Thank you very much for the detailed answer Tom.
If i understand the description correctly, then i can make a conical horn with a rather short transition from round to rectangular instead of an OS horn.
The reason for this seems to be, that the irregularity in the horn throat affects only the frequencies where the wavelength is about equal to the internal diameter of the throat. since the throat diameter is rather small, only very high frequencies are affected.
That makes it alot easier to build.
If i understand the description correctly, then i can make a conical horn with a rather short transition from round to rectangular instead of an OS horn.
The reason for this seems to be, that the irregularity in the horn throat affects only the frequencies where the wavelength is about equal to the internal diameter of the throat. since the throat diameter is rather small, only very high frequencies are affected.
That makes it alot easier to build.
throat to horn tranistion
been thinking for a while about how long the section transitioning from the compression driver flare to the conical section making up the majority of the horn should be. I thought the main criteria should be that there is no discontinuity between the wall angles at either end and that the area expansion should be exponential to minimise distortion and reflections. at higher power the main distortion will be due to 'air overload' distortion so there is an argument for a more rapid flare and shorter transition section.
the cut off frequency for an exponential expansion matching the compression driver throat angle and radius is:
f0=c.tan(angt)/(2.PI.r)
you can then derive an expression for the length of the transition section
x=(r/tan(angt)).ln((tan(ang2)/tan(angt)).sqrt(4/PI))
this is for transition from a round throat of radius r and angle angt to a square horn of angle ang2. note the angles are between the axis and the wall i.e. half the included angle. if the main horn is round omit the sqrt(4/PI) term.
this value of x can then be used to find the area of the transition section where it joins the main horn.
for example a compression driver with a 18mm throat radius and 17degree throat angle connected to a square horn of angle 25degrees would require a 32mm transition section which would be a square of side 55mm when it meets the main horn.
been thinking for a while about how long the section transitioning from the compression driver flare to the conical section making up the majority of the horn should be. I thought the main criteria should be that there is no discontinuity between the wall angles at either end and that the area expansion should be exponential to minimise distortion and reflections. at higher power the main distortion will be due to 'air overload' distortion so there is an argument for a more rapid flare and shorter transition section.
the cut off frequency for an exponential expansion matching the compression driver throat angle and radius is:
f0=c.tan(angt)/(2.PI.r)
you can then derive an expression for the length of the transition section
x=(r/tan(angt)).ln((tan(ang2)/tan(angt)).sqrt(4/PI))
this is for transition from a round throat of radius r and angle angt to a square horn of angle ang2. note the angles are between the axis and the wall i.e. half the included angle. if the main horn is round omit the sqrt(4/PI) term.
this value of x can then be used to find the area of the transition section where it joins the main horn.
for example a compression driver with a 18mm throat radius and 17degree throat angle connected to a square horn of angle 25degrees would require a 32mm transition section which would be a square of side 55mm when it meets the main horn.
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