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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.

Docfoster

Read through that quickly over breakfast.
Sounds exciting dave!

uglymusic

Hope so!

mattlynch

hi 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

uglymusic

Yep. The Briggs stuff goes back to the mid-50s, doesn't it? Some people have been building modern, simplified OBs of about the same dimensions as his radiogram-like OBs.

An inductor is also an option, but I think I'm more attracted to the idea of making changes in the digital domain, rather than adding extra components, albeit just one. One of the attractions this kind of set-up has, of course, is no cross-over.

I'm experimenting with Audio Hijack Pro on my Mac as I write, and it doesn't seem to mess with the overall sq.

mattlynch

yes indeed , the old sfb (sand filled baffle) by Briggs is a master stroke and still stands as a reference today.
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 ,?,

uglymusic

There are many examples of successful twin B200-based OBs out there. I'm planning to emulate them partly because I have an inkling that two B200s will be happier on the end of the TDSs than single ones.

I may not even take the step to twin B200s. A 12- or 15-inch driver may be more sensible, but I don't really have the space to accommodate the baffles needed to mount them.

Who knows, until I get the first B200s into my listening room?

mattlynch

of course , large (read wide) baffles may not be essential to OB happiness, by choosing a very sensitive 12 or 15"bass driver you could conceivably use a simple filter on this driver only to roll it off quite hard (as jamo do with their OB) and leave your chosen full range driver running full range with no filter , this would give you a relatively narrow baffle and keep the mid free from crossover nasties.
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 ,

, interesting speaker at least even if they are domestically unacceptable.
looking forward to reading more of your exploits in the world of the OB Dave,
all the best,
matt
:)

uglymusic

Ah. We seem to have a misunderstanding. I want to experiment with twin B200s running full range. Of course, if bass drivers are used, then there will need to be a sharp roll-off.

Some people have experimented by rolling off the lower of the two B200s so that it runs as a bass driver. That's not the first port of call, though.

mattlynch

aha!! i see , i thought you were using a lowther with the b200 as low end reinforcement, apologies for the confusion,
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

uglymusic

Jim is the Lowther fiend. They cost about £1.5k a pair for the drive units nowadays, so they ain't going to figure in any early experiments.

Also, they're very efficient, and suck me down the tube or class A route, when I don't want to change the TDSs. They do some very special things rhythmically, bass-wise and detail wise.

No probs. I probably wasn't clear enough.

The Remote Lightspeed build will be first, once the boards turn up from Paul Hynes. By my reckoning they should be here about now.

Stupinder

New here and apologies if i've upset anyone posting here on other fora in the past.
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.

Alan

Your first post here, and already you are on about your "very nice...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.

uglymusic

I think what you're thinking of are a pair of line arrays, each containing eight (yes, eight!) B200s, wired in parallel to give a 0.75 ohm load (from memory)! Paul built a special amp to drive them.

Alan

Coooool! Build that! Ok, not what you were talking about, and probably hideously expensive.

But so very right.

uglymusic

Actually, Jim and I have discussed a four drive-unit array, but that would be somewhere along the way.

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!

Alan

Ha! Give up while youre ahead, eh?

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.

uglymusic

OBs tend to be large. Jim currently has twin 15-inch bass units as well as his Lowthers, and his baffles are much narrower than the theory dictates.

OBs also tend to work much further out into the room than I have room for.

Basically, it's an issue of space.

Alan

Yeah, I can see that. Would it be viable to run them in front of the bay window? It would still gobble up your room, but they might work there.

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?

uglymusic

Turning the room round is not feasible :-(

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.

Alan

I had some old Solavox speakers once. No one wanted them on eBay so they got dumped.

Interesting with the dollops though, but I still cant understand how what is needed can be determined without a mic?

Jim

For clarity, these are they:

http://www.supravox.fr/anglais/haut_parleurs/215_RTFBIC.htm

uglymusic

Ha! I was just about to say I typed the wrong manuf.

Welcome back to the man himself!

Alan

Hi Jim, great to hear/see you again!

I suppose I might have guessed you weren't meaning these:

Comet specials, I believe.

Alan

This is what PH did:

uglymusic

Those are they. Fun, huh?

Alan

Best pair of headphones - ever!!

uglymusic

New thread opened for Stu's gear.

Stupinder

sorry - i was asked :-)

uglymusic

No worries at all Stu. If people want to talk about it, that's why we have a Community!

And that's what Modding is about, too.

uglymusic

Jim tells me he has made me a pair of OBs that sound very tasty.

Now all I need to do is get over to his place to pick them up.

Alan

Yes, and some pictures!

will you have digital crossovers?

uglymusic

I'll do some pix once I have them Chez Ugly.

They have one Supravox widebander and rely on digital EQ to stretch the limits. It's kind of ultra-minimalist, with a bit of digital pragmatism.

Jim

uglymusic

Thanks Jim

Don't forget to sign them, will you? :-)

Alan

They look brilliant. What an artisan!

(Leonardo da Jimci?)

