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......

[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

[Altec Best]

You should be getting better bass then your getting especially in a 620 cabinet.I don't like MDF it just sounds muddled to my ears.Any void free plywood sounds the best to me IMHO.With Baltic Birch being tops in my book.If your HF is too bright it will have the effect of your bass being a bit shy.

I also have 604-8G's in 612C cabs that are a bit smaller than the 620.The 620 A/B is supposed to be the right cab for the 604 G,H so it will be your preference to which would sound best.To me I thought my 604's sounded bass shy in the 612 but when I popped a 416B in there, there was plenty of bass.So I'm thinking it is just the 604 duplex that is bass shy IMO.

[GM]

Do you have the HF shelved down [AKA baffle step compensation or BSC] to tonally balance it? This will make it sound too lean if not. Ditto if there's any cab leaks which will turn a reflex alignment into a lossy sealed one with a very high F3/Fb. That said, for deep bass, a very large cab tuned to Fs is required, especially when driven by a high output impedance tube amp.

GM

[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

[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

[KBergsson]

You should be getting better bass then your getting especially in a 620 cabinet.I don't like MDF it just sounds muddled to my ears.Any void free plywood sounds the best to me IMHO.With Baltic Birch being tops in my book.If your HF is too bright it will have the effect of your bass being a bit shy.

I also have 604-8G's in 612C cabs that are a bit smaller than the 620.The 620 A/B is supposed to be the right cab for the 604 G,H so it will be your preference to which would sound best.To me I thought my 604's sounded bass shy in the 612 but when I popped a 416B in there, there was plenty of bass.So I'm thinking it is just the 604 duplex that is bass shy IMO.

Thanks Altec best, maybe the 604s are more bass shy than I expect or would like, I have regrettably no comparison near by (i.e. another set of 604?s)
Regards
Kjartan

[KBergsson]

Do you have the HF shelved down [AKA baffle step compensation or BSC] to tonally balance it? This will make it sound too lean if not. Ditto if there's any cab leaks which will turn a reflex alignment into a lossy sealed one with a very high F3/Fb. That said, for deep bass, a very large cab tuned to Fs is required, especially when driven by a high output impedance tube amp.

GM

Hi GM, im using the J. Markwart filter unchanged (using the 8g suggested values) as published here " Simplified 604-8H EQ Crossover ". I welcome any suggestions to modify this filter.
There could be a small leak due to a small damage on the gasket (between cab and unit) around one mounting hole on one of the speakers.
Im not expecting deep bass and they seem to go reasonably deep if there is real deep bass on the record, but it is more that the bass is very dry and attenuated compared to the mids and top.
Regards
Kjartan

[Todd W. White]

This was a problem with some of the post-Electro-Voice takeover 604's, but should NOT be a problem with yours. I have personally made side-by-side comparisons of a 604E that had been freshly recharged and reconed by GPA and a brand new GPA 604-8H-II, using the same crossovers (designed by Jerry K. Hubbard), and, though the HF sounded a bit different between the two, as one would expect, the LF was identical. Something else is going on here...it's not the speaker's design fault.