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Discussion Starter · #1 ·
Any thoughts? opinions? the only difference I see is you could gain a tad bit of airspace by not having dividers inside the box.
 

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Car Audio Mod #3
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You always want the subs to have their own air space. That way you can accurately calculate the volume allotted to each sub. The volume of the box is ESSENTIAL to a good sounding sub. Also, if one sub goes out, the other now has a box twice as big as it did before, which will probably destroy that sub.
 

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Discussion Starter · #3 ·
Hmm, I see.. The reason why I was asking is I have an old MTX open airspace box that is made for three 10" woofers, I dont know what series they are the only thing I know is they were old and blown. I was planning on getting three eD 11kv.2s in it. I measured the box and calculated the airspace and it is just perfect for them.
 

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BoomGoesTheDynaMitt
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I have always made it a practice to seal each sub in its own enclosure (using a baffle bewteen each sub in a multi sub box). I forget the reasoning behind it but Circuit raised some very valid points. I thought it had more to do with sub1's soundwaves canceling out sub2's soundwaves and vice-versa. I could be wrong though. I do realize that they should be putting out the same waves which should not cancel each other out but real-world nothing is "identical". A baffle should not affect the internal volume that much anyway. If the math in my head is right a 1" baffle inside a 1cuft box would only take up about .1cuft. Am I way off here? Can anyone confirm?
 

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To discuss sub enclosures you need to use the proper terminology in your explanation or you will confuse others and never get an answer you can use.

I am guessing your term open airspace is describing common volume between speakers in a closed enclosure? And the term individual airspace, as two or more sealed enclosures built into one box structure.

Different types of drivers (the speaker itself) require different types of enclosures. Some examples are…
1. Open air or infinite baffle. This is a driver that is designed to work properly without a sealed up air cavity to support the cone excursions as a shock absorber of sorts. It only requires to be mounted to a baffle. The baffle is a board or wall with a hole to accept the mounting of the drivers frame. The larger the baffle the better the sound but both sides of the cone are open to the air. This application is not normally found in cars.
2. Ported enclosure. This is a driver that is designed to work with some controlled air resistance to the moving cone that is supplied by a specified volume and one or more specifically designed ports or air vents. There are many types of ported enclosures and some are appropriate for auto applications.
3. Sealed enclosures that are air tight on one side of the design specific drivers cone are by far the most prevalent type used in cars, and can be configured into many different enclosure types.

If you would like me to go on, I do have specific views on placing multiple drivers in one box that differ from those expressed in this thread, but it takes some explaining to understand the how’s and why’s, and the do’s and don’ts.
 

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Discussion Starter · #6 ·
I was debating on using the term volume but I have heard both of the terms used so I just went with airspace. Anyways, yes I would love for you to go on! I am trying to learn as much as I possibly can about car audio.

Here is the link for for the subwoofer I am looking at for my application.
Elemental Designs
 

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Let it wang
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I can design you a box if you are interested. You can see my work here...
http://s251.photobucket.com/albums/gg294/SMCustomz/SM Customz/

I have designed both common chamber and separate chamber enclosures for multiple subs. The downside to a common chamber is that if by chance one sub is even slightly weaker than the other, then over time that weaker sub will blow. When that sub blows, all of the airspace that before was for two subs is now being used by one sub. That will cause your second sub to blow as well.
 

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BoomGoesTheDynaMitt
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the only difference I see is you could gain a tad bit of airspace by not having dividers inside the box.
I just thought of another reason to use the dividers... They act as braces and prevent the walls of the box fom flexing. This would be more important in a large enclosure (longer pieces flex easier than short ones) or in an enclosure made of thinner/weaker material like 5/8" particleboard as opposed to 3/4" MDF.
 

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Exacerbated Member
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I am working on a post that will, I think be informative and relative to the topic at hand, but in the mean time.

Be careful not to blur the distinction between a structural component and a design component.

Stiffness and the overall imperative for NO flexing is certainly critical, but this can be done without dividing the air space within the box, just as a supporting wall in a house can have a door or window in it.
 

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BoomGoesTheDynaMitt
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I understand that dividers are not needed to have active bracing. Simple 1x1 or 2x2 beams could be used in all the corners but I figured I would let him know one other advantage of using the dividers. It seemed as if he didn't want to use tem as they take up space that would be used for his internal air volume but that make little sense to me seeing that they take up virtually no space.

