Far too lean 604-8Gs in 620 kabs

**voice of the theater** · September 9th, 2011, 10:58 AM

It's possible that your alnico magnets need to be re-charged. Alnico, especially if dropped or played at extremely loud SPL's, can lose some of it's magnetism after 30 years (I hope I'm never told I've lost some of my magnetism in the last 30 years ;P. You also mention in your post that "I don't know the history of my Altecs i bought them used in Norway, but bass membrane and surround looks almost new (or too new for 30 year old speakers)." Maybe they were re-coned with non-Altec or non-GPA cones. Posting photos of them here may help to determine if they are real and/or original Altec cones including photos of the backs of them which show the number printed on the backs of the cones......

**KBergsson** · September 10th, 2011, 03:57 AM

Originally Posted by voice of the theater

....It's possible that your alnico magnets need to be re-charged. ...... Posting photos of them here may help to determine if they are real and/or original Altec cones including photos of the backs of them which show the number printed on the backs of the cones......

Thanks voice of the theater, is there a way to check the alnico charge?
Will post photos later.
Regards
Kjartan

**aeyb701** · September 13th, 2011, 06:03 PM

Bill H. at GPA told me a while back that loos of magnetism led to a loss in the mid freq's., not the low end.
If I may chime in on recones, I had a 604c done by GPA a few years ago and with no disrespect the new suspension was very stiff, and whether or not related there was less bass than in an unreconed version I had around.
I ended up getting another original 604C and mended any tears and brittle areas of the cone with layers of tissue paper interspersed with and made rigid by diluted white glue, then painted. Doesn't look so slick but sounds a charm.

**KBergsson** · September 14th, 2011, 05:41 AM

Intresting, if my 604s have recently been reconed (they look new), bass shyness may be a break in issue. My lowthers took at least 2years break in to be tolerable on most music and continued improving over 10+ years.
Regards
Kjartan

**KBergsson** · September 14th, 2011, 07:34 AM

Just removed the Altecs 604s and removed som fiberglass from 2 sides in each speaker. Initial impression: more open/transparent or lively sound. The bass membranes are stamped 1803035662 and 1803035(5or6) cannot se last two figures.
Does this indicate original membranes or later recones?
Regards
Kjartan

**Todd W. White** · September 14th, 2011, 11:33 AM

Be careful not to remove too much damping material - if you do, you'll set up some nasty standing waves inside, not to mention making the loss of perceived LF response due to wasting the energy wiggling the box.

**KBergsson** · September 14th, 2011, 11:38 AM

Hi Todd, I only removed damping from one side and bottom so that top, back and one side is still covered.
Sounds fine, but no change in bass output.
Regards
Kjartan

**speakerdave** · September 22nd, 2011, 12:38 AM

Originally Posted by KBergsson

Just removed the Altecs 604s and removed som fiberglass from 2 sides in each speaker. Initial impression: more open/transparent or lively sound. The bass membranes are stamped 1803035662 and 1803035(5or6) cannot se last two figures.
Does this indicate original membranes or later recones?
Regards
Kjartan

If anyone responded to this I missed it. Those are not Altec cone numbers for the 515b/604G, so they are apparently recones. I don't recognize the numbers, so i cannot place the source.

**KBergsson** · September 22nd, 2011, 03:45 AM

Originally Posted by speakerdave

If anyone responded to this I missed it. Those are not Altec cone numbers for the 515b/604G, so they are apparently recones. I don't recognize the numbers, so i cannot place the source.

Thanks speakerdave, that explaines why they look "new".
Regards
Kjartan