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  1. #1
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    Latest full range Open Baffle build

    These are 12 inch full range Eminence Beta 12LTA's with super tweeters over Eminence full range Alpha H-frames. Unreal dynamics and surprising detail.


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    Rear view of Eminence Beta over Eminence Alpha


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    These 3 way OBs are 3/4 MDF covered with textured wallpaper and painted with Behr Silver Hill. This is much easier than trying to get a good finish on MDF. Up close the textured wallpaper looks like tooled leather.

    The tweets run a simple 1uf cap as a filter. I may try driving them with a t-amp to see what tri-amping sounds like.

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    Betas ( on left ) next to Tang Bands

    Unlike the Tang Bands ( on the right ) the Beta/H-frames are very affordable and cost under $300 to build. Compared to the more refined Tang Bands, the Betas have that pop factor and will rock out on more types of music. The Betas can handle complex swings in dynamics common in full scale classical movements but may lack some of the hyper detail of the TBs. I like them so much I decided to retired the TBs for awhile. If you want a big sounding OB that will play loud as hell yet has lush mids and tight bass with sparkling highs this should be your next build.

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    Anyone there?

  6. #6
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    Chickenhawk

    Quote Originally Posted by Poultrygeist View Post
    Anyone there?
    When a poultryguist arrives all the chickens scatter; heck no no one is out there.

    I like them. I guess I am starting from the wall out; maybe my wallet out???. When I get to other end of the system you and I are going to talk. I have two systems I am going to work on. One in my dining room and one at my computer. Dining room first.

    I am very interested in doing a tri-fold room divider system making an old pair of maggies the center fold and off to the side on one of the other folds an open woofer. I am thinning like oriental type room divider but knowing me it will come out more European/Scandanavian looking just like the style better.

    After that we are going to talk horns. I have never got the Altec Lancing Voice of the Theater sound out of my head; which I heard over thirty years ago. I noticed they still sell the used horns on ebay and they are not cheap.

    I am definitively in the-do it-your-selfer camp. I majored in Industrial Arts, taught shop, ran a handyman remodeling business. Every time I look at something I think how could I make that or make it better. Which probably really means how can I make myself better by learning something new. A brain loves novelty and my hands love to tinker.

    On the other hand there is much to be admired about manufactured items of high precision. Being able to blend both is the nirvana you probably find in building a speaker.

    Enjoy your day!

  7. #7
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    BoJon,

    You've got some interesting ideas. The Altec Voice of the theater is a true classic. I know a guy in Charlotte who has a pair of Frazier "Dixielanders" which are mammoth theater horns of the same vintage. Those old theater speakers from the 40's and 50's had to be extremely efficient as they were driven by SET's and flea watt tube amps. Of course those great old juke boxes from the 40's and 50's were all open baffled with one huge full range driver powered by a low wattage tube amp. Solid state audio didn't catch on till the mid 60's.

    Being a former shop teacher you are a natural for DIY audio.

  8. #8
    Music Junkie E-Stat's Avatar
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    Do you notice any difference in imaging using the 12" midrange vs. smaller drivers used in some of your other projects?

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    I really did not have great expectations that a $69 12 inch wide bander ( some don't feel it's full range ) could compete with a $250 point source driver like the 8 inch Tang Band W8-1808 ( some say Lowther clone? ) but it does.

    The trade off in unmissed detail yields mammoth sound staging. As you well know E-Stat, getting the mid range "out of the box" and hearing that rear radiation slightly out of phase is the dipole drug that hooks us so completely. The Betas do that well while sounding huge and unencumbered. They offer the spacial perception of music occupying real space in front of my listening position. And while imaging is comparable to the TBs they may lack a bit of the airiness.

    All drivers have warts and the compromises are what keep me going and totally entertained with each build. And while I might miss some of the spit in Miles' horn, the Betas can transform my 16X16 room into a live dance hall. I can't get that with the ultra smooth delicate presentation of the TB's which is perfect for small group jazz. But the Betas make me want to get down with the honking guitars of Dire Straits.

    The demure Tang Bands can't gut with the boisterous Betas but why would they want to?

    The lesson learned from this 3 way build is don't be afraid to go big.

  10. #10
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Poultrygeist View Post
    The trade off in unmissed detail yields mammoth sound staging.
    Actually, I was thinking of the difference in directivity between the "wide bander" and in particular, the super tweeter.

