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I have a pair of EV Sentry IV-A's. They are in the finishing stages of a rebuild as I described in an earlier thread. They have 2 Gefco 12" Alnico woofers per bin, 1823M drivers on SM120 horns and ST350 horn tweeters.There is discussion on another thread about the FR of the ST350 not being much above 12KHz, which is a fact on mine. This is not a major issue for me, as I do enjoy the overall sound of the Sentry's and my HF hearing is probably not much higher anymore. Don't need to go to 20KHz, but an honest 14KHz might be nice. Need to be around 103-105dB/1W/1m. Since the ST350 is essentially the T35 with a different horn, I tried a pair of Crites ST-125's that a buddy has. No much to my taste on the Sentry's, too bright and glaring.
Has anyone tried a different tweeter CD/horn combo that they liked? Not necessarily on the Sentry's, but one that crossover at about 4 to 5 KHz? My current crossover point for the ST350's is 4700Hz/12dB. For those not familiar with the EV Sentry IV's, the tweeter is mounted to the mid horn with rails and sits in the top of the upper bass bin.(see pic) This makes tweeter swapping relatively simple. Would putting a different horn or wave guide on the Eminence APT used for the Crites make a positive difference? Other alternatives?
I sheathed the old ply on the bass bins with 1/2" Baltic birch ply and put a "beauty belt" of solid cherry around the mid band, so no longer looking quite as road worn. The more solid, thicker walls really tightened up the bass, increased the apparent speed/attack and definition.
Quite happy with that!!!Cheers,
Geary
Edits: 10/22/13Follow Ups:
Update! I finally moved the mid/tweeter XO point from 4700Hz to 3500Hz. In combination with the EQ circuit the change had far more overall effect than I expected. The treble is much better, more air and sparkle. The upper midrange seems to be cleaner and have a bit more inner detail.
Thank you, Paul E! So quite honestly, I wish I had done this much, much earlier. But a change to parafeed 300B amps got into the mix and the Sentry's sounded so good...well you know!
Next step is to align the mid & tweeter, per Paul's direction and I will likely be an even happier camper!!!
Cheers,
Geary
Hey Geary, that's great! Sounds like you're having a blast working on this project.Lowering that mid/high xover point improves the sound partly because the mid isn't going as high, where it becomes harsh, and partly because the tweeter has better dispersion in that range.
On the other hand, be aware that you're asking the tweety to go lower, which at high output levels (or with certain instruments like snare drum, cymbals, trumpet, piano, marimba), could kill the voice coil - its excursion is miniscule. Especially with only a 6 dB/octave slope, this is something to be mindful of. And believe me, you DON'T want to have to replace the voice coil. Its wire is so thin that if you look at it the wrong way, it'll fry.
E-V made a product called the "STR tweeter protector", specifically for the ST-350 and the T-350. You might consider finding a couple. I was never a big fan of them for P.A. use, since they would tend to kick in sooner than I'd like, shutting down the tweeter too soon in my opinion. But still, for home use, it might be useful insurance to have.
Carry on!
Edits: 05/23/14
The "magic" appears to be the EQ circuit. I started my XO tests at 3500Hz, originally, but no EQ. It was definitely not the best sounding point. I have listened for several months with the EQ and XO at 4700H. The treble extension was improved to the point that I just settled in and enjoyed. But Paul E.'s recommendation to go back to 3500Hz was always niggling in the background.
As usual, he was spot on. Knowledge and experience, yet again, trumps rudimentary learning!!!
This has been an immensely pleasurable project!! Plus, I get rewarded for the effort every time I listen!
Cheers,
Geary
Well "hat's off" to Paul E. and grindstone. I built the EV recommended EQ circuit on daughter boards, as I'm out of real estate on the main boards. Not an issue as these boards are for testing the XO. It will all go on the final boards.Here is a comparison of the EQ and non-EQ XO's:
Note there was a 1dB difference in the pink noise reference volume between the 2 measurements. (Non EQ 87dB, EQ88dB. Close as I could get with the stepped attenuator on my pre.) They were taken on different days.
This is just adding the EQ circuit to the current XO with the 450/4700hz cuts. The measurements were taken at the listening position, so the room plays in the FR.
I will try to do 1 meter measurements in the next few days. I have coils/caps to try the 3500Hz XO point, but just now I will spend sometime listening to this configuration.
Here is a progress shot on making them prettier. I will update the restoration threads with more pics over the next few days.
