Understanding/dealing with cabin gain

[mrbobian 0]

Ok, I have an s10 ext cab with a Fi Q10, run off a sundown sae-1000D put in a .6ft^3 sealed box. The box is down firing in the back of the cab right in the middle. First off, why does it get soooo much louder when the doors are opened? and second, how do I deal with this? I have been planning on building a ported box but before I go ahead and spend the time on another box, I would like to know if there is anything I can do to overcome the downfalls of a truck cab. Any takers?

Thanks in advance,

Mike B.

[///M5 2,833]

How about when the windows are open?

[KU40 173]

you don't really deal with it. Every "normal" vehicle does get louder with doors/windows open, that I've seen. What's wrong with a truck cab? You have less airspace to pressurize, so you should actually be at an advantage over most cars.

[tezin87 0]

I have a regular cab truck and have the same problem. It sounds much louder and deeper when the windows are down. Don't know what it is, I just figured it was because the subs are right behind the seats.

[audio-neon 34]

Pressure, and volume are two different things. A regular cab truck might sound quieter sealed up, but so do most other vehicles.

[audio-neon 34]

I will expand a little bit. Every vehicle has a resonant frequency. SQ guys eq this down or build boxes that are lacking in output at said frequency (a lot of times the frequency is above the crossover for their subs anyways). Depending on the vehicle this "gain" can be substantial. Walling and the box itself (not to mention different #'s of occupants will change the cabin gain frequency.

Spl guys use the cabin gain to get a better score. They find the resonant frequency, and tune slightly below it so that their box peaks with the cabin's peak for a better score.

You are referring to a bandpass type effect. Basically whenever you put a box in a vehicle you are building a bandpass system. When the doors (or windows) are open, you are porting your "bandpass system". You are making the outer box (the cabin) ported and raising the efficiency of the system. Hence why it sounds louder. (noting that it might not be louder to a mic).

[mrbobian 0]

Okay, thanks guys. So there is really no secretes or tricks. I'll just have to take the doors off. Lol.

[///M5 2,833]

Is this at all frequencies or just some? Have you tried moving your box around the cabin to see if the phenomena changes?

[mrbobian 0]

It is pretty much at all frequencies, I'm far from an audio expert so its hard to tell, but I'll try moving the sub around. maybe pointing up or back will help... we'll see.

[mrray13 30]

i love the "you have less volume to pressurize" response. that's actually the issue. only it's not. ready? i'm not all that technical, so maybe if i lay it out in simple terms, someone can come behind me and explain the physics...

first, by being in the smaller cabin, you do pressurize(i know that's not the right term) faster. but this causes you to lose spl after a certain point, as well as being able to help. why? cancellation. you are also shorter, which means the cycles are hitting each other faster, bouncing back off teh glass into the new notes coming forward. when you open your door/window, the old notes are basiclly released, thereby eliminating most cancellation. and that's what causes the vehicle to be louder open, compared to sealed. the mic/ears only hear the new notes coming forward, and they aren't colliding with the majority of the old notes bouncing back. and no, it can't be fixed completely.

the secret to dealing with small cabins, jsut like big cabins, is finding the wavelength that is needed to be the loudest. cabin length is more important, IMO, then volume. unless one is walling off, running huge subs and massive power and completely sealing up the vehicle for no flexing to overpower the cabin. in street vehicles, building to the wavelength (or quarter, half or three-quarter wave) is going to be the key to being the loudest you can be. simply put, most street beaters jsut don't have the cone area or power to overcome and win by pressure.

and even built to correctly, windows down/doors open will always be louder. IME anyway. hope that helps, and maybe ///M5 can explain the in technical terms what i tried to explain.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[KU40 173]

i love the "you have less volume to pressurize" response. that's actually the issue. only it's not. ready? i'm not all that technical, so maybe if i lay it out in simple terms, someone can come behind me and explain the physics...

first, by being in the smaller cabin, you do pressurize(i know that's not the right term) faster. but this causes you to lose spl after a certain point, as well as being able to help. why? cancellation. you are also shorter, which means the cycles are hitting each other faster, bouncing back off teh glass into the new notes coming forward. when you open your door/window, the old notes are basiclly released, thereby eliminating most cancellation. and that's what causes the vehicle to be louder open, compared to sealed. the mic/ears only hear the new notes coming forward, and they aren't colliding with the majority of the old notes bouncing back. and no, it can't be fixed completely.

the secret to dealing with small cabins, jsut like big cabins, is finding the wavelength that is needed to be the loudest. cabin length is more important, IMO, then volume. unless one is walling off, running huge subs and massive power and completely sealing up the vehicle for no flexing to overpower the cabin. in street vehicles, building to the wavelength (or quarter, half or three-quarter wave) is going to be the key to being the loudest you can be. simply put, most street beaters jsut don't have the cone area or power to overcome and win by pressure.

and even built to correctly, windows down/doors open will always be louder. IME anyway. hope that helps, and maybe ///M5 can explain the in technical terms what i tried to explain.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

hmm. guess I've never gotten into the wavelength side of the equation. However, given that, shouldn't a truck with less airspace that's maximized with it's proper wavelength still be louder than a larger vehicle maximized with it's proper wavelength, given the same equipment, because of less air?

[shizzzon 461]

When i did testing with my meter in my car, every position i tested(24 different) except for one was it louder on the mic with windows down.

The position that was actually louder with everything sealed up and shut was subs forward\port forward.

[mrray13 30]

i love the "you have less volume to pressurize" response. that's actually the issue. only it's not. ready? i'm not all that technical, so maybe if i lay it out in simple terms, someone can come behind me and explain the physics...

first, by being in the smaller cabin, you do pressurize(i know that's not the right term) faster. but this causes you to lose spl after a certain point, as well as being able to help. why? cancellation. you are also shorter, which means the cycles are hitting each other faster, bouncing back off teh glass into the new notes coming forward. when you open your door/window, the old notes are basiclly released, thereby eliminating most cancellation. and that's what causes the vehicle to be louder open, compared to sealed. the mic/ears only hear the new notes coming forward, and they aren't colliding with the majority of the old notes bouncing back. and no, it can't be fixed completely.

the secret to dealing with small cabins, jsut like big cabins, is finding the wavelength that is needed to be the loudest. cabin length is more important, IMO, then volume. unless one is walling off, running huge subs and massive power and completely sealing up the vehicle for no flexing to overpower the cabin. in street vehicles, building to the wavelength (or quarter, half or three-quarter wave) is going to be the key to being the loudest you can be. simply put, most street beaters jsut don't have the cone area or power to overcome and win by pressure.

and even built to correctly, windows down/doors open will always be louder. IME anyway. hope that helps, and maybe ///M5 can explain the in technical terms what i tried to explain.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

hmm. guess I've never gotten into the wavelength side of the equation. However, given that, shouldn't a truck with less airspace that's maximized with it's proper wavelength still be louder than a larger vehicle maximized with it's proper wavelength, given the same equipment, because of less air?

i would say yeah, or there wouldn't be walls. but then again, most walls are huge surface area, power.

shizzon, even in my dodge, with subs foward/ports forward, everything louder with a window open, door open. i'm sure vehicle plays a role, but in every vehicle i've owned, or played with, something open meant louder, regardless of box placement. care to detail your install/ vehicle a bit more? i'm curious.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[shizzzon 461]

it is a scion tc.

Hatchback style vehicle.

In that test i did, i temporarily sealed off any way to fill additional volume behind the front baffle making the remaining volume considerably less.

Box was tuned to peak at 36hz sitting right behind rear seat with seat folded down. Tested on both driver and passenger side with same results.