Planning ahead for car system - Page 4 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #31 of 44 Old 01-10-10, 12:15 AM Thread Starter
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Re: Planning ahead for car system

Lining the inside of the box is a big thing back in the HT forum. It will just help absorb some of the frequencies, and not make the box sound as "boomy", if you want to put it like that.
I would buy some used stuff, but it seems like on every deal that I had gotten on a used item, no matter what the feedback was on the person, I always wound up being screwed with a broken item. Wether it be a week, or a month, it seemed like everything was bound to break. Maybe its different with audio stuff though.
I'll check around to see what kind of used stuff I can find.

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post #32 of 44 Old 01-10-10, 11:14 AM
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Re: Planning ahead for car system

I don't mean to poo poo on anyone's idea of how a sub box should be built, but scientific testing of closed cell foam for sound absorption, in a nutshell, says that the foam has to be of a thickness equal to or greater than the wavelength of the frequency that is targeted for absorption in order to be effective. How does that translate?

60 Hz sound wave = 226 inches long
100 Hz = 135 inches
1000 Hz = 13.5 inches
10,000 Hz = 1.35 inches (this is where your tweeter plays)

So, to effectively absorb 10 KHz you need a material that is 1.35 inches thick. To absorb 100 Hz, you need foam that is 135 inches thick.

Think about it. This is the reason why we can hear the guy with the crazy car subwoofer coming from an eighth mile away in our basement. Those low frequencies penetrate the walls of our homes which are stuffed with 4 inch thick insulation.

For a test, take the CCF that you would line the box with and play some music. Now place it over both of your ears (don't put your hands over your ears though). Hear any difference in the bass or midbass? Nope. Then it doesn't absorb those frequencies.
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post #33 of 44 Old 01-10-10, 12:53 PM
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Re: Planning ahead for car system

I'll just throw this out there. On EBay you can still find the old school Xtant amplifiers cheap (sometimes still new in the box). IMO you just can't beat the soundQ of these amps.....
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post #34 of 44 Old 01-10-10, 01:37 PM Thread Starter
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Re: Planning ahead for car system

Quote:
CasePro wrote: View Post
I don't mean to poo poo on anyone's idea of how a sub box should be built, but scientific testing of closed cell foam for sound absorption, in a nutshell, says that the foam has to be of a thickness equal to or greater than the wavelength of the frequency that is targeted for absorption in order to be effective. How does that translate?

60 Hz sound wave = 226 inches long
100 Hz = 135 inches
1000 Hz = 13.5 inches
10,000 Hz = 1.35 inches (this is where your tweeter plays)

So, to effectively absorb 10 KHz you need a material that is 1.35 inches thick. To absorb 100 Hz, you need foam that is 135 inches thick.

Think about it. This is the reason why we can hear the guy with the crazy car subwoofer coming from an eighth mile away in our basement. Those low frequencies penetrate the walls of our homes which are stuffed with 4 inch thick insulation.

For a test, take the CCF that you would line the box with and play some music. Now place it over both of your ears (don't put your hands over your ears though). Hear any difference in the bass or midbass? Nope. Then it doesn't absorb those frequencies.
As far as my understanding goes, we're not trying to absorb the frequencies, which would in turn cancel them out, but we are just trying to keep them from echoing off of this insides of the box.
All I know is that with my box, with the foam, it made it sound cleaner, and not as boomy.

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post #35 of 44 Old 01-10-10, 02:29 PM
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Re: Planning ahead for car system

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sub_junkie wrote: View Post
As far as my understanding goes, we're not trying to absorb the frequencies, which would in turn cancel them out, but we are just trying to keep them from echoing off of this insides of the box.
All I know is that with my box, with the foam, it made it sound cleaner, and not as boomy.
Lining subs is supposed to damp the backwave and stop the sub from "ringing" or sounding "boomy" as Dylan pointed out. Whether or not open cell foam is effective is a debatable issue. I tried it on two identical subs, one lined, one unlined and I can hear a difference.