I still have to refinsh the tweeters and mounts plus I have quite a bit of touch up and final polishing, but getting close!Here is a pic of the EQ daughter board in action!
Edits: 11/11/13 11/11/13
Whoa, dude! That's great.
Is your measurement gated, or not? If not, the HF roll-off is to be expected, because of the room's contribution, and some of those irregularities can also be room contributions.
If you want to do 1 meter measurements, that's fine, but be aware that you will get noticeably different graphs when you move the microphone up or down even just an inch.
I would suggest that you take that puppy outdoors to a reasonably large open area (a large yard, or a parking lot), and run a bunch of measurements at various distances and vertical mic positions. Also, if you can acquire the software to do gated measurements, that would be very useful. Taking it a step further, do a bunch (8-10) of gated measurements, and compute an average curve from all of them. And, as long as you're outside, I would also encourage you to take off-axis measurements. Heck, if you plan it well, you could take an entire day and maybe fire up a grill and make some baby back ribs while you and your friends do measurements and chat up hot girls who are just there for the beer and margaritas (yeah, that's what you should do!).
The cosmetics are looking excellent, too.
Lastly, make an attempt to normalize the frequency response at some frequency, such as 1000 Hz, for various measurements. That will make it much easier to quickly see differences. For example, in the comparison chart you provided above, adjust them so that 1 KHz is the same for both graphs. This way, even if you offset them by some amount for clarity, you have a reference point from which to assess differences.
Carry on!!!
:)
Gated, no. My measuring is pretty rudimentary. Stereophile Test CD, android tablet with Audio Tool and Dayton Audio iMM-6. I will rerun the tests, setting the reference at 1k from the CD. I will do off axis, but I don't have much width in the room. Crap if I learn what half the options do in Audio Tools, I will be light years ahead of my knowledge today.
Now, as to hauling these "puppies" outside. Ain't gonna happen. I live on a steep hillside. I go up a flight of stairs to get to the main level. I PAID my dues getting those hulking SOB's INTO the house! ;-) Now if the trophy girls will haul them out AND back in for ribs,beers and margaritas, well that may sway me!
I know that I have room issues. The room is 14" wide and 34' long with an 8' to 14' cathedral ceiling. Wood floors with area rugs are also a factor. My wife refers to the room as the living/dining room. Wants furniture within. Go figger!
The speakers are on the narrow wall, one in a corner and the other near the corner, but about 1 1/2' out due to a hearth. I get about 3-5db higher in the bass from 50 to 80Hz on the corner loaded speaker. With the 120 degree dispersion of the mid horn, early reflections are a problem, but not enough to significantly hurt stereo imaging. I am sure that I am loosing some pin point soundstaging. But the tradeoff's are well worth it! (But there is no way that the EV's image like my Gallo Nucleus Solos's positioned 8" from the rear and 3 feet from the sides!!)
I know that your suggestions are spot on! I just can't make them all happen! But don't let that deter commenting, they are greatly appreciated!!
Cheers,
Geary
"I know that I have room issues. The room is 14" wide and 34' long "
That is the funniest damn thing I've read all day.
lol
Typos can be hilarious.
:)
Well I told you "off axis" measurements would be tough! ;-)
Geary
The bad news is that I have done nothing after adding the EQ for the ST350. Thanksgiving rolled into Christmas and, quite honestly, the good news is, I just enjoyed listening. The EQ really made a major improvement! The tree goes out this weekend and with it my excuses.
I will take my measurements referenced to a 1KHz tone and then move the mid/tweeter XO point to 3500Hz.
Paul E., a quick clarification, you wrote:
"Once you get everything working, you can try getting the 1823's and ST350's in phase. To do this you can build a sled so you can mount the tweeters on top of the cab, and slide it back and forth. Reversing the tweeter connections from their normal hookup, you can set an oscillator at the XO freq., and slide the sled back or forth to find the point where you get the greatest cancellation at the XO freq. with a mic placed at your listening position. The test tones on the Stereophile Test CD will work for this if you don't have an oscillator, and a reasonable quality mic plugged into something with a VU meter will suffice. When you reconnect the tweeter normally, the mids and tweeters will support each other at the XO freq."
The ST350 is mounted to the ST120 horn front via metal rails. Should I look at mounting the tweeter to the bass bin brace so it is in its "design" location? I could design an adjustable mount that would allow some front to rear movement, but it would be limited by the brace. The ST120's are mounted to be moveable and even more so with out the metal rails for the ST350.
