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In Reply to: RE: EV Horns posted by SpeakerScott on October 04, 2014 at 17:52:35
Thanks for posting that data sheet! I have T-350s in my system, but have long ago lost the data sheet.
With regard to their output, while it's true that they can be crossed as low as 3,500 Hz, that will limit their output due to excessive diaphragm excursion at those lower frequencies. Trust me, you do NOT want to have to replace that diaphragm! It's a bugger! I had eight T-350s (four per side) in a sound reinforcement system a long time ago. When I had the "opportunity" to repair one, I said "never again!", and raised their x-over frequency.
Even in a home hifi, it's better to cross them higher. Mine are crossed at about 5,500 Hz, high enough so that I can crank the system without concern for over-excursion.
ACMINC, I would advise you not to mess with what is an excellent design. If you look at the data sheet diagrams, you'll see that the horn/phase plug assembly is much more than simply a diffraction horn that you can easily replace with a home-built conical horn. Further, as Scott pointed out, the conical horn won't properly load the diaphragm, increasing the possibility of damaging it. Lastly, the T-350 is a classic high performance driver, and it would be a shame to negatively impact its value by bastardizing it. If you'd rather have something else, I'd consider buying them from you.
:)
Follow Ups:
I agree that it's unlikely that a beginner could design a horn and phase plug to replace the one on the T350, and have it perform as well as the original. The original post here concerned a conical horn for the 1823M to replace the 8HD, and that's certainly feasible.
I don't want to alarm anyone, but I cross my T350's first order at 2500 Hz. My 1823 mid drivers have copper voice coils and the highs roll off lower than the 1823M (or 1824M) which have aluminum voice coils. So the non-M 1823's work better in my application with a lower XO point. For me the forte of the T350 is it's ability to cross this low. I've never blown a T350 diaphragm, but I've been running a Dyna ST70 for a couple of decades, which is currently triode wired with 16 WPC. So your milage on the T350 phrams may vary if you have a very large listening room and big SS amps, and listen at live rock concert levels frequently.
I have'nt found the T350's particularly difficult to work on, however getting good replacement diaphragms has become a problem (see DJK's recent comments here). Great Plains Audio got the tooling to make them from EV, but apparently they are having trouble sourcing the phenolic base which the coil is wound on, at least that's what a friend told me who spoke to GPA and also Bob Crites a while ago. If the weight and/or compliance of this phenolic base is out of spec it can throw the freq. response off. Problems seem to arise in the lower end, and a higher crossover point may become necessary to avoid this. BTW some guy has been rephraming T350's by putting glue on the driver side of the phram so that if you take the driver apart the voice coil leads will break when you separate the horn from the driver! The phram is press fit into the horn assembly and you don't need any glue! It should stay with the horn and terminal assembly when you separate it from the magnet. I have an ST350 which was thusly treated, and I was able to repair the broken leads with Radio Shack wire wrap wire, and it performs as well as it's twin which was not glued. It's hard to tell if this gluing is being done out of ignorance, or to purposely have the diaphragm self destruct if someone decides to disassemble a T350.
Paul
Would an Eminence APT-80 do or is it too fragile?
Dave
Dave
Probably not as it's 104 dB verses the T350's 107 dB. The Eminence 2002S-8 looks interesting with 106 dB, but it is a big 1" driver. It's interesting that the replacement diaphragm for the ABT 80 is phenolic and looks similar to the T350 phram except that the lead outs are on the same side. Anyone know if the diameter of the voice coil is the same as the T350? If so it might be possible to modify the ABT 80 phram as a T350 replacement. Perhaps this is expecting too much of a lucky coincidence.
Paul
The Selenium ST350 Super Tweeter is 111db@1w/1m, & 50 degree dispersion but I have not heard it.
That's an interesting tweeter which I also have not heard, but Selenium's specs have tended to be rather unreliable in the past.
Paul
I guess I'm going to leave the stock horns on the T-350's. But I am going to change out the stock horn on the 1823M. Most likely a conical tractrix design. I too have been thinking of raising the OX to 4000 or 4500 Hz. What are your thoughts on a mid-bass horn design? Straight conical, tractrix, exponential? I have the room and 100% WAF.
ACMINC,
Your first instinct is correct. Getting rid of the fifty year old PA horn, and dropping in something better. It's the best first step for vintage horns.
Building horns and going four-way active is very ambitious, but while you are learning horn theory, and the art of horn construction, let me make a suggestion that you just go ahead and buy a decent pair of horns to listen to while you master all that.
Why do you want conical horns? Ultimate sound quality? Do you prefer a definate sweet spot all the time, or do you want to fill the house with music?
I posted a link below. It's not what you want, but it's just to show you what's out there. $550 and a week, and you could really do a lot for the sound quality of your speakers. Also, you could never build these, so when you build, it will be something different than this. If you want to talk about this horn, or other possibilities that's cool.
