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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
minkwelder
255 posts
 
"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."

Actually, the above quote indicates that the measurement is made from a plumb line extending down from the back of the top edge of the speaker, so the 1/2" is measured at the very bottom of the back.

This would change the angle considerably from what Al has calculated. For instance, if the speaker is 36" tall, the calculation would be arcsin(0.5/36) = 0.796 degrees or 0 degrees, 47 minutes, 45 seconds (a little over 3/4 of a degree).
mofimadness's avatar
mofimadness OP
4,991 posts
 
Mink...thanks for your response. What you said is correct.
You measure the 1/2 inch from the very bottom back of the
speaker to the string on the plumb bob.

Sorry, I tried to be very specific on how the 1/2 inch was
measured, but it's hard to say. Easy to see or draw, if we
could post pictures on here.

The speaker is 38 inches tall. I get .7539 degrees.
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
Thanks, Minkwelder. Based on your interpretation, which Mofi confirms, and based on the 38 inch height, 0.7539 degrees is correct. That would be the angle between the rear surface of the speaker and vertical, which I'm pretty certain is numerically equal to the angle between the top surface of the speaker and horizontal (assuming that the top and rear surfaces of the speaker form a 90 degree angle with each other).

Best,
-- Al
minkwelder
255 posts
 
Yes, 0.7539 degrees. I remember having a pair of Vandersteen 1C's and the manual had setup directions like that which used a plumb line in back and a dimension to the bottom which was based on the distance to the listening position and ear height. I ended up using a plumbed carpenters level resting on the floor and touching the back of the speaker. It was a whole lot easier than measuring from that swinging plumb bob line (and I'm a surveyor!).
timrhu
2,779 posts
 
After you get them set up per manufacturer's specs be sure to tune them by ear. I set up a pair of Vandersteen 2CEs per Vandersteen manual a few years ago and for days I was unhappy with the sound. I performed the stand up sit down test and made some major adjustments in the tilt angle. Ah, there was that three dimensional sound I was expecting.
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