sorry my bad you are correct in that situation but the loading still occurs! The wavelengh will be lenghthened if the boxx is pushed to the far back and faced forward! Sorry i do know better just got overzealous on the post! Thanks
Thread Starter
500 Watt CAFz'r
Joined: Sep 2002
Posts: 679
I tried the woofer in a few different positions and they all sounded like sh**t except for facing back in the middle of the trunk. I found this weird as most people set-up differ from this. I'm guessing it's the cars response?
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Yankee
Joined: Oct 2003
Posts: 3,599
Today I went from a butt ugly Q-box taking up my entire trunk to a pair of glass 'boxes' formed around the area behind my rear wheels. The sound has changed a lot and tuning is in order. I am not 100% positive the glass boxes are stiffer than the ¾ MDF. But there are defiantly some cancellation nodes since the bass is no longer dominating the HF. Also the woofers are facing each other across the trunk (space limitation forced this) rather than facing up, down, or aft. When I faced the old box aft the bass was strong and seemed to be coming from the windshield (up or forward and the sound could be identified as coming from behind and that is with a 90 Hz x-over). The bass is warmer now (seems like the 100-300 Hz area now needs to be lowered) I figure lowering the crossover on the sub-amp will address this. Seems like the thread has some direct application to my setup.
