604's....Why is it so?

[SOOTSHE]

I've been reading a lot of threads about 604's lately & it occurred to me....why do they sound so good when all the theory says that they shouldn't?

I mean, most say that 1500Hz is way too high to cross over at.....that you need multicell horns or the big radials or Mantarays to get the best sound from the top end driver......that 2 inch, or at least 1.4 inch, is superior to 1 inch throat drivers. The odds just seem to be stacked against this speaker, yet all reports are that it is a fine sounding unit.

With regard to the actual driver....is it a 416 driver?....and what is the top end driver...a 902? an 802?

Just curious to see what yars think.

[mah]

Good questions.

[bowtie427ss]

With regard to the actual driver....is it a 416 driver?....and what is the top end driver...a 902? an 802?

AFAIK, all 604 LF sections are based on the 515 motor, and all alnico 604 HF sections are based on the 802, ferrite HF sections are based on the 902.

What makes them so special? IMO, 2 things above all else. A) true "point source" imaging. B) HF and LF sections so well engineered that smooth transitions are easily made between them with minimal crossover topology.

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

[GM]

FWIW, here's a collection of responses I've collected from when this subject has come up before. Maybe one of these days me or? will turn it into a proper historical document.

GM
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To address the original question, besides the frame edge there is some difference in the LF motors of the C and E. Originally the C voice coil was almost the same height as the magnetic gap thickness, same as the B, the LF top plate was champhered to a thinner dimension. This made for almost no linearity in the bass. The E has a full thickness top plate with a shorter voice coil and has more linearity. The E would be the best of these two models for a studio.
The D is a bit of an enigma, some had C cones, some I have seen have original later accordian edge ALTEC cones with the orange hinges. I do not know the thickness of the D top plate, but, it too may have changed along the way also.
From my experience, there were no E or E2 models with a Tangerine Phase plug, it did not come along till much later. The first 604 with a Tangerine plug was the alnico 604-HPLN, which had the C-D-G "eggcrate" horn and a 421 LF voice coil, was made for MI uses. Our tests of the eggcrate horn shows it unloads at about 1700Hz.
A very few late Gs had a tangerine plug, very few, the H was the first that always had the tangerine.
Not all 604Ks are the same either. Early versions had cast iron magnetic returns. They had problems getting the HF passage through the LF pole piece plated and some "grew" rust growths that look like bugs in this area. Later Oklahoma built ones used steel parts which cured the problem. Toward the end of 604K production, EV managers mandated the 604 use a larger EV magnet, this overdamped the LF performance.
The first 604L was made by Oklahoma for their slant front stage monitor (can't remember the #)and the M600 Monitor. This was a late 604K motor with with high temperature-regular length LF coil and standand K cone and Pascolite HF diaphragm.
When ALTEC Pro had GPA build their 604s, they also used the L designation. It was essentially a late 604K, complete with the overdamped LF section.
Later, we at Iconic, working with GPA, got the top plate thickend and restored the proper LF performance. These units, our 704, the last of the ALpro 604Ls and GPA's unit are best sounding and most linear of any of these speakers ever made, period... All three of these speakers differ in their soft parts, naturally we think ours has the best combination. To conclude, there is no hard and fast rules about 604s, every suffix variant differs from the other and must be treated separately in application and crossover. Sorry, no simple explanation, JIM

-------
XO point:

601 = 1.2K
601C = 3K
602C = 3K
604 = 2K
604B = 1K
604C = 1.6K
604D = 1.6K
604E = 1.5K
604-8H = 1.5K
604-8K = 1.5K
605A, B, C = 1.6K
616-8A = 1K
----------------
The N1500A filter supplied with the 604-E used a first order high pass and second order low pass, and was a series filter, i.e., the voice coil loads were placed in series across the amp's output. The 604-8G filter, besides being 8 ohms, used a third order high pass and second order low pass, and had its loads placed in parallel across the amp's output.
Having said that, did they sound very different? Like GuyL said "probably not".
The big improvement in 604 crossovers, in my opinion, came with the mid-frequency EQ Altec introduced with the 604-8H. Not only does it sound different than the 604-8G, its EQ technique can make all older 604s sound much better too!
Jeff
----------------
Dates:

604E 65-72
604-8G 73-79
604-8H 80-81 last of the Alnico's
604-8K 82?-late 90's ceramic (Ferrite) magnets

Well'the 604D actually did exist.Produced from
1958-64.My info also shows that the 605A is circa
1960 and the 605B is circa 1966 so it must be that
both the 604 and 605 were produced side be side for a
while before the 605 was scraped.

