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

[vuki]

Since it's A7 cabinet you could try Hiraga's crossover . It's for a multicell horn, but it should be at least listenable. http://web.archive.org/web/200502060...s/HiragaA5.pdf

[Coendert2011]

Thanks,

Unfortunately it is just a simple sectoral horn. I've been lurking for multicells but found the price uncomfortable (>2k$ for 1505). AFAIK the Hiraga filter is tailored to the 15 cell horn with 288 driver. There is even an lift for HF in the curve, that should make things even worse. Currently the 288-8ks spit out way more HF than the 802s.

For now I think this harshness is not crossover related, but I didn't check out other caps or topology.

[vuki]

I would say that the harshness you hear is caused by sensitivity difference between 802 and 288. 288 has "less" highs than 802, but both need hf boost (on 511). Anyway measuring would be the way to go. 288 properly implemented should sound "nicer" than 802.

[aeyb701]

Ditto cleaning the voice coil gaps. I had rain water and insect debris get in mine (stored over winter in barn -- best to have covered up - and I GENTLY cleaned the coils (do not stress the circular geometry i.e.), and then the gaps with techniques searchable on this forum or on the net generally. Now they work good as new. Replacement diaphragms from GPA (as close to OEM Altec as you can find) aren't cheap for the large-format HF drivers.

[QUOTE=


Maybe you need to clean the gaps on the drivers?[/QUOTE]

[Panomaniac]

My guess is that you're getting an upper midrange bump from the 288 that you're not from the 802. They are different enough that they just can't use the same crossover. The 802 has more high end than the 288, so I doubt it's the top that's too hot.

[gearfreak]

Perhaps the WT3 would be a turnkey solution to measuring the impedance, thus looking for inconsistencies.

If they were dropped, the pole piece could have shifted and may be pinching the coil. This would cause a change.
If you end up trying to take them out, and they resist for no apparent reason/at one particular angle, this may the the reason.

That they both sound the same would seem to lessen the likelyhood of this though. Once you measure, it will be more apparent.

(Point is... don't then try to jam a new good phragm into the same pinched spot!)

If corroded, they will also resist, but this will be more obvious as you will likely not get it out, without destroying the phragm (IME).
Perhaps though they both suffered somewhat equally (stored poorly, in pairs) in this case.

[vuki]

My guess is that you're getting an upper midrange bump from the 288 that you're not from the 802. They are different enough that they just can't use the same crossover. The 802 has more high end than the 288, so I doubt it's the top that's too hot.

yeah, what he said.

[BoydB]

Coen, I have a pair of 288-16K's with the same or similar problem that you are experiencing, they sound like crap, un-listenable. I have a second pair of 288-16K's that sound wonderful, so in directly comparing the 2 pair we can eliminate the issues of the wrong horn, crossover, freq. bump etc. I wouldn't conclude that my faulty pair have only a HF issue, rather they sound like varnish or maple syrup has been applied to the diaphragm. Inspections done years ago showed pristine internals and Altec phragms. I stored this (crappy) pair away many moons ago and they've been almost forgotten. Sorry I can't help you with a solution at this time, my plan was to send them to GPA someday.

[Panomaniac]

Interesting, Boyd. Would be great to know what makes one pair sound good, the other bad.
Coen, if you don't manage to figure it out, I could take a look at one or both for you. Compare them to mine via ear and measurement. Just a thought, if you are in the U.S.

[vuki]

288-8k extension