aurasound tweeter measurements - is this correct

[pjwd]

Hi,

I have measured 3 examples of the tweeter used in the linkwitz pluto (without a baffle) and they all exhibit peaks and dips that I was not not expecting - this was measured outside and was gated to prevent influence of reflections - has anyone had a similar experience.

The 3 plots represent each driver

Regards,

Phil

[AllenB]

Welcome to the learning curve, pjwd. Now to find out what is causing it. I would suggest you try measuring it on a baffle to see if those peaks disappear.

[pjwd]

I will try that but if the driver is as flat as claimed you would expect a pure dipole response - this indicates that is not the case

Regards,

Phil

[AllenB]

The peak and dip are an octave apart so I'd be inclined to guess that this looks like a dipole.

[pjwd]

Allen - this is a seas excell 8" with no baffle - it rolls of at 6db at the low end - rises to a peak and then has a series of decreasing peaks and dips ( confused in this instance by the 5K driver peak)

The aurasound peak is near 10K so it should not have peaks and dips in that range

I was wondering if anyone had obtained measurements of this driver that matched published information

cheers,

Phil

[AllenB]

Not sure of your point. The peak, the dip and the series of peaks are approximately where expected for cone breakup in a driver of this size.

More often than not it is necessary to work backwards and eliminate the problems that tend to crop up in measurements. If you want to see perfection, put the tweeter in a baffle and gate your measurement free of reflections.

[AllenB]

Just wanted to reword that as it may not have come out like I meant...I think it would be a good way to verify your equipment and give you peace of mind if you did attempt achieving the flat measurement.

[6.283]

Phil, do you want to use the Aura as a dipole or was this just some test for a Pluto ?
To me the response you've measured makes perfect sense. The Aura, if driven nude, is more of a U frame because of the cavity at the backside. I assume it is this very cavity that causes the dip at 10KHz, which equals a wavelength of 3.4cm. As indicated by Allen, the peak is a dipole peak and the dip at 3KHz is the first null.
Actually, I wanted to perform this measurement myself one day, although I knew already from hearsay that the Aura suffers from response irregularities when used as a naked dipole tweeter but I never saw a real FR. Thanks for that...saves me some work

Cheers,
Oliver

[pjwd]

Thanks Oliver - I agree 10k is dip due to edge distance - but below that you would expect a rise to a peak and then a slow 6db roll off to a steeper roll off where driver ran out of puff - the wobbly area at 3k and 1.8k indicates it is not a flat a driver as claimed - I will put it in a few different baffles and measure it when I have some time.

A mate is looking at a dipole using these which is the motivation for measuring them - they actually sound pretty good.

Regards,

Phil

[6.283]

Phil,
the Aura is flat. What you see is dipole behavior. The peak is clear and the dip at 3KHz is the first null that only becomes visible if the dispersion of the driver is still "up" (e.g. the driver has not started beaming, yet).
Look at this picture

Electro-acoustic models

This is also a flat driver.
Save the work with the Aura and baffles. Its behavior renders it more or less useless for dipole operation.