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Old 10th May 2007, 06:48 AM   #1
D OB G is offline D OB G  Australia
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Default Wharfedalw ob

I hope open baffle speaker threads belong here.
"There is nothing new under the sun"
Apart from going back to vintage radio obs, Gilbert Briggs of Wharfedale fame came up with an ob design after hearing Peter Walker's Quad ESLs. He was impressed !!(sometime before 1958). Believing that something could be done with dynamic drivers to compete with, especially, the midrange, he came up with a design that was essentially the same size as the Quads. (36"wide by 30" high with tapered side wings reaching 9" deep). A 15" driver was placed center and and at the bottom. An 8" or 10" driver was placed above (both in parallel), behind a diffusing slot. An ambience tweeter was placed behind the baffle pointing upwards, with a 4 uF capacitor in series. The 1/2" ply baffle either side of the drivers was laminated. 1/2" ply, 1/2" dry sand 3/4" ply. i.e 1 3/4 " thick. So we have some sort of pre-Visaton OB, pre-Basszilla OB2. It was obviously not a commercially viable design, and he left the promise to DIYers. All this and more can be found in his excellent book "LOUDSPEAKERS by G. A. BRIGGS"- unfortunately out of print.
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Old 10th May 2007, 10:27 AM   #2
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Indeed. My friend Steve Shiels & I have been playing with exactly this over the last couple of weeks with his Lowthers & a couple of Goodmans 301s. GBs book is still a very entertaining & useful text, as it contains some universal truths that are often forgotten. Such as bigger is almost invariably better. We tend to forget the creativity of some of the pre T/S designs nowadays -applying modern technology & refinements to some of these ideas can reap considerable rewards.
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Old 10th May 2007, 02:56 PM   #3
Geoff H is offline Geoff H  Australia
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Hi Folks,

Another classic Briggs design was a W15RS in a front firing 5 sided dual slot tuned BR corner cab, with a horizontal baffle on struts, supporting a Super 8 and a Super 3. Radiation into the listening area was off the back of the smaller cones. Ambience was from the upward facing fronts.

The slot ports were on the short front/sides, coupling to the adjacent walls. The main cabinet was constructed from 3/8 ply - 2 layers spaced by 11/2" of sand.

With my limited ventures into OBs, I often feel the sound off the back of the cone is more musical than that from the front, though lacking in the top end.

Makes me wonder about the idea of a downward facing B200, into a TQW or BVR, back exposed, and a small ribbon on top. Maybe a Shadow variant.

Regards,
Geoff
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Old 10th May 2007, 03:39 PM   #4
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Does anyone have a photo or drawing of the Wharfeldale OB speaker? Thanks. James
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Old 10th May 2007, 03:55 PM   #5
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Default "Loudspeakers" by G.A. Briggs

After reading this thread I came across this book in Wilmslow Audio's site (.co.uk) where it is for sale at 9.95 STG. I have no connection with this shop
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Old 11th May 2007, 09:41 AM   #6
D OB G is offline D OB G  Australia
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Default Wharfedale ob photo

Hi jimmyd53,

I have a photo, plans, and circuit diagram of the Wharefdale ob speaker, but as a new member I am unable to email them to you yet. I will as soon as I can.

David
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Old 11th May 2007, 09:41 AM   #7
D OB G is offline D OB G  Australia
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Default open baffle design

Apart from using a high Qt driver (say 1 to 1.2 or even up to 1.6 in some examples), in a conveniently sized baffle, there is another approach, that I use in my designs. The woofer is wired in series with a large inductor, or, to reduce the impedence, and therefore the size of the inductor required, two 8 ohm woofers are wired in parallel, which obviously doubles the radiating area and reduces the cone excursion. (Using a single 4 ohm woofer helps with the inductor size at least). Various parameters can be manipulated. The usual 6 dB per octave loss occurs according to the baffle size, which is equalised by the large inductor.
A low fs speaker is chosen, and the size of the inductor is made to accord with this frequency (this is only an approximation, as the impedence characteristics around the resonant frequency are obviously not constant). A typical inductor might be 20- 40 mH depending on the woofers. The series resistance of such an inductor with appropriatedly guaged wire might be 2-3 ohms. So by chosing woofers with the appropriate Qt of somewhere between say,2.8 and say, 3.8, a perfectly damped low frequency response (your choice of 0.56, 0.6, 0.7 e.t.c.- or whatever)can be obtained with a flat response between the inductor high pass frequency (at 12 dB per octave i.e below the resonant frequency), and what becomes the baffle width determined low pass frequency (at 6 dB per octave- ready to crossover to a full-range or mid range at 6 dB per octave). This gives great design control, with the only downside being a loss of efficiency. Using something like a MLSSA (I use an old "Imp" from Liberty Instruments) changes can be readily measured. I have been building speaker like this since 1978, and I suspect that the new Open Baffle design by Jamo uses similar principles.
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Old 11th May 2007, 09:48 AM   #8
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True, though I seem to recall Linkwitz (one of my audio Gods) comenting that the polar response of the recent Jamo baffles could be 'interesting.'
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Old 11th May 2007, 11:49 AM   #9
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Quote:
Does anyone have a photo or drawing of the Wharfeldale OB speaker? Thanks. James
Hi,

I also like the book, because of its oldfashioned looks. For DIYers there are many other books which go more into Details.
In Germany we have the books of Hans Herbert Klinger e.g. from 1968. This was my first book when I started building my own speakers.

Open Baffle is only a very basic attempt. Normally you can get much better results from a given speaker with more elaborate cabinet designs.

Best regards, Johannes LeBong

Here are pictures from the book and from the OB by Briggs.

Click the image to open in full size.

Click the image to open in full size.
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Old 11th May 2007, 02:00 PM   #10
D OB G is offline D OB G  Australia
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Default Jamo Open Baffles

Hi Scottmoose,

I agree with Linkwitz as deity.
Why did he say there might be problems with the polar response of the Jamos?
Incidentally, the baffle can be made just as wide as the drivers. (with further loss in efficiency of course- Celestion did exactly this for a subwoofer I believe).
You then get an excellent figure of eight horizontal polar response up into the 100s of Hertz if you like, which blends very well with the changing polar responses of the mid and high drivers.
And with a smaller baffle you can make it much less resonant (I have used mdf/sand/mdf and mdf/stone/mdf (which uses a lot of glue!!).

David
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