Electro-Voice Sentry IV-A's

[galyons]

I picked up a pair of EV Sentry IV-A's today. The Gefco woofers need new foam surrounds and the boxes are a bit rough. All of the speakers and drivers measure within spec for DCR. So I am hoping that refoaming, cleaning, working over the x-overs and fixing up the bass bins cosmetically will get them back into service.

I plan to run them with my Paramour 2a3's.  I heard the EV's in a "shoot out" with Klipshorns  maybe 15 years ago.  I liked the EV's better =>smoother mid range and high frequencies, but not quite the low-end extension of the K-horns.  The K-horns, obviously took the corners and the EV's were placed next to them, so placement advantage played a role in the perceived bass extensions.  (It wouldn't have been fair to NOT give the K-horns the corners. It was not like we were switching this brutes about constantly!)  I still have a strong aural memory of the dynamics of 100dB plus horns!!  It was pretty amazing.

I know these behemoths are the antithesis of the Orca's, or any other modern single driver speaker, for that matter.  It will take me awhile to get them going.  Then sneak them past the wife with the usual "What new speakers? Those? They have been there for ages!!" 

Anyone using, abusing or just futzing with the old Sentry's? Other '60/70's folded horn bass bins with mids/tweeters? Would love to hear your thoughts !

Cheers,
Geary

 

[galyons]

They are up and running. Still need some work. All of the Gefco 12" woofers now have new foam surrounds. There were three of one production, surround roll up and white glue globs for the leads in the cones. The "odd duck" had all of the same production codes on the back of the magnet strap, but the surround roll was down and the lead glue was clear.

The horns didn't sound all that good on initial fire up...screechy! Replaced the old zip cords connecting the horns and the wire for the woofers with solid core silver plated copper/Teflon...more focused imaging and detail. I took the tweeter protection circuit out...better still. Then I replaced the x-over caps with Russian PIO; KBG 2uf,(tweeter), and MBM 30uf, (mid). The old caps were mylar and one of the 30uf was an electrolytic. Everything smoothed out, timbre was much better, imaging much more focused and a the sound lost a coarse, nasal quality.

So, the bass? One would think, based on the size, and 2 12" woofers per side,  that bass would be subterranean...Nope, doesn't get to the sub woofer realms.  But placed in the corners of my room, (approximately 15'X 40'), the bass has much more impact than my Gallo Solo's, (Rogue Audio M150 Magnums or monoblock modded Golden Tube Audio SE40's) w/ SS powered subs, or my open baffle project, (GTA's or bi amped Bottlehead Paramours). (OB =>Audio Nirvana cast 8 and Eminence Alpha 15). I am running 1 BH Paramour per side. Will try bi-amping with the Paramours, when I figure that out from the x-over schematic. (The 1/4" phono jacks on the bass bin's were replaced with a 2 bladed connector, the x-over switch to bi-amp is actuated via a 1/4" jack.)

What I hear is marvelous. Approximately 102dB 1w/1m is really amazing in terms of dynamics.  I really like the horns. I could probably live with the bass, but the bass bins are huge. As one can see in the pic, there is nowhere for additional subs! So, I am going to indulge on my wife's tolerance and let the new parts in Sentry's burn in for awhile. Still need to work on mounts for the horns. Clean up seems to be never ending as every time I touch the speakers I find new nooks and crannies full of decades of dirt and dust.

Fun project....loving my Paramours!! (and they definitely like the easy lift of 102dB efficiency!)

Cheers,
Geary

 

[Paul Joppa]

Yeah, a 102dB horn woofer smaller than your kitchen is never going to make subterranean bass. Impact, yes and in spades, but not deep. Physics, you know.  :^)

 

[galyons]

Don't give me that Physic's cr@p!!  I see ads for 4" subwoofers that go to 24Hz!!  

Moved the tweets down to the design position in the upper bass bin.  Better integration and got the treble closer to ear level. 

I have never had "Big"  before. No pin point imaging, but I am transported to the venue! Deep and wide...Real scale! 

Ella on Verve, New World Symphony on Vox, Miles KOB on a German import reissue, Famous BlueRaincoat...it was a good evening!!

Cheers,
Geary

 

[galyons]

The original crossover can be switched in by inserting a dummy 1/4"phono jack into the J1 bi-amp switch. This takes the woofers, out of the x-over circuit. To bi-amp one would need to provide an external crossover and amp.  I plan to reduce the x-over to eliminate the tweeter level switch,bi-amp jumper and the STR. Without the level switch the frequency versus power handling for the tweeter is 10w@15K. (See Curve 1 on chart)

This is my x-over revision. This layout can be strapped for single amp or bi-amped. I dropped the .6mH,(Not sure why it was there!) coil in the switch circuit and added a 3uF cap in the mids to maintain 2nd order roll off. These values are basically the stock values. When I model, the crossover points are more like 500Hz & 4750K Hz, 2nd order Bessel. The spec's call out 400/3500 Hz.

I am definitely not real experienced playing around with x-overs. The plan is to replace the current x-over box in it's entirety with the new crossovers, rather than hack up the stock units.

Making some progress....mid horn's chips and broken tweeter mounts have been repaired and threaded inserts installed to hold the tweeter horn mounts and keep the mid horn mouths at proper opening height. Should solve the "Damn the tweeters are loose again, get me an even BIGGER wood screw!" problem. Other than the expected wear and tear, this is the only cosmetic issue that required structural repair.

Crossover components arrived today, so I will start them over the weekend.

Next will be to sand and refinish the mid horns. Then lot'sa cover up of the "Grand Old Girls" age and travel related blemishes on the bass bins.

Still dealing with the "Can I keep them?...WAF issues!" Gotta make them look like furniture...well maybe appliances...wooden refrigerators? But I got the extremely rare admission that they sound "Really nice!"

Cheers,
Geary

 

[galyons]

A quick update on the restoration.  I have made progress on the bass bins and horn cosmetics.  Amazingly they haven't gotten smaller or lighter!! The crossover is maturing. Just added a tweeter EQ circuit that greatly increased the high end extension.  Pretty amazing how good 50 year old speakers can sound, especially with 70 year old tubes!!!!!

Cheers,
Geary

 

[howardnair]

i myself love big speakers -i have built a pair of EV design speakers that are 4 feet tall-2 wide 19" deep-the sound is nice and big -easy to drive -i am not sure how low they go but a 15 inch woofer-seems more than adequate-and not having a wife and only a part-time girlfriend -size does not matter!!!

 

[Mmaxed]

Geary, those look reeeaaaally good.  I have a pair of Vals and you are so right on the big speaker sound. 

 

[galyons]

I used the holidays as an excuse to not mess with the Sentry's and just listen.  The crossovers finally seem to be fully burned-in and wow!  I am really happy. Adding the EQ circuit to the tweeter really improved the upper frequency response and the brilliance.  There was a very steep roll off starting about 10KHz, now that treble extends out to 16KHz, but about 5dB down from 8kHz.

I am getting some guidance from an EV guru on another forum, and the recommendation to add the EQ circuit was spot on.  He has suggested that I move the mid/tweet XO point to 3500Hz from the current 4700Hz....so that will happen in the next week.  This should smooth out the response.

Cheers,
Geary