Billfort's Altec 604 ramblings


Staff member
OK, now you got me started. Here's an old link to where I started with 604s most of it still seems relevant.

Since first hearing Altec 604s, I've been hooked they just have this amazing mix of strengths that let me see past their shortcomings and for low power SETs in regular sized rooms, I find them hard to beat and after 12yrs of listening to alternatives at shows, in showrooms and others systems, I can't think of anything I'd trade them for.

They are good at;
  • imaging their point-source design just gets this right with lots of depth and accuracy
  • dynamics a major one here, Altec 15" woofers and horn loaded compression drivers excel at this.
  • Sensitivity my G's are about 100db/watt efficient which gives you lots of amp options like like the low power SETs I love.
  • Tone I don't know if it's just the Altec driver recipe or some kind of alchemy thing going on with these alnico drivers and the simple SET circuits I use but they seem to get this very right.
  • Design & use flexibility kind of a 'sort of' here but they DO work in regular sized rooms (I once used mine in an 11 x 12 room). They are big drivers and you won't take them far in a small box but if you are creative and use something like a corner cabinet, well, mine took up less of the room pushed into the corners than the stand-mounted mini-monitors they replaced. I have yet to hear a more conventional partially horn loaded speaker that works as well as these in small to midsize rooms.
Not good at;
  • being small they are huge, I get it.
  • Deep bass even the ones likes the Gs onward that are more TS loading friendly are only going to get down to the mid 30s, and that's in huge >9cu. ft. boxes.
  • Mid-range performance a huge 'depends' here and through careful cabinet & crossover design and a good dose of tweaking all the way from the drivers through the system to the room, I feel they can have stellar mid-range. But compromise on the cabinets, crossover, hook them up to the wrong system or use them in a bright, untreated in the forehead, in-your-face, fatiguing, all kinds of bad stuff.
  • Treble extension. - these are 1" compression drivers that just don't play that high the newer flavors with the Tangerine phase plugs are 'supposed' to go higher and crossover design helps here but don't expect extended highs beyond say 15kHz (for Tangerine Gs anyway). To me, they are just right and some try 'add-on' tweeters to go higher but I've never liked the results kind of hurts the 'whole-ocity' (Gizmo Rosenberg term) of the 604.
  • Price and availability they are highly sought-after antiques, and since the results seem to prove out 'you get what you pay for', you usually have to pay. Luckily, they are still being made the right way by Great Plains Audio and their versions might even be better than the used/abused ones out there so this is a very good thing - but still expensive.
My focus is a little limited here towards the 604-8G (which I own), 604E which I've heard extensively and maybe to the 604-8H which I've heard a few times. IMO all the goods and bads above apply to these 3 flavors to varying degrees but they are all great foundations and they all use alnico magnets which I think may just have something to do with what I like so much.


The 604E is pretty plentiful out there and I love these especially in the mids where I think they might just be the best of the lot. They don't go as low as the 8Gs and may not be as extended on top as a Tangerine'ed G or H, but they are close, and hey, those mids! I heard these in massively built (1-1/2" thick HDF) cabinets and nicely done Baltic birch 620A cabinets and I think the BB 620As (or a derivative) is the way to go the HDF just seemed to knock some of the life out of them. I haven't seen a 'Markwart' version of a crossover for these but would seek out or build a Mastering Labs crossover they sound incredible with the ML.


The 604-8G is where I live and most of my opinions on 604s should be taken in this context. I've built a complete system and even a room around getting the most out of this version while pushing back the negatives so I'm a little biased. I think these strike a nice balance between the syrupy sweet Es and 'technically' better performing H but I don't see any of these as the winner they are all good. Mine might be a kind of bastard child actually they have the earlier compression driver covers of the E but have the 'later' Tangerine phase plugs, while most of the Gs I've seen have the same covers as the H below. Not sure what this means but since I bought these off a guy who bought them new, I know they are something 'factory'.