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post #36 of 44 Old 01-12-10, 09:12 PM
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Re: Planning ahead for car system

The only way you can get a 4 1/2cft box in your truck is to remove the back seat or put it on top of the seat, this is if the truck is an extra cab, for the inside I would do the Sonic Barrier from parts-express.





Do the speakers on the door they will sound better. this will give you more left and right defenition on your music, that's if you can hear them over the sub

You dont need to double the front of the box unless you are doing a spl box, do more braces instead.
The wire kit needs to be bigger if you hooking both amps, need at least 2 gauge.

To set the amp where it will not clip you need an oscilloscope to be able to see when the signal is clipping or you can do it by ear but a lot of people cant hear the distortion


What kind of music do you listen to???


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post #37 of 44 Old 01-12-10, 10:26 PM Thread Starter
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Re: Planning ahead for car system

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Rodny Alvarez wrote: View Post
The only way you can get a 4 1/2cft box in your truck is to remove the back seat or put it on top of the seat, this is if the truck is an extra cab, for the inside I would do the Sonic Barrier from parts-express.





Do the speakers on the door they will sound better. this will give you more left and right defenition on your music, that's if you can hear them over the sub

You dont need to double the front of the box unless you are doing a spl box, do more braces instead.
The wire kit needs to be bigger if you hooking both amps, need at least 2 gauge.

To set the amp where it will not clip you need an oscilloscope to be able to see when the signal is clipping or you can do it by ear but a lot of people cant hear the distortion


What kind of music do you listen to???
I mostly listen to stuff like Breaking Benjamin, Mudvayne, Mushroom Head (some songs), some Kottonmouth Kings (mostly as a test), stuff like that.

I will look into that foam that you talked about. It looks pretty promising.

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Last edited by sub_junkie; 01-12-10 at 10:55 PM.
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post #38 of 44 Old 01-12-10, 11:07 PM
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Re: Planning ahead for car system

where are you suggesting that foam be installed? If that foam holds water, you don't want to put it inside the door.

To stop vibration in the door, you need to use a constrained layer dampener on the door skin. This helps to stop the metal from vibrating. There are two types, foil backed types that use the metal foil as a constraining layer (couples to the metal and changes the resonant frequency. The other type uses viscoelastic material and turns it into low level heat.

Sonic barrier appears to be neither of these. I have not looked at the specs, but it appears to be some sort of thin high mass material coupled to foam substrate. This might be similar to mass loaded vinyl and closed cell foam. The mass loaded vinyl blocks noise from on area to the other. In the car, you would often use it to completely cover the floor and the firewall. You put the foam down first, then the mass loaded vinyl over top of it, both under your carpet. It is strictly a noise barrier that prevents air and structure borne noise from getting inside the cabin.

I used CCF and MLV on my install and they significantly lowered the noise floor at highway speeds. They are MUCH MUCH more effective at lowering road noise and allowing your to hear your system than a CLD like Dynamat. I realize that this goes against all of the marketing hype and what most people are doing in their cars, but the fact is that CCF and MLV will work better at blocking noise than several layers of Dynamat or Dm equivalent. Don't buy the hype, go with what actually works.

The second major cause of noise from your doors is the plastic door car vibrating against the metal door skin. Using a thin closed cell foam between the door card and the door skink will go a long way towards helping you out there.
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post #39 of 44 Old 01-13-10, 05:37 AM
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Re: Planning ahead for car system

Quote:
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where are you suggesting that foam be installed?
.
Thats for the inside of the box not the car!


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post #40 of 44 Old 01-15-10, 07:33 PM Thread Starter
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Re: Planning ahead for car system

Would it sound the same in a car as in a Home Theater if I ported the box to 14hz as mine is right now? What I mean is if I put my current box in a car, and played Toccata and Fugue in D Minor, would the low 16hz tones, and lower sound the same? Would the car have a more flat response, or would the low bass just dissipate through the car and go somewhere else?

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