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Variability of the frequency response

of the AURA NSW2-326-8A tweeter

The AURA tweeter is used in PLUTO and Pluto-2 because of its very wide frequency coverage and small baffle size which facilitates the construction of a monopolar source. By using a low crossover frequency of 1 kHz to the small Seas L16RN-SL woofer and mounting the two drivers at the end of tubes the combination maintains omni-directional dispersion.

Here is my setup for testing the variability of the tweeters. Each driver is dropped into the opening of a long cardboard tube. The tube is stuffed to avoid resonances. The microphone capsule is approximately centered above the driver. Its distance from the cone is such that it would just touch a flat sheet of paper that is laid onto the tweeter's roll surround. Electrical drive levels are around 2V to stay far away from thermal compression.

	The close-up frequency response of the two drivers that I use in Pluto-2. I have had these drivers for well over a year. They have small printed circuit boards for soldering the leads to.
	Three more drivers of about the same vintage have been added to the graph. Their frequency responses track well up to about 8 kHz. There is about 1 dB maximum variation in sensitivity between the 5 drivers.
	Here are 4 drivers of recent vintage. They have lugs for connecting the leads. Their frequency response tracks reasonably close with the older units. Their sensitivity is slightly higher. There is considerably more response variation above 10 kHz.
	Here all 9 drivers are plotted on the same graph. Between 700 Hz and 10 kHz the dominant variation is in their sensitivity. Thus individual tweeter level adjustment by comparing left and right loudspeakers - when placed adjacent to each other and playing pink noise - becomes an essential step before adjusting the tweeter level relative to the woofer. Only driver selection can reduce the variability above 10 kHz.

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	What you hear is not the air pressure variation in itself but what has drawn your attention in the streams of superimposed air pressure variations at your eardrums An acoustic event has dimensions of Time, Tone, Loudness and Space Have they been recorded and rendered sensibly?
___________________________________________________________ Last revised: 02/15/2023 - © 1999-2019 LINKWITZ LAB, All Rights Reserved