In your experience, how much offset was required to get the mid and tweeter into phase at 3500Hz?
Happy New Year!!!
Cheers,
Geary
Geary
I didn't know you had any horns but I see you are using a baby cheek and those are fantastic but if you want the best driver outside of a field coil for high end extension,my favorite is the JBL 2435H..Of course I run them on my wood horns from First Octave audio and this is my smaller set but the highs are incredibly good and well extended..The TAD is also excellent but very expensive.The Altec 802s and 902s are very nice also..
Some people like second order distortion in their tube amps,some people like honesty in their tube amps. I like honest!
Hi Mike,
Yeah, I got that bug too. I use the SE40's with Gallo Nucleus Solo's for bombastic orchestral and dino rock. Most everything else goes into EV BottleHead Paramours 45 MQ iron + Sentry's or BottleHead Paramours 2A3 with Altec iron + Econowaves with 10" BR.
My SE40's are not quiet enough for the 102dB/1W/1M Sentry IV's. Borderline on the Econowaves at approx. 97dB.
If the Baby Butt Cheeks are the JBL 2404H, mine are actually EV ST350's, somewhat similar. I may track down a pair of the JBL's to try. I like the looks of the horns in the link!
Cheers,
Geary
http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20(1977-05%20AES%20Preprint)%20-%20LF%20Horn%20Design%20Using%20TS%20Paras.pdf
Note woofer parameters...this a long x-max heavy cone woofer.
This horn will not work properly with a light cone.
It is one of the best folded horns ( 50 Hz or higher) ever made.. for it's size.
The BMS is one of the most effcient tweeters available to 18 kHz. A bit of a bite however.
B&C have a new tiny compression drive the.7 and the.5
I really like them' but not as effcient as the BMS.
If you have the money, theT900 is the best sounding.
Best. Bill
hey Bill - why won't the lighter cone stronger motor 12s work? - in the sheet below from Jim Long, it shows the EVM12L (solid line) as being more efficient in the 150-500Hz area than the "original Alnico woofers" (GEFCO with foam surround)
does your 70Hz horn like the 12pe32?
Karlson Evangelist
The Sentry 4's I saw had a rubber( or foam) surround. I don't recall they were EV 12's
The best modern woofer would be the RCF L12p300.
Just going by memory.. but I was in competion with the Sentry 4 with a single 15 ... and I lost!
It is a very good design if you don't have to go below 60Hz or so.
The best modern double 12 is the Klipsch theater model. I forget the number.
Bill
Mine are Gefco's with foam surrounds. At least they are foam now, when I got them the surrounds had pretty much disintegrated. But the few remnants were definitely foam.
Cheers,
Geary
I'd be hesitant to replace the ST350. It's a fine driver with low distortion. There's also the question of "bastardizing" a very nice vintage product by plugging in 3rd party drivers. Which reminds me - those Gefco woofers, they're not original either, are they? If you replace the ST350 as well, you really don't have a Sentry IV anymore, you've just got a Sentry IV box and midrange. That really diminishes the "vintage value" of them.Looking through my old E-V data sheets, I can't find the Sentry IV - I must have tossed that one decades ago during a major culling. But, if memory serves, that driver has reasonably constant directivity up to a fairly high frequency, and the expectation was that some EQ would be employed to "flatten" the response both on and off axis. In other words, if you measure it on-axis, 30, 45 and 60 degrees off-axis, it remains relatively consistent in its FR, even though it rolls off. So, EQ'ing is not a problem.
Two other related things:
First, the ST350 is a T350 (not T35) with a different horn and less pretty motor housing, but is essentially the same driver. The T350 was designed to have flat on-axis response, but becomes increasingly beamy with rising frequency. The ST350's horn was designed to have a more consistent dispersion pattern over a wider frequency range.
Second, the Sentry IV was designed for high efficiency in the bass region and sacrificed very low bass output to achieve that and used a "utility" cabinet, while the Sentry III was designed for extended low bass and sacrificed some efficiency, and used a pretty "furniture" cabinet. The Sentry III employs the same midrange and tweeter, but uses a bass reflex enclosure instead of the Sentry IV's folded horn for the low end.
While the two products are similar, and in fact identical in some respects, their designs were intended for two different applications: The Sentry III for high fidelity wide frequency range applications such as high output hifi use or small/medium size nightclubs; and the Sentry IV for applications where high output within a slightly more restricted frequency range was more important than extended low frequency performance, such as auditoriums.
