Calculate litrage litres of an angled box

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Please forgive me for this seemingly unintelligent question but I was perfecting my cartoon drawing skills during high school mathematics class.

I have been told that an angled box is good for a sub as it reduces the direct back pressure. This is apparently more of an issue when the box is smaller than the optimal box size.

I have a 15" DVC Option Audio subwoofer as can be viewed here .

I have been told that it should go into a 61L sealed box for optimal response. After being quoted $300+ for a custom box I sought out to get a pre-fabricated box.

I am looking at this item in eBay but I have a few questions:

  • How do I calculate the approximate litres of this box given the angled slopes? I know there's a minimum of 43L in the rectangular part
  • Will the inferior wood cause any loss of performance? If so, what does that translate to in measurable terms (non audiophile)?
  • What does the angled box do sonically different to a rectangular box?

Personally I favour smoother frequencies with ultra low bass and plenty of space between frequency bands.

Thanks in advance
~groover
 
You break the box into seperate sections. The box is a rectangle, with 2 triangles on top. You should minus the thickness of the wood from the outer edges also. For this application the angled box will not make any difference.

...with ultra low bass and plenty of space between frequency bands.
Your statment makes no sense could you rephrase?
 
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An angled box doesn't reduce the back pressure, but it spreads the standing waves over a broader freq range. In a rect box, when the inside box dimensions are equal to half the sound wavelength, you get standing waves. With the angles, you like have many small standing waves all of slightly different freqs.

But as noted above, at LF the wavelengths are so large that they are always (much) larger than the internal dimensions anyway, so the angles don't make a difference.

Edit: I believe 'litrage' is commonly called 'volume' in English ;)

Jan Didden
 
The box is a rectangle, with 2 triangles on top

Yes, I noticed this however is it possible to calculate the top 2 triangles volume without knowing the angles? Can this be approximated in any way?

Your statment makes no sense could you rephrase?

Sorry, I want a bass response that is deep and not too compressed. The 6x9s in the back parcel tray provide clear and distinct mid-bass so the subs purpose is to provide the deeper tones such as 45hz.

I would be most likely be applying a low pass filter that leaves a gap from where the 6x9s roll off.

I like to listen to downtempo styles of music whilst driving. This music often skips large 'chunks' of frequencies offering more at the extreme low and the extreme high. A well mastered piece will often have your mind hearing the in between frequencies without them being present or requiring much of the tracks available amplitude.
 
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groover1234 said:
Yes, I noticed this however is it possible to calculate the top 2 triangles volume without knowing the angles? Can this be approximated in any way?[snip]


If the triangles are equal, you can put them (in your mind) together so they form a rectangle. Then it's just the product of the sides of course. If they are not equal, you can pretend each consists of two equals, calculate the volume, and divide by two, for each triangle.

Jan Didden
 
I believe 'litrage' is commonly called 'volume' in English

haha so it is... please excuse my late night literacy skills.

at LF the wavelengths are so large that they are always (much) larger than the internal dimensions

In which case, assuming the wavelength at 45hz would be in excess of 7 metres, how then would any box size effect the output of the speaker apart from the amount of compression and possibly a cumulative increase in pressure? or have I misunderstood you.

Bracing myself...I don't claim to know anything so please be gentle ;)
 
Just use some acoustic mat on the inside if you're worried about that. You could glue some 3/4 inch carpet underlayment to the walls, for example. You know, that recycled foam mat they use under home carpeting. They sell it at hardware stores by the square yard. You can also find acoustic foam similar to the stuff they use in record studio walls but with trianglular projections and glue it to the walls. I think parts express or mcm sells the stuff
 
Will the inferior wood cause any loss of performance? If so, what does that translate to in measurable terms (non audiophile)?

Well I guess by inferior wood you are refering to it "bending" or not being too stiff. Now remember you will have pressure inside the cabinet, lets say it will be a sealed cabinet, so a 15" woofer moving inside it will compress the air inside like a spring and then release going forward, if the wood is not stiff it will "blow" like a balloon. How does this affect sound, first of all you will loose force in the "spring" of the cabinet and second you will have a big surface moving. Most 15" drivers really move one mm or less while playing and they give good output becuse of the big area of the cone, now if you have a huge side of the cabinet moving less than a milimeter, it will give out sound, mainly distortion.
 
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groover1234 said:


haha so it is... please excuse my late night literacy skills.



In which case, assuming the wavelength at 45hz would be in excess of 7 metres, how then would any box size effect the output of the speaker apart from the amount of compression and possibly a cumulative increase in pressure? or have I misunderstood you.

Bracing myself...I don't claim to know anything so please be gentle ;)


Well, the air mass in the box works by providing an impedance, so to speak, to which the moving cone works. That way, the cone movement is damped. There's a lot more to it, why you need a specific volume with a speaker with given properties like cone mass and resonance frequency.
The other thing is when exactly half a wavelength fits between two walls, then you get a kind of reinforment, the wave is bouncing between the walls and because the walls are half a wave apart, it starts to reinforce itself.
So, these are two completely separate things.

Jan Didden
 
To do the calculation is easy, it is 1/2ab so if the box is 30cms deep at the top and 40cms deep at the bottom and it is 30cms tall and 80cms long your calculation will be to separate the triangle from the equation so it would go 30 x 30 x 80 = 72L then you do the triangle so it is 1/2ab so that is 5 x 30 x 80 = 12L then add them together and you would get 84 litres...
Also 1Cuft is 28.3 litres if that is of any help.
So remember 1/2ab it is as simple as that.....

I hope that this helps some....
 
just a follow up on what I found in case someone is looking at this in the future:

I have a compressed cardboard dual 12" box that my old 900W Earthquake subs were in. I found this local business (Sub Sonic Pro) who manufactures their own custom box design locally. It apparently reduces/ eliminates 'standing waves'.

Basically there's no flat reflecting surface, everything has some form of angle to it. They are made from 18mm MDF and are carpeted with no internal dampening.

I did a side by side comparison of the same sub in my 12" box and one of their boxes using a sweep track. I was astonished at how much of a difference it makes. Whether its because the boxes are "tuned" to a lower note I dont know but I really liked what I heard.

There was none of that harmonic overtone ringing sound that I would hear when pushing the compressed cardboard standard angular design.

Both boxes were similar in thickness but significantly different in shape.

Another thing I noticed was that the sub didn't seem to work as hard in the MDF box and could go much louder before starting to struggle.

I took it a step further and was able to take them home and I hooked them up to a sine wave in an additive synthesis (Reason with the Subtractor for those interested) and proceeded to go up the keys from ultra low.

I had them hooked to my Kenwood 200W RMS hifi amplifier so not as good of a test but I wasn't having it loud. I used Speaker A and Speaker B to switch between the both and a very careful ear.

I noticed that the compressed cardboard box had loud notes and quiet notes yet the MDF box was a lot smoother. At very low frequencies the cardboard box "warbled" and the MDF box sounded tight and clean.

Overall, I've been extremely impressed with the difference a good box makes.
 
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groover1234 said:

I found this local business (Sub Sonic Pro) who manufactures their own custom box design locally. It apparently reduces/ eliminates 'standing waves'.

Basically there's no flat reflecting surface, everything has some form of angle to it.


Hi,
Typically, standing waves are not an issue in a sub enclosure, as the wavelength of the frequencies involved are larger than the box dimensions.
 
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