Gariver--All 604s and 605s are very good. The 604C
uses a paper half-roll surround, the 604D went to the
corrugated cloth, more excursion, better bass. The
paper rolled surrounds on various 604s, 803s and 515s
are a potential problem as they are prone to tears
and rips. The 605 is an interesting speaker and
arguabley the best of the Duplexes for home use. It
has a couple of db less output and effciency but goes
lower in the bass with smaller boxes (but still
pretty big) and still gets very loud. A 604 was
basically a marriage of the 515 woofer and the 802
compression driver, the 605 a marriage of the 416
woofer with the 806 compression driver. As far as I
know the only difference between the 605A and 605B is
the paint job.

605-~1957,rolled paper surround,416+806
605A-~1960,pleated surround,16 ohm,416+806
605B-~1966,16 ohm,515B+802B
so the 605B is different from its predecessors
The 605 was not that popular with sound people,for
whatever reason,and it was finally
discontinued.Another difference between the 605 and
the 604 is that the 605 has a smaller magnet,but
still,I'm sure, huge by today's standards.

Mine shows the 605B in production at the same time as
the 604E. And as the 604 definately used the larger
515-802 type magnets, well it wouldn't make sense for
the 605 to be the same as the 604. Also, from the
pictures on the catalog sheet it looks like the 605B
has smaller magnets compared to the 604E. The story I
get is that Altec intended for the 605A to replace
the 604 entirely and 604D production was stopped.
However sound pros were so keen on the 604 sound that
the 604 was reintroduced as the 604E.

The information you have been given so far is quite
correct. The Mantaray horn was first used on an
Alnico version called the 604-8H in 1977. It was
later replaced by the ferrite magnet 604-8K around
1979.

The decline of the 604 can be largely attributed to
the success of their largest customer - UREI. UREI
developed the famous 813 monitor in 1977 based on a
604-8G as an OEM unit. The 604 system was highly
modified due to a number of deficiencies with the
original design. The cross-over was replaced with a
patented time aligned network that yielded extremely
accurate phase response. The multicell was replaced
with a simple flared horn that was coated with a
damping compound to smooth out the otherwise uneven
high frequency response. A 15" Emminence woofer was
paired with the 604 to increase maximum output and
extend bass response.

The 813 was a very successful monitor. It was the
standard large format monitor used in US studios from
the late 70's to the mid 80's. This success was
largely at the expense of Altec. They were pretty
much driven out of the studio market. The irony of
this is that UREI was taking Altec's market with
Altec's drivers. I assume that Altec felt that this
was tolerable since they were still getting good
revenue from the driver sales.

However, this situation was not to last. Altec was
having significant quality control problems in the
late 70's. UREI became an authorized Altec service
center just to reduce the costs of replacing and
repairing defective 604's. When Altec switched to
ferrite magnets, the situation was compounded. The
new magnet topology resulted a in significantly
different response compared to the original. The
problems became severe enough that UREI looked at
replacements. They finally settled on a composite
design that used a JBL compression driver mounted to
the back of PAS bass driver. By 1983, UREI was sold
to JBL and the 813C became an all JBL driver system.

In the 80's Altec was able to sort our the design and
quality control problems, but by then it was too
late. UREI had stolen the market for large coaxial
monitors and Altec had sold the consumer division
that was the other market for 604's. By the 1990's
the 604 was only advetized as a "premium ceiling
speaker" in Altec catalogs. However, there weren't
many contractors willing to spend $2000 for a ceiling
speaker.

Altec still sold small numbers of 604's as OEM
products to niche speaker manufacturers. Another
little known fact is that Altec themselves sold a
home 604-8K system called the "Milestone" strictly in
Japan. This went on up to the very end. However, the
total production of 604-8K's was very small compared
to the previous versions. For this reason, there are
very few on the market.

All of the 604s were built with the cast aluminum woofer frame, or "basket".
The 604E used gray paint on the motors and gleaming white on the basket-this
is probably what you saw.
In 1943 Altec Lansing built a small quantity of field coil 15" Duplex units,
model 601, ancestor of the 604. This model used a stamped steel basket
sourced from Utah. If anyone knows of the whereabouts of one of these I
would sure like to know about it!

