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

[vuki]

Nice! So this is inclusiding the hi pas isn't it? You removed the bump with a low q notch filter?

Aligning is next on the list, need to find an appropriate method.

Coen

No notch filter, just 12db/oct highpass + attenuation & hf compensation.

The easiest method would be to take off rear cover from the driver, slightly loose the screws that hold diaphragm (so much that it still sits firm, but that you can also move it by gentle tap with some heavier tool eg. screwdriver handle) attach 200-500hz sine tone signal to the driver and listen the tone. By gently taping the side of the diaphragm you'll be able to move and align or misalign it and you will hear the tone changes from clear/soft when aligned to sharp/dirty when misaligned. You can control it via ARTA spl function - just watch for the lowest amount of harmonics. When you find the best position slowly tighten the screws paying attention not to disturb aligment (by listening or measureing while tightening).
Driver doesn't have to be loaded to do it - so you can do it on the table.

[Earl K]

I followed your suggestions and asked for the testing/matching on a price premium. I hoped the units aren't shipped allready.

I sure hope it works, But if it doesn't at least you'll know it's not the phrams.

If I can count on the quality of GPA....

Coen

I feel it's best to think of this request ( for matching & testing ) as a request to "blueprint" the diaphragms to original OEM spec.

That's a common term used in the world of engine re-builders and warrants a premium price point for the necessary extra work .

[Panomaniac]

That's acoustically unloaded? And what do they look for?

I don't think unloaded, but I didn't ask. Listen for any buzzes or the cleanest tone. That's what they said. (I think I was talking to Bill). Use 3 screws just slightly snug then add the other 3.

I only have the replacement instruction using the spider shims for centering.

Yep. And to do that, you need the alignment sleeves, which I do not have. The paper shims come with the 'frams. If you don't have the alignment sleeves (or whatever they are called) then you can't hold the position of the diaphragm once it's removed to take the shim out.

Gpa siad that the jigs/shims are supplied with the new phragms.

Paper spider shims, yes. The driver is supposed to have the sleeves, mine did not.

[Altec Best]

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"THE ALTEC USER BOARD" IS "PRO GPA" ! FOR A REASON ! THEY PRODUCE ORIGINAL ALTEC PARTS !
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If I can count on the quality of GPA....

Coen

And you CAN ! I've been dealing with Bill/GPA for a longtime and have yet to have a problem.Oh wait a minute. I had one issue Bill forgot to add a few washers in a hardware kit I bought for some 288's,(Studs,nuts,washers,gaskets) so he sent me double for the mistake. GPA will stand behind any of their products.You won't find better for Altec parts or diaphragms anywhere else IMHO...

You seem to be doing a great job investigating the issue yourself !! Listen to your own opinion, it won't steer you in the wrong direction.

The best advice I can give you here is go with your instincts... Do your own investigation... It will be the best advice for your application !! Graphs will only get you so far (For Building Crossovers & Enclosures).In the end it is how it sounds to you that is important.

[Coendert2011]

@Vuki,

Thanks for the instruction. I guess GPA is driving the driver into serious distortion anyhow with 200Hz @2V unloaded. I am curious to the experience of moving the diaphragm around and hearing the distortion vary.

@Pano:

You are referring to the 'adjustable Dowel Locating Pins' wich can move a little to center the phragm and be clamped afterwards by a screw. Won't GPA be kind enough to deliver a pair of those for you to get the job done right for once and for all?

So I take it you have a set of permanently misaligned 288s. I saw no distortionlines in your measurementgraph with the 1005 horn (post 48). Does thie misalignment result in bad sound or in "could be better" sound.


@Altec Best

My experience so far has been excellent too. Your confidence is reassuring!

Coen

[Panomaniac]

If you ask GPA for the Dowel locating pins, they may be able to send some. They did not come with my GPA frams as they are supposed to be with the driver. Apparently, they tend to stick in the fram surround and get thrown away at change out time. That most have happened to mine before I got the drivers.

Although it's supposed to be easy to align by ear, I had a devil of a time with it. Sure wish I had the dowels. Maybe you have more finesse than I and will have no trouble.

[Earl K]

Below are Pano(s) distortion sweeps from a couple of years back for one of his ill-fitted 288 diaphragms from GPA ( one can see from the first pic [which is more recent] that he has achieved a somewhat better fitup compared to a couple of years back ) .



Above was made with STEPS , while below was made with HolmImpulse .
.



vs his 291 diaphragm .





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[Panomaniac]

Thanks Earl, I could not find that 291 measurement file. At least you've found the chart! I see that the symbiotic also has the 8.3K hole.

[Coendert2011]

Earl,

For some rason I only see the top graph in Chrome and none of the graphs in Explorer.
Does anyone know what setting to change?

Coen

[Earl K]

For some rason I only see the top graph in Chrome and none of the graphs in Explorer.

Does anyone know what setting to change?

The bottom 4 pics are hosted over at diyAudio . I'm now thinking that one needs to be registered there to see them .

3 are .png files while the other is a .jpg / so I doubt it's a browser setting .



PS : The simplest solution ( I guess ) is to simply register at diyAudio ( unless Pano wants to retrieve the pics & then host them somewhere that will retain their original size ) .