November 8, 2011

Point source horn measurements

Point source horn measurements taken on my polar measurement rig with Arta. Shown below are directivity plots.

See measurement setup >

1. Yorkville Unity
2. S1 - my first prototype (60 x 60)
3. S2 - my second prototype (90 x 45)

What do they show? The Yorkville has a pattern that narrows around 2 - 3k, revealing that the compression driver when mounted on the horn is starting to beam at the low end but when it transitions to the mids, probably somewhere around 1 - 1.5k, the pattern becomes wider. The horn is too small to control directivity any more, a compromise to achieve reasonable size.

S2 is a larger horn which manages to control dispersion more, however it does have some dips on axis, hence it requies some toe-in so that it isn't heard directly on axis. As a result, the plot could not be normalised like the others. A normalised plot is based on a perfectly flat on axis response.

S3 is much larger again and controls dispersion all the way down to 300 Hz, a very good result. The dispersion is more uniform than the others, most likely due to a combination of size as well as a second flare angle to avoid beaming. With S1 there is some slight beaming at the bottom end of the compression driver's passband, below about 1.6k. With S2 the transision is perfectly smooth, and there is nothing in the polar response to suggest the crossover point, while in the other two you can see changes across the crossover.

These plots show the same data, but now it is shown in 3D rather than a birdseye view with SPL represented in colour. Again the order is the same:

1. Yorkville Unity
2. S1 - my first prototype (60 x 60)
3. S2 - my second prototype (90 x 45)


At a glance you can see that the third (S2) is overall much smoother than the others. Both the Yorkville and S1 have some dips on axis suggesting that toe-in should be used to get the smoothest response. This isn't necessary with S2.

Overall this represents very good results. 

Now some comparisons:
The dark line shows the - 6 dB point which is the reference for a given nominal dispersion. The straight line shows the nominal intended dispersion.


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