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Box positioning in trunk?

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=67350
Printed Date: March 28, 2024 at 9:21 PM


Topic: Box positioning in trunk?

Posted By: dzelaya18
Subject: Box positioning in trunk?
Date Posted: November 30, 2005 at 7:31 PM

Okay. I know that having the subs firing toward the rear of the car provides a cleaner bass sound, but how far should they be placed into the trunk? Right now I have two 12" Cerwin Vega's in a '00 Honda Civic 4dr, and it seems to me that the bass sounds better with the box as far near the seats as possible. Am I crazy, or does the extra air space in the trunk make for better bass?

seats - \box = better bass.  seats - \   box = not so great bass.

Also, while we're on this subject, does anyone know if having all four wondows down or just the front windows down makes for better hitting bass? Opening the windows kinda' makes ports for the bass to escape from, right?

Kind of mundane, but just a couple of things that I've always wondered about.  




Replies:

Posted By: tcss
Date Posted: November 30, 2005 at 7:42 PM
You are correct for your car and most sedans on the direction and location of your box. The window thing is kind of quirky. I've got much better bass on some cars when you crack a window open and on other cars it doesn't seem to make a differance. I always thought it had something to do with how airtight the car is. Any ideas guys?

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There is no such thing as free installation!




Posted By: stevdart
Date Posted: November 30, 2005 at 11:19 PM

The difference (in my way of reasoning) in whether the windows are up or down is just this:  when they're down you hear more road noise, which interferes with and cancels out some of the sub bass.  The air in the car remains the same air whether the subs are hitting or not.  The air that comes off a sub cone...or off a port, too....is a wave of air created by the movement of the cone.  It's not an exchange of air from one place to another, that is, it's not coming out of the box or out of the trunk or wherever the sub is located.  It's a sound wave that travels through the air, moving the air as it goes.  It's wake is refilled with air from the same car enclosure;  the air just recirculates back to where the wave displaced it.

Does that make sense?



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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: dzelaya18
Date Posted: November 30, 2005 at 11:39 PM
stevdart wrote:

Does that make sense?


Yeah. But there have been times when I've been in my car and, with the windows rolled up, the bass sounds more compacted, and when they are rolled down, the bass seems to smooth out a bit (this is with the car parked, btw). I wouldn't say hit harder, just a bit cleaner, it seemed. Granted, since moving the box further back, this doesn't seem as noticable...maybe I was just lacking in trunk airspace, I don't know. Or maybe I'm losing my mind...





Posted By: sparkie
Date Posted: December 01, 2005 at 6:02 PM
There are variables that must be factored in to understand why things happen. The reason that there seems to be more bass if the box if faced towards the rear of the car is that there is less cancellation of the sound waves. The sound wave bounced off the back of the car is different in length than the sound wave which travels from the box to the front of the car. If you flip the box to aim forward the length of the sound waves are nearly the same and tend to cancel each other out more. You would get the same affect if you hooked up a sub box and stuck it in the center of a room. If you moved the box to a wall the bass output will seem to increase. If you move to a corner it will increase it further. All you are doing is changing the wavelength of the reflected sound waves. Equal wavelenghts cancel each other out.   The next factor is that by turning the sub box to face a wall or back of the car, you load the front of the woofer. It is similar to putting the sub in a box. The box loads the rear sound wave from the woofer and acts like a spring. Loading causes the sound wave to be compressed.   The other large factor is the design of the box. Depending on whether or not the box is sealed, ported or a bandpass will affect the bass. Certain designs are better suited for different vehicles. There is a lot of physics involved in understanding how a box will sound in a vehicle. The size, porting, and tuning are all critical to performance. In short, box building is one science and applying it to a car is the job of a good and knowledgable installer.

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sparky




Posted By: tcss
Date Posted: December 01, 2005 at 7:05 PM
But why, when sitting in the install bay with the motor off, does the bass get better, deeper, louder which ever you want to use in "some" cars when you crack open a window. Ham, Dyohn, Sedate?