In the H we have the newer Manteray true horn not the sort of 'fake sectional' of the E & G where the section vanes don't go all the way back to the throat. I would jump at a pair of these as they might just have the best performance potential and I've certainly liked what I've heard from them.

Great Plains Audio.

If building a pair of 604 speakers, 'used' might work out great it sure did for me. The above are rare alnico classics though that can be a real crap-shoot (especially now that the internet means supply-and-demand pricing) but Great Plains can keep them alive. They can re-charge those alnico magnets, re-cone the woofers with the correct parts and materials and supply the right diaphragms (I have GPA diaphragms in mine).

But if I was starting new, I would probably consider buying the brand-spanking new GPA 604-8H III (FerriteV magnets) or what would be my preference the alnico 604E Series II. I think I'd even consider the GPA crossovers for these but I'd leave them outside the cabinet I'd want to at least be able to try a Markwart crossover, which have been a key ingredient in what I now listen too. Not sure of the current pricing from GPA but I think new drivers and crossovers would be around $2k the same I bet you 'd pay for good (and risky?) old drivers on the used market.

I'll go on about cabinets and crossovers next if you can stand this rambling.


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Staff member
Ramble on Bill. Thus far this has already been one of the most concise and informative posts I have ever read about the 604's. I look forward to learning more.


Active Member
I'm still tempted to try a pair one day. How much and what kind of room treatments do you feel are necessary for these speakers?


Staff member
I saw my first pair at a shop in Akron around Christmas...they are so BIG! I wasn't able to hear them and have forever been curious. Many people who's opinions on audio I greatly respect, respect them greatly.


Staff member
For 604 cabinets, my experience is a little limited but I've certainly ended up with some preferences and a little success so I'll share my thoughts. My opinions are again limited to the drivers mentioned above and since I have 604-8Gs, everything is aimed specifically at them from a Thiele/Small spec perspective.

My drivers came in home-made plywood cabinets which I think where based on the 620A but a little narrower (although not as narrow as the Stonehenge). They are long gone and I never noted the actual size but I think they had the drivers at the same height as 620A and had about an 8cu.ft. volume. They were made decent enough but were kind of ratty looking and the rectangular shape didn't work real well in the small (11 x 12) room I had at the time so I figured I'd try something to get some space back and maybe gain a little performance.

I did a bit of listening to 604 E, G and Hs in various cabinets and came to some conclusions; I liked the driver up at ear height, bass got good with larger volumes and maybe 40Hz tuning, and I found baffle width made a pretty significant difference in balance. Open baffle mounting was briefly tried (hacked up my old cabinets) and although it initially impressed with a nice, open sound, I felt it hurt one of the 604s major strengths - dynamics - so I ruled it out.

I ran the 604-8Gs specs in winISD and played with the volume and vent tuning till I arrived at this;

No big surprise as this essentially confirmed what I was hearing; 9cu.ft. foot volume for decent bass response, 40Hz vent tuning and with the wide front baffle I liked - I wanted a 620A.

I wanted to vary from this however in the following areas;
  • I wanted the driver up at ear level; the best I heard 604 imaging was when they were up around 36-38" high - bass was a little better lower but I felt it hurt imaging a bit.
  • Wanted the cabinets to be 'corner friendly' for my little room but not corner only - figured they may be positioned conventionally someday so wanted to cover both (and glad I did - they aren't in corners any more).
  • Wanted a large, rectangular vent area to avoid 'huffing' - I sometimes hear it and didn't want it.
  • Did not want that large vent in the front baffle; I sometimes think I hear higher-band 'noise' coming from ports and didn't want that messing with that point-source mojo I was hoping to achieve. Since these where going in corners initially, the back was out, sides good, so split the calculated area in 2 and put them low on both sides.
So into CAD I go; driver up at ear level and played with shape & size until I was able to get the internal volume I was after, that wide front baffle, and utilize 5' x 5' 19mm sheets of Baltic birch and mucho expensive 4' x 8' sheets of wood backed figured cherry veneer ( with the least amount of scrap. It took a while...:)



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Staff member
Construction is all Baltic birch plywood as a direct comparison at a friend's place (604Es in an extremely good system) between 1-1/2" thick HDF 620As and ¾" bb-plywood 620As convinced me the bb sounded more alive and dynamic, the HDF kind of thick and dead. Lots of mortised internal bracing, dadoed corners, glued/air-brad/clamped construction, veneer glued on with solvent-based contact cement.

