Discussion in 'Speakers' started by cptnCanada, Jan 7, 2014.
Great choice Mark. Anxious to see pictures
I couldn't resist trying out the Eminence 12 LTA. I had some unused "Hygeia" Planars available for the Tweeter's.
The LTA's really shine in this application running FR with the Planars highpass @ 8k 2nd LR.
PG has suggested the zeniths really need a tweeter and in the consoles i think they had one. curious re your take on that
have held off on searching for a pair of these cuz i didn't want to mess with 3 way crossover
The Zeniths do benefit from tweeter sizzle on the top and you're correct that their donor consoles used them but those original tweeters were nothing to write home about. The Eminence ASD 1001 is a fantastic match for the Zeniths and I added some rear firing Realistic super tweeters to increase that slightly out-of-phase holographic sound that OB's are famous for. Since my Zeniths run off the same SE amp as the tweeters with only a single 1.5uF cap to block the LF they hardly constitute a 3 way ( including the separate amped woofers ) in the traditional sense.
Here are the Zeniths 49CZ 852. They are running just the driver now. I might hook up the tweets. Amp is a Magnavox 196, updated to DG-SE-1 specs. I'm running this with a Modi Dac, mini pc, Tidal. No preamp. Volume by PC.
Very nice, I need to get mine out of the mock up baffles.
Mark, I always enjoy your DIY efforts. FWIW those light weight Zeniths ( thanks to their aluminum frame and small alnico motor ) were originally mounted in consoles from the rear just as yours are.
I have a pair of 4.5" Fostex that weigh about as much as the 12" Zeniths.
And how appropriate to see a tubed Magnavox powering Zenith speakers - both legends from the golden age of sound.
I found them yesterday, vintage french Cabasse 8" speakes for cca 30 bucks. It looks ideal for some open baffle madness.
It seems like I get to give this a try and document results.
I made two identical cabinets, each with a JBL 2251J. I made backs for the cabinets and currently have one back on (no stuffing) and the other off. I'll have to do some mono listening like this, A/B'ing between the two sitting right next to each other and find what's preferable to me in my room.
I'll be using them with the Heil AMTs so maybe the open back may be the way to go. We'll see.
So far in A/B comparisons watching prime time TV, the open baffle is not doing it for me.
It gives a "spaciness" to the sound and takes away focus and intelligability.
OTOH, The 2251Js are very nice and have more than enough sensitivity to compete with the horns.
Drivers designed for enclosures often don't perform well in open baffles.
Actually, the 2251Js were designed to be used in horns with very small enclosure.
With the open back, I get a much flatter frequency response and this gets me down to ~200-250Hz where I want to cross these over. The closed back doesn't get me anywhere near there.
I take it all back!
The open baffle is not only more efficient (>1 dB overall), it has a smoother FR in the area of interest. I just needed to get everything set up properly for a fair comparison, not use them in conjunction with the L200/300s, and get a decent source through them.
I am currently just using one channel and A/B'ing the closed and open back using no eq or room correction. In this case, the closed back has a bit more bass. But bass below 200-250 Hz is not the issue or even desired here and when I turn on the sub, the open back really shines.
I'm sold and will get some RTA pics showing the diffrence in pink noise when my camera battery recharges.
How open does the open back have to be to be an open back??? Would be nice to leave some back back there to mount the terminal.
OK..., got some RTA screen shots showing the open vs closed back with the 2251Js in ~1/2 cu ft cabinets. The only filtering being used is a 33.6 mfd cap inline with the positive terminal and the speaker is set to "large."
The microphone was placed inline between the two speakers at a distance of 2 meters on a tripod sitting on the couch cushion (legs in). "Close" micing was not performed because this defeats the purpose of the open back. No eq of any type is being used. Of course this does include the effects of the room.
The intent is to run these from ~250 to ~2,500 Hz.
Note that with the closed back, the frequency response "falls" as the frequency is reduced such that between 250 and 2,500 Hz there is a span of about 16 dB (i.e., -83 to -67 dB).
But with the open back, the frequency response remains fairly flat dropping substantially below the crossover point, which is essentially what we want here. The span is reduced to about 9 dB (i.e., -74 to -65). The overall volume is also louder.
It is interesting that even though the closed back sounds like it has more bass, the open back must by responding with things/reflections in the room causing more deep bass. I am simply switching between the two speakers and recording the results without any provisions to equalize their volume. What you see is what the mic hears.
I have found that while no back is better than having a full back..., having some back can produce a flatter bass response than no back. Therefore, I'll cut both backs down to two strips to go along the bottom to hold the terminal cup, and the top to match, leaving about 31.5 sq in in open. This is also roughly the area of the cone so we'll see how that goes.
Meanwhile, I pulled the back off the other one and have each sitting on an L200/300 cabinet. These are wired with 35 mfd in series with the positive lead to the "B" speaker output though my speaker switcher that allows for volume matching. I actually have these turned down by ~8 dB according to the panel markings.
I'm loving it! If you look at the RTA plots you will see that the 2251Js have a nice little "bump" that fills in the gap left by the crossover between the 2235 and 2420. Then you get a near perfect natural rolloff to the 2405 with no electrial filter necessary! Vocals and cymbols become so much clearer, or there where they weren't before. I should have done this years ago.
Actually, I'm betting that the 2251J could easily replace the 2420/horn all together, go much lower, and would be smoother doing it. May just need to turn off the horns and give this a try.
Not to veer too wildly off topic (like a 4 year old thread hasn't veered off topic), but would the dipole woofer arrangement below essentially need drivers that were good for open baffle? I suppose the only commonality between them and open baffle would be the total lack of cushion that's normally provided by an enclosure. NOTE: The three unseen woofers are open on the other side of the enclosure staggered a driver height lower.
I'm contemplating plagiarizing this design a bit and thinking that one of the open baffle favorites, like the Alpha 15, would be a good fit. Maybe a 12 inch rendition to shrink the footprint a bit.
Welcome to the "Dark Side" Will!
Is that a Slot loaded design that would stand upright?
I always thought that slot-loaded was two drivers facing each other with the "slot" off to one side. This is six drivers, all facing downward, with the openings staggered between front and back. Originator Ralph Helmer used the phrase "modified carotid" at one time, I believe, but it could've been tongue in cheek on his part.
My thought is to use two drivers and have them exposed on two, if not all four, sides.
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