Need help with SPL box

[Trixter 10+ year member]

My car is a 95 pontiac firebird. How would I find my car's peak freq?

use a test sub in a sealed box (10", 12" doesn't have to be anything special) play test tones outside of the car and recored the spl of them. you dont need to be loud or anything but make sure the volume and other settings are the same for each freq. played. play a wide range...like 35hz to 60hz or something. now play the same freq. range inside the car and record the results. you will see a peak in the spl for outside and one for inside...they will be different (ie: maybe 40 out side and 50 inside) and then split the difference. you resonant freq. in this example would be 45Hz. when you build you box tune it about 5hz under the resonant freq. if you use something like winisd that shows a graph, you want your box to peak at the resonant freq.

 

[theotherguy 10+ year member]

use a test sub in a sealed box (10", 12" doesn't have to be anything special) play test tones outside of the car and recored the spl of them. you dont need to be loud or anything but make sure the volume and other settings are the same for each freq. played. play a wide range...like 35hz to 60hz or something. now play the same freq. range inside the car and record the results. you will see a peak in the spl for outside and one for inside...they will be different (ie: maybe 40 out side and 50 inside) and then split the difference. you resonant freq. in this example would be 45Hz. when you build you box tune it about 5hz under the resonant freq. if you use something like winisd that shows a graph, you want your box to peak at the resonant freq.

Do I do the test with window's up or down,if up....my car is very quit and it would be like 100 DB's out side. Would that low reading be acurate. Also will the loction of sub in the car affect the car's freq? I would also assume that the sealed box would have to be perfect size for sub.....to avoid the box affecting the freq responce......Am I right?

 

[Trixter 10+ year member]

i would do it with the windows up this way your getting a true inside reading. measure the dB inside the car (for outside testing, have the sub outside of the car). how quite or loud your system is doesnt matter. your just trying to get a dB curve. the location should not have an effect. however, i would have it in about the same location as you normally would have your sub. as long as it's the same box for inside and outside testing, the box doesn't have to be exact because all your testing will remain consistant either way.