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-   -   Calculate litrage litres of an angled box (http://www.diyaudio.com/forums/car-audio/109713-calculate-litrage-litres-angled-box.html)

 groover1234 8th October 2007 03:41 PM

Calculate litrage litres of an angled box

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.

~groover

 ocool_15 8th October 2007 03:52 PM

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.

Quote:
 ...with ultra low bass and plenty of space between frequency bands.
Your statment makes no sense could you rephrase?

 jan.didden 8th October 2007 04:31 PM

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

 groover1234 8th October 2007 04:42 PM

Quote:
 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?

Quote:
 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.

 jan.didden 8th October 2007 04:53 PM

Quote:
 Originally posted by groover1234 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

 groover1234 8th October 2007 05:03 PM

Quote:
 I believe 'litrage' is commonly called 'volume' in English
haha so it is... please excuse my late night literacy skills.

Quote:
 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 ;)

 groover1234 8th October 2007 05:03 PM

:rolleyes: haha so bleeding obvious! thank you janneman.

Please excuse me whilst I go beat my chest and forage for food...

 groover1234 8th October 2007 05:05 PM

Oh and if someone could please comment on

Quote:
 Will the inferior wood cause any loss of performance? If so, what does that translate to in measurable terms (non audiophile)?
Thanks

 ppia600 8th October 2007 06:13 PM

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

 groover1234 8th October 2007 06:20 PM

Quote:
 Just use some acoustic mat on the inside
so there is no real need to use super thick MDF apart from durability?

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