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

Yup I still have the data Pano... You guys should know by now I save everything :Big smile:

Coen i think it is the diaphragms.My 288C's had the diaphragms replaced many years ago By Altec Lansing with the same diaphragm 23763. The 511E is coated with Aquaplas.It is a sound deadening paste that dries very hard.Prevents "Horn Ring" they sound very nice to me.You do need to smooth the throat.Try taping a piece of sandpaper to a broom handle or a dowel,that should make it easier to remove.

There is obviously something wrong, and for me it all starts with the Diaphragm. They should look like this.Also measuring will allow you to pinpoint the location in the frequency response were the problem is located.This should tell you what the problem is.Or if it should be there at all.The diaphragms in the picture and of the measurements I took and are Brand New....


http://www.hostboard.com/forums/hbmc...2012/05/48.jpg

http://www.hostboard.com/forums/hbmc...2010/09/38.jpg

http://www.hostboard.com/forums/hbmc...2012/05/49.jpg

http://www.hostboard.com/forums/hbmc...2010/11/45.jpg

The diaphragm rings are definitely original Altec Lansing manufactured rings and diaphragms.

There were some problems with the K's - if memory serves, they were built in both Anaheim and OKC, and the Anaheim ones would have been built during some of Altec's "tough times", meaning that the QC wasn't always up to par. I have had K's that sound great and K's that didn't, which parallel's your problems.

My greatest suspicion is the diaphragms - if you can send the drivers to GPA and have them checked out, Bill will tell you if they need new ones or not. Be sure and describe your problems precisely so he'll know what to look for.

Thanks,

That's some great information! I think it is a safe bet now to order some current production dias from GPA.
Yet I don't want to stop here. If I manage Ill post pics of the dias, they look exactly like the one above.

I've got myself a little mixer with mic-in so the missing link in the test setup is covered. I'm shure i'm able to produce some results worthwile sharing.

Coen

http://www.hostboard.com/forums/hbmc.../2010/08/1.png

> Here's the natural response of a GPA 288H on a 511E horn . This is unEQed . It was published ( a couple years back as a stamp-size pic ) by GPA .

> Enlarged , it clearly shows the 8K & 10K dips and 12.5K peak in response . These are part of the normal response curve for most all, 288(s) and shouldn't be viewed as "problem" areas, when diagnosing the health of a 288 . .

> If I were you ( living overseas ) , I would have a competent speaker tech ( with test gear ) measure your drivers ( on your horns ) for frequency response & diaphragm fit . Compare to the first pic .

> A healthy 288-8K ( with healthy diaphragms that are seated properly ) will measure very close to what you see above ( since GPAs 288H is closely modeled on the 288-8K, excluding the magnet type ) ..

> For use without a tweeter ( on the 511E ) one needs a midrange suppression/ HF lift circuit in place, to make the driver sound HiFi .

> If you want to experiment with this sort of circuit then copy the top portion of the following pic . Vary the capacitance of C-1, from 3uF to 6uF, according to taste .

http://www.hostboard.com/forums/hbmc...2012/05/50.jpg

Here are two "looks" at my 288-8K ( on an EH-500 radial horn / this horn is similar in size to the 811 ) . This curve is passively EQed and is here to demonstrate the FR that the driver is capable of on a smallish horn . ( Focus on the curve with 1/3 octave smoothing, since this closer to the resolution of most peoples ears ) .

http://www.hostboard.com/forums/hbmc.../2012/05/1.png

:)

Last time I shipped a pair of drivers to GPA, they only charged the cost of frams, nada to install. Might be worth it to ask if still the case, that way a pro looks at them and does the install...if it's only shipping cost fer sure would think about it...

Do they have bug screens?

Quote:

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Originally Posted by cradeldorf

Do they have bug screens?

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I tried with and without. They are even sharper without the screens.

Coen

Earl, those are nice smooth graphs. There is still quite a peak in the resonace area (12,5 kHz?), don't they sound a ltlle 'hot'?

I save the smooting of the fr for a rainy day, first priority is to get rid of the harsh sound. This is probably not a thing of 1/2 a dB, so I'll experiment with my consumer grade stuff first. Finding a ls measuring pro around here is tough, this is not a common skill around here.

Any suggestions on the replacement of the phragms? Should I stick to the same partnumber or is there an alternative tried and tested part#?

Shipping the units two ways to the US is pretty expensive and than I am not even mentioning the customs hassle. I'd rather do as much as possible locally.

Thanks, Coen

For those who still doubt about the originality of the diaphragm.

Attachment 1327

Coen

has anyone mentioned metal fatigue yet? even tho they look good they might have gotten brittle through the years.