604 enclosure

[selmerdave]

Hi folks, new to the forum, first post. I have a set of recently acquired 604E's that I'm trying to get running on a budget. I'm building a couple of simple second order crossovers and for the near future they will be housed in some Bozak cabinets, I think around 4.5 cubic feet. My question is, I know these perform better in larger cabinets but given that I am limited to this is it better to seal the cabinet or to make some kind of bass reflex?

Dave

[jmarkwart]

Hello Dave,
Altec 604s are designed for vented enclosures. If you use them in sealed enclosures they will produce less bass extension and power handling than can be obtained from a vented box of the same, or smaller, volume. Your 4.5ft^3 boxes with 604Es can be vented to produce a -3dB response of 50Hz, but if left sealed the -3dB point would be closer to 113Hz! The other side of this coin is that vented enclosures are harder to properly design that sealed ones, and also have worse transient response/group delay responses. You might want to try it both ways and see what you think.
Might I suggest you look at a copy of the Altec N-1500A crossover schematic (I can fax you one if needed) before you build the second order filters you mentioned? The N-1500A is an elegantly designed, and simple, series filter that compensates nicely for the phase shift created between the 604E's two acoustic centers at 1500Hz.
Jeff

[selmerdave]

Jeff,

Thanks for the info, what would you suggest for a port size then? I would like to see the schematic for the N1500A, I haven't seen it. Let me know when you might be available to fax it (I have to set up my computer to receive). Thanks again.

Dave

[jmarkwart]

Dave,
I got 19 in^2 for a vented port area at 50Hz in a 4.5 ft^3 eclosure when I plugged the 604E T/S numbers into WinISD. You may want to download WinISD and play with it yourself. I'll email you directly about the schematic fax set up.
Jeff

[jmarkwart]

Doug,
You will have some differing opinions and options to weigh – tube versus solid state, passive versus electronic crossover, small box/flat response/limited bass versus large box/non-flat response/deeper bass. There are no pat answers – everything is a tradeoff and needs to suit you and how you intend to use the drivers. Whatever route you take, though, it will be a kick to once again enjoy those great sounding, high-efficiency Altec 604s! So, what is the application? Home stereo? What about budget? Any constraints?
Jeff

[Noblecaptain]

Hi, Jeff!

Yes, budget is a definite factor. I'm looking for a fairly low-cost way to get them playing, then I can work on improvements as time and funds allow.

The application is home stereo in a 13X25 foot space, carpeted and walls not too "live." I have gotten used to flat response - I do some studio voicework/production - but find that for home listening a little color and higher bass response is more pleasant to me as well as to family and friends who would also be using the system. So I would tend to go toward a cabinet size somewhat larger than would be used for "flat" listening.

Power and crossovers....I know there must be lots of choices, but probably fewer as you get less expensive. I'm open to suggestions.

Thanks for the friendly and thoughtful reply! I'm looking forward to getting my ears into this project!

Best,

Doug

[Noblecaptain]

Hi! Jumping in here. My first post also. I have a pair of 604Cs that have been inactive for too too long. My dad owned them and I inherited them from him. I would love to hear them again, but I am not as technically savvy as the old man was.

I need to address all of the concerns of using these, from a beginner perspective - Power - My dad used an old Dynaco amp. What on today's market will do the job well? Also whether to build or purchase crossovers...and plans for vented cabinets.

One is a driver only and at the old homestead was mounted in a closet wall. It sounded beautiful in there. ...the other is in the original cabinet, but the cabinet is not in the best shape. I would appreciate any help getting these great speakers working again!

Best Regards,

Doug

[jmarkwart]

Doug,
I suggest you build a pair of N1500A crossovers for your 604Cs. They will work on any alnico 604 or 605 (16 ohm) to provide crossover and HF shelving, as well as phase correction between the drivers at 1500Hz .
What does the original cabinet look like? Is it a 36H X 36W X 23D triangular cab with a 4.5in X 13in port in the front? (Altec 606) If so, I would recommend you buy or build another. If it’s beyond repair consider building a pair of vented 9.5ft^3 cabinets with the port area listed above.
Jeff

[jmarkwart]

Doug,
Beats me what it is....I looked through some of the old catalogs at the early cabinets from the 40 & 50's (605, 606, 620) but didn't see a match to those dimensions. The only way to ever know might be to make a picture available for some of the guys really familiar with early Altec cabs to look at.
Jeff

[Noblecaptain]

Howdy, again, Jeff!

The cabinet is 36"h x 26"w x 15.5"d and is a dark mahogany color. The vent is 16" wide x 4 3/4" high. It looks like furniture, definitely not a utility cab. It has a metal grille with a "diamond" pattern in front of the cloth that conceals the driver. It has a knob at lower back that appears to be connected to a network of different crossover options. It's a fascinating piece of work.

I assumed that the cab was original, as it looks like a perfect well-built home for a 604...but perhaps it is a custom piece?

This spider of crossover wires and resistors inside the cab is incredible.

For modern use, I would like to match the drivers in terms of treatment. But if the cab is of special or historical interest, I guess I ought to know before I change anything.

Best,

Doug