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Why a single driver open baffle?

Luminary designer Seigfried Linkwitz has been a proponent of multi-way open baffles for many years. Recently, commercial manufacturers like Jamo, AV123 and others have introduced highly successful models. And of course, the panel speaker (electrostat and planar) folks have been there all along. Getting the midrange driver out of the box brings an intoxicating openness and clarity to the sound. The speaker sound big and unencumbered. Voices and instruments sound “there”. Of course, there are downsides. Dipoles need to be positioned out in the room a good distance, as they’ve got sound coming from the rear of the speaker. If you want to fill a big room with deep, chest thumping OB bass, you’ll need 4 woofers. Or a woofer in-a-box on each side.For most folks and most music, the midrange and coherence of single driver OB’s is worth losing a little bass impact. You can leave your OB’s in the corners for background music and TV (something absorptive behind them wouldn’t hurt). When you’re ready for some serious listening, drag them out to the middle of the room. Listen near-field. As you don’t have to worry about driver integration, you can get as close as you want. If you’re like me, you’ll get lost in the midrange. And you’ll hear all of the bass line. It will be perfectly integrated with the music, neither disconnected nor overwhelming.There are practical considerations for the DIY’er too. Betsys work with amplifiers from 1/2 to 300 watts. You don’t need to be able to cut accurately. The bass is neighbor and wife friendly. The rear wave is out of phase, so there are nulls to the sides. You can have bass in the listening position, but it won’t carry through walls. They are also easy to experiment with. Cut some holes and add some helper woofers. You can use plate amps to drive them. Make replacement center baffles so you can try vintage drivers. Buy a pair of cheap subs from Parts Express, some high efficiency tweeters, take off the wings and try a three-way setup with Betsy as the midrange. Or, leave them alone and spend your time and money on a really good source and amplification.Fullrange drivers and open baffles aren’t the right speakers for everybody. It wouldn’t be any fun to spend dozens of hours gluing hundreds of dollars of birch play into a complicated horn only to find out that you would have been happier with a pair of 70’s JBL L100’s. But the Betsy O.B.s are so cheap and easy; why not give ‘em a shot? Mine aren’t my only speakers, but if I had to choose, they sure could be.


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8 Responses to “Why a single driver open baffle?”

  1. mark Says:

    It is the coolest site,keep so!

  2. rjbond3rd Says:

    How low does a Betsy on your (really cool) OB go? Thanks in advance!

  3. dave Says:

    I tried the pioneer b20 on open baffle. they were good and went loud, but the bass suffered.
    your slightly higher qts looks just right to fill the bill. But not so high that they would have
    loose bass with a tube amp.

    I also tried the Moth Cicada drivers on open baffle. these sounded great – you are right about
    the midrange on open baffle – but were not quite tough enough to get sufficiently loud

    I also tried the Ciare ch250 drivers. These went loud enough but lacked in the highs and lows.
    I may have had them on too small of a baffle.

    I would like to recommend covering one side of your OB “cabinets” with Frostking duct insulation
    from Walmart. I don’t care for Walmart, but this stuff will really deaden the panels. You could even
    go with 1/2″ material on the side wings, this stuff works so well. I recommend rangerboard or medite.
    chearper than ply, softer sound than MDF. Not to make too big of a deal about this though, because
    as Wild Burro says, open baffle speakers care MUCH less about what kind of material you use than
    boxes because they do not store as much energy.

    Happy listening to all people who give this driver company a try.

  4. Paul Janda Says:

    The short answer is: into the 70’s, which is enough for many folks. You can get lower, but that means getting bigger!

  5. Paul Janda Says:

    Dave,

    Thanks for your comments! I’ll have to give the duct insulation a try. It sounds easier than the cork recommended in the “darkstar” thread.

    As to driver selection, yes, you do need a Qts around .7 or a little higher. I’ve seen measurements suggesting that some 8″ fullrangers that are commonly and successfully used on OB’s (like the unfortunately discontinued Cicada) have Qts’s more in the range of 1. You can always raise Qts a bit with series resistors, and possibly even really small wire. If you really want to get it higher, try a decent sized (high watts, low ohms) resistor (noninductive) in parallel with the voice coil!

    As you suggest, though higher Qts can net more bass, you can reach a point where the quality suffers. That point will depend greatly on your personal listening preferences and your choice of amplifier (as many tube amps have higher output impedances and thus raise the effective Qts.) The Betsy is an attempt to hit the sweet spot. Playing/tweaking is certainly welcome, but not necessary!

    Again, thanks for your comments, and let me know if you want to give the Betsys a try.

    Paul

  6. Alex Hervet Says:

    I would love to build the OB but my wife is not Ok with the size it would take. I suggested plexiglass but it’s expenseive and she had another idea : covering plywood or MDF with mirrors. How would you think it would sound ?

  7. Paul Janda Says:

    Alex, I don’t see why you couldn’t. I’d make sure you use an adhesive that is fairly damped (PL construction?), otherwise the very stiff combination might ring. And it’d be heavy! Sorry it took me so long to get back to you! -Paul

  8. Fitzpatrick Reid Says:

    Ok I have received my Betsy’s and I must say I totally like the sound. It has a big sound that I like that reminds me of my Quads ELS 63″s which are in need of repair. For anyone one who is undecided just go for it because this is the best $100.00 you are going to spend in audio. I will however add some low end in the future and will seek Paul’s advice who I must say is extreamly helpful.

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