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

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

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

Agree.

Can you post a pic of your phragms?

Are both drivers equally unlistenable?

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.

Which horn?

Horn is the 511-E.

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

I never heard the 511E but if it is similar to the 511B, and I think it might be, that could be your problem right there.

In my estimation, none of the Altec cast aluminum horns are as good as the drivers. Some people like them but I could never make them work. The 511b particularly strikes my ear as rather harsh.

Are you using the 802s on 511s also?

I had 311-90, 31A, 32B, 349A, 511, 811...junked them all. Now retrying the 32B.

I'd say try a good horn...multicell or maybe even a modern creation like a LeCleach. Any 288 in proper working order should be capable of refined smooth sound--maybe even smoother than the 802 (but not as extended on HF).

Maybe you need to clean the gaps on the drivers?

You can't just swap the driver and hope everything would sound fine. The drivers have different sensitivity and frequency response so the crossover should be redone. You can't do it without measuring it.

Quote:

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Originally Posted by Geekstar

I never heard the 511E but if it is similar to the 511B, and I think it might be, that could be your problem right there.

In my estimation, none of the Altec cast aluminum horns are as good as the drivers. Some people like them but I could never make them work. The 511b particularly strikes my ear as rather harsh.

Are you using the 802s on 511s also?

I had 311-90, 31A, 32B, 349A, 511, 811...junked them all. Now retrying the 32B.

I'd say try a good horn...multicell or maybe even a modern creation like a LeCleach. Any 288 in proper working order should be capable of refined smooth sound--maybe even smoother than the 802 (but not as extended on HF).

Maybe you need to clean the gaps on the drivers?

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Thanks. I use the 802 with an adapter, never heard any harshness. The horns are covered with some cementlike stuff and don't ring. They have some nasty peaks when playing loud. They are a little suspicious though, the throat section of the horn is rather ugly. Random blobs of stuff (turned out to be white) Make this a not so smooth transition to the horn.

I have some old pics here: https://picasaweb.google.com/coenski...eat=directlink

I tried to smoothen them out, but got lazy. They are in a hard to reach spot and the stuff is quite resistant too. As a matter of fact they work very well with the 802s at least to my liking.

Without the horn the driver sound 'intense' but not as irritating. You may be right that it is the horn.

I guess gleaning the vc doesn't harm either.

Thanks, Coen

Quote:

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Originally Posted by vuki

You can't just swap the driver and hope everything would sound fine. The drivers have different sensitivity and frequency response so the crossover should be redone. You can't do it without measuring it.

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Good point. I took a redesign of the co into consideration. Yet I would expect that the whole system would be out of balance, not sounding needly (harsh?).

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

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.

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.

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]

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.

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.

Quote:

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Originally Posted by 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.

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yeah, what he said.

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.

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.

http://www.hostboard.com/forums/f700...extension.html

Well, if the horns play well enough to pass with 802s/adapters, I would not expect them to sound totally horrible with 288s.

When I speak out against the 511B, I am being a little bit picky... they are not "needles in ear" bad, just a little hard sounding. I have read forum posts claiming the E is a lot better (with 802s and adapters). 511E is not very common but I am sure somebody around here knows the horn.

If the 802 combo is tolerable, I suspect something more dramatic is at fault than corksniffing horn preferences.

Do you have a test CD or a way to hook up a laptop to the system to run frequency sweeps? Maybe you can hear if the driver is flipping out at certain frequencies...

One other possibility...are you sure the drivers are both wired in phase? Seems obvious but I recently picked up some 802-8Gs and one was wired backwards...that sounded very strange indeed. At first, I thought the diaphragms were fried.

On 288 extension:

I found a note from Altec Best on DIY forum saying 288s on 511E are good out to 12k.

Never saw an FR graph but presumably the acoustic EQ of the horn is such that it would bolt right up to a 288 without requiring correction for the old "3k haircut."

Whoa: Found AB's measurements here:

http://www.audioheritage.org/vbullet...on-a-511E-horn

Good find! AB did those measurements, I did those graphs. I may still have the raw data if AB does not.

Quote:

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Originally Posted by Geekstar

Do you have a test CD or a way to hook up a laptop to the system to run frequency sweeps? Maybe you can hear if the driver is flipping out at certain frequencies...
.

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I agree. I would sweep them slowly with a low level sine wave and see whare they start going bad. The frams could be cracked in a way you can't see but surely would be able to hear.

Ron

Thanks for all the replies and help offers.

I am located in europe so there is no dropping by. I have a tone generator and a low impedance amp. I guess that should suffice for an audible inspection. If i dont forget i will also try with reversed connection.

First i am going to remove the phragms and clean the gap.

The only thing i lack for measuring is a measurement grade mic amp. I've been looking at the little behringer which has a 'flat' setting. I wondered if the ecm8000 measurement mic with phantom supply plugs into my pc mic-in, any idea if this will work?

Thanks again, Coen

I opened up the units and everything looks shiny and brand new. No corrosion whatsoever nor any debris is the vc. Scotch tape came out cleaner than going in, not! Much cleaner anyway than the 802s. The plastic tangerine plug is still glues tightly to the metal.

More details on the phragms: they look very much like the real thing. Part# stamp is 23763, which is the original part for the 288-8k. There are two other stamps. One says 40290 and the other 9798326, probably a batch and a date code...

I hope i can finish the test setup tonight.

Quote:

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Originally Posted by 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.

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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

Well that was easier than anticipated.

288-8k on the 511e, a little hafler, interlink and tonegenerator sweeping slowly for me. Hearing at approximately 1,5m on axis.

What I hear is a slight rising from 500 towards 1kHz, a peak at about 2.8kHz. From 10 k up the unit sounds very sharp. There seems to be a dominant harmonic/resonance, I guess around 12k, that enters the scene. Sound substantially decreases after 13,5kHz. That could also be my ears :). A little louder I can still hear the 14,5kHz.

My ears are limited to 15k on my age. The mic setup could bring more info, but that is a story for another day.

For now we have a hf resonance at 12k and some in band peaks. Not much exiting, since similar graphs have been made with the same unit on a different horn. I found one I will post next in my webpic archive.

If the 12k is about the nastyness, where does this come from and how can it be controlled?

Abe,

Thanks for the sharing. I also am still of the opinion that the dias are suspect # 1. The hf is very loud, especially when people say the unit should have no prominent highs. Even worse, that they have less hf than the 802s (they have plenty more). Very likely all thanks to a 12k resonance that is easily exited.

Maybe some of the forum gurus has a wise observation or hint-tip for further analysis or fixing.

Coen

My 288s have a peak up around 12K too. And a sharp notch at 8K. I've seen at least one other that measured that way. My solution? Cross to a tweeter at about 7KHz. :)
(GPA 'frams)

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.