We used a well-tuned table saw, pretty high-quality plunge router, sharp cutting tools and a few steel templates (punched out on a CNC turret press) nothing too fancy but not basic garage tools either. I didn't produce detailed drawings (other than what I've attached here) but did have the full-scale CAD drawings on a laptop in the shop to provide all the spot-dimensions we needed, when needed.

Some veneer trimming with the router, careful knife and rasp work on those back corner edges, a bunch of sanding, several coats of Watco Danish oil and a few layers of Goddards Cabinet Makers wax and I had a very nice finish. T-nuts and socket-head cap-screws for the drives, 3 Parts Express spiked feet and a friction fit grill MDF router cut with a circle template, rat-shack grill cloth and rubber gasket material to ‘grip' the driver perimeter.

I didn't know where I'd end up with crossovers so took the easy way out just led the thin-gage, solid core copper speaker wires out one of the vent holes, where I soldered them directly to the crossovers (the best connectors being ‘no' connectors). I started with the stock Altec crossovers sitting on the floor beside the speakers and yes, it's a little inconvenient to move and disconnect them but just a quick pass with the soldering iron and it's done.

Very happy with the results they look pretty enough but sound great and the better my rooms and systems have gotten around them, the more I like them. I built some wood moving protectors for them (blanket wrap, wood contraptions and band clamps) so they've successfully been moved between 4 rooms so far without any damage.


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Staff member
They've been in 11 x 12, 12 x 15 and now 12.5 x 21 rooms and the ‘shape' has proven flexible and perfect for finding the right location to load the room. In the current room, they started in the corners but are now out in a more conventional location made possible by the need for less bass loading a pair of Altec 416s in the corners now take care of that. These were a little harder to roll than a rectangular 620A might have been but room flexibility through the turbulent times I've moved through these last dozen years have made these well worth the effort.

11 x 12 first room

Current 12.5 x 21 fully treated, dedicated room


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Very nice work, billfort. :cool:

I want to pull my 604b drivers out of the Karlssons and try them in the same type of OB as my avatar.


Staff member
And then there is this a Markwart crossover with midrange EQ. I like to view this failed bomb-making experiment looking thing as a work-in-progress but the reality is that it's sat in this unfinished state for several years and I'm not in a big rush to mess with it.

This thing just sounds 'right' with these speakers. If I look at those weaknesses mentioned above hot, aggressive midrange, limited treble extension and tricky transition from a cone to compression driver right in the heart of the music I see this piece as the major player in pushing them back.

Compared to the stock crossover, the mid-range with this is smoother, sweeter, SET>alnico goodness oozes forth without the occasional pain encountered with the stocker, particularly with mediocre digital recordings. With the mids more in balance, the treble shines through more, removing any need (IMO) for add-on 'supertweeters' and such that I always felt messed up the point-source magic of these drivers.

Mating a 100db efficient woofer with a 110db efficient (?) compression driver is not so easy to do in a seamless manner the point-source thing helps, as does the wide front baffle but this crossover just seals the deal. When I had 19s I often 'heard' the transition from cone to horn here I don't and it's very cool that this mix can pull this off without hurting the tone and dynamics I love with Altec drivers right on through that midrange.

