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tuning a box to the wave length of a car?


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StealthEs 
Copper - Posts: 326
Copper spacespace
Joined: September 04, 2003
Location: New Jersey, United States
Posted: May 31, 2007 at 1:10 AM / IP Logged  

Hey guys,  on a forum a visit I came across this

"its tuned to the standing wave length of the car ...so in other words its tuned to the subs and the car"

After asking for an explanation I got this. 

"to keep it simple...you measure from the front window to the rear window and then divide that by 1130 which is the speed of sound? correct me if i'm wrong...then that will give you about 125 hz...then you half the frequency to 31.25 and then based on that you figure out your port"

Have any of you guys heard of this before?

Cris
mikegar 
Member - Posts: 15
Member spacespace
Joined: April 07, 2005
Location: United States
Posted: May 31, 2007 at 1:47 AM / IP Logged  
yes. i have. one of the benefits of this is so that when you roll your windows up your system wont get quieter.
jmelton86 
Gold - Posts: 1,228
Gold spacespace
Joined: February 07, 2007
Location: South Carolina, United States
Posted: May 31, 2007 at 4:18 AM / IP Logged  

Anyone have a better way of explaining this? Does the vehicles' fs have anything to do with this?

I'd like to find mine.

2013 Kia Rio -90a alternator
DDX470HD GTO14001 GTO1014D (x3)
Big3 in 1/0G
1/0G to GTO14001
wormy 
Copper - Posts: 76
Copper spacespace
Joined: August 03, 2006
Location: United States
Posted: May 31, 2007 at 7:08 AM / IP Logged  
Is this Standing wave a different frequency than the resonance of the vehicle?  I am definately interested in this.  I'm in the second part of my Physics with Trig.  I'll help as best I can.  What units are being used for your speed of sound.  I know the speed of sound to be 345 m/s I think.  I may be giving the wrong units.
...typically, I just run whatever I randomly pick up off the floor.
1995 Ford Ranger Supercab
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sarcomax 
Copper - Posts: 276
Copper spacespace
Joined: November 09, 2005
Location: California, United States
Posted: May 31, 2007 at 11:19 AM / IP Logged  
at sea level, 70 degrees f, the speed of sound through air is 344m/s or 1128 ft/s, so both are correct. 62.5 is half of 125 though... maybe i missed something there. My brain would (sony) xplode if I was within 1128 feet of a physics with trig class. if you were not looking at me, you wouldn't know for a full second though.
wormy 
Copper - Posts: 76
Copper spacespace
Joined: August 03, 2006
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Posted: May 31, 2007 at 1:22 PM / IP Logged  
lol...I just finished up with that class at 12.  I was so excited when I got to class though, because I just did a lab today along the lines of what he is asking about.  I'm mostly interested in this though, because I'm pretty sure I can use this information at competition.
...typically, I just run whatever I randomly pick up off the floor.
1995 Ford Ranger Supercab
MECA member
Team CSS
wormy 
Copper - Posts: 76
Copper spacespace
Joined: August 03, 2006
Location: United States
Posted: May 31, 2007 at 1:26 PM / IP Logged  
I'm wondering which is more important, the fundamental frequency of the vehicle or the frequency in which the chassis resonates.
...typically, I just run whatever I randomly pick up off the floor.
1995 Ford Ranger Supercab
MECA member
Team CSS
jmelton86 
Gold - Posts: 1,228
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Joined: February 07, 2007
Location: South Carolina, United States
Posted: May 31, 2007 at 7:21 PM / IP Logged  

Vehicles' panels, as any part of the vehicle really, has its own fs. This is due to the size, the way it's held in place, where its held in place, along with innumerable(sp?) other factors that affect the particular piece. Now, the vehicle is actually louder at one frequency than others -just where the panels hit 'common ground' with each other. This is the actual fs of the vehicle.

What I want to know is would building a ported box tuned to the vehicle fs be the best way of getting a comp-worthy vehicle?

Also, since to have the front and rear waves hit the mic at the same time is optimum for comps, how would one going about this? -what this thread was started for, I think.

2013 Kia Rio -90a alternator
DDX470HD GTO14001 GTO1014D (x3)
Big3 in 1/0G
1/0G to GTO14001
wotugot4me 
Copper - Posts: 64
Copper spacespace
Joined: March 09, 2005
Location: United Kingdom
Posted: June 01, 2007 at 7:55 AM / IP Logged  
StealthEs wrote:

"to keep it simple...you measure from the front window to the rear window and then divide that by 1130 which is the speed of sound? correct me if i'm wrong...then that will give you about 125 hz...then you half the frequency to 31.25 and then based on that you figure out your port"

hee hee, just noticed half of 125hz is not 31.25, thats a quarter. I missed that the first time I read it.

zhalverson 
Copper - Posts: 180
Copper spacespace
Joined: January 21, 2005
Location: United States
Posted: June 01, 2007 at 6:32 PM / IP Logged  
StealthEs wrote:

Hey guys,  on a forum a visit I came across this

"its tuned to the standing wave length of the car ...so in other words its tuned to the subs and the car"

After asking for an explanation I got this. 

"to keep it simple...you measure from the front window to the rear window and then divide that by 1130 which is the speed of sound? correct me if i'm wrong...then that will give you about 125 hz...then you half the frequency to 31.25 and then based on that you figure out your port"

Have any of you guys heard of this before?

This sounds like finding the theoretical second order harmonics of the vehicle.  Cutting this frequency in half would give the 1st order or fundamental frequency of the vehicle.  Cutting it in half again like done above is, well, nothing.  I'm no expert but I think this is pretty useless.  I may be wrong but it seems like physics applied incorrectly which seems to happen alot with little methods like this.  Sometimes you just can't simplify things.

Like jmelton said there are many factors that make up the resonant frequency of a vehicle.  I got curious about this so i did some researching and ran across a thread: http://forum.ecoustics.com/bbs/messages/4/345879.html 

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