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There is no such thing as free installation!




Posted By: geepherder
Date Posted: December 01, 2005 at 9:08 PM
It would seem logical to me for the same reason as stated above- less cancellation.  That's why sometimes when you open the trunk on some cars the bass response seems to improve.  I've been fortunate enough to not have this dilemma in my cars, though.

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My ex once told me I have a perfect face for radio.




Posted By: drvnbysound
Date Posted: December 01, 2005 at 10:52 PM
To clarify..

Equal wavelengths in-phase with one another will increase output

Equal wavelengths out-of-phase with one another will cancel each other, thus decrease output

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Posted By: gerriebarnard
Date Posted: December 02, 2005 at 5:28 AM

Hi

 

I am relatively new into sound butt…..

Does anyone know where I can get hold (download) of frequency tracks, ranging from 20 Hz-70 Hz? I need to determine at what frequency my car peaks for an upcoming event.

I don’t know how to determine that though?  Last reading 148.6db.

2x12” pioneer

2x2000w mono-block amps.

spl comp. ported box.



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sound




Posted By: sedate
Date Posted: December 03, 2005 at 12:40 AM
Did I hear my name?

Okay tcss, I'll see what I can do for you guys...but ehh.. no one get mad at me all you guys are barking up weirdo trees and last time I set ya'll straight the thread got locked... sooo... ehh... don't shoot the messenger ya?

I don't know how to address this thread without addressing the individual statements made herein... soo... THIS IS NOT A PERSONAL ATTACK .... here we go:

tcss]I wrote:

always thought it had something to do with how airtight the car is.


Not at all. "Airtight" as a function of system design exists only in relation to the suspension air provides the movement of a woofer cone... for actual sound propagation... 'airtight' is extraordinarily bad.

stevdart wrote:

The air that comes off a sub cone...or off a port, too....is a wave of air created by the movement of the cone. It's not an exchange of air from one place to another, that is, it's not coming out of the box or out of the trunk or wherever the sub is located. It's a sound wave that travels through the air, moving the air as it goes. It's wake is refilled with air from the same car enclosure; the air just recirculates back to where the wave displaced it.


The most careful, probing examination of this prose from the most legalistic intrepretation proves it completely correct. But to clarify, stevdart did not use a key word I would have been far more comfortable with.. 'medium' ...... the air is a *medium* through which the wave moves, air itself however, is *not* the wave. This is a *very* important distinction, especially when getting back to the whole "airtight" idea..

A12Volter wrote:

The reason that there seems to be more bass if the box if faced towards the rear of the car is that there is less cancellation of the sound waves.


This, and the remainder of the meandering post is categorically wrong.

For any other math hobbyists in the room, we've all noticed how
Wavelength = Speed of Sound/Frequency.
and of course how
Speed of Sound = 1100/ft/sec/sea level.. give or take .. well.. alot.. depending on temperature.

But we can at least arrive at the acceptable conclusion of Wavelength = 1100/60 or, 18.3 feet. So.... the wavelength of a 60hz tone is about 18 feet.

Now, to generate a wave that will CANCEL this one, we *MUST* have half distance of the wavelength between the cone and reflective surface... that is, the trunk lid. Ya know... NINE feet. Herses don't have trunks that big.

tcss]B wrote:

t why, when sitting in the install bay with the motor off, does the bass get better, deeper, louder which ever you want to use in "some" cars when you crack open a window. Ham, Dyohn, Sedate?


First off, I just want to express my humble appreciation at being mentioned in the same breath as heamph and our stalwart administrator. Smart guys.

As simply as I can express it, sound really likes space. The *louder* the sound, the *higher* the amplitude... the 'bigger' the wave. Bigger spaces = bigger sound, period. How many of us have moved that crap 40x4 with the coaxials and the 12" from the Civic to the Explorer and suddenly went from "what system?" to "whoa I'm deaf" ?

