urei 813 plans needed

[Stonehenge]

Hi, all can anyone help me find the plans for the original urei/altec 813 studio monitors? There seems to be no reference on the web for these. Any info would be a great help. Thanks Malcolm.

[joyspring]

Stonehenge:

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

This PDF includes the Time-Aligned(tm) network schematic and the overall enclosure dimensions.

A couple things to note:

1. The UREI horn is no longer available; however, UREI 801A (604-8G w/ UREI 800H horns) drivers appear on Ebay occasionally.

2. The 15" LLF driver (UREI 800W / Eminence 800W) is also no longer available. Something fairly close to these Thiele-Small parameters (measured from an original Alnico 800W) will work:

fs = 22hz
Vas = 625 l (~22 ft^3)
Qts = 0.25

3. The enclosure is an `aperiodically damped' sealed enclosure; it is essentially a sealed enclosure with a `leak' (the foam-filled `port) and is also heavily braced with 2x4s and damped internally with fibreglass.

Enclosure volume is not absolutely critical.

4. The system is intended for soffit-mounting - that is, it will NOT give flat frequency response below 200hz in a (typical) free-standing position.

Soffit-mounting in a typical studio is usually somewhere between pi - pi/2 (quarter- to eighth-space) and the UREI 813 is designed to use room loading to achieve flat response.

If you're not soffit-mounting the UREIs, use a separate subwoofer.

Good luck,
BobR

[Stonehenge]

Thanks for all the info bob very interesting. I would love to build these cabs someday in a nice oak finnish. hope there are detailed plans on the net somewhere. I will keep looking. Thanks again malcolm.

[joyspring]

Malcolm,

I would not sweat the exact volume of the enclosure; unlike tuned vented enclosures (i.e. - bass reflex), sealed enclosures will tolerate +/- 10% or even 15% and not appreciably change the alignment and/or -3dB point. BTW, the external dimensions are 36"H x 31"W x 23"D.

However, ensuring an utterly dead enclosure is far more important; the UREI enclosures were all 1" particleboard, double-layered in some areas and heavily braced with 2x4s. They were also heavily damped with fibreglass.

I'd even recommend using MDF, especially if it will be permanently soffit-mounted, and simply veneer the front (baffle).

The `port' is not at all tuned but merely provides a `leak' to offer greater damping. UREI coined this `Pressure Control'.

Additional tuning may be performed by simply adding or subtracting damping material.

Again, please realise that the UREI will not produce flat response below 200hz UNLESS soffit-mounted in quarter-space, despite having two 15" drivers... this is by design as they were intended to be soffit-mounted in a control room.

If not, then add a subwoofer as the response will roll off fairly quickly below 80hz, as indicated on the response curve in the .pdf I linked to above.

BobR