Post by: Dan Brandesky on December 23, 2009, 05:24:16 PM
-Dan
Post by: Art Welter 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.
Art Welter
Post by: Milt Hathaway on December 23, 2009, 07:26:58 PM
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.
Post by: Dan Brandesky on December 23, 2009, 11:21:57 PM
-Dan
Post by: Art Welter 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
Post by: Dan Brandesky on December 24, 2009, 03:14:50 PM
-Dan
Post by: Dan Brandesky on December 28, 2009, 03:54:05 PM
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
Post by: Tim McCulloch on December 28, 2009, 04:34:29 PM
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
Post by: Rob Timmerman on December 28, 2009, 04:50:08 PM
Have you tried running an X-acto around the gasket?
Post by: Dan Brandesky on December 28, 2009, 04:58:01 PM
, so that will take some more careful working, but I'm making progress!-Dan
Post by: Dan Brandesky on December 28, 2009, 06:30:21 PM
-Dan
Post by: Art Welter on December 28, 2009, 07:55:19 PM
| Dan Brandesky wrote on Mon, 28 December 2009 16:30 |
I dunno, I think we can fix it...what do you guys think? -Dan |
Dan,
Since the VC is continuous and the former undamaged, if you were very patient you could actually spool the coil out, rewind it on the former, paint a few coats of shellac over it and be good to go.
All depends on what you think is fun to do with your time...
Art Welter
Post by: Dan Brandesky on December 28, 2009, 08:06:23 PM
-Dan
Post by: Dan Brandesky on December 28, 2009, 09:56:30 PM
EDIT: Nevermind, Mouser website just doesn't seem to have them for some reason. Parts Express to the rescue!
-Dan
Post by: Rob Timmerman on December 28, 2009, 10:09:08 PM
Parts Express has some as well.
Post by: Art Welter on December 29, 2009, 09:30:13 PM
Going with a 12 dB passive filter (coil and cap) would allow more protection, and a lower xover point using a smaller cap.
For instance, a 100 uf cap crosses an 8 ohm driver at about 200 HZ, using a 9 mH coil and 70 uf cap is also 200 HZ.
Do you really want 100 HZ to be only 6 dB down with that horn?
Post by: Dan Brandesky on December 29, 2009, 09:32:56 PM
-Dan
Post by: Art Welter on December 30, 2009, 02:57:27 PM
| Dan Brandesky wrote on Tue, 29 December 2009 19:32 |
Good point. I had seen articles mentioning using a combination cap and coil, but never really got a great indication of how to use it. I already ordered the caps too, but I will look into getting a coil into the equation at some point as well. I'm pretty sure the cap will be sufficient for the most part, as long as I'm not trying to replicate sonic booms through the horns...or causing them. -Dan |
For a second order HP, the cap goes in series and the coil goes in parallel with the driver.
Sonic booms aside, there is a lot of energy in music and even speech below 200 HZ, it is all a matter of level.
A six dB per octave crossover will allow four times the power to the driver an octave below the crossover point than a 12 dB per octave crossover.
Even though that power may not burn the voice coil, it makes for more distortion.
Using it at low level in your living room, no big deal, but using it for something where you actually want to run music through at much level, it is.
It does not take much power to melt the voice coil off the former.
Post by: Dan Brandesky on April 27, 2010, 11:35:33 AM
I still haven't gotten the other one working, as I'm missing 1 part, but I'm looking into getting that right now. More to come...
-Dan
Post by: Art Welter on April 27, 2010, 05:03:36 PM
| Dan Brandesky wrote on Tue, 27 April 2010 09:35 |
Well, I'm back, this time I have questions about actually using these horns for an event I have coming up. I need to cover an ampitheatre, it basically looks like a miniature Roman ampitheatre; half-round seating, stone-and-earth construction, and the seating goes up at about a 45 degree angle. The stage are is the other half of the circle basically. I'm wondering if I should put one horn on each side of the stage, or couple them together on one side of the stage to cover the whole area. I'm also wondering if I should flip them sideways for the greater vertical coverage. I'm pretty sure two of them could cover the audience area even at 60 degrees horizontal coverage, but I'm not sure if it's really necessary to do so or not. I still haven't gotten the other one working, as I'm missing 1 part, but I'm looking into getting that right now. More to come... -Dan |
Get them up high, point them down at the crowd.
