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

**Geekstar** · May 25th, 2012, 01:17 PM

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.

**Geekstar** · May 25th, 2012, 01:24 PM

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

**Panomaniac** · May 25th, 2012, 01:55 PM

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

**RonSSS** · May 25th, 2012, 02:39 PM

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...
.

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

**Coendert2011** · May 25th, 2012, 03:23 PM

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

**Coendert2011** · May 25th, 2012, 04:35 PM

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.

**amandarae** · May 25th, 2012, 05:33 PM

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.

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

**Coendert2011** · May 25th, 2012, 05:58 PM

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?

**Coendert2011** · May 25th, 2012, 06:07 PM

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

**Panomaniac** · May 25th, 2012, 06:38 PM

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)