-----------
I will start with the early 50's Altec 604B. It had a 40X90 HF horn
coaxially mounted crossed at 1000 hz, rated 30 watts, 16 ohms,40 lbs.Alnico
magnets. Freq response:30-16khz, Wrinkled brown paint. All paper cone. In my
opinion these are too old a style for me, but many persons who still have
these models like to listen to them , and they do still sound great if in
good shape. But by now, many have been refurbished with updated
cones/networks to make them sound more up to date. I know that Paramount
Studios, Hollywood Calif. was sending some of these OLD ones into Altec in
OKC just before the factory closed up. Some studios were refurbishing their
old Altec stuff for the sake of originality, and sound properties.(Enough on
that).
Now the VERY popular Altec 604C (which superceded the 604B), was circa: mid
fifties to 1960 or so. It was green hammertone, 16 ohms, 40X90 HF horn in
middle, 35 watts, 50 peak, crossed at 1600 hz, freq response 30-22khz,all
paper cone. Alnico magnets. 40 lbs. This 604C model was a VERY good sounding
and very close sounding to the newer models I am going to mention next. The
604C was also many times updated by the Altec factory to make it into a more
updated model by persons who wanted this done. The 604C was able to handle
more power than the earlier 604's. In my opinion, this model 604C is as
great a model, if in good shape as any of todays speakers, (if not
better).(Next: they only get BETTER):
The Altec green hammertone 604D looked JUST LIKE the 604C. It was out circa:
early to mid 60's. I really do not know what the difference in the 604C, an
604D is? They both sound very alike to me! All paper cones in both. Possibly
a network change to make it smoother at cross-over??
The Altec 604E Super Duplex model circa: 1964-65/late 60's, was light grey
paint, 20-22khz, 40X90 HF horn in middle, 35 watts, 50 peak, "8 to 16 ohms"
Imp, crossed at 1500 hz with newer smoother cross-over network. Alnico V
magnets. 34 lbs. It had a paper cone, but now with an "accordian edge" cloth
surround which by the way, lowered the resonant frequency of the bass cone
some over the previous "all paper" cones. Bass cone free air resonance was
25 hz.
The next 604 in the series was the 604-8G circa early to late 70's. It was
dark grey/black in color, had 40X90 HF horn in middle, 8 ohms, 65 watts,
20-20khz, Alnico V magnets, crossed with newer designed network at 1500 hz.
25 hz free air bass cone resonance. Sensitivity was improved over prior
604's :100 db SPL, 4 ft. on-axis 1 watt input (pink noise band limited from
500-3000khz) The 604-8G basket was changed from previous 604 designs to be
able to rear-mount it if needed, or front-mount could be done. This model
604-8G was offered in a nice system called the model "Seventeen" A vented 9
cubic foot nicely finished beautiful cabinet.
Of these Altec Alnico magnet models of 604's, I like the 604E which I feel
was really nominally 16 ohms, and was the model the 604B,C,D was usually
updated to. The 604-8G is really most likly THE BEST. If you can find a
"pristine" pair of the "8G's, they would be like "Gold".
The next 604's were the 604-8H, and 604-8K. Circa 80's/90's. These were the
latest design ceramic magnet Duplex models,and had radial phase plugs in the
HF drivers, and had more sensitive "SPL" ratings than previous model 604's.
These had smoother HF dispersion , due to the CD "Mantaray" horn in the
middle of the woofer, improved cross-over networks ect. I believe the woofer
frames were larger 16 inch ones on these too.
The Altec 604C,D,E,8G models were, in my opinion "machined" better than the
latest, late 90's ceramic magnet 604's, but this does not mean I don't think
the latest 604's were not "The "Kings" of speakers, which IS what I think!
I once about 10 years ago compared the sound of one Altec M-600 (604-8K),8
ohm circa late 90's,.... to one early 60's Altec green hammertone 604-D, 16
ohm in an Altec 612A bass-reflex utility enclosure. Power was a good 200
watt RMS solid-state amp/pre-amp Dynaco system. Source was Technics CD deck.
The CD is Linda Ronstadt "Mas Canciones". This is Mexican music complete
with all the brass and strings, and her beautiful powerfull voice singing in
Mexican. The speakers were at ear level on-axis. WOW !! the 604-8K with the
Mantaray HF horn was SUPER CLEAR,DETAILED like no other speaker I've heard!
The voice, and instruments were SUPER CLEAR! I stood within four to 20 feet
away in my shop. Sound pressure levels were adjusted to the threshold of me
almost having temporary hearing loss if I kept this up!. (I of course toned
it down after a bit) There's nothing more exciting to me than to just stand
back for a bit, and HEAR what an Altec can do!
Then I replaced the 604-8K with the good old green hammertone 16 ohm 604D,
same set-up,......WOW!!!, the 604D at the same levels did a pretty darn good
job of almost sounding as clear, and loud as the 604-8K!!
(I did NOT run them SO loud to get any distorted sound)
This is where the EFFICIENCY FACTOR comes in ! Only Altecs can be this
uniform as to being very GREAT high-efficiency DESIGNED loudspeakers, even
older models from 30 to 40 years back! This is why I feel Altec's are as
good, and STILL better than today's speakers!
AL
----------

