Far too lean 604-8Gs in 620 kabs

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

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......

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Originally Posted by 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

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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

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.

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

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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......

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

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Originally Posted by amandarae

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

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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

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Originally Posted by 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.

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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

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Originally Posted by 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

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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

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.

Are you guys sound junky purists who use no tone control? I’m a low brow stereo aficionado and use a heavy dose of bottom and top EQ and my A7’s play plenty low, although I have to adjust for every different song and volume change and they sound great whether playing classical, jazz, fussion, or rock. Or play them flat and just stand 100 feet away and then they have all the bass you could ever want.

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Originally Posted by VolvoHeretic

Are you guys sound junky purists who use no tone control? I’m a low brow stereo aficionado and use a heavy does of bottom and top EQ and my A7’s play plenty low, although I have to adjust for every different song and volume change and they sound great whether playing classical, jazz, fussion, or rock. Or play them flat and just stand 100 feet away and then they have all the bass you could ever what.

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My first amp bought in 1974 or 5 (a Sansui au-6500) had tone controls and i used them. I sold it in 1980 and havent had an amp with tone controls since. They fell out of grace with most manufacturers as well as the DIY crowd.
Regards
Kjartan

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Originally Posted by KBergsson

My first amp bought in 1974 or 5 (a Sansui au-6500) had tone controls and i used them. I sold it in 1980 and havent had an amp with tone controls since. They fell out of grace with most manufacturers as well as the DIY crowd.
Regards
Kjartan

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My amps don't have tone controls either, but I have a $60 Radio Shack 15 band EQ which works and sounds amazing and loss in fidelity purity is more than made up with tonality equality(are those even words?).:)

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Originally Posted by amandarae

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.

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Yeah, long, boring story about design cut short, moving the vent to the extreme bottom will cure these problems for most folks, though some [like me] need to additionally critically damp the vent to get a fast transients 'sealed with extra gain' response.

GM

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Originally Posted by KBergsson

Hi GM, im using the J. Markwart filter unchanged.........

There could be a small leak...........

Im not expecting deep bass............ the bass is very dry and attenuated compared to the mids and top.

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I don't have my notes available, so don't recall 620's exact tuning, etc., but it should do 40 Hz solidly. To go lower requires either a larger cab tuned lower or a lower vent tuning and corner loading for the 620.

Even leaks around screws can ruin a reflex's tuning, causing a much higher F3, Fb.

Regardless, once you're sure there's no leaks, Jeff's XO has an adjustable HF shelving pot same as the OEM unit, so as it is dialed up, the tonal balance shifts to an increasingly mid-bass heavy one and if you don't like what it does to the extreme HF you can experiment with higher/lower by-pass cap values [c4].

WRT weak magnet testing, I know of no way for the casual DIYer to test them, but the dead giveaway is that it increases the driver's Qts a lot, meaning you'd be here complaining about having a 'fat'/'slow'/'boom' bass due to the 620 being too small and too high tuned for them without plugging up the vent and even then it maybe too small.

GM

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Originally Posted by VolvoHeretic

Are you guys sound junky purists who use no tone control?

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Not me, once I learned about such things, I've always used some form of response shaping EQ, especially CD horn EQ, and back when dbx first offered a digital RTA/EQ with the ability to save multiple response curves one could choose from its remote 'on the fly', I gladly paid a full month's salary for it, which at the time was quite a 'stretch' for me financially.

It lasted around 25 yrs of ~daily use, so got my money's worth, but its many generations newer replacement is way more than my retirement budget can recover from in these trying economic times.

GM

Thanks for all the good suggestions. Work has been disturbing my hobbies the last couple of days ;)
I haven't had the time to dismount the speakers, take pictures of the membranes and remove some of the fiberglass so I only have top, side and back covered.
I have however been playing with the shelving pot in the JM filters and it does not have a huge effect, everything is a little more up front on the one extreme setting and a little slower/darker on the other extreme. I use the middle position for most of my listening.
If removing damping from the cabinets is not enough i might try closing the front port and cutting a port on the bottom (I have the 620's mounted on wheels so my wife can move them around) and see what that does.
Regardless of the missing bass output, the Altec's still sound quite good and are smooth, detailed and fast.
Regards
Kjartan

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.

