SPL greater with a window open?

[U-H.Com 10+ year member]

Does this make any sense? I'm arguing with a guy about SPL and he is claiming that you can increase your overall sound pressure level with a door or a window open...is this correct? I mean if you stick the mic in the port, then it wouldnt matter, but if its on the dash, how can letting air escape be beneficial?

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[bigbassman Premium Member]

Originally posted by U-H.Com Does this make any sense? I'm arguing with a guy about SPL and he is claiming that you can increase your overall sound pressure level with a door or a window open...is this correct? I mean if you stick the mic in the port, then it wouldnt matter, but if its on the dash, how can letting air escape be beneficial?

yes, you can get a benefit from opening a window / door, depending on the system and install, and frequency used..

Loyd L.

 

[SpeeDFX 10+ year member]

Yeah in my car if I open the windows, the bass gets a bit louder and more "even". I think it has to do with wave cancellation while the windows are closed.

 

[60_cent 10+ year member]

My old system would sound a lot better with the windows down. I have also always wounded why.

 

[Tek 10+ year member]

hm...mine sounds better with windows closed...i thought it was cause the sound was bouncing off the windows, but maybe not.

 

[Nickfireblazer 10+ year member]

Yep...the spl increases and the bass hits harder with a window down and when you open the door forget about it.

 

[FAM4LIFE 10+ year member]

True but not in every instance. There are some vehicles that have greater SPL with doors closed and windows up. Not many but there are a few out there.

 

[FAM4LIFE 10+ year member]

Originally posted by bigbassman yes, you can get a benefit from opening a window / door, depending on the system and install, and frequency used..

 

Loyd L.

Learning lots in MECA. Numbers **** but I can improve. When are you going to hit the loud button?//content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[U-H.Com 10+ year member]

Thanks for the replies guys...It just sounds wierd thats all...I thought by keeping all the sound in the car, the SPL would be greater with it all sealed off...

 

[LBX2G 10+ year member]

true the bass gets louder exspeicaly if is an spl setup. Because the Spl setups work with back pressure. and if u open a door or an window then u are letting the pressure out and that makes the subs work harder.

 

[havoc06 10+ year member]

well as far as the bass sounding louder when you open the windows, that all depends on the frequency of the bass and your set up. Its because bass takes distance to form. For example, a bass wave at 35 htz may take 30 feet to form, so with the windows up, it doesnt create a full wave. Thats why higher frequencies hit harder on mics, because they form faster. And rolling down the windows will only help higher spl numbers if your car isnt set up right, because if your true res freq of your car was found and port tuned correctly, rolling down the windows just throws it all off. Some mics actually measure compression too, not just the speed of the air inside the car, and obvioulsy rolling down the windows wouldnt help on those mics....just my two cents...//content.invisioncic.com/y282845/emoticons/nono.gif.eca61d170185779e0921b0faa9704973.gif

 

[geolemon 10+ year member]

Originally posted by Nickfireblazer Yep...the spl increases and the bass hits harder with a window down and when you open the door forget about it.

This is true with lots of cars, but it generally indicates a problem, or some asymmetry with how the setup is laid out (or at least behaving) in your car... of course, the mic (legal) is offset...
But at any rate, bear in mind that SPL stands for Sound Pressure Level.

In simplest terms, the subwoofers are moving in and out, creating a pressure differential between max excursion out compared to max excursion in... the air pressure inside the car is fluctuating.

Illustration #1

Picture a small length piece of PVC pipe that's capped at one end.

In the open end, you stick a plunger.

And heck, stick an air pressure gauge in that capped end, to measure air pressure inside the cylinder.

Now, as you move the plunger in and out, it's easy to see how you'd be compressing the air trapped in the closed end of the PVC pipe, and decompressing it as you pull the plunger back, right? You could easily read this on the gauge.

And if you drilled a 2" hole in the PVC pipe near that capped end, and moved the gauge in and out, you'd undoubtedly see less pressure fluctuation as you moved the plunger in and out, correct?

Illustration #2

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

The oversimplification

Because of course there's more that goes into it, and both of my illustrations aren't perfect, but of sound theory (no pun intended).. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

At any rate... something to consider:

Hard surfaces reflect and/or vibrate and resonate... the former can help keep sound energy in your interior where it will help the pressure situation, the latter will potentially dissipate some of that sound energy, as it will be vibrating panels rather than microphone consdensers... //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Plush surfaces and objects (ie. seats, carpeting) are absorbtive, and can soak up that valuable sound energy, rather than pressurizing the air in your interior.

Now, if you consider all the possible paths that your sound energy can travel from your subs to the microphone location (or to where you are sitting, whichever you care about more //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif), and consider all the hard surfaces that they pass, and where the sound may reflect to, and consider all the soft surfaces that they pass, and the reflection-free zones that they pass, and consider all the interior panels that shake and vibrate, and how that both soaks up some of that energy and also creates harmonics of that tone...

There can even be cancellations, either between a couple different pathlengths, with respect to some point in your interior.. or between direct and reflected sound, coming off a window, say... even with waves as large as they are!

Obviously, it's complicated, and that the mic could just be sitting in a zone that's been a little "depressurized" relative to other spots in your interior, due to these factors.

Maybe moving your subs around is the answer.

Maybe stiffening some of those interior panels is the answer (or maybe that's just shifting the resonance //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif). Maybe removing the plush interior - or some part of it - is the best answer.

Or, if you aren't going to be that extreme..

Maybe it's just understanding that the soft spots and the hard spots are simply conspiring to never allow you to reach the full SPL potential of the equipment that's in your car...

And so you roll down a window to change the loud-zones and dimmed-zones in your interior, releaving some of those cancellation issues. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

My point is simply that rolling down your window is a very far cry from truly increasing your SPL, particularly with respect to what you COULD do with the same equipment.

It's simply the easiest thing to do, and it's simply helping allieve one type of inherent acoustical degradation due to your interior... not helping to "raise your SPL".

To the contrary, in fact. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[paikiah 5,000+ posts]

wow..spechless...//content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

And all I was told (from an old issue of CA&E) about seemingly increase of SPL was due to raise in midbass, didn't do anything for lower frequencies itself. Hmmm...

 

[bigbassman Premium Member]

Originally posted by FAM4LIFE Learning lots in MECA. Numbers **** but I can improve. When are you going to hit the loud button?//content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

I hit it sunday.. and posted a 153.5 on the toughest mic in MECA... I'll be in the land of 156's when I find a show using a normal reading mic..

that'll be all I turn it up to until finals.. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Loyd L.

 

[bumpin_blazer 5,000+ posts]

Originally posted by bigbassman I hit it sunday.. and posted a 153.5 on the toughest mic in MECA... I'll be in the land of 156's when I find a show using a normal reading mic..

 

that'll be all I turn it up to until finals.. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

Loyd L.

hey with my setup you helped design will it be louder to crack my windows??

adam