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In Reply to: RE: EV Sentry IV-A posted by Geary Lyons on March 27, 2013 at 21:34:02
The Sentry IV was more-or-less Electro-Voice's answer to the Altec A7. High efficiency, high output. Lacking in low bass, but really nice mid and upper range. We put a couple into a new high school auditorium back when they first came out (1974?). If I remember correctly, it uses the same midrange horn as the Sentry III, and it uses the same tweeter. The tweeter, btw, is basically the same as the T350 but with a different horn and a less pretty motor housing. Very nice tweeter, and very nice mid horn/driver.
You might want to consider keeping the mid, tweeter, and crossover, and building a better low end for it, kind of like what E-V did - known as the Sentry III - a very nice speaker.
hth
Follow Ups:
New bass bins are a strong likelihood. The Sentry III traded off efficiency for deeper bass and and a more furniture like form. I want to maintain the efficiency.
Once I get the 12" woofers rebuilt and the cabinets cleaned up, I plan to try placing them in the rooms corners, diagonally and horizontal. This should load the bass better and put the mid and tweeter closer to ear level from a sitting position.
I do have a old pair of passive subs that I can use to supplement the bottom end.
I am looking possible configurations for the bass bins. Any suggestions on a DIY'able plan that maintains the efficiency?
Cheers,
Geary
I have installed and have been tweaking new crossovers. So far I am liking the sound. I made the woofers' high pass second order. Cleaned up the mid transition with the steeper curve.
I tried the factory spec'd 2uf for the tweeter high pass. Lost much of the treble presence of my first crossover using 4750Hz/3uF cap. I went back to the 3uF. I think this is where I will leave the crossover for awhile.
I am going to play around with the 1uf cap paralleled with the 2uF caps for the mid and treble. I will then bypass the mid 30uf cap with small value film or PIO cap. (Thinking .22 or .33 uf).
Cheers,
Geary
I am loving my 45 tubes BottleHead Paramours!! Much of that love is due to the Sentry's! I am really pleased with the music that the Sentry's effortlessly put forth with the SET's flea power!
I am till tweaking mid range bypass caps on the 30uf caps. But other than fine tuning the tweeter crossover point, I am close!!
Now to cosmetics...
The bass bins are 5/8" ply, not 3/4", so I am probably losing some mid/upper bass impact and resolution. I will need to do some sanding and heavy fill, so may still lose more material in the bass bin walls. I think the walls need to be thicker and far less resonant.
To make them more "furniturish" I plan to sheath them in 1/2" BB on the upper and lower sides and back. The BB will be stained a dark black cherry.
The "front" of the folded horn, (the flat 12.5" high front middle), and the same area on the sides will be solid 3/4" cherry forming a "beltline" of hardwood. Not only will this, hopefully, look nice, but in combination with the BB ply substantially decrease the cabinet resonance.
I have sanded down the mid horns and repainted them a 2 stage automotive cherry metallic. Just seems proper that 60/70'ish horns would be Cherry Red Metallic! There IS a REASON that EV splatter textured these horns. OMG there was no end to bumps, dropouts, pin holes and other blemishes from the molding process. Satin Black over heavy texture makes them disappear. Sanding the texture off, well....Every blemish I sanded and or filled made three more stand out proud!!
Here are some pics of the horns...
those SM120's look hot in red - hey, would you know where I could get decent but cheap diaphragms for the Sentry IV tweeters? - the flanges are bent and busted in places on my tweeters too.
that little notch in the upper brace where the tweeter nestles is a flexy spot.
Karlson Evangelist
Simply Speakers, $19.95
http://www.simplyspeakers.com/ev-replacement-speaker-diaphragm-89486a.htmlShould be the same diaphragm as the T35 and Klipsch K77 tweeters.
Bob Crites has some comments:
http://www.critesspeakers.com/klipsch_tweeters.htmlYes, I like the red. Seems a better color for WAF, as well!!
Cheers,
Geary
Edits: 05/19/13
I have finished stripping the bass bins. Messy, time consuming and just plain NO FUN! Started with my belt sander. Not a chance. The EV textured finish gummed the belt almost instantly. Tried coarser belt, still not good. Had to drag out the 7" grinder and get sanding disks to fit. 80 grit and lots of changing disks, but worked. The factory coating was tough stuff!
I had to fill quite a few 1/4" and 3/8" holes in the sides. Must have been used to mount something(s)!? Dowels and glue, good to go!
The entire bass bin was stapled to assemble at the factory, mostly held up well except for the seams at the corners, (well all of the abuse occurs here!). I glued and screwed the entire perimeter. I still need to fill the the countersinks holes and a few gouges and then sand again. Nice improvement in the "knuckle knock" test. Everything is and sounds solid. I will pick up the BB ply and cherry stock and start prepping to convert from beasts to beauties!
I air blasted the sanding dust and blew out the folded horns. I cannot believe the amount of crap that came flying out of the bins. Hell, that's got to improve the bass just having clean soundways!!!
Cheers,
Geary
Edits: 07/07/13 07/07/13
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