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Old 16th February 2004, 12:27 AM   #1
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Default Urei 809 + Behringer 2496 + Gainclone Mod.

Hi Folks,

About a year ago I begin to think about modifying an old pair of Urei 809 speakers that I bought new almost twenty years ago. At that time they were very highly regarded as Studio Monitors and you could see them used in many professional studios (and even today). They were popular and not expensive. (About U$ 1300-1500). They had a big brother (813), which was better.
In January ‘03 I bought a pair of Genelec 1030 active biamped monitors, and I vas shocked by the difference in sound. What I heard was more high-end extension. uncolored mids, very tight and controlled bass, outstanding soundstage and way more definition (this is as long as you do not abuse them producing high SPLs, After all they have a 6.5 woofer)
The difference in sound was that big ( they are used in the same room) that I thought about selling the old Ureis or perhaps do something on them to improve the sound.

What follows is the explanation of what I did. I'm not a speaker designer (I do sound design and mixing for TV/movies for a living) so my first action was gather as much information as I could. I read about speakers and crossover as much as possible and then I asked a few questions in this Forum which produced some very useful suggestions. And here I am now with a pair of modified Urei that I really like.

The original speaker:
The basic design -as you can see in the pictures attached- is a coaxial design in a small/mid ported speaker enclosure. The woofer is a 12" unit and there's a distinctive blue horn for the mid/high range. You can notice that the horn fires from the back of the woofer. Woofer and horn moving coils distance is about 9 cm.
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Old 16th February 2004, 12:30 AM   #2
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Default Passive crossover

They use a passive somehow complex crossover-see picture- that people liked to modify with different degrees of success. The crossover point is around 1.5 K with a couple of controls in a plate located at the front of the speaker. The selling point of this model was that Urei claimed they were "time aligned".
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Old 16th February 2004, 12:32 AM   #3
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Default More photo details

The election of the amplifier for these speakers was said to be very critical. The recommended amp was a Bryston (do not remember the model) but at that time I didn't have the money to buy it so I ended up getting a JBL 6260 amp. (300w/ch/ 4ohm.) What I liked about this amp was the absence of a fan and the massive heatsinks. The sound from this combination was never great. I tried other brands/models but never got "the sound".

I used these speakers all those years as a mid/far field monitor in a medium sized Post-production mixing room. There was no abuse but over the years the woofer's foam surrounds were disintegrating so last year the local JBL representative fixed them and the horn's voce coils where also inspected.

So this was the original situation. Next post: The MODs
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Old 16th February 2004, 02:55 PM   #4
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Default MODs-Part 1

The work covered basically three points:
Upgrade the high freq range.
New active crossover
New amplification


Upgrading the high frequency range:
The frequency vs. power plot of the horn's response shows that it begins to go down at 8 K with little output beyond 15K. I first it was tried to eq the horn but got little improvement so I considered adding a tweeter. At that time I was reading great reviews about Scan-Speak tweeters, so I asked here in this forum about how a SS tweeter would integrate. It was "kindly" suggested to consider another kind of tweeter: the Fostex FT17. This is an inexpensive model praised for its sound and value. That was good news. This Fostex driver cost 1/4 the price of the SS unit. So 3 of them were ordered without even listening to the unit.
Now, where to install the tweeter? The old passive crossover is mounted with a square metal front plate to the front of the speaker. It is exactly the size of the tweeter and is located asymmetrically from the left/right sides of the enclosure. So it was as easy as pop out the crossover and build a little MDF piece -a square piece with a round cut in the middle- to mount the tweeter. To attach it to the enclosure, the same holes holding the crossover plate were used-see picture. Some silicone caulking finished the installation.
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Old 16th February 2004, 03:01 PM   #5
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Default Crosover detail

The crossover's front plate detail
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Old 16th February 2004, 03:19 PM   #6
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Default Tweeter

Now you can see the Fostex tweeter in place.
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Old 17th February 2004, 03:36 PM   #7
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Upgrading the crossover: As the speaker is going to be tri-amped, the old passive crossover must go away. As the woofer/horn/new tweeter combination is not aligned in time by itself, this speaker is an excellent candidate for an active digital crossover. The required unit should have very flexible filters, MUST have delay units per driver band and some equalizers. The Behringer Ultradrive 2496 is an inexpensive device that has all the processing needed. It has 3 analog pro-level inputs and 6 outputs in XLR format. It also includes an AES/EBU input and works in 24 bits/ 96 KHz.
A real bonus is the PC software provided that controls every parameter of the unit by a serial connection. This remote control feature plus the ability to store different patches and be able to recall them "on the fly" were very useful during the long adjustment sessions, where comparing different ser/combination of filter types and slopes was crucial.
Some people in the pro audio business get upset if you ever mention this brand to them but I use some devices made by B. and have not regrets, so far.

Next:Amplifiers
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Old 19th February 2004, 05:01 PM   #8
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Default AMPs

Power amplifiers

The search for the right amplifiers was not difficult. We have locally an active DIY audio club that organizes "listening parties" from time to time. On those occasions everybody shows his or her latest "creations”(Yes, we actually have a couple of shes!) So you have the opportunity to actually listen and see the insides of the different technologies used to amplify audio and that makes selection easier. During 2003 I built everal versions of Gainclones (inverted and NI) and I was (and other people that listened to them) very exited with the performance of this little chips amps. Certainly there are more sofisticated options out there, but these amps are so easy to build.... So the election of some sort of "clone" was a natural one. But 6 of them were needed, so 'the multiclone"was born.
Basically is a 4 U rack enclosure containing 6 NI gainclone amplifiers and massive heatsinks. No fans allowed.
For more details of this unit, you can go to the Chip amps forum and search for "Multiclone". (Next week I'll update the information over there with the finished thing.)

Only two mods were needed to the basic clone design:
1-Insert input capacitors, because the Behringer has 10 mV of offset at the output, which was producing around 220 mV at output. Not good for the horn.
2-An input level attenuator (just two resistors). The amps have a fixed gain of 22 and the crossover output level is way too hot. You could lower the level at the crossover input attenuator, (-15 db) but you'll loose some resolution, or you could lower the gain of the chip amp. This last option is said to affect negatively the sound of the amp, so is better to attenuate those 15 db at the amplifier's input.

Next: adjusting and frequency plots.
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Old 19th February 2004, 05:20 PM   #9
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As an Old 809 user, I find this very interesting.

Can you show us a wide shot of your listening space. Your equipment rack is intriguing.

Thanks.

-Dave
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Old 19th February 2004, 07:18 PM   #10
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Quote:
Originally posted by Ricren
A real bonus is the PC software provided that controls every parameter of the unit by a serial connection.
It is nice to see that the software runs under VirtualPC... to get a serial link do you have a card or a USB->Serial adaptor (or are running a hacked version of OS X on an old beige or somesuch)

Well documented... good on you.

dave
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