Far too lean 604-8Gs in 620 kabs

[KBergsson]

Hi, I have 604-8g in 620 cabinet MDF copies.
I m not getting the bass and tonal richness i expect from the 604's in those cabs (I'm not at bass junky as I used lowther horns for a decade or more).
I thought this was an issue in my previous home, but now i have placed the Altecs in comers on an end wall in my new home, to no avail.

I'm using the Markwart Simplified 604-8H EQ Crossover with values for 604-8g.
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).
Due to a resonance from a cartridge arm mismatch (the cartridge suspension was also throwing in the towel due to high age) I heard that the Altecs where capable to produce an earth shattering low end.

But generally they are far to lean (they are not out of phase).
I'm using a very rich, meat and blood setup, i.e. VPI Classic, Denon DL103, Leben RS28CX, Quicksilver KT88s (with 6L6GCs).
I get the same leanness with digital - AIFF via a reasonable DAC.

The cabinets are probably somewhat over damped (damping material on all internal sides).
I'm using Mundorf MCap RXF Radial Polypropylene Caps ( I got them with the Altecs) they are probably somewhat bright but could probably not have this big an effect.

Any Ideas, I would really love to hear the Altecs at they're best
Best regards
Kjartan

[voice of the theater]

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]

....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]

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]

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]

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]

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.

[speakerdave]

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.

[amandarae]

Hi, I have 604-8g in 620 cabinet MDF copies.
I m not getting the bass and tonal richness i expect from the 604's in those cabs (I'm not at bass junky as I used lowther horns for a decade or more).
I thought this was an issue in my previous home, but now i have placed the Altecs in comers on an end wall in my new home, to no avail.

I'm using the Markwart Simplified 604-8H EQ Crossover with values for 604-8g.
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).
Due to a resonance from a cartridge arm mismatch (the cartridge suspension was also throwing in the towel due to high age) I heard that the Altecs where capable to produce an earth shattering low end.


But generally they are far to lean (they are not out of phase).
I'm using a very rich, meat and blood setup, i.e. VPI Classic, Denon DL103, Leben RS28CX, Quicksilver KT88s (with 6L6GCs).
I get the same leanness with digital - AIFF via a reasonable DAC.

The cabinets are probably somewhat over damped (damping material on all internal sides).
I'm using Mundorf MCap RXF Radial Polypropylene Caps ( I got them with the Altecs) they are probably somewhat bright but could probably not have this big an effect.

Any Ideas, I would really love to hear the Altecs at they're best
Best regards
Kjartan

Assuming that your drivers are fine, I mirror that same experienced of yours. I have the 604-8G's. I used the JM XO, the Altec 604-8G XO and many more variations of it and cannot find the 620 cabs to sound good to my taste. My 612C cabs sounds better to me. To me, the 620 cabs bass is bloated and undefined(could also mean less depending on room interactions) and something is amiss on the midrange compared to the 612C or Open Baffle using the 604-8G's. Just my experience.

Abe

[KBergsson]

Assuming that your drivers are fine, I mirror that same experienced of yours. I have the 604-8G's. I used the JM XO, the Altec 604-8G XO and many more variations of it and cannot find the 620 cabs to sound good to my taste. My 612C cabs sounds better to me. To me, the 620 cabs bass is bloated and undefined(could also mean less depending on room interactions) and something is amiss on the midrange compared to the 612C or Open Baffle using the 604-8G's. Just my experience.
Abe

Hi Abe, my problem is in reality the opposite of bloated, it sound more like it is overcontrolled (very dry) but reduced volume, compared to the middle and top.
Regards
Kjartan