I am gonna be building a box for 3 12in. Autotek subs this winter, and wondering whether I should have them face out or up. I currently have 2 now facing upwards. THey sound pretty good, but I am lookin for optimum sound (BASS). Any suggestions would be greatly appreciated.

 

The best thing I can tell you do is this. Can you move the 2 speakers that you have now around easily in the car? If so move that box to the best of your ablity into different positions. And see how you like the sound. Try pointing it so that the speakers are aiming towards the back of the car. And so on and so on. I would personally do a box where the two on the sides fire inward toward the middle speaker. Have them slighlty tilted back firing upward and toward the back of the car. But its your car but that is what I would do anyway.

 

Subwoofer placement is kind of tricky at the best of times. So many things will affect it that it's hard to say for sure what will work best. Phase relations will play a large part in how well any given positioning will work, and phase shifts with different speakers, crossovers, and sub enclosures. Of course you can also phase shift 180 degrees by reversing the polarity of the speaker leads, as well.

In the end, the only real way to determine the best mounting direction is to put them in and listen.

For my own tastes, I tend to find that the bass is less "Directional" when the subs are facing the back of the car, but that's a purely subjective thing. The only real way to make the bass come from the front is to put the subs in the front.

 

Placement doesn't really matter except that your sub goes in the hatch. The sound frequencies that subs produce are omnidirectional and therefore you don't need to angle them or anything. For optimum bass you need to build the best box you can. Check out this site for instructions http://www.diysubwoofers.org.

 

You want them to point to the back or if not possible point them up. Subs produce a very prolonged sound wave as opposed to regular speakers so the more room you give them to produce their full sound wave the better they will sound. So yes direction has alot to do with a subs sound quality the only problem is if you have the room to do it.

 

Okay,
now look at my picture. You guys are saying that subwoofers work like #1 or that they are directional and need to be aimed in order to sound good. I'm saying that subs work like #2 or that subs are omnidirectional or that the sound emanates in all direction from the box and therefore doesn't need to be aimed. Now according to your idea how would you aim #3 which has two subs clamshelled together and wired in phase. Also how do you aim bandpass boxes when the sub is inside the box? And finally if subs need to be aimed is it that in home systems can place the sub almost anywhere in the room? I'm just curious.


smile.gif

 

I understand what your saying but if you have bass waves bouncing off other objects such as the rear of the car then bouncing off that forward it sounds louder. And yes there isnt way to aim a bandpass box b/c they are built to bounce the sound around in side the box before it leaves through the port. That is why you usually get good sound out of a bandpass box. The move you can bounce the sound of things the better sound you'll have. Have you ever aimed your home speakers at wall in your house at low volumes the sound is more intense then before.

 

One more question why do you put polly fill in a box that is smaller than it needs to be if you don't have space for a larger box? Do you think that makes a difference or not? It basically comes down to box design and power doesn't matter what kind of speakers just the box and power.

 

Guilty:

Well, actually, subs don't work quite like any of your pictures. The waveform for a 50Hz wave is so long that it cannot actually fit inside your car. What this means is that inside your car, the sound wave will be the same loudness, or SPL.

As to direction, there are properties of the sound wave that will "reinforce" when the wave is reflected back over itself. This is called "corner loading" a sub. This is exactly why your home speakers will produce more bass if you fire them into the wall. It is also demonstrated proof that subwoofers DON'T act like your second picture. So if you point the subwoofer at the back of the car, there is a reinforcement effect as the wave reflects off of the back of the car. It *is* treated as a directional wave, much like your first picture, but it has a very long waveform. As such is is capable of acting like your second picture, although not exactly. The truth is somewhere in between.

For a ported or bandpass enclosure, it has nothing to do with "bouncing" the sound around. Ports are designed to resonate at specific frequencies to act as a "helper" to the speaker at those frequencies. Bandpass enclosures use the properites of the sealed and ported enclosures on each side of the cone to maximize the efficiency of the speaker at specific frequencies. A bandpass enclosure can be aimed quite effectively, and can also benefit from corner loading.

The second thing is phase. If you turn the subwoofer 90 degrees (ie, back to top) you introduce a 90 degree shift in relative phase as well. Since the subwoofer has to work in concert with the midbass drivers, that phase shift can make or break the bass response from your system. Remember, this is relative phase, as human ears have been categorically proven to be unable to discern absolute phase. Relative phase is *very* important in how good bass response will sound. An out-of-phase subwoofer/midbass combination will result in bass that is lacking definition. You'll lose the "snap" of the drums hitting.

As for the myth of "non-directional" bass... It's true that human ears can't determine the direction of noises that are below a certain frequency (Typically about 80 Hz or so) but in the case of a high-powered subwoofer, our ears aren't the only tools that we use to locate sound. Our entire bodies FEEL bass notes, and we can tell that the subwoofers are sitting behind us.

Now...

For your question regarding poly-fill... The reason that we tune the size of the enclosure is that we expect a certain damping factor to be introduced by the air that is sealed into the box. This is introduced in part by the actual mass of the air, and by it's compression characteristics. Fibrefill changes those characteristics to a small extent, and increases the mass of the air space inside the speaker chamber. It will help a box that is a bit too small, but can't make up for large deficiencies.

[ October 26, 2001: Message edited by: Dan ]

 

Sweet Jesus Guilty, couldn't you of edited the one post? Instead of making another one.

Good thing it is weekend.

Oh and to stay on topic, what kind of deck do you have erin*pat?