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

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

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.

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

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That said, for deep bass, a very large cab tuned to Fs is required, especially when driven by a high output impedance tube amp.

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Quoted for emphasis.

A graphic analysis of the frequency response characteristics of the amplifier/s would probably help shed some light on "where's the bass?".;)

Hi BBC454SS, i dont know the output impedance of my Quicksilver KT88 monoblocks. But I dont think it is high compared to most pentode tube amps. Quicksilvers have e.g. been regarde a great match for Quad electrostats.
Regards
Kjartan

Hi I exchanged the 25uf Mundorf caps in the J. Markwart crossover with some inexpensive oval GE 25uf caps. Got more bass and much better resolution in the low end. Im going to exchange all the caps in my Markwart crossover, what do you recommend?
I'm not into expensive caps in general, use russian PIOs in my quicksilvers.
Regards
Kjartan

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Originally Posted by KBergsson

Thanks for all the good suggestions.

I have however been playing with the shelving pot in the JM filters and it does not have a huge effect, everything is a little more up front on the one extreme setting and a little slower/darker on the other extreme. I use the middle position for most of my listening.

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You're welcome!

Hmm, something is not right, a 25 ohm pot will convert an 'in your face' sounding speaker down to a muffled sounding wide BW woofer, so with a 30 ohm pot it should have an even more extreme range. Again though, the relatively large by-pass cap will tend to just tone down the lower HF, hence the suggestion to try smaller values to increase the pot's ability to deal with baffle step loss.

Still, the cab is large enough to generate plenty of bass down to around 40 Hz IIRC, so I still think there's a leak somewhere. That, or your speakers are out-of-phase with each other, canceling out much of their bass output.

GM

I agree GM, something is fundamentally wrong, but I cant put my finger on it.

The speakers are not out of phase now because if i reverse the speaker leads on one side, the bass disappears altogether and the instruments appear to be are all over the place on the outside of the speakers.
I have fixed potential leaks around the 604s. I have used some putty to stop potential leaks around the terminals and original crossover.
I have the speakers right up to the walls in corners (solid outer walls).

Bass is there ....but as said before it is severely attenuated compared to higher frequencies, so it never really comes into play, I'm also missing the richness of e.g. contrabass string and box resonance, the inexpensive 25uf cap brought a tiny bit of that into the picture compared to the 25uf mundorf I got with the Altecs.


I'm going to connect the original Altec filter this evening (21uf and 1.8mHy in the bass network and 6uf, 12uf and 0.6mHy in the tweeter network), see what that changes. It should at least uncover if there are errors in my implemetation of the J. Markvart mid EQ.

I'm also going to check if the units (if for example a recone has been performed) are internally out of phase (802 vs woofer). Measure the woofer and compression driver se if there is a mismatch (8 contra 16 ohm or whatever).


Best regards
Kjartan

Let's not forget the amp's potentially huge impact on all this also: http://www.hostboard.com/forums/f700...ml#post1823199

Then there's the signal going to it.............

Corner loaded into massive/rigid outside walls typically requires running the horns pretty 'hot' to balance out the strong mid-bass that defines virtually all the vintage Altec large speaker alignments. Historically, I've often tuned such cabs lower to allow enough CD horn EQ be used to minimize the mids/HF horn's 'honk'/'screeching' highs.