Component mix is a little different but pretty economical. Caps are all paper-in-oil motor runs with one Solen to get to the right values. I heard motor-runs on several occasions in this type of system and love them so bough a bunch surplus and cherry-picked the closest measuring ones. Chokes are copper foil Alpha Core, cheapie sand-cast resistors and my secret-sauce old stock Western-Electric thin-gage copper, cotton covered wire. I'm using this wire from the amp to crossover and through to those terminal strips, still using single strands of CAT-5 from the crossover to the drivers.

Could this thing be better? I have to think so yes.
  • I'd like to try Mills wire-wound resistors in place of those sand-casts.
  • I don't use the level control pot and really want to get that thing out of the circuit need to measure the setting I've arrived at and replace with some Mills.
  • I using brass terminal strips here (yuck!) and need to go with my favorite connectors no connectors and solder everything directly.
  • I have more of the wire I'm using from the amp and want to use it to the drivers but that means pulling the drivers.
  • I think I can come up with something pettier too...
And I'm not sure if I should mess with those Absolute Sound magazine 'footers' either maybe a little double-blind testing next time Erik is over.


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Señor Member
Whatever you do -- just don't try Stereophiles under there...


As I think you know, Bill, my 604Es came with MasteringLabs XOs. Those certainly fix the hot midrange; the midrange of my Duplexes is, by my hardly unbiased estimation just superb. The HF extension remains an issue -- but I have (shhh!) gingerly augmented mine with a coupla Fostex horn supertweeters crossed in very high and padded down a bit; to my ear, the results are value-added (probably completely anathema for the purists, though, of course).

I, too need to replace the variable pads with fixed pads... one of these days.
Not sure I am ready to give up on the audiophile clipleads, though.

IMG_0340 by Mark Hardy, on Flickr
IMG_0341 by Mark Hardy, on Flickr


Staff member
As you know Mark, a friend of mine has 604Es with Mastering Labs crossovers and they may just have the sweetest mids I've heard. That might be flavored with the fact that he is one of the most talented SET builders I have ever heard the wares of but none the less, those Es are spectacular. If I had Es (and I'd be very happy to own them), I'd use Mastering Labs crossovers on them.

I think my hard-ass thoughts on add-on tweeters is based on the the G and H really, which 'to me' seem to play more extended on top. With Es, I'd try them and the last time I was down to see my buddy, I noticed he had a pair of Altec 3000 tweeters sitting on top of his maybe. :)


Señor Member
Actually -- that I had forgotten; sorry!

Gary Kaufman has said categorically that he's never heard supertweeters mate well with Altec horns. Gary knows his Altec hardware (not just their speakers) and he knows good sound -- so there's no doubt in my mind that it's, at the very least, extremely challenging... in other words, I am 100% sure my little T90As with first order XOs aren't the magic bullets (no pun intended), but for me, at least, they are doing more good than harm as currently implemented (and, yes, they really are still clip-leaded in place, mostly due to my extreme laziness).


Staff member
But wait, there's more. :)

One of the diaphragms in the compression drivers went out in the past so both have been replaced with the OEMs that Great Plains sells. Since I'm only using low power amps on these, I left the phenolic loading caps out and lined the inside of the back covers with heavy felt. This again took a little ‘bite' out of the midrange with no downside that I could notice.

I've had flooring friendly feet on these and even left them on carpet for easy sliding around to find their sweet-spot in the room but I'm always in for a little tightening up in the bass and a touch more image focus when I screw in the spiked feet.

I really like these in the corners as it brings the lower bass into better balance and even though you do pay a bit of a price in image depth, it's a surprisingly small price maybe that point source thing again. You often see old pictures of these drivers soffit mounted in studios and I get it corner placement sort of emulates that and they work very well that way.

Adding ‘bass augmentation' in the form of a pair of Altec 416A woofers has worked surprisingly well. The 604s are now out in the room a bit for a little better imaging and since they run full-range with no additional crossover, there was no ‘hurt' put on their well sorted state just a little less bass loading from them. The 416s (on a Behringer DCX2496 crossover/EQ and Harmon Kardon 870 SS amp) seem to have similar tone and dynamics as the 604s so make for a nice, cohesive mix it just sounds like 604s with a LOT more bass potential.

