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newb question about sound with trunk open


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stevdart 
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Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: January 04, 2005 at 11:12 PM / IP Logged  

When a speaker thrusts outward, hits as we say....it compresses the air directly in front of the cone.  That's what creates a sound wave.  Then when the cone fires backward, the air (at a specific volume) inside the enclosure is compressed...which results in maintaining control of the cone movement.  A sound wave is created at that point, too.  That back wave is 180 degrees off the front  wave and can have the effect of cancelling some of the front wave sound if the two waves reach your ears 180 degrees apart.  http://www.installer.com/tech/aiming.html

The space that the enclosure occupies, the barometric pressure and air temperature will have an effect on the sound waves and cone movement, too.  A little bit. 

But the air space in the trunk of a car is considered infinite baffle.  Think about this:  when you use an infinite baffle sub mounted so that the front fires into the cabin and the rear of the speaker goes into the trunk, you're using an infinite baffle arrangement.  That trunk would have to be barely bigger than the sub enclosure to give credibility to the notion that air compression is taking place within the trunk and controlling the cone movement.

You didn't say if the cone looked like it was out of control, or how the sound was from inside the car.  We can only infer that you don't hear the weird sound from inside the car.  And we're working on the assumption that the enclosure was built to proper specs and with proper amp setup.  So, with this much info, I would look into moving the sub enclosure around in the trunk until it sounds right both inside the car and outside with the trunk open.

edit:  just saw your last question..  You couldn't know unless you were willing to get in and allow a trusted friend (preferably your mother!) to close you in the trunk and play the system.  But I wouldn't go there....

bigwise1 
Member - Posts: 39
Member spacespace
Joined: December 28, 2004
Posted: January 04, 2005 at 11:24 PM / IP Logged  
stevdart wrote:
 

But the air space in the trunk of a car is considered infinite baffle.  Think about this:  when you use an infinite baffle sub mounted so that the front fires into the cabin and the rear of the speaker goes into the trunk, you're using an infinite baffle arrangement.  That trunk would have to be barely bigger than the sub enclosure to give credibility to the notion that air compression is taking place within the trunk and controlling the cone movement.

But my subs are firing towards the rear.

stevdart 
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Posted: January 04, 2005 at 11:49 PM / IP Logged  

I didn't make my point clear there.  I was describing an infinite baffle arrangement where the trunk space is considered infinite baffle:  to point out the fact that air space in a trunk is of large enough volume to be considered ineffective in controlling cone movement.  That's not particularly your case as you have a sealed sub setup. 

But the second sentence of that quote does apply to yours: 

"That trunk would have to be barely bigger than the sub enclosure to give credibility to the notion that air compression is taking place within the trunk and controlling the cone movement."

bigwise1 
Member - Posts: 39
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Joined: December 28, 2004
Posted: January 04, 2005 at 11:57 PM / IP Logged  
stevdart wrote:

I didn't make my point clear there.  I was describing an infinite baffle arrangement where the trunk space is considered infinite baffle:  to point out the fact that air space in a trunk is of large enough volume to be considered ineffective in controlling cone movement.  That's not particularly your case as you have a sealed sub setup. 

But the second sentence of that quote does apply to yours: 

"That trunk would have to be barely bigger than the sub enclosure to give credibility to the notion that air compression is taking place within the trunk and controlling the cone movement."

another forum suggested infinite baffle because of a leaking box. guess i'll check tomorrow.

stevdart 
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Posted: January 05, 2005 at 12:20 AM / IP Logged  

"another forum..."   newb question about sound with trunk open - Page 2 -- posted image.

bigwise1 
Member - Posts: 39
Member spacespace
Joined: December 28, 2004
Posted: January 05, 2005 at 12:36 AM / IP Logged  
stevdart wrote:

"another forum..."   newb question about sound with trunk open - Page 2 -- posted image.

just looking for other opinions.  what do you think about the theory of a leaking box?

overworked 
Copper - Posts: 133
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Joined: November 09, 2004
Location: Australia
Posted: January 05, 2005 at 3:00 AM / IP Logged  

Leaking Box? nah, mate ummm how can I explain this a little bit simpler......dunno but I'll try! lol

Sound doesn't just come from the front of the speaker, albeit.....the best quality sound does (although that can be argued in low hz as well) if you put a box around the front of the speaker then it compresses the front as well creating equal pressure on both sides ofd the conethis would create an incredible amount of sound, but.....as always there is a but....you wouldn't hear it properly would you?