Docfoster

Great lookin' rig all round Jim.
I assume you're delighted with the 'speakers...?

uglymusic

Jim's working on the finished version of his OB monsters that are just out of shot. Lowthers, plus twin 15-inchers for that little bit of bass :D

uglymusic

Jim said:

Where are da toobs, Jim? Are you back to bi-amping the Big Boys with trannies?

Jim

@Alan - thank you!

@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.

uglymusic

Ah, Dr Andy :-)

And why wouldn't I be happy to Digitally EQ them? (Rhetorical question ;-) )

Docfoster

Jim,
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?

Jim

Ben

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.

Mervyn

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.

Jim

Thanks Mervyn. They sound good to me but I like OBs a lot. We'll see what Dave makes of them.

Shame we didn't get a chance to talk much at Scalford.

uglymusic

They're gonna be Chez Ugly this weekend :-)

Can't wait!

Mervyn

Jim said:
Thanks Mervyn. They sound good to me but I like OBs a lot. We'll see what Dave makes of them.

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 !!

Jim

It did really fly by didn't it? We missed a couple of rooms which was a shame.

Hmmmm OB bake-off
B-)

uglymusic

How many pairs of OBs do we know of, and will they make a bake-off?

Jim

Not that many. But you never know who's building what.

Jim

I've made some small modifications to Dave's OBs
=)) =))

http://i667.photobucket.com/albums/vv33/mjkempton/daveobsmodified.jpg

Mervyn

Jim said:
I've made some small modifications to Dave's OBs
=)) =))

http://i667.photobucket.com/albums/vv33/mjkempton/daveobsmodified.jpg

Could be totally wrong here Jim but you might just have slightly overdone those mods !

Jim

I was thinking I got it about right
:-))

Alan

The model of restraint, as always...

uglymusic

Going to collect the mk1s this afternoon. Can't fit the others in the car :-(

Docfoster

Jim said:
I've made some small modifications to Dave's OBs
=)) =))

http://i667.photobucket.com/albums/vv33/mjkempton/daveobsmodified.jpg

Ridiculous set up.

That chair Is far to close.
;-)

Jim

Docfoster said:

Jim said:
I've made some small modifications to Dave's OBs
=)) =))

http://i667.photobucket.com/albums/vv33/mjkempton/daveobsmodified.jpg

Ridiculous set up.

That chair Is far to close.
;-)

Ha! Didn't notice that
:))

uglymusic

Well, they're here.

And they're the pickiest pair of speakers I've ever had the pleasure of driving.

Leave it with me guys. I have a lot to do...

Alan

Very exciting, I hope you have fun!

uglymusic

Well, they're certainly different.

Where you normally plop a pair of speakers down and then move them around a bit until they sound OK, with these you've got to do all that and adjust the EQ and try putting cloth round the back of the driver and so on.

Oh, and I'm doing all this while running in a pair of speaker cables.

Too many blinkin' variables, I say.

But I'm getting there, I think. Slowly.

Alan

Glad to hear it, though it sounds like you are gong to be fettling for some time! How about a picture in situ?

uglymusic

Yup. I'll get the pix done as well.

They're more than a bit prototypey, so they go perfectly with my TDSs :-)

Docfoster

Dave, sounds like you're part of the R&D team.
Hope jim's paying you well...
;-)

uglymusic

A few design pointers about the OBs @Jim has built for me:

They had to be as near as possible to the footprint and volume of the RR3s on their stands
OBs normally have large baffles to get sufficient bass extension. I just don't have the space
In recent years, the concept of 'full-range' drivers has given way to 'wide-range'. In other words, no-one expects a single driver to do all the work from bottom to top - Jim's Lowthers need a little help at the bottom end, for example ;-)
My OBs have just one driver per channel - no we're not mad!
My rig now has no crossovers - active or passive
The Supravox drivers in my OBs are known to extend well towards the bass end, but most people agree that they need a (super)tweeter at the top end
Instead of adding drive units and extra electronics, I'm boosting the bass and the high treble using digital EQ. And that's where the fiddling is coming in

uglymusic

Docfoster said:
Dave, sounds like you're part of the R&D team.
Hope jim's paying you well...
;-)

I think it's the other way round. I should be paying Jim for his expertise, experience and the use of his kit!

Mervyn

Very cutting edge intriguing project Dave. So there is no pre-amp or crossovers in the chain - very minimalistic indeed.

Will follow it closely.

ps is that Tellurium Ultra Blacks you are running in btw ?

Jim

uglymusic said:

Docfoster said:
Dave, sounds like you're part of the R&D team.
Hope jim's paying you well...
;-)

I think it's the other way round. I should be paying Jim for his expertise, experience and the use of his kit!

FOC :)

uglymusic

Mervyn said:
Very cutting edge intriguing project Dave. So there is no pre-amp or crossovers in the chain - very minimalistic indeed.

Will follow it closely.

ps is that Tellurium Ultra Blacks you are running in btw ?

