OBs Chez uglymusic?
My visit around to Jim's has got me started thinking about whether OBs (Open Baffles) could be a sensible and/or workable choice for my system. I loved the wide, airy, room-filling imagery and horn-like immediacy.
It's not that I'm dissatisfied with my Royds. They're great. The best small speakers I've ever heard, but I do believe a good biggun will always beat a good littlun. And Jim's OBs are bigguns - at least from the front - containing a Lowther wide-ranger and a 15" bass unit.
Am I getting ahead of myself? Maybe I need to say what Open Baffles are. They're a piece of wood (or acrylic, or glass, or whatever) with a number of holes in them for drive units. Often there's just one hole for a wide-ranger.
Anyway, at this point I need littleuns not bigguns, because of the space and layout considerations of my living room.
However, Jim's OBs break some of the rules of OBs by not having baffles the size of the end of a house. The argument is that the physics of sound waves dictates very large pieces of wood to play low notes (at sufficient volume). So, over e-mail, I started wondering if OBs could be scaled down so that they would present a more room-friendly face still.
I realised that the bass output from a small OB would be less impressive than from Jim's, but over a series of e-mails we put together a design for an OB with another wide-ranger and a couple of eight-inch bass units, all components that Jim had hanging around. The two smaller bass units rather than a single 12-incher allowed us to have a narrow baffle so that the frontal area of the OB was not much bigger than that of the Royds on their stands.
Jim knocked up our Mark 1 UMRFOB (that's uglymusic's room-friendly open baffle) and connected it up to his bi-amped, active-crossover rig. To cut a long story short, it didn't work. Not enough bass, and generally lacking all-round.
Time for me to get reading more about OBs...
So the plan is - once the two cars' MOTs, VAT and my company tax bill have been neutralised - that I'll be:
- buying a couple of Visaton B200 drivers, as featured on this mega thread
- running them in my office system on a small baffle
- seeing what they sound like on an UMRFOB
- probably buying a second pair and using digital EQ (software in the Mac) to push out more bass
That's the plan put together with lots of guidance from Jim. But it's just a plan. We'll see what happens in practice. It may not be possible to make OBs as room-friendly as they need to be here, but it won't be too costly an exercise to find that out.
I've left quite a few holes in this post, just to keep it half-manageable, but I'm aware that I may have left too many, so please fire away with any questions or comments. They may well help with my first foray into speaker design.
Comments
Sounds exciting dave!
OB's have always looked interesting to me, i have been reading a little of what A Briggs wrote on the subject and it would seem that huge baffles are less than ideal , also that circular baffles ,though intuitive, are also less than ideal , from what i understand the room and position of proposed OB's therein will need much experimentation , to squeeze more bottom end from the b200 perhaps a single series inductor could be employed rather than resort to digi eq ,albeit with a loss of sensitivity, this will of course be determined by the full range driver and baffle alignment and room alignment then a little measurement to see where you need the b200 to take over,
using two b200s in one baffle with the drivers stacked will of course give two different bass alignments due to boundary/floor coupling , i have been wondering if two driver could be placed face tp face isobaric stylee with one driver 180 degrees out of phase but in an OB? two motors driving the same volume may give better control and may even lower cone resonance, just a thought!
please keep us posted,
regs,
matt
i take your point on full range OB's and the lack of crossover ,i am though somewhat curious as to how the digital eq will make up for the overlap between drivers in a multi way system, unless you were thinking of allowing the overlap then eq the whole response region 100hz-1000hz digitally ,?,
please excuse my continued prodding here but, i cant see how the full range driver and bass driver can co-exist without a filter of some sort without producing a significant hump in the response over the output range of the bass driver that is employed, hence my mention of the briggs design, he overcame the issue by selecting two large drivers that each would have given a fairly full response on its own , the bigger of the two drivers gave slightly better low end performance while the smaller unit gave better upper performance , when the two outputs are summed they give a surprisingly even response ( when positioned close to a side wall and about 1/3 of the way along the length of the room) and also worked to give the amp an easier load ,
looking forward to reading more of your exploits in the world of the OB Dave,
all the best,
matt
never heard a b200 but the waterfall analysis suggests it rolls off quite quickly above 6k but the response graph suggests it holds up quite well? damn measurements ,
this is what i have been considering since Col let it be known that he had a baby class A in the works ,http://www.troelsgravesen.dk/OBL11.htm , basically a rework of the Briggs sfb , i was really set on trying the eminent lft16 but at 80db 1w@1m i dont think 15 watts will cut it,
sorry again for being a bit of a dufus ,
all the best,
matt
My limited experience in this field was a OB/Horn hybrid. Bass duties were provided by an Eminence 15" unit ( i Forget the model but could find out) in a relatively narrow baffle (which i know shouldn't work). Next up came a cheap full range 8" unit (55 quid off the bay) which was run full out iirc. Mid and tops were horns but take these out of the equation for a moment. Crossover was electronic.