*SAME* exact phenomenon with opening the windows. *Everyone* knows their system sounds wayyy louder that way.. and indeed, that is why... by expanding the airspace you allow your woofers.. or cabin speakers for that matter, you can drastically alter the amplitude, and ensuing volume, you allow the sound in your vehicle. As such, to the *original* question:

A12Volter wrote:

Am I crazy, or does the extra air space in the trunk make for better bass?

seats - \box = better bass. seats - \   box = not so great bass.


Buddy, your not crazy at all. Same thing everyone else finds. Without all that goofy 'cancelation' logic ppl are spewing, the airspace of the trunk *is* effectively increased the further away from the trunk the woofer cone is moved.. here, the trunk lid DOES serve as a reflective surface for the sound waves... and this is sort of the crux of the whole thing... like I was saying, the wavelength of frequencies so low into the sub-bass region have inordinately huge measurements... to actually HEAR the sound you are listening to, like the standing wave thing, you *must* have half the distance of the wavelength between the ear and the cone.. By flipping around the woofer you allow the sound just a few more feet to travel before it hits your ears, providing that audible bass extention ...

To be honest, I find this answer only half-complete. The dynamics of sound waves in enclosed spaces are ruthlessly unpredictable, as well as dynamic vehicle to vehicle acoustics, really makes this thread something of a nonsense "what-if" thread....

In the end, the proper orentation of woofer and box rely far more on individual preference and individual vehicle acoustics than simplistic deductions like "Pointing backwards is less cancelation" or whatever..


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"I'm finished!" - Daniel Plainview




Posted By: bry_gordan
Date Posted: December 08, 2005 at 8:59 PM
this maybe crazy buti have heard that atmospheric pressure can make a diff. Sometimes my system sounds better at night than at day .windows up windows down has to do with pressure in the car

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Brian Gordan




Posted By: haemphyst
Date Posted: December 09, 2005 at 4:53 PM
I'm working on it... I'll have an answer soon!

::::EDIT::::

I bounced this page off to my Harman guyz, and they are both looking into it. We'll get to the BOTTOM of this... posted_imageposted_imageposted_image

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It all reminds me of something that Moličre once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: stevdart
Date Posted: December 09, 2005 at 8:52 PM
I like the "sound likes space" theory....although I can't seem to duplicate this phenomenon in my experimental vehicle (my car!).  I just don't like to take my front windows down so far that the glass passes behind the midbass woofers, because I have deflex pads behind them on top of the Dynamat.  (...can't hear THAT difference either, but anyways...)

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: customsuburb
Date Posted: December 09, 2005 at 9:22 PM
https://www.installer.com/tech/aiming.html

These people did some pretty good experimenting on this topic.




Posted By: sedate
Date Posted: December 10, 2005 at 2:46 AM
stevdart wrote:

I like the "sound likes space" theory....although I can't seem to duplicate this phenomenon in my experimental vehicle (my car!). I just don't like to take my front windows down so far that the glass passes behind the midbass woofers, because I have deflex pads behind them on top of the Dynamat. (...can't hear THAT difference either, but anyways...)


What does this mean exactly?   You don't roll your windows down so you don't know if your woofers are louder with them down? Because your midbasses have deflex pads and Dynamat?

What?

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"I'm finished!" - Daniel Plainview




Posted By: sedate
Date Posted: December 10, 2005 at 2:59 AM
customsuburb wrote:

https://www.installer.com/tech/aiming.html

These people did some pretty good experimenting on this topic.


heh! That's what I've been looking for forever!!!

I dunno about this guy given his gain tutorial I'm not sure if I'd trust his grubby paws on all those computers and mics and occiliscopes ...


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"I'm finished!" - Daniel Plainview




Posted By: Sigfried
Date Posted: December 13, 2005 at 2:04 PM
what if the subs are install in the spare tire comparment and facing up, is this install good?





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