With all that being said, if you insist upon replacing the ST350s, I'll take them off your hands.
Edit: IIRC, you've done quite a lot of work on those cabinets, and have shown us some more recent photos. What's the latest status on them?
:)
Edits: 10/23/13 10/23/13
B model
I have a ST350B EDS pdf, but it does not have this plot or a description of the EQ after an X36. It does mention EQ after the X36 and an AT38 attenuator. Here is a link to my version.
Could post your EDS or a link to it?
Cheers,
Geary
1987 Part no 530321-320
This is the FR plot from the Sentry IV-A EDS. I am not getting the high frequency extension, although my room runs to the bright side of things. Note that the factory crossover has power switches that attenuate the signal to protect the tweeter for high power/volume usage. As well as a tweeter protection circuit. The plots 2,3 & 4 represent the treble reduction in the factory crossover settings. The factory tweeter crossover point is 3500Hz. (I built my own crossover, eliminating the power switch and using a 4700Hz crossover point, no tweeter protection circuit - because, to me, it sounded better!)The EV X36 crosses over at 3500Hz.
Cheers,
Geary
Edits: 10/29/13
Geary
As the pic in Grindstone's post alludes to, the ST350 was meant to be used with a passive EQ circuit following the X36, to compensate for the falling high freq. response of the CD horn. The ST350B EDS shows a 7.5 Ohm resistor in series with an 0.18 mH inductor shunting the plus to minus, followed by a 2.5 to 3 uF cap in series with the ST350 plus terminal. Without this (or something like it) the ST350 will sound very shouty. You don't mention whether your DIY XO incorporates an EQ circuit like this or not. I would try the stock 3500 Hz XO freq. along with this EQ circuit, while adjusting the cap value. Your choice of a 4700 Hz XO point may have somewhat of a similar effect. Just my take on it.
Paul
Geary
Note that the reference by Grindstone and me is the Electro-Voice ST350B EDS (which is gone now from the EV discontinued products website!), while the one linked by you above (and what comes up with a google search) is the University Sound ST350B EDS, which has nothing about the EQ circuit which would follow the X36. Products which were superseded by newer EV products ( but were still being made) were frequently re-badged as University by EV, and got a gray paint job. The Sentry lVA EDS indicates a pro-sound application where active EQ would be present anyway, which explains why the passive circuit following the X36 is dropped in the later versions, but there was a fixation on not blowing the tweeter, which is a non-issue nowadays with a low power SET amp.
Paul
Paul this is great! Thanks. The good news is the XO is still on the test bed board so I can try this! The bad news is that I thought I had the XO done and was finished tossing $$$ at it!Would you provide your thoughts on the possible best way to proceed?
1) Keep my current XO point at 4700hz and do the prescribed EQ after the XO. Reading the new EDS, it sounds like the circuit works for any XO point "at or above" 3000hz?
2) Keep the upper band pass at 4700hz, lower the ST350 high pass to 3600hz and use the prescribed EQ circuit. Would this give me a bump in FR at around 4150hz?
3) Change both mid and high to 3600 and use the prescribed EQ circuit.
I in my listening tests I liked the 4700hz configuration better than the stock at 3500. The transition was more seamless and the high frequency smoother. Additionally the higher point potentially offers a bit more tweeter protection as I removed the STR circuit. You are quite right about the tweeter blowing paranoia. Removing the treble attenuation and STR were big improvements.Thank you for taking the time to "bonehead" this for me!
Cheers,
Geary
Edits: 10/24/13 10/24/13
Geary
The 4700 Hz XO point would have a similar effect to the EQ circuit following the X36, that is to say suppressing the midrange hump at the lower end of the ST350's response as seen in the EV EDS. It's no surprise that you preferred the 4700 Hz to a 3500 XO, the ST350 sounds really harsh without the EQ circuit, and more like a T350 with it. I would at least try it with the 3500 XO and the EQ circuit, and you have the option of adjusting the cap value to fine tune it. Lowering the cap value will decrease the steepness of the ramp beginning at about 2500 Hz and tilting downward towards the highs, at the expense of losing sensitivity as you suck more energy out of the lower end. Use only air core inductors (no iron)! The concern with the 4700Hz XO is that there might be a dip in the response in the area where the 1823M and ST350 integrate, but you'd have to measure this and see. The 1823/1824 family don't have phase plugs and just can't go very high, hence the EV tweeters going lower than others like the JBL's, and why you don't typically see JBL tweeters with these EV mids., but EV T350's can work with JBL etc mids.
