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

[Coendert2011]

Hello,

Another little question for the died in the wool experts on this friendly forum.

For years I have a pair of 288-8ks laying around. When I rediscovered these and bolted them to my horn I immediately remembered why they where laying around. Totally unlistanable.
The culprit is that there is some serious HF issue. It's like someone hammering fine needles in your ear. Very unpleasant and very unlike my 802-Ds which are supersmooth.

The units look visually ok and the only thing I can think of is the diaphragm. I've been informing at GPA and they suggested that I measure for problems. I've been planning for an impedance setup, but can't find the time and energy to build it. Otoh I might just not like the character of these units.

Well, before putting them back in the closet, I thought to post first here to inform if anyone had a similar experience or issue with these.

thanks for the help, Coen

[Old Guy]

First thing to look for is cheap Chinese frams...

[bowtie427ss]

Agree.

Can you post a pic of your phragms?

Are both drivers equally unlistenable?

[Coendert2011]

Hi,

Thanks.
I've no easy way of making and adding a pic. Frams are black lipped frames with '1.4-20-035414' and 'Altec Lansing Corp' cast into the plastic. It looks rather original. The rubber gasket of the rear cover was almost glued. I guess they haven't been open for a long long time, you can almost smell the 80s.

No visible damage on the alu dia either and yes both units have the same issue. They are very identical.

[Geekstar]

Which horn?

[Coendert2011]

Horn is the 511-E.

I've had them on different amp tube and ss...

[amandarae]

Hi,

Thanks.
I've no easy way of making and adding a pic. Frams are black lipped frames with '1.4-20-035414' and 'Altec Lansing Corp' cast into the plastic. It looks rather original. The rubber gasket of the rear cover was almost glued. I guess they haven't been open for a long long time, you can almost smell the 80s.

No visible damage on the alu dia either and yes both units have the same issue. They are very identical.

I had the same experienced! However, mine was a 288C with diaphragms similar to the construction that you described (the ridge is somewhat orange on mine) and has the "Altec Lansing Corp" cast into the plastic as well.

I also tried the 511 for it for a few months with N501 XO, 1st order 500 hz, 1st order 800 hz, 2nd order Linkwitz 500 hz, and 1st order 900 Hz without sucess as the sound is nothing to be proud of (using 416 as LF on 612C cabs). On a whim, I bought the cheap 8-Ohm 288C diaphragms from an online vendor (in Arizona) for $50 a piece. You can tell that this replacements are cheap but I just want to experiment on it to see if there's a difference. There is, and a lot! In my opinion that "ridge" Altec lansing Corp diaphragms sounds like crap. My plan is to buy a pair of the 288 diaphrams from GPA once and for all when I have the time to play with my sound system again.

FWIW, I also have 802's, and 806's. I tried using them on a Le Cleach 350 horn with an adaptor and they sound very nice. Even on the 811 horns, they sound fantastic of course!

I think it is the diaphragms. But there are lots of factors in one's system to influence an "unwanted" presentation.

Regards,

Abe

[Altec Best]

These are the frequency response graphs of the 288's I measured on a 511E horn for my DIY project that I'm building. These graphs are both the 0 degrees on axis measurements.They both have the 23763 diaphragms.While driver #2 has the 8 Khz notch, driver #1 does NOT... It also has a pretty flat response.

I was told when I bought them from an attorney handling the estate of an Altec engineer both drivers had a pretty close matched set of diaphragms.One pair received the 23763 and the second pair received the 25884 and that they were rebuilt and never put into use after rebuild.And I have to agree with that statement.

[Panomaniac]

Both mine have the sharp 8Khz notch. What you see above is smoothed, so the notch appears wider and shallower than in a raw plot.
Sure wish I could figure out why one of your drivers dos NOT have the notch!

[Earl K]

Pano,

Just how deep is the 8K notch on your drivers ?

Here's a close look of mine . The 8K notch is only +/- 2.5db ,, which is nothing, really .



Another ( higher rez ) shot ( raw file//no smoothing ) ;