GM

Hi before I connected the std crossover I decided to try a smaller bypass cap. Used a 2 uf no real improvement but the mid eq showed a lot more difference between min and max. Then I tried bypassing the eq altogether, wow!! Top a little hot but there wa a lot better overall balance. Now I have been playing for a couple of hours, bypassing the mid eq but keeping 3ohms in series with the top (even using the winged c kt88 in the quicksilvers). Something is definitely wrong in my implementation of the mid eq. Bass is back and sound is glorious. Hope this lasts :D
Kjartan

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Originally Posted by KBergsson

Hi before I connected the std crossover I decided to try a smaller bypass cap. Used a 2 uf no real improvement but the mid eq showed a lot more difference between min and max. Then I tried bypassing the eq altogether, wow!! Top a little hot but there wa a lot better overall balance. Now I have been playing for a couple of hours, bypassing the mid eq but keeping 3ohms in series with the top (even using the winged c kt88 in the quicksilvers). Something is definitely wrong in my implementation of the mid eq. Bass is back and sound is glorious. Hope this lasts :D
Kjartan

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Yaayyy!!!!!!!!!!!!!!!!!

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Originally Posted by cradeldorf

Yaayyy!!!!!!!!!!!!!!!!!

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:D :D :D :emot169:

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Originally Posted by KBergsson

Then I tried bypassing the eq altogether, wow!! Top a little hot but there wa a lot better overall balance.

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Greets!

Interesting, sounds like your amp is the real problem, i.e. can't handle the load of all the extra series resistance, causing it to 'lay down' on high current demands. If true, then using a tapped auto-former to adjust the HF's level like was used back when high output impedance was the norm seems the way to go. Regardless, glad you found at least a temporary workaround.

GM

If the OP's amplifiers have multiple taps, i wonder what effect using the 4 ohm taps might have had in coping with the additional series resistance of the JM network.

FWIW, i've kept all my 8 ohm Altecs and they're fed only clean quality(not heavily damped) solid state watts these days. The result for me has been a lot more listening time, and a lot less chasing my tail after "sonic anomalies". My next amplifier project will most likely be a Nelson Pass/Firstwatt F5, that's if i don't get too anxious and get a built model.

Just my .02................. YMMV.

Thanks GM and Bowtie, I'm going to play for a while with the crossover as is (ie bypassing the mid eq) and see if I miss the eq at all.
Using autoformers could be interesting, are there standard (vintage) ones available or do they need to be tailored to the actual speakers?
I will on all account try the 4 ohm taps and see what that does.
Regards
Kjartan

There's a guy from Germany who produces some nice c-core autoformers designed for use with Altecs, you can find him and the autoformers on eBay under the username mast_mutter. You can either buy a complete crossover network or order the autoformers and/or c-core inductors separately, his 604 network is very simple but works very well. PM if you would like his email address, otherwise you can contact him via eBay.

Quote:

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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

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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.

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Originally Posted by omodo

There's a guy from Germany who produces some nice c-core autoformers designed for use with Altecs, you can find him and the autoformers on eBay under the username mast_mutter. You can either buy a complete crossover network or order the autoformers and/or c-core inductors separately, his 604 network is very simple but works very well. PM if you would like his email address, otherwise you can contact him via eBay.

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Thanks Omdodo I will check out mast_mutter.
Just got a homemade headamp yesterday ( j.j. Curcio mc stepup with E88CC / 6922) , so now I got valves all the way - life is good :)
Regards
Kjartan

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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.

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

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Originally Posted by omodo

There's a guy from Germany who produces some nice c-core autoformers designed for use with Altecs, you can find him and the autoformers on eBay under the username mast_mutter. You can either buy a complete crossover network or order the autoformers and/or c-core inductors separately, his 604 network is very simple but works very well. PM if you would like his email address, otherwise you can contact him via eBay.

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Hi omodo, I have ordered the autoformer crossovers for altec 604 from mast_mutter. Look forward to try them :) :)
Regards
Kjartan

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Originally Posted by KBergsson

Hi omodo, I have ordered the autoformer crossovers for altec 604

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I have now connected the autoformer crossovers from Werner Jagusch. They are an incredible improvement compared to the original crossovers and my implementation of the Markwart crossovers. These big speakers disappear and the sound is smooth, effortless and with astonishing realism (Im now using a Shure V15VxMR on my VPI Classic).
Im attenuating the horns approx 4.5db compared to the woofers (if my assumption of 1.5db per step is correct). Gives me a lot better balance than before.
Kjartan