You would have to measure the response of the EQ circuit with a 4700 Hz XO to see what happens, and how it reacts with the higher XO point, but adjusting the EQ cap value should have similar results.
I would try working with the ST350's first before going to other tweeters. The Fostex 900's that RCA Fan recommended look great from the specs, but at $1800 a pair they may make the ST350's start to seem like a good deal. Anyway, let us know how it goes. Good luck from the Electro-Voice Brotherhood!
Paul
Paul,
I am going to stick to the stock ST350's. The EDS that grindstone posted shows 3 alternative XO/EQ examples. 3kHz, 3.5kHz, (X36) and 6kHz. I could go to a 3.5kHz, Linkwitz-Riley alignment, (that is what the X36 appears to be, then add the EQ, but that is more components in the signal path. And I would have to buy new air core inductors. Also, I am concerned with taking the ST350 that low without the tweeter protection circuit, which adds even more! In your opinion, should I be concerned?This is the 3kHz:
I like the current 4700Hz, but you shared some concerns. Since 4500Hz is 1/2 octave above 3000Hz could I not just multiply these values by the SQRT of 2, (1.4)? That give me a C 3.4uF and the L .448mH. That calculates pretty close to a straight Butterworth filter at about 4100Hz, so I assume the EQ is from the filtering of the 3kHz hump in the raw FR.
The 6kHz example has me confused. My electronic mathematical skills are limited, but if I am reading this correctly are they saying to parallel 3 inductors to have an effective inductance of .12mH? .
Here is my confusion, .12mH in the crossover would not get a filter anywhere around 6kHz. Am I missing something here?
The 3kHz bumped half an octave seems the cleanest alignment, with the fewest components. (And close to good foil inductors that I have to hand!)
Is my logic faulty on the "bumped" component values to get to approximately 4.5kHz AND have the desired EQ?I really appreciate your, and everyone's, input on this Sentry odyssey!
Cheers,
Geary
Edits: 10/28/13
The "Fig 5" circuit is a 12dB/octave Butterworth high-pass with a corner of 5300Hz. It therefor attenuates the energy going to the tweeter, 12dB/octave below 5300Hz. So it gives some pretty good tweeter protection.
In conjunction with the tweeter's falling response, then net total acoustic response is roughly equivalent to a highpass at 3000Hz, according to the manufacturer specs being quoted. But that is NOT what the electrical filter is doing, that's just the total effect of filter plus tweeter response.
Thanks PJ,
That makes sense. I can do the XO math, but understanding the total systemic effects mostly alludes me!!! So without more knowledgeable input from experts/wizards/engineers I wind up with lowest common denominator solutions. Just trying to make an even better match for the Paramours!!
Cheers,
Geary
This has a lot of similarities to what we did with the old "Climax" speaker design. A lot of tweeters have non-flat response (especially horns) that can be compensated in the crossover, but the book values have to go out the window to do it.
Thanks PJ,
I am pretty much a book values beginner on this. I started with the original EV crossover box and listened, measured and tweeked from there to get to my current XO. But, admittedly, I used "book values", i.e. the XO formulas in Excel and/or the online crossover calculators.I think the speakers sounds pretty good, with the exception of the high frequency steep roll off. They sound exponentially better than the factory XO boxes, but that is likely due to the much better components that I used versus the nearly 50 year old components. Hopefully the EQ circuit will improve on the tweeter results.
I am always grateful to those who share their experience and expertise, because that allows me to achieve much better results than my limited expertise would provide.
Cheers,
Geary
Edits: 11/04/13
Geary
The Linkwitz-Riley XO comes from direct radiator land where it's useful to focus the main lobe radiated in a 2 way box speaker. In a rig like the Sentry lV, the mid and tweeter horns will dominate the dispersion in their pass bands, and the natural steep bass roll-offs of the horns will dominate at the lower ends, so a 2nd order Butterworth should be fine.
