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Sound pressure doesn't comprise enough of an overall pressure change to change the density of the medium..

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Now thats weird,I always thought an spl of around 170 was like another atmosphere in pressure?

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I needed a sub

Fast as my car

found it - DD 3512/9512
bass that hits like jet lee-
quick, clean, and accurate
- sound as clear as it gets -

Posts: 107 | From: The Start | Registered: Dec 2002  |  IP: Logged | 

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Originally posted by festivaman:
ive done my share of 170 db sit in,s. trust me they hurt. still the most painfull was a 160 db sealeed box. to me that is real pressure. but on the other side these waves are confusing the hell out of me. the magazine says basically yur box has to have the same depth as the "b" pillar or dust cap of speaker to mic location to achieve a 1/4 wave. what gets me is everyone is moving the back walls foward and in reality there actually only using 1/2 of the 1/4 wave.the two waves are still on the same sinc as each other just one wave hits the mic before the other.what i want to know is how to cheet the wave,mainly becuase i connot have a 1/4 unless i lengthen the back wave some how

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Unfortunately, if math worked for SPL, there would be a LOT of competitors doing much better than they are

The 1/4 phoenomenom is very simple.. If you take a look at the response alterations of your car, they have two distinguishing characteristics. A gain which goes up as frequency decreases, starting at some moderately low frequency, and some small "bump" that peaks at some upper frequency. In fact, there is a series of "bumps" as you go up in frequency, but the upper ones are very small.

We can't take advantage of the car's natural gain in the lower frequencies because real SPL at those frequencies requires MUCH MUCH MORE displacement (to do the same SPL at 20hz as 40hz requires four times as much moved air), so the obvious frequency to take advantage of is the first in the series of "bumps," as this occurs under the MIC filter and within a reasonable displacement ability.

However, the center location of this "bump" is natural to the car for certain situations, like, one location of the box, flat response, etc.

If the sub/box combo has a peaky response, the overall maximum SPL occurs at the highest sub+car gain frequency.

Thus the 1/4 theory

ShadowStar

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You can't build a reputation for what you're GOING to do.. But you can build one for TALKING about it!

It's all about knowledge, love and respect.

Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999  |  IP: Logged | 

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Originally posted by chemid51:
I am trying to understand all of this. The distance from my single 12 to the mic is 118 inches. The rear wave has to travel 118x3 (354")!! Lets pretend I can pull this off.
Ex. port close to the sub, so the distance from port to mic is the same as speaker to mic. now to make the port 236" long(354-118). Would that work? Would the sound waves travel faster or slower going through 236" of port. Is it even possible to calculate this. Also crunching some #'s 118" to mic = 28hz <-- 3390/118. The loudest freq. i have found is 51 hz. I will close this with saying i am really confused, and reading all the posts only got me more confused.
Thanks to anyone that can shed some light on this. Mark

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Most of these theories apply to walled vehicles... most of this info would be of no use to a street car...

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Scottie Johnson
Sound Pressure Technologies

Posts: 2351 | From: Morgantown, KY | Registered: Apr 2001  |  IP: Logged |