Calculate Cabin Gain?

[bikinpunk 10+ year member]

I had read in a couple other threads that you can use the

1. longest distance

2. multiply by two

3. divide by 1/4 speed of sound

4. = resonant frequency

However, on step one I'm not sure if I take the longest distance of the trunk or the cabin. I've posted in DIYma 3 times, but haven't gotten any replies yet.

When I use the trunk I get

Cabin Frequency

Longest Length (in) 45

Length * 2 90

Speed of sound (in/s) 13397.244

1/4 of SoS 3349.311

Resonant Frequency 37.21456667

If I were to use Cabin the number would be MUCH lower. Which doesn't seem right since everything I've read says Civics have resonance at 30-50hz. //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

Click to read more...

 

[PhatTonyDeMarco 5,000+ posts]

I wouldn't trust that number for a minute.

Real world > BS equation

 

[bikinpunk 10+ year member]

It could at least get me close.

I have no idea any other way.

 

[PhatTonyDeMarco 5,000+ posts]

It could at least get me close.
I have no idea any other way.

No, I doubt it will.

The ONLY way to determine your vehicles resonance frequency is to get a meter and test with a sealed enclosure.

That equation is bullshit man, the resonance of a vehicle depends on mass not distance...

 

[Immacomputer 10+ year member]

Take the distance from the end of the trunk to the windshield.

This will not really give the resonant frequency but more so the point at which cabin gain will to have an effect. It's not a BS equation and it worked on two of my vehicles. It won't tell you where to tune your enclosure to max output but it will give you an idea where cabin gain begins.

 

[helotaxi 5,000+ posts]

Well there are two things at play. One is the driver interaction with the air volume in the vehicle, basically it's another chamber of the enclosure. The second that the equation is looking at is building a standing wave in the car using quarter wave theory. You have to consider both and figure which will give you the biggest boost in output. Usually its the first one because you can't nearly rely on the second.