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OK, so I'll admit the tonal balance on the open baffles I brought to CAF this year wasn't as good as it could be. The crossovers I was using were originally built for a different co-axial driver, so there's no real surprise there...

So, I'm starting a new crossover project for the Urei 801Bs. Now, I know tomp is going to chime in about using a digital eq, and probably bi-amping with a digital crossover, but that's not the direction I want to go with this project. The plan is to start with the Urei crossover design for these drivers, which should not only allow me to get the tonal balance pretty close, it'll also time-align the drivers (Urei's time-align monitor series were the most widely used large-format studio monitors of all time). I've got the parts to build a pair of prototypes (except one resistor I somehow managed to order only 1 of instead of the two needed for a stereo pair )

Schematic for the crossover can be found on the last page of http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/UREI-813B.pdf, w/o L-5 & C-12, as they're the low-pass section for the 'helper' woofer. Bonus points to anyone who can find a copy of the schematic where one can actually read the value of C-3

Roscoe

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I can explain it to you, but I can’t understand it for you.

The only thing I would like to suggest is using the digital parts to determine what your crossover should be and then you can more efficiently and with greater cost effectiveness make your final passive crossover. You may still want to tweak slightly due to effects of passive crossover deviation from perfect slopes and different amplifier output impedance, but you will be a lot closer a lot faster. Who knows, you may even want more than one that are switch selectable to suit your moods.

I have an extra set and also amps I will not be using until I give the same seminar I did last weekend to the Boston Audio Society in October. You are welcome to use them.

Tom

Tom, I'll probably pass on that, BUT, if you've got appropriate gear so that I can measure in-room response as I go along, that might be a welcome addition to the project.

Roscoe

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I can explain it to you, but I can’t understand it for you.

Roscoe:

I have two ways you can do it. The best way would be for you to come over and borrow my old desktop PC that has Liberty Audio Suite loaded on it. You can then measure quasi-anechoic response of the speaker and crossover without room effects. I have an ACO Pacific measurement mike and other accompanying stuff to make it work.

The other way is to use the Behringer DEQ2496 which has a built in pink noise generator as a source. You can view the RTA of the pink noise being fed to the amp. You can then connect the measurement mike to the DEQ and see the resulting response in the room on the RTA. You can switch back and forth until they look close but I guarantee that you will have to make some tweaks by ear.

If you are never going to move the speakers the second way may be all you need, but if you are going into another listening space you might want to know what it takes to get flat anechoic response. Let me know.

Tom

Everyone to Tomp's house to measure their speakers!

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- Guy

I'm more than happy to work with anyone who has not gone through the process at their house. It is not as hard as it seems, but in the end, your ear/brain interface will rule.

Tom

...If I only had a brain!

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- Guy

Mine's been nothing but trouble

Roscoe

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I can explain it to you, but I can’t understand it for you.

Roscoe,

Got this from someone on the Lansing Forum.

While it doesn't say so, this is the 830 crossover schematic which is the correct crossover for 1 801B duplex in an 811B enclosure. The Crossovers are made in 2 parts with a large umbilcal cord connecting the sections. The time delay section is in the back panel with the signal binding screws and the high pass section, fuses, lights and trim pads are in the front panels. The light bulbs are important too.

https://dl.dropboxusercontent.com/u/450 ... ssover.pdf

https://dl.dropboxusercontent.com/u/450 ... matrix.pdf

Jim

Thanks Jim. There are a couple minor differences between that & what I had, good thing I haven't gotten too far building the xovers. That's a project for this weekend....

Roscoe

_________________
I can explain it to you, but I can’t understand it for you.