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Author Topic: Electro-Voice 848 CDP Horns, remember these?  (Read 31216 times)

Art Welter

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #30 on: October 19, 2010, 12:45:27 PM »

Swap the drivers and you then will know if the difference is due to the drivers or horn.

You may want to blow the horn out with compressed air, cobwebs or other junk in the first part of the horn can have an audible affect.
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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #31 on: December 09, 2010, 11:40:03 PM »

Well, a couple months have passed, but I'm back at this again...

I never got to blow air through the horns to clear them out, but I figured out my issue is definitely driver-related. I have two 1828 drivers: one is actually an 1828T (70 volt model) which I removed the transformer from, and the other is the regular 1828C which I repaired. Other than the housing, the two drivers are identical (the 1828T is longer on the back side to allow room for the transformer, which means the rear horn exit "tube" is longer). What I have observed via listening is that the 1828T has more low to mid-range than the 1828C; overall it sounds more balanced. The 1828C sounds harsh, especially at high volumes, with a lot of high-mids and less of everything else. I reassembled the 1828C in the order which I understood it should be; i.e. the gasket is sandwiched between the diaphragm and the magnet. There is a small amount of gunk around the fromt of the horn exit on the 1828C, but certainly not a large amount, and I can't imagine it's enough to cause drastic sound differences.

Unfortunately, I was not able to remove the magnet from the diaphragm in the 1828T to see if perhaps I missed a reassembly step; I suppose I *could* get the magnet off, but I'm afraid of ripping the diaphragm in the process. Does anyone have suggestions on what to check next?

Thanks again,
Dan
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Art Welter

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #32 on: December 10, 2010, 12:58:08 PM »

Dan Brandesky wrote on Thu, 09 December 2010 21:40


I never got to blow air through the horns to clear them out, but I figured out my issue is definitely driver-related.

The 1828C sounds harsh, especially at high volumes, with a lot of high-mids and less of everything else. I reassembled the 1828C in the order which I understood it should be; i.e. the gasket is sandwiched between the diaphragm and the magnet.  Does anyone have suggestions on what to check next?

Thanks again,
Dan


Blow the crap out of the horn.

Did you clean the gap completely with tape prior to putting in the diaphragm?

A dragging diaphragm will reduce LF output and cause "harshness".

Run a sine wave tone through the driver, start with around 1000 Hz  and reduce frequency, go down to 200 Hz or so, listen for buzzes.
If buzzing, align the diaphragm until the buzzing is gone.





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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #33 on: December 10, 2010, 01:19:34 PM »

Hi Art, I believe the diaphragm may be dragging, however I can't see any way to align it; the whole assembly fits together very snugly, so there wasn't any way to slide the diaphragm around in the first place. I recall considering that as I was assembling it, before I put the glue on. This may very well be an issue I have to take to a professional, especially since I do not yet have an audio function generator (those things are super expensive, even used!).

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

Art Welter

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #34 on: December 10, 2010, 02:02:02 PM »

Dan Brandesky wrote on Fri, 10 December 2010 11:19

Hi Art, I believe the diaphragm may be dragging, however I can't see any way to align it; the whole assembly fits together very snugly, so there wasn't any way to slide the diaphragm around in the first place. I recall considering that as I was assembling it, before I put the glue on. This may very well be an issue I have to take to a professional, especially since I do not yet have an audio function generator (those things are super expensive, even used!).

-Dan

I’ll ask again, did you meticulously clean the gap?
Did you check that the gap was even ?

Alignment is critical, especially on a driver covering such a wide range. Even though you seem convinced the diaphragm fits “snugly”, a tap in one direction or another,  a 1/1000 inch change can make the difference between working properly, and what you describe.

There are plenty of free sine wave downloads, though an analog generator works the best for finding buzzes, which sometimes occur at only one frequency.

index.php/fa/34138/0/

http://www.binkster.net/extras.shtml#cd
Bink Audio Test CD

Has the frequencies you would need for testing.
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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #35 on: January 27, 2011, 09:08:40 PM »

OK, another update (finally). I've been super busy with the holidays, then school starting back up, etc. But I was finally able to get these drivers together with a function generator at school and test them out. I never noticed any driver buzzing, but then again my test setup was a bit ghetto-rigged because our student project lab is a bit new and we didn't have all the right cables I needed (long story...). The driver I repaired did improve some after I cleaned the gap more religiously (it was dirtier than I thought), to a point where, at least at listening levels tolerable in my small living room, they both sound OK. They don't match, but they're at least in the same ballpark.

