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silver bullet
Dodge Dakota
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8/04/2004
01:56:51
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 Subject: can it be done?
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Message:
does anyone have or know someone who has a box with two subs firing down and another box bolted on top of it with those subs firing towards the seat? the box my guys at no limit are building me basically looks like a regular box but turned upside down, but it is made for firing down but its just flat on the top so im wondering if theres anyway i can bolt a box for two more 12's on top of the other box, yeah, im a little bit of an over achiever, ive got jl audio w3v2's if it makes a difference, the dudes at no limit say they personally wouldnt do it, but theyre not me and im crazy as hell
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DSW
Dodge Dakota
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8/04/2004
04:44:24
| RE: can it be done?
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The reason they wouldn't do it it because the downfiring subs might cancel out the front firing subs, or the other way around. If the bass sound waves are out of sync they might cancel each other out which means you might have less bass with all the subs going than just the downfiring subs or just the front firing subs.
Here's a little test, hook up one of your home stereo steakers backwards + to - and - to+. Turn the balance to the left, you got bass, turn the balance to the right, you got bass, turn the balance to the center, you got no bass. It's because the speaker hooked up backwards is canceling out the other speaker.
Get your subs out of sync by facing them in different directions and you can get the same effect, all though probably not to the degree of hooking a speaker up backwards.
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Jim Z
GenI
8/04/2004
21:04:25
| RE: can it be done?
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The reason they wouldn't do it it because the downfiring subs might cancel out the front firing subs, or the other way around.
the wavelength of bass frequencies is so long that this isn't an issue, provided all woofers are in phase with each other. Plus, bass is omnidirectional so the output of the woofers will still essentially sum, regardless of what direction they're facing.
Here's a little test, hook up one of your home stereo steakers backwards + to - and - to+. Turn the balance to the left, you got bass, turn the balance to the right, you got bass, turn the balance to the center, you got no bass. It's because the speaker hooked up backwards is canceling out the other speaker.
This is true, but it's an extreme case. Reverse polarity puts one woofer 180 deg. from the other, which is an almost complete cancellation. Woofers facing different directions shouldn't cause this, especially if they're in a common enclosure.
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DSW
Dodge Dakota
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8/04/2004
21:16:38
| RE: can it be done?
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Guess I have to eat what I said,, Gulp!
JimZ's the audio guy, so listen to what he said.
I have heard from several speaker shops/installers that cancellation can happen, guess it's an old wives tale not to install subs firing in different directions.
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Jim Z
GenI
8/04/2004
22:14:27
| RE: can it be done?
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The biggest problem I see regarding cancellation in a car is due to reflections. For example, let's say you have a sedan, and you put a pair of woofers in the trunk, right up against the rear seat. What can (and usually does) happen is thus: The sound radiates from the woofers in all directions, so while some travels forward to you, some also goes towards the rear of the car and reflects off of the back of the trunk. This reflected sound then moves forward through the car, but is now partially out of phase with the direct sound. What you usually see is a quarter-wave cancellation at around 70-80 Hz, which will put a hole in the response right there and kill the "kick" from the woofers.
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