Downfiring a 12" Atlas

[cheesehead 0]

As the title states I am contemplating designing a down firing box for one 12" Atlas. I have heard this helps increase SPL as well as makes for a stealth install. (no need for a grill)

Here is a link to the discussion I had over @ DIY

http://www.diymobileaudio.com/forum/showth...ight=downfiring

I have also talked with Mr. Marv @

http://community-2.webtv.net/MarvsPlace/MarvsPlace/

Marv has suggested that I look into the following - " There are a couple of things to note however-all subs are not created equal so you definitely want to check with the manufacturer to make sure your sub will not exhibit excessive sag when mounted upside down (from what I understand heavy cone/large motor subs are typically not good candidates). Also, generally I make sure I have a minimum clearance of at least 3" under a 12" sub to keep it from pre-loading."

Anyone from AA what to chime in? Any one else have any thoughts on this?

Thanks in advance for the help.

P.S. I will be utilizing a box size of 1.25 cu.ft sealed for the enclosure

[DevilDriver 28]

Driver sag is strictly a function of the suspension stiffness and the mass of the moving assembly. This is very intuitive: a stiffer suspension will decrease sag, while more mass will increase sag. How much sag is acceptable? This will vary from opinion to opinion, but usually no more than 10% of Xmax should be considered acceptable.

Where:

Sag = distance from rest that diaphragm sags (m)

Cms = stiffness of suspension

Mms = mass of moving assembly (g)

g = the rate of acceleration of gravity, which is 9.81 m/s

Sag = Cms * Mms *g

If the value of Sag is less than 10% of your total Xmax, then it is fairly suitable for downfiring. The less sag, the better, in my opinion.

Kind of an off-topic but interesting note as well: the concept of sag applies in virtually every direction, to a certain extent anyways. This is kind of hard to see with your eyes, but if you use a speaker in a sealed enclosure (particularly with a Qtc that would be considered underdamped) and play sinewaves through it over extended periods of time, you'll see the assembly slowly creep forward.

[cheesehead 0]

Driver sag is strictly a function of the suspension stiffness and the mass of the moving assembly. This is very intuitive: a stiffer suspension will decrease sag, while more mass will increase sag. How much sag is acceptable? This will vary from opinion to opinion, but usually no more than 10% of Xmax should be considered acceptable.

Where:

Sag = distance from rest that diaphragm sags (m)

Cms = stiffness of suspension

Mms = mass of moving assembly (g)

g = the rate of acceleration of gravity, which is 9.81 m/s

Sag = Cms * Mms *g

If the value of Sag is less than 10% of your total Xmax, then it is fairly suitable for downfiring. The less sag, the better, in my opinion.

Kind of an off-topic but interesting note as well: the concept of sag applies in virtually every direction, to a certain extent anyways. This is kind of hard to see with your eyes, but if you use a speaker in a sealed enclosure (particularly with a Qtc that would be considered underdamped) and play sinewaves through it over extended periods of time, you'll see the assembly slowly creep forward.

Thanks for the reply!

With what you have stated does the Atlas make a good candidate for downfiring in your opinion?

What are your thought as far a output/sq ect. compared to conventional rear firing towards the hatch/window?

[DevilDriver 28]

They say that if you teach a man to fish, he learns to feed himself.

12" Atlas

Xmax = 18mm

Cms = 0.395mm/N = 0.000395m/N

Mms = 119g = 0.119kg

g = 9.81m/s

Sag = Cms * Mms * g

Sag = 0.000395m/N * 0.119kg * 9.81m/s

Sag = 0.000461m = .461mm

% Sag = Sag/Xmax*100

% Sag = 2.56%

On the topic of positioning, there are a couple reasons why firing to the rear hatch often works best. First, you are loading off of a boundary. Second, the pathlength from the pointsource to your ears becomes longer and the frequency at which the first null cancellations occurs at a lower frequency (all nulls are usually shifted lower in frequency). This usually leads to improved output. Downfiring provides a similar effect in respect to the former (boundary loading) and but often lacks the increased pathlength. However, downfiring does have an added advantage: the boundary you are loading off of is usually much more rigid, dense, and stores less energy.

Each have their own advantages. What vehicle will this be in?

[cheesehead 0]

They say that if you teach a man to fish, he learns to feed himself.

12" Atlas

Xmax = 18mm

Cms = 0.395mm/N = 0.000395m/N

Mms = 119g = 0.119kg

g = 9.81m/s

Sag = Cms * Mms * g

Sag = 0.000395m/N * 0.119kg * 9.81m/s

Sag = 0.000461m = .461mm

% Sag = Sag/Xmax*100

% Sag = 2.56%

On the topic of positioning, there are a couple reasons why firing to the rear hatch often works best. First, you are loading off of a boundary. Second, the pathlength from the pointsource to your ears becomes longer and the frequency at which the first null cancellations occurs at a lower frequency (all nulls are usually shifted lower in frequency). This usually leads to improved output. Downfiring provides a similar effect in respect to the former (boundary loading) and but often lacks the increased pathlength. However, downfiring does have an added advantage: the boundary you are loading off of is usually much more rigid, dense, and stores less energy.

Each have their own advantages. What vehicle will this be in?

It will be going in a 4dr. Chevy s-10 blazer

[DevilDriver 28]

From personal experience in a Blazer, you're probably better off firing towards the rear of the vehicle.

[///M5 2,833]

They say that if you teach a man to fish, he learns to feed himself.

Not quite...

Buy a man fish and he has dinner.

Teach a man to fish and he will sit in a boat and drink beer all day.

To the OP, I would take a step back and ask what you are looking to have in the long run. Either option can work well, but your purpose and desires might make a different alignment more optimal. Knowing what car and potentially what power/amp you are running will help as well.

[cheesehead 0]

Driver sag is strictly a function of the suspension stiffness and the mass of the moving assembly. This is very intuitive: a stiffer suspension will decrease sag, while more mass will increase sag. How much sag is acceptable? This will vary from opinion to opinion, but usually no more than 10% of Xmax should be considered acceptable.

12" Atlas

Xmax = 18mm

Cms = 0.395mm/N = 0.000395m/N

Mms = 119g = 0.119kg

g = 9.81m/s

Sag = Cms * Mms * g

Sag = 0.000395m/N * 0.119kg * 9.81m/s

Sag = 0.000461m = .461mm

% Sag = Sag/Xmax*100

% Sag = 2.56%

2.56% = good candidate!

[///M5 2,833]

I obviously took too long to post. I'm with DD on the blazer, downfiring isn't going to buy you anything.

[cheesehead 0]

I'm with DD on the blazer, downfiring isn't going to buy you anything.

Will I lose anything from firing down? SQ,SPL? The only advantage I can see is that I can build a false floor of sorts and be able to utilize my hatch area more.

[///M5 2,833]

Most likely both SQ & SPL, but if it makes the vehicle more usable I wouldn't hesitate. Just make sure to give the cone a lot of clearance. A decent eq can really help if there are issues as well.

[cheesehead 0]

Great! Thanks Guys!