Waiting to see your report on this! :corn2:
 

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I'm surprised to see that noone has mentioned specific tuning in the box. Using volumetric airspace in a speaker box enables it carry a specific resonate frequency in conjection to amperage/volume. In a nut shell its easier to tune an open airspace then it would be if it had dividers. By measuring the impidence of a speaker and the amount of power being delievered can greatly effect the tuning of which you have your crossovers set to. this will tell you how much airspace is required to specifically tune the box.

Alot of people still managed to screw this up becuase tuning a box to match 40htz at a 1000 watts is really only for deep bass which is only neccessary for hiphop/rap/techno. if you've listened to metallica with a sub tuned at 40 htz, it absolutly sounds like shit. so you have to consider what type of music you listen to and the varience you are looking for.

However circut is correct about damaged speakers. there are very few speakers that are capable of overcoming this issue but they come with a heavy price.
 

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Discussion Starter · #12 ·
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However circut is correct about damaged speakers. there are very few speakers that are capable of overcoming this issue but they come with a heavy price.
Yeah I thought about this before i posted and that was one thing that came to mind. But the subwoofers I am going to be running are IB capable, and also the will be given a small enclosure. .5 cu. ft. each to be exact. So if I have a total of three drivers and one cuts out that means the others get approx. .75 cu. ft each.. I dont see them being in any danger.
 

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I should tell you right off the bat that I am not an expert in car audio specifically. My formal training is in acoustics, specifically architectural, and in theatrical sound reinforcement systems, but the basic principals apply and the science of speaker enclosure design is universally understood across the whole range of applications.

The basic distinction relevant to a vehicle application is that concessions are made to favor higher SPL’s and smaller size.

One very important thing to keep in mind when discussing options is this. Just because one option generates more, for example distortion, than another, it is important to know just how much distortion are we talking about. In other words, is it a small amount or a significant amount? We need to know this to weight it against the advantages the design offers relevant to our specific application.

So, if the topic at hand is multiple drivers in one enclosure there are both pros and cons that are relevant to this.

One of the cons is that, because for each speaker there is a specified volume of air required to have it function properly, when you add more speakers you need to do some math to recalculate the new volume required for both to work in unison (as one) in a shared space. There are some other cons but they are way over shadowed by the advantages.

The function of the cone of the speaker is to move air in a pattern that corresponds to that required to generate a tone at your ear. So with that in mind the larger the surface area of the speaker cone, relates to a greater volume of air that can be moved. The only other variable in a sealed box enclosure is the excursion length of the cone (how far in and out it can move) So, a 12” speaker has 4 (a little more) times the surface area of a 6” cone. And it fits in less (slightly) space than the four mounted on one flat surface.

For a driver that is designed to work in a box, the function of the trapped air behind the cone or cones is to supply dynamic resistance for the cone to work agenst, much like the shock absorbers on a car. By itself the cone is not supported properly and cannot develop the long controlled excursions required for deep base notes without destroying itself. Different drivers have different requirements it’s true, but similar drivers have very similar requirements.

The critical thing when two drivers share the same sealed air space is that they both move in unison. In other words they must be the same model speaker and they must be connected electrically so that both cones move outwards at the same time and inwards at the same time. This way the cones of four 6” drivers compress and expand the same amount of trapped air as one 12” cone (within some small degree of tolerance)

We have already stated one advantage to a single large driver, lets look at the disadvantages. One 12” driver needs a single flat surface of 14” or more to mount where as four 6” drivers could mount on 4 separate smaller surfaces of a box. In addition to this real estate advantage A large cone is much more flexible and prone to shape distortions than a smaller cone of similar construction. This unavoidable flexing is a major cause of distortion or deviation from the intended signal the amplifier is asking the coil of the speaker to produce. It turns out that a 12” cone generates about 6 or more times as much distortion through uncontrolled flexing than a 6” cone does. In addition to this the distortion of four separate cones need not be added together or summed, because the distortions are not exactly the same or are they in phase. The actual result is that the four separate distortions have a tendency to even each other out or cancel each other.


I know this is getting long and I am short on time to spend on this, so I will leave it at that for now.
I will answer questions on what we have covered or try to make clear anything that is confusing.
 
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