    Quote Originally Posted by Poultrygeist View Post
    As you well know E-Stat, getting the mid range "out of the box" and hearing that rear radiation slightly out of phase is the dipole drug that hooks us so completely.
    Coherency with the rest of the frequency range is also part of the allure for me.

  11. #11
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    Using a horn super tweeter in OB is a compromise but can still give decent dispersion especially when toed in. Not like a Raal ribbon but that would wreck my price point. Since I only crave top end air and cymbal shimmer I tame my tweets considerable which makes for a good blend with the Betas.

    I'll soon cut off the Beta dust caps to make way for phase plugs for increased smoothness.

    At 98dbs and a Qts over .5 the 12 inch Beta cones move lots of air which is critical for OB.

    I guess the OB concept, as old as it is, is still foreign to most folks. Of course if you don't build a pair your chances of hearing them are quite remote. I'm convinced that their simplicity scares companies away as they don't look profitable. There are a few exceptions and Jamo is one. I may build a clone of Jamo's double woofer 3 way someday.

    I've noticed that OBs get lots of love on AC.

  12. #12
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Poultrygeist View Post
    Using a horn super tweeter in OB is a compromise but can still give decent dispersion especially when toed in. Not like a Raal ribbon but that would wreck my price point.
    Sorry, I'm not being very clear. The issue I see is the transition between the extremely narrow dispersion at the upper end of a 12" driver vs. the wider dispersion of most tweeters. What is the crossover/blending frequency?

    A friend's JBL taught me an interesting lesson about imaging. It used a 5" midrange beyond its useful range where the directivity gets very narrow - then transitioned to a wide dispersion tweeter. The effect was like that of a fun mirror. The apparent stage was wide at the bottom and the top, but pinched in the middle. Very peculiar.

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    While this might be an issue with conventional speakers, it's not the same with full range speakers. The Betas could go it alone and don't require a tweeter. I added the tweeter for the cymbal shimmer and it's barely audible on anything else with a 1uf cap. I tried several cap values and listened until it sounded right.

    E-Stat, you need to get some full rangers to play with.

  14. #14
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Poultrygeist View Post
    While this might be an issue with conventional speakers, it's not the same with full range speakers.
    Exactly how does the speaker know this?

    The cone size of a 12" driver is likely about 11" - the wavelength of which translates to a frequency of about 1100 hz. Any wavelengths substantially shorter will have a narrower radiation pattern. As an example, the large Advent uses a 10" woofer with a measured cone size of 9". Its wavelength translates to a frequency of 1500 hz - which happens to be the crossover point to the 2" tweeter. While the "fried egg" tweeter doesn't have the extension and wider dispersion of smaller domes, I think it is a better match for the size woofer.

    Quote Originally Posted by Poultrygeist View Post
    E-Stat, you need to get some full rangers to play with.
    I'm sure I would enjoy some true full rangers of the smaller variety like Ed Shilling's design. Perhaps I'm just overly sensitive to coherence issues since I've used full range stats for 35 years.

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    There are many pages on several forums regarding the Betas in OB. Maybe you can find some answers in this thread.

    Beta 12LTA + Beta 12A-2: is this open baffle concept viable? - Page 2 - diyAudio

    I live only a few miles from Ed and have heard his horns many times.

  16. #16
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    Lightbulb

    Quote Originally Posted by Poultrygeist View Post
    There are many pages on several forums regarding the Betas in OB. Maybe you can find some answers in this thread.
    Once again, it seems that I'm not doing a particularly good job of describing what I hear. That thread is about frequency response and, in particular, low end cutoff. What I refer to polar response and how the inherent directivity of the drivers(s) in a multi-driver affect imaging. You want to match them as closely as possible.

    With "conventional" speakers, each driver is selected for use across its intended range understanding not only its frequency range, but its radiation pattern as well. Which is why you won't find anyone transitioning a 12" midrange to a dome tweeter.

    When you start, however, with a full range driver allowing it to operate freely (albeit with narrower directivity at the top of its range) and THEN add a wider dispersion tweeter on top of that, you end up introducing what I find to be an audible discontinuity. The harmonics and overtones of some instruments will sound as though they came from differently sized sources. That challenge is avoided when the driver is allowed to gracefully narrow its radiation on its own - without a another driver "showing it up" at the same frequency with superior response.