Less emphasis on squeezing the most bass out of the 604s has also provided more options for fine-tuning the amp balance with them. I used to think 300Bs where about the minimum power-wise (I like big dynamics) but now, the 2A3 is really the sweet spot. Even in that 2A3 amp I can shoot for a little more upper bass/midrange sweetness which comes with the Jensen paper-foil-in-oil caps and old-stock RCA tubes had to trade some of this off when searching for bass.

Even the 45 tube (my favorite within its power limits) is now viable and oh-so nice with some kinds of music blues, jazz and female vocals are done as good as it gets in my room when using a good 45 on these speakers.

So it's low power SETs, a separate SS based sub-system, a tube pre-amp, copper thin-gage wires, a silky-smooth moving coil cartridge into a tube phono-stage and a very ‘analog' sounding digital front end based on high sample-rate DSD (SDM5.6) a whole system wrapped around those 604s playing to their strengths and trying to ameliorate their weaknesses.

The room is below-grade, has concrete block walls behind the drywall and the speakers couple through spikes to a poured concrete floor this room does very good bass. Extensive treatments in the ceiling and mid-range focused acoustic panels at first reflection points, a favorable LxWxH ratio and decently balance reverb time again, all focused to helping the good and push the bad back with these drivers.

I've tried other speakers in there AudioNotes, Tannoys, my old DQ-10s, but at the end of the day, they didn't have a chance I like these Altecs and have totally stacked the deck against anything else in there which is just fine with me.


Active Member
Very cool thread, Bill. Thanks for taking the time to post.
Are the 416s in the pics, I don't see them? I run 416s in ~10 cu/ft cabs and get pretty good bass. I read your strengths and weaknesses section, and what your speakers seem to do well that mine don't is imaging/soundstaging. Lucky for me that that particular aspect is not too important to me, although when I hear a system image well it sure does add to the enjoyment of it.

(I saw your link to Luther's website - I didn't know you had any connection to him. Great about a guy who isn't afraid to try things out)


Staff member
Yeah, they are there in the last pic Mike, in the shadows behind the 604s. Never thought 15" Altec 416s would go unoticed but...did I mention those 604 cabinets are big? :)

The 416As are really not in the right cabinets and I have to address that someday but they sound pretty good with some EQ and I think do a nice job of making the 604 presentation better without drawing any attention to themselves. Might have a lot to do with them being cut from the same cloth so-to-speak as the 604-8G so things like tone, speed, 'snap', etc. are very similar.

It really has been nice to be able to experiment and tweak these on their own circuit (highly configurable crossover, EQ, SS amp) without affecting the 604s that I spent so much time getting right - truly an enhancement to the big picture with no downsides I can think of. They really load the room nicely placed where they are too which lets me get the 604s out where I can really exploit the imaging thing - kind of the best of both worlds.

And yes, I do know Luther - met him about 12yrs ago and we used to see each other every year - he IS a great guy and wish I could take in one of his meets someday, he always has very interesting rooms full of equipment.


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Staff member
Yes, 9cuft internal volume, 12.5' x 21' room (pic above). It's a dedicated basement room with 1 door so it actually seems pretty roomy in there, or at least as roomy as can-be with 4 Altec 15" speakers in there. :)


Active Member
Reason I asked is because I'm wanting to do new cabinets for my EV's. Just making sure my room would be big enough to contain such a beast. The room in my basement is roughly 12' x 18'. I'm throwing around the idea of running my 12TRXB's in some 8 cubic foot sealed cabinets. I ran some sims in WinISD and it seems that's the sweet spot between cabinet size and low end extension. There's a nice slow roll off of the bass. 50Hz at -3dB and 32Hz -10dB. Going to get ahold of my carpenter buddy and see what he can cobble together for me, and for how much. Going to get on the horn with a few lumber yards later and see about prices on some Baltic Birch.