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

[Coendert2011]

I just ordered two new GPA diaphragms.

They were a bit hesitant to sell them to me, assuming I did not like the 288 character. Kudos to that attitude, wich I think is a good customer relation is all about!
In hindsight I think reports on people not liking the 288-k has more to with faulty diaphragms than with an alnico or a circumferential-slotted phaseplug preference. Those will matter in the end, but are in the realm of "288-k ok, good but not my thing" rather than "dude switch off immediately".

Which brings me to an offer to you. i will off course measure again with the new dias but I wondered is there anyone who would like to measure my distortion makers in their units?

There is off course a tiny risk that the new dias don't work out and the cause is elsewere....

Coen

[Panomaniac]

I would, but I don't have the darn locater sleeves. Talked to GPA this afternoon and they said to center them with a 200Hz tone at 2V. That's how they do it. Sure wish I had the sleeves, it would be much faster and easier.

[Earl K]

Coen,

I wish I had posted my thoughts before you ordered those diaphragms ( maybe it's not too late to get GPA to do the following ) .

Thought :

• Whether you agree ( or realize it ) , GPAs current pricing for a 288 diaphragm is a steal . So ;
• Offer them a $50.00 premium over the going rate ( for each diaphragm ) to test each for performance ( FR & Distortion, obviously ) / as well as matching specs to each other ( which is fairly critical for HiFi based listening, unless you are a whiz at creating passive EQ correction ) .
• This extra $100.00 is well spent towards avoiding the head-aches ( & nastiness ) of a getting a mediocre performing diaphragm, due to some liberal QC standards.
• This "Insurance Premium" would nicely address GPA's ( very real ) concerns about selling components to those of us who actually measure things for their expected performance traits ( & don't just readily accept the Kool-Aid of "How Great It Was In The Past" ) .

That was my main thought ( for the day ) that I wanted to share .



<>

[cradeldorf]

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

[vuki]

Nice work!

Those pics are unfortunately awefully small. Left of 1kHz is hi passed away?
Interesting peaks on 10 and 12kHz. So these could be related to the 802-g radial phase plug that is in our 288-ks as well....

Did you use any compensation for the bumps/nothces?

Coen

That was with 15uF capacitor. No compensation.

Here is 802 with hf compensation
KOMPATT.jpg


BTW Why don't you try to align the diaphragms in those 288s?

[Coendert2011]

I would, but I don't have the darn locater sleeves. Talked to GPA this afternoon and they said to center them with a 200Hz tone at 2V. That's how they do it. Sure wish I had the sleeves, it would be much faster and easier.

That's acoustically unloaded? And what do they look for? I only have the replacement instruction using the spider shims for centering.

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

Coen

[Coendert2011]

Coen,

I wish I had posted my thoughts before you ordered those diaphragms ( maybe it's not too late to get GPA to do the following ) .

Thought :

• Whether you agree ( or realize it ) , GPAs current pricing for a 288 diaphragm is a steal . So ;
• Offer them a $50.00 premium over the going rate ( for each diaphragm ) to test each for performance ( FR & Distortion, obviously ) / as well as matching specs to each other ( which is fairly critical for HiFi based listening, unless you are a whiz at creating passive EQ correction ) .
• This extra $100.00 is well spent towards avoiding the head-aches ( & nastiness ) of a getting a mediocre performing diaphragm, due to some liberal QC standards.
• This "Insurance Premium" would nicely address GPA's ( very real ) concerns about selling components to those of us who actually measure things for their expected performance traits ( & don't just readily accept the Kool-Aid of "How Great It Was In The Past" ) .

That was my main thought ( for the day ) that I wanted to share .

<>

Thanks a lot cor the advice. I hardly crossed my mind that the new GPA dias could have the same problem. I was actually counting on a good reference. I have a pair of new small format gpa dias that are very close. Thats the one I measured I few posts back. Distortion is under the noise floor.

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

Coen

[vuki]

That's acoustically unloaded? And what do they look for? I only have the replacement instruction using the spider shims for centering.

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

Coen

You can even do it by ear - listen for the cleanest tone - with the least amount of harmonics. Of course you can check it with ARTA - on the spectrum analizer look for the smallest amount of harmonics.

[Coendert2011]

That was with 15uF capacitor. No compensation.

Here is 802 with hf compensation
KOMPATT.jpg


BTW Why don't you try to align the diaphragms in those 288s?

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

[Coendert2011]

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