Low Frequency Waves need to develop?

[KingstonRock]

I read about this in a car audio installation article and saw it mentioned in a thread here. It's not really a studio building question. More of an acoustics one.

The article talked about how a subwoofer box should be aimed facing the rear of the car because low frequency waves can be as long as 40 ft from crest to crest and take room to develop. Having the woofers fire backwards would mean that the waves had to hit the trunk, reflect, than travel to your ears. At the time I read it I decided it was valid. But when I saw it mentioned here, I realized that no matter where you are, you ears can only be at one point in a sound wave, its the oscillation of the wave that allows you to here it.

I only ask because I'm wondering if I am wrong and sitting only 2 feet from my monitors I am losing low frequencies, I dont think I am, but I have really no basis for comparison.

I'm thinking that maybe the car audio guy is trying to create standing waves to increase the bass, but there's no way to ensure that your creating frequency doubling at any of the various listening postitions in a car, and not totally doubled waves would just screw up the bass and you certainly wouldnt want cancellation. PLus I doubt that a car provides enough refelction for standing waves to occur. That's another thing. A trunk is not a very refelctive surface. But at the same time, there are waves coming off both the front and back surface of the driver. Though the waves coming of the rear of the cone may be lessened by the fact that the rear of the cone is in a box. All installations I've seen done have the woofers firing outward, i guess it just looks cool.

But the guy who wrote the article was a fairly well respected car audio guy if i remember, whatever that means, an audiophile with a garage?

Eric

 

[Ethan Winer]

Eric,

> because low frequency waves can be as long as 40 ft from crest to crest and take room to develop ... the guy who wrote the article was a fairly well respected car audio guy <

A lot of respected people are clueless when it comes to acoustics. There is no merit at all to that argument. You actually came very close to the right answer:

> you ears can only be at one point in a sound wave <

Yes.

> I doubt that a car provides enough reflection for standing waves to occur. <

And that's the exact point. Low frequencies go right through the relatively thin car walls. This is one reason that testing your mixes in a car works. The walls are so thin that standing waves at the lowest frequencies are much less strong than in a typical room with sheetrock walls. So for whatever other problems a typical car stereo may have, a poor low frequency response due to room reflections is not one of them.

This is explained in my Acoustics FAQ in the sidebar "Big waves, small rooms" 10th in the list on my Articles page:

www.ethanwiner.com/articles.html

--Ethan

 

[TexRoadkill]

A lot of it depends on how low you are talking about. The lows from a subwoofer are going to be much lower than typical near field monitors.

Usually you would want a sub to be a bit farther away from you then a near field monitor. That is the reason I have always heard for putting subs in the trunk (apart from the fact that is the only place they aren't in the way). The firing backwards to bounce off the trunk sounds pretty ridiculous.

 

[KingstonRock]

Ethan - Thank you very much for your explanation, both in your post and in your article.

Tex - I was only talking about subs for arguments sake really, I'm only concerned with nearfield placement. I guess everything is all right the way I'm doing it now.

It's still good to be reassured though,

Eric