question about how cabin volume effects SPL

[Ed Lester 10+ year member]

And my SS 1-2 car with 2 15s worked best with a 24 cubic foot enclosure.

 

[spencer321 10+ year member]

And my SS 1-2 car with 2 15s worked best with a 24 cubic foot enclosure.

wow thats a big *** enclosure for 2 15's

 

[spencer321 10+ year member]

When the size of the box starts to match or be bigger than the size of the effective cabin, it is in many ways like you are reversing the two, and the cabin becomes the enclosure, as it will dampen and load the cone(s) more than the box will. Have you ever tried sticking a meter in a port or inside a box?
Granted, your actual box is alot more air tight and better built to generate acoustic energy than any part of your cabin is, but you get the idea.

that actually made sense

 

[Ed Lester 10+ year member]

wow thats a big *** enclosure for 2 15's

It was good for 160 dB on 16,000w.

Others had as much as 35 cubes and as little as 15 cubes.

 

[BringDaBoom 10+ year member]

Simple physics. Take a bowl and fill it with water. Stick your hand in flat towards teh bottom and watch the water rise. By decreasing the volume where the water stands it rises. If the water had no where to go and poked a hole in the bowl, the water would squirt out at a higher pressure than if not compressed.

The same goes with air. Decrease the space for which it has to move/escape and seal it with nowhere to go and pressure will rise as soundwaves increase. The air wants to move and spread and dissapate but the walls/windows of the vehicle won't allow it. Thus...pressure builds

Now.....as with everything....it's not that simple. If it where, then the best SPL vehicles would consistantly be really small cars. There is a threshold, and fine line of balance between the maximum amount of pressure relating to cabin size. Depending on where the mic is going, what size subwoofer/s you have, how much power is going through it, what type of enclosure the subs are in, and how those subwoofers are positioned in relation to the interior design and volume of the cabin....will determine the optimal size cabin for the given set-up. For that, you need to bust out some Algebra.

But as a general rule of thumb, yes, the better sealed and smaller the cabin area, the higher pressure readings one would get.

 

[Ed Lester 10+ year member]

Simple physics. Take a bowl and fill it with water. Stick your hand in flat towards teh bottom and watch the water rise. By decreasing the volume where the water stands it rises. If the water had no where to go and poked a hole in the bowl, the water would squirt out at a higher pressure than if not compressed.
The same goes with air. Decrease the space for which it has to move/escape and seal it with nowhere to go and pressure will rise as soundwaves increase. The air wants to move and spread and dissapate but the walls/windows of the vehicle won't allow it. Thus...pressure builds

Now.....as with everything....it's not that simple. If it where, then the best SPL vehicles would consistantly be really small cars. There is a threshold, and fine line of balance between the maximum amount of pressure relating to cabin size. Depending on where the mic is going, what size subwoofer/s you have, how much power is going through it, what type of enclosure the subs are in, and how those subwoofers are positioned in relation to the interior design and volume of the cabin....will determine the optimal size cabin for the given set-up. For that, you need to bust out some Algebra.

But as a general rule of thumb, yes, the better sealed and smaller the cabin area, the higher pressure readings one would get.

Sounds like you studied fluid dynamics.

You also touched on something we call power compression.

This is where pressure builds on the cones of the subs and limits how much they can move. So you can add more amplifier power, but your SPL will no longer increase, but will infact decrease due to the extra strain on the electrical system.

 

[Rashaddd 5,000+ posts]

Sounds like you studied fluid dynamics.
You also touched on something we call power compression.

This is where pressure builds on the cones of the subs and limits how much they can move. So you can add more amplifier power, but your SPL will no longer increase, but will infact decrease due to the extra strain on the electrical system.

Really? I thought we were kinda expected to have realized that by like 8th grade? Is this not common knowledge?

 

[spencer321 10+ year member]

Sounds like you studied fluid dynamics.
You also touched on something we call power compression.

This is where pressure builds on the cones of the subs and limits how much they can move. So you can add more amplifier power, but your SPL will no longer increase, but will infact decrease due to the extra strain on the electrical system.

correct me if im wrong but im assuming "power compression" based on your description would be when the pressure on the exterior portion of the cone is greater than the pressure inside the enclosure?

 

[Ed Lester 10+ year member]

correct me if im wrong but im assuming "power compression" based on your description would be when the pressure on the exterior portion of the cone is greater than the pressure inside the enclosure?

Could be behind or in front of the driver.

Its always there, its just a matter of it is causing ill effects or not.

In most cases we havent reached the levels of power to see any ill effects. Its usually only in big powered competition systems. Or moderately powered systems with small enclosures.

Extreme cars see this more than anything.

Ever notice how some cars have a higher SPL in competition when you dont hold the doors and windows? Thats because the flex allows for the drivers to move and reduce impedance rise.

 

[Rashaddd 5,000+ posts]

correct me if im wrong but im assuming "power compression" based on your description would be when the pressure on the exterior portion of the cone is greater than the pressure inside the enclosure?

Power compression essentially involves the law of diminishing return. The more you do something the less marginal benefit there is for doing more of it. If you increase power from 100 watts to 1000 watts, you will get MUCH louder. Increase again by 1000 watts and you will get a little louder. Again by 1000 and you will get even less gain from it, and so on. Not only does this happen with laws of energy, but with laws of pressure, heat, etc which all are effecting the output of a sub as well

What he was specifically talking about is the amount of force it takes to keep moving the cone farther. The farther you are moving it in each stroke, the higher the amount of energy it takes to do this which increases exponentially, while at the same time as its getting exponentially more difficult, the motor (magnet) is getting less and less powerful as the coil moves farther away from it or closer to the center of its pull (which eventually would only cause outward pressure on the coil rather than pulling it rearward if we got to an extreme, subs bottom out lonnng before they could ever reach that point)