Forgive me if this has been discussed already, (I searched and didn't see it).

I got the torpedo subwoofer that is offered from the dealer. It sounds great and I'm very happy with it but I noticed something odd: The little info card that came with it says to set the treble and bass of the radio to zero, and make sure the phase switch on the subwoofer is up. I notice that mine is down. (or was that up? whatever...it's opposite of what the card suggests)

It seems to be working, and I presume the dealer knew what he was doing when he installed it...yet I'm curious. Since I know less than nothing about the tech aspects of sound systems I thought I'd post this here, and see what the audiophiles and experts can tell me.

(and the perverse little imp in my brain is wondering: if I flip that switch will the thing explode?)

 

The phase switch controls whether the output of the sub is in phase or out of phase with the other speakers in the car. Just put it in the position that it sounds the best in but normally in phase sounds best if the sub is not pointing directly rearward.

 

Thanks, chadfo! I'll try the other switch position.

btw I am curious...can you explain why having the sub pointing rearward affects the phase relationship? (I promise to try to understand your explanation without asking any annoying questions )

 

Please tell us how the factory setup works. I'm very curious about whether the subwoofer can be controlled from the deck or not. Can you set the crossover frequency or change the volume of the subwoofer from the deck? Or do you have to dial that in on the subwoofer itself? Thanks.

 

I might not be able to give the most accurate description but basically sound travels in waves like the waves you see if you drop something into a calm body of water. The waves have a high point and a low point. To get the most accurate and clean sound from a stereo system you want all of the speakers to have those waves in phase or coming to your ears with the high points and low points matching. When your sub is pointing directly away from you all of those waves are going the opposite direction of the waves from the other speakers in the car. The waves have to bounce off the rear and then back to your ears. This causes them to be out of phase. Normally if the subs are pointing any other direction you are getting at least some of the sound in phase because of the wide dispersion of sound radiating from the speaker.

That's very generic and there's a much more technical and accurate description that I have long since forgotten but that should give you an idea.

 

good description, but to be a physicist *****, sound waves are more like pressure waves, rather than water which is like light, if I remember my physics correctly. The waves move forward and back away from the source, rather than up and down, imagine a conga line moving at the speed of sound.

But what he's sayin is still basically correct, from what I understand. . . I'm just bein an a hole.

It's like wiring up an electric motor. You reverse the polarity of the contacts, and it will go backwards. Same with a speaker. However if you take that same motor, wire it correctly, and you turn it around and mount it backwards, it will also go backwards.

Now with a car, you want all your wheels to turn the same direction. . . same with your audio system.

But I also hear an argument against doing this (wire a sub out of phase when placed backwards) is that the sound you hear is still reflected off the back of the car, it just has to travel a longer distance, but the speed of sound is so great, that your ears cannot pick up the difference. For example, if you were to honk your horn in a garage, the sound you hear is primarily the reflected sound overpowering the sound naturally being dispersed through the air.

So in other words, the sound that would be backwards(out of phase) is over powered by the sound that is reflected off the rear of the car, in phase. I dunno if our brains are fast enough to detect the difference in time it takes for the reflected sound to hit vs the direct sound, since cars are basically microscopic at that speed. So the majority of the sound should still technically be in phase, by this theory.

Secondly, because a sound wave is a pressure wave, it does not reflect backwards, the same way a sin or light wave does. The high and low points are high and low pressures. Just because it reflects off the wall does not turn it backwards nor does it change the pressure (energy is conserved, it reflects at the exact same velocity and pressure. I'm not saying you are worng, just that I personally tend to agree with this theory. . . and my take on this could be wrong as well. . . I've studies a lot of physics, but my degrees are in business and economics. Any audioshop pros wanna chime in?

 

Regarding the timing of sound waves getting to the ear my first thought was... wait a minute I have a speaker two feet in front of me to the left, another one four feet away to the right, two more somewhere behind me at slightly larger distances, and the subwoofer even farther back, so how can any of them really be in phase, since each speaker's sound is reaching me at a slightly different time?!?!?!?