As I recall you mentioned using a 45 or 2A3 SET amp which would indicate a music listening application for the Sentry lV's, and it's rather unlikely you would blow an ST350 with a sub 5 Watt amp. You would have to push the amp into hard clipping with a test signal long term to do it. I use my ST350A's as rear firing tweeters in a 3 way di-pole horn rig with 6 drivers per side, and I cross them at 2500 Hz with a first order series crossover. The forward firing tweeters are T350's, and I've been running them with 2500 Hz 1st order XO's for well over a decade and I have never blown one. Ditto for the T35's which the ST350's recently replaced. If you are concerned about this, you can use the STR tweeter protection modules, but I had these back in the 80's and never heard one switch out even with a 100 WPC SS amp playing loud rock'n roll, so they went in the parts box. BTW the EQ circuit will in itself offer some protection to the tweeter as it's shunting energy through the resistor. I just don't see tweeter protection here as an issue, but as I don't have control over your rig, I'm not gonna guarantee your voice coils ; )
I don't have a freq. resp. graph for the 1823M, but my 1823 and 1824M's start to roll off quite steeply much above 2500 Hz with my DIY tractrix horns, hence my choice of this XO. Crossing the 1823M and ST350 at 6 K would guarantee a dip in the response between them. Though a 4500 Hz XO may give acceptable results, a dip could be expected there too. Once again, you could straiten this out to a degree with active EQ, which would be there anyway for feedback suppression in a pro sound setting.
I'm not sure exactly what you mean with the "bumped" XO idea. If you parallel three 0.12 mH inductors, they would function as a single 0.04 mH inductor in a circuit. Why EV spec'd it this way is hard to say, perhaps it was cheaper to do it this way than a single 0.04 unit due to parts availability, and they had 0.12's on hand from something else. You can connect inductors in parallel to get a lower value, or in series to get a higher value. Caps have a reverse effect and are connected in parallel for a higher value, and series for a lower value. There are online calculators for this (do a search with "parallel inductor calculator" etc), as well as calculators for XO's and notch filters (which the ST350 EQ circuit is), see link below.
BTW The spec'd 7.5 Ohm resistor in the EQ circuit can be hard to source, so I used two 8 Ohm resistors in series, and paralleled with one 8 Ohm resistor from RS which is close enough. I use a 0.20 mH Jantzen foil inductor, and I settled on a 2.20 uF cap. Larger caps (up to 10 uF) did'nt seem to do much, while smaller caps (down to 0.68 uF) shunted so much energy out of the ST350's that the old T35's could easily drown them out, along with some roughness appearing at the upper end of the ST350's with the 0.68. I think you're just going to have to break down and buy some parts. Don't worry, you'll use them from the parts box sometime down the line. I always do.
Paul
OK! OK! 3500Hz it is!! ;-)!! You are quite right on the 1823M roll off, as well. This is from the 1823M EDS with PA horns but, probably similarly applicable with the ST120's.
My reference to the X36 being Linkwitz-Riley was due to the values of the capacitors and inductors that they used. A L-R alignment with those values is about 3500kHz.
My alignments are Butterworth. I prefer Butterworth, so...will the EQ be affected with approximately C = 4uf and L = .5mH for the XO before the EQ rather than the X36 values?
Just for grins & giggles,I am not sure about what EV engineers meant for inductor value on the 6K. I couldn't find what the referenced part number value is. I got the same .04mH paralleling 3 x .12mh and thought "no way!". So three of those referenced parts yielding .12mH was my conclusion, but still doesn't work out to 6K for me!!!
Off to make a BOM!!! Butterworth or X36 values? What did you use?
Thanks for all of your practical experience!!!!
Cheers,
Geary
Geary
The X36 is a Constant K crossover, the main feature of which is a low insertion loss, and secondary to this is the use of two identical value inductors: 0.727 mH (see the X36 EDS for more, if it's still up on the EV site). Constant K's are seldom seen now except in line level stuff, but EV championed them back in the 70's, which always seemed odd to me due to the fact that the T350 (107 dB) and 1823/1824 (105+ dB) mids had to be padded down to mate with even high efficiency direct radiators in boxes. Anyway, the three parallel inductors in the 6K XO for the ST350 start to make sense in the light of this. The sensitivity of the ST350 is listed in the EDS as 101 dB with the aforementioned EQ circuit used, and the use of 3 paralleled inductors was most likely an attempt to maintain as low a DCR as possible to maximize sensitivity, without having to source a single low DCR (and thus heavier wire) choke of the necessary value.
