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The Rescue of my home theater (1 Viewer)

RobertR

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I've had my VMPS main speakers for almost 24 years. The front baffles are 3 inches thick. The overall weight is 350 lbs. The woofers are made of carbon fiber. The bass is rated to be down 3 dB at 14 Hz. In short, the build quality is much better than the typical speaker, more typical of very high end models costing tens of thousands of dollars. Around 2000, I upgraded the tweeters and the midrange to ribbon drivers. The larger version of the ribbon midrange (Bohlender Graebener) has been used in the $300,000 Genesis Dragon, which gives an idea how highly regarded it is. I loved the sound of them. Clear, open, superbly dynamic, with bass that could be bested only by paying a LOT more money (with Anthem Room Correction, they are flat within +- 1 dB to 20 Hz). I paid $9500 for them, which is a fantastic bargain in today's market.

About two months ago, disaster struck. The midrange on the right speaker died. Of course, I had no ability to repair it myself, and it couldn't be fixed by the usual reconing / new voice coil repair job. The really bad news was that that midrange is no longer made. I looked high and low on the Net for a replacement. No luck. This was serious. Without a midrange I had no speaker. No music, no movies, nothing. All that beautiful construction quality--the cabinet, the woofers,the external crossover, the ribbon tweeters, would have been wasted. It would be impossible to match these speakers without spending tens of thousands of dollars. What to do?

The I noticed on Parts Express that Bohlender Graebener did still make a ribbon midrange: The Neo 8s. Could this be the answer? I looked at the specs: 8 ohms instead of 4 ohms. Could only go down to 400 Hz instead of the 168 Hz of the old driver. 7 dB more efficient. Comparable width, but 8 inches tall instead of 50 inches. I came up with a plan: The old drivers (I had to replace the left one as well, couldn't have a mismatch) were attached to wooden frames that matched the 68 inch height of the speakers. I found a woodworker who would fabricate new frames for me. I made an Autocad drawing for him, showing precise specifications. I sanded and stained the frames. My plan was to stack eight of the new drivers in a line array configuration. By wiring them using a combination of parallel and series resistance, I would be able to match the 4 ohm impedance of the old drivers. The new configuration would be 64 inches tall instead of 50 inches.

The crucial component to make it all work was my Behringer DCX2496. It's a wonderfully flexible component. It can adjust crossover points, the type of crossover, levels, even time delay between drivers. It's also a parametric equalizer. My speakers are actively biamped, that is, the woofers and midrange/tweeter are driven by different amplifier channels. The crossover for the tweeters/midrange is a passive external crossover. The crossover between the woofers and the midrange is set by the Behringer. The first thing I set was the level of the midrange relative to the woofers and tweeters. That took care of the increased efficiency of the midrange. The next step was to set the bass crossover at 400 Hz, and leave the crossover between the midrange and tweeters alone.

Then came the moment of truth. Would everything work as an integrated whole? Did I wire everything correctly? I ran it through ARC, and was overjoyed to see that I was getting curves very much like the old ones. After correction, they were essentially identical. But how did it sound? Well, after a few weeks, I'm happy to report that my speakers sound as good as they ever did. The new ribbons probably have even lower mass than the old ones. Since I'm running eight of them, power handling has gone from 270 watts to 1200 watts. The clarity, the soundstage, it's all there.

Before:

Right speaker in Long Beach smaller.jpg



After:


20180705_110624.jpg
 
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Mike Frezon

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That's an amazing story, Robert.

Much of it (the specs) is above my paygrade, but the drive behind your desire to make things work is something with which I think nearly all HTF members can identify.

And the final results are striking. Kudos to both you and your woodworker! :thumbsup:
 

RobertR

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Dec 19, 1998
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Thanks Mike! It was exhausting work, both physically and mentally, but as you said, I was driven to make the whole thing work. These speakers are just too valuable to give up on them easily. I was pretty sure the idea would work (after doing a lot of reading on crossovers), but it was a huge sigh of relief when it became a reality.
 

Mike Frezon

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A huge effort...electronically (getting the new drivers to play nice in the new environment) and physically (getting them to fit and look like they have always belonged).

I would love to be able to hear what they sound like.
 

RobertR

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Messages
10,665
Thank you John, I appreciate your comments and all that you've shared with me. :)
 
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