To my ears, we didn't measure the response, the bass end of things went very low (i know it shouldn't) was very tuneful and fast - the bass end was being fed with a large pro-style amp. Whilst 300Bs did mid duties and T amp upper freqs.
I reckon mattylynch is right here with the caveat that I reckon the full ranger will need some help in the upper freqs. I think you could gt away with a large bass driver driven by a big amp in a relatively narrow enclosure the full ranger run open and a decent tweeter.
I'm sure folk will tell me that this goes against the laws of physics but what i heard sounded very nice indeed, particularly at the bottom end.
welcome Stu, good to see you here.
I seem to remember Paul Hynes doing something very nice with Eminence drivers, in some kind of OB array. I'll have to see if I can find a link when I get back to my 'puter, but he had a very narrow baffle on it. In his case, I should imagine the multiple drivers would somehow reinforce each other across the frequency range.
But so very right.
Paul H's set aren't that expensive, really. Just over £2K for the drive units, plus the baffle and a metal frame to hold the thing together.
The main problem I have at this stage is that my room isn't OB friendly, but Jim and I are going to have a play and see what we can do. In fact, he says he has an idea that he is planning to try soon, which may work in my room. Our first idea sounded so bad that Jim hasn't even kept it together so I can hear it!
It all is most interesting, and utterly beyond me for that matter.
What makes you room OB unfriendly? Is it alcoves either side of a chimney breast, or a near-field layout? As I understand it, an array powers the whole room, while monitors in a near-field setup avoid exciting the room.
OBs also tend to work much further out into the room than I have room for.
Basically, it's an issue of space.
Thats the second time in this thread we've heard of narrower than standard baffles working too, and perhaps ten inches could be sufficient for your room?
The version that didn't work had twin 8-inch bass cones in a 10-inch baffle.
Jim is currently looking into a simple design using some Solarvox drive units he has and a dollop of digital EQ as I already have the digital EQ working well here.
Interesting with the dollops though, but I still cant understand how what is needed can be determined without a mic?
http://www.supravox.fr/anglais/haut_parleurs/215_RTFBIC.htm
Welcome back to the man himself!
I suppose I might have guessed you weren't meaning these:
Comet specials, I believe.
will you have digital crossovers?
(Leonardo da Jimci?)
I assume you're delighted with the 'speakers...?
@Ben - delighted is perhaps too strong a word. They need help at the top and bottom. I've only done them that size coz Dave is happy doing digital Eq. They approximate a baffle 27" wide, I've folded them back to save space. They should get down to 100Hz ish before roll-off, room placement will help as will some Eq.
@Dave - yup, SS all the way just now. But one of my 807 amps is at the amplifier hospital, Dr Andy is rebuilding it :-)
My new pair should be singing in a day or two. I'll post photos when they're in place.
I'd love to hear 'em one day. :-)
Is this an ongoing project? Ie is there a mk2 in the pipeline?
Also, can you explain to he who is simple what equating to a 27 inch baffle means?
You're welcome to a listen mate.
The widths of front and both sides adds to 27", therefore the front wave has 27" to travel before it meets it round the back. So it's nearly as good as a full width baffle. But not quite, IME folds introduce a very small amount of resonance but nothing like as bad as a box.
If Dave "gets" the OB thing there will be a MK2 but not until he has the room I expect.
Great work Jim. Nice clean simple design, Even I might be able to get them past swmbo !
I am sure they sound better than the OB's I heard at Scalford ( white ones in the AOS room I think ). They were very thin and tinny albeit the room acoustics did not help.
Shame we didn't get a chance to talk much at Scalford.
Yes pity that Jim. The day just flew by. Maybe at an OB bake-off !!Hmmmm OB bake-off
B-)
http://i667.photobucket.com/albums/vv33/mjkempton/daveobsmodified.jpg