[GM]

Part two:

///////////////////////////

OK, the early 604s, all those with the paper hinge cone,604, 604B, 604C and earlier Ds have the same woofer magnetic top plate as the original 515. It is chamfered and the usable magnetic gap is not as deep as the later alnico 604s-later D, E, G, and H which have the deeper 515B top plate. The early voice coils were almost the same length as the gap and the speaker is very overdamped. It works great in the mids, but any lengthy excursion will immediately take it out of linearity, works great for low power amps. The later units with the accoridion hinge cone have a the longer gap and a shorter voice coil for increased linearity. The early speakers are probably a bit more efficient than the later ones, they all have the same size alnico magnet. The G and H are some better as their cast pot is more magnetically efficient. The best result of a recone of the older units would be to use the later cone and voice coil. The result will not be the same as a complete later unit, probably a bit more efficient, more overdamped, but will have more linearity than the early cone assembly and will produce some more bass with the increased compliance. So you cannot make a C, D, or E into a G. Later Ds and Es will be close. There are very few B horns around, I do believe that they will fit the later alnico units. B horns were fragile and broke, so that compounds the problem. A B model with later parts is a great unit, especially in 8 ohms. Someday we will make a good retrofit horn for the C, D, E, and G models, but only after we finish a few of our other projects first. JIM
----------
It's odd people are finding D's. The D was never a catalog item, officially the 605 had replaced the 604. There however, remained a demand for the 604 and the factory built custom 604D's for studios and the like. From what I have seen, the early D was merely a 604C with n N1600 xover
from the 605. I have seen later original D's with the 416-515B-604E cone in them and was once told by a long departed ALTEC person that the later D was very simlar to the E but painted green like the C. If the speaker has the paper hinge cone, you have an early D. If it has the accordian hinge cone, you--may-- have a later one. Look for the original ALTEC cone number and the older real goopy hinge dope. In reality, the only way to tell if it is a later D is to take out the cone and see which bass top plate it has , as it may have been reconed somewhere along the way by either a proper reconer or ALTEC. Either way it's still agreat speaker. The problem is which way to rebuild them if they need it, and probably only one of them does need it. More fun and games. JIM


-----------
I don't believe there was a distinct break between the 604E and 604-8G since there were evolutions within each model name. Somewhere I have an old spec sheet that refers to the 8 ohm conversion of the 604E as the 604E-8G, which was subsequently contracted to 604-8G. This is why there never was a 604-8F. It looked identical to the original 604E and still used the white 15" frame. The 16" black frame had nothing to do with any engineering requirement. Brazil, in support of a fledgling pro speaker industry, imposed massive duties on imported loudspeaker components. However, they only applied on drivers up to 15" in diameter. Altec upped the diameter of their drivers as a way of avoiding their duties and maintaining a presense in this significant South American market. The ad copy about the greater strength came later Once converted to the 16" black frame, there was a futher change in the 604-8G with the introduction of the tangerine phase plug. Production changed to this device in 1976 with no change in model number. Therefore, 604-8G's can be found with either the older circumferential phase plugs or newer radial phase plugs with no indication on the driver label. I'm not entirely sure when the cross-over design changed, but was most likely introduced with the original 8 ohm E version and before the 16" frame G version.
---------

[whitebroncoii]

I've been reading a lot of threads about 604's lately & it occurred to me....why do they sound so good when all the theory says that they shouldn't?

