View Full Version : Questions about enclosure internal volume and tuning with 604 speaker

05-23-2017, 03:51 PM

I have some 12 cubit ft. (internal volume) 1" MDF sub woofer boxes, made for 18's. I also found a pair of empty old Altec 612 cabinets.
I have a pair of used GPA 604 type speakers, and plans (schematics) for a XO both from GPA and Jeff Markwart, both have 2 L-pads and are similar,
but JM's claims to correct phase. ? Any preference or suggestions? Questions: Is the stock port size on the 612's "ideal" for a 604, or is it advised to tune it somehow? Can I use the 12' box's for a 604? If yes, how would I tune it, or what math or port size is applied? Any advantage to this? Can I get "better" or lower extension in the bass? Could I use an 18" and the 604 together in the same box? Biamped or ? Or is the 612 "almost as good as it gets" ?

Any advise appreciated.

05-24-2017, 07:51 AM
We have a number of diehard 604 fans on this site. I'm sure they will be along to answer your questions as soon as they see your posts.

You should also post your question at the Altec Users Board:


And at AudioKarma:


Both sites have very dedicated 604 enthusiasts who will be happy to help you out.


05-24-2017, 08:49 AM
Welcome to the forum.

Although I don't have 604's, I would try the following with what you have already.

-Place the 604's in the 612 cabinets using the Markwart phase correct crossover.
-Load the 12cf cabinets with 18's if you still have them (I'd use JBL 2245's and use the port size found here :http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm)
-Cross the 604's over to the 18's starting at ~80hz. Use REW to see the best crossover point


-Run the 604's as a 2 way using the cabinet size GPA recommends. Still use the Markwart crossover. Pair with a nice Mcintosh amp.

The above is what I would do, It may not work for everyone.

Should be a fun project, please keep us posted. What series 604's do you have? I always wanted 604's.


05-25-2017, 03:36 AM
if you have 612 cabinets http://www.lansingheritage.org/images/altec/plans/1970%27s-lf-plans/enclosures05.jpg Use them.

put on the bottom the Sub with 2245 (two is better....) and drive them in biamp (solid state for 2245) and a TUBE AMP for 604 (example a nice 300b or what you prefer from 1 to 10W, you don't need more).

one nice enclosure for 604 is the 620 cabinet http://www.lansingheritage.org/images/altec/plans/1970%27s-lf-plans/enclosures07.jpg

Or enjoy special cabinets: https://s-media-cache-ak0.pinimg.com/originals/13/e2/b8/13e2b8de960655b7f7280c022285876f.jpg

You have in your hands probably one of the best coaxial speaker ever made.

05-28-2017, 04:27 PM
Hi, thanks for all the responses, I hadn't realized I posted on the wrong forum, I thought "Lansing" was "Altec Lansing", but now I understand.

I do have some JBL 2245 18's that are in the 12' boxes tuned as recommended by the plans I copied.

I had been biamping before with SS running the 18's and using homebrew tube amps for JBL 2113's and some Beyma tweeters.
XO was at about 200hz, the lower limit of the 2113's.

I ended up preferring the single point source sound of coax's which is why I'm trying to head back to the 604's, GPA types.

I will start by trying the 612 cabinets with the Markwart XO, I just have to order the parts and make a pair.
I'll miss the deep low end, I'm sure, yet having 2 12' box's AND a pair of 612's in the same room, is doubtful.

If I could use the 12' boxes for the 604's, and get better bass than the 612's, then maybe that.
I guess I can't put a 604 and a 2245 in the same box? or can I ?

Earl K
05-28-2017, 07:02 PM
Here's a start to your education ( click the pic ).

http://www.wardsweb.org/Billfort/tubesttnaltecs.jpg (http://www.audioheritage.org/vbulletin/showthread.php?7272-604-8G-in-620-cabinet-Bass-responce)