Open windows and bass

Discussion in 'Archived Threads 2001-2004' started by Shawn Solar, Oct 8, 2002.

  1. Shawn Solar

    Shawn Solar Supporting Actor

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    I just closed my windows in the livingroom. they are crank out style and have one on either side of the room they ar about 4ft high and 2ft wide. I closed the far side window and did not notice any difference but have just recently closed the side closest to the subwoofer. And wow what a difference. Much louder and deeper. I think I have to re-eq the sub now. Anyone else experience this?
    I also don't notice a difference when I open the door into the next room. Just the window. I guess you could say the bass got up and jumped out the window[​IMG]
     
  2. That is pretty common. You should EQ the sub for the way the room will be when played. ..or with the BFD have a Summer (windows open) setting, and a Winter (closed) setting [​IMG]
     
  3. John Parris

    John Parris Stunt Coordinator

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    Same concept as car audio... you're going to get a much higher SPL with the windows closed because the waves don't go out.
     
  4. Shawn Solar

    Shawn Solar Supporting Actor

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    Actually I get more bass with the windows down in my car[​IMG] That's why it so weird. I am wondering if it only affects a certain range of frequencies. I am going to do some measurements when I have time.
     
  5. Cam S

    Cam S Screenwriter

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    Ya, I get way more bass with the windows down, and even in competitions, they make sure you keep the windows up ( don't compete though).
     
  6. Shawn Solar

    Shawn Solar Supporting Actor

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    Roll down the windows=more bass(car)
    close window=more bass(home)
    I have air conditioning in the car so I drive windows up. I don't have air in the house so I open the windows. both=less bass I think the laws of physics are playing a rotten trick on me[​IMG]
    Must be the same people responsible that make all the things that are bad for you taste good and all the things good for you taste bad. Sheesh!
     
  7. John Parris

    John Parris Stunt Coordinator

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    You mean that 3rd dozen of doughnuts (you know... the one that tastes REALLY good?) is ... BAD for me? [​IMG]
    Ive actually heard an explanation as to why you achieve a higher SPL with the windows down in a car... I'll have to dig it up from ClubRSX archives...
    Edit: DER! Yes, it's late, and I'm not thinking properly. CANCELATION, SMART GUY! Argh... I'm going to be kicking myself for days now for not realizing it... when you roll the windows down in your CAR there's a huge reduction in cancelation...with the wide open spaces of your living room or home theater, cancelation is less of an issue. Hope I'm getting this right now... it IS past my bedtime [​IMG]
     
  8. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    The results are dependent on several factors and won't be the same for everyone. I would take in account what frequencies you are listening to when making your conclusion of "more/less" bass and also take in consideration the listener/mic's location.
    Lets take the example of a home theater room that's shaped like a cube. This will cause an immense drop in the first order resonance at the center location which is at the null of 3 standing waves. Open one plane up and one of those standing waves is elminated therefore boosting the bass in the HT when the "window is down".
    On a side note, speed could also be a factor since driving 80mph with the windows down you may get less "perceived" bass than driving 80mph with the windows up. This is due to the ambient noise increase that lowers the audible bass. (Perhaps due to the limitations and ability of human hearing to adapt and process acoustic info)
    Let me see if I can explain the bass dips/spikes:
    I think people are forgetting that where there's cancellation of frequencies, there are reinforcements as well. For example... the axial standing wave of a 70hz tone in an 8 foot length sealed cube will cause a drop in decibels in the center of the cube. However move towards any surface inside the cube and the SPLs will rise. (70hz is the calculated first order resonance in an 8 foot length, see my site for a calculator.
    It's not like the sealed cabins of cars are capable of destroying sound waves, there's always a place to hear them even if it's on the surface of the driver that is resonating in free air. Unless you guys have cars that have helmholtz resonators/bass traps in your car, I think what you are experiencing is the shift in location of bass and the change in volume at certain (resonating) frequencies.
    When you are in a sealed cabin there is a another resonant frequency referred to as cabin gain (Which is what car audio competitions use to obtain crazy SPL). This is dependent on the overall volume of the cabin and is not an axial mode. I very much doubt that this frequency will drop if you open the windows.
    A different test: take an SPL meter in your car and play an un-eq'd bass sweep with windows down, and then up. The windows down should be very erratic and spike up and down, which will also vary depending on the location of the mic in the car. With enough windows down, your sub will perform close to it's anechoic response which should be a lot smoother.
    Due to the human ear focusing on the lack of bass at those resonant suck outs, some may conclude the bass is overall lower with the windows up, however, if you took the average SPL from both measurements they should be pretty much equal. (never tried, just a guess)
     
  9. Shawn Solar

    Shawn Solar Supporting Actor

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    I thought the car was two small for standing waves. If you take the width=4ft 565/4ft=141hz out of the passband of the subwoofer. 565/8ftlength=70.65hz still pretty high. And under 50hz there is no standing waves. I find he car harder to explain and I will have to post measurements maybe this weekend.Could it be that the car's internal pressure change the qts of the system like making a sealed box into a ported?

    I will also have to measure room response both window open and closed to see if I am just hearing things.
     
  10. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I know there are different types of standing waves, some of them are tangential and oblique which involves planes that arn't parallel and some work with weird shapes. I can assume that a combination of standing waves, resonating surfaces, and cabin gain causes the erratic response in a sealed car.

    I guess the axial ones are more for rooms because they start at 8feet and get larger. I know I wouldn't even bother calculating axial modes in a car probably because none of the surfaces are parallel.

    I guess I forgot to include this above, it was 5:40AM in the morning so I could have been rambling.
     
  11. Mark gas

    Mark gas Second Unit

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    You will get more bass in car with windows down if your box is to small for max spl you want to have a large ported box in an air tight vehicle.
     
  12. Shawn Solar

    Shawn Solar Supporting Actor

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    Mark,
    that could be another reason. I have my sub in a ported in the house and a sealed in the car.
     

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