I mean, most say that 1500Hz is way too high to cross over at.....that you need multicell horns or the big radials or Mantarays to get the best sound from the top end driver......that 2 inch, or at least 1.4 inch, is superior to 1 inch throat drivers. The odds just seem to be stacked against this speaker, yet all reports are that it is a fine sounding unit.

With regard to the actual driver....is it a 416 driver?....and what is the top end driver...a 902? an 802?

Just curious to see what yars think.

I had a very interesting discussion with an EV engineer once. When he finished measuring the 604-8G for AcoustaCadd, he called to tell me how bad the coverage measured. He then went on to say he thought the 604 sounded wonderful.

This story is to illustrate a couple of things . . .
First: You will not know what a speaker sounds like from looking at the specs
Second: The 604 is a near-field monitor and sounds best from 10 or 12 feet away

"1500Hz crossover is too high"
The LF of an early 604 is very similar to an early 515. Later the LF was a bit of a combination of 416 and 515 (per an Altec engineer in OKC, about 1990). The 416 and 515 have very light moving mass and are relatively "fast" or accurate when a signal is applied. They are fast enough to stay up with the 802/902 at 1500Hz and deliver a warmth that would be missing at a 1000Hz crossover. This lack of warmth in the HF driver is likely a function of the very small horn.

The A7-500 gets away with the same type components crossed over at 500Hz. I suggest the much larger HF horn is supporting this success. I also would point out that a stock A7-500 is very "fat" in the mid-range and needs lots of work before it is usable as a hi-fi speaker. Not so with the 604.

604 Duplex vs Two-way . . .
The biggest issue here is that the ear can easily detect, from 10 feet away, that there is a distance between the HF and LF on a two-way system. As you get a further away this is no longer an issue. The 604 Duplex has the HF and LF sources together.

"that 2 inch, or at least 1.4 inch, is superior to 1 inch throat drivers . . . "
As with most things, there is some truth in this thinking. At high sound pressure levels the 1" driver starts to break up and distort before the larger driver. Some people have morphed this into a flat statement that the larger driver is better. My comment is; it depends. A larger driver is my choice when high SPL is needed. If I were building a home hi-fi speaker and was bound and determined to use a 500 - 600Hz crossover, I would want to use a larger HF driver on a medium-to-large horn. My A700-8A speakers are loaded with 902/515G and crossed over at 1200Hz.

Many people base their beliefs on facts that sometimes do not apply to the need at hand. Others are simply defending their decision to use this driver and that horn.

[whitebroncoii]

Part two:

///////////////////////////

OK, the early 604s, all those with the paper hinge cone,604, 604B, 604C and earlier Ds have the same woofer magnetic top plate as the original 515. It is chamfered and the usable magnetic gap is not as deep as the later alnico 604s-later D, E, G, and H which have the deeper 515B top plate. The early voice coils were almost the same length as the gap and the speaker is very overdamped. It works great in the mids, but any lengthy excursion will immediately take it out of linearity, works great for low power amps. The later units with the accoridion hinge cone have a the longer gap and a shorter voice coil for increased linearity. The early speakers are probably a bit more efficient than the later ones, they all have the same size alnico magnet. The G and H are some better as their cast pot is more magnetically efficient. The best result of a recone of the older units would be to use the later cone and voice coil. The result will not be the same as a complete later unit, probably a bit more efficient, more overdamped, but will have more linearity than the early cone assembly and will produce some more bass with the increased compliance. So you cannot make a C, D, or E into a G. Later Ds and Es will be close. There are very few B horns around, I do believe that they will fit the later alnico units. B horns were fragile and broke, so that compounds the problem. A B model with later parts is a great unit, especially in 8 ohms. Someday we will make a good retrofit horn for the C, D, E, and G models, but only after we finish a few of our other projects first. JIM
----------
It's odd people are finding D's. The D was never a catalog item, officially the 605 had replaced the 604. There however, remained a demand for the 604 and the factory built custom 604D's for studios and the like. From what I have seen, the early D was merely a 604C with n N1600 xover
from the 605. I have seen later original D's with the 416-515B-604E cone in them and was once told by a long departed ALTEC person that the later D was very simlar to the E but painted green like the C. If the speaker has the paper hinge cone, you have an early D. If it has the accordian hinge cone, you--may-- have a later one. Look for the original ALTEC cone number and the older real goopy hinge dope. In reality, the only way to tell if it is a later D is to take out the cone and see which bass top plate it has , as it may have been reconed somewhere along the way by either a proper reconer or ALTEC. Either way it's still agreat speaker. The problem is which way to rebuild them if they need it, and probably only one of them does need it. More fun and games. JIM


