Coverage Angle Formula

[gac800]

Is there a formula for calculating the coverage angle of a horn? I am unsure if I should be measuring the angle from:
a. The bottom of the throat
b. The centerline
c. The wall angle

see the attached drawing.

 

[AllenB]

The lower one presumes your wavefront fits the horn, which is not a bad default position these days. However before you get too comfortable with it I'd do some hornresp sims to look at the scope of it, such as the frequency range and what happens around it.

 

[gac800]

@AllenB hornresp will only give me that info for a round horn correct? This is the conical horizontal flare on a rectangular horn. The vertical being exponential or tractrix.

 

[AllenB]

You can often fudge it up on hornresp with a little effort.

Conical will usually give you the lowest frequency control, and will stay wide up higher. Once the horn becomes curved and narrow going to wide, the lower frequencies get less control and the highs get narrow.

You have chosen a tractrix horn so I'm not even sure this is your priority, maybe you wanted a horn for loading?

 

[gac800]

@AllenB yeah the directivity isn’t actually crucial, I am more interested in the loading as this horn is only going to play up until 500Hz. I just want to make sure that there will be a wide enough vertical coverage area so that my seating position is covered.

 

[gac800]

@AllenB im also considering making all 4 sides exponential, even though it would be a little harder to build. Is there a way to predict the coverage angle of an expo horn?

 

[AllenB]

You can fudge it up in hornresp by finding an equivalent curve.

By the way, are you going to make it flat on the bottom with double expansion on the top so it works with the floor?

 

[gac800]

@AllenB so you mean model a round horn in hornresp with the same exit angle (if exponential) or side wall angle (if conical) as my rectangular horn and figure out what the -6db angle is for each side.

I hadn’t considered using the floor like that, but it is a good idea!

 

[AllenB]

Yes, that's what I meant 🙂