The 604-8G's

**Mark Kelepouris** · February 28th, 2004, 06:06 AM

Hi everyone,
This is my first post to this group and I wish to inform the group that I have a pair of 604-8G's that have never been in their correct environment.
I obtained these about 15 years ago and not knowing what I was doing at the time, whacked them in some small boxes (3.5 cu.ft) with cheap and lousey crossovers.
Its time I did the right thing by them because they do sound pretty good even in the situation they're in.
Can anyone here provide some up to date designs for xover's and enclosure's of about nine cu.ft?
I, after learning much more about the significance of these drivers really want to give them what they deserve. (btw, i'm up to the task when it comes to woodwork and basic electronics)
Thanks to any people who can help.

Mark Kelepouris

**jmarkwart** · February 28th, 2004, 02:37 PM

Mark,

The original Altec 620 enclosure plans can be had at http://www.lansingheritage.org/images/altec/plans/1970's-lf-plans/enclosures07.jpg

Do a search on this site for <u>604B & 605A/B crossovers</u> for an interesting discussion of duplex crossovers that has relavance to the 604-8G.

Jeff

**joyspring** · February 29th, 2004, 01:51 AM

Markel,

If you're looking to rebuild your 604-8G based systems, you may consider upgrading them to UREI Time-Align(tm) control room monitor specs.

You may want to have a look at these docs:

http://www.jblproservice.com/pdf/Vin...s/UREI-811.pdf
http://www.jblproservice.com/pdf/Vin...s/UREI-813.pdf

The original UREI 811 and 813 Time-Align(tm) control room monitors were based on stock Alnico 604-8Gs and were a vast improvement over the stock Altec 604-8G/620A system in terms of frequency response (flatness rather than extension) and, of course, time domain behavior.

The UREI 811 houses a single 604-8G in a 5 ft^3 enclosure. It is an `aperiodically' damped enclosure - in other words, it is essentially a sealed box heavily damped that has a non-tuned (non-resonant) resistively-leaky port.

Because the 604-8G has such a low total Q, the cutoff is rather high at 80hz; I use an additional subwoofer with my UREI 811A monitors.

The UREI 813 uses an additional UREI Eminence 800W 15" driver in a 10 ft^3 enclosure that cuts off at 40hz. The 800W is no longer available but a 15" driver approximating these Thiele-Small parameters will suit:

fs = 22hz
Vas = 640 l (22 ft^3)
Qts = 0.25
sensitivity = 95 db 1W/1M

The pdf docs also include full schematics for the Time-Align(tm) networks. They're a bit complex as they do incorporate out-of-passband low-pass filters for LF delay and EQ to flatten the response curve, particularly through the mid-band.

You will also require the blue UREI 800H horns as well; these are slightly larger than the stock multicell and do load a little lower as the high-pass filter has a very shallow slope (have a look at the images in the UREI pdfs).

The UREI 800H horns (the ones without the foam or `shadow slots') may be difficult to source though they do come up on ebay every now and again.

An acquaintance has had good luck by cutting the `cells' out of a stock 604 horn and `extending' the horn lips approximating a radial shape with thin sill plate foam and glue.

Yet another idea to consider...

BobR

**joyspring** · February 29th, 2004, 02:03 AM

I also recall a thread where someone mentioned that Bill at GPA has the original moulds for the UREI 800H or 800HA horns...

Todd, would it be possible to verify this?

BobR

**thevott** · February 29th, 2004, 04:00 AM

Mark,
Welcome!
I am not a 604 expert but I do have Altec Technical Letter No. 281 (Altec Lansing "604's" Forever) which states:

"All 604 models are well behaved, even when mounted in rather small enclosures. The most efficient enclosure for any 604 is 6.5 cubic feet, tuned to 40 Hz. Here are a few tuning suggestions:
3.0 cu. ft. tuned to 50Hz -- 2 ducts; 3" dia. x 3.6" long,
4.0 cu. ft. tuned to 45Hz -- 2 ducts; 3" dia. x 3" long,
5.0 cu. ft. tuned to 40Hz -- 2 ducts; 3" dia. x 3" long,
6.5 cu. ft. tuned to 40Hz -- 2 ducts; 3" dia. x 1.4" long"
(end of quote)

As far as crossovers go, I personally am a firm believer in biamping (which incidentally is an option supported by technical letter 281 as well).

Good luck and enjoy!

MP

**Mark Kelepouris** · February 29th, 2004, 04:01 PM

Thanks for the welcome and replies,
The 620 cabinet is ideal and the 604a xover is probably the one I'll make if I can find decent components.
I have looked at the standard 620 enclosure design but i'm not sure about the port size.
Altec's AN #5 is suggesting a port area of 67.07 sq. in. for the 604-8k (620C enclosure) should I follow this or the 620 standard which has it at 27 sq. in.?
Also I'll be using 1 inch baffle not 75 in.
How do I work out the new port size based on this?
Another question is how do I decide exactly where to position the port?

Thanks again.

Mark Kelepouris

**jmarkwart** · February 29th, 2004, 06:48 PM

Mark,

You said:

>I have looked at the standard 620 enclosure design but i'm not sure about the port size. Altec's AN #5 is suggesting a port area of 67.07 sq. in. for the 604-8k (620C enclosure) should I follow this or the 620 standard which has it at 27 sq. in.?

The 604-8G used the 620A cabinet, which I believe had a 27 in^2 vent. The 604-8K has different Fs, Vas, and Qts parameters than the 8G and would not ordinarily utilize the same enclosure and vent area.

>Also I'll be using 1 inch baffle not 75 in. How do I work out the new port size based on this?

A 1 inch baffle with a 9 ft^3 enclosure will have lower box tuning by approximately 1Hz over the same box with a .75 inch baffle. You may not be able to detect that difference. If it's a concern, build your new baffle .75 inch thick; decrease the Vb .5ft^3; or use an on-line port calculator program to calculate a new port area.

>Another question is how do I decide exactly where to position the port?

I would utilize Altec's 620A plans - they did all that design work 30 years ago.

Jeff