Altec 604c crossovers? bi-amp?

Hi Everyone

A little while ago I posted this on audiokarma and I was encouraged by my self-appointed "speaker guru" (much to his chagrin) to post the question here, as I may have more success

this is the thread at AK
Altec 604c crossovers?

so it looks like I have stumbled into a pair of Altec 604c's with Altec N-1600A crossovers, and I'm over the moon about my luck. Since I got the first one I have been reading everywhere about how best to hear what these drivers have to deliver. My plan at the moment is to put them into EV Empire cabinets which are available locally until I get the ability to build a pair of "Billfort" cabinets or similar (and am able to fit such into my place). The Empire cabs are just at the edge of what can feasibly be put in my rather small place, I would lift them off the ground by about 20"

here are the specs on the Empire Cabs EDS.pdf

So from what I am able to gather from reading, 604's are markedly improved by updating the crossover, a la Jeff Markwart designs. I've done a huge amount of reading (My eyes are a little "crossed over"), and maybe have missed something - but it seems all the designs I have found are for other variants of the 604, and not the C - I found one experience suggesting that using the published plans for the B with the MF EQ was successful with the 604C.

I exchanged a couple emails with Jeff Markwart, who was kind enough to take an out of the blue cry for help from a complete stranger, but he suggested that he didn't think the B crossover he suggested would work as laid out in his plans, he pointed out "While the acoustic centers of the B and C are in same locations, the differences of the horns and woofer responses of a B and C are enough that a B crossover would not be optimized for a C. Close, yes, but not optimized. You probably would be able to detect an audible difference between them. It really would take a bit more engineering and listening to know"

I do know that Werner Jagusch does offer Autoformer Crossovers for the 604c on ebay, but those are honestly somewhat out of my budget at the moment

this is all complicated by the fact that I am not that technical a guy - OK, all honesty, not technical at all, and would be relying on someone else to build me such a crossover, as long as I can find things like a schematic, parts suggestions etc.

Can anyone point me in the right direction?

After a little more thinking, my plan at the current time is to bi-amp the 604c's with a Rane AC22S Crossover, using Dynaco MKIII's for the woofers. I'm looking into local possibilities for the tweeters - there's a fixed up Maggie 8802 locally and I'm also fixing up a Heathkit AA-40, which might be a possibility as well

I'd welcome thoughts and advice on how best to use these beauties

Even just listening to them "naked", just resting on the floor out of cabinets with the stock crossover was pretty satisfying, but probably not a long term plan




Junior Member
here is my AK altec 604 thread:
Altec 604C Project; and a true AK hero!
mine were reconed as 604Es.
EarlK is super super knowledgeable. i would follow his advice.
I built my own crossovers (see posts starting w #21 in my thread). sounds like that is not in your current skill set (soldering is easy!). so earl is saying use the crossovers you have for now and try to get them updated (new caps). where are you located? must be some tech who could do that job.
you will probably want a sub with the empire cabinets. billfort is on this forum so you can PM him re the plans for his cabinets.
Thanks! Yes my skill set is very limited. I do have various subs around so that is a possibility if more bass is needed (but I am not really a big bass guy nor do I listen to very bass heavy music)

I'm just north of Chicago and I do have access to good techs, which is a possibility in terms of the re-capping and why I was looking around for crossover designs (so that someone else might build for me)


Staff member
Hi Zim, welcome to HiFiHaven! I have a busy weekend ahead but will share my thoughts on all this when I get a minute.

Cool to hear you are considering my cabinet design - there are few of them around now and I think if your 'want' list is similar to what I published on that old (maybe 15yrs ago?) webpage, you might find they hit the mark. Actually, 604s in those cabinets have been a 15yr constant in my system and they aren't going anywhere.

I've never seen TS parameters for the Cs so don't know if the 9cuft/40Hz tuning I used for my Gs would work with them, but I will say that the shape I settled on worked amazingly well in a small (11 x 12) room, providing you can free up the corners. As huge as these are, pushing them into what were mostly unused corners gave me more living space in that little room than I had with the stand mounted mini-monitors the Altecs replaced.

I bounced around a lot on crossovers including some side trips into active and will share some of that later, but in a nutshell; in an analog focused system like mine in a room with extensive passive room tuning, the Markwart designed passive is what I like on the 604s and where I'll be staying.


Señor Member
Passive crossovers are pretty easy to build, even for a non-DIYer. They're also very safe (no high voltage/high current involved) -- one only needs to be careful when wiring things together to avoid accidental short- or open-circuits to be "seen" by the amplifier.

One could even get away without soldering the components, using either wire nuts or screw terminal strips, e.g., and still feel good about oneself :)

... and of course, there're always clip leads.

You've seen my Frankenaltec crossovers, yes? :)

DSC_9782 (3) by Mark Hardy, on Flickr


Welcome to The Haven, @zim bida :)

I just found a match for my 604C and will be embarking on a similar journey.

Luckily, I have a 14' x 25' room and so will probably just go directly to the @billfort cabinets. I have some nice Karlson enclosures for the 15" subs.

