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

**Earl K** · June 3rd, 2012, 11:34 AM

Originally Posted by jOHN

Back to the 288's.You should really work on fixing the locating dowel pins on those 288-8K's.As Pano & GM have said you need those to center the diaphragm easily and in a timely fashion.Once you have the pins you will make quick work of it before it drives you crazy or just takes too much of your time.. My point is it can become tedious..

But your doing a great job ! Keep up the great work Coen.

Fitting old drill bits in the holes and then cutting them to size is a great idea as GM posted.If not GPA should be able to provide them for you.

Sheesh AB,

The newer series 288s include a 2-piece dowel system ( which includes a hollow over-sized sleeve & a small bolt that holds that sleeve in place ) .

It is not, a solid metal pin that can be simply replaced by a small piece of metal rod ( cut to length and stuck in the threaded hole as you & GM suggest ) .

BTW, Pano is missing the 2 over-sized sleeves that are snugged-up inside the 2 locator holes within the diaphragm & held there by the set-screw . ( Look at the picture I posted of Panos open-backed driver to see the set-screws ) .

The center "hole" in the sleeve is larger than the diameter of set-screw, essentially allowing the sleeve to "float" or slop around a bit ( when the set-screw is loose ). This "play" when used in conjunction with the spider shim is what allows for an accurate fitup in the new system .

Coen's description of what he has seen in his 288s suggests he might have a fully functional ( adjustable dowel ) system ( compare to the pic above ) .

He simply needs to read the instructions on how to use it ( along with the included spider shims coming from GPA ) .

DownLoad & Read ;Altec Lg-Format Driver Diaphragm Replacement Instructions

GM · June 3rd, 2012, 12:15 PM

Originally Posted by Earl K

It is not, a solid metal pin that can be simply replaced by a small piece of metal rod ( cut to length and stuck in the threaded hole as you & GM suggest ) .

Just to be clear, I was responding solely to Pano's post and did not say nor imply cutting the drill bits to suit [though of course one can do so when appropriate if they have the means to cut such a hard material!], but merely to use them to quickly align the VC for fine tuning as I've found that while the positioning may be geometrically correct, it isn't necessarily the best performing location IME with small format drivers.

Note too that my Altec large format driver 'hands on' experience is limited to just the 288B and even that was at a time when I assumed that the factory assembly was already 'optimized', so in retrospect shouldn't have posted on this thread and have deleted my misleading post.

GM

**Earl K** · June 3rd, 2012, 12:26 PM

Thank-you GM ! for deleting your misleading post ( now maybe AB will follow suit ) .

**vuki** · June 3rd, 2012, 12:47 PM

Since Coen is going to use drivers for home listening, once he determines and fixes position of the diaphragms, the drivers will be good for the next few decades. So, adjustable dowels, although nice and convenient detail, are not indispensable in this case.

**Altec Best** · June 3rd, 2012, 12:52 PM

Originally Posted by Earl K

Sheesh AB,

If not GPA should be able to provide them for you

Are you kidding ? I was only talking as a temporary means to align the diaphragm while he is tighten the diaphragm screws to help keep the diaphragm centered and from shifting.My advice as you know is to always Contact GPA first for obvious missing parts.! As I will always recommend buying original replacement Altec parts first... Bill/GPA I'm sure probably has these laying around. At the end of my post I said to call GPA for the missing pins...

BTW - As I previously posted I think Coen is doing pretty darn well himself IMHO ! Keep up the Good Work Coen ! Just keep measuring everything you can,practice will make perfect.I'm pretty sure you have a good handle on things.

**Panomaniac** · June 4th, 2012, 09:53 PM

Originally Posted by Altec Best

Bill/GPA I'm sure probably has these laying around. At the end of my post I said to call GPA for the missing pins..

Well they were hesitant to send me some, so suggested I try the 200Hz tone. If that didn't work, I think they'll see some. I'd be happy to buy a set and pay all postage, so I'll let GPA know that. I really don't know if they have a bunch of them hanging around. I think they were afraid of charging me too much postage for a few little pins.

**bowtie427ss** · June 5th, 2012, 08:05 AM

Originally Posted by Earl K

Sheesh AB,

The newer series 288s include a 2-piece dowel system ( which includes a hollow over-sized sleeve & a small bolt that holds that sleeve in place ) .

It is not, a solid metal pin that can be simply replaced by a small piece of metal rod ( cut to length and stuck in the threaded hole as you & GM suggest ) .

BTW, Pano is missing the 2 over-sized sleeves that are snugged-up inside the 2 locator holes within the diaphragm & held there by the set-screw . ( Look at the picture I posted of Panos open-backed driver to see the set-screws ) .

The center "hole" in the sleeve is larger than the diameter of set-screw, essentially allowing the sleeve to "float" or slop around a bit ( when the set-screw is loose ). This "play" when used in conjunction with the spider shim is what allows for an accurate fitup in the new system .

Coen's description of what he has seen in his 288s suggests he might have a fully functional ( adjustable dowel ) system ( compare to the pic above ) .

He simply needs to read the instructions on how to use it ( along with the included spider shims coming from GPA ) .

DownLoad & Read ;Altec Lg-Format Driver Diaphragm Replacement Instructions

I'm a bit shocked that Earl had to post this as i thought it was fairly common knowledge here.

**cradeldorf** · June 6th, 2012, 12:09 AM

I've never seen it, Never knew there was such a thing as adjustable locating pins. It does make great sense to do it that way.

**Altec Best** · June 6th, 2012, 12:20 AM

Originally Posted by Panomaniac

Well they were hesitant to send me some, so suggested I try the 200Hz tone. If that didn't work, I think they'll see some. I'd be happy to buy a set and pay all postage, so I'll let GPA know that. I really don't know if they have a bunch of them hanging around. I think they were afraid of charging me too much postage for a few little pins.

I don't know why they would be hesitant to sell them to you.It makes it much harder to align them without them.Agree with the last part probable don't want to charge you too much.Just ask for a dozen make it worthwhile.

Originally Posted by bowtie427ss

I'm a bit shocked that Earl had to post this as i thought it was fairly common knowledge here.

And it is !!! When you don't have them in front of you it is easy to make a mistake..

**RonSSS** · June 6th, 2012, 12:47 PM

I'm glad you guys zero'd in on the alignmentof the VC in the gap.
When I swapped the OEM frams out of my 904 duplex (symbiotic) to new GPA frams, the speaks just sounded bad. So I set up my spectrum analyzer with tracking gen and a mike and looked at the response. Huge suckouts. I put the original frams back in and they were gone. So just because this later model uses the od of the fram assembly to center, I tried loosenig the screws and guess what, suckouts gone! These speakers actually had a thin gasket between the fram and the hf driver body. Anyway, I ended up moving the fram around a bit and found the sweet spot and simply tightened the screws just enough to keep it that way.
It about drives you nuts listening to the thing sweep, but the results were worthwhile.
I am fortunate to have the test setup. a Tek 7L5 Sa withtracking Generator option. My mike is simply a Radio shack SLM with an output that feeds the SA. Not accurate for sure, but for this it worked perfectly.

Ron