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Speaker Set Up...Math/Geometry Experts Please Help

Hey guys, I need your help. I am helping a friend of mine set up his speakers and can't figure something out.

His speakers need to be tilted back to time align the drivers. According to the graph supplied from the manufacturer, we need a rake (tilt) of a 1/2 inch. This is measured using a plumb bob hanging from the back of the speaker, (which is perfectly flat). You measure the distance from the string to the back bottom of the speaker. The problem we are having is that even if we let the plumb bob settle, as soon as we try to measure the distance, the string moves just from the air disturbance around the string. We are having trouble getting an exact reading.

My question is: Can you convert the 1/2 inch distance to a degree? I have a really nice digital level that we can put on top of the speaker, start with it perfectly level and zero out the level. My level only reads in degrees, so I need to know how many degrees correspond to 1/2 inch tilt.

I've actually done this a few times in the past and always used the plumb bob method, but with current technology, was hoping to get it perfect.

Maybe this can't be converted? I've tried looking it up online, but Geometry was always my weak subject.

Thanks guys!
128x128mofimadness
mofimadness's avatar
mofimadness OP
4,982 posts
 
Sorry, I should also add that we can't measure the distance
from the top and bottom of the speaker to the front wall,
(the wall behind the speaker) because he has a bunch of stuff
that sits back there and none of it has even edges.

I thought that maybe a laser tape measure would work, but
there are no even/flat surfaces that are the same from the
top of the speaker to the bottom of the speaker that we could
bounce the laser off of.
almarg's avatar
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almarg
9,670 posts
 
Hi Mofi,

First, let me make sure I understand how the 1/2 inch tilt is being defined. I think what you are saying is that the speaker should end up tilted back such that if the level is rested against the top front edge of the speaker, and the level is placed perfectly horizontally, the top back edge of the speaker would be 1/2 inch below the point where that level passes above it.

If so, the required angle would be arcsin(0.5/the depth of the top of the speaker in inches). "Arcsin" = "the angle whose sine is," also known as "inverse sine."

If my interpretation of the requirement is correct, and you let me know the depth of the top of the speaker, in inches, I have a scientific calculator which can easily compute the answer. Or you can use the calculator that is built into Windows, under "Accessories." You would set the calculator to scientific mode under its "view" menu. You would then press the "inv" button to cause the inverse sine button to appear.

Best,
-- Al
mofimadness's avatar
mofimadness OP
4,982 posts
 
Al...thank you for responding. I was hoping you would know the answer.

I think what you stated above is correct. The digital level would be placed on the top of the speaker, but facing from front to back not side to side?

The depth of the top is 10 inches. I tried to use the calculator you suggested, but again, not my forte. I think I got an answer of 2.3 degrees. If you could check that, that would be great.

Thanks again sir!
almarg's avatar
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almarg
9,670 posts
 
Yes, I was envisioning that the level would be oriented front to back, not side to side.

I get 2.866 degrees, based on the inverse sine of (0.5/10).

Best,
-- Al
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