However, the 1828T driver still has a bit more lower midrange, whereas the 1828C has a bit more upper mids. Which brings me to my next thought: would the added length of the 1828T's body modify the acoustic characteristics of the horn in the way I described? The 1828T is maybe 2 inches longer than the 1828C, which means the rear driver exit is 2 inches or so further from the horn than the 1828C's rear exit is. Am I grasping at straws again, or could I be on to something?

The only thing I haven't done yet is blasted the horn out with some compressed air, because I don't have access to an air pump at the moment. Either way, I don't think that's the issue.

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

Art Welter

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #36 on: January 28, 2011, 02:33:31 PM »

Dan Brandesky wrote on Thu, 27 January 2011 19:08


However, the 1828T driver still has a bit more lower midrange, whereas the 1828C has a bit more upper mids. Which brings me to my next thought: would the added length of the 1828T's body modify the acoustic characteristics of the horn in the way I described? The 1828T is maybe 2 inches longer than the 1828C, which means the rear driver exit is 2 inches or so further from the horn than the 1828C's rear exit is. Am I grasping at straws again, or could I be on to something?

The only thing I haven't done yet is blasted the horn out with some compressed air, because I don't have access to an air pump at the moment. Either way, I don't think that's the issue.

Thanks again,
Dan

The 1828T has a transformer in it, even at the 30 watt setting it is 166 ohms.
The transformer will make it sound different than the 1828C, which has no transformer and is 8 ohms. A rolled off upper response would be expected.

If you are using series capacitors, a 5 microfarad capacitor on the T model would be about equal to a 100 microfarad capacitor on the C. The same value capacitor used on each will allow the T model to play much lower in frequency, so it would have more LF output.

You must bypass the transformer to make any valid comparisons between the two drivers.

If the actual driver housing is different in size and shape, the response will be different between the two drivers.

If the "T" driver  is 2 inches different between the front and rear threaded exits, the internal size is not the same.

The spec sheet does not show a different depth for the drivers, so my guess is the actual compression chambers are the same for both, and the "T" simply has a larger housing to fit the transformer.

The spec sheet does not mention differences in frequency response, your differences are probably mostly due to the transformer.

That said, differences of several dB between old drivers is quite common, you have different vintage diaphragms, so I'd expect they won't have the same response even if you bypass the transformer, and have perfectly aligned both diaphragms.

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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #37 on: January 28, 2011, 02:41:37 PM »

Thanks Art. I should have mentioned, I removed the transformer from the 1828T so I could use it as a regular 8 ohm driver. I imagine the "vintage" has something to do with the difference in sound. I'll just have to see how they compare once I get them outside on a gig someday and can run them closer to program levels without damaging myself or others in the process.

-Dan
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Art Welter

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #38 on: January 28, 2011, 02:52:27 PM »

Dan Brandesky wrote on Fri, 28 January 2011 12:41

Thanks Art. I should have mentioned, I removed the transformer from the 1828T so I could use it as a regular 8 ohm driver. I imagine the "vintage" has something to do with the difference in sound. I'll just have to see how they compare once I get them outside on a gig someday and can run them closer to program levels without damaging myself or others in the process.

-Dan


Or, as I suggested before, download some free test tones and do the comparison at reasonable levels, no need to hurt your (or your neighbors)ears.

Is the depth between thread exits actually different?
If it is, the drivers will sound different, nothing you can do but use separate EQ for each.
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Dan Brandesky

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Re: Electro-Voice 848 CDP Horns, remember these?
« Reply #39 on: January 28, 2011, 02:55:13 PM »

Art Welter wrote on Fri, 28 January 2011 14:52

Dan Brandesky wrote on Fri, 28 January 2011 12:41

Thanks Art. I should have mentioned, I removed the transformer from the 1828T so I could use it as a regular 8 ohm driver. I imagine the "vintage" has something to do with the difference in sound. I'll just have to see how they compare once I get them outside on a gig someday and can run them closer to program levels without damaging myself or others in the process.

-Dan


Or, as I suggested before, download some free test tones and do the comparison at reasonable levels, no need to hurt your (or your neighbors)ears.

Is the depth between thread exits actually different?
If it is, the drivers will sound different, nothing you can do but use separate EQ for each.


Right, I do need to look into downloading one of those gens, though now I have access to a nice little function generator at the school lab, which is also bigger than my 11x13 bedroom.

The 1828T does have a longer rear exit, due to the added body for the transformer housing. The threads are the same length as the 1828C though; they're just further away from the rear of the diaphragm. It's basically like the back of the 1828C was extruded, and a box was added on the bottom for the transformer.

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