-----------
I don't believe there was a distinct break between the 604E and 604-8G since there were evolutions within each model name. Somewhere I have an old spec sheet that refers to the 8 ohm conversion of the 604E as the 604E-8G, which was subsequently contracted to 604-8G. This is why there never was a 604-8F. It looked identical to the original 604E and still used the white 15" frame. The 16" black frame had nothing to do with any engineering requirement. Brazil, in support of a fledgling pro speaker industry, imposed massive duties on imported loudspeaker components. However, they only applied on drivers up to 15" in diameter. Altec upped the diameter of their drivers as a way of avoiding their duties and maintaining a presense in this significant South American market. The ad copy about the greater strength came later Once converted to the 16" black frame, there was a futher change in the 604-8G with the introduction of the tangerine phase plug. Production changed to this device in 1976 with no change in model number. Therefore, 604-8G's can be found with either the older circumferential phase plugs or newer radial phase plugs with no indication on the driver label. I'm not entirely sure when the cross-over design changed, but was most likely introduced with the original 8 ohm E version and before the 16" frame G version.
---------

There is so much here that is questionable . . .

[GM]

Dunno, my 'hands on' 604 duplex experience is limited to the 'E' and regrettably, I didn't save the complete posts, so don't know which forum they were posted on, but IIRC most (all?) were from Todd White, Jim Dickinson, Steve Schell.

If you have more accurate info, please add/correct............

GM

[joyspring]

I've been reading a lot of threads about 604's lately & it occurred to me....why do they sound so good when all the theory says that they shouldn't?

I mean, most say that 1500Hz is way too high to cross over at.....that you need multicell horns or the big radials or Mantarays to get the best sound from the top end driver......that 2 inch, or at least 1.4 inch, is superior to 1 inch throat drivers. The odds just seem to be stacked against this speaker, yet all reports are that it is a fine sounding unit.

Like everything in life, loudspeaker systems are a balance of trade-offs; the 604 series are not excepted from this rule.

The 604 being a point-source offers excellent stereophonic imaging (phantom images) at short-to-medium listening distances.

Its deficiencies (the older `vintage' units in particular) are in two areas: on-axis frequency response and - more importantly - off-axis power response.

While passive or active filters and a more modern horn (for instance, UREI) ensured a relatively smooth on-axis frequency response, the off-axis behaviour is the 604's weak point.

Ideally, a loudspeaker system will have a flat power response -- otherwise, the best compromise is a smooth rise in directivity with frequency. This is why two-way systems utilising 15" drivers are crossed over at 500 hz -- this is done to match the rising directivity of the LF driver with the typical 90 deg. horn. This was also a strong motivator for development of constant-directivity horns.

As you've alluded to in your post, the 604 cannot be fitted with a horn that has a low enough cutoff to match the directivity between the LF and HF without shadowing of the LF cone so the resulting power response is not smooth with an abrupt change in DI (directivity index) at the crossover point.

The 604s are only accurate on-axis in a rather small `sweet spot' and must have the reverberant field treated to suit their uneven power response. Chips Davis' LEDE (Live-End Dead-End) control rooms in the late-70s / early-80s utilised the UREI 800-series monitors effectively in such a manner. However, further research in control rooms / monitors moved towards more live, natural, diffuse and spectrally-balanced reverberant acoustical treatment and control room monitors that have an even, smoothly rising power response (i.e. - JBL 4430/4435).

All said, personally I like the Duplex drivers as the 605A was my first loudspeaker and I've used (and still use) the 604-8G / 8K-equipped UREI Time Align monitors throughout my career. They sound good to me and I can rely on them to make aesthetic decisions.

So yes, the 604s can and do sound good; they were great for pre-1980s technology and acoustical research. If you're a vintage enthusiast, I'd go with a brand-new 604 from GPA. Be advised however that accuracy and integration into a listening environment for the aforementioned reasons are not the 604's strong points so if those criteria are important, it's best to look at more modern alternatives.

BobR

[Cal Weldon]

Quote from GM's post:

"The big improvement in 604 crossovers, in my opinion, came with the mid-frequency EQ Altec introduced with the 604-8H. Not only does it sound different than the 604-8G, its EQ technique can make all older 604s sound much better too!"


Couldn't agree more.