Why do my 288-8Ks sound like cr@p?

[Coendert2011]

@ Earl, I will logon DIYaudio to get the cookie.

Just a little note from the centering activity of tonight.

The 288-Ks don't have the dowel pins. There are the two little bolts that have an oversized washer around them that is part of the diaphragm. I think the adea is to get audibly rid of the nasty resonance caused by the scraping of the voicecoil against the sides of the gap and then fix um.

I had a little rattle on one unit (the measured one) and the other is 'totally' clean. 200Hz at 2V works fine, you have a lot of movement in the diaphragm and any misalignment is easily observed (heard).
It was a hell of a job to get rid of the rattle, there is only one position that the rattle disappears (almost). I have the impression that the gap isn't evenly distributed, iow the phaseplug isn't totally in the centre. I have to measure to be shure.

Sorry no measurements yet of the recentered unit with the horn in place, next week more results in this theatre.

At last, I checked the other 802 and it exibited a higher distortion. After a lot of searching it turned out that the metal strips on the diaphragm (where the Voice Coil is soldered to) stuck out a little. I carfeully scraped the excess away with a watchmakers tool. Putting it back it didn't work out completely satisfactory. A definite improvement yet I discovered that I had to play with the pressure on the fixing screws to make distortion disappear. Thia was also the case with the better diaphragm of the other unit when inserted this one, so this is an imperfection of the unit itself (I should check the gap here too!).

A very instructive night!

Coen

[vuki]

Good work Coen! Waiting for the new graphs

[gearfreak]

I have the impression that the gap isn't evenly distributed, iow the phaseplug isn't totally in the centre. I have to measure to be shure.

On mine, it was the result of an impact, and the site was clearly externally noticable.
Of course, if it impacted the cover, the cover could be switched around, but only in so many possible orientations.

But of course maybe there are other reasons, pole pieces shift? idk.

* Ahh - and editing. I see you mention the phase plug specifically. I am sure we have seen mention of them coming loose/regluing in other posts, but I have not experienced this myself.