I guess those differences don't mean much when the speed of sound is something like 700 feet per second or so...the brain can't tell that the sounds are coming at different times.

anyhooo...I flipped that phase switch to the other position and noticed that the bass sound was noticably louder. I don't know if it sounded "better", but it was certainly louder. I haven't decided if I'll leave it this way or return it to the way it was.

Oh, about wnsham's question about controlling it...there are no controls up front for this. I don't know if there is a control for crossover frequency. I can change the volume with a dial that is located on the subwoofer, (not really convenient for the driver while he is driving.) But I don't anticipate ever needing to make changes on that very often.

 

That's what I just wrote, above, but in more words. And there is flipping of sound waves, when the reflect, as they are pressure waves, not sin waves.

 

no flipping I mean, damn typos

 

You might want to revisit those physics books. Sound waves are pressure waves and pressure is what causes the ripples in the water.

Most of the speakers are firing at their pressure waves at you creating the higher pressure on the positive part of the signal a rearward facing sub is firing its pressure rearward away from you in creating low pressure on the backside hence being out of phase.

 

Quoting myself:

When I did that I was listening to a cd that was new to me, (thus I was unfamiliar with how the music should sound). Now that I've had more time I feel that with the phase switch up the bass sounds a bit muddy, but in the position the dealer had it in things sound more clear. So maybe there really is something to all this phase talk.

Thanks, everyone, for your input. I learned a bit about sound systems from you all. :D

 

mooooved to ICE, Electrical and Interior

 

I especially liked your other typo: I'll have everyone know that I tolerate no sinning in my xB! :twisted:

 

Actually no. . . you can't increase pressure in water, unless you are talking about water depth, and the weight of the water above creates pressure. . . simply try this, take water, will it into a container, and try to crush the container. You can't. . . you can make the container deform, but you can't compress water. . . it is impossible. You can also spray water with pressure, by changing velocity, but you cannot change the pressure itself.

The waves you see in water, are energy waves.

Sound travels in pulses. . . and the waves you can see on a crossover type graph, is only a pictoral representation. Sound waves move in the same way the speaker moves-- back and forth and very rapid speeds. One particle of air hits another and hits another and hits another, causing a chain reaction of air particles colliding at a specific frequency, until it hits your ears. Sound DOES NOT move like waves in water, that I am sure of.

 

just look it up

 

I understand what you are saying, that the mechanics of a sound wave are different from those of a wave on the surface of the water. However I have to be a prankster and point out that a sound wave underwater works just the same as a sound wave in air. :twisted:

And then I must ask a question: if we could find a place where the atmosphere ended rather abruptly the way the water ends abruptly at the surface of an ocean, would we find that a sound wave in the top of the atmosphere would disturb the surface of the atmosphere in a manner similar to a wave on the surface of the ocean? (in other words...can we see the ocean wave as just the interaction of a sound wave in the water as it interacts with a boundary?)

 

Simple answer no. A sound wave is a sound wave. An ocean wave is an ocean wave. A sound wave can travel through my anus, and it would still be a sound wave. There are two types of waves in physics, and their properties are different. There is an ocean wave, and there is a sound wave. . . they are completely different. It is no prank. . . sound waves can coexist with water waves, as sound travels through everything. Water waves have to do with the gravity of the earth and moon, and the movement of water.

The best way to understand how sound waves work, is to look at a speaker. If it were to work like water waves, it would have to move up and down very fast, sending energy out at tangents, every 360 degrees. A speaker, conversely, sends the energy outward, forward, but the energy does move in every direction, 360 degrees as well (why you can hear someone shout, even if they aren't facing you).

But back to the point, a speaker moves forward and backward, moving air in pulses, forward and backward. Just take a look at something rattle: it will rattle forward and backward in a perpendicular vector to the source.