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Author Topic: Electro-Voice 848 CDP Horns, remember these?  (Read 25246 times)

Dan Brandesky

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Electro-Voice 848 CDP Horns, remember these?
« on: December 23, 2009, 05:24:16 pm »

Just wondering if anyone has fond memories of these horns. I don't have any pics, but here is a link to the Engineering Data Sheet. I found 4 of them in a local shop, 3 of which still work. I'm thinking of buying one and maybe offering them a smaller amount for the non-working one, I'm guessing it's a blown driver (what else could it be, it's a horn). I couldn't find any info on the driver but I'm assuming it can be repaired. Anyone have thoughts/memories on this one?

-Dan
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Art Welter

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #1 on: December 23, 2009, 06:21:34 pm »

Dan Brandesky wrote on Wed, 23 December 2009 15:24

Just wondering if anyone has fond memories of these horns. I don't have any pics, but here is a link to the Engineering Data Sheet. I found 4 of them in a local shop, 3 of which still work. I'm thinking of buying one and maybe offering them a smaller amount for the non-working one, I'm guessing it's a blown driver (what else could it be, it's a horn). I couldn't find any info on the driver but I'm assuming it can be repaired. Anyone have thoughts/memories on this one?

-Dan


The Electro-Voice 848 CDP Horn is a good sounding wide range public address loudspeaker.
Compound Diffraction means put the horn vertical (the taller way) for the wider dispersion axis to be horizontal.
For the size/SPL/power level,the CDP is hard to beat, I can't think of anything better coming down the pike in the last 40 years. The loading of both the front and back of the diaphragm to extend HF was a good trick.

I think diaphragms are still available.

index.php/fa/26998/0/

Art Welter
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Milt Hathaway

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #2 on: December 23, 2009, 07:26:58 pm »

There's no driver info because it is a permanent part of this horn. EV still makes two different 70V versions: http://electrovoice.com/products/177.html

Depending upon the vintage of the horns you found, replacement diaphragms are likely to be available.

Their size and horn length make them very good sounding horns for Public Address uses.
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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #3 on: December 23, 2009, 11:21:57 pm »

Thanks for the info, guys! Art, you mentioned the horn should be oriented vertically to get the greatest horizontal dispersion; how exactly does this work?

-Dan
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Art Welter

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #4 on: December 24, 2009, 02:14:35 pm »

Dan Brandesky wrote on Wed, 23 December 2009 21:21

Thanks for the info, guys! Art, you mentioned the horn should be oriented vertically to get the greatest horizontal dispersion; how exactly does this work?

-Dan


The CDP stands for Compound Diffraction Projector, the large and small horn use the diffraction principle fto get wide horizontal dispersion.

From Wikipedia:
“Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Similar effects are observed when light waves travel through a medium with a varying refractive index or a sound wave through one with varying acoustic impedance. Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, x-rays and radio waves. As physical objects have wave-like properties (at the atomic level), diffraction also occurs with matter and can be studied according to the principles of quantum mechanics.”

While diffraction occurs whenever propagating waves encounter such changes, its effects are generally most pronounced for waves where the wavelength is on the order of the size of the diffracting objects.”

In the case of many horns that EV made the vertical dispersion is determined by the horn wall angle, while the narrow dimension makes a wider dispersion due to the small opening relative to the wave length.

The JBL Smith horn ( DSH distributed source horn) uses this effect to get wide vertical dispersion out of a very narrow horn, only 1” or 2”  interior vertical height.

Horns with narrow vertical dispersion that are not tall enough exhibit “pattern flip” below the wavelength of the vertical opening. The HF dispersion is determined by the horn wall angle, but at lower frequencies the waves diffract, resulting in a pattern that may go from 30 degrees to 110 degrees over the course of an octave or so.

Art Welter
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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #5 on: December 24, 2009, 03:14:50 pm »

Thanks again, Art, that was helpful. Very interesting technology! I've always had this idea in the back of my mind to set up a concert some day in the "old school" style: two paging horns and a vocal mic or two. I may have to get one or two of these and try that out.  Cool

-Dan
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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #6 on: December 28, 2009, 03:54:05 pm »

Well, I bought the pair of these horns today. Very Happy I'm pretty happy with the sound (at least the one that works). I bought both, knowing that one had a blown diaphragm (paid half price for it). I've got the bad driver out, and I got the back cover off, but I can't get the so-called "pot structure" off. Is it glued on or something? Should I try heating it with a heat gun to get it apart? I suppose I can't do any real damage to the old diaphragm, but I wanted to make sure. The EV info sheet that explains how to repair the diaphragm is located here (the pot structure is #7 on the diagram). Thanks for the help!

-Dan
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Tim McCulloch

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #7 on: December 28, 2009, 04:34:29 pm »

Dan-

You can't separate the pot from the diaphragm/front cover assy?  It's possible that a previous repair used too much rubber cement or used another adhesive.

Heat would be one possiblity, another would be WD-40 applied around the gasket several times and allowing the kerosene to attack the adhesive.

Unless I'm not understanding you correctly or don't grok the EV diagram...

Have fun, good luck.

Tim Mc
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Rob Timmerman

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #8 on: December 28, 2009, 04:50:08 pm »

Depending on the material used for the gasket, it is possible that the gasket has fused itself in place.

Have you tried running an X-acto around the gasket?
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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #9 on: December 28, 2009, 04:58:01 pm »

Thanks guys, it turned out a little leverage with a screwdriver was all I needed. The diaphragm was definitely hosed, too; when I hooked it up, I got highs but no lows from it, and when the magnet finally popped off, the voice coil basically fell apart; I think it was over excursion-ed (sp?), because half the voice coil was basically wedged up in the magnet. Of course now it appears that someone also glued the fiberboard gasket to the diaphragm, and glued the diaphragm to the front piece  Mad , so that will take some more careful working, but I'm making progress!

-Dan
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Why do I need cymbal overheads? I'll just use SM58s on the vocals.
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