All the sound coming from one side will probably sound lop sided.
Orient the horn so the dispersion pattern matches what you are trying to cover, typically you need to cover more horizontally than vertical, so the diffraction horn would be mounted long axis up and down.
Post by: Dan Brandesky on April 27, 2010, 05:26:13 PM
I found a neat way to mount these on stands using speaker stand mounts like this one. All I have to do is use a bolt and a wing nut to attach the horn bracket to the mount, and plop it down on a pole. If I really squeeze them together I can even get two on one mount.
I also found the perfect amplifier for them today, for the perfect price on ebay: $9.99.
It's a 60W University Sound 1808-60 amplifier. The peak power of the horns is 60W at 8 ohms, so if I connect both of them together in parallel I get about 30W per horn, which is nice and safe and should be plenty of power. It also has an interesting "trumpet protect" switch, which according to the schematic is a .01uF capacitor that gets connected in line with the audio to the output transistors. I don't really know what frequency this correlates to, so I'll have to try it out, but I imagine it should work pretty well. Even then I'll still have the fall-back 100uF capacitors connected to each horn. I'm actually wiring them in line with the input cords on the horns so they can't be goofed up. 100uF isn't an awesome HPF, but it at least helps; the corner frequency is about 200Hz at 8 ohms so that at least puts 100Hz at about -6dB, better than nothing. Depending on how this "trumpet protect" thing works I may revise my HP filtering later but I think I'm OK for now.-Dan
Post by: Dan Brandesky on May 07, 2010, 12:40:04 AM
I received the University Sound 1808-60 amp and it works great, the trumpet protect circuit seems to be the right low cut for these horns so I'll use that in lieu of my simple capacitor filters. I also found a spare 1828T driver on ebay for $40 so I picked that up as well. I took the transformer out when I got it since I don't plan on using these on 70V.
Now that I finally have 2 drivers and 2 horns, I got to do some playing around today, and discovered something interesting: it seems that there were two different drivers used in the 848 horns. The original driver appears under the "Drivers" section of the EV archives site as the "848HF". The EDS actually appears to be talking about the characteristics of both the driver and the horn at the same time, and doesn't give any specifics of the driver itself, but from visual inspection I can see that the 848HF has a larger diaphragm, and slightly different construction. Overall it is swappable with the 1828, as the threading and general mounting are all the same.
The really interesting thing is the audible difference, though. To my ears, the 848HF sounds more pleasant, at least with music playing. It has a little bit more midrange and less of the harsh upper mids that are typical of horn drivers, but it does have less high frequency response than the 1828. The 848HF also has more bass response (I know, bass response in a horn is kind of silly sounding, but it really does!). It really makes the 1828 in the 848 horn sound like a reentrant horn by comparison. The frequency plot listed on the 848HF is also markedly different than that of the 848A data sheet in the archives (under Horns, not drivers). Ideally I'd love to have a pair of the 848HF drivers, but it doesn't look like I can get replacement parts for them anyway, so it looks like I will need to get my other 1828 driver working so I have matching drivers in these horns. Still working on getting that stupid diaphragm washer I need. Darn $2 parts!
-Dan
Post by: Dan Brandesky on May 07, 2010, 12:41:49 AM
-Dan
Post by: Tim Padrick on May 07, 2010, 10:15:05 AM
Post by: Art Welter on May 07, 2010, 02:29:18 PM
| Dan Brandesky wrote on Thu, 06 May 2010 22:41 |
Also, another thought I had that I wanted to ask the gurus here: do you all typically use any additional equalization on horn systems, or do you generally just run them "as-is"? I was thinking of hooking up a graphic EQ with the horns some time to see if I could make them sound a bit flatter, but I imagine that can quickly cut into the efficiency of the horn so it's probably a pretty fine line. -Dan |
EQ has nothing to do with efficiency.
