Would you consider this an OB?

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talaerts

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Joined 2005
All, at 6 Moons they cover a speaker that interested me as it uses 4 FR drivers and a ribbon tweeter:

6moons audio reviews: J.A.F. Bombard

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The thing is, it is marketed as an innovative kind of open baffle.
Now, considering that there are 4 drivers, and a narrow open slit at the back, wouldn't it behave more like a bass reflex box?
 
norman bates

norman bates

Member
Joined 2003
8" drivers don't have squat dispersion, so multiples (vertically) shouldn't interfere with each other. The hemptone climbs past 1khz (from posts I've seen), so that should help off axis not falling off too badly. And lastly the impedence of the tweet (and cap) stays low while the impedence of the fullrangers skyrocket as it goes higher, so the response of the fullrangers will be rolling (higher than if run wide open) off due to the energy flowing to the lower resistance load. And they use a coil to roll off some more from the woofs.

Seeing from earlier thread on "whizzers and intelligibility", I suppose we need the whizzer to help the off axis a bit past 2khz (for an 8" driver), but maybe use a flatish 8" but add a 3" phase plug ?

Neat neat idea. But how nicely does the hemptone do for 1-5khz ? That would be the question. People have liked them, but I'm not sure I want to drop $420 to find out. Maybe I'll run 4 x silver flute but add a phase plug. Then I'd need a stout tweet also (96db or so)

Norman
 
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rjbond3rd

Member
Joined 2007
Viewed from above, it's a tapered (~10-to-1) TL with a line length of ~12" and no driver offset :)

GM blew my mind with this:

GM said:
Viewed another way, an OB is the inverse of a high gain TL, so as the long TL that only has the same pipe area as the driver's effective piston area (Sd) wants a strong motor (low Qts), the unfolded TL (OB) wants a proportionally weaker motor (higher Qts) and smaller baffle.
Click to expand...

Link: http://www.diyaudio.com/forums/full-range/96583-qts-ob-explanation-needed-4.html#post2191638
 
norman bates

norman bates

Member
Joined 2003
whizzer? On an 8" coral driver, the whizzer pulled down the freq response past 1khz-4khz, helped improve dispersion from 2-4khz, and added some high end past 4khz . I'm sure the fr8 (hemp) sounds pretty good (omega loudspeakers). And you save lots of money when you buy in 100 or 1,000 lot quantities.

I like the design. I'm not sure about pushing an 8" up to 5khz or so.................. I'd like to try the wild burro, but that hump in response would not be my cup of tea without a notch. If I was him, I'd pay someone with test equipment and work up some notch filter values. The seas fa22rcz looks really nice, but I'd also like to see the Z-plot of a bare driver. I don't believe those are measured graphs on the seas "Please see the effects of the two proposed networks". But it does have a copper cap, so the impedence should stay low. And it still has a narrow spike at 3khz.

Wild Burro Audio Labs - Fullrange Speakers - The Betsy & Betsy-K Drivers
https://www.madisound.com/store/manuals/fa22rcz_appnote.pdf

Norman
 
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rjbond3rd

Member
Joined 2007
Speaking strictly as a newb: just consider the cabinet types as lying along a contiuum. Very simplistically and randomly:

OB (TL of zero length) -> TL (long straight vent) -> BLH (long expo "vent")-> BVR (bigger chamber, shorter expo "vent")-> BR (short straight vent) -> Aperiodic (resistive vent) -> IB (infinite volume, neglible vent) -> Sealed (no vent, shrinking volume) etc.
 
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