Thanks Mervyn

It seems to me that there are some components in an all-digital rig that are a hangover from vinyl - e.g. the pre-amp - and other components whose function may be better achieved digitally - e.g. crossovers. Or perhaps even a different approach to speaker design, such as Jim came up with here. These components can usefully be ditched IMHO.

I'm really working on 'the best component is no component' here.

Yup. The speaker cables are the Ultra Blacks, and very good they are, too. I wondered when someone would notice I'd edited my signature :-)

In this kind of minimalist rig, I think everything in the signal chain has to be considered, so I have Paul (@PAC) lined up to make me some more custom phono-to-SMA cables using even better components and

cabling than he did for me last year. They'll be ordered once I've got what I have in the rig now working as I want it to.

uglymusic

Jim said:

uglymusic said:

Docfoster said:
Dave, sounds like you're part of the R&D team.
Hope jim's paying you well...
;-)

I think it's the other way round. I should be paying Jim for his expertise, experience and the use of his kit!

FOC :)

Thank you ;-)

Docfoster

uglymusic said:
It seems to me that there are some components in an all-digital rig that are a hangover from vinyl - e.g. the pre-amp - and other components whose function may be better achieved digitally - e.g. crossovers.

^This.
At least it's a good general point. Time will tell just which components can be taken over digitally.

uglymusic

Just a quick update. I haven't had too long to play with the OBs this evening, so I've decided to stop messing with EQ and just play some music.

I'm starting to think there could be something special here.

One test will be going back to the Royds.

Alan

Taking orders yet Jim? Baa... ;)

Would love to hear them sometime when you're happy with them Dave, if you're so inclined...

uglymusic

Of course. Taking bookings...

Jim

Alan, I love building stuff. If you want some just ask!

Alan

Jim said:
Alan, I love building stuff. If you want some just ask!

Thanks Jim :-bd I'll have a listen to Dave's sometime so I can 'learn' what they do. Have you heard Dave's Royds? I'm using the same and rate them (I suppose I ought to say "for a box speaker"!) and it would be interesting to know what else is out there. My dream is exactly what I have, but more efficient, with more scale.

It would interesting to see what can be done.

Jim

No problem. I've heard Dave's stuff a few times and used Minstrels for a while so am familiar with the Royd sound.

Efficiency is always good - less distortion for one thing. But there are other advantages.

Scale is a difficult one to get into.

uglymusic

Scale is somewhere the OBs win over the Royds, without a shadow of a doubt.

They also hammer the Royds on efficiency, which may lead to problems with volume control in the digital domain, according to some people. That is another tin of earth movers, though.

Jim

I'm not sure what scale means in a HiFi context. I've heard speakers described as "doing scale" and all I've heard was loud - no comment on quality.

What do people mean by scale?

uglymusic

It's nothing to do with loudness or sound quality. It's to do with presenting instruments and performers in a believable way in relation to each other and the sound space set up in your room. I'm assuming you have a large sound space set up in your room.

Alan

Yeah, 'room filling' I guess. My speaks' give a scaled down but accurate (imo) facsimile of a live performance, I'd be looking to retain all those good points but have a more palpable sense of 'scale'.

uglymusic

Good news on the OB front. The Supravox drivers can be repaired for considerably less than the price of two new drive units.

They'll be off to France in the not-too-distant future.

Maybe I shouldn't say this within Jim's earshot, but maybe if digital armageddon had to happen it was as well the Royds didn't get fried. There are no parts available any more.

Alan

Trudat! Not a happy outcome in any event, but at least a repair is on the horizon.

Jim

uglymusic said:
Good news on the OB front. The Supravox drivers can be repaired for considerably less than the price of two new drive units.

They'll be off to France in the not-too-distant future.

Maybe I shouldn't say this within Jim's earshot, but maybe if digital armageddon had to happen it was as well the Royds didn't get fried. There are no parts available any more.

That did occur to me last night after you phoned.

Sacrificial Supravox has a nice ring to it don't you think

=)) =))

uglymusic

Maybe we could have a little plaque made up for the front of each completed speaker:

Sacrificial Supravox Mk2

Jim

Working on it.....

RobHolt

Jim said:
I've made some small modifications to Dave's OBs
=)) =))

http://i667.photobucket.com/albums/vv33/mjkempton/daveobsmodified.jpg

Good Lord, is that what happens when you can't decide which driver to choose - use all of them at once!

Jim

Now there's a thought.

I could probably make one of those with the stuff I have laying around!

uglymusic

@Jim. Have you seen the acrylic baffles used in the pair of OBs on eBay? (See eBay thread)

Any thoughts about using acrylic on mine?

Jim

Thorsten Loesch made a pair with acrylic and Supravox drivers. It generated a huge thread on Diy Audio a few years back. I heard them at a show when he made them commercially. Pretty good actually.

I'd forgotten all about them!

Acrylic is fairly light and pretty self damped so no reason why it won't work well.

Should be quite transparent =))

uglymusic

Owwww!!!!

I'm thinking wider and transparent...

uglymusic

Looks like we'll be doing some wooden mock-ups and then later costing some acrylic baffles.

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