SO, we dont create enclosure for the front of speakers (unless it is a bandpass box and that is a WHOLE other topic!) but if you were to put a speaker in a small area......your boot, then it is like an enclosure to a certain extent, it will compress the air around the cone creating a small amount of pressure making it harder for the cone to move....lowering the effiency of the woofer and raising it's wavelength (I still dont think I explained that right.....|) thus allowing you too push more power into the coil(s)so now lets talk numbers theoretical numbers mind you

each woofer is capable of 100 watts

and with the trunk closed your pushing in about 100-200(p) watts, so in all fairness everything is working fine........until............you open the boot

then all the pressure that was contained in the boot is gone, and the cones are able to freely forwards raising their effiency....forcing the volume up slightly and also now you pushing in 200 watts into the speaker and it's peaking like crazy maybe not distorting but it will be slammed forwards with subh momentum that it will almost make a popping noise or maybe a cracking noise......I think it was wise I your instaler to tell you this and you should pay heed to what he has said.......and under no circumstances are you too goto another forum!, hope this helps just ask if there is anymore questions

~AFAccord~ 
Copper - Posts: 59
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: December 18, 2004
Location: Korea, South
Posted: January 05, 2005 at 11:16 AM / IP Logged  

    For the most part I agree with every post here.  I think what  Bigwise is looking for is what everyone's already stated, but in a simpler form. 

    Bigwise, your assumption about your subs distorting was correct.  The noise you are hearing with the trunk open is in fact distortion.  The same thing is happening with the trunk closed, but it's not so drastic since the closed trunk area is providing a moderate amount of control for the woofers, and various other things like rattles and the physics of sound drown out any audible distortion from inside the car. 

    The installer at the shop was correct about being cautious when playing the subs with the trunk open.  It may sound cool for a while, but it really is doing your subs more harm than good.  As some people already stated, the lack of pressure with an open trunk allows the subs to be much more efficient and move much further.  That extra distortion can easily damage your subs.

    The last thing to remember is that all setups respond differently.  The subs, the enclosure, the vehicle, they all make a difference how the system plays, whether the trunk/hatch/door is open or closed, they will all sound different.  A setup in an SUV might be well adapted to sound nice in a free-air environment, while the subs in your trunk my handle much more power or sound better, they probably work best in a sealed, pressurized environment. 

    I hope this has helped answer your questions.  Just reply in this post if anything's still not clear.  Later man.

Black Cherry
"Experience is something you never get until just after you need it."
tuanmerica@juno 
Member - Posts: 9
Member spacespace
Joined: January 02, 2005
Location: United States
Posted: January 06, 2005 at 2:46 AM / IP Logged  
Do you drive your car fast with an opened trunk?
If so that is the reason why you have your music becomes distorted. Just imagine your audio is a low frequency that travel slower than the win flow in your car. Scientifically, the audio of your voice or music is very slow when it moves from point A to point B. For example, if you are standing infront of a high speed fan, your voice will be distorted because the wind of the fan is flowing a little faster than your voice on the opposite direction that causes your voice to be delayed between the fan and your ears. Therefore, the audio sometimes travels at the same speed with the wind speed on the same direction that cause your ear to hear nothing at that movement.
Listen to the music with the trunk open while you park your vehicle will not make the sound distorts at all. I do not think that happens. If so, you may have a bad speakers.
~AFAccord~ 
Copper - Posts: 59
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: December 18, 2004
Location: Korea, South
Posted: January 06, 2005 at 3:11 AM / IP Logged  
Hmmmm...  I belive tuanmerica is trying to describe the doppler effect.  Bigwise, I hope this isn't what you are asking about. lol  If you're riding down the road with your trunk open, then you have other problems to worry about...
Black Cherry
"Experience is something you never get until just after you need it."
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