I did'nt take the 6K XO seriously in fig. 6 due to the fact that you would realistically need active boosting in the area between the 1823M and ST350 to make it work, but it 's a stand alone XO for the 1823M and ST350 none the less, which slipped by me. You can use one of the online calcs I linked to design your own 6K XO for the ST350, and then design a notch filter to pull down the ST350 mid hump centering around 2.5K Hz., and see what you get for comparison. As Paul Joppa's post notes: the XO, the accompanying EQ , and non-flat response of the CD horn ST350 are all a working unit. You would have to try the EQ circuit with a Butterworth and see how it performs, but I would'nt expect any drastic departures from what I've seen.
For the easiest way to go, just combine the X36 with the EQ circuit already discussed. You'd need just 2 caps, 2 coils and a few resistors from Parts Express, and then see how you like it. You can probably even run the ST350 wide open with no L-pad. Note Inmate's post from a few days ago concerning matching the coverage pattern of horn drivers. The ST350 is probably a better match to the ST120 mid in this regard than many others. I love the Fostex alnico horn tweeters, but they have been criticized by some for being a bit beamy. You may run into problems however in a small room (or a rectangular room with the Sentrys on the short wall) with reflections off the side walls from a mid horn with a wide horizontal coverage pattern like that, resulting in smearing of the stereo image, but you don't seem to be complaining about that so far.
I moved on from my X36's (and X8's) some years ago after measuring the response of my 1823's and T350's with no crossover. First order 500/2500 Hz parallel seemed the obvious way to go, and later first order series crossovers. That's perhaps a bigger can of worms than you wanted to open though.
Paul
Paul,
I have a plan....I will go with the 3500hz, but with the Butterworth alignment rather than the X36 alignment. I brought the woofer/mid up to 550Hz, may help a woofer dip from about 250-400Hz. Comparing all of the available EDS FR plots, (lot's of assumption/extrapolation, since none really are the component mix in the Sentry's), I do think I will get the smoothest FR with this alignment. Thank you for pointing out the 1824M drop off above 2500Hz. The 1823M, with the PA horns, looks like that drop starts around 3000Hz to 3400Hz so that really focused the XO point.
I validated using the calculators in the link that you provided. It is more sophisticated, allowing the selection of an initial slope of 3dB or 6dB. (BTW, great link. Much good stuff there!! I saw why I was getting vastly different component values from different formulas and calculators! That's my handicap...good at math, weak on what the results mean acoustically in the real world!) If the EQ gets the ST350 10kHz -15kHz up eliminating the steep drop off, I will be a happy camper....and an EV purist!! ;-)
I will go with this to listen/test/tweak. I have some 15ohm Mills 12W, (overkill) I can parallel for the 7.5ohm and caps from 2-3.3uf to try. I will probably start with a 2.2uf as I have some Russian mylar/paper/oil caps that may be perfect for the tweeter. So I have to hit Parts Express for the .18mH copper foils. Timing is everything...PEx sent me a "Come Back" 5% discount code!
Thanks again for your time and valuable input!!! If you have other thoughts it would be great to hear them.
Cheers,
Geary
Geary
The XO between the mid and bass is an area to look into as the 1823's roll off steeply around 500 Hz at the bottom end, and I see the Sentry lV uses a 400 Hz XO point.
Once you get everything working, you can try getting the 1823's and ST350's in phase. To do this you can build a sled so you can mount the tweeters on top of the cab, and slide it back and forth. Reversing the tweeter connections from their normal hookup, you can set an oscillator at the XO freq., and slide the sled back or forth to find the point where you get the greatest cancellation at the XO freq. with a mic placed at your listening position. The test tones on the Stereophile Test CD will work for this if you don't have an oscillator, and a reasonable quality mic plugged into something with a VU meter will suffice. When you reconnect the tweeter normally, the mids and tweeters will support each other at the XO freq.
Keep us posted on your progress!
Paul
I guess I was thinking about the Fostex T500 which currently costs $1034.40 ea., while the T900A actually costs $535.50 ea. from Madisound.
Paul
I will only add that, frequency curves aside, you should also be looking for a smooth transition from the mid to the tweeter with regard to dispersion. This has a major effect on the reverberant sound in the room.:)
Edits: 10/25/13
Hey Geary,
Paul has a good bead on this. I would only remind you that the x-over isn't just about FR curves, it's also about SPL and diaphragm excursion. The ST350 phenolic diaphragm is fairly "delicate" (which partially accounts for its excellent HF performance). Depending on your SPL desires, you'll want to cross to it at a reasonably high frequency and/or steep slope, so you don't make it go too far one way or the other. While E-V specs (I think) 3000 Hz as a low end, that depends on how loud you're playing the system. I cross to my T350 at about 5500 Hz, at 12 dB/octave, for home use, and I can crank it 'til I'm happy, with no worries.