Learn what the difference is between hyperbolic, exponential, and conical, and what theoretical cutoff is, and you will be a long way to understanding audio horns. It will help you decide what you want, and what you are able to do, and the trade-offs, always with the trade-offs.
Jamie
Big speakers and little amps blew my mind!
Conical horns and tractrix horns are two different animals, though hybrids incorporating features of each are possible. I prefer tractrix horns on compression drivers for the midrange, but I've heard some good conical mid horns. The selection of a different high crossover point with the 1823M should be based on data from measurements. The 1823M does not have a phase plug and subsequently just can't go all that high compared to mids with phase plugs. Raising the crossover much beyond the 3500 Hz point spec'd by EV will tend to result in a hole in the response between the 1823M and T350. In the meantime you've got some work ahead prototyping some conical mid horns. You can quickly fabricate a functional conical mid horn with poster board and duct tape which will show you if you are on the right track. BTW the 8HD is a diffraction horn and will have a broader horizontal coverage pattern if the long dimension of the horn is vertical, though this may seem counter intuitive. Ditto for the T350. You should set them up this way for comparison to anything you may build.
Paul
hi Paul. The 1823M does have a phase plug.
You can see it when you open it up.
Quirck
The EV data sheets for the 1823 and 1824M make no mention of a phase plug or loading plug. Neither do the data sheets for the similar 1824S. A loading plug is promoted in detail as an important feature in the data sheets for the T350/T35 however. One could argue that the volume and geometry of the air chamber in front of the diaphragm in a driver like the 1823/1824 is designed to minimize destructive cancellation in the sound waves, and that this is the same task a loading plug would be put to. However they are quite different things. To be honest I have'nt currently disassembled any of my 1823's or 1824M's to examine this area, but a picture of something resembling a phase/loading plug in one of these drivers would make me a believer.
Paul
Hi, I have sent you two pictures, cannot post them here.
Quirck
Thanks for the correction and the pix! There was probably a patent concern for the reason that this was not mentioned in any of the data sheets. I have never replaced a diaphragm on any of my 1823/1824's but I did open an 1823 up some years ago, and if you don't remove the diaphragm then you won't see the plug. Also there's a metal screen obscuring a view of the plug from the mouth of the driver. BTW the pix came through fine (I've attached one here) but the two text attachments were blank, maybe because I'm running a Mac.
Paul
I made a conical horn to replace the B&C ME20 horn and the improvement was well worth while. I think conical is the way to go for hifi use. It doesn't have any 'horn' sound and provides a flat response up to 45 degrees off axis. Make sure you radius the baffle and transition nicely on the horn exit. I would avoid a round conical horn in open space as this focuses too much boost at one frequency due to edge diffraction. Mounted to a square baffle will give you a smoother frequency response. Also, pay special attention to the compression driver itself, noticing the geometry coming out the unit and making sure your horn matches with no abrupt changes in horn profile. Using digital EQ you can compensate for any loss in output near the cutoff.
Obviously, you have not studied the characteristics of conical and exponential horns.
Conical horns suck.
Here are my findings. Please post your horn builds with measurements.
http://croweaudio.blogspot.ca/2013/05/oblate-speherical-waveguide-diy-project.html
http://croweaudio.blogspot.ca/2014/06/oblate-spheroidal-horn-completed.html
http://croweaudio.blogspot.ca/2014/07/frequency-response-measurements-for.html
I don't build horns. I leave that to the pros.
All you have to do is to look at the data to know that conical horns aren't hi-fi.
Look up earl Geddes OS horns and reviews. Stop being so obstinate and insulting.
"I cross my T350's first order at 2500 Hz"I didn't sleep last night... that sentence just kept replaying in my head.
You must like living on the edge. lol
Tell us you're using the STR tweeter protector!
:)
Edits: 10/06/14
My STR's went in the parts box a couple of decades ago. I never heard one switch a tweeter out even when I was playing the Stones loud through a Hafler 200, though I did use 2nd order crossovers back then. The spec sheet warns about not playing test tones below 3500 Hz, and not exceeding 5 Watts RMS continuously with a test tone. They added "Naturally, sustained signals of this kind are never remotely approached in program material". Power handling is further listed as 50 Watts program; 100 Watts peak. A test tone is about the only way I could see blowing a T350 in the average listening room, and it would exceed 120 dB! Two of them driven this way would become painful very quickly. Now you are one up on me, as you've actually heard a T350 blow. I assume it was in an outdoor PA setting, Dyna ST70's were not the amps, and the music being played was not a string quartet ; )
Ken, you still there? The 3500 Hz crossover (EV X36) will work fine with the 1823M/T350 as long as you observe the above cautions.
Paul
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