If I didn't have room for the @billfort cabinets, I'd either go with the @je2a3 JELabs Open Baffles or the Altec 612 or 620 cabinets.


As far as crossovers, I've never been a fan of bi-amping in the middle of the frequency range when using different amps for the lows/mids and mids/highs. Subs? Sure, but I still run the main speakers full range and only use the active crossover as a low pass filter.

Passives for the 604? I defer to @billfort and his years of experience with the 604. Yes, there will be differences between his 8Gs and your Cs but I am sure that those differences in characteristics can be accounted for by the experts in the dark arts of passive crossover design (like Jeff Markwart).

And, if you do have to use clipleads, please make sure that they are official @mhardy6647 approved clipleads. ;) ;)
Two things - If you're going to bi-amp, consider a MiniDSP with a 2-way crossover plugin. The basic unit is $95 and offers huge adjustability. Secondly, the HF compression driver is quite sensitive - you will want a very quiet amp, and try before you buy if at all possible.
Thanks Everyone for welcomes and the suggestions this is exactly the kind of suggestions I was hoping for.

@mhardy6647, I hadn't seen those crossovers - they offer encouragement for persons with my abilities

@TubeHiFiNut, thanks for those enclosure plans, one of my 604c's came in one of those barzilay cabinets, but that didn't seem adequate - the other came in an Altec 606, though incomplete and beat up, but I'd love to have found a pair, and if I had.... well, I would have somehow figured a way to get it in my house

@billfort, I'd love to hear your experiences with active crossovers and why you settled in on the Markwart design, oh and thanks for those cabinet designs you've put up - I think at some point I'd like to get there as in terms of footprint they actually won't be that much larger than the EV just going more vertical

@AndyN I was looking into MiniDSP as a possibility as well - does the 2-way crossover plugin have the ability to time delay? How is the sound quality vs analog crossover units?
Yes, time delay up to 7.5 mSec. For reasons lost to the mists of time, I'm running my 605s with 0.42 mSec delay on the LF channels. Sound quality is acceptable for my low standards. In the analog domain, I've tried both the factory n1600 crossover and a custom-built-from-my-junkbox Markwart. However my room is an open-plan family room with minimal acoustic treatments; I'm one of those "bits is bits" heathens who also believes room quality outweighs magic wire by a wide margin.

Another thing to mention: To wire those properly in phase, the "1" connector on the woofer is positive, whereas the "2" connector on the HF is positive. It's an Altec carryover of an old WE practice about numbering terminals so positive voltage on 1 yields movement of the coil into the gap. The net effect is that the specified wiring launches an in-phase wavefront.


Punker X

Junior Member
A couple of thoughts... Pretty sure those original crossovers are potted in a black goo and would be major pain to recap.

I've tried bi-amping and was never really satisfied with the outcome.

Dgwojo has his 604's bi-amped, using a digital crossover. His sounds really good, but uses to identical amps with individual volume controls for each channel.

I think the results of Markwart crossover that is not quite ideal will sound better than going active with mis-matched amps. I come down firmly in the KISS camp, "Keep It Simple Stupid".


Senior Nobody
I would encourage you to go the Minidsp route initially.
It is relatively cheap, and will take a short time to get pretty good results.
Then you are up and running and can find your long term game plan from there.
I have one I bought initially for subwoofer duty and when I first got my Altecs I used it to find the crossover point I liked best, then ordered frequence boards for my Merchand tube xo.
Hey Nate!

Thanks for all the suggestions folks - MiniDSP does look like fun!

@AndyN - thanks for that tip on the wiring - I would never have thought of that

I've set aside today to move stuff around the house and play with speakers so I hope to have these beauts up and running in the Empire Cabs with the stock crossovers today and at least listen without tinkering to start off with.

To be honest, these sounded pretty darn nice even just sitting on the floor without cabs


Just Call Me Junior
To be honest, these sounded pretty darn nice even just sitting on the floor without cabs
I tested my 8G's sans cabs for the first time in '85 or 6 the same way. Blew my mind, and I was completely enamored of them.

Welcome the 604 club! I'm looking forward to reading where they lead you...


Señor Member
FWIW, gratuitous, ego-centric interjection on naked Duplexes. :)

My first exposure to Duplexes was a bare pair of 604Cs (with their stock Altec XOs) sittin' on the floor at Gary Kaufman's house, playin' Ella through one of his DIY SE DHT amps (I don't remember which one any more), He had just gotten them from an eBAY auction and said, in essence, "hey, let's try these things!" -- I was hooked in moments.

Pretty much the same reaction I had the first time I heard a pair of ESL-57s.

Flashbulb memories of both.
Superb midrange from both.


Senior Nobody
There is a pair GPA 604's on DIYaudio for a reasonible price today
If didn't have to write a fat check to uncle sam next month I would buy them
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So I got things set up and the 604's clothed20190311_154641.jpg


I had other stuff I needed to so this afternoon, but instead spent most of it thinking "I wonder how this one would sound on these" and listening to a lot of favorites. Vocal harmonies, in particular are amazing.

Now if these are going to be substantially improved with crossovers and different cabinets, I may just have to do a Wayne's World style "we're not worthy" bow

I'm a pretty happy camper