:)
Agreed! I doubt I listen to these much over 80-85dB. I was listening more for smooth integration and transition from the mid horn to the ST350 than FR. Quite honestly I started at the stock 3500hz and tried XO points every 250hz. Right about 4750hz sounded really nice. I don't think I heard much difference at 5KHz, so stopped. Maybe I should have tried higher!?
The ST350 is 3-4dB/1W/1M less efficient than the 1823M/ST120 mid combination. The tweeter attenuation in the stock crossover was for protection, not level matching or FR.
This discussion has been most helpful and explains what I was hearing and my measurements. Since this EQ is only on the ST350 I won't be mucking up the midrange.
Wish I started this discussion months ago!!!
Cheers,
Geary
Thanks Paul, that sheds some light on the plot and dispersion graph. Here is my current XO schematic. When I build out the final board it will be with bi-wire for the bass bins. I need to remeasure with this xover. I measured with a xover closer to stock, but need to borrow a mike again.
Thanks to Grindstone for the data and polar plots, and thanks to you for the x-over and EQ insight.
All of that jives with my recollection of the ST350 driver.
Ya know, it's funny. Sometimes, we think "heck, I'll never need this spec sheet again" and then toss it out. Then, 20 years later, ya get onto an Internet forum, and someone's asking about that exact product!
Another reason to never throw anything out!
:)
Yes, the Gefco's were stock in the early Sentry IV's. I think the components changed moving to the A, then B models. Mine are early, 1823M drivers and ST350 round magnets.I recently looked at a IV-B pair that had EVM12L's for the bass, 1824M for the mid and ST350A or B, (square magnet). The mid horn looked much the same from the front, other than mine only mount on the sides and these were ST120A's with a full perimeter flange. The rear looks substantially different, with molded compartments behind the front.
I will probably keep the ST350's. Since the mounting is so simplistic, thought I might try a more "modern", similarly sized and spec'd tweeter. I run 45 mono blocks, so keeping the mid range I have is the major factor. Definitely not looking for 20-20K!!
Thank you for the correction on the T350 versus the T35/T-125. The T-125's definitely did not please my ears!
The face-lifted bass bins are pretty much done, just require touching up the interior black and rubbing out the clear. I still need to do the "permanent" x-over on nicer platforms than the current test mules. I will take some updated pics in the next week or so. Thanks for your input.
Cheers,
Geary
Edits: 10/23/13
Beyma CP25
Add JBL 2404 to that list as well.
APT s OK but a bit hard sounding. I would use a bms 4528ND or beyma cp25.
The APT200 and Beyma 4528ND factory frequency plots look much like what I am measuring in room on my ST350's. Pretty steep drops after 10K. I would rather not EQ. Am I reading them correctly?The Beyma CP25 looks better, to me, per their FR plot. My current crossover would overlap at the dip at 5K and they look good out to 16K, although another 5db dip around 10K.
I appreciate the recommendations!
Cheers,
Geary
Edits: 10/23/13
I replaced the midrange horns in my Klipsch LaScalas with EV SM120, stock klipsch (atlas) driver
replaced the K77M tweeters (EV T35) with Beyma CP25, and that was the biggest improvement. Plus it matches the polar pattern of the new mid horn much better and integrates well. To my ears at least... x-over frequency is 6Khz.
I now have what used to be Klipsch but now look a bit like an EV / Klipsch mixture...
Hey KanedaK, that CP 25 frequency response curve looks very nice. When/if I ever have a need for something like that, I'll look into its impulse response and distortion figures as well. It just might be a good candidate for a high output system. Right now, my current project involves a Dynaudio D54AF and D21AF, and those puppies better deliver!
:)
That beyma is a very nice tweeter indeed. And cheap!
A JBL Babycheek would probably sound even better, but at what price?
Makes the original Klipsch-EV tweeter sound like a grasshopper... haha
only "problem", at least with my ALK "universal" crossovers, it runs a bit too hot... more output than a T35 for sure... so I had to add an L-pad in front of it. Wich I don't like, but I still need to hear the "prejudice" an L-pad is supposed to cause to the sound... my ears don't hear any difference, and at least the tweeter is now at correct output.
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