    A couple of years ago, I visited an retired engineer in Ohio who I met at another audio forum. I was on a business trip and had some extra time. He graciously invited me to his home. He is also an Advent fancier and had performed a number of modifications on his pair. He also has tweaked a pair of JBL L-110s, the less popular but more neutral sounding cousin to the L-100 Century. We first listened to a few tracks on the Advents and then switched to the JBLs. Immediately, I noticed two things: the JBLs had a more extended and superior top end to the Advents. That was good. On the other hand, the dome tweeter had audibly wider dispersion than the 5" midrange did at the highish 4k crossover point. Usually, tweeters are crossed over an octave lower, but that limits power handling. The result was certain instruments took on a fun house mirror effect with respect to imaging. The harmonic was one width while the overtones were another. I found it very distracting. Part of the piano was one size while another part was different! My friend, however, didn't notice the effect that night. He did later after we discussed it at length following my visit.

    Since I am one who highly values coherency, I would gladly sacrifice the extension of the JBLs for the coherency of the Advents. Or, most likely, the notion of allowing a full ranger to do its thing and run by itself. My brain more easily forgives sins of omission vs sins of commission. In this case, bandwidth vs oddball imaging.

  17. #17
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    I don't do well at discussing that which I've never heard.

    Full range drivers and SETs are considered benchmarks for coherency.

  18. #18
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Poultrygeist View Post
    Full range drivers and SETs are considered benchmarks for coherency.
    I concur entirely having used full range drivers for 35 years. Without augmentation at either end by different drivers. Every square inch of radiating area is identical to the next in bandwidth and directivity.

    As for amplification, coherency depends upon whether or not you use the same amp(s) across the full range since there are variations in distortion spectra, noise, dynamics, and tonal balance among different designs.

    The 12" driver by itself would indeed speak with a single voice.
    Last edited by E-Stat; 05-09-2012 at 06:39 PM.

  19. #19
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    Nice speakers Poultrygeist. Quite frankly though, I can't get off the Betsy open baffles

  20. #20
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    Hey Mark,

    The Betsy folding baffle OB's ( Wild Burro Audio Labs ) are just stupid good. I've heard $1000+ speakers that couldn't touch the $100 Betsy's. Didn't you prefer them over the expensive Omega's?

    If I had to choose a "desert island" single driver OB it would be the Betsy's. You must be the only person on this forum that tried a pair after reading my raves and now you're hooked.

  21. #21
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    I haven't heard the Omegas, so can't comment. And yes, I am hooked on the Betsy OB thanks to you. I probably would have never heard about the Betsys let alone an OB design if you hadn't posted it on here, so a big thanks goes to you. I also agree that these speakers sound as good as some $1000 speakers, and from experience, they sound better to me than my Revel Concerta M12's, which I think is a fine speaker for the $1000 range or under. Enjoy the weekend I think I'm going to get an early start with a Brooklyn Lager........

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    Mark, now I remember it was the Revels you compared the Betsys too. Someone else pm'ed me they liked the Betsys better than their Omegas. I'm amazed that others here don't give them a try. They are so easy to put together a ten year old could build them. They sure got me started in DIY. where for me building is almost as much fun as listening.

    I'm enjoying a long weekend thanks to Confederate Memorial Day. I'm shocked we still get this day off in the SC. I'm having a cold one myself. Take care and have a great one.

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    "Box speakers and solid state mimic the master tape best while single ended triodes and open baffle speakers mimic live music best" - AC member

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    Quote Originally Posted by Poultrygeist View Post
    "Box speakers and solid state mimic the master tape best while single ended triodes and open baffle speakers mimic live music best" - AC member
    I had never heard that quote before, but it is spot on. The low watt SETs and OB combinations that I heard at PG's house produced a level of realism that I had previously heard only once before, through Maggie 1.7s. Before hearing the Maggies, I didn't know that was even achievable. The fact that SET/DIYOB delivers it for less than half the price of a pair of 1.7s is a major breakthrough in high end Hi-Fi.

  25. #25
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    Quote Originally Posted by cackalacky View Post
    I had never heard that quote before, but it is spot on. The low watt SETs and OB combinations that I heard at PG's house produced a level of realism that I had previously heard only once before, through Maggie 1.7s. Before hearing the Maggies, I didn't know that was even achievable. The fact that SET/DIYOB delivers it for less than half the price of a pair of 1.7s is a major breakthrough in high end Hi-Fi.
    The Maggie-OB similarity obviously stems from their dipolar designs.

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