EQ in moderation can compensate for the frequency response of the horn /driver.
Attempting to EQ in top and bottom frequencies that the horn is lacking can use up your available amp headroom and cook the voice coil.
Why haven't you simply made those shims you need out of card stock or thin plastic?
Post by: Dan Brandesky on May 07, 2010, 03:39:14 PM
-Dan
Post by: Art Welter on May 08, 2010, 02:26:52 PM
| Dan Brandesky wrote on Fri, 07 May 2010 13:39 |
I haven't made the "shims" because I would have to cut out a donut-shaped piece out of the material, and I would want to find a material that wouldn't compress (like cardboard) or get brittle (like cork), so I really think my best bet would be to get the correct part. -Dan |
Card stock won't compress at the torque you would use for a diaphragm. You would strip the screws before compressing plastic.
Draw the circles with a compass, cut out with a sharp knife, takes about a minute per shim.
Post by: Dan Brandesky on May 08, 2010, 06:13:57 PM
-Dan
Post by: Dan Brandesky on October 18, 2010, 09:36:32 PM
Anyway, I put both drivers back in the horns, and noticed the two horns sounded somewhat different. Before, I thought it was because one of my drivers was a modern 1828, while the other was the older 828, which had a larger diaphragm. However, now I have identical 1828 drivers in both horns, and the older horn still sounds different; it seems to have a little bit more in the low to low-mid range. I can only guess one of two things: either the newer horn has something odd in the tube leading to the back of the larger part of the horn, or there's some difference in material between the two horns that causes a tonal difference. The older horn is made of a more grey fiberglass, while the newer one is more tan, but other than that they look to be the same. However, looks can be deceiving...
Anyone have thoughts here? I swear I'm not crazy this time...
-Dan
Post by: Kristian Johnsen on October 19, 2010, 03:55:36 AM
I have no experience with the exact horns you are using, but I have experience reworking old "finds" like this and made the rather interesting experience that the horns sound different based on how far into the magnet gap the voice coils are located. I read something about new shims further up in the thread? What happened to me was that I got the shim/gasket thickness wrong at first and had to experiement with several ones to get the voice coil just far enough into the gap.
Post by: Art Welter on October 19, 2010, 12:45:27 PM
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.
Post by: Dan Brandesky on December 09, 2010, 11:40:03 PM
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
Post by: Art Welter 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.
Post by: Dan Brandesky on December 10, 2010, 01:19:34 PM
-Dan
Post by: Art Welter 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.
http://www.binkster.net/extras.shtml#cd
Bink Audio Test CD
Has the frequencies you would need for testing.
Post by: Dan Brandesky on January 27, 2011, 09:08:40 PM
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
Post by: Art Welter 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.
Post by: Dan Brandesky on January 28, 2011, 02:41:37 PM
-Dan
Post by: Art Welter 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.
Post by: Dan Brandesky on January 28, 2011, 02:55:13 PM
| Art Welter wrote on Fri, 28 January 2011 14:52 | ||
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
Post by: brian maddox on February 01, 2011, 07:25:17 AM
my first big project when i got to work at a 'real' sound shop was to go through all the 848 horns in the shop. probably 50 or more of them. legend had it that they had been used in martin luther king's 'i have a dream' speech. not sure if that was true, although they definitely were purchased from the company that did sound for that speech.
at any rate, they had all had long lives lived outdoors. there were also a variety of different vintages, 70v transformers, etc.
i think it took me the better part of a month getting those things even close to serviceable. good times.
i do remember the shop had literally no space to store these things, so someone had rigged up ropes and pulleys so that these things hung in the rafters 2 to a line. clever solution.
i was surprised that the horizontal dispersion was greater when they were oriented 'vertically'. counter-intuitive. but i never bothered to actually look at any of the specs to learn this little fact. goes to show that there is always something more to learn...
brian
edit: added 'interesting legend'