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EV Sentry III Midrange Horns (SM120A, EV1823M)


Jer_Hy
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I’ve been wanting to hear the difference between the standard K400 horn and a different variety so I picked up this pair of horns a few weeks ago. I’ve seen a few posts from almost 20 years ago claiming some success using them as the midrange in the Klipschorn, so I figured it would be worth a shot. 

I really wanted to be able to A/B between the two horns so I’ve hooked up a on/off/on switch between the output of the midrange from the crossover to the two horns. Very excited to listen for a while switching back and forth. The only improvement I now want to make is rather than two switches on the top hats, having just one that I can control from listening position, but I haven't quite thought that through yet.

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My initial impression is they are more similar than I had imagined, with the biggest differences from the EV’s being a small boost in 2500-5000 range and a dip in the crossover point between the bass horn and the mid range. Over all the effect is a heavier low end and some nice clarity in the upper midrange with a slight lack in the deeper end of the midrange. If after some time I continue to enjoy the EVs I may create a top hat for them, and mount the tweeter directly above the horn mouth using the bracket holes placed by EV for their tweeter.

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This is all running on a basic setup of mixer -> power amp -> AA crossovers with Dave A’s smahls in place of the K-77s (they were fried when I bought the Khorns) 

Edited by Jer_Hy
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30 minutes ago, Jer_Hy said:

I’ve been wanting to hear the difference between the standard K400 horn and a different variety so I picked up this pair of horns a few weeks ago. I’ve seen a few posts from almost 20 years ago claiming some success using them as the midrange in the Klipschorn, so I figured it would be worth a shot. 

I really wanted to be able to A/B between the two horns so I’ve hooked up a on/off/on switch between the output of the midrange from the crossover to the two horns. Very excited to listen for a while switching back and forth. The only improvement I now want to make is rather than two switches on the top hats, having just one that I can control from listening position, but I haven't quite thought that through yet.

IMG_3453.thumb.jpg.addde2492b0a0d130ad9ac7381fc0fcc.jpg

IMG_3464.thumb.jpg.c102ba4c21fac8bb23508c651958d1a4.jpg

 

My initial impression is they are more similar than I had imagined, 

to sound better , the SM120A horn should be placed  way ahead of the speaker ,  the bottom  lip of the horn should be placed at the farthest point of the Khorn's top hat 

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Some years back I made a comparison of a number of horns with a 24uF cap and junk EV CDP driver with the rear exit plugged.  With the driver, SM120 exhibited a response dip towards the bottom which looked like the devil sign made with hand and fingers.  (that response problem did not occur with my K55V)  At the time I had the idea it was partly due to the relatively short horn path and where the impedance dips and peaks lay.  Do you have a shunt inductor across the driver?  If not I'd try one.

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good observation absolve2525- IIRC my 1823M were 8 ohms nominal vs 16 for a K55V. -  SM120 was the only horn in my test to have a weird dip vs Cobraflex and 511.  Its 1/4 wave path is awfully short and made for a bad match .  Odd order networks can exhibit wild interactions with driver/horn;cabinet impedance peaks and dips.

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1 hour ago, karlson3 said:

Some years back I made a comparison of a number of horns with a 24uF cap and junk EV CDP driver with the rear exit plugged.  With the driver, SM120 exhibited a response dip towards the bottom which looked like the devil sign made with hand and fingers.  (that response problem did not occur with my K55V)  At the time I had the idea it was partly due to the relatively short horn path and where the impedance dips and peaks lay.  Do you have a shunt inductor across the driver?  If not I'd try one.

Thanks! not quite sure what shunt inductor does, but I'll look into it. What would the outcome of adding one?

 

40 minutes ago, absolve2525 said:

Are using the same horn drivers for your comparisons? Are the EVs 16 ohms like the Klipsch? That would make a difference in the crossover point. 

They are 1823 drivers that read 8 ohms. the K55s on my 1977 Khorns read about 10.5 ohms

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I'm talking about a 2nd order highpass for the midhorn driver vs just a cap (Type A/AA)  The inductor is parallel with the horn driver (in this case right before a fixed resistor L-pad) making it "2nd order" (electrical if not acoustic)

 

Here's a Sentry IV schematic - look at "T1"  - that's the inductor but this copy (from these forums) is illegible.  (Is that "3mH" ? "5mH" ?)  - Sentry IV users probably know. 

 

The basshorn is good within its range and think a late - great Ray Newman design.

 

With strong 12" even Kappa 12A, Sentry IV is louder in the upper mids than a K-horn (but limited in LF extension)  (Pyle's PYM1298 was made by Eminence and pretty much the same driver as their Kappa12A)

 

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I've been using mine on top of LaScala bass bins for quite a while, crossed over at 400Hz, and it was ok, but I have to say, now that I use them on top of FH1 bass bins loaded with Kappa 15C woofers, and I'm able to cross them at 500Hz 24dB, that is when they truly shine. 400Hz while doable isn't optimal I feel with those horns.

I also use Crites A55G drivers to great effect.

IMG_7388.jpg

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17 hours ago, geezin' said:

Are those hokey pucks under the speaker?

Yes. They come in very handy! I can even slide the bass bins around on the tiles, for precise positioning adjustement, and in my room they bring everything at the right height for my ears. They are also quite effective at decoupling - but I use subs, so the perceived loss in low bass that may come from raising the bass bins off the floor doesn't bother me.

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On 9/13/2021 at 3:52 AM, Rolox said:

I've been using mine on top of LaScala bass bins for quite a while, crossed over at 400Hz, and it was ok, but I have to say, now that I use them on top of FH1 bass bins loaded with Kappa 15C woofers, and I'm able to cross them at 500Hz 24dB, that is when they truly shine. 400Hz while doable isn't optimal I feel with those horns.

I also use Crites A55G drivers to great effect.

IMG_7388.jpg

What do you cross your tweeters at? I'm assuming that's the Beyma CP-25? Looks nice! I have some of those EV horns and Beyma tweeters to play with eventually on some Lascalas. 

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